Method and polishing pad design enabling improved wafer removal from a polishing pad in a CMP process

Abstract

The invention provides a chemical mechanical polishing pad and method that enables improved wafer removal from the polishing pad after completion of chemical mechanical polishing of the wafer.

Description

PRIORITY REFERENCE TO PRIOR APPLICATIONS

[0001] This application claims benefit of and incorporates by reference U.S. patent application serial No. 60/430,947, entitled “Method And Polishing Pad Design Enabling Improved Wafer Removal From The Polishing Pad In A CMP Process,” filed on Dec. 4, 2002, by inventors Alejandro Reyes, Gerard Moloney, Cormac Walsh, and Ernesto Saldana.

TECHNICAL FIELD

[0002] This invention relates generally to chemical mechanical polishing (CMP), and more particularly, but not exclusively, provides a CMP polishing pad and method for improving the removal of a wafer from a polishing pad after CMP.

BACKGROUND

[0003] CMP is a combination of chemical reaction and mechanical buffing. A conventional CMP system includes a polishing head with a retaining ring that holds and rotates a substrate (also referred to interchangeably as a wafer) against a polishing pad surface rotating in the same direction. The polishing pad can be made of cast and sliced polyurethane (or other polymers) with a filler or a urethane coated felt.

[0004] During rotation of the substrate against the polishing pad, a slurry of silica (and/or other abrasives) suspended in a mild etchant, such as potassium or ammonium hydroxide, is dispensed onto the polishing pad. The combination of chemical reaction from the slurry and mechanical buffing from the polishing pad removes vertical inconsistencies on the surface of the substrate, thereby forming an extremely flat surface.

[0005] In order to reduce operating costs and human intervention into the CMP system there has been a push to use CMP consumables with a longer operating life. An example of one of these consumables is what is referred to within the industry is a perforated polishing pad. An example of a perforated polishing pad is a polishing pad 130a as shown in FIG. 1 and FIG. 2 (not to scale). The polishing pad 130a has a plurality of holes or perforations 170 spread uniformly over the surface of the polishing pad 130a. The perforations 170 act to distribute slurry locally during CMP when the polishing pad 130a is compressed.

[0006] However, one of the drawbacks of the perforated pad 130a is the difficulty of lifting a wafer from the pad after polishing. The holes 170 in the pad 130a act as suction cups and the vacuum force applied through the polishing head to the back side of the wafer can not easily overcome this suction force between the front side of the wafer and the pad.

[0007] For example, FIG. 1 shows a conventional CMP system 100a with a perforated polishing pad 130a. The polishing pad 130a rests on a platen 140 on a turn table 150. The polishing head 180 includes a carrier 120 and a retaining ring 110 that retains a wafer 160 during CMP and can also include other components not shown. After CMP is complete, a vacuum force is applied to a backside of the wafer 160 (i.e., the side of the wafer 160 facing the carrier 120) and the polishing head 180 lifts the wafer 160 off of the polishing pad 130a.

[0008] Applying the vacuum to the backside of the wafer 160 causes the wafer 160 to bow since the edge of the wafer is sealed against the pad at points 165. This bowing of the wafer 160 causes a secondary vacuum force between the pad 130a and the wafer 160 thereby making it more difficult for the polishing head 180 to lift the wafer 160.

[0009] One solution to this deficiency to improve the ease of removing the wafer 160 from the polishing head 180 after CMP includes moving the polishing head 180 and wafer 160 over the edge of the polishing pad 130a to relieve the vacuum force between the polishing pad 130a and the wafer 160. However, this can lead to increased wafer defects and scratches as the edge of the polishing pad 130a entraps polishing debris that can damage the wafer 160. Further, moving the wafer 160 to the edge of the polishing pad 130a can lead to breakage of the wafer 160 since this leads to uneven stress distribution on the wafer 160 as a portion of the wafer is overhanging the polishing pad 130a prior to liftoff.

[0010] Therefore, a new polishing pad and method are needed that overcome the above-mentioned shortcomings while substantially decreasing the chance of wafer damage.

SUMMARY

[0011] Embodiment of the invention provides a chemical mechanical polishing pad and method of using the same to ease removal of a wafer from the pad after completion of CMP. The pad includes a top surface and at least one venting inlet. The top surface has a structure that forms a vacuum between the pad and a wafer during chemical mechanical polishing. The at least one venting inlet releases the vacuum when the wafer is located over the venting inlet. In one embodiment of the invention, the structure includes perforations. In another embodiment, the structure includes grooves.

[0012] An embodiment of the method starts with the applying of a vacuum to a backside of the wafer. After applying the vacuum, a polishing head retaining the wafer is moved to a periphery of the polishing pad. The polishing pad is then rotated so that at least one venting inlet passes underneath the wafer, thereby releasing the vacuum between the pad and the wafer. The vacuum on the backside of the wafer is then released and wafer removed from the polishing head.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

[0014] FIG. 1 is a diagram illustrating a conventional CMP system;

[0015] FIG. 2 is a diagram illustrating a conventional perforated polishing pad;

[0016] FIG. 3 is a diagram illustrating a perforated polishing pad according to an embodiment of the invention;

[0017] FIG. 4A-FIG. 4E are diagrams illustrating cross-sections of polishing pads according to different embodiments of the invention;

[0018] FIG. 5 is a diagram illustrating a CMP system using the perforated polishing pad of FIG. 3; and

[0019] FIG. 6 is a flowchart illustrating a method of CMP using the perforated polishing pad of FIG. 3.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0020] The following description is provided to enable any person of ordinary skill in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the embodiments will be readily apparent to those skilled in the art, and the principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles, features and teachings disclosed herein.

[0021] FIG. 3 is a diagram illustrating a perforated polishing pad 130b according to an embodiment of the invention. The polishing pad 130b is circular in shape with a thickness between about 50 and about 80 mils. The polishing pad 130b can comprise a plurality of planar layers. The diameter of the polishing pad 130b can range from about 66 centimeters to about 81 centimeters. The polishing pad 130b can be made of cast and sliced polyurethane (or other polymers) with a filler or a urethane coated felt. It will be appreciated by one of ordinary skill in the art that the polishing pad 130b can have a thickness or diameter greater than or smaller than the thickness and diameter ranges described above. Further, the polishing pad 130b can also be made of other materials than described above.

[0022] The polishing pad 130b includes a plurality of perforations 170 spread uniformly across a planar top and a planar bottom surface of the polishing pad 130b. In an alternative embodiment, the polishing pad 130b may include grooves in place of or in addition to the perforations 170 in the top surface of the polishing pad 130b. In another embodiment of the invention, the polishing pad 130b can include any structures that tend to form a vacuum force between the wafer 160 and the polishing pad 130b.

[0023] The polishing pad 130b also includes four angled venting inlets 300 that are distributed along on the periphery of the polishing pad 130b and extend inwards from the edge of the polishing pad 130b towards the center of the polishing pad 130b. The venting inlets 300 can be evenly or unevenly distributed along the top surface of the polishing pad 130b.

[0024] Each venting inlet 300 includes a mouth 310 at the periphery of the polishing pad 130b and a terminus 320 at an interior end of the venting inlet 300 thereby forming an axial length there between. The axial length of the venting inlets 300 should not extend any farther than necessary to ensure venting of the vacuum between the polishing pad 130b and the wafer 160 after CMP and so that the venting inlets 300 do not extend underneath the wafer 160 during CMP as that could lead to an uneven wafer removal profile. The terminus 320 can comprise any shaped ending, including an oval ending, a flat ending, a circular ending, a spherical ending, etc.

[0025] The venting inlets 300 can have a width of about 5 to about 10 mm with a length of about 20 mm. The width of the venting inlets 300 are preferably minimized to limit wafer 160 deflection but large enough so that residual water or other fluids from the CMP process do not help maintain a seal and stop the vacuum from venting though the venting inlets 300. The venting inlets 300 can travel through the full thickness of the polishing pad 130b or only travel through a portion (e.g., 10 mils) of the full thickness (e.g., 50 mils) of the polishing pad 130b. The venting inlets 300 are angled along the top surface of the polishing pad 130b at about 45 degrees from the edge of the polishing pad 130b. The venting inlets 300 are angled so as to increase water and/or other fluid removal from the venting inlets via centrifugal force. It will be appreciated by one of ordinary skill in the art that the venting inlets 300 can also be straight (i.e., perpendicular to the edge of the polishing pad 130b) or be angled at other than 45 degrees from the edge of the polishing pad 130b. In addition, it will be appreciated that the polishing pad 130b can have fewer (i.e., 1) or additional venting inlets 300. For example, in one embodiment of the invention, the polishing pad 130b has 24 venting inlets 300.

[0026] FIG. 4A-FIG. 4E are diagrams illustrating cross-sections of polishing pads 130b according to different embodiments of the invention. In one embodiment shown in FIG. 4A, a polishing pad 130b.1 has at least one venting inlet 300.1 that extends inwards from a mouth 310.1 at the periphery of the polishing pad 130b.1 to a terminus 320.1 at an inner end of the venting inlet 300.1. The venting inlet 300.1 is planar and parallel to a top surface and a bottom surface of the polishing pad 130b.1. Further, the venting inlet 300.1 only extends through a portion of the thickness of the polishing pad 130b.1, specifically, from the top surface of the polishing pad 130b.1 to a depth of, for example, about 20 mils in a polishing pad having a thickness of 50 mils.

[0027] FIG. 4B illustrates a cross-section of another polishing pad 130b.2 that has at least one venting inlet 300.2 that extends inwards from a mouth 310.2 at the periphery of the polishing pad 130b.2 to a terminus 320.2 at an inner end of the venting inlet 300.2. The venting inlet 300.2 only extends through a portion of the thickness of the polishing pad 130b.2, specifically, from the top surface of the polishing pad 130b.2 to a sloped surface 400 having a first depth at the terminus 320.2 and second depth, which is greater than the first depth, at the mouth 310.2. For example, the first depth can be about 20 mils and the second depth can be about 30 mils. The sloped surface 400 enables increased water or other fluid removal from the venting inlet 130b.2 due to gravity.

[0028] FIG. 4C illustrates a cross-section of another polishing pad 130b.3 that has at least one venting inlet 300.3 that extends inwards from a mouth 310.3 at the periphery of the polishing pad 130b.3 to a terminus 320.3 at an inner end of the venting inlet 300.3. The venting inlet 300.3 extends through the full depth of the polishing pad 130b.3.

[0029] FIG. 4D illustrates a cross-section of another polishing pad 130b.4 that has at least one venting inlet 300.4 that tunnels inwards and under the pad 130b.4 from a mouth 310.4 at the periphery of the polishing pad 130b.4 to a terminus 320.4 on a top surface of the polishing pad 130b.4 at an inner end of the venting inlet 300.4. The venting inlet 300.4 uses a top surface of the platen 140 as a bottom surface of the venting inlet 300.4.

[0030] FIG. 4E illustrates a cross-section of another polishing pad 130b.5 that has at least one venting inlet 300.5 that tunnels inwards and upwards from a mouth 310.5 at the periphery of the polishing pad 130b.5 to a terminus 320.5 on a top surface of the polishing pad 130b.5 at an inner end of the venting inlet 300.5. The sloped surface of the venting inlet 300.5 increases the rate of water or other fluid removal from the pad 130b.5 due to gravity. Alternatively, the venting inlet 300.5 can include a flat surface.

[0031] FIG. 5 is a diagram illustrating a CMP system 100b capable of using the perforated polishing pad 130b (i.e., any of 130b.1 to 130b.5). The polishing pad 130b rests on a platen 140 on a turn table 150. The polishing head 180 includes a carrier 120 and a retaining ring 110 that retains a wafer 160 during CMP and can include other components not shown. After CMP is complete, a vacuum force is applied to a backside of the wafer 160 and the polishing head 180 moves the wafer 160 towards the periphery of the polishing pad 130b so that the wafer 160 overhangs a venting inlet 130 (but does not overhang the periphery of the polishing pad 130b).

[0032] The venting inlet 300 enables the venting of air between the polishing pad 130b and the wafer 160, thereby releasing any vacuum forces between the polishing pad 130b and the wafer 160. Accordingly, the polishing head 180 can then pick up the wafer 160 without the risk of damage to the wafer 160 that is associated with conventional polishing pads.

[0033] In an embodiment in which the polishing pad 130b has only a single venting inlet 300, the polishing head 180 must move the wafer 160 to the periphery of the polishing pad 130b having the venting inlet 300. Alternatively, the polishing pad 130b can be rotated so that the venting inlet 300 passes beneath the wafer 160. However, in an embodiment in which the polishing pad 130b has a plurality of venting inlets 300, the polishing head 180 need only move the wafer 160 to the periphery of the polishing pad 130b to ensure that the wafer 160 overlaps one or more venting inlets 300. Accordingly, there is no need to move the wafer to a specific section of the periphery of polishing pad 130b or to rotate the polishing pad 130b.

[0034] FIG. 6 is a flowchart illustrating a method 600 of CMP using the perforated polishing pad 130b. First, chemical mechanical polishing is completed (610) using the polishing pad 130b. Next, a vacuum is applied (620) to the backside of the wafer 160. The polishing head 180 and wafer 160 are then moved (630) to the periphery of the polishing pad 130b. In another embodiment of the invention, the moving (630) can take place before the applying (620).

[0035] If necessary, the polishing pad 130b is then rotated (640) so that at least one venting inlet 300 passes underneath the wafer 160 so as to release any vacuum formed between the wafer 160 and the polishing pad 130b. If the polishing pad 130b has a plurality of venting inlets 300, then rotation (640) may not be needed since moving (630) the head 180 and wafer 160 to the periphery of the polishing pad 130b is sufficient for passing the wafer 160 over a venting inlet 300.

[0036] After rotating (640) or moving (630), the polishing head 180 and wafer 160 are lifted (650) from the polishing pad 130b. As the vacuum between the wafer 160 and the polishing pad 130b has been released, the polishing head 180 and wafer 160 are relatively easily lifted from the polishing pad 130b, thereby limiting the stress on the wafer 160. The polishing head 180 is then moved (660) to a wafer unload position and a vacuum is released (670) from the backside of the wafer 160. The wafer 160 is then removed (680) from the polishing head 180. The method 600 then ends.

[0037] The foregoing description of the illustrated embodiments of the present invention is by way of example only, and other variations and modifications of the above-described embodiments and methods are possible in light of the foregoing teaching. For example, the venting inlets 300 can be perpendicular or angled with respect to the edge of the polishing pad 130b. The embodiments described herein are not intended to be exhaustive or limiting. The present invention is limited only by the following claims.

Claims

1. A chemical mechanical polishing pad, comprising:

a top surface having a structure that forms a vacuum between the pad and a wafer during chemical mechanical polishing; and

at least one venting inlet capable of releasing the vacuum when the wafer is located over the venting inlet.

2. The pad of claim 1, wherein the structure includes a plurality of perforations.

3. The pad of claim 1, wherein the structure includes a plurality of grooves.

4. The pad of claim 1, wherein the at least one venting inlet is connected to atmospheric pressure.

5. The pad of claim 1, wherein the at least one venting inlet extends from the periphery of the top surface towards the center of the top surface.

6. The pad of claim 1, wherein the at least one venting inlet is angled relative to a diameter of the pad.

7. The pad of claim 1, wherein the at least one venting inlet passes through the full depth of the polishing pad.

8. The pad of claim 1, wherein the at least one venting inlet passes through a portion of the depth of the polishing pad.

9. The pad of claim 1, wherein the at least one venting inlet has a sloped surface.

10. The pad of claim 1, wherein the at least one venting inlet tunnels through the pad to connect with the top surface of the pad.

11. The pad of claim 1, wherein the at least one venting inlet tunnels underneath the pad to connect with the top surface of the pad and wherein a platen forms a bottom surface of the at least one venting inlet.

12. A method for removing a wafer from a polishing head after chemical mechanical polishing, comprising:

applying a vacuum to a backside of the wafer;

moving the polishing head retaining the wafer so that the wafer is positioned over a venting inlet of a polishing pad;

releasing the vacuum from the backside of the wafer; and

removing the wafer from the polishing head.

13. The method of claim 12, wherein the polishing pad has a top surface having a plurality of perforations.

14. The method of claim 12, wherein the polishing pad has a top surface having a plurality of grooves.

15. The method of claim 12, wherein the venting inlet is connected to atmospheric pressure.

16. The method of claim 12, wherein the venting inlet extends from the periphery of a top surface of the pad towards a center of the top surface.

17. The method of claim 12, wherein the venting inlet is angled relative to a diameter of the pad.

18. The method of claim 12, wherein the venting inlet passes through the full depth of the polishing pad.

19. The method of claim 12, wherein the venting inlet passes through a portion of the depth of the polishing pad.

20. The method of claim 12, wherein the venting inlet has a sloped surface.

21. The method of claim 12, wherein the venting inlet tunnels through the pad to connect with a top surface of the pad.

22. The method of claim 12, wherein the venting inlet tunnels underneath the pad to connect with a top surface of the pad and wherein a platen forms a bottom surface of the venting inlet.

23. The method of claim 12, wherein the method is performed in the order recited.

24. The method of claim 12, wherein the moving is performed before the applying.

25. A method for removing a wafer from a polishing head after chemical mechanical polishing, comprising:

applying a vacuum to a backside of the wafer;

moving the polishing head retaining the wafer to a periphery of a polishing pad;

rotating the polishing pad so that a venting inlet of the polishing pad is positioned under the wafer;

releasing the vacuum from the backside of the wafer; and

removing the wafer from the polishing head.

26. The method of claim 25, wherein the polishing pad has a top surface having a plurality of perforations.

27. The method of claim 25, wherein the polishing pad has a top surface having a plurality of grooves.

28. The method of claim 25, wherein the venting inlet is connected to atmospheric pressure.

29. The method of claim 25, wherein the venting inlet extends from the periphery of a top surface of the pad towards a center of the top surface.

30. The method of claim 25, wherein the venting inlet is angled relative to a diameter of the pad.

31. The method of claim 25, wherein the venting inlet passes through the full depth of the polishing pad.

32. The method of claim 25, wherein the venting inlet passes through a portion of the depth of the polishing pad.

33. The method of claim 25, wherein the venting inlet has a sloped surface.

34. The method of claim 25, wherein the venting inlet tunnels through the pad to connect with a top surface of the pad.

35. The method of claim 25, wherein the venting inlet tunnels underneath the pad to connect with a top surface of the pad and wherein a platen forms a bottom surface of the venting inlet.

36. The method of claim 25, wherein the method is performed in the order recited.

37. The method of claim 25, wherein the moving is performed before the applying.