U.S. patent application number 13/955398 was filed with the patent office on 2015-02-05 for low density polishing pad.
The applicant listed for this patent is NexPlanar Corporation. Invention is credited to William C. Allison, Richard Frentzel, Ping Huang, Robert Kerprich, Paul Andre Lefevre, Diane Scott.
Application Number | 20150038066 13/955398 |
Document ID | / |
Family ID | 51263570 |
Filed Date | 2015-02-05 |
United States Patent
Application |
20150038066 |
Kind Code |
A1 |
Huang; Ping ; et
al. |
February 5, 2015 |
LOW DENSITY POLISHING PAD
Abstract
Low density polishing pads and methods of fabricating low
density polishing pads are described. In an example, a polishing
pad for polishing a substrate includes a polishing body having a
density of less than 0.5 g/cc and composed of a thermoset
polyurethane material. A plurality of closed cell pores is
dispersed in the thermoset polyurethane material.
Inventors: |
Huang; Ping; (Beaverton,
OR) ; Allison; William C.; (Beaverton, OR) ;
Frentzel; Richard; (Murrieta, CA) ; Lefevre; Paul
Andre; (Portland, OR) ; Kerprich; Robert;
(Portland, OR) ; Scott; Diane; (Portland,
OR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NexPlanar Corporation |
Hillsboro |
OR |
US |
|
|
Family ID: |
51263570 |
Appl. No.: |
13/955398 |
Filed: |
July 31, 2013 |
Current U.S.
Class: |
451/529 ;
451/527; 51/296 |
Current CPC
Class: |
B24D 11/04 20130101;
B24D 11/006 20130101; B24B 37/24 20130101; B24B 37/205
20130101 |
Class at
Publication: |
451/529 ;
451/527; 51/296 |
International
Class: |
B24D 11/04 20060101
B24D011/04; B24D 11/00 20060101 B24D011/00; B24B 37/20 20060101
B24B037/20 |
Claims
1. A polishing pad for polishing a substrate, the polishing pad
comprising: a polishing body having a density of less than 0.5 g/cc
and comprising: a thermoset polyurethane material; and a plurality
of closed cell pores dispersed in the thermoset polyurethane
material.
2. The polishing pad of claim 1, wherein the polishing body is a
homogeneous polishing body.
3. The polishing pad of claim 1, wherein each of the plurality of
closed cell pores comprises a physical shell comprising a material
different from the thermoset polyurethane material.
4. The polishing pad of claim 3, wherein the physical shells of a
first portion of the plurality of closed cell pores comprise a
material different than the physical shells of a second portion of
the plurality of closed cell pores.
5. The polishing pad of claim 1, wherein each of only a portion of
the plurality of closed cell pores comprises a physical shell
comprising a material different from the thermoset polyurethane
material.
6. The polishing pad of claim 1, wherein each of the plurality of
closed cell pores does not comprise a physical shell of a material
different from the thermoset polyurethane material.
7. The polishing pad of claim 1, wherein the plurality of closed
cell pores provides a total pore volume in the thermoset
polyurethane material approximately in the range of 55-80% of the
total volume of the thermoset polyurethane material.
8. The polishing pad of claim 1, wherein the polishing body further
comprises: a first, grooved surface; and a second, flat, surface
opposite the first surface.
9. The polishing pad of claim 1, wherein each of the plurality of
closed cell pores is essentially spherical.
10. The polishing pad of claim 1, wherein the plurality of closed
cell pores has a bi-modal distribution of diameters having a first
diameter mode with a first peak of size distribution and a second
diameter mode with a second, different, peak of size
distribution.
11. The polishing pad of claim 10, wherein the closed cell pores of
the first diameter mode each comprise a physical shell comprising a
material different from the thermoset polyurethane material.
12. The polishing pad of claim 11, wherein the closed cell pores of
the second diameter mode each comprise a physical shell comprising
a material different from the thermoset polyurethane material.
13. The polishing pad of claim 12, the physical shell of each of
the closed cell pores of the second diameter mode comprises a
material different from the material of the physical shells of the
closed cell pores of the first diameter mode.
14. The polishing pad of claim 10, wherein the first peak of size
distribution of the first diameter mode has a diameter
approximately in the range of 10-50 microns, and wherein the second
peak of size distribution of the second diameter mode has a
diameter approximately in the range of 10-150 microns.
15. The polishing pad of claim 10, wherein the first diameter mode
overlaps with the second diameter mode.
16. The polishing pad of claim 10, wherein the first diameter mode
has essentially no overlap with the second diameter mode.
17. The polishing pad of claim 10, wherein a total population in
count number of the first diameter mode is not equal to a total
population in count number of the second diameter mode.
18. The polishing pad of claim 10, wherein a total population in
count number of the first diameter mode is approximately equal to a
total population in count number of the second diameter mode.
19. The polishing pad of claim 10, wherein the bi-modal
distribution of diameters is distributed essentially evenly
throughout the thermoset polyurethane material.
20. The polishing pad of claim 1, wherein the polishing body is a
molded polishing body.
21. The polishing pad of claim 1, wherein the polishing body
further comprises: an opacifying filler distributed approximately
evenly throughout the polishing body.
22. The polishing pad of claim 1, further comprising: a foundation
layer disposed on a back surface of the polishing body.
23. The polishing pad of claim 1, further comprising: a detection
region disposed in a back surface of the polishing body.
24. The polishing pad of claim 1, further comprising: a sub pad
disposed on a back surface of the polishing body.
25. The polishing pad of claim 1, further comprising: a local area
transparency (LAT) region disposed in, and covalently bonded with,
the polishing body.
26. A polishing pad for polishing a substrate, the polishing pad
comprising: a polishing body having a density of less than
approximately 0.6 g/cc and comprising: a thermoset polyurethane
material; and a plurality of closed cell pores dispersed in the
thermoset polyurethane material, the plurality of closed cell pores
having a bi-modal distribution of diameters having a first diameter
mode with a first peak of size distribution and a second diameter
mode with a second, different, peak of size distribution.
27. The polishing pad of claim 26, wherein the polishing body is a
homogeneous polishing body.
28. The polishing pad of claim 26, wherein the closed cell pores of
the first diameter mode each comprise a physical shell comprising a
material different from the thermoset polyurethane material.
29. The polishing pad of claim 28, wherein the closed cell pores of
the second diameter mode each comprise a physical shell comprising
a material different from the thermoset polyurethane material.
30. The polishing pad of claim 29, the physical shell of each of
the closed cell pores of the second diameter mode comprises a
material different from the material of the physical shells of the
closed cell pores of the first diameter mode.
31. The polishing pad of claim 26, wherein the first peak of size
distribution of the first diameter mode has a diameter
approximately in the range of 10-50 microns, and wherein the second
peak of size distribution of the second diameter mode has a
diameter approximately in the range of 10-150 microns.
32. The polishing pad of claim 26, wherein the first diameter mode
overlaps with the second diameter mode.
33. The polishing pad of claim 26, wherein the first diameter mode
has essentially no overlap with the second diameter mode.
34. The polishing pad of claim 26, wherein a total population in
count number of the first diameter mode is not equal to a total
population in count number of the second diameter mode.
35. The polishing pad of claim 26, wherein a total population in
count number of the first diameter mode is approximately equal to a
total population in count number of the second diameter mode.
36. The polishing pad of claim 26, wherein the bi-modal
distribution of diameters is distributed essentially evenly
throughout the thermoset polyurethane material.
37. A method of fabricating a polishing pad, the method comprising:
mixing a pre-polymer and a chain extender or cross-linker with a
plurality of microelements to form a mixture, each of the plurality
of microelements having an initial size; and heating, in a
formation mold, the mixture to provide a molded polishing body
comprising a thermoset polyurethane material and a plurality of
closed cell pores dispersed in the thermoset polyurethane material,
the plurality of closed cell pores formed by expanding each of the
plurality of microelements to a final, larger, size during the
heating.
38. The method of claim 37, wherein expanding each of the plurality
of microelements to the final size comprises increasing a volume of
each of the plurality of microelements by a factor approximately in
the range of 3-1000.
39. The method of claim 37, wherein expanding each of the plurality
of microelements to the final size comprises providing a final
diameter of each of the plurality of microelements approximately in
the range of 10-200 microns.
40. The method of claim 37, wherein expanding each of the plurality
of microelements to the final size comprises reducing a density of
each of the plurality of microelements by a factor approximately in
the range of 3-1000.
41. The method of claim 37, wherein expanding each of the plurality
of microelements to the final size comprises forming an essentially
spherical shape for each of the plurality of microelements of the
final size.
42. The method of claim 37, wherein mixing the pre-polymer and the
chain extender or cross-linker with the plurality of microelements
further comprises mixing with a second plurality of microelements
to form the mixture, each of the second plurality of microelements
having a size.
43. The method of claim 42, wherein the heating is performed at a
temperature sufficiently low such that the size of each of the
second plurality of microelements is essentially the same before
and after the heating.
44. The method of claim 43, wherein the heating is performed at a
temperature of approximately 100 degrees Celsius or less, and
wherein the second plurality of microelements has an expansion
threshold of greater than approximately 130 degrees Celsius.
45. The method of claim 42, wherein the second plurality of
microelements has an expansion threshold greater than an expansion
threshold of the plurality of microelements.
46. The method of claim 45, wherein the expansion threshold of the
second plurality of microelements is greater than approximately 120
degrees Celsius, and the expansion threshold of the plurality of
microelements is less than approximately 110 degrees Celsius.
47. The method of claim 42, wherein a mixture of the pre-polymer,
the chain extender or cross-linker, and the second plurality of
microelements has a viscosity, and the mixture of the pre-polymer,
the chain extender or cross-linker, the plurality of microelements
having the initial size, and the second plurality of microelements
essentially has the viscosity.
48. The method of claim 47, wherein the viscosity is a
predetermined viscosity, and a relative amount of the second
plurality of microelements in the mixture is selected based on the
predetermined viscosity.
49. The method of claim 47, wherein the plurality of microelements
has little to no effect on the viscosity of the mixture.
50. The method of claim 42, wherein heating provides the molded
polishing body comprising the thermoset polyurethane material, the
plurality of closed cell pores dispersed in the thermoset
polyurethane material and formed by expanding each of the plurality
of microelements to the final size having a first diameter mode
with a first peak of size distribution, and a second plurality of
closed cell pores dispersed in the thermoset polyurethane material
and formed from the second plurality of microelements having a
second diameter mode with a second, different, peak of size
distribution.
51. The method of claim 50, wherein the plurality of closed cell
pores and the second plurality of closed cell pores provides a
total pore volume in the thermoset polyurethane material
approximately in the range of 55-80% of the total volume of the
thermoset polyurethane material.
52. The method of claim 37, wherein heating the mixture to provide
the molded polishing body comprises forming the polishing body
having a density of less than 0.5 g/cc.
53. The method of claim 52, wherein the mixture has a density of
greater than 0.5 g/cc prior to the heating.
54. The method of claim 37, wherein the mixing further comprises
injecting a gas into the pre-polymer and the chain extender or
cross-linker, or into a product formed there from.
55. The method of claim 37, wherein the pre-polymer is an
isocyanate and the mixing further comprises adding water to the
pre-polymer.
56. The method of claim 37, wherein mixing the pre-polymer and the
chain extender or cross-linker comprises mixing an isocyanate and
an aromatic diamine compound, respectively.
57. The method of claim 37, wherein the mixing further comprises
adding an opacifying filler to the pre-polymer and the chain
extender or cross-linker to provide an opaque molded polishing
body.
58. The method of claim 37, wherein heating the mixture comprises
first partially curing in the formation mold and then further
curing in an oven.
59. The method of claim 37, wherein heating in the formation mold
comprises forming a groove pattern in a polishing surface of the
molded polishing body.
60. The method of claim 37, wherein each of the plurality of
microelements having the initial size comprises a physical shell,
and wherein each of the plurality of microelements having the final
size comprises an expanded physical shell.
61. The method of claim 37, wherein each of the plurality of
microelements having the initial size is a liquid droplet, and
wherein each of the plurality of microelements having the final
size is a gas bubble.
Description
TECHNICAL FIELD
[0001] Embodiments of the present invention are in the field of
chemical mechanical polishing (CMP) and, in particular, low density
polishing pads and methods of fabricating low density polishing
pads.
BACKGROUND
[0002] Chemical-mechanical planarization or chemical-mechanical
polishing, commonly abbreviated CMP, is a technique used in
semiconductor fabrication for planarizing a semiconductor wafer or
other substrate.
[0003] The process involves use of an abrasive and corrosive
chemical slurry (commonly a colloid) in conjunction with a
polishing pad and retaining ring, typically of a greater diameter
than the wafer. The polishing pad and wafer are pressed together by
a dynamic polishing head and held in place by a plastic retaining
ring. The dynamic polishing head is rotated during polishing. This
approach aids in removal of material and tends to even out any
irregular topography, making the wafer flat or planar. This may be
necessary in order to set up the wafer for the formation of
additional circuit elements. For example, this might be necessary
in order to bring the entire surface within the depth of field of a
photolithography system, or to selectively remove material based on
its position. Typical depth-of-field requirements are down to
Angstrom levels for the latest sub-50 nanometer technology
nodes.
[0004] The process of material removal is not simply that of
abrasive scraping, like sandpaper on wood. The chemicals in the
slurry also react with and/or weaken the material to be removed.
The abrasive accelerates this weakening process and the polishing
pad helps to wipe the reacted materials from the surface. In
addition to advances in slurry technology, the polishing pad plays
a significant role in increasingly complex CMP operations.
[0005] However, additional improvements are needed in the evolution
of CMP pad technology.
SUMMARY
[0006] Embodiments of the present invention include low density
polishing pads and methods of fabricating low density polishing
pads.
[0007] In an embodiment, a polishing pad for polishing a substrate
includes a polishing body having a density of less than 0.5 g/cc
and composed of a thermoset polyurethane material. A plurality of
closed cell pores is dispersed in the thermoset polyurethane
material.
[0008] In another embodiment, a polishing pad for polishing a
substrate includes a polishing body having a density of less than
approximately 0.6 g/cc and composed of a thermoset polyurethane
material. A plurality of closed cell pores is dispersed in the
thermoset polyurethane material. The plurality of closed cell pores
has a bi-modal distribution of diameters having a first diameter
mode with a first peak of size distribution and a second diameter
mode with a second, different, peak of size distribution.
[0009] In yet another embodiment, a method of fabricating a
polishing pad involves mixing a pre-polymer and a chain extender or
cross-linker with a plurality of microelements to form a mixture.
Each of the plurality of microelements has an initial size. The
method also involves heating, in a formation mold, the mixture to
provide a molded polishing body composed of a thermoset
polyurethane material and a plurality of closed cell pores
dispersed in the thermoset polyurethane material. The plurality of
closed cell pores is formed by expanding each of the plurality of
microelements to a final, larger, size during the heating.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1A is a top down view of a POLITEX polishing pad, in
accordance with the prior art.
[0011] FIG. 1B is a cross-sectional view of a POLITEX polishing
pad, in accordance with the prior art.
[0012] FIGS. 2A-2G illustrate cross-sectional views of operations
used in the fabrication of a polishing pad, in accordance with an
embodiment of the present invention.
[0013] FIG. 3 illustrates cross-sectional views at 100.times. and
300.times. magnification of a low density polishing pad including
closed cell pores which are all based on a porogen filler, in
accordance with an embodiment of the present invention.
[0014] FIG. 4 illustrates cross-sectional views at 100.times. and
300.times. magnification of a low density polishing pad including
closed cell pores, a portion of which based on a porogen filler and
a portion of which is based on gas bubbles, in accordance with an
embodiment of the present invention.
[0015] FIG. 5A illustrates a plot of population as a function of
pore diameter for a broad mono-modal distribution of pore diameters
in a low density polishing pad, in accordance with an embodiment of
the present invention.
[0016] FIG. 5B illustrates a plot of population as a function of
pore diameter for a narrow mono-modal distribution of pore
diameters in a low density polishing pad, in accordance with an
embodiment of the present invention.
[0017] FIG. 6A illustrates a cross-sectional view of a low density
polishing pad having an approximately 1:1 bimodal distribution of
closed-cell pores, in accordance with an embodiment of the present
invention.
[0018] FIG. 6B illustrates a plot of population as a function of
pore diameter for a narrow distribution of pore diameters in the
polishing pad of FIG. 6A, in accordance with an embodiment of the
present invention.
[0019] FIG. 6C illustrates a plot of population as a function of
pore diameter for a broad distribution of pore diameters in the
polishing pad of FIG. 6A, in accordance with an embodiment of the
present invention.
[0020] FIG. 7 illustrates an isometric side-on view of a polishing
apparatus compatible with a low density polishing pad, in
accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
[0021] Low density polishing pads and methods of fabricating low
density polishing pads are described herein. In the following
description, numerous specific details are set forth, such as
specific polishing pad designs and compositions, in order to
provide a thorough understanding of embodiments of the present
invention. It will be apparent to one skilled in the art that
embodiments of the present invention may be practiced without these
specific details. In other instances, well-known processing
techniques, such as details concerning the combination of a slurry
with a polishing pad to perform chemical mechanical planarization
(CMP) of a semiconductor substrate, are not described in detail in
order to not unnecessarily obscure embodiments of the present
invention. Furthermore, it is to be understood that the various
embodiments shown in the figures are illustrative representations
and are not necessarily drawn to scale.
[0022] One or more embodiments described herein are directed to the
fabrication of polishing pads having a low density of less than
approximately 0.6 grams/cubic centimeter (g/cc) and, more
particularly, a low density of less than approximately 0.5 g/cc.
The resulting pads may be based on a polyurethane material having a
closed cell porosity which provides for the low density. The low
density pads may be used, e.g., as buff polishing pads or as
polishing pads designed for special chemical mechanical polishing
(CMP) applications such as liner/barrier removal. Polishing pads
described herein may, in some embodiments, be fabricated to have a
density as low as in the range of 0.3 g/cc to 0.5 g/cc, such as
approximately 0.357 g/cc. In a particular embodiment, a low density
pad has a density as low as approximately 0.2 g/cc.
[0023] To provide context, a typical CMP pad has a density around
0.7 to 0.8 g/cc, and is generally at least higher than 0.5 g/cc.
Conventionally, a typical CMP buff pad is has a "poromeric" design
using large cells open to the surface. A composite polyurethane
skin is included on a support, such as in the case of a POLITEX
polishing pad. Conventionally, buff pad are very soft and low
density made with open cell porosity (e.g., a fiber pad and
"poromeric" pad). Such pads typically are associated with two
fundamental issues for CMP: short life time and less consistent
performance as compared with conventional closed cell polyurethane
(but higher density) CMP pads. FIGS. 1A and 1B are a top down view
and cross-sectional view, respectively, of a POLITEX polishing pad,
in accordance with the prior art. Referring to FIG. 1A, a portion
100A of a POLITEX polishing pad is shown as magnified 300 times in
a scanning electron microscope (SEM) image. Referring to FIG. 1B, a
portion 100B of a POLITEX polishing pad is shown as magnified 100
times in a scanning electron microscope (SEM) image. Referring to
both FIGS. 1A and 1B, the open pore structure of the prior art pad
is readily visible.
[0024] More generally, one of the fundamental challenges is to
fabricate a closed cell polyurethane pad having high porosity and
low density. Our own investigations in the fabrication of low
density polyurethane pads by a molding or casting process has shown
difficulty in merely adding increased volumes of a porogen into a
pad formulation mixture to ultimately provide closed cell pores in
the pad material based on the added porogen. In particular, adding
more porogen than for a typical pad formulation can increase the
viscosity of the formulation to levels unmanageable for a casting
or molding process. The case can be particularly difficult for the
inclusion of pre-expanded porogens or porogens that retain
essentially the same volume throughout the molding or casting
process. In accordance with an embodiment of the present invention,
un-expanded porogens or porogens that increase volume throughout
the molding or casting process are included in a pad formulation
for ultimate for generation. In one such embodiment, however, if
all final closed cell pores are generated from unexpanded porogens,
the viscosity of the formulation may be too low for manageability
in casting or molding. As such, in one embodiment, in addition
forming a formulation to include un-expanded porogens or porogens
that increase volume throughout the molding or casting process,
pre-expanded porogens or porogens that retain essentially the same
volume throughout the molding or casting process are also included
to enable viscosity tuning of the pad formulation.
[0025] Accordingly, in an embodiment, Unexpanded Porogen Filler or
Underexpanded Porogen Filler (both referred to as UPF) that expands
at above ambient temperature is used to create porosity in a
polishing pad during manufacture by casting or molding. In one such
embodiment, a large quantity of UPF is included in a
polyurethane-forming mixture. The UPF expands during the pad
casting process and creates a low density pad with closed cell
pores. The above approach to creating a polishing pad can have
advantages over other techniques that have been used to form low
density pads with open cells. For example, fabrication of final pad
porosity based solely on gas injection or entrainment may require
specialized equipment, and may be accompanied by difficulty in
controlling final pad density and difficulty in controlling final
pore size and distribution. In another example, fabrication of
final pad porosity based solely on in situ gas generation, e.g.,
water reaction with an isocyanate moiety (NCO) to create CO.sub.2
bubbles can be accompanied by a difficulty in controlling pore size
distribution.
[0026] In an aspect of the present invention, low density polishing
pads may be fabricated in a molding process. For example, FIGS.
2A-2G illustrate cross-sectional views of operations used in the
fabrication of a polishing pad, in accordance with an embodiment of
the present invention.
[0027] Referring to FIG. 2A, a formation mold 200 is provided.
Referring to FIG. 2B, a pre-polymer 202 and a curative 204 (e.g., a
chain extender or cross-linker) are mixed with a plurality of
microelements to form a mixture. In an embodiment, the plurality of
microelements is a plurality of porogens 206, such as filled or
hollow microspheres. In another embodiment, the plurality of
microelements is a plurality of gas bubbles or liquid droplets, or
both, 208. In another embodiment, the plurality of microelements is
a combination of a plurality of porogens 206 and a plurality of gas
bubbles or liquid droplets, or both, 208.
[0028] Referring to FIG. 2C, the resulting mixture 210 from FIG. 2B
is shown at the base of the formation mold 200. The mixture 210
includes a first plurality of microelements 212, each of the first
plurality of microelements having an initial size. A second
plurality of microelements 214 may also be included in the mixture
210, as described in greater detail below.
[0029] Referring to FIG. 2D, a lid 216 of the formation mold 200 is
brought together with the base of the formation mold 200 and the
mixture 210 takes the shape of the formation mold 200. In an
embodiment, the mold 200 is degassed upon or during bringing
together of the lid 216 and base of the formation mold 200 such
that no cavities or voids form within the formation mold 210. It is
to be understood that embodiments described herein that describe
lowering the lid of a formation mold need only achieve a bringing
together of the lid and a base of the formation mold. That is, in
some embodiments, a base of a formation mold is raised toward a lid
of a formation mold, while in other embodiments a lid of a
formation mold is lowered toward a base of the formation mold at
the same time as the base is raised toward the lid.
[0030] Referring to FIG. 2E, the mixture 210 is heated in the
formation mold 200. Each of the plurality of microelements 212 is
expanded to a final, larger, size 218 during the heating.
Additionally, referring to FIG. 2F, the heating is used to cure the
mixture 210 to provide a partially or fully cured pad material 220
surrounding the microelements 218 and, if present, the
microelements 214. In one such embodiment, the curing forms a
cross-linked matrix based on the materials of the pre-polymer and
the curative.
[0031] Referring collectively to FIGS. 2E and 2F, it is to be
understood that the ordering of expanding microelements 212 to the
final, larger, size 218 and the curing the mixture 210 need not
necessarily occur in the order illustrated. In another embodiment,
during the heating, the curing of the mixture 210 occurs prior to
expanding the microelements 212 to the final, larger, size 218. In
another embodiment, during the heating, the curing of the mixture
210 occurs at the same time as expanding the microelements 212 to
the final, larger, size 218. In yet another embodiment, two
separate heating operations are performed to cure the mixture 210
and to expand the microelements 212 to the final, larger, size 218,
respectively.
[0032] Referring to FIG. 2G, in an embodiment, the above described
process is used to provide a low density polishing pad 220. The low
density polishing pad 222 is composed of the cured material 220 and
includes the expanded microelements 218 and, in some embodiment,
additional microelements 214. In an embodiment, the low density
polishing pad 222 is composed of a thermoset polyurethane material
and the expanded microelements 218 provide a plurality of closed
cell pores dispersed in the thermoset polyurethane material.
Referring again to FIG. 2G, the bottom portion of the Figure is the
plan view of the upper cross-sectional view which is taken along
the a-a' axis. As seen in the plan view, in an embodiment, the low
density polishing pad 222 has a polishing surface 228 having a
groove pattern therein. In one particular embodiment, as shown, the
groove pattern includes radial grooves 226 and concentric circular
grooves 228.
[0033] Referring again to FIGS. 2D and 2E, in an embodiment, each
of the plurality of microelements 212 is expanded to the final size
218 by increasing a volume of each of the plurality of
microelements by a factor approximately in the range of 3-1000. In
an embodiment, each of the plurality of microelements 212 is
expanded to the final size 214 to provide a final diameter of each
of the plurality of microelements 218 approximately in the range of
10-200 microns. In an embodiment, each of the plurality of
microelements 212 is expanded to the final size 218 by reducing a
density of each of the plurality of microelements 212 by a factor
approximately in the range of 3-1000. In an embodiment, each of the
plurality of microelements 212 is expanded to the final size 218 by
forming an essentially spherical shape for each of the plurality of
microelements 218 of the final size.
[0034] In an embodiment, the plurality of microelements 212 is an
added porogen, gas bubble or liquid bubble that is then expanded
within the pad material formulation to form closed cell pores
within a finished polishing pad material. In one such embodiment,
the plurality of closed cell pores is a plurality of larger
porogens formed by expanding corresponding smaller porogens. For
example, the term "porogen" may be used to indicate micro- or
nano-scale spherical or somewhat spherical particles with "hollow"
centers. The hollow centers are not filled with solid material, but
may rather include a gaseous or liquid core. In one embodiment, the
plurality of closed cell pores begins as un-expanded gas-filled or
liquid-filled EXPANCEL.TM. distributed throughout a mixture. Upon
and/or during forming a polishing pad from the mixture, e.g., by a
molding process, the un-expanded gas-filled or liquid-filled
EXPANCEL.TM. becomes expanded. In a specific embodiment, the
EXPANCEL.TM. is filled with pentane. In an embodiment, each of the
plurality of closed cell pores has a diameter approximately in the
range of 10-100 microns in its expanded state, e.g., in the final
product. Thus, in an embodiment, each of the plurality of
microelements having the initial size includes a physical shell,
and each of the plurality of microelements having the final size
includes an expanded physical shell. In another embodiment, each of
the plurality of microelements 212 having the initial size is a
liquid droplet, and each of the plurality of microelements 218
having the final size is a gas bubble. In yet another embodiment,
for form the plurality of microelements 218 having the final size,
mixing to form the mixture 210 further involves injecting a gas
into the pre-polymer and the chain extender or cross-linker, or
into a product formed there from. In a specific such embodiment,
the pre-polymer is an isocyanate and the mixing further involves
adding water to the pre-polymer. In any case, in an embodiment, the
plurality of closed cell pores includes pores that are discrete
from one another. This is in contrast to open cell pores which may
be connected to one another through tunnels, such as the case for
the pores in a common sponge.
[0035] Referring again to FIGS. 2C-2E, in an embodiment, mixing the
pre-polymer 202 and the chain extender or cross-linker 204 with the
plurality of microelements 212 further involves mixing with a
second plurality of microelements 214 to form the mixture 210. Each
of the second plurality of microelements 214 has a size. In one
such embodiment, the heating described in association with FIG. 2E
is performed at a temperature sufficiently low such that the size
of each of the second plurality of microelements 214 is essentially
the same before and after the heating, as is depicted in FIG. 2E.
In a specific such embodiment, the heating is performed at a
temperature of approximately 100 degrees Celsius or less, and the
second plurality of microelements 214 has an expansion threshold of
greater than approximately 130 degrees Celsius. In one other
embodiment, the second plurality of microelements 214 has an
expansion threshold greater than an expansion threshold of the
plurality of microelements 212. In one specific such embodiment,
the expansion threshold of the second plurality of microelements
214 is greater than approximately 120 degrees Celsius, and the
expansion threshold of the plurality of microelements 212 is less
than approximately 110 degrees Celsius. As such, in an embodiment,
during the heating, the microelements 212 expand during to heating
to provide expanded microelements 218, while the microelements 214
essentially remain unchanged.
[0036] In an embodiment, each of the second plurality of
microelements 214 is composed of pre-expanded and gas-filled
EXPANCEL.TM. distributed throughout (e.g., as an additional
component in) the polishing pad. That is, any significant expansion
that could occur for the microelements 214 is carried our prior to
their inclusion in a polishing pad formation, e.g., before being
included in mixture 210. In a specific embodiment, the pre-expanded
EXPANCEL.TM. is filled with pentane. In an embodiment, the
microelements 214 provide a plurality of closed cell pores (shown
again as 214 with little to no change during the molding process)
has a diameter approximately in the range of 10-100 microns. In an
embodiment, the resulting plurality of closed cell pores includes
pores that are discrete from one another. This is in contrast to
open cell pores which may be connected to one another through
tunnels, such as the case for the pores in a common sponge.
[0037] As described above, increasing porosity by adding more
porogen than for a typical pad formulation can increase the
viscosity of the formulation to levels unmanageable for a casting
or molding process. The case can be particularly difficult for the
inclusion of pre-expanded porogens or porogens that retain
essentially the same volume throughout the molding or casting
process. On the other hand, if all final closed cell pores are
generated from unexpanded porogens, the viscosity of the
formulation may be too low for manageability in casting or molding.
In order to address such situations, in accordance with an
embodiment of the present invention, conceptually, a mixture of the
pre-polymer 202, the chain extender or cross-linker 204, and the
second plurality of microelements 214 has a viscosity. Meanwhile,
the mixture of the pre-polymer 202, the chain extender or
cross-linker 204, the plurality of microelements 212 having the
initial size, and the second plurality of microelements 214
essentially has the same viscosity. That is, the inclusion of the
plurality of microelements 212 having the initial (smaller) size
has little to no impact on the viscosity of the mixture. In an
embodiment, then, a described viscosity for optimal molding
conditions may be selected based on the inclusion of the second
plurality of microelements with a size that remains essentially
constant throughout the molding process. In one such embodiment,
then, the viscosity is a predetermined viscosity, and a relative
amount of the second plurality of microelements 214 in the mixture
210 is selected based on the predetermined viscosity. And, in one
embodiment, the plurality of microelements 212 has little to no
effect on the viscosity of the mixture 210.
[0038] Referring again to FIG. 2E, in an embodiment, in a case
where two different pluralities of microelements are included, each
of the plurality of microelements 218 having the expanded final
size is of approximately the same shape and size as each of the
plurality of microelements 214 which do not expand through the
heating process, as is depicted. It is to be understood, however,
that each of the plurality of microelements 218 having the expanded
final size need not have the same shape and/or size as each of the
plurality of microelements 214. In an embodiment, as described in
greater detail below in association with FIGS. 6A-6C, the resulting
molded polishing body of pad 222 includes, as closed cell pores,
the plurality of expanded microelements 218 having a first diameter
mode with a first peak of size distribution. Also included, also as
closed cell pores, is the second plurality of microelements 214
having a second diameter mode with a second, different, peak of
size distribution. In one such embodiment, the plurality of closed
cell pores of microelements 218 and the second plurality of closed
cell pores of microelements 214 provides a total pore volume in the
thermoset polyurethane material approximately in the range of
55-80% of the total volume of the thermoset polyurethane material
of low density polishing pad 222.
[0039] Referring again to FIGS. 2D-2G in an embodiment, heating the
mixture 210 to provide the molded polishing body 222 involves
forming the polishing body 222 having a density of less than 0.5
g/cc. In one such embodiment, however, the mixture 210 has a
density of greater than 0.5 g/cc prior to the heating. In an
embodiment, the pre-polymer 202 is an isocyanate and the chain
extender or cross-linker 204 is an aromatic diamine compound, and
the polishing pad 222 is composed of a thermoset polyurethane
material 220. In one such embodiment, forming mixture 210 further
involves adding an opacifying filler to the pre-polymer 202 and the
chain extender or cross-linker 204 to ultimately provide an opaque
molded polishing body 222. In a specific such embodiment, the
opacifying filler is a material such as, but not limited to, boron
nitride, cerium fluoride, graphite, graphite fluoride, molybdenum
sulfide, niobium sulfide, talc, tantalum sulfide, tungsten
disulfide, or Teflon. In an embodiment, as mentioned briefly above,
the mixture 210 is only partially cured in the mold 200 and, in one
embodiment, is further cured in an oven subsequent to removal from
the formation mold 220.
[0040] In an embodiment, the polishing pad precursor mixture 210 is
used to ultimately form a molded homogeneous polishing body 222
composed of a thermoset, closed cell polyurethane material. In one
such embodiment, the polishing pad precursor mixture 210 is used to
ultimately form a hard pad and only a single type of curative 204
is used. In another embodiment, the polishing pad precursor mixture
210 is used to ultimately form a soft pad and a combination of a
primary and a secondary curative (together providing 210) is used.
For example, in a specific embodiment, the pre-polymer 202 includes
a polyurethane precursor, the primary curative includes an aromatic
diamine compound, and the secondary curative includes an ether
linkage. In a particular embodiment, the polyurethane precursor is
an isocyanate, the primary curative is an aromatic diamine, and the
secondary curative is a curative such as, but not limited to,
polytetramethylene glycol, amino-functionalized glycol, or
amino-functionalized polyoxypropylene. In an embodiment, a
pre-polymer 202, a primary curative, and a secondary curative
(together 204) have an approximate molar ratio of 106 parts
pre-polymer, 85 parts primary curative, and 15 parts secondary
curative, i.e., to provide a stoichiometry of approximately 1:0.96
pre-polymer:curative. It is to be understood that variations of the
ratio may be used to provide polishing pads with varying hardness
values, or based on the specific nature of the pre-polymer and the
first and second curatives.
[0041] Referring again to FIG. 2G, as described above, in an
embodiment, heating in the formation mold 200 involves forming a
groove pattern in the polishing surface 224 of the molded polishing
body 222. The groove pattern as shown includes radial grooves and
concentric circular circumferential grooves. It is to be understood
that radial grooves or circumferential grooves may be omitted.
Furthermore, the concentric circumferential grooves may instead be
polygons, such as nested triangles, squares, pentagons, hexagons,
etc. Alternatively, the polishing surface may instead be based on
protrusions instead of grooves. Furthermore, a low density
polishing pad may be fabricated without grooves in the polishing
surface. In one such example, a non-patterned lid of a molding
apparatus is used instead of a patterned lid. Or, alternatively,
the use of a lid during molding may be omitted. In the case of the
use of a lid during molding, the mixture 210 may be heated under a
pressure approximately in the range of 2-12 pounds per square
inch.
[0042] In an aspect, a low density pad may be fabricated having
closed cell pores. For example, in an embodiment, a polishing pad
includes a polishing body having a density of less than 0.6 and
composed of a thermoset polyurethane material. A plurality of
closed cell pores is dispersed in the thermoset polyurethane
material. In a particular embodiment, the density is less than 0.5
g/cc. In an embodiment, the plurality of closed cell pores provides
a total pore volume in the thermoset polyurethane material
approximately in the range of 55-80% of the total volume of the
thermoset polyurethane material. In an embodiment, each of the
plurality of closed cell pores is essentially spherical. In an
embodiment, the polishing body further includes a first, grooved
surface; and a second, flat, surface opposite the first surface, as
described in association with FIG. 2G. In an embodiment, the
polishing body is a homogeneous polishing body, as is described in
greater detail below.
[0043] In one exemplary embodiment, each of the plurality of closed
cell pores includes a physical shell composed of a material
different from the thermoset polyurethane material. In such a case,
the closed cell pores may be fabricated by including a porogen in a
mixture that is molded for ultimate pad fabrication, as described
above.
[0044] In another exemplary embodiment, each of the plurality of
closed cell pores includes a physical shell composed of a material
different from the thermoset polyurethane material. The physical
shells of a first portion of the plurality of closed cell pores are
composed of a material different than the physical shells of a
second portion of the plurality of closed cell pores. In such a
case, the closed cell pores may be fabricated by including two
types of porogens (e.g., expanded and unexpanded) in a mixture that
is molded for ultimate pad fabrication, as described above.
[0045] In another exemplary embodiment, each of only a portion of
the plurality of closed cell pores includes a physical shell
composed of a material different from the thermoset polyurethane
material. In such a case, the closed cell pores may be fabricated
by including both porogens and gas bubbles or liquid drops in a
mixture that is molded for ultimate pad fabrication, as described
above.
[0046] In another exemplary embodiment, each of the plurality of
closed cell pores does not include a physical shell of a material
different from the thermoset polyurethane material. In such a case,
the closed cell pores may be fabricated by including gas bubbles or
liquid drops, or both, in a mixture that is molded for ultimate pad
fabrication, as described above.
[0047] FIG. 3 illustrates cross-sectional views at 100.times. and
300.times. magnification of a low density polishing pad 300
including closed cell pores which are all based on a porogen
filler, in accordance with an embodiment of the present invention.
Referring to FIG. 3, all pores shown are formed from a porogen and,
as such, all include a physical shell. A portion of the pores is
formed from a pre-expanded Expancel porogen. Another portion is
formed from an unexpanded Expancel porogen which expanded during a
molding process used to fabricate polishing pad 300. In one such
embodiment, the un-expanded Expancel expands at low temperature by
design. The molding or casting process temperature is above the
expansion temperature and the Expancel rapidly expands during the
molding or casting. The density of pad 300 is approximately 0.45
and all pores in the pad are closed cell pores.
[0048] FIG. 4 illustrates cross-sectional views at 100.times. and
300.times. magnification of a low density polishing pad 400
including closed cell pores, a portion of which based on a porogen
filler and a portion of which is based on gas bubbles, in
accordance with an embodiment of the present invention. Referring
to FIG. 4, the small pores shown are formed from a porogen and, as
such, include a physical shell. More specifically, the small pores
are formed from a pre-expanded Expancel porogen. The large pores
are formed using a gas. More specifically, the large pores are
formed using a small quantity of water and surfactant injected into
a pad formulation mixture just prior to molding or casting. During
the chemical reaction for chain extension, there is a competing
chemical reaction of the water with NCO to form CO.sub.2 and create
pores. It is to be understood that the surfactant type and
concentration, as well as catalyst type and level, controls pore
size and the closes/open cell pore ratio. The density of pad 400 is
approximately 0.37 and a significant majority of the pores in the
pad are closed cell pores.
[0049] In an aspect, a distribution of pore diameters in a
polishing pad can have a bell curve or mono-modal distribution. For
example, FIG. 5A illustrates a plot of population as a function of
pore diameter for a broad mono-modal distribution of pore diameters
in a low density polishing pad, in accordance with an embodiment of
the present invention. Referring to plot 500A of FIG. 5A, the
mono-modal distribution may be relatively broad. As another
example, FIG. 5B illustrates a plot of population as a function of
pore diameter for a narrow mono-modal distribution of pore
diameters in a low density polishing pad, in accordance with an
embodiment of the present invention. Referring to plot 500B of FIG.
5B, the mono-modal distribution may be relatively narrow. In either
the narrow distribution or the broad distribution, only one maximum
diameter population, such as a maximum population at 40 microns (as
shown as an example), is provided in the polishing pad.
[0050] In another aspect, a low density polishing pad may instead
be fabricated with a bimodal distribution of pore diameters. As an
example, FIG. 6A illustrates a cross-sectional view of a low
density polishing pad having an approximately 1:1 bimodal
distribution of closed-cell pores, in accordance with an embodiment
of the present invention.
[0051] Referring to FIG. 6A, a polishing pad 600 includes a
homogeneous polishing body 601. The homogeneous polishing body 601
is composed of a thermoset polyurethane material with a plurality
of closed cell pores 602 disposed in the homogeneous polishing body
601. The plurality of closed cell pores 602 has a multi-modal
distribution of diameters. In an embodiment, the multi-modal
distribution of diameters is a bimodal distribution of diameters
including a small diameter mode 604 and a large diameter mode 606,
as depicted in FIG. 6A.
[0052] In an embodiment, the plurality of closed cell pores 602
includes pores that are discrete from one another, as depicted in
FIG. 6A. This is in contrast to open cell pores which may be
connected to one another through tunnels, such as the case for the
pores in a common sponge. In one embodiment, each of the closed
cell pores includes a physical shell, such as a shell of a porogen.
In another embodiment, however, some or all of the closed cell
pores does not include a physical shell. In an embodiment, the
plurality of closed cell pores 602, and hence the multi-modal
distribution of diameters, is distributed essentially evenly and
uniformly throughout the thermoset polyurethane material of
homogeneous polishing body 601, as depicted in FIG. 6A.
[0053] In an embodiment, the bimodal distribution of pore diameters
of the plurality of closed cell pores 602 may be approximately 1:1,
as depicted in FIG. 6A. To better illustrate the concept, FIG. 6B
illustrates a plot 620 of population as a function of pore diameter
for a narrow distribution of pore diameters in the polishing pad of
FIG. 6A, in accordance with an embodiment of the present invention.
FIG. 6C illustrates a plot 630 of population as a function of pore
diameter for a broad distribution of pore diameters in the
polishing pad of FIG. 6A, in accordance with an embodiment of the
present invention.
[0054] Referring to FIGS. 6A-6C, the diameter value for the maximum
population of the large diameter mode 606 is approximately twice
the diameter value of the maximum population of the small diameter
mode 604. For example, in one embodiment, the diameter value for
the maximum population of the large diameter mode 606 is
approximately 40 microns and the diameter value of the maximum
population of the small diameter mode 604 is approximately 20
microns, as depicted in FIGS. 6B and 6C. As another example, the
diameter value for the maximum population of the large diameter
mode 606 is approximately 80 microns and the diameter value of the
maximum population of the small diameter mode 604 is approximately
40 microns.
[0055] Referring to plot 620 of FIG. 6B, in one embodiment, the
distributions of pore diameters are narrow. In a specific
embodiment, the population of the large diameter mode 606 has
essentially no overlap with the population of the small diameter
mode 604. However, referring to plot 630 of FIG. 6C, in another
embodiment, the distributions of pore diameters are broad. In a
specific embodiment, the population of the large diameter mode 606
overlaps with the population of the small diameter mode 604. It is
to be understood that, a bimodal distribution of pore diameters
need not be 1:1, as is described above in association with FIGS.
6A-6C. Also, a bimodal distribution of pore diameters need not be
uniform. In another embodiment, the multi-modal distribution of
diameters of closed cell pores is graded throughout the thermoset
polyurethane material with a gradient from the first, grooved
surface to the second, flat surface. In one such embodiment, the
graded multi-modal distribution of diameters is a bimodal
distribution of diameters including a small diameter mode proximate
to the first, grooved surface, and a large diameter mode proximate
to the second, flat surface.
[0056] In an embodiment, then, low density polishing pad has a
plurality of closed cell pores with a bi-modal distribution of
diameters having a first diameter mode with a first peak of size
distribution and a second diameter mode with a second, different,
peak of size distribution. In one such embodiment, the closed cell
pores of the first diameter mode each include a physical shell
composed of a material different from the thermoset polyurethane
material. In a specific such embodiment, the closed cell pores of
the second diameter mode each include a physical shell composed a
material different from the thermoset polyurethane material. In a
particular such embodiment, the physical shell of each of the
closed cell pores of the second diameter mode is composed of a
material different from the material of the physical shells of the
closed cell pores of the first diameter mode.
[0057] In an embodiment, the first peak of size distribution of the
first diameter mode has a diameter approximately in the range of
10-50 microns, and the second peak of size distribution of the
second diameter mode has a diameter approximately in the range of
10-150 microns. In an embodiment, the first diameter mode overlaps
with the second diameter mode. In another embodiment, however, the
first diameter mode has essentially no overlap with the second
diameter mode. In an embodiment, a total population in count number
of the first diameter mode is not equal to a total population in
count number of the second diameter mode. In another embodiment,
however, a total population in count number of the first diameter
mode is approximately equal to a total population in count number
of the second diameter mode. In an embodiment, the bi-modal
distribution of diameters is distributed essentially evenly
throughout the thermoset polyurethane material. In another
embodiment, however, the bi-modal distribution of diameters is
distributed in a graded fashion throughout the thermoset
polyurethane material.
[0058] In an embodiment, low density polishing pads described
herein, such as polishing pad 222, 300 or 400, or the above
described variations thereof, are suitable for polishing
substrates. In one such embodiment, the polishing pad is used as a
buff pad. The substrate may be one used in the semiconductor
manufacturing industry, such as a silicon substrate having device
or other layers disposed thereon. However, the substrate may be one
such as, but not limited to, a substrates for MEMS devices,
reticles, or solar modules. Thus, reference to "a polishing pad for
polishing a substrate," as used herein, is intended to encompass
these and related possibilities.
[0059] Low density polishing pads described herein, such as
polishing pad 222, 300 or 400, or the above described variations
thereof, may be composed of a homogeneous polishing body of a
thermoset polyurethane material. In an embodiment, the homogeneous
polishing body is composed of a thermoset, closed cell polyurethane
material. In an embodiment, the term "homogeneous" is used to
indicate that the composition of a thermoset, closed cell
polyurethane material is consistent throughout the entire
composition of the polishing body. For example, in an embodiment,
the term "homogeneous" excludes polishing pads composed of, e.g.,
impregnated felt or a composition (composite) of multiple layers of
differing material. In an embodiment, the term "thermoset" is used
to indicate a polymer material that irreversibly cures, e.g., the
precursor to the material changes irreversibly into an infusible,
insoluble polymer network by curing. For example, in an embodiment,
the term "thermoset" excludes polishing pads composed of, e.g.,
"thermoplast" materials or "thermoplastics"--those materials
composed of a polymer that turns to a liquid when heated and
returns to a very glassy state when cooled sufficiently. It is
noted that polishing pads made from thermoset materials are
typically fabricated from lower molecular weight precursors
reacting to form a polymer in a chemical reaction, while pads made
from thermoplastic materials are typically fabricated by heating a
pre-existing polymer to cause a phase change so that a polishing
pad is formed in a physical process. Polyurethane thermoset
polymers may be selected for fabricating polishing pads described
herein based on their stable thermal and mechanical properties,
resistance to the chemical environment, and tendency for wear
resistance.
[0060] In an embodiment, the homogeneous polishing body, upon
conditioning and/or polishing, has a polishing surface roughness
approximately in the range of 1-5 microns root mean square. In one
embodiment, the homogeneous polishing body, upon conditioning
and/or polishing, has a polishing surface roughness of
approximately 2.35 microns root mean square. In an embodiment, the
homogeneous polishing body has a storage modulus at 25 degrees
Celsius approximately in the range of 30-120 megaPascals (MPa). In
another embodiment, the homogeneous polishing body has a storage
modulus at 25 degrees Celsius approximately less than 30
megaPascals (MPa). In one embodiment, the homogeneous polishing
body has a compressibility of approximately 2.5%.
[0061] In an embodiment, low density polishing pads described
herein, such as polishing pad 222, 300 or 400, or the above
described variations thereof, include a molded homogeneous
polishing body. The term "molded" is used to indicate that a
homogeneous polishing body is formed in a formation mold, as
described in more detail above in association with FIGS. 2A-2G. It
is to be understood that, in other embodiments, a casting process
may be used instead to fabricate low density polishing pads such as
those described above.
[0062] In an embodiment, the homogeneous polishing body is opaque.
In one embodiment, the term "opaque" is used to indicate a material
that allows approximately 10% or less visible light to pass. In one
embodiment, the homogeneous polishing body is opaque in most part,
or due entirely to, the inclusion of an opacifying filler
throughout (e.g., as an additional component in) the homogeneous
thermoset, closed cell polyurethane material of the homogeneous
polishing body. In a specific embodiment, the opacifying filler is
a material such as, but not limited to, boron nitride, cerium
fluoride, graphite, graphite fluoride, molybdenum sulfide, niobium
sulfide, talc, tantalum sulfide, tungsten disulfide, or Teflon.
[0063] The sizing of the low density polishing pads, such as pads
222, 300 or 400, may be varied according to application.
Nonetheless, certain parameters may be used to fabricate polishing
pads compatible with conventional processing equipment or even with
conventional chemical mechanical processing operations. For
example, in accordance with an embodiment of the present invention,
a low density polishing pad has a thickness approximately in the
range of 0.075 inches to 0.130 inches, e.g., approximately in the
range of 1.9-3.3 millimeters. In one embodiment, a low density
polishing pad has a diameter approximately in the range of 20
inches to 30.3 inches, e.g., approximately in the range of 50-77
centimeters, and possibly approximately in the range of 10 inches
to 42 inches, e.g., approximately in the range of 25-107
centimeters.
[0064] In another embodiment of the present invention, a low
density polishing pad described herein further includes a local
area transparency (LAT) region disposed in the polishing pad. In an
embodiment, the LAT region is disposed in, and covalently bonded
with, the polishing pad. Examples of suitable LAT regions are
described in U.S. patent application Ser. No. 12/657,135 filed on
Jan. 13, 2010, assigned to NexPlanar Corporation, and U.S. patent
application Ser. No. 12/895,465 filed on Sep. 30, 2010, assigned to
NexPlanar Corporation. In an alternative or additional embodiment,
a low density polishing pad further includes an aperture disposed
in the polishing surface and polishing body. The aperture can
accommodate, e.g., a detection device included in a platen of a
polishing tool. An adhesive sheet is disposed on the back surface
of the polishing body. The adhesive sheet provides an impermeable
seal for the aperture at the back surface of the polishing body.
Examples of suitable apertures are described in U.S. patent
application Ser. No. 13/184,395 filed on Jul. 15, 2011, assigned to
NexPlanar Corporation. In another embodiment, a low density
polishing pad further includes a detection region for use with,
e.g., an eddy current detection system. Examples of suitable eddy
current detection regions are described in U.S. patent application
Ser. No. 12/895,465 filed on Sep. 30, 2010, assigned to NexPlanar
Corporation.
[0065] Low density polishing pads described herein, such as
polishing pad 222, 300 or 400, or the above described variations
thereof, may further include a foundation layer disposed on the
back surface of the polishing body. In one such embodiment, the
result is a polishing pad with bulk or foundation material
different from the material of the polishing surface. In one
embodiment, a composite polishing pad includes a foundation or bulk
layer fabricated from a stable, essentially non-compressible, inert
material onto which a polishing surface layer is disposed. A harder
foundation layer may provide support and strength for pad integrity
while a softer polishing surface layer may reduce scratching,
enabling decoupling of the material properties of the polishing
layer and the remainder of the polishing pad. Examples of suitable
foundation layers are described in U.S. patent application Ser. No.
13/306,845 filed on Nov. 29, 2011, assigned to NexPlanar
Corporation.
[0066] Low density polishing pads described herein, such as
polishing pad 222, 300 or 400, or the above described variations
thereof, may further include a sub pad disposed on the back surface
of the polishing body, e.g., a conventional sub pad as known in the
CMP art. In one such embodiment, the sub pad is composed of a
material such as, but not limited to, foam, rubber, fiber, felt or
a highly porous material.
[0067] Referring again to FIG. 2G as a foundation for description,
individual grooves of a groove pattern formed in a low density
polishing pad such as those described herein may be from about 4 to
about 100 mils deep at any given point on each groove. In some
embodiments, the grooves are about 10 to about 50 mils deep at any
given point on each groove. The grooves may be of uniform depth,
variable depth, or any combinations thereof. In some embodiments,
the grooves are all of uniform depth. For example, the grooves of a
groove pattern may all have the same depth. In some embodiments,
some of the grooves of a groove pattern may have a certain uniform
depth while other grooves of the same pattern may have a different
uniform depth. For example, groove depth may increase with
increasing distance from the center of the polishing pad. In some
embodiments, however, groove depth decreases with increasing
distance from the center of the polishing pad. In some embodiments,
grooves of uniform depth alternate with grooves of variable
depth.
[0068] Individual grooves of a groove pattern formed in a low
density polishing pad such as those described herein may be from
about 2 to about 100 mils wide at any given point on each groove.
In some embodiments, the grooves are about 15 to about 50 mils wide
at any given point on each groove. The grooves may be of uniform
width, variable width, or any combinations thereof. In some
embodiments, the grooves of are all of uniform width. In some
embodiments, however, some of the grooves of a concentric have a
certain uniform width, while other grooves of the same pattern have
a different uniform width. In some embodiments, groove width
increases with increasing distance from the center of the polishing
pad. In some embodiments, groove width decreases with increasing
distance from the center of the polishing pad. In some embodiments,
grooves of uniform width alternate with grooves of variable
width.
[0069] In accordance with the previously described depth and width
dimensions, individual grooves of the groove patterns described
herein, including grooves at or near a location of an aperture in a
polishing pad, may be of uniform volume, variable volume, or any
combinations thereof. In some embodiments, the grooves are all of
uniform volume. In some embodiments, however, groove volume
increases with increasing distance from the center of the polishing
pad. In some other embodiments, groove volume decreases with
increasing distance from the center of the polishing pad. In some
embodiments, grooves of uniform volume alternate with grooves of
variable volume.
[0070] Grooves of the groove patterns described herein may have a
pitch from about 30 to about 1000 mils. In some embodiments, the
grooves have a pitch of about 125 mils. For a circular polishing
pad, groove pitch is measured along the radius of the circular
polishing pad. In CMP belts, groove pitch is measured from the
center of the CMP belt to an edge of the CMP belt. The grooves may
be of uniform pitch, variable pitch, or in any combinations
thereof. In some embodiments, the grooves are all of uniform pitch.
In some embodiments, however, groove pitch increases with
increasing distance from the center of the polishing pad. In some
other embodiments, groove pitch decreases with increasing distance
from the center of the polishing pad. In some embodiments, the
pitch of the grooves in one sector varies with increasing distance
from the center of the polishing pad while the pitch of the grooves
in an adjacent sector remains uniform. In some embodiments, the
pitch of the grooves in one sector increases with increasing
distance from the center of the polishing pad while the pitch of
the grooves in an adjacent sector increases at a different rate. In
some embodiments, the pitch of the grooves in one sector increases
with increasing distance from the center of the polishing pad while
the pitch of the grooves in an adjacent sector decreases with
increasing distance from the center of the polishing pad. In some
embodiments, grooves of uniform pitch alternate with grooves of
variable pitch. In some embodiments, sectors of grooves of uniform
pitch alternate with sectors of grooves of variable pitch.
[0071] Polishing pads described herein may be suitable for use with
a variety of chemical mechanical polishing apparatuses. As an
example, FIG. 7 illustrates an isometric side-on view of a
polishing apparatus compatible with a low density polishing pad, in
accordance with an embodiment of the present invention.
[0072] Referring to FIG. 7, a polishing apparatus 700 includes a
platen 704. The top surface 702 of platen 704 may be used to
support a low density polishing pad. Platen 704 may be configured
to provide spindle rotation 706 and slider oscillation 708. A
sample carrier 710 is used to hold, e.g., a semiconductor wafer 711
in place during polishing of the semiconductor wafer with a
polishing pad. Sample carrier 710 is further supported by a
suspension mechanism 712. A slurry feed 714 is included for
providing slurry to a surface of a polishing pad prior to and
during polishing of the semiconductor wafer. A conditioning unit
790 may also be included and, in one embodiment, includes a diamond
tip for conditioning a polishing pad.
[0073] Thus, low density polishing pads and methods of fabricating
low density polishing pads have been disclosed. In accordance with
an embodiment of the present invention, a polishing pad for
polishing a substrate includes a polishing body having a density of
less than 0.5 g/cc and composed of a thermoset polyurethane
material. A plurality of closed cell pores is dispersed in the
thermoset polyurethane material. In one embodiment, the polishing
body is a homogeneous polishing body.
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