SUBSTRATE PRECESSION MECHANISM FOR CMP POLISHING HEAD

Abstract

A substrate precession apparatus for a carrier head is provided. The apparatus enables substrate precession, which is the rotational movement of the substrate relative to the carrier head during polishing of the substrate. The carrier head and a retaining ring assembly may be de-coupled and move independently of one another to promote substrate precession during a CMP process.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments described herein generally relate to a chemical mechanical polishing carrier head. More specifically, embodiments described herein relate to a substrate precession mechanism for a carrier polishing head.

2. Description of the Related Art

An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon substrate. One fabrication step involves depositing a filler layer over a non-planar surface, and planarizing the filler layer until the non-planar surface is exposed. For example, a conductive filler layer may be deposited on a patterned insulative layer to fill trenches or holes in the insulative layer. The filler layer is then polished until a raised pattern of the insulative layer is exposed. After planarization, portions of the conductive layer remaining between the raised pattern of the insulative layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. In addition, planarization is needed to planarize the substrate surface for photolithography.

Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head of a CMP apparatus. The exposed surface of the substrate is placed against a rotating polishing disk pad or belt pad. The polishing pad may be either a standard pad or a fixed-abrasive pad. A standard pad may have a durable roughened surface, whereas a fixed-abrasive pad may have abrasive particles held in a containment media. The carrier head provides controllable load on the substrate to push the substrate against the polishing pad. The carrier head may have a retaining ring which holds the substrate in place during polishing. A polishing liquid, such as a slurry, including at least one chemically reactive agent and abrasive particles, may be supplied to the surface of the polishing pad during polishing.

Maintaining a uniform removal profile of the substrate is an important aspect of a CMP process. Maintaining the relatively uniform profile across a surface of the substrate in both the polar and radial directions may be desirable. As such, it may be important to employ methods which reduce localized non-uniformities of the planarization profile.

SUMMARY OF THE INVENTION

Embodiments described herein generally relate to a substrate precession mechanism for a CMP carrier head. A substrate precession apparatus for a CMP carrier head is provided. The apparatus enables substrate precession, which is the rotational movement of the substrate relative to the carrier head during polishing of the substrate. The carrier head and a retaining ring assembly that may be de-coupled, allowing the carrier head and retaining ring assembly to move independently of one another to promote substrate precession during a CMP process.

In one embodiment, an apparatus for polishing a substrate is provided. The apparatus comprises a head assembly, and a retaining ring assembly. The retaining ring assembly comprises an internal gear and a bearing disposed between the head assembly and the retaining ring assembly. The bearing is adapted to decouple the retaining ring assembly from the head assembly. A drive assembly adapted to rotate the retaining ring assembly relative to the head assembly is also provided.

In another embodiment, a retaining ring assembly for a polishing head is provided. The retaining ring assembly comprises a retaining ring having an upper annular portion and a lower annular portion and a carrier ring coupled to the upper annular portion. The retaining ring assembly further comprises a bearing clamp coupled to the carrier ring, the bearing clamp adapted to receive a bearing, and an internal gear coupled to the bearing clamp.

In yet another embodiment, a method of operating a polishing apparatus is provided. The method comprises providing a polishing head assembly and a retaining ring assembly. The retaining ring assembly is decoupled from the polishing head assembly. The method also provides for rotating the polishing head at a first speed and rotating the retaining ring assembly at a second speed greater than the first speed.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

FIG. 1 is a partial cut-away view of a carrier head having a de-coupled retaining ring assembly.

FIG. 2 is a partial perspective view of the carrier head of FIG. 1.

FIG. 3 is a schematic bottom view of a retaining ring assembly and a substrate.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

Embodiments described herein generally relate to a substrate precession mechanism for a CMP carrier head. A substrate precession apparatus for a carrier head is provided. The apparatus enables substrate precession, which is the rotational movement of the substrate relative to the carrier head during polishing of the substrate. A carrier head and a retaining ring assembly may be de-coupled and move independently of one another to promote substrate precession during a CMP process.

Generally, varying pressures may be applied to various radial zones of a membrane member to create a backside pressure that may chuck a substrate to the CMP head. Varying the pressures may across the zones provides for a predetermined removal profile in each radial zone. However, adjusting the pressures in the radial zones does not completely adjust for non-uniformities in a polar direction. A non-uniformity of the membrane member may cause a non-uniform removal profile in the substrate. As such, providing “polar asymmetry” in the polishing process may remove or reduce the effect of local non-uniformities in the removal profile.

Embodiments described herein are generally provided with regard to polishing 300 mm substrates. However, embodiments described herein may be adapted to polishing substrates of other sizes, such as 100 mm or 450 mm substrates. The CMP head which may be adapted to benefit from the embodiments described herein is the TITAN HEAD™ or TITAN CONTOUR, available from Applied Materials, Inc., Santa Clara, Calif. However, it is contemplated that carrier heads available from other manufacturers may be adapted to employ the embodiments described herein.

FIG. 1 is a partial cut-away view of a conventional carrier head 100. The carrier head 100 includes a housing 106, a head assembly 102, and a retaining ring assembly 104. The housing 102 may generally be circular in shape and may be connected to a drive shaft (not shown) to rotate therewith during polishing. There may be passages (not shown) extending through the housing 102 for pneumatic control of the carrier head 100. The carrier head 100 also includes a retaining ring assembly 104 which includes a retaining ring 120, a carrier ring 140, a bearing clamp 110, and an internal gear 112. A bearing 130 may de-couple the head assembly 102 from the retaining ring assembly 104.

FIG. 2 is a partial perspective view of the carrier head 100 of FIG. 1 having a head assembly 102 and a de-coupled retaining ring assembly 104. The head assembly 102 may comprise the housing 106 which may generally be circular in shape and may be connected to a drive shaft (not shown) to rotate therewith during polishing. There may be passages (not shown) extending through the housing 106 for pneumatic control of the carrier head 100. A carrier body 208 may be flexibly coupled to the housing 106 and co-rotate with the housing 106. The carrier body 208 may also be coupled to a flexible membrane 250 that may be adapted to chuck a substrate 201 during a CMP process. The flexible membrane 250 may define a plurality of pressurizable chambers for chucking the substrate 201.

As previously described, the retaining ring assembly 104 may comprise a retaining ring assembly 120, carrier ring 140, a bearing clamp 110, and an internal gear 112. The carrier ring 140 may be a substantially ring-like structure. The carrier ring 140 may have an annular upper portion 244 and an annular lower portion 242. The annular upper portion 244 may be disposed adjacent to and below the bearing clamp 110. The annular lower portion 242 may be disposed adjacent to and above the retaining ring 120. The carrier ring 140 may have a recess or hole disposed therethrough to accommodate a fastening apparatus, such as a screw or bolt (not shown), to couple the bearing clamp 110, carrier ring 140, and retaining ring 120.

The retaining ring 120 may be formed from two rings, a lower annular ring 224 and an upper annular ring 222. The lower annular ring 224 and upper annular ring 222 may be coupled together. When the lower annular ring 224 and the upper annular ring 222 are joined, the two rings have substantially the same dimensions at the inner and outer diameters on their adjacent surfaces such that the lower annular ring 224 and the upper annular ring 222 form a flush surface where they are joined.

In embodiments configured for 300 mm substrates, the substrate 201 may have an outer diameter of about 11.811 in. In one embodiment, an inner diameter of the lower annular ring 224 may be between about 11.830 in and about 11.870 in, such as 11.852 in. In this embodiment, a gear ratio between the substrate 201 outer diameter and the lower annular ring 224 inner diameter may be about 0.99654. In another embodiment, the inner diameter of the lower annular ring 224 may be between about 11.890 in and about 11.950 in, such as about 11.912 in. In this embodiment, a gear ratio between the substrate 201 outer diameter and the lower annular ring 224 inner diameter may be about 0.99152.

In certain embodiments, the lower annular ring 224 and upper annular ring 222 may be attached by a bonding material (not shown) at their adjacent surfaces. The interface between the lower annular ring 224 and the upper annular ring 222 may prevent trapping of a slurry material in the retaining ring 120. The bonding material may be an adhesive material, such as a slow-curing or fast-curing epoxy. A high temperature epoxy may resist degradation of the bonding material due to high heat during the CMP process. In certain embodiments, the epoxy includes polyamide and aliphatic amines.

The upper annular ring 222 may have an inner surface 228 which may be adapted to couple with and provide support to the flexible membrane 250. The upper annular ring 222 may be formed from a material that may be more rigid than the lower annular ring 224, such as a metal, e.g. stainless steel, molybdenum, aluminum, ceramic materials, or other exemplary materials.

The lower annular ring 224 may be disposed adjacent to and below the upper annular ring 222. The lower annular ring 224 may have a substrate retaining surface 226 which may be adapted to retain the substrate 201 during the CMP process. The lower annular ring 224 may be formed from a material that is chemically inert in a CMP process, such as a plastic, for example, polyphenylene sulfide (PPS). The lower annular ring 224 may also be adapted to provide durability and a low wear rate. The lower annular ring 224 may be sufficiently compressible so that contact of the substrate 201 edge against the lower annular ring 224 does not cause the substrate 201 to chip or crack. However, the lower annular ring 224 should not be so elastic that downward pressure on the retaining ring 120 causes the lower annular ring 224 to extrude during the CMP process.

The bearing clamp 110 may be substantially ring-like. The bearing clamp 110 may be disposed adjacent to and above the annular upper portion 244 of the carrier ring 140. The bearing clamp 110 may be coupled to the carrier ring 140 by a fastener 213, such as a screw or bolt. The bearing clamp 110 may be formed from a material such as a metal, e.g. stainless steel, molybdenum, aluminum, ceramic materials, or other exemplary materials. An upper portion 216 of the bearing clamp 110 may provide support for the internal gear 112. The bearing clamp 110 may comprise a plurality of holes (not shown) which may be aligned with a plurality of holes (not shown) of the internal gear 112. A bearing receiving region 218 may be adapted to receive a bearing 130.

The bearing 130 may be coupled between the bearing clamp 110 and heads body 208. The bearing 130 may comprise a first annular surface 232 which may be coupled to and disposed adjacent to the bearing receiving region 218 of the bearing clamp 110. A second annular surface 234 may be coupled to and disposed adjacent to the carrier body 208. A plurality of ball bearings 236 may be disposed between the first annular surface 232 and the second annular surface 234 and may be adapted to decouple the head assembly 102 from the retaining ring assembly 104. The bearing 130 may provide an additional degree of rotational freedom to the carrier head 100. The additional degree of rotational freedom allows the retaining ring assembly 104 to rotate independently of the head assembly 102.

The internal gear 112 may be substantially ring-like. The internal gear 112 may be formed from a material such as a metal, e.g. stainless steel, molybdenum, aluminum, ceramic materials, or other exemplary materials. The internal gear 112 may be disposed adjacent to and coupled with an upper portion 216 of the bearing clamp 112. The plurality of holes (not shown) may be disposed through the internal gear 112 and adapted to receive the fastener (not shown) which may be adapted to secure the internal gear 112 to the bearing clamp 110. A plurality of teeth 214 may comprise an interior surface of the internal gear 112.

In certain embodiments, a drive assembly 290 may be configured to provide rotational motion to the retaining ring assembly 104 independent of rotation of the head assembly 102. The drive assembly 290 includes a cover ring 258, a bracket 256, a actuator 260, a spindle 261, and a worm drive 262. The drive assembly 290 actuates a transmission 292 which may cause the retaining ring assembly 104 to rotate relative to the head assembly 102.

The cover ring 258 may be disposed adjacent to and above a portion of the carrier body 208. The cover ring 258 may be coupled to the carrier body 208 such that the cover ring 258, and elements coupled thereto, move in the same rotational manner as the head assembly 102. The bracket 256 may be disposed above and coupled to a top surface 259 of the cover ring 258. The bracket 256 may be adapted to support the actuator 260 in a fixed position. The actuator 260, such as an air motor, may be coupled to a pressure source 274 via a transport line 272. The pressure source 274 may be adapted to provide a pressurized gas or fluid via the transport line 272 to the actuator 260. A spindle 261 extends from the actuator 260 and a worm drive 262 may be coupled to the spindle 261. The actuator 260 generally imparts rotational movement to the spindle 261 and causes the worm drive 262 to rotate.

The transmission 292 may be actuated by the worm drive 262. The transmission 292 comprises a worm gear 264, a spur gear 268, a drive shaft 266, and a shaft encoder 270. The worm gear 264 may be disposed around a first end 265 of the drive shaft 266. The worm gear 264 may be coupled to the worm drive 262 and adapted to translate the rotational movement of the worm drive 262 to the drive shaft 266. The spur gear 268 may be disposed around the drive shaft 266 below the worm gear 264 at a region 269 substantially parallel to the teeth 214 of the internal gear 112. The spur gear 268 may translate rotational movement of the drive shaft 266 to the internal gear 112. Thus, the retaining ring assembly 104 may be rotated independently from the rotation of the head assembly 102.

The shaft encoder 270 may be disposed below the spur gear 268 on the drive shaft 266. The shaft encoder 270, such as an electro-mechanical device, may convert the rotational motion of the drive shaft 266 to an analog or digital code. The shaft encoder 270 may be coupled to a controller (not shown) which may be coupled to the actuator 260. The controller may be adapted to control the rotational speed at which the retaining ring 104 is rotated relative to the head assembly 102.

A housing assembly 280 may be disposed in a portion of the carrier body 208 and may be adapted to receive the drive shaft 266. The housing assembly 280 may have a bottom 286 and a plurality of side walls 282. A second end 267 of the drive shaft 266 may be disposed within the housing assembly 280. A plurality of bearings 284 may also be disposed within the housing assembly 280. The plurality of bearings 284 may be disposed between the sidewalls 282 of the housing assembly 280 and the drive shaft 266. The plurality of bearings 284 may couple the drive shaft 266 to the housing assembly 280 and allow for rotational movement of the drive shaft 266 relative to the housing assembly 280.

In certain embodiments, the retaining ring assembly 104 may be driven at a speed greater than the rotational speed of which the head assembly 102 may be rotated. For example, during a 60 second CMP polishing process, the head assembly 102 may be rotated at a speed achieving about 60 rpm to about 120 rpm. In this example, the rotational speed of the retaining ring assembly 104 may be greater than the rotational speed of the polishing head which may encourage substrate precession. It is contemplated that the retaining ring assembly 104 may be rotated in the same of opposite direction relative to the rotational direction of the head assembly 102. Moreover, the substrate precession may be affected by the rotational direction of a polishing pad against which the substrate 201 is polished.

FIG. 3 is a schematic bottom view of the retaining ring assembly 104 and substrate 201. The inner diameter of the retaining ring assembly 104 may be greater than the outer diameter of the substrate 201. A rotation direction 306 of the retaining ring assembly 104 encourages substrate 201 rotation 308 in a direction relative to a head assembly (not shown), such as head assembly 102 (See FIG. 2). The rotation 308 of the substrate 201 relative to the head assembly may be defined as substrate precession as previously discussed.

A previously described, substrate precession is the degree of rotation or slip experienced by the substrate 201 relative to the membrane 250 on the head assembly 102. It is believed that encouraging substrate precession may “average out” any potential local non-uniformities in a substrate removal profile over a given polishing time. It is believed that the polar asymmetry created by substrate precession results in an averaging effect with regard to local non-uniformities in the membrane 250 or the polishing pad. The local non-uniformities may result in a non-planar removal profile and therefore it may be advantageous to reduce the effects of the local non-uniformities.

It is also believed that substrate precession may be dictated by the relationship between the substrate 201 outer diameter and the retaining ring assembly 104 inner diameter. The relationship between the substrate 201 outer diameter and the retaining ring assembly 104 inner diameter may be described in terms of a gear ratio. A smaller gear ratio between the retaining ring assembly 104 inner diameter and the substrate 201 outer diameter will result in increased substrate precession.

It is further believed that driving the retaining ring assembly 104 at a speed greater than a speed of the head assembly 102 may further encourage substrate precession. In one embodiment, a head assembly 102 rotational speed of about 60 rpm in combination with a retaining ring assembly 104 inner diameter of about 11.852 in may provide about 90° of substrate precession. In another embodiment, a head assembly 102 rotational speed of about 90 rpm in combination with a retaining ring assembly 104 inner diameter of about 11.852 in may provide about 135° of substrate precession. In another embodiment, a head assembly 102 rotational speed of about 120 rpm in combination with a retaining ring assembly 104 inner diameter of about 11.852 in may provide about 100° of substrate precession. The gear ratio of the above embodiments may be about 0.99654. In the aforementioned embodiments, the retaining ring assembly 104 maybe co-rotated or counter-rotated at a rotational speed greater than the rotational speed of the head assembly 102.

In one embodiment, a head assembly 102 rotational speed of about 60 rpm in combination with a retaining ring assembly 104 inner diameter of about 11.912 in may provide about 180° of substrate precession. In another embodiment, a head assembly 102 rotational speed of about 90 rpm in combination with a retaining ring assembly 104 inner diameter of about 11.912 in may provide about 270° of substrate precession. In another embodiment, a head assembly 102 rotational speed of about 120 rpm in combination with a retaining ring assembly 104 inner diameter of about 11.912 in may provide about 360° of substrate precession. The gear ratio of the above embodiments may be about 0.99152. In the aforementioned embodiments, the retaining ring assembly 104 maybe co-rotated or counter-rotated at a rotational speed greater than the rotational speed of the head assembly 102.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. An apparatus for polishing a substrate, comprising:

a head assembly;

a retaining ring assembly comprising: an internal gear; and a bearing disposed between the head assembly and the retaining ring assembly, wherein the bearing is adapted to decouple the retaining ring assembly from the head assembly; and

a drive assembly adapted to rotate the retaining ring assembly relative to the head assembly.

2. The apparatus of claim 1, wherein the head assembly further comprises:

a housing;

a carrier body; and

a flexible membrane.

3. The apparatus of claim 1, wherein the head assembly further comprises a cover plate coupled to the drive assembly.

4. The apparatus of claim 1, further comprising:

a transmission comprising: a first gear; a second gear; a shaft encoder; and a drive shaft.

5. The apparatus of claim 4, wherein the first gear is rotatably coupled to the drive assembly.

6. The apparatus of claim 4, wherein the second gear is rotatably coupled to the internal gear.

7. The apparatus of claim 4, wherein the first gear and the second gear are coupled to the drive shaft.

8. The apparatus of claim 1, wherein the drive assembly comprises:

an actuator;

a spindle coupled to the actuator; and

a worm drive coupled to the spindle.

9. The apparatus of claim 8, wherein the actuator is an air motor.

10. The apparatus of claim 1, wherein the internal gear comprises a plurality of teeth.

11. The apparatus of claim 1, wherein an inner diameter of the retaining ring assembly is between about 11.830 in and about 11.870 in.

12. The apparatus of claim 1, wherein an inner diameter of the retaining ring assembly is between about 11.890 in and about 11.950 in.

13. A retaining ring assembly for a polishing head, comprising:

a retaining ring having an upper annular portion and a lower annular portion;

a carrier ring coupled to the upper annular portion;

a bearing clamp coupled to the carrier ring, the bearing clamp adapted to receive a bearing; and

an internal gear coupled to the bearing clamp.

14. The apparatus of claim 13, wherein the bearing decouples the retaining ring assembly from a polishing head assembly.

15. A method of operating a polishing apparatus, comprising:

providing a polishing head assembly and a retaining ring assembly, wherein the retaining ring assembly is decoupled from the polishing head assembly;

rotating the polishing head at a first speed; and

rotating the retaining ring assembly at a second speed greater than the first speed.

16. The method of claim 15, wherein the first speed is between about 60 rpm and about 120 rpm.

17. The method of claim 15, wherein the polishing head assembly and the retaining ring assembly are rotated in the same direction.

18. The method of claim 15, wherein the polishing head assembly and retaining ring assembly are rotated in opposite directions.

19. The method of claim 15, wherein a rotation direction of the polishing head assembly and a rotation direction of a polishing pad are the same.

20. The method of claim 15, wherein the rotation direction of the polishing head assembly and a rotation direction of a polishing pad are opposite.