US20090023362A1

US20090023362A1 - Retaining ring for chemical mechanical polishing, its operational method and application system

Info

Publication number: US20090023362A1
Application number: US11/778,650
Authority: US
Inventors: Tzu-Shin Chen; Chih-Chin Yang; Min-Hao Yeh; Kai-Chun Yang; Chan Lu; Tzu-Hui Wu; Cheng-Hsun Wu
Original assignee: United Microelectronics Corp
Current assignee: United Microelectronics Corp
Priority date: 2007-07-17
Filing date: 2007-07-17
Publication date: 2009-01-22

Abstract

A retaining ring for CMP is disclosed. The retaining ring has a plurality of grooves. The grooves have rounded sidewalls. Because the sidewalls of the grooves of the retaining ring are rounded, the slurry is not apt to accumulate around them and the pad is less scratched. Accordingly, the micro-scratches on the wafer surface are reduced and the yield of the CMP step is increased. Its operational method and application system are also disclosed in this invention.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention mainly relates to a retaining ring for CMP. More particularly, the present invention relates to a retaining ring for reducing the micro-scratches on the wafer surface.
2. Description of the Prior Art
Chemical mechanical polishing (CMP) is frequently used in the semiconductor processes. The CMP can planarize the uneven surface caused by any deposition treatment on the wafer. A retaining ring is usually used for fixing the wafer during the CMP. For example, U.S. Pat. No. 6,386,962 discloses a retaining ring with a rounded leading edge, as shown in FIG. 1. The wafer 41 and the retaining ring 42 are on the polishing pad 43. The leading edge 44 is shaped to distribute pressure over a larger surface and thus substantially reduces the ring-related edge effects and enhances the uniform planarization of the wafer 41.
There are many known CMP methods. For example, a CMP method called fixed abrasive web type involves a scroll-like polishing pad. Pre-covered fixed abrasives are evenly distributed on the polishing pad. The retaining ring accommodates the wafer and applies a force on the wafer. When the wafer lies against the polishing pad, the pre-covered fixed abrasives which are evenly distributed on the polishing pad are released and undergo an effective planarization on the wafer because the retaining ring drives the wafer to perform a relative movement against the polishing pad.
However, when the wafer performs the relative movement against the polishing pad and releases the fixed abrasives, the sharp sidewalls on the grooves of the retaining ring on one side promotes the slurry to accumulate around it and on the other side, and the sharp sidewalls along with the accumulations easily scratch the polishing pad, which promotes the micro-scratches on the wafer surface and jeopardizes the total yield of the CMP process.
It is necessary to provide a retaining ring to solve the problems.

SUMMARY OF THE INVENTION

The present invention provides a novel retaining ring for CMP. The corners on the grooves of the retaining ring are rounded so the slurry is not apt to accumulate around them and the pad is less scratched. Accordingly, the micro-scratches on the wafer surface are reduced and the yield of the CMP step is increased.
The retaining ring of the present invention has a plurality of grooves. The bottom of the sidewalls of the grooves have rounded corners.
The present invention provides a CMP method for fixed abrasives. First a wafer, a retaining ring including a plurality of grooves with rounded corners, a polishing pad and a flat sub-pad are provided. The wafer is in the center of the retaining ring and on the polishing pad. The flat sub-pad supports the polishing pad. The retaining ring moves relatively against the polishing pad in the presence of a slurry. The polishing pad includes 5-50% (area/area) a plurality of fixed abrasives. The slurry includes L-proline and fluoroaliphatic esters surfactants. The retaining ring provides a 0.5-3.0 psi downward force to make the active surface of the wafer contact the polishing pad.
The present invention further provides a CMP system for fixed abrasives, including a retaining ring having a plurality of grooves with rounded corners for fixing a wafer, under the retaining ring a polishing pad which includes the fixed abrasives and contacts the retaining ring, a driving device for driving the retaining ring to move relatively against the polishing pad, and a slurry provider for providing the wafer, the retaining and the polishing pad with a slurry.
Because on the retaining ring of the present invention the corners of the grooves are rounded, the slurry is not apt to accumulate around them and the pad is less scratched. Accordingly, the micro-scratches on the wafer surface are reduced and the yield of the CMP step is increased. In addition, the CMP system of the present invention also promotes the remove rate of the oxides and the remove selectivity of oxides/nitrides.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a retaining ring in the prior art.

FIG. 2 illustrates a preferred embodiment of the retaining ring of the present invention.

FIG. 3 illustrates the CMP method of the present invention.

FIG. 4 illustrates the CMP system for fixed abrasives of the present invention.

DETAILED DESCRIPTION

Because the conventional retaining ring for fixing the wafer has sharp sidewalls on the grooves, they promote the slurry to accumulate around them and cause the polishing pad scratched, which causes the micro-scratches on the wafer surface. The retaining ring of the present invention has rounded corners on the sidewalls, so the micro-scratches on the wafer surface are reduced and the problems encountered in the prior art are solved.
FIG. 2 illustrates a preferred embodiment of the retaining ring 100 for CMP of the present invention. The retaining ring 100 has a plurality of grooves 110, 12-24 grooves for example, to facilitate the flow of a slurry (not shown). It is to be noticed that the sidewalls 111 on the grooves 110 are rounded to form rounded corners 112 with a radius around 1-5 mm. The grooves 110 may have a depth of 2-4.5 mm and a width of 2-4.5 mm.
In addition, based on other requirements, the other parts on the retaining ring 100 may be rounded to further reduce the micro-scratches on the wafer surface. For example, the inner periphery 120 of the retaining ring 100 has rounded corner 121, the outer periphery 130 of the retaining ring 100 has rounded corner 131 and opening 140 has at least one rounded corner 141. Those rounded corners may resemble the rounded corners 112.
In one preferred embodiment of the present invention the size of the retaining ring 100 depends on the size of the wafer. For example, in a 12-inch wafer process the inner diameter of the retaining ring 100 may be 299.5-302 mm and the outer diameter may be 345-349 mm. Furthermore, the material of the retaining ring 100 may depend on the composition of the slurry and the material of the polishing pad. For example, PEEK or PS may be used.
On the retaining ring of the present invention the sidewalls on the grooves are all rounded, so the particles (from the slurry or the polishing process) will not accumulate around the grooves and will not scratch the polishing pad so that the micro-scratches on the wafer surface are reduced and the yield of the CMP step is increased.
FIG. 3 illustrates the CMP method for fixed abrasives of the present invention. First a retaining ring 200 is provided. There is a wafer 210 in the center of the retaining ring 200 which includes a plurality of grooves 201, 12-24 grooves for example, with rounded corners of a radius around 1-5 mm. The grooves 210 may have a depth of 2-4.5 mm and a width of 2-4.5 mm. The retaining ring 200 is on the polishing pad 220 and makes the active surface of the wafer 210 contact the polishing pad 220. There is a flat sub-pad 230 under the polishing pad 220 and supporting the polishing pad 220.
As mentioned, based on other requirements, the other parts on the retaining ring 200 may be rounded to further reduce the micro-scratches on the wafer 210 surface. For example, the inner periphery 202, the outer periphery 203 or opening 204 of the retaining ring 200 each may have at least one rounded corner. Those rounded corners may resemble the rounded corners as shown. The size of the retaining ring 200 depends on the size of the wafer 210. For example, if the wafer 210 is 12-inch in diameter, the inner diameter of the retaining ring 200 may be 299.5-302 mm and the outer diameter may be 345-349 mm. In addition, the material of the retaining ring 200 may depend on the composition of the slurry and the material of the polishing pad. For example, PEEK or PS may be used.
Then the retaining ring 200 drives the wafer 210 to move relatively against the polishing pad 220 in the presence of the slurry 250. In order to increase the efficiency of the CMP process on the wafer 210, to reduce the micro-scratches on the wafer 210 surface, to promote the remove rate of the oxides and the remove selectivity of oxides/nitrides, one preferred embodiment of the present invention involves multiple operational conditions. For example, the polishing pad may include 5-50% (unit) a plurality of fixed abrasives 221. The fixed abrasives 221 may include ceria, silica and the like. The retaining ring 200 preferably provides a 0.5-3.0 psi downward force to make the active surface of the wafer 210 contact the polishing pad 220 to reduce the micro-scratches on the wafer surface.
Because the flat sub-pad 230 which supports the polishing pad 220 includes no “rib,” the remove rate and uniformity may be therefore increased. In addition, the slurry 250 may preferably comprise L-proline and surfactants such as fluoroaliphatic esters surfactants. Preferred fluoroaliphatic esters surfactants may include fluoroaliphatic esters of the following structure: CH₂═C(R¹)—C(O)O—R⁶—NHCO₂(CH₂)_p(CF₂)_q—O—((CF₂)_a—CFXO)_m(CF₂)_r-Z, wherein each R⁶is independently selected from substituted or unsubstituted C₁-C₁₀alkyl, cyclic alkyl, or aryl groups, wherein each a is independently selected from 0-3, wherein each X is independently selected from —F, —CF₃or —CF₂CF₃, wherein each p is independently selected from 1-4, each q is independently selected from 1-5, each r is independently selected from 1-5, each m is independently selected from 1-50, each Z is independently selected from —F and —(CH₂)_nOH, and each s is independently selected from 1-4 in the concentration of 1%-5%. It is believed that the mixture of L-proline and fluoroaliphatic esters surfactants may enhance the remove rate of the oxides and the remove selectivity of oxides/nitrides.
Because the CMP method for fixed abrasives of the present invention uses the retaining ring with rounded sidewalls on the grooves along with the polishing pad including fixed abrasives, the flat sub-pad with no rib, a 0.5-3.0 psi downward force and the slurry containing L-proline and fluoroaliphatic esters surfactants, the micro-scratches on the wafer surface are effectively reduced and the remove rate of the oxides and the remove selectivity of oxides/nitrides are enhance.
FIG. 4 illustrates the CMP system for fixed abrasives of the present invention. The CMP system 300 includes a retaining ring 310, a polishing pad 320, a driving device 330 and a slurry provider 340.
The retaining ring 310 includes a plurality of grooves 311, 12-24 grooves for example, with rounded corners of a radius around 1-5 mm for fixing a wafer (not shown). The grooves 311 may have a depth of 2-4.5 mm and a width of 2-4.5 mm. If necessary, the other parts on the retaining ring 310 may also be rounded to further reduce the micro-scratches on the wafer surface. For example, the inner periphery 312, the outer periphery 313 or opening 314 of the retaining ring 310 each may have at least one rounded corner. Those rounded corners may resemble the rounded corners as shown. The size of the retaining ring 310 depends on the size of the wafer. For example, the inner diameter of the retaining ring 310 may be 299.5-302 mm and the outer diameter may be 345-349 mm. Furthermore, materials such as PEEK or PS may be used for the retaining ring 310.
The polishing pad 320 under the retaining ring 310 may include 5-50% (unit) a plurality of fixed abrasives 321. The fixed abrasives 321 may include ceria, silica and the like. The driving device 330 is useful in driving the retaining ring 310 to move relatively against the polishing pad 320 to perform the CMP. The slurry provider 340 provides a slurry (not shown) for facilitating the polishing pad 320 performing the CMP process on the wafer which is in the center of the retaining ring 310.
The slurry may preferably comprise L-proline and surfactants such as fluoroaliphatic esters. Preferred fluoroaliphatic esters surfactants may include fluoroaliphatic esters of the following structure: CH₂═C(R¹)—C(O)O—R⁶—NHCO₂(CH₂)_p(CF₂)_q—O—((CF₂)_a—CFXO)_m(CF₂)_r-Z, wherein each R⁶is independently selected from substituted or unsubstituted C₁-C₁₀alkyl, cyclic alkyl, or aryl groups, wherein each a is independently selected from 0-3, wherein each X is independently selected from —F, —CF₃or —CF₂CF₃, wherein each p is independently selected from 1-4, each q is independently selected from 1-5, each r is independently selected from 1-5, each m is independently selected from 1-50, each Z is independently selected from —F and —(CH₂)_nOH, and each s is independently selected from 1-4 in the concentration of 1%-5%. It is believed that the mixture of L-proline and fluoroaliphatic esters surfactants may enhance the selectivity of the CMP process. The retaining ring 310 preferably provides a 0.5-3.0 psi downward force to make the active surface of the wafer contact the polishing pad 320 to reduce the micro-scratches on the wafer surface. Because the flat sub-pad 350 which is under and supports the polishing pad 320 includes no “rib,” the remove rate of the oxides and the remove selectivity of oxides/nitrides may be therefore enhanced.
Because the CMP system for fixed abrasives of the present invention uses the retaining ring with rounded sidewalls on the grooves along with the polishing pad including fixed abrasives, the flat sub-pad with no rib, a 0.5-3.0 psi downward force and the slurry containing L-proline and fluoroaliphatic esters surfactants, the micro-scratches on the wafer surface (scratch level) are effectively reduced from 2% to 1% and the remove rate of the oxides and the remove selectivity of oxides/nitrides are enhanced.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.

Claims

1. A retaining ring for CMP characterized in that said retaining ring comprises a plurality of grooves with sidewalls which all comprise first rounded corners.

2. The retaining ring for CMP of claim 1, wherein said retaining ring comprises 12-24 grooves.

3. The retaining ring for CMP of claim 1, wherein said retaining ring comprises an inner periphery comprising a second rounded corner.

4. The retaining ring for CMP of claim 1, wherein said retaining ring comprises an outer periphery comprising a third rounded corner.

5. The retaining ring for CMP of claim 1, wherein said grooves further comprise at least one opening comprising at least one fourth rounded corner.

6. A CMP method for fixed abrasives, comprising:

providing a wafer, a retaining ring comprising a plurality of grooves comprising a first rounded corner, a polishing pad and a flat sub-pad, wherein said wafer is in the center of said retaining ring and on said polishing pad, the active surface of said wafer contacts said polishing pad and said flat sub-pad supports said polishing pad; and

promoting said retaining ring moving relatively against said polishing pad in the presence of a slurry, wherein said polishing pad comprises 5-50% a plurality of fixed abrasives, said slurry comprises L-proline and fluoroaliphatic esters surfactants, and said retaining ring provides a 0.5-3.0 psi downward force to make the active surface of said wafer contact said polishing pad.

7. The method of claim 6, wherein said retaining ring comprises 12-24 grooves.

8. The method of claim 6, wherein said retaining ring comprises an inner periphery comprising a second rounded corner.

9. The method for CMP of claim 6, wherein said retaining ring comprises an outer periphery comprising a third rounded corner.

10. The method of claim 6, wherein said grooves further comprise at least one opening comprising at least one fourth rounded corner.

11. The method of claim 6, wherein said fixed abrasives are selected from the group consisting of ceria and silica.

12. A CMP system for fixed abrasives, comprising:

a retaining ring comprising a plurality of grooves comprising rounded corners for fixing a wafer;

under said retaining ring a polishing pad comprising said fixed abrasives and contacting said retaining ring;

at least one driving device for driving said retaining ring to move relatively against said polishing pad; and

at least one slurry provider for providing said wafer, said retaining and said polishing pad with a slurry.

13. The CMP system of claim 12, wherein said polishing pad comprises 5-50% said fixed abrasives.

14. The CMP system of claim 12, wherein said slurry comprises L-proline and fluoroaliphatic esters surfactants.

15. The CMP system of claim 12, wherein said retaining ring provides a 0.5-3.0 psi downward force.

16. The CMP system of claim 12, further comprising a flat sub-pad for supporting said polishing pad.

17. The CMP system of claim 12, wherein said retaining ring comprises 12-24 grooves.

18. The CMP system of claim 12, wherein said retaining ring comprises an inner periphery comprising a second rounded corner.

19. The CMP system of claim 12, wherein said retaining ring comprises an outer periphery comprising a third rounded corner.

20. The CMP system of claim 12, wherein said grooves further comprise at least one opening comprising at least one fourth rounded corner.

21. The CMP system of claim 12, wherein said fixed abrasives are selected from the group consisting of ceria and silica.