Minimizing particle contamination of semiconductor wafers during pressure evacuation by selective orientation and shielding

Abstract

A method including placing a wafer active side down in a chamber and reducing the pressure in the chamber. An apparatus or system including a chamber having an interior volume suitable to accommodate a semiconductor wafer and capable of maintaining a vacuum; and a support to maintain a wafer in the volume of the chamber with minimum or no contact with an active side of the wafer, wherein an amount of particles that an active side of a wafer is exposed to during a pressure change in the chamber is minimized when the wafer is loaded in the chamber in an active side down configuration.

Description

BACKGROUND

FIELD

Semiconductor processing.

BACKGROUND

In the field of semiconductor processing, particularly, at the wafer level, semiconductor substrates (e.g., wafers) are subject to a number of processing operations in one or more processing chambers. One processing environment is a under vacuum condition. To bring a condition to a vacuum, a substrate, such as a wafer, is generally placed in a chamber and the chamber evacuated to bring the pressure to a vacuum. Often times, the vacuum processing is a multi-chamber operation in which a substrate is placed in a first chamber or load lock. The first chamber or load lock is connected to a second chamber (processing chamber) where modifications to the substrate are made. Utilizing a load lock means that a wafer can be loaded into a processing chamber without having to pump-down the processing chamber again. One reason for utilizing the load lock is that a subsequent pumping down to a pressure required in a processing chamber tends to introduce contaminants as particles can get on the substrate during the pump-down. Accordingly, a substrate is loaded in a load lock which is then pumped down to the desired pressure of the processing chamber. After the load lock opens, the substrate is moved into the processing chamber.

Currently, substrates (e.g., wafers) are predominantly in an active side up orientation while pump-down and purging/venting is done. By active side up orientation is meant that a side of a wafer having either devices formed therein/thereon or intended to have devices formed therein/thereon faces a direction opposite the direction of gravity. In this state, the gravitational forces within the chamber act to pull particles onto an active surface of the substrate particularly during pump down.

Particle contamination in reduced pressure chambers, such as in a vacuum load lock environment may be a significant source of defects. These particles come from the chamber material itself, from handling operations, from previous operations in the chamber, etc. It is appreciated that contaminating particles have a varied size distribution. The number of small particles (e.g., sub-micron sized particles) far exceeds the number of larger particles. As critical densities increase on wafers, the contribution of smaller particles to particle contamination increases.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, aspects, and advantages of embodiments will become more thoroughly apparent from the following detailed description, appended claims, and accompanying drawings in which:

FIG. 1 shows a schematic process sequence of loading a wafer into a load lock.

FIG. 2 shows a wafer in a load lock chamber and illustrates a purge process.

FIG. 3 shows the load lock of FIG. 2 during a pump down process.

FIG. 4 shows the load lock of FIG. 3 at a process pressure.

FIG. 5 shows the wafer of FIG. 4 being loaded from a load lock into a processing chamber at a desired pressure.

FIG. 6 shows a schematic top view of a wafer supported in an active side down configuration with a support serving also as a particle deflection plate.

FIG. 7 shows a schematic top view of a wafer supported in an active side down configuration by a support with a particle deflection plate between the support and the wafer.

FIG. 8 shows a schematic top side view of a wafer supported by an electrostatic charge in an active side down configuration with a particle deflection place beneath the wafer.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates the loading of a substrate (e.g., wafer) into a load lock. Referring to FIG. 1, load lock 100 includes chamber 110 that is, for example, a metal (e.g., aluminum) material having a volume 105 that is capable of maintaining a reduced pressure environment, including a vacuum or zero pounds per square inch (psi). Volume 105 is also sized to accommodate at least one wafer (e.g., a 200 millimeters (mm) or 300 mm wafer) therein. Chamber 110 includes exhaust port 120 that may be used to evacuate chamber 110. Also connected to chamber 110 is pressure sensor 130 such as Baratrome pressure sensor. A pressure indication of pressure sensor 130 may be read by processor 140. Processor 140, in one example, includes machine-readable program instructions to record pressure measurements of volume 105, and to perform a method to evacuate chamber through exhaust port 120 to a predetermined pressure. Chamber 110 also includes gas entry port 155 to introduce a gaseous species into volume 105. In the embodiment shown in FIG. 1, purge gas 150 is connected to entry port 155. Gas source 150 is, for example, a purge gas, such as nitrogen (N₂). Introduction of a gas through gas source 150 is regulated by valve 160. Valve 160 is controlled, in this example, by processor 140 and machine-readable instructions therein (e.g., instructions to perform a method to purge chamber 110).

FIG. 1 also shows arm 175 such as a robotic arm, holding wafer 170. In an initial holding phase, wafer 170 includes active side 180 facing, as viewed, upward or against gravity. In one embodiment, arm 175 may be actuated to rotate so that active side 180 of wafer 170 is directed at gravity (e.g., rotated 180 degrees downward as viewed). Arm 175 may maintain wafer 170 in an active side down (with gravity) configuration by, for example, side clamping, electrostatic forces or a vacuum or similar reduced pressure on a back side of wafer 170. Arm 175 may be advanced to introduce wafer 170 into chamber 110 in an active side down configuration and retracted to be free from the chamber. Machine-readable program instructions in processor 140 or a separate processor may be used to control among other functions the securing of wafer 170 by arm 175, the rotation of arm 175, and the placement of wafer 170 into chamber 110.

Referring again to the contents of volume 105 of chamber 110, volume 105 also includes, in one embodiment, particle displacement plate 190. In one embodiment, particle displacement plate 190 has a diameter that is equal to or slightly less than a diameter of wafer 170. By slightly less, it is meant, in one embodiment, but not necessarily limited to, one millimeter to three millimeters less in diameter (e.g., 5-7 mm for a 200 mm wafer or 9-11 mm for a 300 mm wafer). In the embodiment shown, particle displacement plate 190 is supported by stage 195 that may be moved up or down (as viewed) within chamber 105 such movement optionally controlled by program instructions in processor 140 or another processor. In one embodiment, particle displacement plate 190 is advanced to a position, in one embodiment, within a few millimeters (e.g., 1-4 mm) from active side 180 of wafer 170.

FIGS. 2-4 illustrate a series of processing operations within chamber 110 of load lock 100. Referring to FIG. 2, wafer 170 is placed in chamber 110, volume 105 of chamber 110 is sealed and purge gas 210 is introduced. In one embodiment, purge gas 210 is a nitrogen gas.

FIG. 3 shows chamber 110 during a pump-down operation. In one embodiment, volume 105 of chamber 110 is reduced in pressure (pumped down) to a vacuum condition. Referring to FIG. 1, pressure sensor 130 may be used to monitor the pressure in chamber 110 and exhaust port 120 may be used to evacuate chamber 110. With wafer 170 in an active side down (with gravity) position, the pump down process occurs in such a way to allow gravitational force to act against particles moving towards wafer 170. Particle displacement plate 190 inhibits particles from bouncing towards active side 180 of wafer 170. As the pressure drops during a pump down process, a Stokes drag experienced by particles 310 decreases significantly. If particles 310 achieve ballistic velocities, the particles can suffer multiple collisions with chamber 110 and other surfaces and ultimately end up on active side 180 of wafer 170. Particle displacement plate 190 inhibits the possibility of colliding particles ending up on active side 180.

FIG. 4 shows chamber 110 following the pump down process. In FIG. 4, the pressure in volume 105 of chamber 110 is selected to be, in one embodiment, equivalent to a pressure in a processing chamber where wafer 170 will be transferred. The number of unwanted particles on active side 180 of wafer 170 have been reduced due to the configuration of wafer 170 in chamber 110 and, in this embodiment, the presence of particle displacement plate 190.

FIG. 5 shows wafer 170 transferred from chamber 110 to processing chamber 510. In one embodiment, chamber 110 is connected to processing chamber 510 through entry port 520 that may be sealed while chamber 110 is undergoing a pump down process. In one embodiment, a volume of chamber 510 has been pumped down to a pressure equivalent to the pumped down pressure of volume 105 of chamber 110. Wafer 170 may be transferred to chamber 510 in an active side up or active side down configuration depending on the desired processing environment. In chamber 510, one or more semiconductor processing operations may be performed on wafer 170. Representative processing operations that may be performed under vacuum conditions include implant, etch, extreme ultraviolet lithography, and masked-beam processing. Following processing, wafer 170 may optionally be returned to chamber 110 in an active side down configuration and purging operations may be performed. In this manner, after processing the potential of particle contaminants contacting active side 180 of wafer 170 may be reduced.

FIGS. 6-8 show various ways to support a wafer within a chamber, such as a load lock, during a pump down process. Each embodiment shows a wafer in an active side down (in a direction with gravity) configuration. FIG. 6 shows wafer 670 supported by support 690. In this embodiment, support 690 serves as a support and as a particle displacement plate. Wafer 670 is supported by support 690 in an active edge grip support configuration with vertical supports 695 (e.g., a few millimeters in length) supporting wafer 670 outside an active area (e.g., at several points along an edge of wafer 670). FIG. 7 shows a second embodiment where wafer 770 is supported in an active edge grip configuration by support 775 with vertical supports 795. Particle displacement plate 790 is placed on support 775 (and supported by vertical supports 777) and, in one embodiment, has a diameter smaller than support 775. In one embodiment, support 775 has a diameter equal to or greater than a diameter of wafer 770.

FIG. 8 shows a third embodiment where wafer 870 is chucked by chuck 875. A passive side of wafer 870 is supported by chuck 875 through, for example, electrostatic forces. In this embodiment, particle displacement plate 890 is not in contact with an active side of wafer 870.

In the preceding detailed description, reference is made to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

Claims

1. A method comprising:

placing a wafer active side down in a chamber; and

reducing the pressure in the chamber.

2. The method of claim 1, wherein reducing the pressure comprises reducing the pressure from a first pressure to a vacuum.

3. The method of claim 1, wherein the chamber is a first chamber, the method further comprising:

after reducing the pressure in the first chamber, transferring the wafer to a second chamber.

4. The method of claim 3, further comprising modifying the active side of the wafer in the second chamber.

5. The method of claim 4, wherein modifying comprises an extreme ultraviolet light patterning technique.

6. The method of claim 4, further comprising, after modifying, transferring the wafer from the second chamber to the first chamber.

7. An apparatus comprising:

a chamber having an interior volume suitable to accommodate a semiconductor wafer and capable of maintaining a vacuum; and

a support to maintain a wafer in the volume of the chamber with minimum or no contact with an active side of the wafer,

wherein an amount of particles that an active side of a wafer is exposed to during a pressure change in the chamber is minimized when the wafer is loaded in the chamber in an active side down configuration.

8. The apparatus of claim 7, further comprising a plate disposed beneath an active side of a wafer when the wafer is loaded in the chamber in an active side down configuration.

9. The apparatus of claim 8, wherein the plate comprises the support.

10. The apparatus of claim 8, wherein the plate is disposed between the support and an active side of a wafer when a wafer is loaded in the chamber in an active side down configuration.

11. The apparatus of claim 8, wherein the plate has a dimension similar to a dimension of an active side of a wafer.

12. The apparatus of claim 7, wherein the chamber is a first chamber adapted to be coupled to a second chamber such that a pressure in the first chamber can be maintained on a transfer of a wafer from the first chamber to the second chamber.

13. A system comprising:

a first chamber having an interior volume suitable to accommodate a semiconductor wafer and capable of maintaining a vacuum, the first chamber comprising: a support to maintain a wafer in the volume of the chamber with minimum or no contact with an active side of the wafer; a plate disposed between and a wall of the chamber and an active side of a wafer when the wafer is loaded in the chamber in an active side down configuration; and

a second chamber coupled to the first chamber and having an interior volume suitable to accommodate a semiconductor wafer and capable of maintaining a pressure established in the first chamber on transfer of a wafer from the first chamber to the second chamber, wherein the second chamber is capable of performing an operation to modify an active site of a wafer.

14. The system of claim 13, wherein the plate comprises the support.

15. The system of claim 13, wherein the plate has a dimension similar to a dimension of an active side of a wafer.

16. The system of claim 13, wherein the plate has a diameter less than a diameter of a wafer within the volume of the first chamber.