Apparatus and method for slurry distribution

Abstract

A assembly for a chemical mechanical polishing apparatus includes a carrier head and a polishing liquid delivery ring. The carrier head has a substrate receiving surface and a retaining ring surrounding the substrate receiving surface. The polishing liquid delivery ring is coupled to the carrier head and surrounds the retaining ring. The polishing liquid delivery ring includes a reservoir to hold a liquid and an outlet in fluid communication with the reservoir and positioned to dispense the liquid to a location on a polishing surface outside the retaining ring.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Serial No. 60/822,920, filed on Aug. 18, 2006, which is incorporated herein by reference.

BACKGROUND

The present invention relates generally to distribution of a polishing liquid during chemical mechanical polishing.

Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, it is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly nonplanar. This nonplanar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.

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, and pressed against a polishing surface, such as a rotating pad or linear belt. A polishing liquid, such as a slurry with abrasive particles, can be introduced onto the polishing pad to assist the polishing process.

SUMMARY

In one aspect, the invention is directed to an assembly for a chemical mechanical polishing apparatus that includes a carrier head and a polishing liquid delivery ring. The carrier head has a substrate receiving surface and a retaining ring surrounding the substrate receiving surface. The polishing liquid delivery ring is coupled to the carrier head and surrounds the retaining ring. The polishing liquid delivery ring includes a reservoir to hold a liquid and an outlet in fluid communication with the reservoir and positioned to dispense the liquid to a location on a polishing surface outside the retaining ring.

In another aspect, the invention is directed to a method for delivering a polishing liquid. The method includes delivering a polishing liquid into a reservoir of a polishing liquid delivery ring coupled to a carrier head, and dispensing the polishing liquid from the reservoir through an outlet in fluid communication with the reservoir to a location on a polishing surface outside a retaining ring of the carrier head.

Implementations of either invention may include one or more of the following features. The reservoir may be a recess, e.g., an annular recess surrounding the carrier head, formed in an upper surface of the polishing liquid delivery ring. A passage may be formed through the polishing liquid delivery ring from the reservoir to the outlet. The passage may be essentially vertical or tilted, e.g., angled outwardly from top to bottom. The outlet may be located on a bottom surface of the retaining ring. The polishing liquid delivery ring may include a plurality of outlets in fluid communication with the reservoir, each outlet positioned to dispense the liquid to an associated location on the polishing surface outside the retaining ring. The retaining ring may have a bottom surface with slurry delivery channels. The polishing liquid delivery ring may include an inwardly extending flange positioned on a top surface of the carrier head. The flange may be positioned on a top surface of the retaining ring, e.g., between the top surface of the retaining ring and a bottom surface of a housing of the carrier head. Te polishing liquid delivery ring may be coupled to the carrier head by a bearing. A supply tube may have an outlet positioned at least intermittently over the polishing liquid delivery ring. A carrier head support may hold the carrier head, and a pump may be supported on the carrier head support to pump polishing liquid through the supply tube. A polishing liquid supply fluidly may be coupled to the pump and secured to the carrier head support. The pump is configured to dispense the polishing slurry into the reservoir intermittently or continuously during polishing.

The invention may provide one or more of the following advantages. The slurry distribution system can provide slurry to an area immediately adjacent the substrate. This can ensure more uniform slurry distribution near the substrate edge, thus improving within-wafer nonuniformity and decreasing edge exclusion. In addition, slurry consumption can be reduced, thus reducing both consumable costs and the occurrence of dried slurry, thereby reducing defects.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a top view of a chemical mechanical polishing apparatus.

FIG. 2 is a cross-sectional view of an exemplary carrier head having an external feed line and slurry delivery ring.

FIG. 3 is an expanded view of the slurry delivery ring.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

As shown in FIG. 1, a substrate 10 is polished at a polishing station 25 of a chemical mechanical polishing (CMP) apparatus 20. A description of a suitable CMP apparatus may be found in U.S. Pat. No. 5,738,574, the entire disclosure of which is incorporated herein by reference. This type of CMP apparatus includes a machine base 22 that supports three polishing stations 25 and a transfer station 27. Each polishing station includes a rotatable platen 30 on which is placed a polishing pad 32. Each polishing station 25 may further include a pad conditioner to maintain the abrasive condition of the polishing pad 32.

As shown in FIGS. 1 and 2, this implementation of the CMP apparatus 20 also includes a cross-shaped rotatable multi-head carousel 40 that supports four carrier heads 50. The carousel 40 can rotate to orbit the carrier heads 50, and the substrates 10 attached thereto, between the polishing stations 25 and the transfer station 27. Each carrier head 50 can independently rotate about its own axis, and can laterally oscillate in a radial slot 42 formed in a carousel support plate 44. A drive shaft 46 extends through the slot 42 connecting a motor 48 to the carrier head 50. The motor 48 and drive shaft 46 can be supported on a slider (not shown) that is linearly driven along the slot 42 by a radial drive motor (not shown) to laterally oscillate the carrier head 50.

As shown in FIG. 2, the carrier head 50 can include a housing or base 52 and a flexible membrane 54 clamped to the housing 52 to form a loading chamber 56. The housing 52 is connected to the drive shaft 46, and may be generally circular in shape to correspond to the circular configuration of the substrate 10. Fluid can be injected into the loading chamber 56 through a passage in the housing 52 and the drive shaft 46 to pressurize the loading chamber 56 and apply a load (i.e., a downward pressure) to the substrate. The carrier head 50 can include other elements that are not shown, for example, more complicated pneumatics, e.g., a chamber to control pressure on the retaining ring or multiple chambers to apply independently controllable pressures on different portions of the substrate. A discussion of a similar carrier head is found in U.S. Patent Publication No. 2006-0154580, the entire disclosure of which is incorporated herein by reference.

The carrier head 50 also includes a retaining ring 60 secured to the bottom of the housing 52, e.g., by bolts (not shown). The retaining ring 60 has an inner surface 62 to engage the substrate 10 and prevent the substrate from slipping or sliding from beneath the carrier head 50 during polishing, and a bottom surface 64 which can contact and compress the polishing pad. The bottom surface 64 can be substantially flat, or optionally, slurry distribution channels can be formed in the bottom surface 64 of the retaining ring 60.

Referring to FIGS. 2 and 3, the slurry delivery ring 100 is attached to the outer circumference of the carrier head 50. The slurry delivery ring 100 can be a generally annular body with a recess 102 formed in its top surface 104 to provide a reservoir for a polishing liquid, such as slurry 34. The recess 102 can be an annular depression extending entirely around the carrier head. The recess can have a generally semi-circular cross section. Alternatively, the recess can have be a parallelepiped, and can have inner and outer walls that are slanted outwardly from top to bottom. The depth of the recess 102 determines the available volume for the slurry reservoir.

The slurry delivery ring 100 can include an inwardly projecting flange 120 that, when the slurry delivery ring 100 is lowered onto the carrier head 50, rests on a horizontal surface of the retaining ring 60 or the housing 52 to hold the slurry delivery ring 100 in place. Alternatively, the flange 120 can be clamped between a top surface of the retaining ring 60 and a bottom surface of the housing 52. In either case, in this position, a bottom surface 106 of the slurry delivery ring 100 is spaced away and does not contact the polishing pad 32. The slurry delivery ring 100 can be constructed of a plastic such as polyphenyl sulfide (PPS) or a metal such as stainless steel, and the passages 110 can be formed by precision machining.

A plurality of passages 110, e.g., three to twelve passages, such as four or eight passages, are formed through the slurry delivery ring 100 to fluidly couple the recess 102 to corresponding outlets 112 on the bottom surface 106 of the slurry delivery ring 110. Specifically, gravity causes the slurry 35 in the recess 102 to drain through the passages 110 and out of the outlets 112 and onto the surface of the polishing pad 32. In particular, the outlets 112 are positioned to dispense the liquid to a location on a polishing surface that is near yet outside the outer diameter 64 of the retaining ring 60.

The passages can be distributed at equal angular intervals around the slurry delivery ring. In one implementation, the passages 110 are essentially vertical. Alternatively, the passages can be tilted. The diameter and angle of the passages 110 determines the speed at which the reservoir will drain. If the passages are angled inwardly from top to bottom, centrifugal forces will tend to prevent the slurry from flowing through the passage, thereby decreasing the slurry delivery rate. On the other hand, if the passages are angled outwardly from top to bottom, centrifugal forces will tend to aid flow the slurry through the passage, thereby increasing the slurry delivery rate. Increasing the passage diameter will increase the slurry flow rate, whereas decreasing the passage diameter will reduce the slurry flow rate.

The recess 102 is open to the atmosphere, and can be fed slurry 35 by an external feed tube 70. In one implementation, the feed tube 70 is extends below the underside of the carousel 40 and has an outlet 72 positioned over the recess 102. The slurry 35 can be metered through the feed tube 70 by a metering pump (not shown) that is located in the carousel 40. A slurry supply from which the slurry is pumped can be located in the carousel 40, or in the machine base, or outside the polishing apparatus 20. The slurry can be dispensed at a rate sufficient to replace slurry that is consumed during polishing. If the feed tube 70 is attached to the slider and oscillates laterally with the carrier head, then slurry can be dispensed into the into the delivery ring either on a continuous basis or intermittently. Alternatively, if the feed tube 70 is attached to carousel but does not oscillate laterally with the carrier head, then the slurry can be dispensed intermittently, e.g., each time that the sweep of the carrier head carries the slurry delivery ring 100 beneath the outlet of the feed tube 70. If the slurry is dispensed intermittently, sufficiently slurry may be dispensed into the reservoir to polish a set number of substrates, e.g., one substrate. When the set number of substrate has been polished, the carrier head 50 is moved into position with the slurry delivery ring 100 carrier and the slurry reservoir is refilled.

In the implementation described above, the slurry delivery ring 100 rotates with the carrier head 50. However, the slurry delivery ring 100 could be mounted on carrier head 50 with a clutch or bearing assembly so that the delivery ring sweeps but does not necessarily rotate with the carrier head.

By providing slurry to an area proximate to the interface between the substrate and a rotating polishing pad, the invention can improve and enhance the uniformity of planarization of the substrate, reduce edge exclusion, and reduce the amount of slurry applied to the pad.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the slurry delivery ring could be used with other configurations of carrier head, such as a carrier with a rigid backing member, with other polishing articles, such as linear polishing belts, and other polishing system architectures, such as polishing systems with different number or configuration of polishing stations or polishing systems that do not use a carousel at all. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. An assembly for a chemical mechanical polishing apparatus, comprising:

a carrier head with a substrate receiving surface and a retaining ring surrounding the substrate receiving surface; and

a polishing liquid delivery ring coupled to the carrier head and surrounding the retaining ring, the polishing liquid delivery ring including a reservoir to hold a liquid and an outlet in fluid communication with the reservoir and positioned to dispense the liquid to a location on a polishing surface outside the retaining ring.

2. The assembly of claim 1, wherein the reservoir comprises a recess formed in an upper surface of the polishing liquid delivery ring.

3. The assembly of claim 2, wherein the recess is an annular recess surrounding the carrier head.

4. The assembly of claim 2, wherein a passage is formed through the polishing liquid delivery ring from the reservoir to the outlet.

5. The assembly of claim 4, wherein the passage is essentially vertical.

6. The assembly of claim 4, wherein the passage is tilted.

7. The assembly of claim 6, wherein the passage is angled outwardly from top to bottom.

8. The assembly of claim 1, wherein the outlet is located on a bottom surface of the retaining ring.

9. The assembly of claim 1, wherein the polishing liquid delivery ring includes a plurality of outlets in fluid communication with the reservoir, each outlet positioned to dispense the liquid to an associated location on the polishing surface outside the retaining ring.

10. The assembly of claim 1, wherein the retaining ring has a bottom surface with slurry delivery channels.

11. The assembly of claim 1, wherein the polishing liquid delivery ring includes an inwardly extending flange positioned on a top surface of the carrier head.

12. The assembly of claim 1, wherein the flange is positioned on a top surface of the retaining ring.

13. The assembly of claim 12, wherein the flange is positioned between the top surface of the retaining ring and a bottom surface of a housing of the carrier head.

14. The assembly of claim 1, wherein the polishing liquid delivery ring is coupled to the carrier head by a bearing.

15. The assembly of claim 1, further comprising a supply tube having an outlet positioned at least intermittently over the polishing liquid delivery ring.

16. The assembly of claim 15, further comprising a carrier head support to hold the carrier head and a pump supported on the carrier head support to pump polishing liquid through the supply tube.

17. The assembly of claim 16, further comprising a polishing liquid supply fluidly coupled to the pump and secured to the carrier head support.

18. The assembly of claim 16, wherein the pump is configured to dispense the polishing slurry into the reservoir intermittently during polishing.

19. The assembly of claim 16, wherein the pump is configured to dispense the polishing slurry into the reservoir continuously during polishing.

20. A method for delivering a polishing liquid, comprising:

delivering a polishing liquid into a reservoir of a polishing liquid delivery ring coupled to a carrier head; and

dispensing the polishing liquid from the reservoir through an outlet in fluid communication with the reservoir to a location on a polishing surface outside a retaining ring of the carrier head.