U.S. patent application number 14/823956 was filed with the patent office on 2015-12-03 for soft polishing pad for polishing a semiconductor substrate.
The applicant listed for this patent is William C. Allison, Richard Frentzel, Ping Huang, Robert Kerprich, Diane Scott. Invention is credited to William C. Allison, Richard Frentzel, Ping Huang, Robert Kerprich, Diane Scott.
Application Number | 20150343595 14/823956 |
Document ID | / |
Family ID | 43881168 |
Filed Date | 2015-12-03 |
United States Patent
Application |
20150343595 |
Kind Code |
A1 |
Allison; William C. ; et
al. |
December 3, 2015 |
SOFT POLISHING PAD FOR POLISHING A SEMICONDUCTOR SUBSTRATE
Abstract
Soft polishing pads for polishing semiconductor substrates are
described. A soft polishing pad includes a molded homogeneous
polishing body having a thermoset, closed cell polyurethane
material with a hardness approximately in the range of 20 Shore D
to 45 Shore D.
Inventors: |
Allison; William C.;
(Beaverton, OR) ; Scott; Diane; (Portland, OR)
; Kerprich; Robert; (Portland, OR) ; Huang;
Ping; (St. Louis Park, MN) ; Frentzel; Richard;
(Murrieta, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Allison; William C.
Scott; Diane
Kerprich; Robert
Huang; Ping
Frentzel; Richard |
Beaverton
Portland
Portland
St. Louis Park
Murrieta |
OR
OR
OR
MN
CA |
US
US
US
US
US |
|
|
Family ID: |
43881168 |
Appl. No.: |
14/823956 |
Filed: |
August 11, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12832908 |
Jul 8, 2010 |
9156124 |
|
|
14823956 |
|
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Current U.S.
Class: |
451/527 ;
451/526; 51/296 |
Current CPC
Class: |
B32B 2307/72 20130101;
C08G 18/7621 20130101; B32B 27/065 20130101; B32B 2307/41 20130101;
B32B 2266/0278 20130101; B32B 2307/732 20130101; B32B 2307/412
20130101; B32B 27/308 20130101; B32B 7/12 20130101; B32B 2307/536
20130101; B32B 25/045 20130101; B32B 27/36 20130101; B24B 37/26
20130101; B24B 37/24 20130101; B32B 7/06 20130101; B24D 11/003
20130101; B32B 2266/08 20130101; B32B 5/18 20130101; C08G 18/3206
20130101; B32B 25/08 20130101; B32B 27/08 20130101; B24B 37/205
20130101; B32B 3/30 20130101; B32B 2307/40 20130101; B32B 5/142
20130101; B32B 2457/00 20130101 |
International
Class: |
B24B 37/24 20060101
B24B037/24; C08G 18/32 20060101 C08G018/32; C08G 18/76 20060101
C08G018/76; B24B 37/26 20060101 B24B037/26; B24D 11/00 20060101
B24D011/00 |
Claims
1. A method of fabricating a soft polishing pad for polishing a
semiconductor substrate, the method comprising: mixing a
pre-polymer, a primary curative, and a secondary curative different
from the primary curative to form a mixture, wherein the primary
curative is a diamine compound and the secondary curative is a diol
compound; and curing the mixture to provide a homogeneous polishing
body comprising a thermoset, closed cell polyurethane material
having a hardness between about 20 Shore D and about 35 Shore
D.
2. The method of claim 1, wherein the pre-polymer comprises a
polyurethane precursor and the primary curative is an aromatic
diamine compound.
3. The method of claim 2, wherein the polyurethane precursor is an
isocyanate and the secondary curative is polytetramethylene
glycol.
4. The method of claim 1, wherein curing the mixture comprises
partially curing in a formation mold to provide a polyurethane
material, and further curing in an oven to provide the homogeneous
polishing body comprising the thermoset, closed cell polyurethane
material.
5. The method of claim 1, wherein the homogeneous polishing body
comprises a first, grooved surface, and a second, flat surface
opposite the first surface.
6. The method of claim 1, wherein the mixing further comprises
mixing an opacifying lubricant with the pre-polymer, the primary
curative, and the secondary curative, and wherein the homogeneous
polishing body is opaque.
7. The method of claim 4, further comprising: prior to mixing the
pre-polymer and the primary curative and the secondary curative,
mixing an aromatic urethane pre-polymer with a curative in a
second, separate, formation mold to form a second mixture;
partially curing, in the second formation mold, the second mixture
to form a molded gel; and positioning the molded gel in a
designated region of the formation mold, wherein mixing the
pre-polymer and the primary curative and the secondary curative to
form the mixture comprises forming the mixture at least partially
surrounding the molded gel, and wherein curing the mixture to
provide the homogeneous polishing body further comprises curing the
molded gel to provide a local area transparency (LAT) region
disposed in, and covalently bonded with, the homogeneous polishing
body.
8. The method of claim 7, wherein curing the mixture comprises
partially curing, in the formation mold, to provide the
polyurethane material and to provide an LAT region precursor, and
further curing in the oven to provide the homogeneous polishing
body comprising the thermoset, closed cell polyurethane material
and to provide the LAT region.
9. The method of claim 7, wherein the aromatic urethane pre-polymer
comprises polytetramethylene glycol-toluene diisocyanate, and the
curative comprises thioether aromatic diamine.
10. The method of claim 7, wherein the partial curing of the second
mixture is performed solely with thermal energy.
11. The method of claim 1, wherein the pre-polymer is
polytetramethylene glycol-toluene diisocyanate, the primary
curative is a thioether aromatic diamine, and the secondary
curative is polyoxytetramethylene glycol.
12. The method of claim 1, wherein the mixture further includes a
catalyst.
13. The method of claim 1, wherein a molar amount of the primary
curative is greater than a molar amount of the secondary
curative.
14. A soft polishing pad for polishing a semiconductor substrate,
the soft polishing pad comprising: a homogeneous polishing body
comprising a thermoset, closed cell polyurethane material
fabricated from polytetramethylene glycol-toluene diisocyanate as a
pre-polymer, a thioether aromatic diamine as a primary curative,
and polyoxytetramethylene glycol as a secondary curative, the
homogeneous polishing body having a hardness between about 20 Shore
D and about 35 Shore D.
15. The soft polishing pad of claim 14, wherein the homogeneous
polishing body comprises a first, grooved surface, and a second,
flat surface opposite the first surface.
16. The soft polishing pad of claim 14, wherein the homogeneous
polishing body comprises an opacifying lubricant.
17. The soft polishing pad of claim 14, wherein the polyurethane
material fabricated is further fabricated from a catalyst.
18. The soft polishing pad of claim 14, wherein the homogeneous
polishing body is a molded homogeneous polishing body.
19. The soft polishing pad of claim 14, wherein a molar amount of
the primary curative is greater than a molar amount of the
secondary curative.
20. A method of fabricating a soft polishing pad for polishing a
semiconductor substrate, the method comprising: mixing, in a
formation mold, a pre-polymer, a primary curative, and a secondary
curative different from the primary curative to form a mixture,
wherein the primary curative is a diamine compound and the
secondary curative is a diol compound; and curing the mixture to
provide a molded homogeneous polishing body comprising a thermoset,
closed cell polyurethane material having a hardness between about
20 Shore D and about 35 Shore D.
21. The method of claim 20, wherein the pre-polymer comprises a
polyurethane precursor, the primary curative comprises an aromatic
diamine compound, and the secondary curative comprises an ether
linkage.
22. The method of claim 21, wherein the polyurethane precursor is
an isocyanate, the primary curative is an aromatic diamine, and the
secondary curative is selected from the group consisting of
polytetramethylene glycol, amino-functionalized glycol, and
amino-functionalized polyoxopropylene.
23. The method of claim 20, wherein the mixing further comprises
mixing an opacifying lubricant with the pre-polymer, the primary
curative, and the secondary curative, and wherein the molded
homogeneous polishing body is opaque.
24. The method of claim 20, wherein the pre-polymer is
polytetramethylene glycol-toluene diisocyanate, the primary
curative is a thioether aromatic diamine, and the secondary
curative is polyoxytetramethylene glycol.
25. The method of claim 20, wherein the mixture further includes a
catalyst.
26. The soft polishing pad of claim 20, wherein a molar amount of
the primary curative is greater than a molar amount of the
secondary curative.
27. A soft polishing pad for polishing a semiconductor substrate,
the soft polishing pad comprising: a homogeneous polishing body
comprising a thermoset, closed cell polyurethane material
fabricated from a polyurethane precursor pre-polymer, a primary
curative, and a secondary curative different from the primary
curative, wherein the primary curative is a diamine compound and
the secondary curative is a diol compound, the homogeneous
polishing body having a hardness between about 20 Shore D and about
35 Shore D.
28. The soft polishing pad of claim 27, wherein the homogeneous
polishing body comprises a first, grooved surface, and a second,
flat surface opposite the first surface.
29. The soft polishing pad of claim 27, wherein the homogeneous
polishing body comprises an opacifying lubricant.
30. The soft polishing pad of claim 27, wherein the polyurethane
material fabricated is further fabricated from a catalyst.
31. The soft polishing pad of claim 27, wherein the homogeneous
polishing body is a molded homogeneous polishing body.
32. The soft polishing pad of claim 27, wherein a molar amount of
the primary curative is greater than a molar amount of the
secondary curative.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/832,908, filed on Jul. 8, 2010, the entire
contents of which are hereby incorporated by reference herein.
TECHNICAL FIELD
[0002] Embodiments of the present invention are in the field of
chemical mechanical polishing (CMP) and, in particular, soft
polishing pads for polishing semiconductor substrates.
BACKGROUND
[0003] 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.
[0004] The process uses 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
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 with different axes of rotation (i.e., not
concentric). This removes 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 45 nm technology node.
[0005] 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. The
process has been likened to that of a child eating a gummy candy.
If the candy sits on the tongue without being scraped around, the
candy becomes covered with a gel coating, but the majority of the
candy is not affected. Only with a vigorous scraping does the candy
dissolve away. Another analogy is the act of brushing one's teeth.
The toothbrush is the mechanical part and the toothpaste is the
chemical part. Using either the toothbrush or the toothpaste alone
will get one's teeth somewhat clean, but using the toothbrush and
toothpaste together makes a superior process.
[0006] Accordingly, in addition to advances in slurry technology,
the polishing pad plays a significant role in increasingly complex
CMP operations. However, additional improvements are needed in the
evolution of CMP pad technology.
SUMMARY
[0007] In an embodiment, a soft polishing pad includes a molded
homogeneous polishing body including a thermoset, closed cell
polyurethane material having a hardness approximately in the range
of 20 Shore D to 45 Shore D.
[0008] In another embodiment, a soft polishing pad includes a local
area transparency (LAT) region disposed in, and covalently bonded
with, a molded homogeneous polishing body including a thermoset,
closed cell polyurethane material having a hardness approximately
in the range of 20 Shore D to 45 Shore D.
[0009] In another embodiment, a method of fabricating a soft
polishing pad for polishing a semiconductor substrate includes
mixing, in a formation mold, a pre-polymer, a primary curative, and
a secondary curative different from the primary curative to form a
mixture. The method also includes curing the mixture to provide a
molded homogeneous polishing body including a thermoset, closed
cell polyurethane material having a hardness approximately in the
range of 20 Shore D to 45 Shore D.
[0010] In another embodiment, a method of fabricating a soft
polishing pad for polishing a semiconductor substrate includes,
prior to mixing a pre-polymer and a primary curative and a
secondary curative in a formation mold, mixing an aromatic urethane
pre-polymer with a curative in a second, separate, formation mold
to form a second mixture. The method also includes partially
curing, in the second formation mold, the second mixture to form a
molded gel. The method also includes positioning the molded gel in
a designated region of the formation mold. Then, mixing the
pre-polymer and the primary curative and the secondary curative to
form the mixture includes forming the mixture at least partially
surrounding the molded gel. Curing the mixture to provide the
molded homogeneous polishing body further includes curing the
molded gel to provide a local area transparency (LAT) region
disposed in, and covalently bonded with, the molded homogeneous
polishing body.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 illustrates an isometric side-on view of a polishing
apparatus compatible with a soft polishing pad for polishing a
semiconductor substrate, in accordance with an embodiment of the
present invention.
[0012] FIG. 2 illustrates a cross-sectional view of a soft
polishing pad for polishing a semiconductor substrate, in
accordance with an embodiment of the present invention.
[0013] FIG. 3 illustrates a top-down view of a soft polishing pad
for polishing a semiconductor substrate, in accordance with an
embodiment of the present invention.
[0014] FIG. 4 is a Flowchart representing operations in a method of
fabricating a soft polishing pad for polishing a semiconductor
substrate, in accordance with an embodiment of the present
invention.
[0015] FIG. 5A illustrates a cross-sectional view of the
fabrication of a soft polishing pad for polishing a semiconductor
substrate, corresponding to operation 402 of the Flowchart of FIG.
4, in accordance with an embodiment of the present invention.
[0016] FIG. 5B illustrates a cross-sectional view of the
fabrication of a soft polishing pad for polishing a semiconductor
substrate, corresponding to operation 404 of the Flowchart of FIG.
4, in accordance with an embodiment of the present invention.
[0017] FIG. 5C illustrates a cross-sectional view of the
fabrication of a soft polishing pad for polishing a semiconductor
substrate, corresponding again to operation 404 of the Flowchart of
FIG. 4, in accordance with an embodiment of the present
invention.
[0018] FIG. 6A illustrates a cross-sectional view of the
fabrication of a soft polishing pad for polishing a semiconductor
substrate, corresponding to operation 402 of the Flowchart of FIG.
4, in accordance with an embodiment of the present invention.
[0019] FIG. 6B illustrates a cross-sectional view of the
fabrication of a soft polishing pad for polishing a semiconductor
substrate, corresponding to operation 404 of the Flowchart of FIG.
4, in accordance with an embodiment of the present invention.
[0020] FIG. 6C illustrates a cross-sectional view of the
fabrication of a soft polishing pad for polishing a semiconductor
substrate, corresponding again to operation 404 of the Flowchart of
FIG. 4, in accordance with an embodiment of the present
invention.
[0021] FIG. 7 illustrates a cross-sectional view of a soft
polishing pad for polishing a semiconductor substrate, the soft
polishing pad including a local area transparency (LAT) region, in
accordance with an embodiment of the present invention.
[0022] FIG. 8 illustrates an angled view of a portion of a soft
polishing pad having a local area transparency (LAT) region
incorporated therein, in accordance with an embodiment of the
present invention.
DETAILED DESCRIPTION
[0023] Soft polishing pads for polishing semiconductor substrates
are described herein. In the following description, numerous
specific details are set forth, such as specific soft polishing pad
and local area transparency (LAT) formulation mixtures, 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 the combination of a slurry with a polishing
pad to perform 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.
[0024] Disclosed herein are soft polishing pads for polishing
semiconductor substrates. In one embodiment, a soft polishing pad
includes a molded homogeneous polishing body including a thermoset,
closed cell polyurethane material having a hardness approximately
in the range of 20 Shore D to 45 Shore D. In one embodiment, a soft
polishing pad includes a local area transparency (LAT) region
disposed in, and covalently bonded with, the molded homogeneous
polishing body. In one embodiment, a soft polishing pad includes a
molded homogeneous polishing body including a thermoset, closed
cell polyurethane material having a hardness approximately in the
range of 60 Shore A to 95 Shore A.
[0025] Also disclosed herein are methods of fabricating soft
polishing pads for polishing semiconductor substrates. In one
embodiment, a method includes mixing, in a formation mold, a
pre-polymer, a primary curative, and a secondary curative different
from the primary curative to form a mixture. The mixture is cured
to provide a molded homogeneous polishing body including a
thermoset, closed cell polyurethane material having a hardness
approximately in the range of 20 Shore D to 45 Shore D. In one
embodiment, a method includes, prior to mixing the pre-polymer and
the primary curative and the secondary curative, mixing an aromatic
urethane pre-polymer with a curative in a second, separate,
formation mold to form a second mixture. In the second formation
mold, the second mixture is partially cured to form a molded gel.
The molded gel is positioned in a designated region of the
formation mold. In that embodiment, mixing the pre-polymer and the
primary curative and the secondary curative to form the mixture
includes forming the mixture at least partially surrounding the
molded gel, and curing the mixture to provide the molded
homogeneous polishing body further includes curing the molded gel
to provide a local area transparency region disposed in, and
covalently bonded with, the molded homogeneous polishing body.
[0026] Soft polishing pads described herein may be suitable for use
chemical mechanical polishing apparatuses. FIG. 1 illustrates an
isometric side-on view of a polishing apparatus compatible with a
soft polishing pad for polishing a semiconductor substrate, in
accordance with an embodiment of the present invention.
[0027] Referring to FIG. 1 a polishing apparatus 100 includes a
platen 104. The top surface 102 of platen 104 may be used to
support a soft polishing pad. Platen 104 may be configured to
provide spindle rotation 106 and slider oscillation 108. A sample
carrier 110 is used to hold, e.g., a semiconductor wafer in place
during polishing of the semiconductor wafer with a soft polishing
pad. Sample carrier is further supported by a suspension mechanism
112. A slurry feed 114 is included for providing slurry to a
surface of a soft polishing pad prior to and during polishing of
the semiconductor wafer.
[0028] In accordance with an embodiment of the present invention, a
"soft" pad (soft in relative Shore D values to conventional pads)
is provided for use with a polishing apparatus, such as polishing
apparatus 100. The soft polishing pad may be used in chemical
mechanical polishing (CMP) of semiconductor substrates. In an
embodiment, the soft polishing pad is a cylindrical closed cell,
thermoset polyurethane pad approximately 20 inches (e.g.,
approximately in the range of 50-52 centimeters) or approximately
30 inches (e.g., approximately in the range of 75-78 centimeters)
in diameter. The soft polishing pad may each have an opaque portion
with an optional local area transparency portion. In accordance
with another embodiment of the present invention, the soft
polishing pad is a cylindrical closed cell, thermoset polyurethane
pad having a diameter approximately in the range of 42-48 inches
and is suitable for 450 mm wafer processing.
[0029] In an embodiment, the upper part of each polyurethane pad is
a polishing surface having a grooved design, e.g., for contacting a
semiconductor substrate during polishing on a polishing apparatus
such as polishing apparatus 100. In an embodiment, the flat bottom
surface of the polyurethane pad is covered completely with a
polyethylene teraphthalate (PET) carrier film with a thickness
approximately in the range of 0.5-3 mils, and that is ideally
approximately 0.5 mils thick (e.g., approximately in the range of
10-15 microns thick). The PET carrier film may be semi-transparent
to light. The PET carrier film may be adhered to the bottom pad
surface via a first pressure sensitive adhesive that completely
covers that one side of the PET carrier film. In one embodiment,
completely covering the other side of the PET carrier film is a
second pressure sensitive adhesive layer. A PET release liner that
is approximately 2.5 mils thick (e.g., approximately in the range
of 60-65 microns) may be attached to the PET carrier film via this
second pressure sensitive adhesive. In one embodiment, the first
pressure sensitive adhesive is a rubber type, while the second
pressure sensitive adhesive is an acrylic type. In an alternative
embodiment, the PET carrier film and one of the pressure sensitive
adhesives is omitted so that the PET release liner is directly
adhered to the bottom surface of the polyurethane pad by a single
layer of pressure sensitive adhesive.
[0030] In an aspect of the present invention, a soft polishing pad
for use in chemical mechanical polishing of semiconductor substrate
surfaces is provided. FIG. 2 illustrates a cross-sectional view of
a soft polishing pad for polishing a semiconductor substrate, in
accordance with an embodiment of the present invention.
[0031] Referring to FIG. 2, a soft polishing pad 200 includes a
molded homogeneous polishing body 202 composed of a thermoset,
closed cell polyurethane material having a hardness approximately
in the range of 20 Shore D to 45 Shore D. In an embodiment, the
term "homogeneous" is used to indicate that the composition of the
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
freezes to a very glassy state when cooled sufficiently. In an
embodiment, the term "molded" is used to indicate that molded
homogeneous polishing body 202 is formed in a formation mold, as
described in more detail below.
[0032] In an embodiment, molded homogeneous polishing body 202
includes a first, grooved surface 204, and a second, flat surface
206 opposite the first surface 204. As an example of a pattern for
first, grooved surface 204, FIG. 3 illustrates a top-down view of a
soft polishing pad for polishing a semiconductor substrate, in
accordance with an embodiment of the present invention. Referring
to FIG. 3, a molded homogeneous polishing body 300 includes a
grooved surface having, e.g., a plurality of concentric circles 302
along with a plurality of radial lines 304.
[0033] In an embodiment, molded homogeneous polishing body 202 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, molded homogeneous polishing body 202 is
opaque in most part, or due entirely to, the inclusion of an
opacifying lubricant throughout (e.g., as an additional component
in) the homogeneous thermoset, closed cell polyurethane material of
molded homogeneous polishing body 202. In accordance with an
embodiment of the present invention, the opacifying lubricant is a
material such as, but not limited to, graphite, boron nitride,
tungsten disulfide, Teflon, Cerium fluoride, Molybdenum sulfide,
Graphite fluoride, Niobium sulfide, Tantalum sulfide, or talc.
[0034] In an embodiment, molded homogeneous polishing body 202
includes porogens. In one embodiment, the term "porogen" is used to
indicate micro- or nano-scale 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,
molded homogeneous polishing body 202 includes as porogens
pre-expanded and gas-filled EXPANCEL throughout (e.g., as an
additional component in) the homogeneous thermoset, closed cell
polyurethane material of molded homogeneous polishing body 202. In
a specific embodiment, the EXPANCEL is filled with pentane.
[0035] Referring again to FIG. 2, soft polishing pad 200 further
includes a carrier film 208 disposed above molded homogeneous
polishing body 202. In an embodiment, carrier film 208 is composed
of polyethylene teraphthalate (PET). In one embodiment, carrier
film 208 has a thickness of approximately 0.5 mils, e.g.,
approximately in the range of 10-15 microns. In one embodiment,
carrier film 208 is semi-transparent to light.
[0036] Referring again to FIG. 2, soft polishing pad 200 further
includes a first pressure-sensitive adhesive layer 210 disposed
between carrier film 208 and molded homogeneous polishing body 202.
In an embodiment, first pressure-sensitive adhesive layer 210 is
composed of a rubber-type material.
[0037] Referring again to FIG. 2, soft polishing pad 200 further
includes a second pressure-sensitive adhesive layer 212 disposed
above carrier film 208. In an embodiment, second pressure-sensitive
adhesive layer 212 is composed of an acrylic-type material.
[0038] Referring again to FIG. 2, soft polishing pad 200 further
includes a release liner 214 disposed above second
pressure-sensitive adhesive layer 212. In an embodiment, release
liner 214 is composed of polyethylene teraphthalate (PET). In an
alternative embodiment (not shown), soft polishing pad 200 further
includes a release liner disposed directly on molded homogeneous
polishing body 202, without intervening carrier film or first and
second pressure-sensitive adhesive layers.
[0039] It is to be understood that the sizing of molded homogeneous
polishing body 202 may be varied according to application.
Nonetheless, certain parameters may be used to make soft polishing
pads including such a molded homogeneous polishing body 202
compatible with conventional processing equipment or even with
conventional chemical mechanical processing operations. For
example, in accordance with an embodiment of the present invention,
molded homogeneous polishing body 202 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, molded
homogeneous polishing body 202 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. In one embodiment, molded homogeneous polishing body
202 has a hardness of approximately 35 Shore D. In one embodiment,
molded homogeneous polishing body 202 has a pore density
approximately in the range of 18%-30% total void volume, and
possibly approximately in the range of 15%-35% total void volume.
In one embodiment, molded homogeneous polishing body 202 has a
porosity of the closed cell type. In one embodiment, molded
homogeneous polishing body 202 has a pore size of approximately 40
micron diameter, but may be smaller, e.g., approximately 20 microns
in diameter. In one embodiment, molded homogeneous polishing body
202 has a compressibility of approximately 2.5%. In one embodiment,
molded homogeneous polishing body 202 has a density approximately
in the range of 0.80-0.90 grams per cubic centimeter, or
approximately in the range of 0.95-1.05 grams per cubic
centimeter.
[0040] It is to be understood that removal rates of various films
using a soft polishing pad including molded homogeneous polishing
body 202 may vary depending on polishing tool, slurry,
conditioning, or polish recipe used. However, in one embodiment,
molded homogeneous polishing body 202 exhibits a copper removal
rate approximately in the range of 30-900 nanometers per minute. In
one embodiment, molded homogeneous polishing body 202 exhibits an
oxide removal rate approximately in the range of 30-900 nanometers
per minute. In one embodiment, molded homogeneous polishing body
202 has an elastic storage modulus, E, of approximately 30 MPa at
25 degrees Celsius. In one embodiment, molded homogeneous polishing
body 202 has an elastic storage modulus, E, of approximately 25 MPa
at 40 degrees Celsius. In one embodiment, molded homogeneous
polishing body 202 has an elastic storage modulus, E, of
approximately 20 MPa at 70 degrees Celsius. In one embodiment,
molded homogeneous polishing body 202 has an elastic storage
modulus, E, of approximately 18 MPa at 90 degrees Celsius. In one
embodiment, molded homogeneous polishing body 202 has a tan delta
that varies with temperature, from approximately 0.04 at T=-75
degrees Celsius to approximately 0.23 at T=-15 degrees Celsius,
with a value of approximately 0.19 at 25 degrees Celsius. In one
embodiment, molded homogeneous polishing body 202 has a kinetic
energy loss factor, KEL (1/Pa) of approximately 10,500 at 25
degrees Celsius, approximately 13,500 at 40 degrees Celsius, or
approximately 15,500 at 70 degrees Celsius. In accordance with an
embodiment of the present invention, a soft polishing pad has a KEL
approximately in the range of 2000-45,000 at 45 degrees
Celsius.
[0041] In an aspect of the present invention, a soft polishing pad
includes a molded homogeneous polishing body, such as molded
homogeneous polishing body 202, fabricated from a non-polymeric
urethane precursor that forms a single type of polyurethane
polymer. For example, in accordance with an embodiment of the
present invention, a molded homogeneous polishing body is
fabricated by reacting (a) an aromatic urethane pre-polymer, such
as AIRTHANE 60: polytetramethylene glycol-toluene diisocyanate, (b)
a porogen, such as EXPANCEL 40: acrylonitrile vinylidiene chloride
with an isobutene or pentane filler, (c) a lubricant and whiting
agent filler (d) a polyol, such as Terathane T-2000:
polyoxytetramethylene glycol, and (e) a catalyst, such as DABCO
1027 with (f) a curative, such as CURENE 107: thioether aromatic
diamine, (g) a thermal stabilizer, such as PUR68, and (g) a UV
absorber, such as Tinuvin 213 to form a nearly opaque buff-colored
thermoset polyurethane having a substantially uniform
microcellular, closed cell structure. The nearly opaque molded
homogeneous polishing body may not be made from a plurality of
polymeric materials, and a mixture of polymeric materials may not
be formed by the above reaction. Instead, in an embodiment, the
opaque pad molded homogeneous polishing body is made from a
non-polymeric urethane precursor that forms a single type of
polyurethane polymer. Also, in an embodiment, the molded
homogeneous polishing body portion of a fabricated soft polishing
pad does not include any water-soluble particles dispersed in the
water-insoluble polymeric matrix opaque material. In one
embodiment, the opaque region is uniformly hydrophobic in nature.
In a specific embodiment, upon conditioning, portions become more
hydrophilic so as to be wettable. In an embodiment, the above noted
EXPANCEL material does not have a liquid core which is
substantially all water. Instead the core of the EXPANCEL is a gas
and the average pore size of each EXPANSEL unit is approximately in
the range of 20 to 40 microns.
[0042] As noted above, a soft polishing pad may be fabricated from
a non-polymeric urethane precursor that forms a single type of
polyurethane polymer. FIG. 4 is a Flowchart 400 representing
operations in a method of fabricating a soft polishing pad for
polishing a semiconductor substrate, in accordance with another
embodiment of the present invention. FIGS. 5A-5C illustrate
cross-sectional views of the fabrication of a soft polishing pad
for polishing a semiconductor substrate, corresponding to the
operations of Flowchart 400, in accordance with an embodiment of
the present invention.
[0043] Referring to FIG. 5A and corresponding operation 402 of
Flowchart 400, a method of fabricating a soft polishing pad for
polishing a semiconductor substrate includes mixing, in a formation
mold 504, a pre-polymer, a primary curative, and a secondary
curative (combination 502) different from the primary curative to
form a mixture 506.
[0044] In accordance with an embodiment of the present invention,
the pre-polymer includes a polyurethane precursor, the primary
curative includes an aromatic diamine compound, and the secondary
curative includes an ether linkage. In one 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 polyoxopropylene. In an embodiment,
pre-polymer, a primary curative, and a secondary curative
(combination 502) has an approximate molar ratio of 100 parts
pre-polymer, 85 parts primary curative, and 15 parts secondary
curative. It is to be understood that variations of the ratio may
be used to provide soft polishing pads with varying Shore D values,
or based on the specific nature of the pre-polymer and the first
and second curatives. In an embodiment, the mixing further includes
mixing an opacifying lubricant with the pre-polymer, the primary
curative, and the secondary curative.
[0045] Referring to FIG. 5B and corresponding operation 404 of
Flowchart 400, the method of fabricating a soft polishing pad for
polishing a semiconductor substrate also includes curing mixture
506 to provide a molded homogeneous polishing body 508.
[0046] In accordance with an embodiment of the present invention,
curing mixture 506 includes partially curing, in formation mold
504, to provide a polyurethane material. In that embodiment, curing
mixture 506 includes further curing, in an oven, to provide molded
homogeneous polishing body 508. In an embodiment, formation mold
504 includes a lid 505 having a grooved pattern 507 formed thereon
or formed therein, as depicted in FIG. 5B. The partial curing prior
to the oven curing may be, in an embodiment, performed in the
presence of lid 505 which encloses mixture 506 in formation mold
504, at a temperature approximately in the range of 200-260 degrees
Fahrenheit and a pressure approximately in the range of 2-12 pounds
per square inch.
[0047] Referring to FIG. 5C and again to corresponding operation
404 of Flowchart 400, molded homogeneous polishing body 508 is
composed of a thermoset, closed cell polyurethane material having a
hardness approximately in the range of 20 Shore D to 45 Shore D. In
an embodiment, as a result of grooved pattern 507 of lid 505 of
formation mold 504, molded homogeneous polishing body 508 includes
a first, grooved surface 510, and a second, flat surface 512
opposite first surface 510, as depicted in FIG. 5C. In an
embodiment, molded homogeneous polishing body 508 is opaque. In one
embodiment, molded homogeneous polishing body 508 is opaque due to
the inclusion of an opacifying lubricant.
[0048] In another aspect of the present invention, a soft polishing
pad may be fabricated to include grooves formed during a molding
process operation, but the grooved pattern need not necessarily be
formed from inclusion of a grooved pattern in the lid of a
formation mold. FIG. 4 is a Flowchart 400 representing operations
in a method of fabricating a soft polishing pad for polishing a
semiconductor substrate, in accordance with another embodiment of
the present invention. FIGS. 6A-6C illustrate cross-sectional views
of the fabrication of a soft polishing pad for polishing a
semiconductor substrate, corresponding to the operations of
Flowchart 400, in accordance with an embodiment of the present
invention.
[0049] Referring to FIG. 6A and corresponding operation 402 of
Flowchart 400, a method of fabricating a soft polishing pad for
polishing a semiconductor substrate includes mixing, in a formation
mold 604, a pre-polymer, a primary curative, and a secondary
curative (combination 602) different from the primary curative to
form a mixture 606.
[0050] In accordance with an embodiment of the present invention,
the pre-polymer includes a polyurethane precursor, the primary
curative includes an aromatic diamine compound, and the secondary
curative includes an ether linkage. In one 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 polyoxopropylene. In an embodiment,
pre-polymer, a primary curative, and a secondary curative
(combination 502) has an approximate molar ratio of 100 parts
pre-polymer, 85 parts primary curative, and 15 parts secondary
curative. It is to be understood that variations of the ratio may
be used to provide soft polishing pads with varying Shore D values.
In an embodiment, the mixing further includes mixing an opacifying
lubricant with the pre-polymer, the primary curative, and the
secondary curative.
[0051] Referring to FIG. 6B and corresponding operation 404 of
Flowchart 400, the method of fabricating a soft polishing pad for
polishing a semiconductor substrate also includes curing mixture
606 to provide a molded homogeneous polishing body 608.
[0052] In accordance with an embodiment of the present invention,
curing mixture 606 includes partially curing, in formation mold
604, to provide a polyurethane material. In that embodiment, curing
mixture 606 includes further curing, in an oven, to provide molded
homogeneous polishing body 608. In an embodiment, formation mold
604 includes a lid 605. However, different from lid 505 described
above, lid 605 has a flat surface in contact with mixture 606.
Instead, a grooved pattern 607 is included at the bottom surface of
formation mold 604, as depicted in FIGS. 6A and 6B. The partial
curing prior to the oven curing may be, in an embodiment, performed
in the presence of lid 605 which encloses mixture 606 in formation
mold 604, at a temperature approximately in the range of 200-260
degrees Fahrenheit and a pressure approximately in the range of
2-12 pounds per square inch.
[0053] Referring to FIG. 6C and again to corresponding operation
404 of Flowchart 400, molded homogeneous polishing body 608 is
composed of a thermoset, closed cell polyurethane material having a
hardness approximately in the range of 20 Shore D to 45 Shore D. In
an embodiment, as a result of grooved pattern 607 at the bottom of
formation mold 604, molded homogeneous polishing body 608 includes
a first, grooved surface 610, and a second, flat surface 612
opposite first surface 610, as depicted in FIG. 6C. In an
embodiment, molded homogeneous polishing body 608 is opaque. In one
embodiment, molded homogeneous polishing body 608 is opaque due to
the inclusion of an opacifying lubricant.
[0054] Embodiment for the formation of a soft polishing pad as
described above may be readily applicable to more complex chemical
formulations. For example, in accordance with another embodiment of
the present invention, a method of fabricating a soft polishing pad
for polishing a semiconductor substrate includes reacting, in a
formation mold, an aromatic urethane pre-polymer, a porogen, a
lubricant and whiting agent filler, a polyol, and a catalyst with a
curative, a thermal stabilizer, and a UV absorber to form a
mixture. In an embodiment, the aromatic urethane pre-polymer is
composed of polytetramethylene glycol-toluene diisocyanate, the
porogen is composed of acrylonitrile vinylidiene chloride with an
isobutene or pentane filler, the lubricant and whiting agent filler
is composed of an opacifying lubricant, the polyol is composed of
polyoxytetramethylene glycol, the catalyst is composed of DABCO
1027, the a curative is composed of thioether aromatic diamine, the
thermal stabilizer is composed of PUR68, and the UV absorber is
composed of Tinuvin 213. The method of fabricating the soft
polishing pad for polishing a semiconductor substrate may also
include curing the above complex mixture to provide a molded
homogeneous polishing body of the soft polishing pad.
[0055] In accordance with an embodiment of the present invention,
the method of fabricating the soft polishing pad for polishing a
semiconductor substrate further includes forming a carrier film
above a surface of the molded homogeneous polishing body. In one
embodiment, the carrier film is composed of polyethylene
teraphthalate (PET). In one embodiment, the carrier film has a
thickness of approximately 0.5 mils, e.g., approximately in the
range of 10-15 microns. In one embodiment, the carrier film 414 is
semi-transparent to light. In a specific embodiment, the carrier
film is composed of polyethylene teraphthalate (PET), has a
thickness of approximately 0.5 mils, e.g., approximately in the
range of 10-15 microns, and is semi-transparent to light. In an
embodiment, the carrier film is a MYLAR.RTM. polyethylene
teraphthalate film. In a specific embodiment, the MYLAR.RTM. film
is completely impermeable to water and has no holes formed
therein.
[0056] In accordance with an embodiment of the present invention,
the method of fabricating the soft polishing pad for polishing a
semiconductor substrate further includes forming a first
pressure-sensitive adhesive layer between the surface of the molded
homogeneous polishing body and the carrier film. In an embodiment,
the first pressure-sensitive adhesive layer is formed directly
between the surface of the molded homogeneous polishing body and
the carrier film. In one embodiment, forming the first
pressure-sensitive adhesive layer includes forming a rubber-type
material. In an embodiment, the first pressure-sensitive adhesive
layer is a permanent-bond type adhesive.
[0057] In accordance with an embodiment of the present invention,
the method of fabricating the soft polishing pad for polishing a
semiconductor substrate further includes forming a second
pressure-sensitive adhesive layer above the carrier film. In an
embodiment, the second pressure-sensitive adhesive layer is formed
directly on the carrier film. In one embodiment, forming the second
pressure-sensitive adhesive layer includes forming an acrylic-type
material. In an embodiment, the second pressure-sensitive adhesive
layer is a releasable-bond type adhesive.
[0058] In accordance with an embodiment of the present invention,
the method of fabricating the soft polishing pad for polishing a
semiconductor substrate further includes forming a release liner
above the second pressure-sensitive adhesive layer. In an
embodiment, the release liner is formed directly above the second
pressure-sensitive adhesive layer. In one embodiment, the release
liner is composed of polyethylene teraphthalate (PET). In an
embodiment, the release liner is a layer of MYLAR.RTM. polyethylene
teraphthalate film having a thickness of approximately 2.5 mils,
e.g., approximately in the range of 60-65 microns. In an
alternative embodiment, however, the release liner is composed of a
material such as, but not limited to, paper or polypropylene.
Alternatively, a soft polishing pad may include only the molded
homogeneous polishing body and a release liner. As such, in
accordance with an alternative embodiment of the present invention,
a method of fabricating a soft polishing pad for polishing a
semiconductor substrate includes forming a release liner directly
on a flat surface of the molded homogeneous polishing body. In one
embodiment, the release liner is composed of polyethylene
teraphthalate (PET).
[0059] In another aspect of the present invention, a local area
transparency may be included in a soft polishing pad. For example,
in an embodiment, a technique requiring visible access to the top
surface of a substrate during a CMP operation is used to detect an
end-point of the operation. However, as described above, the soft
polishing pad may be opaque and therefore restrictive of a variety
of possible techniques for such an end-point detection. FIG. 7
illustrates a cross-sectional view of a soft polishing pad for
polishing a semiconductor substrate, the soft polishing pad
including a local area transparency region, in accordance with an
embodiment of the present invention.
[0060] Referring to FIG. 7, a molded homogeneous polishing body 702
of a soft polishing pad, such as soft polishing pad 200 described
in association with FIG. 2, further includes a local area
transparency (LAT) region 704 disposed in, and covalently bonded
with, the molded homogeneous polishing body 702.
[0061] In an embodiment, molded homogeneous polishing body 702 is
opaque, while LAT region 704 is not opaque. In one embodiment,
molded homogeneous polishing body 702 is opaque due at least in
part to inclusion of an inorganic substance in the material used to
fabricate the molded homogeneous polishing body portion of a soft
polishing pad. In that embodiment, the local area transparency
region is fabricated exclusive of the inorganic substance and is
substantially, if not totally, transparent to, e.g., visible light,
ultra-violet light, infra-red light, or a combination thereof. In a
specific embodiment, the inorganic substance included in molded
homogeneous polishing body 702 is an opacifying lubricant, whereas
the local area transparency portion does not contain any inorganic
materials, including the opacifying lubricant. Thus, in one
embodiment, molded homogeneous polishing body 702 is opaque and
includes boron-nitride, while LAT region 704 is essentially free
from an opacifying lubricant. In an embodiment, LAT region 704 is
effectively transparent (ideally totally transparent) in order to
enable transmission of light through a soft polishing pad for,
e.g., end-point detection. However, it may be the case that LAT
region 704 cannot or need not be fabricated to be perfectly
transparent, but may still be effective for transmission of light
for end-point detection. For example, in one embodiment, LAT region
704 transmits as little as 80% of incident light in the 700-710
nanometer range, but is still suitable to act as a window within a
soft polishing pad.
[0062] In an embodiment, molded homogeneous polishing body 702 and
LAT region have different hardnesses. For example, in one
embodiment, molded homogeneous polishing body 702 has a Shore D
less than the Shore D of LAT region 704. In a specific embodiment,
molded homogeneous polishing body 702 has a Shore D approximately
in the range of 20-45, while LAT region 704 has a Shore D of
approximately 60. Although the hardnesses may differ, cross-linking
(e.g., via covalent bonding) between LAT region 704 and molded
homogeneous polishing body 702 may still be extensive. For example,
in accordance with an embodiment of the present invention, the
difference in Shore D of molded homogeneous polishing body 702 and
LAT region 704 is 10 or greater, yet the extent of cross-linking
between molded homogeneous polishing body 702 and LAT region 704 is
substantial.
[0063] It is to be understood that the dimensions of a soft
polishing pad and a LAT region disposed therein may vary according
to desired application. For example, in one embodiment, molded
homogeneous polishing body 702 is circular with a diameter
approximately in the range of 75-78 centimeters, and LAT region 704
has a length approximately in the range of 4-6 centimeters along a
radial axis of molded homogeneous polishing body 702, a width
approximately in the range of 1-2 centimeters, and is positioned
approximately in the range of 16-20 centimeters from the center of
molded homogeneous polishing body 702.
[0064] With respect to vertical positioning, the location of a LAT
region on a molded homogeneous polishing body may be selected for
particular applications, and may also be a consequence of the
formation process. For example, by including a LAT region in a
molded homogeneous polishing body via the molding process, the
positioning and accuracy achievable may be significantly more
tailored than, e.g., a process in which a polishing pad is cut
after formation and a window insert is added after the formation of
the pad. In an embodiment, by using a molding process as described
below, an LAT region is included in a molded homogeneous polishing
body to be planar with the bottoms of the troughs of a grooved
surface of the molded homogeneous polishing body. In a specific
embodiment, by including the LAT region to be planar with the
bottoms of the troughs of a grooved surface of the molded
homogeneous polishing body, the LAT region does not interfere with
CMP processing operations throughout the life of a soft polishing
pad fabricated from the molded homogeneous polishing body and the
LAT region.
[0065] In another embodiment, by using a molding process as
described below, an LAT region is included in a molded homogeneous
polishing body to be planar with the opposing flat surface of the
molded homogeneous polishing body. This planarity may be achieved
by grinding the back-side of the molded homogeneous polishing body
until the LAT region is exposed or may be made planer at the time
of molding. In either case, in accordance with an embodiment of the
present invention, there is no recess of the LAT region into the
back-side of the molded homogeneous polishing body. As such, there
is little to no likelihood of undesirably trapping air or moisture
between a platen of a CMP tool and an LAT region of a soft
polishing pad when the soft polishing pad is used with the CMP tool
for CMP process operations.
[0066] In an embodiment, a soft polishing pad including an LAT
region may be adhered to the CMP platen by a sticky film or residue
interface without the addition of intervening layers. For example,
in one embodiment, the backing (planar side opposite the grooved
surface) of the molded homogeneous polishing body portion of a soft
polishing pad with an LAT region has a layer of transfer tape
disposed thereon. Upon removal of the transfer tape, e.g. at the
time of use of the soft polishing pad on a CMP tool, a sticky
interface is created enabling application of the molded homogeneous
polishing body and the LAT region directly to a platen of the CMP
tool. In an embodiment, the LAT region is placed over a
light-emitting end-point detection system included with the platen.
In one embodiment, the sticky interface between the molded
homogeneous polishing body and the platen, and hence between the
LAT region and the platen, is entirely or mostly transparent and
does not interfere with the transmission of light from an end-point
detection system through the LAT region. In a specific embodiment,
the sticky interface is an acrolate interface. In an embodiment,
since additional polishing pad layers are not retained between the
molded homogeneous polishing body and the platen, the cost and time
associated with otherwise cutting windows in and aligning such
layers with the LAT region are not required.
[0067] Accordingly, in an embodiment, a local area transparency
region is incorporated into a soft polishing pad. In one
embodiment, the local area transparency is included during the
actual molding and formation of the pad, such that reactant
precursors used to form the pad are disposed to surround a
pre-fabricated local area transparency positioned in a formation
mold. The soft polishing pad material is then cured in the presence
of the local area transparency, thus incorporating the local area
transparency into the soft polishing pad itself. For example, FIG.
8 illustrates an angled view of a portion of a soft polishing pad
having a local area transparency incorporated therein, in
accordance with an embodiment of the present invention. Referring
to FIG. 8, soft polishing pad 802 includes a local area
transparency (LAT) region 804 incorporated therein. In an
embodiment, local area transparency region 804 is recessed below
grooves 806 of the grooved surface of soft polishing pad 802, as
depicted in FIG. 8.
[0068] The local area transparency region may have a dimension and
be located in a position compatible with various end-point
detection techniques and suitable for inclusion in a soft polishing
pad fabricated by a molding process. For example, in accordance
with an embodiment of the present invention, a local area
transparency region has a length of approximately 2 inches, e.g.
approximately in the range of 4-6 centimeters, and a width of
approximately 0.5 inches, e.g. approximately in the range of 1-2
centimeters. In an embodiment, the local area transparency region
is positioned approximately 7 inches, e.g. approximately in the
range of 16-20 centimeters from the center of a soft polishing pad,
such as but not limited to a soft polishing pad having a diameter
of 30 inches, e.g. a diameter approximately in the range of 75-78
centimeters.
[0069] The local area transparency region may be composed of a
material compatible with various end-point detection techniques and
suitable for inclusion in a soft polishing pad fabricated by a
molding process. For example, in accordance with an embodiment of
the present invention, a local area transparency region is formed
to be housed in a molded homogeneous polishing body during
operations 402 and 404 of Flowchart 400, described above.
[0070] For example, in accordance with an embodiment of the present
invention, the method of fabricating the soft polishing pad for
polishing a semiconductor substrate, as described in association
with Flowchart 400, further includes, prior to mixing the
pre-polymer and the primary curative and the secondary curative,
mixing an aromatic urethane pre-polymer with a curative in a
second, separate, formation mold to form a second mixture. The
second mixture is then partially cured in the second formation mold
to form a molded gel. The molded gel is then positioned in a
designated region of the formation mold.
[0071] In accordance with an embodiment of the present invention,
mixing the pre-polymer and the primary curative and the secondary
curative to form the soft polishing pad mixture includes forming
the soft polishing pad mixture at least partially surrounding the
molded gel. In an embodiment, curing the soft polishing pad mixture
to provide the molded homogeneous polishing body further includes
curing the molded gel to provide a local area transparency (LAT)
region disposed in, and covalently bonded with, the molded
homogeneous polishing body.
[0072] In one embodiment, curing the soft polishing pad mixture and
the molded gel includes partially curing, in the soft polishing pad
formation mold, to provide a polyurethane material (polishing body
precursor) and to provide an LAT region precursor. In that
embodiment, curing the soft polishing pad mixture and the molded
gel includes further curing, in an oven, to provide the molded
homogeneous polishing body composed of a thermoset, closed cell
polyurethane material, and to provide the LAT region.
[0073] In accordance with an embodiment of the present invention,
in forming the LAT region, the aromatic urethane pre-polymer
includes polytetramethylene glycol-toluene diisocyanate, and the
curative includes thioether aromatic diamine. In one embodiment,
partial curing of the second (LAT region precursor) mixture is
performed solely with thermal energy. In an embodiment, the
aromatic urethane pre-polymer is composed of a high molecular
weight polyol.
[0074] In an embodiment, a method of fabricating a local area
transparency region for a soft polishing pad includes reacting, in
a formation mold, an aromatic urethane pre-polymer with a curative
to form a mixture. In one embodiment, the aromatic urethane
pre-polymer is composed of polytetramethylene glycol-toluene
diisocyanate (AIRTHANE 60), and the curative is composed of
thioether aromatic diamine (CURENE 107). Thus, in an embodiment,
the local area transparency region is not made from a plurality of
polymeric materials, and a mixture of polymeric materials is not
made by the above reaction. Instead, the local area transparency
region is made from a non-polymeric urethane precursor that forms a
single type of polyurethane polymer. Also, the resulting polymer
forming the local area transparency region is not a non-ambering
urethane elastomer. Furthermore, in an embodiment, there are no
water-soluble particles dispersed in the water-insoluble polymeric
matrix used to form the local area transparency region. In an
embodiment, the local area transparency region is not made of
gas-permeable material, a glass or, a crystalline material. The
optional local area transparency regions may be made by first
mixing the above-noted local area transparency region precursor
ingredients (except for the curative) together in blend tank
equipped with a mechanical stirrer and nitrogen gas head space. In
accordance with an embodiment of the present invention, the
mixture, after being thoroughly blended, is transferred to a
formation mold via a mixing head where the curative is added to the
mixture used to form the molded homogeneous polishing body portion
of the soft polishing pad.
[0075] In an embodiment, a method of fabricating a local area
transparency region for a soft polishing pad also includes
partially curing, in a formation mold, the above mixture to form a
molded gel that will ultimately be transformed to provide the LAT.
In an embodiment, the mixture is partially cured in the LAT
formation mold to make a transparent gel-like article of the
desired local area transparency region shape. In one embodiment,
the mixture is partially cured solely by thermal energy, and not by
photo-curing or other techniques.
[0076] In an embodiment, a method of fabricating a local area
transparency (LAT) region for a soft polishing pad also includes
forming, at the top surface of the molded gel, a support film. In
accordance with an embodiment of the present invention, the support
film is composed of a polyimide film (e.g., a commercially
available KAPTON polyimide film). In one embodiment, the support
film is positioned at the top of the molded gel to support the
window-precursor during transfer to a larger pad formation
mold.
[0077] In an embodiment, a method of fabricating a local area
transparency region for a soft polishing pad also includes
positioning the molded gel in a designated region of the lid of a
soft polishing pad formation mold. In an embodiment, the support
film is removed at this point. In accordance with an embodiment of
the present invention, the designated region is designed to accept
and position the molded gel. In an embodiment, a polymeric sleeve
is not used to hold the molded gel in or on the lid of the soft
polishing pad formation mold. In an embodiment, the molded gel is
positioned in the soft polishing pad formation mold such that the
top of a local area transparency region formed there from is below
the level of the portion of the lid of the soft polishing pad
formation mold provided to generate a polishing surface (or groove
area) in a soft polishing pad formed surrounding the local area
transparency region.
[0078] In an embodiment, a method of fabricating a local area
transparency region for a soft polishing pad also includes
reacting, in the soft polishing pad formation mold, soft polishing
pad precursors to form a mixture surrounding the molded gel in the
designated region once the lid of the soft pad formation mold is
placed on the soft polishing pad precursor mixture. In accordance
with an embodiment of the present invention, the soft polishing pad
mixture is composed of materials and is formed in a manner similar
to or the same as mixture 506 described in association with
operation 402 of Flowchart 400.
[0079] In an embodiment, a method of fabricating a local area
transparency region for a soft polishing pad also includes
completely curing the soft polishing pad mixture and the molded gel
to provide a molded homogeneous polishing body having a local area
transparency region disposed therein. In accordance with an
embodiment of the present invention, the molded homogeneous
polishing body is composed of materials and is formed in a manner
similar to or the same as molded homogeneous polishing body 508
described in association with operation 404 of Flowchart 400.
[0080] Upon fabrication of a molded homogeneous polishing body
having a local area transparency region disposed therein,
additional operations (such as the addition of backing layers,
thinning the pad, etc.) may optionally be performed to further
complete fabrication of a soft polishing pad. Thus, a soft
polishing pad may be fabricated to include a local area
transparency region, e.g., for end-point detection. The end-point
detection may include the transmission of light through the LAT of
the soft polishing pad. Further details that may be used to form
such a soft polishing pad with a local area transparency region are
provided below.
[0081] In accordance with an embodiment of the present invention,
to form a soft polishing pad, liquid opaque pad precursors are
added to three or four separate blend tanks each equipped with a
mechanical stirrer and nitrogen gas head space. A first blend tank
contains a pre-polymer, an opacifying lubricant and whiting agent
filler, and a porogen. A second blend tank contains a curative, a
UV stabilizer and a heat stabilizer. A third blend tank contains a
polyol and a catalyst. Alternatively, the catalyst may be held in a
fourth blend tank. The mixtures in blend tanks, after being
thoroughly mixed, are transferred to a separate day tank via a
vacuum. When ready for use, each mixture is transferred to a CMP
soft polishing pad mold via a mixing head where the ingredients
react. The opaque precursor mix is added into the mold to fill up
the rest of the mold and generally surround a local area
transparency region. In an embodiment, the mixing apparatus used in
this operation is a Baule mixing system.
[0082] In an embodiment, prior to adding the optional gel-like
insert (LAT precursor) and the opaque portion, the mold is
preheated to approximately 250 degrees Fahrenheit, or approximately
121 degrees Celsius. After the insert is positioned in the mold and
the opaque portion fills the rest of the mold, the mold is closed
and heated for about 8 minutes to partially cure the opaque
material and further cure the gel insert (transparent material).
Since the thermal mass of the top and bottom portions of the mold
may make it impractical to cycle the mold temperature during the
production of a soft polishing pad, the inside of the mold stays at
about the processing temperature consistently while production is
being performed. In an embodiment, the partially cured material
which is solid-like is "demolded" and removed from the mold.
[0083] In an embodiment, the solid-like partially cured pad is then
moved to a curing oven and heated for approximately 12 hours at
approximately 200 degrees Fahrenheit, or approximately 93 degrees
Celsius. The heating may completely cure the pad. The cured pad is
then removed from the oven, and the back side of the pad and the
local area transparency region is machined (the front or grooved
side is not treated at all), so that the bottom surface of the
opaque portion of the pad is flush with the bottom surface of the
local area transparency region. Furthermore, the machining may
cause the desired pad thickness to be achieved.
[0084] In an embodiment, a transparent MYLAR.RTM. layer is then
disposed over the bottom surface of the cured and machined pad. A
roll of MYLAR.RTM. film having a first pressure sensitive adhesive
on one side of the film and a second pressure sensitive adhesive
and release sheet on the other side is unrolled and brought into
contact with the bottom pad surface through a laminator. The
MYLAR.RTM. roll is positioned and cut so that MYLAR.RTM. carrier
film covers the overall bottom surface of the pad. Thus, a
composite of the pad/adhesive layer/MYLAR.RTM. film/adhesive
layer/MYLAR.RTM. release layer is created. Alternatively, a
"transfer adhesive" is used instead of the above described roll of
MYLAR.RTM. film. This "transfer film" may be an adhesive/release
sheet which is unrolled and the adhesive layer is adhered to the
bottom of the soft polishing pad. In that embodiment, the release
pad is left in contact with that adhesive layer.
[0085] In an embodiment, the above described layer composite is
then cleaned, inspected and packed for shipment as a soft polishing
pad. In an embodiment, when the pad is needed for use, the release
layer is removed from the composite, exposing the second adhesive
layer. The composite is then positioned against a CMP machine
platen with the exposed adhesive layer adhering to the platen. The
release layer may be disposed of after removal. Alternatively, if
the soft polishing pad has no carrier film, the release liner may
be removed, and the single adhesive layer placed against the
platen. In an embodiment, the installed soft polishing pad is then
ready to be used in the CMP polishing operation.
[0086] It is to be understood that the properties of soft polishing
pads achievable based on the above disclosed approaches may be
varied to be slightly different (e.g., in hardness) for specific
applications. For example, in accordance with another embodiment of
the present invention, a soft polishing pad suitable for polishing
semiconductor substrates is provided. The soft polishing pad
includes a cast polyurethane polymeric material having a hardness
of about 20 Shore D to about 40 Shore D, a density of about 0.85
grams per cubic centimeter to about 1.00 grams per cubic
centimeter, a KEL of about 1050 to about 1400 (1/Pa at 40 degrees
Celsius), and a porosity of about 10% to about 30% by volume. In
one embodiment, the soft polishing pad has a hardness from about 20
Shore D to about 35 Shore D. In one embodiment, the soft polishing
pad has a density from about 0.88 grams per cubic centimeter to
about 0.95 grams per cubic centimeter. In one embodiment, the soft
polishing pad has a KEL from about 1100 to 1350 (1/Pa at 40 degrees
Celsius). In one embodiment, the soft polishing pad has a porosity
from about 15% to 25% by volume.
[0087] It is also to be understood that curing reaction products,
"completely curing, may still leave some residual reactants or
by-products in the final soft polishing pad. For example, in
accordance with another embodiment of the present invention, a soft
polishing pad suitable for polishing semiconductor substrates is
provided. The soft polishing pad includes a cast polyurethane
polymeric material formed from polymeric microspheres, wherein the
polymeric microspheres constitute about 10 to about 40 volume
percent of the soft polishing pad. The soft polishing pad also
includes an isocyanate-terminated reaction product having from
about 6 to about 8 weight percent unreacted NCO. In an embodiment,
the isocyanate-terminated reaction product is cured with a curative
agent including a mixture of at least one curative polyamine
compound and at least one curative hydroxyl-functional compound. In
an embodiment, the molar ratio of the curative polyamine compound
to the hydroxyl-functional compound is from about 1:1 to about
20:1. In an embodiment, the soft polishing pad has a porosity of at
least 0.1 volume percent and a hardness of about Shore D 20 to
about Shore D 40, e.g., approximately in the range of about Shore A
60 to about Shore A 90.
[0088] Thus, soft polishing pads for polishing semiconductor
substrates have been disclosed. In accordance with an embodiment of
the present invention, a soft polishing pad includes a molded
homogeneous polishing body including a thermoset, closed cell
polyurethane material having a hardness approximately in the range
of 20 Shore D to 45 Shore D. In one embodiment, the molded
homogeneous polishing body includes a first, grooved surface, and a
second, flat surface opposite the first surface. In one embodiment,
a local area transparency (LAT) region is disposed in, and
covalently bonded with, the molded homogeneous polishing body. In
accordance with another embodiment of the present invention, a
method of fabricating a soft polishing pad for polishing a
semiconductor substrate includes mixing, in a formation mold, a
pre-polymer, a primary curative, and a secondary curative different
from the primary curative to form a mixture. The mixture is cured
to provide a molded homogeneous polishing body including a
thermoset, closed cell polyurethane material having a hardness
approximately in the range of 20 Shore D to 45 Shore D. In one
embodiment, the pre-polymer includes a polyurethane precursor, the
primary curative includes an aromatic diamine compound, and the
secondary curative includes an ether linkage.
* * * * *