US20050113002A1

US20050113002A1 - CMP polishing heads retaining ring groove design for microscratch reduction

Info

Publication number: US20050113002A1
Application number: US10/720,409
Authority: US
Inventors: Feng Chen; Cing Lim; Lup Leong; Sim Wang
Original assignee: Chartered Semiconductor Manufacturing Pte Ltd
Current assignee: GlobalFoundries Singapore Pte Ltd
Priority date: 2003-11-24
Filing date: 2003-11-24
Publication date: 2005-05-26

Abstract

A chemical-mechanical polish (CMP) machine and fabrication process using the same. The CMP machine has a CMP retaining ring comprising: an inner peripheral surface; an outer peripheral surface; a lower surface adapted to contact and depress an upper surface of a polishing pad during chemical mechanical polishing of a lower surface of a substrate. The substrate is contained within the inner peripheral surface of the retaining ring during chemical mechanical polishing. At least a groove on the lower surface of the retaining ring. At least a portion of the groove has a rounded contour. In an aspect, the groove has a semicircle profile. In another aspect, the groove has a semicircle profile and a curved top corner profile at adjacent to the lower surface of the retaining ring. The retaining ring with a curved portion of groove reduces the accumulation of dried slurry in the groove and thus reduces micro-scratches.

Description

BACKGROUND OF INVENTION

1) Field of the Invention
Embodiments of this invention relate to Chemical Mechanical Polishing (CMP) methods and machines, and particularly to retaining ring designs for CMP heads and more particularly to retaining ring designs with curved grooves for reducing microscatches on semiconductor structures.
2) Description of the Related Art
In semiconductor fabrications, the chemical-mechanical polish (CMP) technique is widely used for the global planarization of semiconductor wafers that are used for the fabrication of VLSI (very large-scale integration) and ULSI (ultra large-scale integration) integrated circuits.
FIGS. 1A and 1B are schematic diagrams showing a conventional CMP machine. The CMP machine comprises a polishing table 10 on which a polishing pad 12 is layered, a polishing head 14 for holding a semiconductor wafer 16 in position, and a nozzle 18 for applying a mass of slurry to the semiconductor wafer 16 during the CMP process.
FIG. 1C shows a respective view of the structure inside of the polishing head 14. As shown, the polishing head 14 includes an air-pressure means 20 which applies air pressure to a wafer loader 22 used to hold the wafer 16. In addition, a retainer ring 24 is mounted around the loader 22 and the wafer 16, which can retain the wafer 16 in fixed position during the CMP process. Moreover, a cushion pad (not shown) is placed between the wafer 16 and the loader 22.
A problem of current chemical-mechanical polish (CMP) machines and process is the micro-scratches formed on the substrate during the CMP process.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering U.S. Pat. No. 6,386,962 (Gotkis et al.) that shows a wafer carrier with retainer ring for a chemical-mechanical polish (CMP) apparatus.
U.S. Pat. No. 6,527,624 B1 (Tollers et al.) shows a retaining ring.
U.S. Pat. No. 6,110,025 (Williams et al.) teaches a retainer ring with passages.
U.S. Pat. No. 6,293,850 B1 (Lin et al.) shows retaining ring with slurry passages at the bottom of the retainer ring.
U.S. Pat. No. 6,224,472 B1 (Lai et al.) teaches a retaining ring with channels.
However, the retaining rings can be further improved.

SUMMARY OF THE INVENTION

It is an object of example embodiments of the present invention to provide a retaining ring for use in a chemical-mechanical polish (CMP) machine.
It is an object of example embodiments of the present invention to provide a CMP method and a retaining ring having channels with rounded contour or rounded corners or curved surfaces for use in a chemical-mechanical polish (CMP) machine.
An example embodiment of the present invention provides a retaining ring which is characterized as follows. A CMP retaining ring, comprising:

- an inner peripheral surface;
- an outer peripheral surface;
- a lower surface adapted to contact and depress an upper surface of a polishing pad during chemical mechanical polishing of a lower surface of a substrate; the substrate is contained within the inner peripheral surface of the retaining ring during chemical mechanical polishing; and
- at least a groove on the lower surface of the retaining ring and extending from a position at or adjacent the inner peripheral surface of the retaining ring, to a position at or adjacent the outer peripheral surface of the retaining ring;
- at least a portion of the groove has a rounded contour.

In another aspect, the groove has a semicircle profile.
In another aspect, the groove has a semicircle profile and the groove has a rounded top corner adjacent to the lower surface of the retaining ring.
An example embodiment of a process of the invention is described as follows. A process for chemical-mechanical polish (CMP) a wafer comprising:

- the wafer is disposed within a polishing head with the deposition layer facing a polishing table; the wafer is retained within the polishing head by a retainer ring, and
- at least a portion of the groove has a rounded contour;
- supplying a slurry to the polish table and/or polish head;
- rotating the polishing table and spinning the polishing head to chemically polish the wafer.

Another aspect further includes: forming a deposition layer on the surface of the wafer and chemical mechanically polishing the deposition layer.
Another aspect further includes: the groove has a semicircle profile.
Another aspect further includes: the groove has a semicircle profile and the groove has a rounded corner adjacent to the lower surface of the retaining ring.
The above advantages and features are of representative embodiments only, and are not exhaustive and/or exclusive. They are presented only to assist in understanding the invention. It should be understood that they are not representative of all the inventions defined by the claims, to be considered limitations on the invention as defined by the claims, or limitations on equivalents to the claims. For instance, some of these advantages may be mutually contradictory, in that they cannot be simultaneously present in a single embodiment. Similarly, some advantages are applicable to one aspect of the invention, and inapplicable to others. Furthermore, certain aspects of the claimed invention have not been discussed herein. However, no inference should be drawn regarding those discussed herein relative to those not discussed herein other than for purposes of space and reducing repetition. Thus, this summary of features and advantages should not be considered dispositive in determining equivalence. Additional features and advantages of the invention will become apparent in the following description, from the drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of a retaining ring and methods thereof according to example embodiments the present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate similar or corresponding elements, regions and portions and in which:
FIG. 1A is a schematic top view of a chemical-mechanical polish (CMP) machine for performing a CMP process on a semiconductor wafer according to the prior art.
FIG. 1B is a schematic section view of the chemical-mechanical polish (CMP) machine of FIG. 1A according to the prior art.
FIG. 1C is a cross sectional view showing an inside structure of the polishing head used on the CMP machine of FIGS. 1A and 1B according to the prior art.
FIG. 2A is perspective view of a retaining ring having rectangular grooves 204.
FIG. 2B is a close up perspective view a groove in a retaining ring having rectangular grooves 204 as shown in FIG. 2A.
FIG. 2C is a cross sectional view of a groove that has slurry particles that cause the problems as discovered by the inventors.
FIG. 3A is perspective view of a retaining ring that has non-rectangular grooves 304 according to an aspect of the invention.
FIG. 3B is a close up perspective view of an embodiment where the groove has a semicircle profile according to an aspect of the invention.
FIG. 3C is a cross sectional view of a groove that has a semicircle profile according to an aspect of the invention.
FIG. 3D is a cross sectional view of a groove that has rounded or curved or non-angular bottom corners and curved sidewalls 316 according to an aspect of the invention.
FIG. 3E is a cross sectional view of a groove that has rounded or curved or non-angular bottom corners 311, rounded top corners 320 and slanted or sloped sidewalls 322 according to an aspect of the invention.
FIG. 3F is a cross sectional view of a groove 304F that has rounded or curved or non-angular bottom corners and about vertical sidewalls 316 and a flat bottom 316 according to an aspect of the invention.
FIG. 4A is perspective view of a retaining ring that has non-rectangular grooves 404 and curved top corners according to an aspect of the invention.
FIG. 4B is a close up perspective view of an embodiment where the groove has curved top corners according to an aspect of the invention.
FIG. 4C is a cross sectional view of a groove that has a semicircle profile and curved top corners according to an aspect of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Introduction
Referring now to the drawings and more particularly to FIGS. 2A, 2B, and 2C, there is shown a retaining ring 200 over which the aspects of the present invention are an improvement. It is to be understood in this regard that no portion of FIGS. 2A, 2B and 2C is admitted to be prior art as to the present invention. Rather, this these diagrams are an effort to provide an improved understanding of some of the problems that are overcome by the aspects of the invention.
FIG. 2A is perspective view of a retaining ring 200 having rectangular shaped grooves 204. The ring has a lower surface 201 (polishing surface or pad side surface) that in operation faces the polish pad.
FIG. 2B is a close up perspective view a groove 204 that has non-curved corners or edges in the a retaining ring 200.
FIG. 2C is a cross sectional view of a groove 204 that has slurry particles or other debris 208 that cause the problems as discovered by the inventors.
Microscratches are a defect caused by the CMP process. Big particles and/or dry slurry are causes of the microscrathes. Big particle size can be control by filtration in the supplier's factory and the dried slurry is hard material normally found the in-house slurry delivery related components. The forming of dried slurry can occur when the water vaporizes from the slurry droplet spilled on the surface of some polishing machine components.
The inventors have found that the retaining ring in the chemical-mechanical polish (CMP) machine is a source of dried slurry. As shown in FIG. 2C, the corner of the groove of the wafer polishing head's retaining ring was found to accumulate a few chunks of dried slurry. A purpose of these grooves is to allow the slurry flow in to the wafer polishing head for efficient planarization process. Unfortunately, the design of the current retaining ring grooves can cause slurry particles to accumulate and increase micro scratches.

Example Embodiments of the Grooves of the Invention

Example embodiments of the grooves of the invention have at least a portion of the groove or the surface adjacent to the groove is curved. Examples of curvilinear portions of groove are: semicircle shaped grooves, arc shapes grooves, groves with rounded bottom corners, grooves with rounded top corners, grooves with curved sidewalls, grooves with slanted sidewalls, and combinations thereof. The example embodiment of the grooves reduce the buildup of dried slurry in grooves and thus reduce microscratches.
As shown in FIG. 3A, a chemical-mechanical polish (CMP) retaining ring 300 comprises: an inner peripheral surface 303; an outer peripheral surface 302; and a lower surface 301. The lower surface 301 is adapted to contact and depress an upper surface of a polishing pad during chemical mechanical polishing of a lower surface of a substrate contained within the inner peripheral surface of the retaining ring during chemical mechanical polishing.
The retaining ring can be economically and speedily fabricated through the injection molding, casting or other molding processes. The mold can be built to contain the sizable cavity with the retaining ring's net shape. The most commonly used materials for retaining ring, normally but not limited to thermosetting or thermoplastic polymer, is heated to highly plastic state and forced to flow into the cavity. The solidified molded part or the retaining ring is removed from the cavity and sent for other finishing or shaping processes.
The retaining ring 300 has grooves 304 on the lower surface 301. The grooves 304 preferably extend from a position at or adjacent the inner peripheral surface of the retaining ring, to a position at or adjacent the outer peripheral surface of the retaining ring. The cross sectional area of the groove can be constant or changes along the length of the groove. Preferably, at least a portion of the groove 304 has a rounded contour. Preferably the cross sectional shape of the groove is rounded or has rounded corners. Preferably the cross section of the groove does not contain a portion (possibly other than the top corner) where two flat areas meet at a angle, such as a 90 degree angle. Preferably, the groove has a shape that reduces the amount of dried slurry and other particles that accumulates in the groove during a polish operation.
The term “rounded” can mean: curved, or with curved parts: having curved, not straight or angular, surfaces or edges.
The grooves may not have the same cross sectional area along the length of the groove. The grooves can preferably have a depth between 2 and 15 mm. From a top down view, the groove can have any shape, such as a straight shape as shown in FIG. 3A or can be curved or some combination thereof.
FIG. 3B shows a closer view of a preferred embodiment of the invention where the groove 304C has an about semicircle profile.
FIG. 3C shows a cross sectional view of a groove 304C that has a semicircle cross-sectional profile 310 with a radius 311. The grooves 304C have a semicircle profile preferably with a radius 311 between 2 mm and 15 mm. The semicircle profile of the groove helps prevent the slurry particles from accumulating in the groove.
In the aspect shown in FIG. 3D, the groove 304D has curved sidewalls 316 and a rounded bottom corner 312 and a flat bottom 314. The grooves can have at least one rounded corner. The grooves have rounded corners/edges 312 adjacent to the bottom 314 of the grooves. The rounded corners, edges or surfaces 312 can prevent slurry form accumulating in the groove.
In an aspect, the retaining ring has grooves with rounded top edges adjacent to the lower surface 301 of the retaining ring.
Referring to FIG. 3E, an aspect is shown where the groove 304E has a rounded top corner 320 near the lower surface of the ring. The groove has a sloped sidewall 322. The groove has a slanted contour. Slanted means the sidewall has a least a section that is not at about a 90 degree angle with the lower surface 301 of the ring. The groove has a rounded bottom corner 311 and a flat 316 bottom. The bottom can be flat or curved.
In an aspect shown in FIG. 3F, the CMP retaining ring has a groove has with about vertical sidewalls 330 and an about horizontal flat bottom 316 and at least one rounded corner 311 between the vertical sidewalls 330 and the horizontal bottom 316. The grooves can have a width between 1 and 30 mm.
FIG. 4A shows another embodiment where the groove 404 has top corner or edge with a curved shape.
FIG. 4B shows a perspective view of the groove 404 with the rounded top corner 420. In the aspect shown in FIGS. 4B and 4C the groove has a semicircle profile 410 and top rounded corners 420.
FIG. 4C shows a preferred embodiment of the invention of a groove 404C with rounded top corners 420 and a semicircle profile 410. In an option, the rounded top corners 420 can have the shape of a arc of a circle having a radius 413. In an option, the semicircle profile 410 can have radius 411.
The retaining ring can have other channels on the lower surface. Also, the lower surface of the retaining ring can further comprise a plurality of protrusions and recesses or a mixture of both. In addition, the retaining ring can have other passages thru the ring such as a passage connecting the grooves to the top side of the ring. See e.g., U.S. Pat. No. 6,527,624 B1.
It will be understood that CMP retaining rings embodiments of the invention may be advantageously used with any type of CMP polishing system, pad material and/or polishing slurry, such as where the lower (or pad-side) surface of the retaining ring contacts the polishing pad during polishing. Examples of suitable CMP slurries include, but are not limited to, Cabot “SS25”, Cabot “SS12”.
It should be noted that the retaining ring and wafer carriers of the present invention may be used with any suitable CMP systems such as linear CMP apparatus or rotary CMP apparatus.
Process Using the Retaining Ring of Aspects of the Invention
The retaining rings of the aspects of the invention can be used in a process to CMP a substrate. The substrate is preferably a wafer with layers formed or deposited thereover. The layers can be insulating and/or conducting layers. The insulating layers can be comprised of oxide, (e.g., oxide made from tetraethylorthosilicate (TEOS)) or low-k materials. The conductive layers can be metal layers such as copper alloys, or Aluminum alloys.
A process for chemical-mechanical polishing a wafer comprises the following.
The wafer is disposed within a polishing head with the deposition layer facing a polishing table. The wafer is retained within the polishing head by a retainer ring.
The retaining ring is a ring according to an aspect of the invention describe above. For example, at least a portion of the groove has a rounded contour.
We supply a slurry to the polishing table or the polish head.
We move the polishing table and/or the polishing head to chemically polish the wafer. Preferably, we rotate the polishing table and spin the polishing head to chemically polish the wafer. Preferably the polish table has a polish pad thereover and the polish pad polishes the substrate.
In the above description numerous specific details are set forth in order to provide a more thorough understanding of the present invention. It will be obvious, however, to one skilled in the art that the present invention may be practiced without these details. In other instances, well known process have not been described in detail in order to not unnecessarily obscure the present invention.
Given the variety of embodiments of the present invention just described, the above description and illustrations show not be taken as limiting the scope of the present invention defined by the claims.
While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention. It is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.

Claims

1. A CMP retaining ring, comprising:

an inner peripheral surface;

an outer peripheral surface;

a lower surface adapted to contact and depress an upper surface of a polishing pad during chemical mechanical polishing of a lower surface of a substrate;

at least a groove on said lower surface of said retaining ring; and said groove extending from a position at or adjacent said inner peripheral surface of said retaining ring, to a position at or adjacent said outer peripheral surface of said retaining ring;

at least a portion of said groove has a rounded contour or slanted contour.

2. The CMP retaining ring of claim 1 wherein said groove has a semicircle profile.

3. The CMP retaining ring of claim 1 wherein said groove has a semicircle profile and said groove has a rounded top corner adjacent to the lower surface of the retaining ring.

4. The CMP retaining ring of claim 1 wherein said groove has a semicircle profile with a radius between 2 and 15 mm.

5. The CMP retaining ring of claim 1 wherein said groove has at least one rounded corner.

6. The CMP retaining ring of claim 1 wherein said groove has rounded corners adjacent to the bottom of said grooves.

7. The CMP retaining ring of claim 1 wherein said groove has rounded top corners adjacent to the lower surface of said retaining ring.

8. The CMP retaining ring of claim 1 wherein the cross-sectional area of said groove changes along the length of said groove.

9. The CMP retaining ring of claim 1 wherein said groove has a width between 1 mm and 30 mm; said groove has a depth between 1 and 15 mm.

10. The CMP retaining ring of claim 1 wherein said groove has vertical sidewalls or sloped sidewalls.

11. The CMP retaining ring of claim 1 wherein said groove has vertical sidewalls and an about horizontal bottom and at least one rounded corner between said vertical sidewalls and said horizontal bottom.

12. The CMP retaining ring of claim 1 wherein said groove has straight sidewalls and top and bottom corners; at least one of said corners is rounded or curvilinear.

13. The CMP retaining ring of claim 1 wherein said retaining ring can further comprise other channels; the lower surface of the retaining ring can further comprise a plurality of protrusions and recesses or a mixture of both.

14. A process for chemical-mechanical polishing a substrate comprising:

said substrate is disposed within a polishing head facing a polishing table; said substrate is retained within the polishing head by a retainer ring, and at least a portion of said groove has a rounded contour;

supplying a slurry to said polishing table or to said polish head;

moving the polishing table and/or the polishing head to chemically polish the wafer.

15. The process of claim 14 which further includes: said substrate is a wafer; forming a deposition layer on the surface of said wafer and chemical mechanically polishing said deposition layer.

16. The process of claim 14 wherein said groove has a semicircle profile.

17. The process of claim 14 wherein said groove has a semicircle profile and said groove has a rounded corner adjacent to the lower surface of the retaining ring.

18. The process of claim 14 wherein said groove has at least one rounded corner.

19. The process of claim 14 wherein said grooves has at least one rounded bottom corner.

20. The process of claim 14 wherein said groove has rounded edges adjacent to the bottom of said grooves.

21. The process of claim 14 wherein said groove has rounded top edges adjacent to the lower surface of said retaining ring.

22. The process of claim 14 wherein said groove has a width between 1 and 30 mm; said groove has a depth between 1 and 15 mm.