AIR-BEARING CHUCK

Abstract

An air-bearing chuck includes a nozzle portion and a gas channel portion. The nozzle portion is provided with a plurality of support force nozzles for generating an air cushion on a top surface of the nozzle portion. The gas channel portion includes a first gas channel configured to transmit a first gas to the plurality of support force nozzles to provide support force. Embodiments of the present application can implement that the first gas channel transmits the first gas to the plurality of support force nozzles to provide support force, and an air cushion is generated on the top surface of the nozzle portion by regulating gas flow of the first gas in the first gas channel, thereby keeping a supported object supported by the air cushion stably floating up on one side, away from the top surface of the nozzle portion, of the air cushion.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of International Application No. PCT/US2020/049009 filed on Sep. 2, 2020, which claims priority to U.S. 62/953,696 filed on Dec. 26, 2019. And this application also claims priority to Chinese patent applications No. 202011569044.8 filed on Dec. 25, 2020, and No. 202023200409.8 filed on Dec. 25, 2020. These applications are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present application relates to the technical field of chuck structure design, and in particular to an air-bearing chuck.

BACKGROUND

A wafer is usually fixed on a chuck in a clamping manner during preparation, measurement or the like of the wafer. However, when clamping force is relatively large, an original shape of the wafer is easily changed. In addition, debris particles or other contaminants are easily introduced on the wafer because it is difficult to guarantee cleanliness of a clamping tool, therefore measurement errors are caused to the original shape of the wafer.

SUMMARY

In view of this, embodiments of the present application provide an air-bearing chuck, to implement that an air cushion is generated on a top surface of a nozzle portion, so as to keep a supported object such as a wafer supported by the air cushion stably floating up on one side, away from the top surface of the nozzle portion, of the air cushion, thereby avoiding measurement errors caused by a clamping tool to an original shape of the wafer.

An embodiment of the present application provides an air-bearing chuck. The air-bearing chuck includes: a nozzle portion, provided with a plurality of support force nozzles for generating an air cushion on a top surface of the nozzle portion; and a gas channel portion, including a first gas channel configured to transmit a first gas to the plurality of support force nozzles to provide support force.

In an embodiment of the present application, the nozzle portion further includes a plurality of openings, and the plurality of openings are arranged alternately with the plurality of support force nozzles.

In an embodiment of the present application, the plurality of support force nozzles and the plurality of openings are arranged in an axisymmetric pattern on the top surface of the nozzle portion.

In an embodiment of the present application, the plurality of support force nozzles and the plurality of openings are arranged in a plurality of concentric nozzle rings equally spaced at an interval of ΔR.

In an embodiment of the present application, a radius of a nozzle ring, farthest from the center of the air-bearing chuck, of the plurality of concentric nozzle rings is 0 mm-20 mm smaller than a radius of the air-bearing chuck.

In an embodiment of the present application, each support force nozzle and an adjacent opening that are on any one of the plurality of concentric nozzle rings are tangentially spaced at a constant distance ΔT.

In an embodiment of the present application, as a distance between per nozzle ring of the plurality of concentric nozzle rings and the center of the air-bearing chuck increases, a total number of nozzles on per nozzle ring increases in an even number, and the even number includes any one of 2, 4, 6, 8 and 10.

In an embodiment of the present application, a difference between ΔR and ΔT is less than 5 mm.

In an embodiment of the present application, the plurality of openings include a plurality of suction force nozzles. The gas channel portion further includes a second gas channel, and the second gas channel is configured to transmit a second gas to the plurality of suction force nozzles to provide suction force.

In an embodiment of the present application, a plurality of first gas through holes corresponding to the plurality of support force nozzles are disposed on both the nozzle portion and the gas channel portion, and a plurality of second gas through holes corresponding to the plurality of openings are disposed on both the nozzle portion and the gas channel portion. The first gas channel is connected to the plurality of support force nozzles through the plurality of first gas through holes, and the second gas channel is connected to the plurality of openings through the plurality of second gas through holes.

In an embodiment of the present application, the first gas channel includes a first annular channel and a plurality of first channels connected to the first annular channel, and the second gas channel includes a second annular channel and a plurality of second channels connected to the second annular channel.

In an embodiment of the present application, the gas channel portion includes a first gas layer and a second gas layer that are stacked. The first gas channel is located in the first gas layer, and the second gas channel is located in the second gas layer.

In an embodiment of the present application, the first gas layer is provided with a first groove for accommodating the first gas channel, and the second gas layer is provided with a second groove for accommodating the second gas channel.

In an embodiment of the present application, the air-bearing chuck further includes an air pressure regulator. The air pressure regulator is configured to regulate a flow rate of a gas in each of the first gas channel and the second gas channel to hold a wafer at a predetermined distance from the top surface of the nozzle portion, so as to measure a geometry of the wafer, and the geometry of the wafer includes one or more of a flatness and a shape of the wafer.

In an embodiment of the present application, the air-bearing chuck further includes a controller. The controller is configured to control the air pressure regulator to regulate the flow rate of the gas in each of the first gas channel and the second gas channel to hold the wafer at the predetermined distance from the top surface of the nozzle portion, so as to measure the geometry of the wafer.

In an embodiment of the present application, the predetermined distance ranges from 0 μm to 50 μm when the air-bearing chuck is configured to measure the flatness of the wafer.

In an embodiment of the present application, the predetermined distance ranges from 60 μm to 1500 μm when the air-bearing chuck is configured to measure the shape of the wafer.

In an embodiment of the present application, the plurality of openings include a plurality of flow guide holes. The plurality of flow guide holes are configured to guide the first gas ejected from the plurality of support force nozzles to flow back to the nozzle portion when the first gas encounters a to-be-measured object. The gas channel portion further includes a third gas channel, and the third gas channel is configured to make the first gas that has flowed back to the nozzle portion flow out of the air-bearing chuck.

In an embodiment of the present application, the air-bearing chuck has a mirror polished surface higher than or equal to level N4 in accordance with an ISO standard.

In an embodiment of the present application, a material of the nozzle portion includes any one of aluminum, glass, microcrystalline silicon and ceramic. The material is configured to be mirror polished. The top surface, obtained after being polished, of the nozzle portion is sufficiently flat, so that interference fringes are shown on the top surface of the nozzle portion.

According to technical solutions provided in the embodiments of the present application, a plurality of support force nozzles are arranged on an air-bearing chuck, and an air cushion is generated on a top surface of a nozzle portion, so as to keep a supported object such as a wafer supported by the air cushion stably floating up on one side, away from the top surface of the nozzle portion, of the air cushion. Since there is no need to use a clamping tool to clamp the wafer during measurement, a shape of the wafer is not affected, thus reducing errors during measurement of the wafer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1a is a schematic structural diagram of an air-bearing chuck according to an embodiment of the present application.

FIG. 1b and FIG. 1c are schematic top views of the air-bearing chuck in FIG. 1a.

FIG. 2a is a schematic structural diagram of an air-bearing chuck according to another embodiment of the present application.

FIG. 2b to FIG. 2k are schematic top views of an air-bearing chuck.

FIG. 3a is a schematic top view of the first gas channel in FIG. 2b.

FIG. 3b is a schematic top view of the second gas channel in FIG. 2b.

FIG. 4a is a schematic top view of the first gas channel in FIG. 2e.

FIG. 4b is a schematic top view of the second gas channel in FIG. 2e.

FIG. 5 is a schematic structural diagram of an air-bearing chuck according to another embodiment of the present application.

FIG. 6 is a schematic structural diagram of an air-bearing chuck according to still another embodiment of the present application.

FIG. 7 is a schematic structural diagram of an air-bearing chuck according to yet another embodiment of the present application.

FIG. 8a and FIG. 8b show an exemplary air-bearing chuck with vacuum nozzles and pressure nozzles for holding a wafer on an air cushion.

FIG. 8c is a schematic diagram of connection layers of pressure nozzles and vacuum nozzles of an air-bearing chuck.

FIG. 8d is a schematic side view of a stacked structure of an air-bearing chuck according to an embodiment of the present application.

FIG. 8e is a schematic side view of a stacked structure of an air-bearing chuck according to another embodiment of the present application.

FIG. 8f shows a top surface of a top plate of the stacked structure in FIG. 8e.

FIG. 8g shows a bottom surface of a top plate of the stacked structure in FIG. 8e.

FIG. 8h is a top view of an exemplary manifold plate of the stacked structure in FIG. 8e.

FIG. 8i is a bottom view of an exemplary manifold plate of the stacked structure in FIG. 8e.

FIG. 8j is a top view of a back cover plate of the stacked structure in FIG. 8e.

FIG. 8k is a bottom view of a back cover plate of the stacked structure in FIG. 8e.

FIG. 9a and FIG. 9b are schematic structural diagrams of an exemplary manifold chamber according to an embodiment of the present application.

FIG. 10a is a schematic structural diagram of a dual Fizeau interferometer-based tool.

FIG. 10b is a schematic structural diagram of a shearing interferometer-based tool.

FIG. 10c is a schematic structural diagram of an architecture for measuring a wafer geometry.

FIG. 10d is a schematic diagram showing positions of a position sensor and a capacitive sensor relative to a wafer.

FIG. 10e is a schematic diagram of calibration of a position sensor.

FIG. 10f is a schematic diagram of a relationship between a position sensor reading Vx and a capacitive sensor reading CPn during calibration of a position sensor.

FIG. 11a and FIG. 11b are schematic diagrams of performing a measuring method of a wafer flatness TTV by utilizing the architecture shown in FIG. 10c.

FIG. 12a and FIG. 12b are schematic diagrams of performing a measuring method of a wafer shape by utilizing the architecture shown in FIG. 10c.

FIG. 13 is a schematic diagram illustrating that a wafer in a vertical position is prone to shape change when tilted.

FIG. 14 is a schematic structural diagram of an exemplary goniometer for measuring a patterned wafer tilt platform according to an embodiment of the present application.

FIG. 15a is a schematic diagram of a chuck mark or artifact occurred when a wafer is vacuum down on a vacuum chuck.

FIG. 15b is a schematic diagram of a wafer floating up on an air-bearing chuck.

FIG. 16a to FIG. 16c are schematic diagrams of a method for differentiating between real features and chuck marks or artifacts on a wafer surface.

DESCRIPTION OF EMBODIMENTS

The following clearly and completely describes the technical solutions in the embodiments of the present application with reference to the accompanying drawings required to be used in the embodiments of the present application. Apparently, the following descriptions of the accompanying drawings are merely some but not all of the embodiments of the present application.

It should be noted that all related embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

In the embodiments of the present application, an air-bearing chuck is provided, which is described in detail below.

It should be understood that, the air-bearing chuck in the embodiments of the present application may be configured to support a supported object such as a wafer, and may be applied to the field of wafer geometry measurement, semiconductor manufacturing, or the like. The application fields of the air-bearing chuck are not specifically limited in the embodiments of the present application. A top surface of a nozzle portion of the air-bearing chuck may be in a circular, rectangular, square, or another regular or irregular shape. The shape of the top surface of the nozzle portion is not specifically limited in the embodiments of the present application.

FIG. 1a is a schematic structural diagram of an air-bearing chuck according to an embodiment of the present application. FIG. 1b and FIG. 1c are schematic top views of the air-bearing chuck 100 in FIG. 1a. Referring to FIG. 1a to FIG. 1c, the air-bearing chuck 100 includes a nozzle portion 110 and a gas channel portion 120. The nozzle portion 110 includes a plurality of support force nozzles 111, and the plurality of support force nozzles 111 are configured for generating an air cushion 10 on a top surface 1 of the nozzle portion 110. The gas channel portion 120 includes a first gas channel 121 configured to transmit a first gas to the plurality of support force nozzles 111 to provide support force.

It should be understood that, the plurality of support force nozzles 111 may be arranged on a plurality of concentric rings (as shown in FIG. 1b) surrounding the center of the nozzle portion 110, and each concentric ring may be provided with one or more support force nozzles 111; or the plurality of support force nozzles 111 may also be arranged on a plurality of parallel lines (as shown in FIG. 1c); or the plurality of support force nozzles 111 may also be arranged on a plurality of radii extending from the center of the nozzle portion 110 all the way out, as long as the air cushion 10 may be generated on the top surface 1 of the nozzle portion 110. The arrangement manner of the plurality of support force nozzles 111 is not specifically limited in the embodiment of the present application. The plurality of support force nozzles 111 may be in any regular or irregular shape such as a circular, triangular, elliptical, annular, or the like, which is not specifically limited in the embodiment of the present application. In addition, the air cushion 10 may be generated by a gas ejected from the plurality of support force nozzles 111. The air cushion 10 is configured to keep a supported object such as a wafer floating up on one side, away from the top surface 1 of the nozzle portion 110, of the air cushion 10. The plurality of support force nozzles 111 may be spread over the entire top surface 1 of the nozzle portion 110 to equalize support force received by the supported object such as a wafer that is supported by the air cushion 10, thereby facilitating maintaining an original shape of the wafer, and accurately measuring a geometry of the supported object when the supported object is in a floating state.

According to the technical solution provided in the embodiment of the present application, a plurality of support force nozzles are disposed on a nozzle portion of an air-bearing chuck, and a first gas channel for transmitting a first gas to the plurality of support force nozzles to provide support force is disposed on a gas channel portion of the air-bearing chuck, so that the first gas is transmitted to the plurality of support force nozzles through the first gas channel to provide support force, and an air cushion is generated on a top surface of the nozzle portion by utilizing the support force, thereby keeping a supported object such as a wafer supported by the air cushion stably floating up on one side, away from the top surface of the nozzle portion, of the air cushion. Since there is no need to use a clamping tool to clamp the wafer during geometry measurement, and a shape of the wafer is not affected, errors during measurement of the wafer are reduced.

FIG. 2a is a schematic structural diagram of an air-bearing chuck 200 according to another embodiment of the present application. The embodiment illustrated in FIG. 2a is a modified example of the embodiment illustrated in FIG. 1a. FIG. 2b to FIG. 2k are schematic top views of an air-bearing chuck 200 according to some embodiments of the present application. Referring to FIG. 2a to FIG. 2k, a difference between the two embodiments lies in that, in the embodiment illustrated in FIG. 2a to FIG. 2k, the nozzle portion 110 further includes a plurality of openings 112, and the plurality of openings 112 are arranged alternately with the plurality of support force nozzles 111.

It should be understood that, the plurality of support force nozzles 111 and the plurality of openings 112 that are alternately arranged may be arranged in a non-axisymmetric manner (as shown in FIG. 2b), or may be arranged in an axisymmetric manner (as shown in FIG. 2c to FIG. 2g). The plurality of support force nozzles 111 and the plurality of openings 112 that are alternately arranged may be arranged in a plurality of concentric nozzle rings such as concentric rings (as shown in FIG. 2e, FIG. 2g, FIG. 2h, and FIG. 2k), concentric polygons such as pentagons (as shown in FIG. 2f), and the like; or may be arranged on a plurality of parallel lines (as shown in FIG. 2b to FIG. 2d, and FIG. 2i to FIG. 2j); or may be arranged in another regular or irregular pattern. The plurality of support force nozzles 111 and the plurality of openings 112 that are alternately arranged may be arranged on a same nozzle ring of concentric nozzle rings or a same parallel line with a single support force nozzle 111 and a single opening 112 as repeating units (as shown in FIG. 2d to FIG. 2f); or may be arranged on a same nozzle ring or a same parallel line with a plurality of support force nozzles 111 or a plurality of openings 112 arranged on the nozzle ring (as shown in FIG. 2g) or the parallel line (as shown in FIG. 2c); or may be arranged on a same parallel line with a single support force nozzle 111 and a plurality of openings 112 as repeating units or with a plurality of support force nozzles 111 and a single opening 112 as repeating units (as shown in FIG. 2b). As for the plurality of support force nozzles 111 and the plurality of openings 112 that are alternately, total numbers of support force nozzles 111 and openings 112 (e.g., suction force nozzles) on every two adjacent nozzle rings of concentric nozzle rings may be the same (as shown in FIG. 2f), or may be different (as shown in FIG. 2e and FIG. 2g); and total numbers of support force nozzles 111 and openings 112 on every two adjacent parallel lines of a plurality of parallel lines may be the same (as shown in FIG. 2d), or may be different (as shown in FIG. 2b and FIG. 2c), as long as the air cushion may be generated on the top surface of the nozzle portion 110. The arrangement manner of the plurality of support force nozzles 111 and the plurality of openings 112 that are alternately arranged is not specifically limited in the embodiment of the present application. A number of the plurality of support force nozzles 111 may be the same as that of the plurality of openings 112 (as shown in FIG. 2h and FIG. 2i), or may be different from that of the plurality of openings 112 (as shown in FIG. 2i and FIG. 2k).

It should also be understood that, one or more of the plurality of support force nozzles 111 and the plurality of openings 112 may be in a circular (as shown in FIG. 2b as well as FIG. 2e to FIG. 2g), triangular (as shown in FIG. 2d), quadrilateral (as shown in FIG. 2d), pentagonal (as shown in FIG. 2c), annular (as shown in FIG. 2c), or another regular or irregular shape. Shape sizes of the plurality of support force nozzles 111 or the plurality of openings 112 may be the same (as shown in FIG. 2c to FIG. 2e as well as FIG. 2g), or may be different (as shown in FIG. 2f). Shapes of the plurality of support force nozzles 111 or the plurality of openings 112 may be the same or may be different. A shape of the plurality of support force nozzles 111 and a shape of the plurality of openings 112 may be the same (as shown in FIG. 2b as well as FIG. 2e to FIG. 2g), or may be different (as shown in FIG. 2c and FIG. 2d). Intervals between any one of every two adjacent support force nozzles 111, every two adjacent openings 112, and every two adjacent support force nozzle and opening may be the same, or may be different.

The plurality of openings 112 may make a first gas flowed back to the nozzle portion flow out of the air-bearing chuck, and the plurality of openings 112 may also be connected to an apparatus for providing suction force, to make the plurality of openings transmit a second gas to provide suction force, which is not specifically limited in the present application.

According to the technical solutions provided in the embodiments of the present application, a plurality of support force nozzles and a plurality of openings that are alternately arranged are disposed on an air-bearing chuck, so that the plurality of support force nozzles and the plurality of openings are uniformly distributed, which helps absorb, by utilizing the plurality of openings, a first gas that flows back to a nozzle portion, and avoid an impact of the first gas that has flowed back to the nozzle portion on stability of a supported object floating above the air-bearing chuck, thereby keeping the supported object such as a wafer stably floating up on one side, away from a top surface of the nozzle portion, of an air cushion. Since there is no need to use a clamping tool to clamp the wafer during measurement, a shape of the wafer is not affected, thus reducing errors during measurement of the wafer.

In an embodiment of the present application, the plurality of openings 112 include a plurality of suction force nozzles 1121. The gas channel portion 120 further includes a second gas channel 122, and the second gas channel 122 is configured to transmit a second gas to the plurality of suction force nozzles 1121 to provide suction force. It should be understood that, the air cushion 10 may be generated by a gas ejected from the plurality of support force nozzles 111 and a gas sucked from the plurality of suction force nozzles. The air cushion 10 is configured to keep a supported object such as a wafer floating up on one side, away from the top surface of the nozzle portion 110, of the air cushion. The first gas channel 121 may be provided with a pipeline connected to the plurality of support force nozzles 111, to transmit the first gas to the plurality of support force nozzles 111, thereby providing support force. Alternatively, the nozzle portion may be provided with a plurality of through holes that are corresponding to the plurality of support force nozzles 111 and communicated with a plurality of through holes disposed on the first gas channel, thereby transmitting the first gas to the plurality of support force nozzles 111 to provide support force, which is not specifically limited in the embodiment of the present application. The first gas channel 121 and the second gas channel 122 may be set to have two layers of independent structures in the gas channel portion 120, or may be set to have an overall structure in which the first gas channel 121 and the second gas channel 122 are staggered with each other but does not affect each other, as long as the first gas channel 121 may transmit the first gas to the plurality of support force nozzles 111 to provide support force, and the second gas channel 122 may transmit the second gas to the plurality of suction force nozzles 1121 to provide suction force, which is not specifically limited in the embodiment of the present application. The second gas channel 122 and the first gas channel 121 may be disposed in a same manner or different manners, and there may be one or more first gas channels 121 or second gas channels 122, which is not specifically limited in the embodiment of the present application. A flow rate of a gas in both the first gas channel 121 and the second gas channel 122 may be controlled by using a device such as a controller or an air pressure regulator, or may be controlled by using a plurality of combined devices such as a controller and an air pressure regulator, or may be controlled by using computer software. A control method of the flow rate of the gas in both the first gas channel 121 and the second gas channel 122 is not specifically limited in the embodiment of the present application.

In the embodiment of the present application, a plurality of support force nozzles and a plurality of suction force nozzles that are alternately arranged are disposed on an air-bearing chuck, and an air cushion is generated above a top surface of a nozzle portion, which helps keep a supported object such as a wafer supported by the air cushion stably floating up on one side, away from the top surface of the nozzle portion, of the air cushion. Since there is no need to use a clamping tool to clamp the wafer during measurement, a shape of the wafer is not affected, thus reducing errors during measurement of the wafer.

In an embodiment of the present application, the plurality of openings 112 include a plurality of flow guide holes, the plurality of flow guide holes are configured to guide the first gas ejected from the plurality of support force nozzles to flow back to the nozzle portion when the first gas encounters a to-be-measured object, the gas channel portion 120 further includes a third gas channel 123, and the third gas channel 123 is configured to make the first gas that has flowed back to the nozzle portion flow out of the air-bearing chuck.

The plurality of flow guide holes 112 are configured to guide the first gas ejected from the plurality of support force nozzles 111 to flow back to the nozzle portion 110 when the first gas encounters a to-be-measured object such as the wafer. One or more corresponding support force nozzles may be disposed for one flow guide hole, or one or more corresponding flow guide holes may be disposed for one support force nozzle, as long as it may be ensured that a flow guide hole is provided, when the first gas ejected from each support force nozzle flows back to the nozzle portion, to make the first gas that has flowed back to the nozzle portion flow out of the air-bearing chuck, which is not specifically limited in the present application.

In some specific implementation modes, the plurality of openings 112 may all be flow guide holes, or may all be suction force nozzles. A disposing manner of the third gas channel 123 may be the same as that of the second gas channel 122. The second gas channel 122 may be replaced with the third gas channel 123, and the third gas channel 123 is configured to make the first gas that has flowed back to the nozzle portion flow out of the air-bearing chuck.

In some other specific implementation modes, when suction force are required to provide, the plurality of openings 112 may all be configured as suction force nozzles; and when no suction force are required to provide, the plurality of openings may all be configured as flow guide holes. The second gas channel 122 may be configured to not only transmit the second gas to the plurality of suction force nozzles to provide suction force, but also make the first gas that has flowed back to the nozzle portion flow out of the air-bearing chuck.

In some other specific implementation modes, some of the plurality of openings 112 may be flow guide holes, the other openings 112 may be suction force nozzles, and the plurality of flow guide holes may be disposed alternately with the plurality of suction force nozzles. The second gas channel 122 may be only configured to transmit the second gas to the plurality of suction force nozzles to provide suction force, and the third gas channel 123 may be only configured to make the first gas that has flowed back to the nozzle portion flow out of the air-bearing chuck.

In the embodiments of the present application, flow guide holes and a third gas channel are disposed, which makes a first gas that has flowed back to a nozzle portion flow out of an air-bearing chuck, and helps ensure that a wafer is not affected by the first gas that has flowed back and is kept stably floating up on a top surface of the nozzle portion. In addition, the third gas channel is disposed, so that the first gas that has flowed back to the nozzle portion is made flow out of the air-bearing chuck, to generate a stable air cushion.

In an embodiment of the present application, the plurality of support force nozzles 111 and the plurality of openings 112 are arranged in an axisymmetric pattern on the top surface 1 of the nozzle portion 110.

It should be understood that, the axisymmetric pattern arranged by the plurality of support force nozzles 111 and the plurality of openings 112 may have only one axis of symmetry (as shown in FIG. 2d), or may have a plurality of axes of symmetry (as shown in FIG. 2c as well as FIG. 2e to FIG. 2g).

In the embodiment of the present application, a plurality of support force nozzles and a plurality of openings are arranged in an axisymmetric pattern on a top surface of a nozzle portion, so that both numbers and shapes of support force nozzles and openings disposed on both sides of an axis of symmetry are the same, which helps keep a supported object such as a wafer supported by an air cushion floating up on a plane at a same height as the top surface of the nozzle portion.

In an embodiment of the present application, adjacent nozzles in the plurality of support force nozzles 111 and the plurality of openings 112 are arranged at an equal interval or unequal interval.

It should be understood that, adjacent nozzles in the plurality of support force nozzles 111 and the plurality of openings 112 may be arranged at an equal interval or unequal interval, as long as the wafer may be kept stably floating up on the air-bearing chuck. When the plurality of support force nozzles 111 and the plurality of openings 112 are arranged in concentric nozzle rings, adjacent nozzles on a same nozzle ring may be arranged at an equal interval, or adjacent nozzles on two adjacent concentric nozzle rings are arranged at an equal interval, or adjacent nozzles on a same nozzle ring may be arranged at an interval equal to an interval between adjacent nozzles arranged on two adjacent concentric nozzle rings. When the plurality of support force nozzles 111 and the plurality of openings 112 are arranged on a plurality of parallel lines, adjacent nozzles on a same parallel line may be arranged at an equal interval, or adjacent nozzles on two adjacent parallel lines are arranged at an equal interval, or adjacent nozzles on a same parallel line may be arranged at an interval equal to an interval between adjacent nozzles arranged on two adjacent parallel lines.

In the embodiment of the present application, when adjacent nozzles in a plurality of support force nozzles and a plurality of openings are disposed at an equal interval or unequal interval, a corresponding opening is disposed around each support force nozzle, so that a wafer may be kept stably floating up on one side, away from a top surface of a nozzle portion, of an air cushion. If the plurality of openings include a plurality of suction force nozzles, when adjacent nozzles in the plurality of support force nozzles and the plurality of suction force nozzles are set to be arranged at an equal interval, support force and suction force may be further equalized, which further helps keep a supported object such as a wafer supported by the air cushion stably floating up on one side, away from the top surface of the nozzle portion, of the air cushion. If the plurality of openings include a plurality of flow guide holes, when adjacent nozzles in the plurality of support force nozzles and the plurality of flow guide holes are set to be arranged at an equal interval, each time the first gas flows back to the air-bearing chuck, the first gas may flow out of the air-bearing chuck through the plurality of flow guide holes.

In some specific implementation modes, the plurality of support force nozzles 111 and the plurality of openings 112 are arranged in a Cartesian coordinate system or a polar coordinate system.

A plurality of support force nozzles and a plurality of openings are arranged in a Cartesian coordinate system or a polar coordinate system, so that the plurality of support force nozzles and the plurality of openings are arranged on a top surface of a nozzle portion more uniformly, which further helps generate an air cushion above a top surface of a nozzle portion.

In some specific implementation modes, shapes of the plurality of support force nozzles and the plurality of openings include one or more of a triangle, an oval, an annular ring, and a circle.

It should be understood that, the shapes of the plurality of support force nozzles and the plurality of openings include but are not limited to one or more of a triangle, an oval, an annular ring, a circle, and another regular or irregular shape, which is not specifically limited in the present application.

The shapes of the plurality of support force nozzles and the plurality of openings are set to include one or more of a triangle, an oval, an annular ring, a circle, and another regular or irregular shape, so that a stable air cushion is generated above a top surface of a nozzle portion by utilizing a plurality of manners.

FIG. 3a is a schematic top view of the first gas channel 121 in FIG. 2b. FIG. 3b is a schematic top view of the second gas channel 122 in FIG. 2b. FIG. 4a is a schematic top view of the first gas channel 121 in FIG. 2e. FIG. 4b is a schematic top view of the second gas channel 122 in FIG. 2e.

In some specific implementation modes, referring to FIG. 3a, the first gas channel 121 includes a first annular channel 1211 and a plurality of first channels 1212 connected to the first annular channel 1211. Referring to FIG. 3b, the second gas channel 122 includes a second annular channel 1221 and a plurality of second channels 1222 connected to the second annular channel 1221.

In some other specific implementation modes, referring to FIG. 4a, the first gas channel 121 includes a first annular channel 1211′ and a plurality of first channels 1212′ connected to the first annular channel 1211′. Referring to FIG. 4b, the second gas channel 122 includes a second annular channel 1221′ and a plurality of second channels 1222′ connected to the second annular channel 1221′.

It should be understood that, the first annular channel or the second annular channel may be an annular channel farthest from the center of an air-bearing chuck (as shown in FIG. 3a, FIG. 3b and FIG. 4b), may be an annular channel closest to the center of the air-bearing chuck (as shown in FIG. 4a), or may be an annular channel located at any position on the air-bearing chuck, which is not specifically limited in the embodiment of the present application.

According to technical solutions provided in the embodiments of the present application, a structure of a first gas channel is set to include a first annular channel and a plurality of first channels connected to the first annular channel, and a structure of a second gas channel is set to include a second annular channel and a plurality of second channels connected to the second annular channel. Thus, the structures of the first gas channel and the second gas channel are set as a whole, making a flow rate in the first gas channel or the second gas channel be uniform and also be regulated uniformly.

FIG. 5 is a schematic structural diagram of an air-bearing chuck 300 according to another embodiment of the present application. The air-bearing chuck further includes an air pressure regulator 130. The air pressure regulator 130 is configured to regulate a flow rate of a gas in each of a first gas channel 121 and a second gas channel 122 to hold a wafer at a predetermined distance from a top surface of a nozzle portion, so as to measure a geometry of the wafer, and the geometry of the wafer includes one or more of a thickness and a shape of the wafer.

It should be understood that, the air pressure regulator 130 may be a general term of two regulators respectively configured to regulate a flow rate of a gas in the first gas channel 121 and a flow rate of a gas in the second gas channel 122, or may be a regulator configured to simultaneously regulate the flow rate of the gas in both the first gas channel 121 and the second gas channel 122. The air pressure regulator 130 may be disposed on a side of a gas channel portion 120, or may be disposed below the gas channel portion 120.

According to the technical solution provided in the embodiment of the present application, an air pressure regulator is disposed, so that a flow rate of a gas in a first gas channel and a flow rate of a gas in a second gas channel may be effectively regulated, further helping control a height and stability of an air cushion generated above a top surface of a nozzle portion.

In an embodiment of the present application, the air-bearing chuck 300 further includes a controller 140. The controller 140 is configured to control the air pressure regulator 130 to regulate the flow rate of the gas in each of the first gas channel 121 and the second gas channel 122 to hold the wafer at a predetermined distance D from the top surface of the nozzle portion, so as to measure the geometry of the wafer.

It should be understood that, the predetermined distance D may be understood as a height of an air cushion 10 or a floating height. A specific value of the predetermined distance may be adjusted according to actual requirements.

According to the embodiment of the present application, an air pressure regulator is controlled by a controller to regulate a flow rate of a gas in each of a first gas channel and a second gas channel, so that accuracy of regulating the flow rate of the gas in each of the first gas channel and the second gas channel can be effectively improved, and when an air-bearing chuck is configured to hold a wafer at a predetermined distance from a top surface of a nozzle portion, the predetermined distance can be accurately adjusted.

In an embodiment of the present application, the predetermined distance D ranges from 0 μm to 50 μm when the air-bearing chuck is configured to measure the flatness of the wafer.

It should be understood that, the predetermined distance D may be, for example, 0 μm, 5 μm, 10 μm, 20 μm, 30 μm, or 50 μm.

According to the embodiment of the present application, the predetermined distance D is set to range from 0 μm to 50 μm, which helps maintain a flatness of a back surface of a wafer to be almost as flat as a surface of an air-bearing chuck under an action of suction force when the air-bearing chuck is configured to support the wafer, and further helps apply the air-bearing chuck to wafer flatness measurement after a shape of the surface of the air-bearing chuck is calibrated.

In an embodiment of the present application, the predetermined distance D ranges from 60 μm to 1500 μm when the air-bearing chuck is configured to measure the shape of the wafer.

It should be understood that, the predetermined distance D may be, for example, 60 μm, 300 μm, 350 μm, 1000 μm, or 1500 μm, which is not specifically limited in the embodiment of the present application.

According to the embodiment of the present application, a predetermined distance D is set to range from 60 μm to 1500 μm, so that any change of a wafer shape due to external force is avoided when an air-bearing chuck is configured to support the wafer, and thus an original state of the wafer can be effectively maintained, helping ensure measurement accuracy when the air-bearing chuck is applied to shape measurement.

FIG. 6 is a schematic structural diagram of an air-bearing chuck 400 according to still another embodiment of the present application. A disposing manner of a second gas channel is similar to that of a third gas channel. Herein the second gas channel is taken as an example for description. As shown in FIG. 6, this embodiment has the following differences from the embodiment illustrated in FIG. 2a: A plurality of first gas through holes 113 corresponding to a plurality of support force nozzles 111 and a plurality of second gas through holes 114 corresponding to a plurality of suction force nozzles 1121 are disposed on both a nozzle portion 110 and a gas channel portion 120. A first gas channel 121 is connected to the plurality of support force nozzles 111 through the plurality of first gas through holes 113, and a second gas channel 122 is connected to the plurality of suction force nozzles 1121 through the plurality of second gas through holes 114.

It should be understood that the plurality of first gas through holes 113 may be directly integrated with the first gas channel 121, or may be connected to the first gas channel 121 by screws or adhesives, or may be connected by a pipe embedded in the first gas channel 121, which is not specifically limited in the embodiment of the present application. The first gas channel 121 and the second gas channel 122 may be located on different planes, or may be located on a same plane, which is not specifically limited in the embodiment of the present application.

According to the technical solution provided in the embodiment of the present application, a plurality of first gas through holes corresponding to a plurality of support force nozzles and a plurality of second gas through holes corresponding to the plurality of suction force nozzles are disposed on a nozzle portion and a gas channel portion. A first gas channel is connected to the plurality of support force nozzles through the plurality of first gas through holes, and a second gas channel is connected to the plurality of suction force nozzles through the plurality of second gas through holes, so that a gas in the first gas channel is transmitted to a position above a top surface of the nozzle portion through the plurality of first gas through holes and the plurality of support force nozzles, a gas in the second gas channel is sucked out of an air-bearing chuck through the plurality of second gas through holes and a plurality of suction force nozzles, and a stable air cushion is generated under a combined action of the two manners.

In an embodiment of the present application, the gas channel portion 120 includes a first gas layer 123 and a second gas layer 124 that are stacked. The first gas channel 121 is located in the first gas layer 123, and the second gas channel 122 is located in the second gas layer 124.

It should be understood that, the first gas layer 123 may be located above the second gas layer 124, or may be located below the second gas layer 124, which is not specifically limited in the embodiment of the present application.

According to the embodiment of the present application, a first gas channel and a second gas channel are respectively disposed in a first gas layer and a second gas layer that are stacked in a gas channel portion, so that the first gas channel and the second gas channel are located in different planes, which helps the first gas channel and the second gas channel independently transmit a first gas and a second gas.

FIG. 7 is a schematic structural diagram of an air-bearing chuck according to yet another embodiment of the present application. The embodiment illustrated in FIG. 7 is a modified example of the embodiment illustrated in FIG. 6. A difference between the two embodiments lies in that, in an air-bearing chuck 500 of the embodiment illustrated in FIG. 6, the first gas layer 123 is provided with a first groove 1231 for accommodating the first gas channel 121, and the second gas layer 124 is provided with a second groove 1241 for accommodating the second gas channel 122. A plurality of support force pipes 1131 connected with the first gas channel 121 are disposed in the plurality of first gas through holes 113, and a plurality of suction force pipes 1141 connected with the second gas channel 122 are disposed in the plurality of second through holes 114.

It should be understood that, a manner in which the first groove 1231 is configured for accommodating the first gas channel 121 may be that the first groove 1231 is equivalent to the first gas channel 121, may be that the first gas channel 121 is embedded in the first groove 1231, or may be another manner, which is not specifically limited in the embodiment of the present application. A manner in which the second groove 1241 is configured for accommodating the second gas channel 122 may be the same as or different from the manner in which the first groove 1231 is configured for accommodating the first gas channel 121, which is not specifically limited in the embodiment of the present application.

According to the technical solution provided in the embodiment of the present application, a first gas layer is provided with a first groove for accommodating a first gas channel, and a second gas layer is provided with a second groove for accommodating a second gas channel, so that a space is provided for each of the first gas channel and the second gas channel on the first gas layer and the second gas layer, respectively, so as to ensure that a first gas is transmitted to a plurality of support force nozzles through the first gas channel to provide support force and a second gas is transmitted to a plurality of suction force nozzles through the second gas channel to provide suction force.

FIG. 8a shows an air-bearing chuck with vacuum nozzles and pressure nozzles for holding a wafer on an air cushion. The embodiment illustrated in FIG. 8a is an example of the embodiment illustrated in FIG. 2a to FIG. 2f. A difference between the two embodiments lies in that, in an air-bearing chuck 600A of the embodiment illustrated in FIG. 8a, pressure nozzles 601 are an exemplary implementation mode of the support force nozzles 111 in the embodiment illustrated in FIG. 2a to FIG. 2f, vacuum nozzles 602 are an exemplary implementation mode of the openings 112 in the embodiment illustrated in FIG. 2a to FIG. 2f, and the plurality of pressure nozzles 601 and the plurality of vacuum nozzles 602 are arranged alternately in concentric nozzle rings equally spaced at an interval of ΔR. In some specific implementation modes, as shown in FIG. 8a, the concentric nozzle rings are concentric rings. On a same nozzle ring of the concentric nozzle rings, the plurality of pressure nozzles 601 and the plurality of vacuum nozzles 602 are arranged with a single pressure nozzle 601 and a single vacuum nozzle 602 as repeating units. The plurality of pressure nozzles 601 and the plurality of vacuum nozzles 602 are in a circular shape, and both shapes and sizes of the plurality of pressure nozzles 601 and the plurality of vacuum nozzles 602 are the same, which is not specifically limited in the embodiment of the present application.

It should be understood that, ΔR denotes an interval between every two adjacent nozzle rings of the plurality of concentric nozzle rings.

According to the technical solution provided in the embodiment of the present application, a plurality of pressure nozzles and a plurality of vacuum nozzles are arranged in concentric nozzle rings, and distances between every two adjacent concentric nozzle rings of the plurality of concentric nozzle rings are the same, so that the plurality of pressure nozzles and the plurality of vacuum nozzles are uniformly arranged on a top surface of a nozzle portion, which facilitates equilibrium distribution of vacuum suction force and pressure support force on any one of the concentric nozzle rings, thereby generating a stable air cushion on the top surface of the nozzle portion.

Vacuum suction force and pressure support force may keep a wafer floating up on an air cushion of a few microns to hundreds of microns above the air-bearing chuck 600A. The thinner the air cushion, the greater the air flow, and the stiffer the air bearing. With a proper flow rate of vacuum and pressure, the air bearing may be very stiff (e.g., larger than 1 N/um). For an air gap of about 20 μm, the air bearing also has a significant capability to keep the wafer flat. However, the stiffness of a 100 μm thick air bearing may be as low as one-tenth of 1 N/μm, where force that deforms a shape of the wafer is very small.

To measure a wafer flatness or TTV from a front surface of the wafer, a back surface of the wafer may be flattened by the air-bearing chuck 600A and matched with a surface of the air-bearing chuck 600A. The front surface of the wafer is a surface, away from the air-bearing chuck, of the wafer, and is not limited to a specific surface of the wafer. When the air gap is set at a proper height (e.g., 15 μm to 20 μm), artifacts are not detected on the air-bearing chuck 600A. To measure a shape of the wafer, the wafer is floated up on the surface of the air-bearing chuck 600A, with the air gap ranging from 60 μm to 300 μm, and the wafer is supported by the air cushion generated by the air-bearing chuck 600A and maintains its original shape due to the suction force being very small at large air gap.

For example, in a Wafer Geometry Tool (WGT) for wafer flatness and shape measurement, the air-bearing chuck 600A may have the following features, as shown in FIG. 8a.

(1) The pressure nozzles 601 and vacuum nozzles 602 are arranged alternately in concentric and axisymmetric nozzle rings.

(2) A radius of the nozzle ring farthest from the center of the nozzle rings is smaller than the radius of the wafer. The nozzles, such as the vacuum nozzles or the pressure nozzles, extend from the center of the nozzle rings all the way out to a position about 0 mm to 20 mm (greater than 0), such as 2 mm to 4 mm, away from the circumference of the air-bearing chuck 600A, so as to support the wafer. For example, for a 200 mm chuck, the nozzles, such as the pressure nozzles 601 or vacuum nozzles 602, extend radially such that the centers of the last set of nozzles are located on a circumference of a circle with a diameter of any one of 199 mm, 198 mm, 196 mm, 190 mm, and 180 mm on the air-bearing chuck. The surface of the air-bearing chuck 600A may be larger than that of the wafer, so that the wafer does not overhang beyond the edge of the air-bearing chuck 600A.

In an embodiment of the present application, a radius of the nozzle ring farthest from the center of the plurality of concentric nozzle rings is 0 mm to 20 mm smaller than the radius of the air-bearing chuck.

In the embodiment of the present application, a radius of a nozzle ring, farthest from the center of an air-bearing chuck, of a plurality of concentric nozzle rings is set to be 0 mm-20 mm smaller than a radius of the air-bearing chuck, which helps keep, when a wafer is supported by utilizing the air-bearing chuck, the wafer floating above a top surface of the air-bearing chuck in an evenly stressed manner, and further facilitates controlling a distance at which the wafer is held from the top surface of the air-bearing chuck by regulating magnitude of vacuum suction force and pressure support force.

(3) In an embodiment of the present application, each vacuum nozzle and an adjacent pressure nozzle that are on any one of the plurality of concentric nozzle rings are tangentially spaced at a constant distance ΔT.

It should be understood that, ΔR and ΔT may be the same or different, which is not specifically limited in the embodiment of the present application.

In the embodiment of the present application, each vacuum nozzle and an adjacent pressure nozzle that are on any nozzle ring are set to be tangentially spaced at a constant distance ΔT, so that vacuum nozzles and pressure nozzles on a same nozzle ring are uniformly distributed, which helps equalize vacuum suction force and pressure support force, and further makes an air cushion have a uniform height above the same nozzle ring.

In an embodiment of the present application, to keep nozzles tangentially spaced at a constant distance, as a distance between each nozzle ring of the plurality of concentric nozzle rings and the center of the air-bearing chuck increases, a total number of nozzles on the nozzle ring is set to increase in an even number m, for example, expressed by a formula: N=m×n, and m denotes an increased number of nozzles (m=2, 4, 6, 8, 10, or . . . ), n is the n^th nozzle ring of a specific concentric nozzle ring, and N denotes a number of nozzles per nozzle ring.

It should be understood that, the even number includes but is not limited to 2, 4, 6, 8, or 10.

In the embodiment of the present application, as a distance between each nozzle ring of a plurality of concentric nozzle rings and the center of an air-bearing chuck increases, a total number of nozzles on the nozzle ring is set to increase in an even number, so that an increased number of support force nozzles and an increased number of suction force nozzles are the same on each concentric nozzle ring, which further helps equalize vacuum suction force and pressure support force.

In an embodiment of the present application, a difference between ΔR and ΔT is less than 5 mm.

Specifically, as the radius increases, there is an increase of 6 nozzles per nozzle ring while the tangential separation between nozzles is maintained at a constant. To achieve this, the following formula is used: N=6×n, and n=0 is the first “nozzle ring” at the center of the wafer 400, and m=6. The number “6” is selected in order to achieve about the same displacement between nozzles in both the radial and tangential directions as well when m=6.

The selection of the number of “6” is based on the following method. The separation ΔT between the pressure nozzles 601 and the vacuum nozzles 602 in tangential direction may be the same across the whole air-bearing chuck 600A. The adjacent nozzle rings are separated by a constant distance ΔR. For a given ΔR, ΔT may be calculated based on the following method.

It is assumed that, as radius increases, a quantity of nozzles for each adjacent nozzle ring increases by an even integer m, and even integer is used because vacuum nozzle and pressure nozzle are paired.

$N=m\times n$

Where “N” denotes the number of nozzles per nozzle ring.

“n” denotes the n^th nozzle ring of a specific nozzle ring; and every two adjacent nozzle rings are separated by ΔR, and the radius of the n^th nozzle ring is Rn=n×ΔR.

“m” is an even-integer (such as 2, 4, 6, 8, 10) because the number of nozzles increases in pairs.

$\Delta T=2p\times n\times \Delta R/N=2p\times \Delta R/m=\left(2p/6\right)\times \Delta R$

Where p is equal to π. When m=6, ΔR and ΔT have almost the same value based on the above formula.

It should be understood that, values of ΔR and ΔT may be completely the same, or may be approximately the same. Specific values of ΔR and ΔT are not limited as long as a difference between ΔR and ΔT is less than 5 mm. For example, as shown in FIG. 8a, ΔR=7.9 mm, and ΔT=6.2 mm. Since the difference between ΔR and ΔT is 1.7 mm, it may be considered that ΔR and ΔT are approximately the same.

In the embodiment of the present application, a difference between ΔR and ΔT is set to be less than 5 mm, for example, a difference between numbers of nozzles on every two adjacent concentric nozzle rings of a plurality of concentric nozzle rings is set to be 6, so that values of ΔR and ΔT are approximately the same, which helps the air-bearing chuck provide vacuum suction force and pressure support force that are uniformly distributed, and further facilitates generation of a stable air cushion with a uniform height.

(4) A chuck flatness of a WGT 200 (a wafer geometry tool for measuring the wafer geometry of 200 mm wafers) may be less than or equal to 1.5 μm. A chuck flatness of a WGT 300 (a wafer geometry tool for measuring the wafer geometry of 300 mm wafers) may be less than or equal to 2 μm. For example, when applied to flatness measurement of an advanced wafer, a chuck flatness of a WGT 300 may be 0.5 μm or even less than 0.5 μm.

(5) The chuck surface polished to be mirror like finish, higher than or equal to level N4 per ISO standard.

In an embodiment of the present application, the air-bearing chuck 600A has a mirror polished surface higher than or equal to level N4 in accordance with an ISO standard.

In the embodiment of the present application, an air-bearing chuck is set to have a mirror surface higher than or equal to level N4 in accordance with an ISO standard, so that surface defects of the air-bearing chuck are reduced, and a surface of the air-bearing chuck is kept sufficiently flat.

(6) A diameter of the air-bearing chuck 600A may be 10 mm greater than a diameter of the wafer. An area of the air-bearing chuck that is larger than the wafer may be configured for calibration during wafer measurement since this part is not blocked by the wafer.

(7) There are three wafer grippers 603, two fixed (90 degrees apart, configured to fix any two wafer grippers 603), and one actuating griper for center wafer. Force on the wafer may be adjustable (e.g., 0.05 lb-1 lb).

(8) There are four lift pins 604 that may lift the wafer up from the chuck 600A in a smooth manner, to facilitate removal of the wafer from the chuck.

FIG. 8b shows an exemplary air-bearing chuck with vacuum nozzles and pressure nozzles. In air-bearing chuck 600B, the vacuum nozzles and pressure nozzles are arranged according to ΔR and ΔT shown in FIG. 8b, ΔR=11.0 mm, and ΔT=9.0 mm. Since the difference between ΔR and ΔT is 2 mm, it may be considered that ΔR and ΔT are approximately the same.

FIG. 8c is a schematic diagram of connection layers of pressure nozzles and vacuum nozzles of an air-bearing chuck. FIG. 8c provides a top view of stacked layers of the air-bearing chuck 600C. The stacked layers include a pressure manifold layer 610c, a vacuum manifold layer 620c, and a top chuck layer 630c. The vacuum manifold layer 620c connects all the vacuum channels 621c and vacuum supply. The pressure manifold layer 610c connects all the pressure channels 611c and pressure supply. The top chuck layer 630c includes a plurality of through holes connecting the vacuum channels 621c in the vacuum manifold layer 620c to the vacuum nozzles on the top surface of the top chuck layer 630c. The top chuck layer 630c further includes additional through holes connecting the pressure channels 611c in the pressure manifold layer 610c to the pressure nozzles on the top surface of the top chuck layer 630c. The through holes for vacuum and pressure are arranged in an alternating fashion corresponding to the vacuum and pressure nozzle arrangements shown in FIG. 8a and FIG. 8b.

FIG. 8d is a schematic side view of a stacked structure of an air-bearing chuck 600D according to an embodiment of the present application. The embodiment illustrated in FIG. 8d is an example of the embodiment illustrated in FIG. 2a. A difference between the two embodiments lies in that, in the embodiment illustrated in FIG. 8d, a top chuck layer 630d is corresponding to the nozzle portion 110 in the embodiment illustrated in FIG. 2a, a combined structure of a vacuum manifold layer 620d and a pressure manifold layer 610d is corresponding to the gas channel portion 120 in the embodiment illustrated in FIG. 2a. The air-bearing chuck 600D includes a top chuck layer 630d, a vacuum manifold layer 620d, and a pressure manifold layer 610d. There are alternating through holes 631d and 632d connecting the vacuum channels 621d and pressure channels 611d, respectively, to the vacuum nozzles and pressure nozzles on the top surface of the air-bearing chuck 600D. As shown in the side view of the air-bearing chuck of FIG. 8d, the separation ΔT between the alternating vacuum nozzles and pressure nozzles may be substantially the same.

FIG. 8e is a schematic side view of a stacked structure of an air-bearing chuck 600E according to another embodiment of the present application. The embodiment illustrated in FIG. 8e is an example of the embodiment illustrated in FIG. 2a. A top plate 610e is corresponding to the nozzle portion 110 in the embodiment illustrated in FIG. 2a, and a manifold plate 620e is corresponding to the gas channel portion 120 in the embodiment illustrated in FIG. 2a. In addition, the stacked structure may include a top plate 610e, a back cover plate 630e, and a manifold plate 620e sandwiched between the top plate 610e and the back cover plate 630e. The top plate 610e may be composed of any one of aluminum, ceramic, glass, and microcrystalline silicon, and a thickness of the top plate 610e ranges from 10 mm to 60 mm. Similar to the embodiment illustrated in FIG. 8d, through holes 611e and 612e alternately disposed in the top plate 610e provide pressure support force and vacuum suction force, respectively, to keep the wafer floating on an air cushion.

It should be understood that, a diameter of the through holes 611e and 612e may range from 1 to 3 mm, further, may range from 1.25 to 1.5 mm. The diameter of the through holes may be the same as or different from a diameter of nozzles disposed on a top surface of the top plate, which is not specifically limited in the embodiment of the present application.

In an embodiment of the present application, a material of the nozzle portion, for example, the top plate 610e, includes aluminum, glass, microcrystalline silicon, or ceramic. The material is rigid, and may be mirror polished. The top surface, obtained after being polished, of the nozzle portion is sufficiently flat, so that interference fringes are shown on the top surface of the nozzle portion.

It should be understood that, the material of the nozzle portion, for example, the top plate 610e, may be aluminum, glass, microcrystalline silicon, or ceramic, and a thickness of the material ranges from 15 mm to 20 mm. In addition to aluminum, glass, microcrystalline silicon, or ceramic, the material of the top plate 610e may alternatively be another rigid material that may be mirror-polished, which is not specifically limited in the embodiment of the present application.

In the embodiment of the present application, a material of a nozzle portion is set to be aluminum, glass, microcrystalline silicon, or ceramic, so that not only rigidity of the material is guaranteed, but also a top surface of a top plate may be mirror polished; in addition, the selected material keeps a top surface, obtained after being polished, of the nozzle portion sufficiently flat, which helps interference fringes be shown on the top surface of the nozzle portion.

A top surface and a bottom surface of the manifold plate 620e may each have one or more grooves in which a pressure channel 621e and a vacuum channel 622e may be located, respectively. In an example illustrated in FIG. 8e, the vacuum channel 622e may be embedded in a groove on the top surface of the manifold plate 620e, and connects vacuum nozzles on the top plate 610e of the stacked structure to vacuum outlets 632e on a bottom plate of the stacked structure through the through holes 612e. Similarly, the pressure channel 621e may be embedded in a groove on the bottom surface of the manifold plate 620e, and connects pressure nozzles on the top plate 610e of the stacked structure to pressure outlets 631e on the bottom plate of the stacked structure through the through holes 611e. The grooves on the top surface and the bottom surface of the manifold plate may be arranged according to the structure of the vacuum channel and the pressure channel, respectively, and may be several millimeters wide and several millimeters deep, for example, may be 2 mm wide and 2 mm deep.

FIG. 8f shows a top surface of the top plate of the stacked structure in FIG. 8e. The top surface 1f of the top plate 610e includes equally or nonequally spaced alternating pressure nozzles 601f and vacuum nozzles 602f (or vacuum holes) with for example, 5 mm to 25 mm radial and tangential spacing, for another example, 8 mm to 12 mm radial and tangential spacing, respectively. The vacuum nozzles 602f may have a diameter of several millimeters, such as 1.5 mm. The pressure nozzles 601f may have a diameter of several millimeters, such as 1.25 mm. Both the vacuum nozzles 602f and the pressure nozzles 601f may have chamfers.

In some specific implementation modes, when a plurality of vacuum nozzles and a plurality of pressure nozzles are in a circular shape, a diameter of the plurality of vacuum nozzles and the plurality of pressure nozzles ranges from 0.5 mm to 3 mm.

It should be understood that, the diameter of the plurality of vacuum nozzles and the plurality of pressure nozzles may be, such as, 0.5 mm, 0.75 mm, 1 mm, 1.1 mm, 1.25 mm, 1.3 mm, 1.35 mm, 1.5 mm, 1.73 mm, 2 mm, or 3 mm. For example, the diameter of the plurality of vacuum nozzles and the plurality of pressure nozzles ranges from 1.25 mm to 1.5 mm. The diameter of the plurality of vacuum nozzles and the plurality of pressure nozzles may be designed based on a size of an air-bearing chuck and density of nozzles required for generating an air cushion. A diameter of the vacuum nozzles and a diameter of the pressure nozzles may be the same or different. The diameter and the diameter range of the plurality of vacuum nozzles and the plurality of pressure nozzles are not specifically limited in the embodiment of the present application.

A diameter of a plurality of vacuum nozzles and a plurality of pressure nozzles is set to range from 0.5 mm to 3 mm, which helps arrange a sufficient number of vacuum nozzles and pressure nozzles on a top surface of a top plate, to generate a stable air cushion above the top surface of the top plate.

FIG. 8g shows a bottom surface 1g of the top plate 610e of the stacked structure in FIG. 8e, and shows the same pattern of pressure nozzles 601g and vacuum nozzles 602g. The bottom surface 1g may also include M3.5 or M4 threaded holes 2g for fastening the plates of the stacked structure together and sealing the vacuum channels and pressure channels. Alternatively, the glue may also be configured to hold the plates together, and this method may improve a flatness of the top surface. If glue is configured, no M3.5 or M4 or any other threaded holes are required on the plate.

FIG. 8h is a top view of the manifold plate of the stacked structure in FIG. 8e. All vacuum nozzles from the top plate are connected to corresponding vacuum holes 612h in the top surface 1h of the manifold plate 620e. In comparison, all pressure nozzles from the top plate are connected to corresponding pressure holes 611h in the grooves on the top surface the manifold plate 620e, to form straight holes from the top plate down through the manifold plate 620e (as shown in FIG. 8e), thereby connecting the pressure nozzles on the top plate to the pressure channels 621h (shown in FIG. 8i) embedded in the grooves at the bottom of the manifold plate 620e. In some specific implementation modes, vacuum channels 622h on the top surface of the manifold plate 620e may be patterned as shown in FIG. 8h. The channels are aligned with the vacuum nozzles on the top plate and are connected by an outer circular channel 623h along the edge of the manifold plate 620e. FIG. 8h also shows M3.5 or M4 threaded holes 2g for fastening the plates of the stacked structure together. FIG. 8i is a bottom view of an exemplary manifold plate 620e of the stacked structure in FIG. 8e. The pressure channels or grooves 621i may be in an inner ring-like pattern (“pressure supply ring”), and connects pressure holes that are through the manifold plate 620e. Since a cross section of the pressure supply ring increases, the pressure supply ring may be less resistance. The bottom view of FIG. 8i also shows the M3.5 or M4 threaded holes 2g shown in the top view of FIG. 8h. Although the bottom view also shows the superimposed vacuum channels 622h, it should be understood that this is only for illustrative purposes. As shown in FIG. 8h, the actual vacuum channels 622h are situated in grooves on the top surface of the manifold plate 620e.

FIG. 8j is a top view of the back cover plate 630e of the stacked structure in FIG. 8e. FIG. 8k is a bottom view of the back cover plate 630e of the stacked structure in FIG. 8e. As shown in FIG. 8j, the top surface 1j of the back cover plate 630e may be polished to seal the manifold bottom surface of the manifold plate embedded with the pressure grooves. In some specific implementation modes, there are three openings 3j for connecting the pressure channels from the bottom surface of the manifold plate 620e to a pressure fitting. In addition, there are three other openings 4j for connecting the vacuum channels from the top surface of the manifold plate to a vacuum fitting. The same pressure openings 3k and vacuum openings 4k are also shown in the bottom view of the back cover plate 630e in FIG. 8k. The top view of the back cover plate 630e shown in FIG. 8j and the bottom view of the back cover plate 630e shown in FIG. 8k also show M3.5 or M4 threaded holes 2g for fastening the back cover plate to other plates in the stacked structure.

Although FIG. 8e to FIG. 8k show a stacked structure of an air-bearing chuck, and the stacked structure has pressure channels and vacuum channels respectively located in grooves on the bottom surface and top surface of the manifold layer, it should be understood that, these channels may alternatively be embedded in grooves of another layer. For example, the vacuum channels may be located in grooves on the bottom layer of the top plate, and the pressure channels may be located in grooves on the top layer of the back cover plate. Furthermore, it should be understood that, the arrangement of the vacuum channels and the pressure channels may be interchangeable. In various specific implementation modes, numbers of vacuum nozzles may be different, numbers of pressure nozzles may be different, or numbers of both of vacuum nozzles and pressure nozzles may be different. Paths of the vacuum channels and pressure channels may be adjusted according to the number and position of the nozzles. Numbers of vacuum fittings and pressure fittings at the bottom of the stacked structure are not limited, for example, may be three or more.

FIG. 9a and FIG. 9b are schematic structural diagrams of an exemplary manifold chamber 900 according to an embodiment of the present application. The manifold chamber 900 is an example of the gas channel portion 120 shown in FIG. 2a. The manifold chamber 900 is configured to separate pressure nozzles from vacuum nozzles. As shown in FIG. 9a and FIG. 9b, the manifold chamber 900 includes a pressure manifold chamber 921 and a vacuum manifold chamber 922. All vacuum nozzles are connected to the vacuum manifold chamber 922. All pressure nozzles pass through the vacuum manifold chamber 922 and directly reach the pressure manifold chamber 921 located below the vacuum manifold chamber 922. A computer fluid dynamics (Computational fluid dynamics, CFD) simulation shows that such kind of manifold chamber greatly improves uniformity of the vacuum nozzles and the pressure nozzles. The manifold chamber may provide a uniform amount of gas and optimize an increased channel size to the greatest extent. In addition, a height of the chamber may be adjusted to minimize a change in orifice flow.

An air cushion configured to support a wafer also has a gas damping capability, which effectively isolates ground vibration and sound vibration, thus removing or reducing a need for sound isolation boxes and active vibration isolation systems.

There are other advantages of using the air-bearing chuck in the above embodiments. For example, accuracy of thickness measurement of a mask layer applied on a wafer may be improved. In a 3-D flash memory (3D NAND) process, thickness measurement of a highly non-transparent hard mask (or film) does not meet requirements because a conventional optical method cannot be well applied to the non-transparent film. Characteristics of thickness measurement of a WGT wafer may be configured for thickness measurement of a hard mask. For example, two types of thickness measurement are performed: One is thickness measurement on a pre-mask wafer (pre-mask, T_Pre), and the other is thickness measurement on a post-mask wafer (T_post).

$T_{pre}=T_0+\mathrm{E\_RTE}\mathrm{\_pre}$ $T_{\mathrm{post}}=T_1+\mathrm{E\_RTE}\mathrm{\_post}$

T₀and T₁ denote measured values of thicknesses of the pre-mask wafer and the post-mask wafer, respectively. E_RTE_pre and E_RTE_post denote Ray Tracing Error (RTE) of the pre-mask wafer and the post-mask wafer, respectively.

Therefore, the thickness ΔT of the mask layer is as follows: ΔT=T_post−T_pre=(T₁−T₀)+(E_RTE_post−E_RTE_pre).

The wafer may be sharply warped after a mask is applied. As a result, RTE (namely, E_RTE_post−E_RTE_pre) may apparently affect measurement results of T_Pre and T_Post, causing significant errors during ΔT calculation. After the mask layer is applied on a surface of the wafer, the wafer may be kept basically flat by utilizing suction force generated by the air-bearing chuck, so that shapes of the pre-mask wafer and the post-mask wafer are basically the same. Therefore, RTE is minimized (that is, E RTE-post−E_RTE_pre≈0), and accuracy of thickness measurement is improved.

The air-bearing chuck may be configured to reduce or eliminate the ray tracking errors of an interferometer by forcing a wafer with a large warp to match a top surface of the air-bearing chuck, or may be configured to reduce warps of the post-mask wafer, so that a shape of the pre-mask wafer is consistent with a shape of the post-mask wafer. Therefore, ray tracing errors are eventually eliminated when a thickness of a film is obtained by subtracting a thickness of a wafer obtained before the film is deposited from a thickness of the wafer obtained after the film is deposited. When the method is applied to thickness measurement of a non-transparent hard mask layer, ray tracing errors caused by a large warp of the wafer can be greatly reduced.

In the present specification, “wafer geometry” may refer to wafer shape parameters (e.g., bow and warp), as well as local flatness parameters (also referred to as local plainness parameters, such as Site Flatness (SFQR), Site flatness Back Ideal Range (SBIR), and Global Flatness Back Ideal Range (GBIR)). Wafer flatness, also referred to as Total Thickness Variation (TTV), may refer to high density raw data (e.g., ≥4M pixels/wafer) that may be configured for deriving SFQR, GBIR, and many other related parameters. Flatness data is normally associated with both front surface and back surface information of a wafer. For example, the wafer shape parameters may be derived from a height map of a single surface, and the single surface may be a front surface or a back surface of a wafer, or may be medium of the two surfaces (e.g., wafer shape defined by Semiconductor Equipment and Materials International (SEMI)). For advanced 300 mm wafer, there is a very small difference between a shape obtained by medium value of the front surface and the back surface of the wafer, a shape only obtained by the front surface of the wafer, and a shape only obtained by the back surface of the wafer. This is because the wafer shape is in the order of a few micron to a few hundred micron, while TTV or GBIR is in the order of tens or hundreds of nanometers. In a patterned wafer geometry tool, wafer shape may be calculated from either the front surface or the back surface, depending on suppliers of the tools.

Wafer geometry tool (Wafer Geometry Tool, “WGT” for short) is a metrology tool that may be configured in Si wafer manufacturing fabs for characterizing wafer flatness, nano-topography and shape (e.g., bow and warp), and may also be configured in glass wafer fabs. Typically, each wafer has to be certified by WGT type of tools before shipping to a customer. There are several existing tools serving this purpose. For example, capacitive sensor-based wafer geometry tools are widely used in 200 mm wafer fabs. FIG. 10a is a schematic structural diagram of a dual Fizeau interferometer-based tool. The tool may be configured to measure the wafer geometry of 300 mm wafers. Interferometer-based wafer geometry tool has the advantage in both precision and throughput. Its precision is about one to two magnitude better than that of capacitive sensor-based tool, despite of the fact that 300 mm wafer is more prone to vibration than that of 200 mm wafer. However, there have been no interferometer-based 200 mm wafer geometry tool on the market. Capacitive sensor-based wafer geometry tools were designed for 250 nm, 180 nm, and 130 nm, node processes. Capacitive sensor tool cannot keep up with the precision and throughput requirement for design nodes smaller than 90 nm.

FIG. 10b is a schematic structural diagram of a shearing interferometer-based tool. The shearing interferometer may also be configured together with the air-bearing chuck in the present application to measure geometries such as wafer shape and flatness.

WGT Architecture

The present application relates to a semiconductor device architecture for measuring a wafer flatness and a wafer shape for various types of wafers such as 200 mm wafers. The architecture may have better precision and throughput than capacitive sensor or optical sensor-based scanning tools. Embodiments of the architecture in the present application may also be configured for 300 mm and 450 mm wafer geometry tools. In addition to wafer geometry tools, the architecture in the present application may also be configured in patterned wafer geometry (Patterned Wafer Geometry, PWG) tools. An air cushion is configured in the air-bearing chuck to support a wafer during measurement of the wafer shape. The air-bearing film or air cushion of the air-bearing chuck has very small stiffness and exerts sufficient force on the wafer to help to keep the shape unchanged, which is ideal for measuring of the wafer shape.

FIG. 10c is a schematic structural diagram of an architecture for measuring a wafer geometry. The architecture may perform the same measurement as a dual Fizeau tool, but at a fraction of the cost. The architecture has many obvious advantages over existing dual Fizeau tools in measuring a wafer shape. As shown in FIG. 10c, an architecture 1000 may include a single Fizeau interferometer. The single Fizeau interferometer includes a camera 1002, a relay lens 1004, a Polarization Beam Splitter or Combiner (PBSC) 1006, a light source (e.g., an illumination light) 1008, a collimator 1010, and a Transmission Flat (TF) 1012, all as shown in FIG. 10c. The operation of a Fizeau interferometer is well known and thus is not described in detail herein. In this architecture, the single Fizeau interferometer is configured to measure the geometry of a wafer 1014. It should be understand that, the transmission flat may also be referred to as a test flat, a transmission flat, or the like. The architecture is not limited to the use of the Fizeau interferometer, and another type of vertically incident interferometer may alternatively be configured, such as a grating-based shearing interferometer.

As shown in FIG. 10c, the wafer 1014 may be horizontally placed on an air cushion generated above a top surface of an air-bearing chuck 1016. The air-bearing chuck 1016 may include a plurality of alternating pressure channels 1030 and vacuum channels (or guide channels) 1032, for generating and maintaining the air cushion above the top surface of the air-bearing chuck 1016. The air-bearing chuck 1016 may also include a Z-tip-and-tilt stage 1018, and the Z-tip-and-tilt stage 1018 may make the air-bearing chuck 1016 be tipped and/or tilted. A plurality of lift pins 1020 may be configured to lift the wafer up from the top surface of the air-bearing chuck 1016.

In addition, referring to FIG. 10c, a combination of a capacitive sensor 1022 at the bottom of wafer 1014 (e.g., embedded in the air-bearing chuck 1016) and one or more optical position sensors 1026 (bi-cell or PSD, Position Sensing Diode) along with a laser 1024 on the top of the wafer 1014 are incorporated into the architecture 1000 to measure a thickness of the wafer 1014. FIG. 10d is a schematic diagram showing positions of a position sensor and a capacitive sensor relative to a wafer. The wafer may be a calibration wafer, or may be another to-be-measured object. FIG. 10e is a schematic diagram of calibration of a position sensor. In combination with FIG. 10d and FIG. 10e, a position sensor reading Vx may be calibrated by utilizing a wafer 1011 with a known thickness, namely, a calibration wafer 1011. A position of the position sensor may be correlated to a height of a top surface of the wafer. The capacitive sensor 1022 may be configured to measure a position of a bottom surface of the wafer. The combined information of the top and bottom surface positions may be configured for accurately determining the thickness of the wafer 1014. The elliptical structure in FIG. 10d and FIG. 10e represents a spot on a surface of the calibration wafer 1011.

There is an added advantage of the bi-cell or PSD position sensor disposed at the top of wafer 1014. The position sensor reading may be correlated directly to wafer thickness. The position sensor readings above the wafer 1014 may also tell the relative motion or vibration between the wafer 1014 and the TF 1012. The vibration of the wafer may be caused by one or more of the air-bearing chuck, flange and supporting mechanism, which cannot be sensed by the capacitive sensor 1022, because the capacitive sensor 1022 moves with the unit that includes the wafer 1014 and the air-bearing chuck 1016.

The interferometer tool may be configured to calibrate the capacitive sensor and optical (bi-cell or PSD) position sensors. Both the capacitive sensor 1022 and the optical (bi-cell or PSD) position sensors 1026 may sense air-bearing stability, but only the optical (bi-cell or PSD) sensors may sense the vibration of chuck assembly. This may be useful when there is a need to isolate the source of vibration.

It should be understand that, the architecture shown in FIG. 10c for measuring wafer geometries including a wafer shape and a thickness variation (also referred to as wafer flatness or wafer plainness) is not limited to the use of Fizeau interferometer, and another interferometer such as a shearing interferometer may also be configured in the architecture of the present application provided with a reflective air-bearing chuck.

A method of determining an optimal angle at which one or more of a laser and a position sensor is located is disclosed. Referring to FIG. 10d, to obtain an optimal Z-axis resolution, a position sensor 1026 may be located at a position and a size of the position sensor is allowed and a maximum angle β is formed with the calibration wafer 1011. If Δh is a Z-axis resolution (or z-sensitivity), the angle β is dominant. The formula is as follows.

$\Delta h=\Delta L\times \mathrm{Cos}\beta /\left(2\mathrm{Cos}\alpha \right)$

Where ΔL is a minimum displacement detectable by the position sensor 1026. The position sensor 1026 may be a commercially available sensor, for example, the minimum displacement of the sensor may be about 0.75 μm.

$\Delta h=\Delta L/M$ $\mathrm{Where}M={\left[\mathrm{Cos}\beta /\left(2\mathrm{Cos}\left(\alpha \right)\right)\right]}^{⩓}-1$

Due to a grazing angle α incidence, Cos(α) is approximately equal to 1, and α is an angle between a light source (e.g., a laser), and the calibration wafer 1011, and values of a generally is set as 10 degrees to 15 degrees. As β increases, M also increases based on the above formula, which means that the sensitivity of the position sensor 1026 also increases. However, β may not be too large due to a potential enlarging effect on a size of a spot on a detector in the position sensor 1026 (e.g., the size of the spot have a size lager than what the detector can detect). There may also be physical limitations about how far the position sensor may be disposed in the device. For example, at this grazing angle, the size of the spot of the laser on a sensor surface may be increased by 1/Sin(90°−β)=1/Sin 30°. Table 1 below lists various PSD resolutions (in nm) obtained based on different values of α and β.

	TABLE 1
	α (°)	10.00	0.0175	10.00	10.00
	β (°)	0.00	45.00	60.00	75.00
	Mag (M)	1.97	2.79	3.94	7.61
PSD Res	250.000	126.93	89.75	63.46	32.85
(nm)

As shown in FIG. 10e, to calibrate the position sensor 1026, the calibration wafer 1011 may be adjusted up and down at various positions. In this example, although each wafer is slightly different, the thickness TO of the calibration wafer 1011 may be set to 725 μm. The thickness of the calibration wafer 1011 may be measured by a Coordinate Measuring Machine (CMM) or another thickness measuring tool. The calibration wafer 1011 has a zero floating height when being located at a position 188. The position 188 may be a position of the calibration wafer 1011 located when the calibration wafer 1011 is placed on an air-bearing chuck or vacuumed onto the air-bearing chuck, and a capacitive sensor reading obtained when the calibration wafer 1011 is located at position 188 is denoted by CP0. CP0 may be obtained by setting CPn to 0. Then the position sensor reading (V0 (±10V)) may be obtained from the position sensor 1026. Thereafter, the pressure or both the vacuum and pressure may be regulated to hold the calibration wafer 1011 at a position 190. A capacitive sensor reading obtained at the position 190 is CP1, and CP1 minus CP0 equals to 20 μm (or approximately equals to 20 μm). A position sensor reading V1 obtained when CP1 minus CP0 is equal to 20 μm is recorded.

Thereafter, the pressure or both the vacuum and pressure may be regulated again until the calibration wafer 1011 is held at a position 192. A capacitive sensor reading obtained at the position 192 is CP2, and CP2 minus CP0 approximately equals to 30 μm. A position sensor reading V2 obtained when CP2 minus CP0 is equal to 30 μm is recorded. The above steps may be repeated, and isochronal differences 40 μm, 50 μm, and 60 μm are obtained when the capacitive sensor readings are CP3, CP4, and CP5, respectively.

Next, Δ(CPn−CP0) may be calculated, such as CP1−CP0, and CP2−CP0. Table 2 shows the calculated exemplary results.

TABLE 2
	0	1	2	3	4	5
Capacitive	CP0 =	CP1 =	CP2 =	CP3 =	CP4 =	CP5 =
sensor	500	520	530	540	550	560
reading CPn
(μm)
Δ (CPn −	0	20	30	40	50	60
CP0) = hx
PSD	V0	V1	V2	V3	V4	V5
position
voltage

With the above data, hx vs Vx may be plotted, and linear fitted to obtain the slope S (μm/V) (referring to FIG. 10f). hx is a difference between the capacitive sensor reading CPn and a reference capacitive sensor reading CP0, namely, a relative height of a wafer surface. Calibration data include: (1) slope: S (μm/V); (2) wafer thickness: T0=725 μm; (3) reference PSD reading: V0; and (4) reference capacitive sensor reading: CP0. The calibration data may be saved, and a software implementation of the calibration may be performed by using the following formula:

$T_{\mathrm{Wafer}}=T0+\left(CP0-CPn\right)+S\times \left(Vx-V0\right).$

CPn is a capacitive sensor reading obtained when the wafer is located at a predetermined floating height.

CP0 is a capacitive sensor reading obtained when the wafer is placed on an air-bearing chuck or vacuumed onto the air-bearing chuck.

Vx is a position sensor reading, in Volt.

The capacitive sensor reading in μm may be calculated from a plant calibration constant C, C=Δh/ΔV, (μm/volt). The capacitive sensor reading CPn in μm is obtained according to the formula: CPn=C×ΔVcp.

An exemplary method of measuring a wafer shape and thickness by utilizing the architecture 1000 shown in FIG. 1c is provided in detail below with reference to FIG. 11a, FIG. 11b, FIG. 12a, and FIG. 12b.

There are many advantages to a measuring method of a wafer geometry performed by utilizing an air-floating chuck and a single interferometer. For example, the air-bearing chuck may provide effective air damping capability to a wafer disposed above the air-bearing chuck. The air damping capability not only makes measurement of an interferometer more accurate, but also helps to reduce the cost due to the absence of expensive active vibration isolation systems and heavy acoustic isolation vibrators. Due to simplification of the wafer loading process, the air damping capability also reduces the cost of wafer transfer within the architecture, for example, horizontally loading the wafer under a single interferometer. Compared to a dual Fizeau interferometer architecture, the single interferometer architecture reduces cost by eliminating an interferometer and related optics. Also not needed is the mechanism for rotating a wafer 90 degrees from horizontal to vertical required in the dual Fizeau interferometer architecture. The acoustic isolation box in the dual Fizeau interferometer architecture is also not needed in the architecture. In addition, the air cushion may provide air damping capability. The whole architecture has very few moving parts, making it more reliable than the duel Fizeau interferometer architecture. The wafer may be loaded directly to the air-bearing chuck to reduce wafer transport time as required when a dual Fizeau interferometer-based tool is configured. The advantage of the WGT architecture is even greater for 300 mm or 450 mm wafers, and vibration of 300 mm or 450 mm wafers may be a major source of noise, making it difficult to achieve a high precision in flatness measurement. For devices configured for 300 mm or 450 mm wafers, optics components collimators, transmission flats, and folding mirrors are all large and expensive. An interferometer, a wafer vertical loading system, an acoustic isolation box, and a channel of data acquisition system are eliminated, which may significantly reduce the cost for Original Equipment Manufacturers (OEMs) as well as to their customers.

TTV Measuring Method

FIG. 11a and FIG. 11b are schematic diagrams of performing a measuring method of a wafer flatness TTV by utilizing the architecture shown in FIG. 10c. Referring to FIG. 11a, an optical cavity formed by a transmission flat TF 1102 and a reflective air-bearing chuck 1104 is measured. In other words, a distance variation between opposing surfaces of the transmission flat TF 1102 and the air-bearing chuck 1104 is measured. The TF 1102 may sag in the middle due to gravity. A surface of the air-bearing chuck 1104 may not be completely flat, as illustrated in FIG. 11a and FIG. 11b. These imperfections need to be calibrated to make wafer flatness measurement accurate. Cavity calibration is to measure a cavity thickness variation. Mathematically, the cavity thickness variation is a difference between a transmission flat surface S_TF(x, y) and a chuck surface S_CK(x, y): ΔS_Cavity=S_TF−S_CK. In this step, there is no wafer on the chuck.

Referring to FIG. 11b, after calibration, a wafer 1106 is placed on the surface of the air-bearing chuck 1104. To measure a flatness of the wafer 1106, the wafer is kept floating up on the top of the air-bearing chuck 1104 at a small air gap (for example, 5 μm to 50 μm; for another example, 5 μm to 30 μm) generated by the air-bearing chuck 1104. At these small air gaps, the air-bearing chuck 1104 is designed to have great suction force, to keep a back surface of the wafer 1106 flat or make the back surface (S_{Back surface}) of the wafer 1106 match the surface (S_CK) of the air-bearing chuck 1104. In this case, location information of a front surface (S_{Front surface}) of the wafer 1106 is a sum of location information of the surface S_CK of the air-bearing chuck 1104 and a total thickness variation TTV of the wafer 1106, that is, S_{Front surface}=S_CK+TTV. The front surface of the wafer may also be referred to as a top surface of the wafer. However, the back surface of the wafer is not completely matched with the surface S_CK of the air-bearing chuck. In actual application, to accurately determine the location information of the front surface S_{Front surface} of the wafer, a nonconforming item (S_N.C.) needs to be added: S_{Front surface}=(S_CK+TTV+S_N.C.).

During measurement by utilizing an interferometer, a distance between the wafer 1106 and the transmission flat may be measured: ΔS_WFR=(S_TF−S_{Front surface})=(S_TF−S_CK−TTV−S_N.C.).

Next, TTV may be calculated by measuring a difference (ΔS_Cavity−ΔS_WFR) between the cavity and a surface of the wafer. Subsequently, the total thickness variation may be calculated by using the following formula: TTV_actual=(ΔS_Cavity−ΔS_WFR−S_N.C.), and ΔS_Cavity and ΔS_WFR may be measured by utilizing the interferometer in the WGT architecture shown in FIG. 10c. S_N.C. may be obtained through calibration. If necessary, a wafer thickness may be measured, and information about the wafer thickness is further configured to correct the nonconforming item. S_N.C. may be obtained by utilizing a wafer with a known TTV (such as a double-side polished 200 mm wafer): S_N.C.=(ΔS_cavity−ΔS_WFR−TTV_known).

S_N.C. may drift over time, and needs to be calibrated from time to time by utilizing the wafer with the known TTV. S_N.C. is a function of a wafer thickness, a temperature, a floating height FH, and a chuck flatness. All these parameters may be measured simultaneously with interferometer data, or may be configured also for correction.

In addition, a double-side polished wafer, such as some 200 mm or 300 mm wafers, may be inverted and measured upward to obtain a shape of a back surface of the wafer. A TTV of the wafer is then obtained in combination with the shape of the back surface of the wafer, a shape of the front surface of the wafer, and a thickness result measured by a thickness gauge.

Shape Measuring Method

FIG. 12a and FIG. 12b are schematic diagrams of performing a measuring method of a wafer shape by utilizing the architecture shown in FIG. 10c. Referring to FIG. 12a, to measure the wafer shape, a reference TF 1202 (TF-ref) is first placed on a top surface of an air-bearing chuck 1204 to calibrate a TF 1200 in an apparatus based on the following formula: Cal=S_TF−S_TF-ref. A flatness of the reference TF (in nm) may be much higher than the flatness of the wafer (in μm). Therefore, S_TF-ref is a translation term that may be removed. If TF 1200 is thick and there is minimum TF sag, the cavity calibration step may be skipped as well. In this step, there is no wafer on the chuck. This calibration may be completed before delivery. Assuming that a TF shape does not change, tilt correction may be done at measurement time.

Referring to FIG. 12b, in a next step, a wafer 1206 is placed on the top surface of the air-bearing chuck 1204. To measure the wafer shape, the wafer 1206 is held at a relatively large air gap (for example, 60 μm to 1500 μm; for another example, 60 μm to 300 μm). The air-bearing chuck is designed and operated in such a way that a pressure can balance the gravity, so that there is no additional force that deforms the wafer. Therefore, at these relatively large air gaps, the wafer 1206 maintains its natural shape while being supported by an air cushion.

$\mathrm{SWFR}=\left(S_{\mathrm{TF}}-S_{\mathrm{Front}\mathrm{surface}}\right)$

Next, based on an obtained difference between Cal and a measured value of the front surface of the wafer, the wafer shape is calculated as follows:

$\mathrm{Wafer}\mathrm{shape}=\mathrm{Cal}-\mathrm{SWFR}=\left(S_{\mathrm{TF}}-S_{\mathrm{Tf}\text{-}\mathrm{ref}}\right)-\left(S_{\mathrm{TF}}-S_{\mathrm{Front}\mathrm{surface}}\right)=S_{\mathrm{Front}\mathrm{surface}}-S_{\mathrm{TF}\text{-}\mathrm{ref}}=S_{\mathrm{Front}\mathrm{surface}}.$

Since the reference TF has a relatively high flatness, S_TF-ref may be equivalent to a constant. Both S_{Front surface}−S_TF-ref and S_{Front surface} may be configured to reflect the wafer shape, namely, the shape of the front surface of the wafer. Shape measurement performed according to the above steps is accurate, and does not need correction so long as the air gap is set properly. This could be an ideal tool architecture for a patterned wafer geometry (Patterned Wafer Geometry, PWG) tool. In addition, the architecture of the present application has better precision, matching, and lower cost than the dual Fizeau interferometer architecture. In this architecture, a grating-based shearing interferometer may be configured to replace the Fizeau interferometer, and the air-bearing chuck may be configured to replace three lift pins for support, thereby improving measurement accuracy of the shearing interferometer and increasing the measured warp dynamic range by tilting the wafer.

For a wafer with a relatively large warp, a 2-D tilt platform may be configured to overcome limitations to a dynamic range of the interferometer in the architecture shown in FIG. 10c. When the wafer is tilted, a shape of the wafer 1306 in a horizontal position may be better maintained than a same wafer 1306′ in the vertical position. As shown in FIG. 13, when the same wafer 1306′ is in the vertical position, if the wafer 1306′ is not completely vertical, the shape of the wafer 1306′ may be changed by gravity.

Specifically, FIG. 13 illustrates that the wafer 1306′ in a vertical position is prone to shape change when tilted. This is because when the vertically clamped wafer 1306′ is tilted, a torque T is applied to the wafer 1306′. The torque will change the shape of the wafer. Measurement accuracy of a traditional dual Fizeau interferometer is affected. In comparison, the architecture disclosed in the present application supports the wafer 1306 on a thin air cushion that helps maintain a natural shape of the wafer 1306 even when the wafer 1306 is at a relatively small tilt angle (usually less than a fraction of one degree), as shown in the horizontal setting of FIG. 13.

The architecture disclosed in the present application may be configured to measure a warp of a thin wafer. When the wafer is tilted in the vertical position, the wafer is too thin to be put in the vertical position or too thin to keep its shape unchanged. For some thin wafers, it may be too thin to form a support at two points on the edge of the wafer. In this architecture, the wafer is in the horizontal position and supported by the air cushion. When the wafer is tilted, a very small radial force is applied to the wafer to maintain the position of the wafer. At proper floating height, vacuum setting and pressure setting, the warp of a thin wafer may be measured.

Accordingly, a wafer geometry tool and a patterned wafer geometry tool that use the above method may have high precision and high throughput, but at about half price as compared with the dual Fizeau interferometer architecture. This method provides a cost-effective and high precision solution for wafer flatness, nano-topography, and shape measurement tools for wafers of any size such as 200 mm, 300 mm, and 450 mm.

FIG. 14 is a schematic structural diagram of an exemplary goniometer 1400 for measuring a patterned wafer tilt platform according to an embodiment of the present application. The steps in the present application include two stacked goniometers 1400 that are utilized to increase a warp dynamic range of a wafer and throughput. When the wafer is tilted, the wafer may be maintained to be focused. It should be noted that, an X platform 1402 and a Y platform 1404 intersect at an angle of 90 degrees. In FIG. 14, the X platform 1402 and the Y platform 1404 are drawn on a same plane to facilitate illustration of a common rotation center.

Method for Differentiating Between a Real Feature and a Chuck Mark (or Artifact) on a Surface Wafer

The embodiment of the architecture 1000 shown in FIG. 10c may implement an artifact-free measurement. In the architecture 1000, the wafer 1014 may be loaded to measurement chamber directly from handler end effector.

In the embodiment of the WGT architecture 1000 shown in FIG. 10c, a total thickness variation and a wafer shape are measured by utilizing a vertically mounted Fizeau interferometer. However, in actual application, this method has many challenges. An air-bearing chuck itself may not be flat and there may be artifacts, such as particles, on a top surface of the air-bearing chuck. When a wafer is vacuumed on the air-bearing chuck, the artifacts may show up on a top surface of the wafer. For example, FIG. 15a illustrates an example in which a chuck mark or artifact occurred when a wafer is vacuum down on a chuck. A large particle 1502 may appear as a bulge on a wafer 1504a on a top side of an air-bearing chuck 1500a, as illustrated in FIG. 15a. These types of artifacts may be calibrated by utilizing a method disclosed in the present application. FIG. 15b is a schematic diagram of a wafer 1504b floating up on an air-bearing chuck 1500b, where no chuck marks and artifacts are found on the wafer 1504b.

FIG. 16a to FIG. 16c are schematic diagrams of a method for differentiating between real features 1604 and chuck marks (or artifacts) 1606 on a wafer surface 1610. FIG. 16a is a schematic diagram of wafer geometry measurement on a surface S1. The real features 1604 are mixed with the chuck marks (or artifacts) 1606 during measurement of the interferometer. FIG. 16b is a schematic diagram of wafer geometry measurement on a surface S2. The surface S2 is a chuck surface obtained by rotating a chuck 180 degrees from an original location where the measurement on the surface S1 is performed. When the chuck marks (or artifacts) 1606 rotate 180 degrees with a chuck 1600, the real features 1604 remain in the same location. Thus, the wafer 1610 is placed on the chuck surface S2 (as shown in FIG. 16b) obtained after the rotation by 180 degrees, and a measurement result obtained when the wafer 1610 is on the surface S2 is compared with a measurement result obtained when the wafer 1610 is on the surface S1 of 0 degrees (as shown in FIG. 16a), so that real features 1604 (those remain in the same location in the wafer coordinate system before and after the rotation) of the wafer 1610 may be identified. On the contrary, when the wafer 1610 is rotated 180 degrees, a location of the chuck marks (or artifacts) 1606 is off by 180 degrees in the wafer coordinate system.

FIG. 16c provides a S1 and S2 difference map showing a pair of chuck artifacts 1616 and 1620. These chuck artifacts may be calibrated if they do not move around on the chuck. These chuck artifacts also have specific features that allow them to be removed by utilizing an algorithm if the chuck is clean and the chuck artifacts are isolated. When there are limited artifacts on any one or more of a top surface of the chuck and a back surface of the wafer, a wafer or chuck rotation method may be configured to identify these artifacts and remove them.

Although the embodiments of the present application have been fully described with reference to the accompanying drawings, it should be noted that, various changes and modifications will become apparent to those skilled in the art. Such changes and modifications should be understood to be included in the scope of the embodiments of the present application defined by the appended claims.

Claims

1. An air-bearing chuck, comprising:

a nozzle portion, provided with a plurality of support force nozzles for generating an air cushion on a top surface of the nozzle portion; and

a gas channel portion, comprising a first gas channel configured to transmit a first gas to the plurality of support force nozzles to provide support force.

2. The air-bearing chuck according to claim 1, wherein the nozzle portion further comprises a plurality of openings, and the plurality of openings are arranged alternately with the plurality of support force nozzles.

3. The air-bearing chuck according to claim 2, wherein the plurality of support force nozzles and the plurality of openings are arranged in an axisymmetric pattern on the top surface of the nozzle portion.

4. The air-bearing chuck according to claim 2, wherein the plurality of support force nozzles and the plurality of openings are arranged in a plurality of concentric nozzle rings equally spaced at an interval of ΔR.

5. The air-bearing chuck according to claim 4, wherein a radius of a nozzle ring, farthest from the center of the air-bearing chuck, of the plurality of concentric nozzle rings is 0 mm-20 mm smaller than a radius of the air-bearing chuck.

6. The air-bearing chuck according to claim 4, wherein each support force nozzle and an adjacent opening that are on any one of the plurality of concentric nozzle rings are tangentially spaced at a constant distance ΔT.

7. The air-bearing chuck according to claim 6, wherein as a distance between per nozzle ring of the plurality of concentric nozzle rings and the center of the air-bearing chuck increases, a total number of nozzles on per nozzle ring increases in an even number, and the even number comprises any one of 2, 4, 6, 8 and 10.

8. The air-bearing chuck according to claim 6, wherein a difference between ΔR and ΔT is less than 5 mm.

9. The air-bearing chuck according to claim 2, wherein the plurality of openings comprise a plurality of suction force nozzles, the gas channel portion further comprises a second gas channel, and the second gas channel is configured to transmit a second gas to the plurality of suction force nozzles to provide suction force.

10. The air-bearing chuck according to claim 9, wherein a plurality of first gas through holes corresponding to the plurality of support force nozzles are disposed on both the nozzle portion and the gas channel portion, and a plurality of second gas through holes corresponding to the plurality of openings are disposed on both the nozzle portion and the gas channel portion, the first gas channel is connected to the plurality of support force nozzles through the plurality of first gas through holes, and the second gas channel is connected to the plurality of openings through the plurality of second gas through holes.

11. The air-bearing chuck according to claim 9, wherein the first gas channel comprises a first annular channel and a plurality of first channels connected to the first annular channel, and the second gas channel comprises a second annular channel and a plurality of second channels connected to the second annular channel.

12. The air-bearing chuck according to claim 9, wherein the gas channel portion comprises a first gas layer and a second gas layer that are stacked, the first gas channel is located in the first gas layer, and the second gas channel is located in the second gas layer.

13. The air-bearing chuck according to claim 12, wherein the first gas layer is provided with a first groove for accommodating the first gas channel, and the second gas layer is provided with a second groove for accommodating the second gas channel.

14. The air-bearing chuck according to claim 9, further comprising:

an air pressure regulator, configured to regulate a flow rate of a gas in each of the first gas channel and the second gas channel to hold a wafer at a predetermined distance from the top surface of the nozzle portion, so as to measure a geometry of the wafer, wherein the geometry of the wafer comprises one or more of a flatness and a shape of the wafer.

15. The air-bearing chuck according to claim 14, further comprising:

a controller, configured to control the air pressure regulator to regulate the flow rate of the gas in each of the first gas channel and the second gas channel to hold the wafer at the predetermined distance from the top surface of the nozzle portion, so as to measure the geometry of the wafer.

16. The air-bearing chuck according to claim 15, wherein the predetermined distance ranges from 0 μm to 50 μm when the air-bearing chuck is configured to measure the flatness of the wafer.

17. The air-bearing chuck according to claim 15, wherein the predetermined distance ranges from 60 μm to 1500 μm when the air-bearing chuck is configured to measure the shape of the wafer.

18. The air-bearing chuck according to claim 2, wherein the plurality of openings comprise a plurality of flow guide holes, the plurality of flow guide holes are configured to guide the first gas ejected from the plurality of support force nozzles to flow back to the nozzle portion when the first gas encounters the wafer, the gas channel portion further comprises a third gas channel, and the third gas channel is configured to make the first gas that has flowed back to the nozzle portion flow out of the air-bearing chuck.

19. The air-bearing chuck according to claim 1, wherein the air-bearing chuck has a mirror polished surface higher than or equal to level N4 in accordance with an ISO standard.

20. The air-bearing chuck according to claim 1, wherein a material of the nozzle portion comprises any one of aluminum, glass, microcrystalline silicon and ceramic, the material is mirror polished, and the top surface, obtained after being polished, of the nozzle portion is sufficiently flat, so that interference fringes are shown on the top surface of the nozzle portion.