METHODS AND APPARATUS FOR ACTIVE SUBSTRATE PRECESSION DURING CHEMICAL MECHANICAL POLISHING

Abstract

In some aspects, a chemical mechanical polishing (CMP) apparatus is provided that includes a polishing head having (a) a rotatable spindle; (b) a membrane coupled to the rotatable spindle and adapted to press a substrate against a polishing pad during polishing of the substrate; and (c) a retaining ring rotatable coupled to the spindle and adapted to surround a substrate being pressed against a polishing pad during polishing and to limit lateral movement of the substrate relative to the polishing head. The CMP apparatus also includes a drive mechanism coupled to the retaining ring and adapted to drive the retaining ring at a different rate of rotation than the spindle during polishing. Numerous other aspects are provided.

Description

FIELD OF THE INVENTION

The present invention relates to semiconductor device processing, and more particularly to active substrate precession during chemical mechanical polishing.

BACKGROUND OF THE INVENTION

During semiconductor device manufacturing, numerous material layers are deposited, patterned and etched to form electronic circuitry and/or electrical connections on the substrate. In many instances, a top surface of a substrate may be planarized between processing steps. Such planarization typically is performed using an etch-back step or chemical mechanical polishing (CMP).

During CMP, a substrate is placed face down on a polishing pad and pressed against, and rotated relative to, the polishing pad via a polishing head in the presence of a slurry. The slurry may contain abrasive particles and/or chemicals that assist in material removal from the substrate. Polishing is continued until enough material is removed to form a planar surface on the substrate.

Maintaining uniformity across a substrate during CMP is important to ensure uniform layer thicknesses for devices formed on the substrate. However, maintaining thickness uniformity across the entire surface of a substrate is difficult. This is particularly true for larger diameter substrates. Therefore, a need exists for methods and apparatus for improving uniformity during chemical mechanical polishing, particularly for large substrate sizes.

SUMMARY OF THE INVENTION

In some aspects, a chemical mechanical polishing (CMP) apparatus is provided that includes a polishing head having (a) a rotatable spindle; (b) a membrane coupled to the rotatable spindle and adapted to press a substrate against a polishing pad during polishing of the substrate; and (c) a retaining ring rotatable coupled to the spindle and adapted to surround a substrate being pressed against a polishing pad during polishing and to limit lateral movement of the substrate relative to the polishing head. The CMP apparatus also includes a drive mechanism coupled to the retaining ring and adapted to drive the retaining ring at a different rate of rotation than the spindle during polishing.

In some aspects, a chemical mechanical polishing apparatus is provided that includes a polishing head having (a) a rotatable spindle; (b) a membrane coupled to the rotatable spindle and adapted to press a substrate against a polishing pad during polishing of the substrate; (c) a retaining ring coupled to the spindle and adapted to surround a substrate being pressed against a polishing pad during polishing and to limit lateral movement of the substrate relative to the polishing head; and (d) at least one rotation mechanism coupled to the retaining ring, adapted to contact a substrate during polishing and adapted to allow the substrate to rotate at a different rate than the spindle during the during polishing.

In some aspects, a method of polishing a substrate is provided that includes pressing the substrate against a polishing pad using a polishing head having (a) a rotatable spindle; (b) a membrane coupled to the rotatable spindle and adapted to press the substrate against the polishing pad during polishing of the substrate; and (c) a retaining ring rotatable coupled to the spindle and adapted to surround the substrate being pressed against the polishing pad during polishing and to limit lateral movement of the substrate relative to the polishing head. The method includes rotating the spindle and membrane of the polishing head at a first rotation rate during polishing; and rotating the retaining ring of the polishing head at a second rotation rate during polishing so as to cause the substrate to rotate relative to the membrane of the polishing head.

In some aspects, a method of polishing a substrate is provided that includes pressing the substrate against a polishing pad using a polishing head having (a) a rotatable spindle; (b) a membrane coupled to the rotatable spindle and adapted to press the substrate against the polishing pad during polishing of the substrate; (c) a retaining ring coupled to the spindle and adapted to surround the substrate being pressed against the polishing pad during polishing and to limit lateral movement of the substrate relative to the polishing head; and (d) at least one rotation mechanism coupled to the retaining ring, adapted to contact the substrate during polishing and adapted to allow the substrate to rotate at a different rate than the spindle during the during polishing. The method includes rotating the spindle and membrane of the polishing head at a first rotation rate during polishing; and rotating the at least one rotation mechanism coupled to the retaining ring of the polishing head at a second rotation rate during polishing so as to cause the substrate to rotate relative to the membrane of the polishing head.

Numerous other aspects are provided. Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram depicting a side view of an example chemical-mechanical planarization system for polishing substrates according to embodiments of the present invention.

FIGS. 2A-2B are top schematic views of a substrate and retaining ring during polishing in accordance with embodiments of the present invention.

FIG. 3 is a schematic side view of a first embodiment of an example polishing system provided in accordance with the present invention.

FIG. 4A is a schematic side view of a second embodiment of an example polishing system provided in accordance with the present invention.

FIGS. 4B-4E are schematic top views of example embodiments of the polishing system of FIG. 4A in accordance with the present invention.

DETAILED DESCRIPTION

The present invention provides methods and apparatus for improving uniformity during chemical mechanical polishing of large substrates (e.g., semiconductor wafers, glass substrates used for liquid crystal displays (LCDs) or solar cells, or any other similar underlying and/or supporting layer/structure).

As stated, during CMP a substrate is placed face down on a polishing pad and pressed against, and rotated relative to, the polishing pad via a polishing head. A slurry containing abrasive particles and/or chemicals may be supplied to the polishing pad to assist in material removal from the substrate as the substrate is pressed against and rotated relative to the polishing pad. In this manner, the top surface of the substrate may be planarized.

FIG. 1 illustrates a side view of an example chemical-mechanical planarization (CMP) system 100 for polishing substrates in accordance with the present invention. The system 100 includes a load cup assembly 102 for receiving a substrate (not shown in FIG. 1) to be polished and for holding the substrate in place for a polishing head 104 to pick up. The polishing head 104 is supported by an arm 106 that is operative to move the head 104 between the load cup assembly 102 and a polishing pad 108 on a rotating platen 110. In operation, the polishing head 104 picks up the substrate from the load cup assembly 102 and carries it to the polishing pad 108. As the polishing pad 108 is rotated on the platen 110, the head 104 rotates and pushes the substrate down against the polishing pad 108. For example, an expandable membrane (not shown) within the polishing head 104 may contact and press the substrate against the polishing pad 108. Note that in the embodiment shown, the diameter of the polishing pad 108 is more than twice that of the substrate. Other platen, polishing pad and/or substrate sizes may be used.

With reference to FIGS. 2A-2B, to maintain a substrate 202 in position under a polishing head 104, the polishing head 104 includes a retaining ring 204 that surrounds the substrate 202 and limits its lateral movement during polishing. The substrate 202 has a slightly smaller diameter D₁ than a diameter D₂ of the retaining ring 204 (forming a gap 206 between the substrate 202 and retaining ring 204 which is exaggerated in FIGS. 2A-2B). In some embodiments, the gap 206 may be about 0.01 inches, although other gap sizes may be used.

Rotation of the polishing pad 108 during polishing generates a force that presses the substrate 202 against the retaining ring 204 as shown in FIG. 2B (causing the center of rotation of the substrate 202 to no longer align with the center of rotation of the polishing head 104/retaining ring 204). As mentioned, the polishing head 104 is rotated during polishing, which causes the retaining ring 204 to similarly rotate. This rotation of the retaining ring 204 causes rotation (precession) of the substrate 202 in a manner similar to a gear wheel due to the misalignment of the centers of rotation of the substrate 202 and retaining ring 204. (Note that the membrane of the polishing head 104 used to press the substrate 202 against the polishing pad 108 typically has a low coefficient of friction, allowing the substrate 202 to rotate relative to the membrane of the polishing head 104 during polishing.)

Due to alignment and/or tolerances within the polishing head 104, the polishing head 104 may generate a non-concentric pressure profile as it presses the substrate 202 against the polishing pad 108. Such a non-concentric pressure profile may produce a non-concentric and/or asymmetrical polish profile on the substrate 202, and is thus undesirable. However, rotation (precession) of the substrate 202 relative to the polishing head 104 during polishing, as described above, may alleviate the affects of the non-concentric pressure profile produced by the polishing head 104. For example, for a 300 mm substrate, the mismatch between the diameter of the substrate 202 and the retaining ring 204 is typically large enough to allow the substrate 202 to precess about 180 degrees or more relative to the polishing head 104 during polishing. This is generally sufficient to reduce and/or mask any asymmetric polishing profile that might otherwise result from a polishing head's non-concentric pressure profile. However, any asymmetric polishing profile is undesirable. Furthermore, for larger substrate sizes such as 450 mm substrates, asymmetric polishing profiles may be more pronounced. For example, the amount a substrate precesses relative to the retaining ring 204 is proportional to the gap between the substrate and retaining ring divided by the diameter of the substrate:

amount of precession˜(D₂−D₁)/D₁=(gap 206)/D₁

Accordingly, if the gap 206 remains relatively constant as substrate size is increased, the amount the substrate 202 precesses during polishing is reduced. This reduced precession may be insufficient to mask the asymmetric polishing profile resulting from a non-concentric polishing head pressure profile.

In accordance with embodiments of the present invention, a polishing head/retaining ring configuration is employed that allows active control over the amount a substrate precesses during polishing. Such “active precession” allows a substrate to precess sufficiently to reduce and/or minimize the asymmetric polishing profile resulting from a non-concentric polishing head pressure profile. This is beneficial to substrates of any size (e.g., 200 mm, 300 mm, 450 mm or other sized semiconductor wafers, or any other substrate type or size).

FIG. 3 is a schematic side view of a first embodiment of an example polishing system 300 provided in accordance with the present invention. With reference to FIG. 3, the polishing system 300 includes polishing head 104 coupled to a controller 302. The controller 302 may be a computer, a microcontroller, a programmable logic controller or any other suitable controller.

Polishing head 104 includes a central spindle 304 rotatably coupled to a retaining ring 204 via one or more bearing assemblies 306. A membrane 308 is coupled to the central spindle 304 and may contact substrate 202, pressing substrate 202 against polishing pad 108. The membrane 308 is adapted to expand to press the substrate 202 against the polishing pad 108. For example, the membrane 308 may be a liquid or gas filled bladder. In some embodiments, the portion of the membrane 308 that contacts the substrate 202 may be a low friction material such as polytetrafluoroethylene (PTFE) or a similar material.

Spindle 304 is coupled to a first drive mechanism 310 and retaining ring 204 is coupled to a second drive mechanism 312 to allow the spindle 304 and retaining ring 204 to be driven at different rotation rates. In some embodiments, a single drive mechanism may be used through suitable gearing and/or belts to cause spindle 304 and retaining ring 204 to rotate at different rates. Any suitable drive mechanisms may be used such as one or more motors. Controller 302 may include computer program code for directing rotation of spindle 304 and/or retaining ring 204 during polishing as described further below.

Bearing assembly 306 keeps retaining ring 204 concentric with membrane 308 and may comprise any suitable bearing assembly such as ball bearings, roller bearings, slide bearings, track bearings, non-contact bearings, or the like. The components of the bearing assembly 306, such as the balls and races, may be formed of a material compatible with the chemistry used during chemical mechanical polishing within the polishing system 300 so as not to degrade rapidly or generate particles that could contaminate a substrate being polished. For instance, the bearing assembly 306 may be formed of a suitable polymer material. Alternatively or additionally, the bearing assembly 306 may be shielded, sealed or otherwise isolated from the polishing chemistry.

In operation, substrate 202 is placed on the polishing pad 108 and is pressed against the polishing pad 108 by polishing head 104 (via expansion of membrane 308). Retaining ring 204 surrounds substrate 202 within the polishing head 104, and also contacts polishing pad 108. Note that a suitable abrasive slurry (not shown) may be applied to the polishing pad 108 before and/or during polishing of the substrate 202.

Controller 302 causes drive 310 to rotate spindle 304 and membrane 308 as indicated by arrow 314, and drive 312 to rotate retaining ring 204 as indicated by arrow 316. Polishing pad 108 is also rotated using the same or a different drive mechanism under control of controller 302 or another controller (not shown). As stated, rotation of polishing pad 108 causes substrate 202 to slide into contact with retaining ring 204 as indicated by arrow 318.

In some embodiments, retaining ring 204 is rotated at a faster rate than spindle 304. In other embodiments, retaining ring 204 is rotated at a slower rate than spindle 304. In either case, retaining ring 204 and spindle 304 rotate at different rates so that substrate 302 is actively precessed relative to membrane 308 (e.g., so that substrate 202 fully rotates beneath membrane 308 during polishing).

In one or more embodiments, spindle 304 may be rotated at a rate of about 10 to about 150 rotations per minute (RPM), while retaining ring 204 may be rotated at a rate of about 5 to about 300 RPM. For example, in some embodiments, retaining ring 204 may be rotated at about one-half the rotation rate of spindle 304, while in other embodiments, retaining ring 204 may be rotated at about twice the rotation rate of spindle 304. Other rotation rates may be used for the spindle 304 and/or retaining ring 204. Retaining ring 204 may be rotated during a portion of or the entire time spindle 304 is rotated, and/or may be maintained stationary one or more times during polishing. Further, in some embodiments, retaining ring 204 may switch direction of rotation during polishing.

Polishing of substrate 202 continues until a desired amount of material is removed from the substrate 202. Because retaining ring 204 rotates at a different rate than spindle 204, substrate 202 is actively precessed relative to membrane 308 and non-concentric or otherwise asymmetric polishing head pressure profile is averaged out during polishing (e.g., producing a more uniform polish). This is beneficial to substrates of any size (e.g., 200 mm, 300 mm, 450 mm or other sized semiconductor wafers, or any other substrate type or size).

FIG. 4A is a schematic side view of a second embodiment of an example polishing system 400 provided in accordance with the present invention. The polishing system 400 of FIG. 4A is similar to the polishing system 300 of FIG. 3. However, in the polishing system 400 of FIG. 4A, the retaining ring 204 remains stationary during polishing as indicated by coupling 402, and one or more rollers 404 are employed to rotate substrate 202 relative to membrane 308 during polishing. FIG. 4B is a schematic top view of the polishing system 400 showing two rollers 404a and 404b. It will be understood that other numbers of rollers may be used (e.g., 3, 4, 5, etc.).

Rollers 404a and 404b may be formed from any suitable material such as polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyethylene terephthalate (PET) or the like. Exemplary diameters for the rollers 404a-b may range from about 0.5 to about 2 inches. In some embodiments, the rollers 404a-b may be spaced apart by about 1 to 5 inches. Other materials, sizes and/or spacings may be used for the rollers.

Controller 302 causes drive 310 to rotate spindle 304 and membrane 308 as indicated by arrow 314, and drive 312 to rotate rollers 404a and 404b as indicated by arrow 416. In some embodiments a single drive mechanism may be used to rotate spindle 304, roller 404a and/or roller 404b through use of appropriate belts, gears or the like; or a separate drive mechanism may be used as shown in FIG. 4A. Polishing pad 108 is also rotated using the same or a different drive mechanism under control of controller 302 or another controller (not shown). Rotation of polishing pad 108 causes substrate 202 to slide into contact with rollers 404a and 404b as indicated by arrow 418. This region may be referred to as the trailing edge of the retaining ring 204, while the opposite side may be referred to as the leading edge of the retaining ring 204.

In some embodiments, rollers 404a and 404b are rotated at a faster rate than spindle 304. In other embodiments, rollers 404a and 404b are rotated at a slower rate than spindle 304. In either case, rollers 404a-b and spindle 304 rotate at different rates so that substrate 302 is actively precessed relative to membrane 308 (e.g., so that substrate 202 fully rotates beneath membrane 308 during polishing).

In one or more embodiments, spindle 304 may be rotated at a rate of about 10 to about 150 rotations per minute (RPM), while rollers 404a-b may be rotated at a rate of about 30 to about 3600 RPM (depending on the diameter of the rollers). For example, in some embodiments, rollers 404a-b may be rotated so that substrate 202 rotates at about one-half the rotation rate of spindle 304, while in other embodiments, rollers 404a-b may be rotated so that substrate 202 rotates at about twice the rotation rate of spindle 304. Other rotation rates may be used for the spindle 304 and/or rollers 404a-b. Rollers 404a-b may be rotated during a portion of or the entire time spindle 304 is rotated, and/or may be maintained stationary one or more times during polishing. Further, in some embodiments, rollers 404a-b may switch direction of rotation during polishing.

Polishing of substrate 202 continues until a desired amount of material is removed from the substrate 202. Because rollers 404a-b rotate at a different rate than spindle 204, substrate 202 is actively precessed relative to membrane 308 and any non-concentric or otherwise asymmetric polishing head pressure profile is averaged out during polishing (e.g., producing a more uniform polish). This is beneficial to substrates of any size (e.g., 200 mm, 300 mm, 450 mm or other sized semiconductor wafers, or any other substrate type or size).

In general, retaining ring 204 may be formed from any suitable material such as polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyethylene terephthalate (PET) or the like. In embodiments in which rollers 404 are employed, such as in FIGS. 4A-4C, the retaining ring 204 may be modified to improve substrate edge polish behavior. For example, features used to allow entry of slurry into the polishing head 104 may be modified depending on the application. In some embodiments, it may be desirable to have slurry build up during polishing so additional slurry grooves may be provided along the leading edge of the retaining ring 204 relative to the trailing edge of the retaining ring 204 (near rollers 404a-b). Likewise, in some embodiments it may be desirable to have little slurry build up during polishing, so more slurry grooves may be provided along the trailing edge of the retaining ring 204 (near rollers 404a-b) than along the leading edge of the retaining ring 204. Similarly, different forces may be applied along the trailing edge of the retaining ring 204 relative to the leading edge of the retaining ring 204 to better control pad rebound during polishing. Similarly, the retaining ring 204 may have different geometries (e.g., widths) along the trailing and leading edges of the retaining ring 204.

While retaining ring 204 is shown as being a single ring section, it will be understood that retaining ring 204 may comprise multiple ring sections as illustrated by ring sections 204a and 204b in FIG. 4C. More than two ring sections may be used, as may inner or outer ring sections. FIG. 4D illustrates a retaining ring 204 having larger and/or more slurry grooves 420a along a leading edge of the retaining ring 204 than slurry grooves 420b along the trailing edge of the retaining ring 204. Such an arrangement may be reversed if desired. FIG. 4E illustrates a retaining ring 204 that is wider along a leading edge of the retaining ring 204 than along a trailing edge of the retaining ring 204. Such an arrangement may be reversed if desired.

Accordingly, while the present invention has been disclosed in connection with example embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.

Claims

1. A chemical mechanical polishing apparatus comprising:

a polishing head comprising: a rotatable spindle; a membrane coupled to the rotatable spindle and adapted to press a substrate against a polishing pad during polishing of the substrate; and a retaining ring rotatable coupled to the spindle and adapted to surround a substrate being pressed against a polishing pad during polishing and to limit lateral movement of the substrate relative to the polishing head; and

a drive mechanism coupled to the retaining ring and adapted to drive the retaining ring at a different rate of rotation than the spindle during polishing.

2. The chemical mechanical polishing apparatus of claim 1 further comprising a controller adapted to cause the drive mechanism to rotate the retaining ring at a different rate of rotation than the spindle during polishing.

3. The chemical mechanical polishing apparatus of claim 2 wherein the controller is adapted to cause the drive mechanism to rotate the retaining ring at about twice the rate of rotation of the spindle during polishing.

4. The chemical mechanical polishing apparatus of claim 2 wherein the controller is adapted to cause the drive mechanism to rotate the retaining ring at about one-half the rate of rotation of the spindle during polishing.

5. A method of polishing a substrate comprising:

pressing the substrate against a polishing pad using a polishing head having: a rotatable spindle; a membrane coupled to the rotatable spindle and adapted to press the substrate against the polishing pad during polishing of the substrate; and a retaining ring coupled to the spindle and adapted to surround the substrate being pressed against the polishing pad during polishing and to limit lateral movement of the substrate relative to the polishing head;

rotating the spindle and membrane of the polishing head at a first rotation rate during polishing; and

rotating the retaining ring of the polishing head at a second rotation rate during polishing so as to cause the substrate to rotate relative to the membrane of the polishing head.

6. The method of claim 5 wherein the first rate is less than the second rate.

7. The method of claim 5 wherein the first rate is greater than the second rate.

8. A chemical mechanical polishing apparatus comprising:

a polishing head comprising: a rotatable spindle; a membrane coupled to the rotatable spindle and adapted to press a substrate against a polishing pad during polishing of the substrate; a retaining ring rotatable coupled to the spindle and adapted to surround a substrate being pressed against a polishing pad during polishing and to limit lateral movement of the substrate relative to the polishing head; and at least one rotation mechanism coupled to the retaining ring, adapted to contact a substrate during polishing and adapted to allow the substrate to rotate at a different rate than the spindle during the during polishing.

9. The chemical mechanical polishing apparatus of claim 8 wherein the at least one rotation mechanism comprises at least one roller rotatably coupled to a trailing edge of the retaining ring.

10. The chemical mechanical polishing apparatus of claim 8 wherein the retaining ring is stationary during polishing.

11. The chemical mechanical polishing apparatus of claim 8 wherein the retaining ring comprises multiple retaining ring sections.

12. The chemical mechanical polishing apparatus of claim 8 wherein the retaining ring has a different number of slurry grooves along a leading edge of the retaining ring than along a trailing edge of the retaining ring.

13. The chemical mechanical polishing apparatus of claim 8 wherein the retaining ring has a different width along a leading edge of the retaining ring than along a trailing edge of the retaining ring.

14. A method of polishing a substrate comprising:

pressing the substrate against a polishing pad using a polishing head having: a rotatable spindle; a membrane coupled to the rotatable spindle and adapted to press the substrate against the polishing pad during polishing of the substrate; a retaining ring coupled to the spindle and adapted to surround the substrate being pressed against the polishing pad during polishing and to limit lateral movement of the substrate relative to the polishing head; and at least one rotation mechanism coupled to the retaining ring, adapted to contact the substrate during polishing and adapted to allow the substrate to rotate at a different rate than the spindle during the during polishing;

rotating the spindle and membrane of the polishing head at a first rotation rate during polishing; and

rotating the at least one rotation mechanism coupled to the retaining ring of the polishing head at a second rotation rate during polishing so as to cause the substrate to rotate relative to the membrane of the polishing head.

15. The method of claim 14 wherein the at least one rotation mechanism comprises at least one roller rotatably coupled to a trailing edge of the retaining ring.

16. The method of claim 14 wherein the retaining ring is stationary during polishing.

17. The method of claim 14 wherein the retaining ring comprises multiple retaining ring sections.

18. The method of claim 14 wherein the retaining ring has a different number of slurry grooves along a leading edge of the retaining ring than along a trailing edge of the retaining ring.

19. The method of claim 14 wherein the retaining ring has a different width along a leading edge of the retaining ring than along a trailing edge of the retaining ring.

20. The method of claim 14 further comprising applying a different pressure along a leading edge of the retaining ring than along a trailing edge of the retaining ring during polishing.