U.S. patent application number 12/891612 was filed with the patent office on 2011-05-05 for chemical mechanical planarization pad with surface characteristics.
Invention is credited to Ashish Bhatnagar, Yongqi Hu, Kadthala Ramaya Narendrnath.
Application Number | 20110105000 12/891612 |
Document ID | / |
Family ID | 43826868 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110105000 |
Kind Code |
A1 |
Hu; Yongqi ; et al. |
May 5, 2011 |
Chemical Mechanical Planarization Pad With Surface
Characteristics
Abstract
A polishing pad includes a polymer matrix and polyhedral
oligomeric silsequioxane ("POSS") molecules or soluble particles
and a surfactant dispersed within the polymer matrix. A polishing
pad can be formed by casting a liquid polymer on a conveyer belt
having a casting surface with a set of projections and curing the
liquid polymer on the conveyer belt such that a polymer matrix has
a surface with a second set of projections complimentary to the
first set of projections.
Inventors: |
Hu; Yongqi; (Fremont,
CA) ; Narendrnath; Kadthala Ramaya; (San Jose,
CA) ; Bhatnagar; Ashish; (Fremont, CA) |
Family ID: |
43826868 |
Appl. No.: |
12/891612 |
Filed: |
September 27, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61247411 |
Sep 30, 2009 |
|
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Current U.S.
Class: |
451/540 ; 51/296;
51/298 |
Current CPC
Class: |
B24B 37/24 20130101;
B24D 3/32 20130101; B24D 3/344 20130101; B24D 3/346 20130101 |
Class at
Publication: |
451/540 ; 51/298;
51/296 |
International
Class: |
B24B 41/00 20060101
B24B041/00; B24D 3/32 20060101 B24D003/32; B24D 3/34 20060101
B24D003/34 |
Claims
1. A polishing pad comprising: a polymer matrix; and polyhedral
oligomeric silsequioxane ("POSS") molecules dispersed within the
polymer matrix.
2. The polishing pad of claim 1, wherein the POSS molecules are
chemically linked to the polymer matrix.
3. The polishing pad of claim 1, wherein the POSS molecules include
a functional group, and wherein the functional group is selected
from a group consisting of NH.sub.2, OH, SH, R--NH, --NCO, and
COOH.
4. The polishing pad of claim 1, wherein the polymer matrix
comprises polyurethane.
5. The polishing pad of claim 1, wherein the polymer matrix is
porous.
6. The polishing pad of claim 5, wherein the pores of the polymer
matrix are filled with a gas.
7. The polishing pad of claim 5, wherein the pores of the polymer
matrix comprise 15-40% of the polishing pad by volume.
8. The polishing pad of claim 1, wherein the hardness of the
polishing pad is between approximately 40 and 75 Shore D.
9. The polishing pad of claim 1, wherein the POSS molecules
comprise approximately 5 to 15 percent of the polishing pad by
weight.
10. A method of making a polishing pad comprising: mixing a polymer
solution and polyhedral oligomeric silsequioxane ("POSS") molecules
together to form a mix; and curing the mix such that a polymer
matrix having POSS particles is formed.
11. The method of claim 10, wherein the polymer solution comprises
polyurethane.
12. The method of claim 10, further comprising bubbling gas through
the mix prior to curing.
13. A polishing pad comprising: a polymer matrix; soluble particles
dispersed within the polymer matrix; and a surfactant dispersed
within the polymer matrix.
14. The polishing pad of claim 13, wherein the polymer matrix is
porous.
15. The polishing pad of claim 13, wherein the soluble particles
are chosen from a group consisting of CaCO.sub.3, K.sub.2SO.sub.4,
phenolic novolac, and polyethylene glycol ether.
16. The polishing pad of claim 13, wherein the soluble particles
are approximately 1 to 25 micrometers in size.
17. The polishing pad of claim 13, wherein the soluble particles
comprise approximately 1 to 15% of the polishing pad by weight.
18. The polishing pad of claim 13, wherein the polymer matrix
comprises polyurethane.
19. The polishing pad of claim 13, wherein the surfactant is chosen
from a group consisting of copolymers, block copolymers, and
nonionic surfactants.
20. The polishing pad of claim 15, wherein the hardness of the
polishing pad is between approximately 60 and 75 Shore D.
21. A method of making a polishing pad comprising: casting a liquid
polymer on a conveyer belt, wherein the conveyer belt comprises a
casting surface with a first set of projections; and curing the
liquid polymer on the conveyer belt such that a polymer matrix is
formed, wherein the polymer matrix has a surface with a second set
of projections, the second set of projections being complimentary
to the first set of projections.
22. The method of claim 21, further comprising injecting a gas
through the liquid polymer prior to casting.
23. The method of claim 21, wherein the casting surface of the
conveyer belt comprises a material chosen from a group consisting
of stainless steel, Teflon, and silicone.
24. The method of claim 21, wherein the polymer comprises
polyurethane.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Application Ser.
No. 61/247,411, filed on Sep. 30, 2009, the entire disclosure of
which is incorporated by reference.
TECHNICAL FIELD
[0002] The present disclosure relates generally to a chemical
mechanical planarization pad.
BACKGROUND
[0003] An integrated circuit is typically formed on a substrate by
the sequential deposition of conductive, semiconductive, or
insulative layers on a silicon wafer. One fabrication step involves
depositing a filler layer over a non-planar surface and planarizing
the filler layer until the non-planar surface is exposed. For
example, a conductive filler layer can be deposited on a patterned
insulative layer to fill the trenches or holes in the insulative
layer. The filler layer is then polished until the raised pattern
of the insulative layer is exposed. After planarization, the
portions of the conductive layer remaining between the raised
pattern of the insulative layer form vias, plugs, and lines that
provide conductive paths between thin film circuits on the
substrate. In addition, planarization is needed to planarize the
substrate surface for photolithography.
[0004] Chemical mechanical polishing (CMP) is one accepted method
of planarization. This planarization method typically requires that
the substrate be mounted on a carrier or polishing head. The
exposed surface of the substrate is placed against the polishing
surface of a polishing pad, such as a rotating polishing disk or
linearly advancing belt. The carrier head provides a controllable
load on the substrate to push it against the polishing pad. A
polishing liquid, which can include abrasive particles, is supplied
to the surface of the polishing pad, and the relative motion
between the substrate and polishing pad results in planarization
and polishing.
[0005] One objective of a chemical mechanical polishing process is
to achieve wafer to wafer polishing uniformity. If different
substrates are polished at different rates, it becomes difficult to
achieve a uniform target layer thickness between multiple wafers.
Another objective of a chemical mechanical polishing process is to
achieve within wafer polishing uniformity. If different areas on
the substrate are polished at different rates, then it is possible
for some areas of the substrate to have too much material removed
("overpolishing") or too little material removed
("underpolishing"), which can result in non-uniform topography
across the substrate.
SUMMARY
[0006] In general, in one aspect, a polishing pad includes a
polymer matrix and polyhedral oligomeric silsequioxane ("POSS")
molecules dispersed within the polymer matrix. This and other
embodiments can optionally include one or more of the following
features. The POSS molecules can be chemically linked to the
polymer matrix. The POSS molecules can include a functional group,
and wherein the functional group is selected from a group
consisting of NH.sub.2, OH, SH, R--NH, --NCO, and COOH. The polymer
matrix can include polyurethane. The polymer matrix can be porous.
The pores of the polymer matrix can be filled with a gas. The gas
can be nitrogen. The pores can include 15-40% of the polishing pad
by volume. The hardness of the polishing pad can be between
approximately 40 and 75 Shore D. The POSS molecules can include
approximately 5 to 15 percent of the polishing pad by weight.
[0007] In general, in one aspect, a method of making a polishing
pad includes mixing a polymer solution and polyhedral oligomeric
silsequioxane ("POSS") molecules together to form a mix and curing
the mix such that a polymer matrix having POSS particles is
formed.
[0008] This and other embodiments can optionally include one or
more of the following features. The polymer solution can include
polyurethane. The method can further include bubbling gas through
the mix prior to curing. The gas can include nitrogen.
[0009] In general, in one aspect, a polishing pad includes a
polymer matrix, soluble particles dispersed within the polymer
matrix, and a surfactant dispersed within the polymer matrix.
[0010] This and other embodiments can optionally include one or
more of the following features. The polymer matrix can be porous.
The soluble particles can be chosen from a group consisting of
CaCO.sub.3, K.sub.2SO.sub.4, phenolic novolac, and polyethylene
glycol ether. The soluble particles can be approximately 1 to 25
micrometers in size. The soluble particles can include
approximately 1 to 15% of the polishing pad by weight. The polymer
matrix can include polyurethane. The surfactant can be chosen from
a group consisting of copolymers, block copolymers, and nonionic
surfactants. The hardness of the polishing pad can be between
approximately 60 and 75 Shore D.
[0011] In general, in one aspect, a method of making a polishing
pad includes casting a liquid polymer on a conveyer belt, wherein
the conveyer belt comprises a casting surface with a first set of
projections, and curing the liquid polymer on the conveyer belt
such that a polymer matrix is formed, wherein the polymer matrix
has a surface with a second set of projections, the second set of
projections being complimentary to the first set of
projections.
[0012] This and other embodiments can optionally include one or
more of the following features. The method can further include
injecting a gas through the liquid polymer prior to casting. The
gas can be nitrogen. The casting surface of the conveyer belt can
include a material chosen from a group consisting of stainless
steel, Teflon, and silicone. The polymer can include polyurethane.
The method can further include detaching the matrix from the
conveyer belt.
[0013] Certain implementations may have one or more of the
following advantages. Having POSS molecules dispersed within the
polymer matrix can decrease pad wear by both making the polishing
pad harder and increasing the lubrication of the surface of the
polishing pad. Dispersing soluble particles within the polymer
matrix can increase the polishing pad hardness, thereby reducing
pad wear, and can increase surface roughness of the polishing pad,
thereby increasing the removal rate of the polishing surface during
CMP. Dispersing a surfactant within the polymer matrix can
uniformly disperse the POSS and/or particles, thus also increasing
surface roughness. Further, a pad as described herein can be made
thicker than traditional pads because the polymer walls between the
grooves are stronger and therefore are less likely to collapse.
Curing liquid polymer on a mold having ridges can eliminate the
need to put grooves in after curing, thereby saving money and time.
Likewise, curing the liquid polymer on a mold having ridges can
minimize pad to pad variation that can be caused by grooving knives
if grooves are formed after curing.
[0014] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, aspects, and advantages of the invention will
become apparent from the description, the drawings, and the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic of a cross-section of a polishing pad
having a polymer matrix.
[0016] FIG. 2 is a schematic of a cross-section of a polishing pad
having nanoparticles dispersed throughout a polymer matrix.
[0017] FIG. 3 is a schematic of a cross-section of a polishing pad
having soluble particles dispersed throughout a polymer matrix.
[0018] FIG. 4 is a schematic of a system for creating air bubbles
in a liquid polymer mix.
[0019] FIG. 5A is a schematic of a system for curing a liquid
polymer mix over a substrate.
[0020] FIG. 5B is a schematic showing a close-up of a grooved
substrate for curing a liquid polymer mix.
[0021] Like reference numbers and designations in the various
drawings indicate like elements.
DETAILED DESCRIPTION
[0022] During chemical mechanical polishing, a lack of surface
roughness of the polishing surface of the polishing pad can result
in a low removal rate. Furthermore, polishing pads can have a high
wear rate, causing short pad life and requiring frequent
replacement of the polishing pads. Polishing pad surface roughness
can be increased by dispersing soluble particles and/or surfactant
within the polishing pad. Likewise, the wear rate of the polishing
pad can be reduced by dispersing molecules, e.g., nanoparticles,
that increase the hardness of the pad material, such as polyhedral
oligomeric silsequioxane ("POSS") molecules, and/or soluble
particles within the polishing pad.
[0023] Referring to FIG. 1, a polishing pad 100 can include a
polishing surface 101 and a matrix 102. The matrix 102 can be a
polymer matrix, for example, a polyurethane, nylon, expoxy, or
poly(methyl methacrylate) (PMMA) matrix. The matrix 102 can include
pores 104. The pores 104 can be approximately 15-60 .mu.m, such as
19-50 .mu.m in diameter and approximately 15-40% of the total
volume of the polishing pad 100. The pores 104 can be filled with a
gas, e.g. substantially pure nitrogen.
[0024] In one implementation, shown in FIG. 2, nanoparticles 202
can be incorporated into matrix 102. The nanoparticles can be
dispersed homogeneously through the polishing pad. As an example,
the nanoparticles 202 can be, for example, particles of polyhedral
oligomeric silsequioxane ("POSS"). The functional group in the POSS
can be, for example, OH, NH.sub.2, COOH, R--NH, SH, or --NCO, and
can chemically bond to matrix 102. Thus, for example, the
functional groups of POSS nanoparticles can cross-link with
polyurethane in the matrix 102. The nanoparticles 202, e.g. POSS
particles, can have a diameter of approximately 5-20 nm, such as
5-10 nm, at the molecular level. As another example, the
nanoparticles 202 can be inorganic or organic nanoparticles, such
as colloidal silicon nanoparticles. Such nanoparticles 202 need not
be chemically bonded to the matrix 102, but may be physically
bonded to the matrix 102 instead. The nanoparticles 202 can make up
approximately 5-15% of the polishing pad 100 by weight. The
incorporation of nanoparticles 202 into the polishing pad 100 can
increase the hardness of the polishing pad 100 to, for example,
40-75 Shore D.
[0025] In another implementation, shown in FIG. 3, soluble
particles 302 can be incorporated into the matrix 102. The soluble
particles 302 can be organic or inorganic particles, such as
CaCO.sub.3, K.sub.2SO.sub.4, phenolic novolac, or polyethylene
glycol ether and can measure between approximately 1 .mu.m and 10
.mu.m in diameter. The soluble particles 302 can be dispersed
homogeneously through the polishing layer and can make up
approximately 1-15%, such as 1-5%, of the polishing pad by weight.
The soluble particles 302 on the polishing surface of polishing pad
100 can dissolve when contacted with polishing liquid during the
CMP process, leaving further recesses or pits in the polishing
surface and thereby enhancing the surface roughness of the
polishing pad 100. The incorporation of soluble particles 302 can
increase the surface roughness of the polishing pad 100 when the
soluble particles 302 on the surface dissolve. The incorporation of
soluble particles 302 can also increase the hardness of the
polishing pad 100 to, for example, 60-75 shore D, such as 62-70
shore D.
[0026] Further, a surfactant can be included in the polymer matrix,
which, as discussed below, can increase the surface roughness of
the pad 100. The surfactant can be, for example, a copolymer, block
copolymer, or nonionic surfactant.
[0027] Referring to FIG. 4, a polishing pad 100 is manufactured by
stirring a liquid polymer mix 402 with a mixer 404 in a vat 406.
Gas 408, e.g. substantially pure nitrogen gas, is injected into the
liquid polymer mix 402 to create bubbles 410. Some of the bubbles
410 remain in the liquid polymer mix 402 to create pores 104 in the
cured polishing pad 100 (see FIGS. 1-3). In some implementations,
nanoparticles 202 are added to the liquid polymer mix 402 in the
vat 406 such that nanoparticles will be incorporated into the
polishing pad 100. Likewise, in other implementations, soluble
particles 302 are added to the liquid polymer mix 402 in vat 406
such that the soluble particles will be incorporated into the
polishing pad 100. Moreover, in some implementations, a surfactant
is added to the liquid polymer mix 402 in the vat 406 to stabilize
the bubbles 410, nanoparticles, and/or the soluble particles
302.
[0028] After mixing, the contents of the vat 406 can be poured
through an ejector 502 over a mold 504, as shown in FIG. 5A. The
mold 504 can be a conveyor belt and can continuously move, e.g. on
rollers 506, such that a sheet 508 of liquid polymer mix 402 is
formed on top of the mold 504. The sheet 508 can then be allowed to
cure over the mold 504. As shown in FIG. 5B, the mold 504 can have
projections, e.g. ridges 510, along its top surface such that a
complimentary set of ridges 512 is formed in the bottom surface of
the sheet 508 as the sheet 508 cures. The ridges 510 can be in the
shape, for example, of concentric circles, a rectangular grid
(sometimes called an "XY pattern"), or spirals along the top
surface of the substrate 504, so that the complimentary set of
ridges 512 are also concentric circles, an XY pattern, or
spirals.
[0029] Although not shown, once the sheet 508 has cured, a stamp
can cut individual polishing pads 100 from the sheet 508. The
polishing pads 100 can then be removed from the substrate 504. The
substrate 504 can be made of, for example, stainless steel, a
Teflon material, a silicone material, or a material coated with
Teflon or silicon such that the polishing pads 100 can be easily
removed from the substrate 504 after curing. The polishing pad 508
can then be placed in a CMP apparatus (not shown) for CMP
polishing.
[0030] The properties of a polishing pad can affect the polishing
rate of a substrate during CMP. For example, large, poorly
distributed pores (as opposed to evenly spaced small pores) in the
polishing pad can reduce the surface roughness of the polishing
pad. Reduced surface roughness, in turn, can decrease the polishing
rate by reducing polishing liquid transport during polishing and
decreasing the abrasiveness of the pad. By introducing soluble
particles during the production of the polishing pad, the polishing
rate can be increased, as before the soluble particles on the
polishing surface dissolve, they can act as abrasives, and after
the soluble particles on the polishing surface dissolve, the
surface roughness can be increased due to small voids left behind.
Furthermore, the introduction of surfactants to the formulation can
increase the polishing rate by allowing for better distribution of
voids, POSS nanoparticles, or soluble particles, and can thereby
increase the surface roughness.
[0031] The polishing rate can be further increased by incorporating
macro-texture or grooves into the surface of the polishing pad,
which can facilitate the transport of polishing liquid during
polishing. However, the creation of macro-texture after curing of
the polishing pad can be extremely timely and expensive. By casting
the precursor polishing pad mixture onto a substrate with grooves,
the pad grooves can be generated during curing, thereby reducing
the cost of creating grooves after curing.
[0032] The properties of the polishing pad can also affect the wear
rate of the pad itself. In particular, if a polishing pad has high
porosity, the wear rate of the pad can be high. By incorporating
molecular level POSS into the polishing pad, the hardness of the
pad can be increased, and the surface friction can be reduced, both
of which can reduce the polishing pad wear rate. Likewise, the
polishing pad wear rate can be reduced by incorporating soluble
organic or inorganic particles into the polishing pad, which can
increase the hardness of the polishing pad.
[0033] Particular embodiments of the invention have been described.
Other embodiments are within the scope of the following claims.
* * * * *