U.S. patent application number 16/368190 was filed with the patent office on 2019-07-18 for polishing pad and method for manufacturing the polishing pad.
This patent application is currently assigned to KURARAY CO., LTD.. The applicant listed for this patent is KURARAY CO., LTD.. Invention is credited to Mitsuru KATO, Hirofumi KIKUCHI, Kimio NAKAYAMA, Nobuo TAKAOKA.
Application Number | 20190218697 16/368190 |
Document ID | / |
Family ID | 41663704 |
Filed Date | 2019-07-18 |
United States Patent
Application |
20190218697 |
Kind Code |
A1 |
NAKAYAMA; Kimio ; et
al. |
July 18, 2019 |
POLISHING PAD AND METHOD FOR MANUFACTURING THE POLISHING PAD
Abstract
Disclosed herein is a method for manufacturing a polishing pad,
including the step of filling the interior of bundles of ultrafine
fibers which have an average fineness of from 0.01 to 0.8 dtex with
a polymeric elastomer having a glass transition temperature of
-10.degree. C. or below, storage moduli at 23.degree. C. and
50.degree. C. of from 90 to 900 MPa, and a water absorption ratio,
when saturated with water at 50.degree. C. of from 0.2 to 5 mass %.
Also disclosed herein are polishing pads obtained by the method
above.
Inventors: |
NAKAYAMA; Kimio;
(Kurashiki-shi, JP) ; TAKAOKA; Nobuo;
(Kurashiki-shi, JP) ; KATO; Mitsuru;
(Kurashiki-shi, JP) ; KIKUCHI; Hirofumi;
(Kurashiki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KURARAY CO., LTD. |
Kurashiki-shi |
|
JP |
|
|
Assignee: |
KURARAY CO., LTD.
Kurashiki-shi
JP
|
Family ID: |
41663704 |
Appl. No.: |
16/368190 |
Filed: |
March 28, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13058016 |
Feb 8, 2011 |
|
|
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PCT/JP2009/063802 |
Aug 4, 2009 |
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16368190 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D04H 3/016 20130101;
D04H 3/10 20130101; B24B 37/24 20130101 |
International
Class: |
D04H 3/016 20060101
D04H003/016; B24B 37/24 20060101 B24B037/24; D04H 3/10 20060101
D04H003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 8, 2008 |
JP |
2008-205981 |
Claims
1-10. (canceled)
11: A method for manufacturing a polishing pad, the method
comprising: filling the interior of bundles of ultrafine fibers
which have an average fineness of from 0.01 to 0.8 dtex with a
polymeric elastomer having a glass transition temperature of
-10.degree. C. or below, storage moduli at 23.degree. C. and
50.degree. C. of from 90 to 900 MPa, and a water absorption ratio,
when saturated with water at 50.degree. C., of from 0.2 to 5 mass
%.
12: The method for manufacturing a polishing pad according to claim
11, wherein the polymeric elastomer is filled into the interior of
an ultrafine fiber-entangled body composed of the bundles of the
ultrafine fibers such that void areas in the polishing pad have a
volume ratio of at least 50%.
13: The method for manufacturing a polishing pad according to claim
11, further comprising: obtaining a sheet of entangled webs by
stacking and entangling a plurality of filament webs composed of
composite fibers containing a water-soluble thermoplastic resin and
a water-insoluble thermoplastic resin; binding fiber bundles by
impregnating the entangled web sheet with an aqueous liquid of
polymeric elastomer and dry coagulating the elastomer; and forming
ultrafine fibers by dissolving the water-soluble thermoplastic
resin in hot water.
14: A polishing pad, which is obtained by the method according to
claim 11.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. Non-provisional
application Ser. No. 13/058,016, which was filed on Feb. 8, 2011.
U.S. Non-provisional application Ser. No. 13/058,016 is a National
Stage of PCT/JP09/063802, which was filed on Aug. 4, 2009. This
application is based upon and claims the benefit of priority to
Japanese Application No. 2008-205981, which was filed on Aug. 8,
2008.
TECHNICAL FIELD
[0002] The present invention relates to a polishing pad, and more
particularly to a polishing pad for polishing various devices,
substrates and other products on which planarization or mirror
polishing are carried out, examples of which include semiconductor
substrates, semiconductor devices, compound semiconductor devices,
compound semiconductor substrates, compound semiconductor products,
LED substrates, LED products, bare silicon wafers, silicon wafers,
hard disk substrates, glass substrates, glass products, metal
substrates, metal products, plastic substrates, plastic products,
ceramic substrates and ceramic products, and to a method for
manufacturing the polishing pad.
BACKGROUND ART
[0003] In recent years, with the increasing levels of integration
and multilayer interconnection in integrated circuits, there has
existed a need for high-precision flatness on the semiconductor
wafers where the integrated circuits are formed.
[0004] One known process for polishing semiconductor wafers is
chemical mechanical polishing (CMP). CMP is a process for polishing
a substrate surface to be polished with a polishing pad while
slowly dispensing a slurry of abrasive grains onto the surface.
[0005] Patent Documents 1 to 4 below disclose polishing pads
adapted for use in CMP which are composed of a polymer foam having
a closed cell structure and being produced by foam molding a
two-component curing polyurethane. Because such polishing pads have
a high stiffness compared with the nonwoven fabric-type polishing
pads described below, they are advantageously used in, for example,
the polishing of semiconductor wafers requiring high-precision
flatness.
[0006] Polishing pads composed of a polymer foam having a closed
cell structure are produced by, for example, subjecting a
two-component curing polyurethane to a cast-foam-molding. Because
such polishing pads have a relatively high stiffness, convex parts
on the substrate being polished tend to incur selective loading
during polishing, resulting in a relative high polishing rate.
However, when clumped abrasive grains are present on the polishing
surface, because such clumped abrasive grains also selectively
incur loading, scratches are readily formed on the surface being
polished. In particular, as described in Non-Patent Document 1,
when a substrate having copper wiring that is scratched easily or a
material with a low dielectric constant and with weak interfacial
adhesion is polished, there is a particular tendency for scratches
and interfacial separation to occur. Moreover, in a
cast-foam-molding, because it is difficult to uniformly foam a
polymeric elastomer, variability tends to arise in the flatness of
the substrate being polished and in the polishing rate during the
polishing operation. Moreover, in a polishing pad having closed
cells, the voids that originate from the closed cells become
clogged with abrasive particles and abrasion debris. As a result,
when the polishing pad is used for an extended period of time, the
polishing rate decreases as abrasion proceeds (this characteristic
is also referred to as polishing stability).
[0007] Patent Documents 5 to 14 disclose, as a different type of
polishing pad, nonwoven fabric-type polishing pads obtained by
impregnating a nonwoven fabric with a polyurethane resin and
wet-coagulating the resin. Nonwoven fabric-type polishing pads have
an excellent flexibility. For this reason, when clumped abrasive
grains are present on the polishing surface of a substrate being
polished, the polishing pad deforms, thereby suppressing the
selective loading at the clumped abrasive grains. However, the
polishing characteristics of nonwoven fabric-type polishing pads
have a tendency to change readily over time, making such pads
difficult to use for a precise planarization treatment. Also,
because the polishing pad is too flexible and deforms so as to
follow the surface shape of the substrate being polished, it is
difficult to obtain a high planarization performance (the ability
to render the substrate being polished flat). In addition, the
fibers have a fineness of 2 to 10 dtex and are thus large, making
it difficult to avoid local stress concentration.
[0008] In such nonwoven fabric-type polishing pads, there has come
to be known, more recently, a nonwoven fabric-type polishing pad
which is obtained by using a nonwoven fabric formed of bundles of
ultrafine fibers, which is intended to achieve a higher
planarization performance (e.g., see Patent Documents 15 to 18).
Specifically, Patent Document 15 describes a polishing pad in the
form of a sheet composed of both a nonwoven fabric formed of
entangled bundles of ultrafine polyester fibers having an average
fineness of from 0.0001 to 0.01 dtex and a polymeric elastomer made
primarily of a polyurethane present in spaces at the interior of
the nonwoven fabric. This publication states that a polishing
treatment at a higher precision than before is achieved with such a
polishing pad.
[0009] However, because the polishing pads like those described in
Patent Documents 15 to 18 make use of a nonwoven fabric obtained by
needlepunching ultrafine staple fibers having a low fineness, such
pads have a low apparent density and a high void volume. Hence,
only soft polishing pads with low stiffness can be obtained.
Because these polishing pads deform so as to follow the surface
shape, a sufficiently high planarization performance cannot be
achieved.
[0010] Also, none of these documents provide details concerning the
polymeric elastomer used in such nonwoven fabric-type polishing
pads. Nor do these documents sufficiently describe the stability of
the polishing pads over time. [0011] Patent Document 1: Japanese
Patent Application Laid-open No. 2000-178374 [0012] Patent Document
2: Japanese Patent Application Laid-open No. 2000-248034 [0013]
Patent Document 3: Japanese Patent Application Laid-open No.
2001-89548 [0014] Patent Document 4: Japanese Patent Application
Laid-open No. H11-322878 [0015] Patent Document 5: Japanese Patent
Application Laid-open No. 2002-9026 [0016] Patent Document 6:
Japanese Patent Application Laid-open No. H11-99479 [0017] Patent
Document 7: Japanese Patent Application Laid-open No. 2005-212055
[0018] Patent Document 8: Japanese Patent Application Laid-open No.
H3-234475 [0019] Patent Document 9: Japanese Patent Application
Laid-open No. H10-128674 [0020] Patent Document 10: Japanese Patent
Application Laid-open No. 2004-311731 [0021] Patent Document 11:
Japanese Patent Application Laid-open No. H10-225864 [0022] Patent
Document 12: Japanese Translation of PCT Application No.
2005-518286 [0023] Patent Document 13: Japanese Patent Application
Laid-open No. 2003-201676 [0024] Patent Document 14: Japanese
Patent Application Laid-open No. 2005-334997 [0025] Patent Document
15: Japanese Patent Application Laid-open No. 2007-54910 [0026]
Patent Document 16: Japanese Patent Application Laid-open No.
2003-170347 [0027] Patent Document 17: Japanese Patent Application
Laid-open No. 2004-130395 [0028] Patent Document 18: Japanese
Patent Application Laid-open No. 2002-172555 [0029] Non-Patent
Document 1: M. Kashiwagi et al., "CMP no saiensu [The science of
CMP]", Science Forum KK; Aug. 20, 1997, pp. 113-119
SUMMARY OF THE INVENTION
[0030] It is an object of the present invention to provide a
polishing pad which is less likely to cause scratches and has both
an excellent planarization performance and polishing
efficiency.
[0031] In one aspect, the invention relates to a polishing pad
which comprises an ultrafine fiber-entangled body formed of
ultrafine fibers having an average fineness of 0.01 to 0.8 dtex,
and a polymeric elastomer, wherein the polymeric elastomer has a
glass transition temperature of -10.degree. C. or below, storage
moduli at 23.degree. C. and 50.degree. C. of 90 to 900 MPa, and a
water absorption ratio, when saturated with water at 50.degree. C.,
of 0.2 to 5 mass %.
[0032] The objects, features, aspects and advantages of the
inventions will become more apparent from the following detailed
description.
MODE FOR CARRYING OUT THE INVENTION
[0033] Backing materials made of ultrafine fibers generally have a
large surface area and a low flexural modulus. For this reason,
hitherto known polishing pads of a type obtained by impregnating a
polymeric elastomer into a nonwoven fabric composed of ultrafine
fibers have a large contact surface area with the substrate being
polished, enabling to carry out a soft polishing. However, it has
been possible to obtain in this way only the polishing pads having
a low stiffness and falling short in terms of their planarizing
characteristics and polishing stability over time. Because the
voids in the nonwoven fabric become slurry reservoirs, thus giving
the nonwoven fabric a high ability to retain the abrasive slurry,
the polishing rate is easily increased. Yet, given that voids
account for more than one-half of the apparent volume, polishing
pads of a type obtained by impregnating hitherto known nonwoven
fabrics with a polymeric elastomer, while capable of carrying out a
highly efficient polishing, have a low stiffness and thus leave
something to be desired in terms of the planarizing ability and the
polishing stability over time.
[0034] The inventors have arrived at the present invention after
discovering that: (1) a polishing pad having a high stiffness can
be obtained by using an ultrafine fiber-entangled body of ultrafine
fibers and a polymeric elastomer having a specific glass transition
temperature, specific storage moduli and a specific water
absorption ratio, and the structure of such a polishing pad is
maintained even during polishing, enhancing the polishing stability
over time; (2) the fibers readily form fibrils at the surface of
the polishing pad during polishing, thereby increasing the contact
surface area with the substrate being polished and concurrently the
wettability, which in turn increases the retention of the abrasive
slurry, resulting in an increased polishing rate; and (3) on
account of the ultrafine fibers, the surface of the polishing pad
makes soft contact to the substrate, minimizing stress
concentration during polishing treatment, and making it less likely
for scratches to form on the substrate being polished. The
inventors have also found that, by setting the void volume of the
polishing pad to 50% or more, it is possible to provide the pad
with both an increased retention of the abrasive slurry and a high
stiffness, which is particularly ideal for polishing bare silicon
wafers.
[0035] Thus, the polishing pad of the present embodiment is
composed of an ultrafine fiber-entangled body formed of ultrafine
fibers having an average fineness of 0.01 to 0.8 dtex, and a
polymeric elastomer, wherein the polymeric elastomer has a glass
transition temperature of -10.degree. C. or below, storage moduli
at 23.degree. C. and 50.degree. C. of 90 to 900 MPa, and a water
absorption ratio, when saturated with water at 50.degree. C. of 0.2
to 5 mass %.
[0036] The composition, method of manufacture and method of use of
the polishing pad according to the present embodiment are described
below.
[0037] Composition of Polishing Pad
[0038] The ultrafine fiber-entangled body is formed of ultrafine
fibers having an average fineness in a range of from 0.01 to 0.8
dtex, and preferably from 0.05 to 0.5 dtex. When the ultrafine
fibers have an average fineness below 0.01 dtex, the ultrafine
fiber bundles near the surface of the polishing pad do not fully
fibrillate, as a result of which the abrasive slurry retention will
decrease, which may result in decreases in the polishing efficiency
and the polishing uniformity. On the other hand, when the ultrafine
fibers have an average fineness greater than 0.8 dtex, the surface
of the polishing pad becomes too coarse, lowering the polishing
rate. In addition, the stress in polishing with the fibers
increases, making scratches more likely to arise.
[0039] The ultrafine fiber-entangled body is composed of bundles of
preferably 5 to 70 ultrafine fibers, and more preferably 10 to 50
ultrafine fibers. When the number of ultrafine fibers collected
into a bundle exceeds 70, the fibers near the surface of the
polishing pad may not fully fibrillate, as a result of which the
retention of abrasive slurry may decrease. On the other hand, when
the number of ultrafine fibers collected into a bundle is less than
5, the fineness becomes substantially larger or the fiber density
at the surface tends to decreases, which may make the surface of
the polishing pad too coarse and lower the polishing rate. In
addition, the stress in polishing with the fibers increases, making
scratches more likely to arise.
[0040] Examples of ultrafine fibers include aromatic polyester
fibers formed of polyethylene terephthalate (PET), isophthalic
acid-modified polyethylene terephthalate, sulfoisophthalic
acid-modified polyethylene terephthalate, polybutylene
terephthalate or polyhexamethylene terephthalate; aliphatic
polyester fibers formed of polylactic acid, polyethylene succinate,
polybutylene succinate, polybutylene succinate adipate or
polyhydroxybutyrate-polyhydroxyvalerate copolymer; polyamide fibers
formed of polyamide 6, polyamide 66, polyamide 10, polyamide 11,
polyamide 12 or polyamide 6-12; polyolefin fibers formed of
polypropylene, polyethylene, polybutene, polymethylpentene or a
chlorinated polyolefin; modified polyvinyl alcohol fibers formed of
modified polyvinyl alcohol containing 25 to 70 mol % of ethylene
units; and elastomer fibers formed of a polyurethane elastomer,
polyamide elastomer or polyester elastomer. These may be used alone
or as combinations of two or more types thereof. In view of
enabling the formation of a compact, high-density ultrafine
fiber-entangled body, it is especially preferable for the ultrafine
fibers in the present embodiment to be formed of polyester
fibers.
[0041] Of the above ultrafine fibers, fibers which are formed of a
thermoplastic resin having a glass transition temperature (T.sub.g)
of at least 50.degree. C., and especially at least 60.degree. C.,
and a water absorption ratio, when saturated with water at
50.degree. C., of 0.2 to 2 mass %, are preferred. When the glass
transition temperature of the thermoplastic resin is in the above
range, a higher stiffness can be maintained, thereby enabling the
planarization performance to become even higher. Moreover, even
during polishing, the stiffness does not decrease over time,
enabling to obtain a polishing pad having excellent polishing
stability and polishing uniformity. From the standpoint of
industrial production, the upper limit in the glass transition
temperature, although not subject to any particular limitation, is
preferably 300.degree. C. or less, and more preferably 150.degree.
C. or less.
[0042] The ultrafine fibers of the present embodiment are
preferably formed of a thermoplastic resin having a water
absorption ratio, when saturated with water at 50.degree. C., of
0.2 to 2 mass %. In other words, it is preferable that the
thermoplastic resin used to form the ultrafine fibers has a water
absorption ratio, when saturated with water at 50.degree. C., of
0.2 to 2 mass %. By setting the water absorption ratio to at least
0.2 mass %, the abrasive slurry is easily retained and the
polishing efficiency and polishing uniformity are readily enhanced.
By setting the water absorption ratio to 2 mass % or less, the
polishing pad does not absorb too much abrasive slurry, thereby
better suppressing a decrease in the stiffness over time. In such
cases, there can be obtained a polishing pad in which the decrease
in planarization performance over time is suppressed and the
polishing rate and polishing uniformity do not readily fluctuate.
Owing to ready availability or good manufacturability in addition
to the water absorption, it is preferable that the thermoplastic
resin from which the ultrafine fibers in the embodiment are formed
is a polyester polymer, and especially a semi-aromatic polyester
polymer in which an aromatic ingredient is used as one of the
starting components.
[0043] Illustrative examples of the thermoplastic resin include
aromatic polyester fibers formed of polyethylene terephthalate
(PET; T.sub.g, 77.degree. C.; water absorption ratio when saturated
with water at 50.degree. C. (referred to below as simply the "water
absorption ratio"), 1 mass %), isophthalic acid-modified
polyethylene terephthalate (T.sub.g, 67 to 77.degree. C.; water
absorption ratio, 1 masst %), sulfoisophthalic acid-modified
polyethylene terephthalate (T.sub.g, 67 to 77.degree. C.; water
absorption ratio, 1 to 3 mass %), polybutylene naphthalate
(T.sub.g, 85.degree. C.; water absorption ratio, 1 mass %) or
polyethylene naphthalate (T.sub.g, 124.degree. C.; water absorption
ratio, 1 mass %); and semi-aromatic polyamide fibers formed of a
copolymeric polyamide of terephthalic acid with nonanediol and
methyloctanediol (T.sub.g, 125 to 140.degree. C.; water absorption
ratio, 1 to 3 mass %). PET and modified PET such as isophthalic
acid-modified PET are especially preferred, for example, in that
they undergo considerable crimping in the below-described wet heat
treatment operation in which the ultrafine fibers are formed from
an entangled web sheet composed of islands-in-the-sea type
composite fibers, thus enabling a compact and high-density
fiber-entangled body web of entangled fibers to be formed, in that
the stiffness of the polishing sheet is easily increased, and in
that changes over time owing to moisture during polishing do not
readily arise.
[0044] The polishing pad according to the embodiment is preferably
composed of an ultrafine fiber-entangled body formed of preferably
fiber bundles into which the above-described ultrafine fibers are
collected together, and a polymeric elastomer.
[0045] The polymeric elastomers which may be used in the embodiment
are not specifically limited as long as they satisfy the
below-described glass transition temperature, storage moduli and
water absorption ratio conditions. Illustrative examples of such
polymeric elastomers include elastomers which are composed of
polyurethane resins, polyamide resins, (meth)acrylate resins,
(meth)acrylate-styrene resins, (meth)acrylate-acrylonitrile resins,
(meth)acrylate-olefin resins, (meth)acrylate-(hydrogenated)
isoprene resins, (meth)acrylate-butadiene resins, styrene-butadiene
resins, styrene-hydrogenated isoprene resins,
acrylonitrile-butadiene resins, acrylonitrile-butadiene-styrene
resins, vinyl acetate resins. (meth)acrylate-vinyl acetate resins,
ethylene-vinyl acetate resins, ethylene-olefin resins, silicone
resins, fluororesins and polyester resins.
[0046] As the polymeric elastomer of the embodiment,
hydrogen-bonding polymeric elastomers are preferred because of
their good ability to have ultrafine fibers converge as bundles and
to restrain and bind the ultrafine fiber bundles. Examples of
resins which form the hydrogen-bonding polymeric elastomers include
polymeric elastomer resins that crystallize or aggregate under
hydrogen bonding, such as polyurethane resins, polyamide resins,
polyvinyl alcohol resins. The hydrogen-bonding polymeric elastomer
has a high adhesion, a high fiber bundle restraining ability, and
minimizes the loss of fibers.
[0047] The polymeric elastomer used in the embodiment has a glass
transition temperature of -10.degree. C. or below. At a glass
transition temperature higher than -10.degree. C., the polymeric
elastomer becomes brittle, as a result of which the polymeric
elastomer sheds more readily during polishing, which tends to give
rise to scratching. In addition, the ultrafine fiber bundle
convergence owing to the polymeric elastomer becomes weaker, which
tends to result in a decline in stability over time during
polishing. The glass transition temperature is preferably
-15.degree. C. or below. Although there is no particular lower
limit, in terms availability and other considerations, a lower
limit of -100.degree. C. or above is preferred. The glass
transition temperature is computed from the peak temperature of the
loss modulus in the tensile mode during measurement of the dynamic
viscoelasticity. Because the glass transition temperature is
dependent on the peak temperature of a dispersion by the polymeric
elastomer, it is preferable to suitably select the ingredients
making up the polymeric elastomer so as to set the glass transition
temperature of the polymeric elastomer to -10.degree. C. or below.
For example, when a polyurethane resin is used as the polymeric
elastomer, the composition of the polyols serving as the soft
component and the relative proportions of the hard component
(isocyanate component and chain extender component) and the soft
component are selected in such a way as to set the glass transition
temperature to -10.degree. C. or below. Specifically, it is
desirable to select a polyol having a glass transition temperature
of -10.degree. C. or below, preferably -20.degree. C. or below, and
to select a composition in which the mass ratio of the polyol
component within the polyurethane is at least 30 wt %, and
preferably at least 40 wt %.
[0048] The polymeric elastomer used in the embodiment has storage
moduli at 23.degree. C. and 50.degree. C. of in a range from 90 to
900 MPa. The storage moduli of polyurethanes at 23.degree. C. and
50.degree. C. are generally less than 90 MPa. However, at storage
moduli at 23.degree. C. and 50.degree. C. of less than 90 MPa, the
polymeric elastomer which restrains the fiber bundles readily
deforms, resulting in inadequate pad stiffness during polishing and
thus lowering the planarizing ability. Moreover, the polymeric
elastomer swells more readily due to the slurry, etc. during
polishing, as a result of which the stability over time tends to
decline. On the other hand, when the storage moduli at 23.degree.
C. and 50.degree. C. exceed 900 MPa, the polymeric elastomer
becomes brittle, as a result of which the polymeric elastomer sheds
more readily during polishing, which tends to give rise to
scratching. In addition, the ultrafine fiber bundle convergence
decreases, as a result of which the stability over time during
polishing readily worsens. The storage moduli at 23.degree. C. and
50.degree. C. are preferably from 200 to 800 MPa. Because the
storage moduli of the polymeric elastomer are dependent on the
composition of the polymeric elastomer, that is, on the respective
elastic moduli of and the weight ratio between the hard component
and the soft component making up the polymeric elastomer, it is
preferable to select the composition of and the weight ratio
between the hard component and the soft component in such a way as
to set the storage moduli in the above range.
[0049] For example, when a polyurethane resin is used as the
polymeric elastomer, illustrative examples of the soft component
(polyol component) include polyether polyols such as polyethylene
glycol, polypropylene glycol, polytetramethylene glycol and
poly(methyltetramethylene glycol), and copolymers thereof;
polyester polyols such as polybutylene adipate diol, polybutylene
sebacate diol, polyhexamethylene adipate diol,
poly(3-methyl-1,5-pentylene adipate) diol,
poly(3-methyl-1,5-pentylene sebacate) diol, isophthalic acid
copolymeric polyol, terephthalic acid copolymeric polyol,
cyclohexanol copolymeric polyol and polycaprolactone diol, and
copolymers thereof; polycarbonate polyols such as polyhexamethylene
carbonate diol, poly(3-methyl-1,5-pentylene carbonate) diol,
polypentamethylene carbonate diol, polytetramethylene carbonate
diol, poly(methyl-1,8-octamethylene carbonate) diol, polynonane
methylene carbonate diol and polycyclohexane carbonate, and
copolymers thereof; and polyester carbonate polyols. Also, if
necessary, a polyfunctional alcohol such as a trifunctional alcohol
(e.g., trimethylolpropane) or a tetrafunctional alcohol (e.g.,
pentaerythritol); or a short-chain alcohol such as ethylene glycol,
propylene glycol, 1,4-butanediol or 1,6-hexanediol, may be
concomitantly used. These may be used singly or as combinations of
two or more thereof. In particular, it is preferable to include a
polycarbonate polyol such as an alicyclic polycarbonate polyol, a
linear polycarbonate polyol or a branched polycarbonate polyol in
an amount of 60 to 100 mass % of the overall polyol component, and
to include especially a noncrystalline polycarbonate polyol having
a melting point of 0.degree. C. or below in an amount of 60 to 100
mass % of the overall polyol component, because the stability over
time during polishing is good on account of high resistance to the
slurry used in polishing and because the water absorption and the
storage moduli can easily be set within the above range of the
embodiment.
[0050] Moreover, in order to set the storage moduli at 23.degree.
C. and 50.degree. C. in a range of from 90 to 900 MPa, it is
preferable to select a polyol having a glass transition temperature
of -10.degree. C. or below, and preferably -20.degree. C. or below.
Illustrative examples include the above-mentioned branched
polycarbonate polyols; polyether polyols such as polypropylene
glycol, polytetramethylene glycol and poly(methyltetramethylene
glycol), and copolymers thereof; polyester polyols such as
polybutylene sebacate diol, poly(3-methyl-1,5-pentylene adipate)
diol, poly(3-methyl-1,5-pentylene sebacate) diol and
polycaprolactone diol, and copolymers thereof; polycarbonate
polyols such as poly(3-methyl-1,5-pentylene carbonate) diol and
poly(methyl-1,8-octamethylene carbonate) diol, and copolymers
thereof; and polyester carbonate polyols. In addition to the above
polyols, further examples include those polyols whose glass
transition temperature can be set to -10.degree. C. or below by
copolymerization.
[0051] Because polyurethane resins containing polyalkylene glycol
groups with up to 5 carbons, and especially up to 3 carbons, have
an especially good wettability to water, it is preferable to use a
polyurethane resin containing from about 0.1 to about 10 mass % of
such polyalkylene glycol groups.
[0052] By using a soft component (polyol component) having a glass
transition temperature of -10.degree. C. or below and thereby
setting the glass transition temperature of the polyurethane to
-10.degree. C. or below, and by selecting such a polyol component
and adjusting the mass ratio of the polyol component in the
polyurethane, the storage moduli of the polyurethane at 23.degree.
C. and 50.degree. C. can be set in a range of from 90 to 900
MPa.
[0053] When a polyurethane resin is used as the polymeric
elastomer, the isocyanate component used in the hard component
(isocyanate component and chain extender component) may be a
non-yellowing diisocyanate which is an aliphatic or alicyclic
diisocyanate, such as hexamethylene diisocyanate, isophorone
diisocyanate, norbornene diisocyanate and 4,4'-dicyclohexylmethane
diisocanate; or an aromatic diisocyanate, such as 2,4-tolylene
diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane
diisocyanate and xylylene diisocyanate polyurethane. If necessary,
concomitant use may be made of a polyfunctional isocyanate such as
a trifunctional isocyanate or a tetrafunctional isocyanate. These
may be used singly or as combinations of two or more thereof. Of
these, 4,4'-dicyclohexylmethane diisocyanate, 2,4-tolylene
diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane
diisocyanate and xylylene diisocyanate are preferred because they
have a high adhesion to ultrafine fibers and increase the ultrafine
fiber bundle convergence, thereby enabling a polishing pad having a
high hardness to be obtained.
[0054] As the other hard component (chain extender component), a
hard component which has a high cohesiveness and a high elastic
modulus and is composed of a combination of a short-chain polyol,
such as a diol (e.g., ethylene glycol, propylene glycol,
1,4-butanediol, 1,4-bis(p-hydroxyethoxy)benzene, 1,4-cyclohexane
diol), triol (e.g., trimethylolpropane), pentaol (e.g.,
pentaerythritol) or aminoalcohol (e.g., aminoethyl alcohol,
aminopropyl alcohol), with a short-chain polyamine, such as a
diamine (e.g., hydrazine, ethylenediamine, propylenediamine,
hexamethylenediamine, xylylenediamine, isophoronediamine,
piperazine and derivatives thereof, adipic acid dihydrazide,
isophthalic acid dihydrazide), triamine (e.g., diethylenetriamine)
or tetramine (e.g., triethylenetetramine), may be selected for use
as the chain extender component. Examples which may be used
together with the chain extender at the time of the chain-extending
reaction include a monoamine (e.g., ethylamine, propylamine,
butylamine), a carboxyl group-containing monoamine compound (e.g.,
4-aminobutanoic acid, 6-aminohexanoic acid), or a monool (e.g.,
methanol, ethanol, propanol, butanol). By concomitantly using a
carboxyl group-containing diol such as
2,2-bis(hydroxymethyl)propionic acid,
2,2-bis(hydroxymethyl)butanoic acid or
2,2-bis(hydroxymethyl)valeric acid, ionic groups such as the
carboxylic groups can be introduced onto the skeleton of the
polyurethane elastomer, making it possible to further enhance the
wettability to water.
[0055] From the standpoint of setting the storage moduli of the
polyurethane at 23.degree. C. and 50.degree. C. within a range of
from 90 to 900 MPa, the proportion of the soft component (polyol
component) is set to preferably from 40 to 65 mass %, and more
preferably from 45 to 60 mass %. At an amount of the soft component
below 40 mass %, the temperature dependence of the storage moduli
at 23.degree. C. and 50.degree. C. becomes higher, making it
difficult to achieve a range of from 90 to 900 MPa. On the other
hand, if the amount of the soft component exceeds 65 wt %, the
storage moduli tend to fall below 90 MPa.
[0056] From the standpoint of more easily increasing the storage
moduli of the polyurethane, it is especially preferable for the
soft component to be a polycarbonate-type polyol, such as a
branched polycarbonate polyol; poly(3-methyl-1,5-pentylene
carbonate) diol or poly(methyl-1,8-octamethylene carbonate) diol;
or a polycarbonate polyol obtained by copolymerizing such
polycarbonate polyols as poly(3-methyl-1,5-pentylene carbonate)
diol, poly(methyl-1,8-octamethylene carbonate) diol,
polyhexamethylene carbonate diol, polypentamethylene carbonate
diol, polytetramethylene carbonate diol, polynonanemethylene
carbonate diol and polycyclohexane carbonate.
[0057] Moreover, it is preferable for the polymeric elastomer in
the present embodiment to have a ratio of the storage modulus at
23.degree. C. to the storage modulus at 50.degree. C. (storage
modulus at 23.degree. C./storage modulus at 50.degree. C.) of 4 or
less. By setting the ratio of the storage modulus at 23.degree. C.
to the storage modulus at 50.degree. C. (storage modulus at
23.degree. C./storage modulus at 50.degree. C.) to 4 or less, the
storage moduli are less subject to change even when temperature
changes arise during polishing, thereby enhancing the stability
over time during polishing. It is especially preferable to set the
ratio of the storage modulus at 23.degree. C. to the storage
modulus at 50.degree. C. (storage modulus at 23.degree. C./storage
modulus at 50.degree. C.) to 3 or less. The lower limit value is
not subject to any particular limitation; however, in order for the
storage modulus to be less subject to change due to the temperature
during polishing, a value of 1/3 or more is preferred.
[0058] The foregoing range can be achieved by suitably adjusting
the soft component and the hard component so as to set the storage
moduli in the above-described range.
[0059] For example, in cases where a polyurethane resin is employed
as the polymeric elastomer, it is desirable to use a soft component
(polyol component) having a glass transition temperature of
-10.degree. C. or below so as to set the glass transition
temperature of the polyurethane to -10.degree. C., to select as the
hard components (isocyanate component and chain extender component)
an alicyclic diisocyanate or an aromatic diisocyanate, and a chain
extender component having a high cohesiveness and a high elastic
modulus which is obtained from a combination of a short-chain
polyol (examples of which include diols, triols and pentaols) with
a short-chain polyamine (examples of which include diamines,
triamines and tetramines), and to set the ratio of the soft
component at preferably from 40 to 65 mass %, and more preferably
from 45 to 60 mass %. Also, a polycarbonate polyol is preferred as
the soft component of the polyurethane because it makes the elastic
modulus of the polyurethane easy to increase.
[0060] In order to adjust, for example, the performance or
manufacturability of the polishing pad, two or more polymeric
elastomers may be included. The storage moduli at 23.degree. C. to
50.degree. C. of the polymeric elastomer in such a case can be
theoretically calculated as the sum of the values obtained by
multiplying the storage modulus of each polymeric elastomer by the
mass fraction thereof.
[0061] Moreover, the polymeric elastomer of the present embodiment
has a water absorption ratio, when saturated with water at
50.degree. C., of 0.2 to 5 mass %. At a water absorption ratio
below 0.2 mass %, retaining the abrasive slurry becomes difficult,
as a result of which the polishing efficiency and the polishing
uniformity tend to decline. At above 5 mass %, the polymeric
elastomer which restrains the fiber bundles absorbs water and
softens, as a result of which the change over time during polishing
tends to increase. Moreover, it is preferable for the water
absorption ratio when saturated with water at 50.degree. C. to be
in a range of from 0.5 to 3 mass %. When the water absorption ratio
of the polymeric elastomer is in such a range, a high wettability
of the polishing pad by the abrasive slurry is maintained, in
addition to which a decline over time in the stiffness can be
better suppressed. This enables a high polishing rate, polishing
uniformity and polishing stability to be maintained.
[0062] The water absorption ratio of polymeric elastomer, which
will be subsequently described in greater detail, refers herein to
the water absorption ratio when a polymeric elastomer film that has
been subjected to drying treatment is immersed in room-temperature
water and allowed to swell to saturation. The water absorption
ratio in cases where two or more types of polymeric elastomer are
included can be theoretically calculated as the sum of the values
obtained by multiplying the water absorption ratio of each
polymeric elastomer by the mass fraction thereof.
[0063] The polymeric elastomer having such a water absorption ratio
can be obtained, for example, by adjusting the composition and
crosslink density of the polymers making up the polymeric
elastomer, introducing hydrophilic functional groups, and selecting
the amounts thereof.
[0064] For example, the water absorption ratio and hydrophilicity
can be adjusted by introducing to the polymeric elastomer at least
one type of hydrophilic group selected from the group consisting of
carboxylic groups, sulfonic acid groups, and polyalkylene glycol
groups having 3 or fewer carbons. In this way, the wettability of
the polishing pad by the abrasive slurry can be increased. Such
hydrophilic groups may be introduced onto the polymeric elastomer
by the copolymerization of a monomer having hydrophilic groups as a
monomer component during production of the polymeric elastomer.
Setting the copolymerization ratio of such a monomer component
having hydrophilic groups at from 0.1 to 10 mass %, and especially
from 0.5 to 5 wt %, is preferable from the standpoint of minimizing
swelling and softening due to water absorption and increasing the
water absorption ratio and wettability.
[0065] The polymeric elastomers may be used singly or as
combinations of two or more thereof. Of such polymeric elastomers,
a polyurethane resin is preferred in that it has excellent adhesive
properties for packing ultrafine fibers into bundles or for
restraining and binding together the fiber bundles, in addition to
which it increases the hardness of the polishing pad and has an
excellent stability over time during polishing. Also, the
polyurethane resin having at least one type of hydrophilic group
selected from the group consisting of carboxylic groups, sulfonic
acid groups and polyalkylene glycol groups of 3 or fewer carbons is
desirable from the standpoint of the polishing pad stiffness,
wettability and stability over time during polishing.
[0066] In cases where the polymeric elastomer is the polyurethane
resin, specific examples of carboxylic groups include the
carboxylic groups of 2,2-bis(hydroxymethyl)propionic acid,
2,2-bis(hydroxymethyl)butanoic acid and
2,2-bis(hydroxymethyl)valeric acid. By concomitantly using, for
example, these diols having the carboxylic groups, it is possible
to introduce carboxylic groups onto the skeleton of the
polyurethane elastomer. Illustrative examples of polyalkylene
glycol groups having 3 or fewer carbons include polyethylene
glycol, polypropylene glycol and copolymers thereof. Although
polyurethane resins having at least one type of hydrophilic group
selected from among carboxylic groups, sulfonic acid groups and
polyalkylene glycol groups of 3 or fewer carbons do have the
advantage of an enhanced wettability, the water absorption ratio
tends to rise and is generally from 5 to 15 mass %. Therefore, in
order to set the water absorption ratio in the range of 0.2 to 5
mass % in the present embodiment, it is desirable to set the amount
of at least one hydrophilic group selected from the group
consisting of carboxylic groups, sulfonic acid groups and
polyalkylene glycol groups of 3 or fewer carbons to preferably from
0.1 to 10 mass %, and more preferably from 0.5 to 5 mass %. In
addition, it is preferable to use as the polyol a component having
low water absorption, such as the above-described polyester polyol
or polycarbonate polyol.
[0067] For example, in cases where the polymeric elastomer is a
polyurethane resin obtained by using as the polyol component a
noncrystalline polycarbonate diol together with a carboxylic
group-containing diol, and using an alicyclic diisocyanate as the
diisocyanate component, the use of such a polymeric elastomer is
preferred because of the ease of setting the glass transition
temperature of the polymeric elastomer to -10.degree. C. or below,
setting the storage moduli at 23.degree. C. and 50.degree. C. to
from 90 to 900 MPa, and setting the water absorption ratio when
saturated with water at 50.degree. C. to from 0.2 to 5 mass %.
[0068] The hard components (isocyanate component and chain extender
component) of the polyurethane resin used in the embodiment may be,
for example, the above-described isocyanate component and the
above-described chain extender component having a high
cohesiveness. Also, the ratio of the soft component (polyol
component) is preferably set to 65 mass % or less, and more
preferably 60 mass % or less. At an amount of the soft component in
excess of 65 wt %, the water absorption ratio tends to become high.
In cases where the polymeric elastomer is an aqueous polyurethane,
to achieve a water absorption ratio of from 0.2 to 5 mass %, it is
preferable for the aqueous polyurethane to have an average particle
size of from 0.01 to 0.2 .mu.m. At an average particle size of less
than 0.01 .mu.m or more than 0.2 .mu.m, the water absorption ratio
will tend to exceed 5 mass %.
[0069] In cases where the polymeric elastomer is a polyurethane
resin, to control the water absorption ratio and the storage
moduli, it is preferable also to form a crosslinked structure by
adding a crosslinking agent having in the molecule two or more
functional groups capable of reacting with the functional groups in
the above-mentioned monomer units which form the polyurethane, or
by adding a self-crosslinking compound such as a polyisocyanate
compound or a polyfunctional block isocyanate-type compound.
[0070] Examples of combinations of the functional group in the
above-mentioned monomer unit with the functional group in the
crosslinking agent include a carboxylic group with an oxazoline
group, a carboxylic group with a carbodiimide group, a carboxylic
group with an epoxy group, a carboxylic group with a cyclocarbonate
group, a carboxylic group with an aziridine group, and a carbonyl
group with a hydrazine derivative or a hydrazide derivative. Of
these, combinations of the monomer unit having the carboxylic group
with the crosslinking agent having the oxazoline group, the
carbodiimide group or the epoxy group, combinations of the monomer
unit having the hydroxyl group or the amino group with the
crosslinking agent having the block isocyanate group, and
combinations of the monomer unit having the carbonyl group with the
hydrazine derivative or the hydrazide derivative are especially
preferred on account of the ease of crosslinkage formation and the
excellent stiffness and wear resistance of the polishing pad
thereby obtained. Formation of the crosslinked structure in a heat
treatment step following impregnation of the fiber-entangled body
with an aqueous liquid of the polyurethane resin is preferred from
the standpoint of maintaining the stability of the aqueous liquid
of the polymeric elastomer. Of the above, the carbodiimide group
and/or the oxazoline group are especially preferred on account of
their excellent crosslinking ability and the pot life of the
aqueous liquid, and also because these pose no problems in terms of
safety. Illustrative examples of crosslinking agents having the
carbodiimide group include water-dispersible carbodiimide compounds
such as Carbodilite E-01, Carbodilite E-02 and Carbodilite V-02,
all available from Nisshinbo Industries, Inc. Illustrative examples
of crosslinking agents having the oxazoline group include
water-dispersible oxazoline compounds such as Epocros K-2010E,
Epocros K-2020E and Epocros WS-500, all available from Nippon
Syokubai Co., Ltd. The amount of the crosslinking agent included in
the polyurethane resin, expressed in terms of the active ingredient
of the crosslinking agent with respect to the polyurethane resin,
is preferably from 1 to 20 mass %, and more preferably from 1.5 to
10 mass %.
[0071] In order to increase adhesion with the ultrafine fibers and
increase the rigidity of the fiber bundles, and in order to
facilitate adjustments, such as setting the glass transition
temperature to -10.degree. C. or below, setting the storage moduli
at 23.degree. C. and 50.degree. C. in a range of 90 to 900 MPa, and
setting the water absorption ratio when saturated with water at
50.degree. C. to 0.2 to 5 mass %, the content of the polyol
component in the polyurethane resin is preferably 65 mass % or
less, and more preferably 60 mass % or less. Also, the content of
at least 40 mass %, and especially at least 45 mass %, is preferred
in that a suitable elasticity is imparted, making it possible to
minimize the occurrence of scratches.
[0072] The polyurethane resin may additionally include, within
ranges that do not compromise the advantageous effects of the
invention: penetrating agents, foam inhibitors, lubricants, water
repellents, oil repellents, thickeners, bulking agents, curing
accelerators, antioxidants, ultraviolet absorbers, mold inhibitors,
blowing agents, water-soluble polymeric compounds such as polyvinyl
alcohol and carboxymethyl cellulose, dyes, pigments, and inorganic
fine particles.
[0073] Preferably, the polymeric elastomer is present inside
ultrafine fiber bundles of from 5 to 70 ultrafine fibers having an
average fineness of 0.01 to 0.8 dtex which make up the ultrafine
fiber-entangled body. The ultrafine fibers converge as bundles
under the effect of the polymeric elastomer present inside the
ultrafine fiber bundles. Owing to the convergence of the ultrafine
fibers, a part or all of the interior of the fiber bundle converges
as a bundle, in addition to which the bundle of ultrafine fibers is
restrained. The convergence of the ultrafine fibers as a bundle,
together with the restraint of the fiber bundle, increases the
stiffness of the polishing pad, which is advantageous from the
standpoint of enhancing the planarizing performance, the polishing
uniformity and the stability over time.
[0074] A volumetric ratio of a portion excluding voids in the
polishing pad (also referred to below as the filling ratio of the
polishing pad) is preferably in a range of from 40 to 95 wt %. That
is, the presence of the voids such that the void volume is in a
range of from 5 to 60% is preferable both for a suitable stiffness
of the polishing pad and for slurry retention by the polishing
pad.
[0075] In this case, the void volume in the polymeric
elastomer-impregnated polishing pad of 50% or more is desirable
because slurry retention, suitable stiffness and moreover
cushionability are concurrently achieved, which is excellent for
polishing bare silicon wafers. An upper limit in this case of 70%
or less is desirable because this results in a good polishing rate
and flatness in rough polishing such as bare silicon wafer
polishing.
[0076] From the standpoint of enhancing slurry retention, it is
more desirable for some of the voids to form continuous pores which
afford communication with the interior of the polishing pad.
[0077] Moreover, the polymeric elastomer is preferably an aqueous
polyurethane because of the good wettability to abrasive slurry,
and the aqueous polyurethane preferably has an average particle
size of 0.01 to 0.2 .mu.m. At an average particle size of at least
0.01 .mu.m, the water resistance is good, resulting in an excellent
stability over time during polishing. An average particle size of
0.2 .mu.m or less enhances the fiber bundle restraining strength,
confers good planarizing properties, and increases the pad life
during polishing, providing good stability over time. To adjust the
above particle size, it is preferable, for example, that the
polymeric elastomer includes at least one type of hydrophilic group
selected from the group consisting of carboxylic groups, sulfonic
acid groups and polyalkylene glycol groups having 3 or fewer
carbons.
[0078] The mass ratio of the ultrafine fiber-entangled body to the
polymeric elastomer (ultrafine fiber-entangled body/polymeric
elastomer) is preferably from 55/45 to 95/5. A mass ratio for the
ultrafine fiber-entangled body of 55% or more has a good effect for
the stability over time during polishing, and tends to enhance the
polishing efficiency. At a mass ratio for the ultrafine
fiber-entangled body of 95% or less, the restraining strength of
the polymeric elastomer at the interior of the fiber bundles is
maintained, resulting in excellent planarizing properties and
little pad wear during polishing. The mass ratio of the ultrafine
fiber-entangled body to the polymeric elastomer is most preferably
in a range of from 60)/40 to 90/10.
[0079] To maintain a good slurry retention and maintain a high
stiffness, the apparent density of the polishing pad of the
embodiment is preferably in a range of 0.4 to 1.2 g/cm.sup.3, and
more preferably from 0.5 to 1.0 g/cm.sup.3. In a use for bare
silicon wafer polishing, to achieve both an enhanced polishing rate
and planarity, the apparent density is preferably from 0.3 to 0.75
g/cm.sup.3, and more preferably from 0.4 to 0.65 g/cm.sup.3.
[0080] In the present embodiment, the average length of the
ultrafine fiber bundles is not subject to any particular
limitation. However, having the average length be at least 100 mm,
and preferably at least 200 mm, is desirable in that the fiber
density can be easily increased, the stiffness of the polishing pad
can be easily increased, and the loss of fibers can be suppressed.
If the length of the fiber bundles is too short, a higher fiber
density will be difficult to achieve, in addition to which a
sufficiently high stiffness is not attained, and ultrafine fibers
will have a greater tendency to shed during polishing. The upper
limit is not subject to any particular limitation. For example,
when an ultrafine fiber-entangled body from a nonwoven fabric
manufactured by the below-described spunbonding process is
included, fibers having lengths of several meters, several hundreds
of meters, several kilometers or more may be included as far as
they are not physically cut.
[0081] The polishing pad of the embodiment preferably has a
composite construction obtained by filling the polymeric elastomer
into the ultrafine fiber-entangled body.
[0082] In the polishing pad of the embodiment, having the polymeric
elastomer present at the interior of the ultrafine fiber bundles is
preferable for increasing the stiffness of the polishing pad, and
it is more preferable for the ultrafine fibers which make up the
ultrafine fiber bundles to be bundled under the effect of the
polymeric elastomer. By having the ultrafine fibers bundled in this
way, the stiffness of the polishing pad is further increased.
Bundling the ultrafine fibers makes it difficult for the individual
fibers to move, thereby increasing the stiffness of the polishing
pad and enabling a high planarizing performance to be readily
achieved. Also, the loss of fibers decreases and the aggregation of
abrasive particles at fibers that have been shed can be prevented,
thereby minimizing the occurrence of scratches. As used herein, the
feature that the ultrafine fibers are bundled refers to a state
where a large portion of the ultrafine fibers present at the
interior of the ultrafine fiber bundles (preferably at least 10%,
more preferably at least 20%, even more preferably at least 50%,
and most preferably at least 60%, of the number of fibers) are
bonded and restrained by the polymeric elastomer present at the
interior of the ultrafine fiber bundles.
[0083] Moreover, it is also preferable for a plurality of ultrafine
fiber bundles to be mutually bonded by the polymeric elastomer
present outside of the ultrafine fiber bundles, and to exist in a
bulk state. By binding together the ultrafine fiber bundles in this
way, the shape stability of the polishing pad is enhanced, thus
increasing the polishing stability.
[0084] The bundled and restrained state of the ultrafine fibers and
the bound state between the ultrafine fiber bundles can be
confirmed from electron micrographs of cross-sections of the
polishing pad.
[0085] The polymeric elastomer which bundles the ultrafine fibers
and the polymeric elastomer which binds together the ultrafine
fiber bundles is preferably a nonporous elastomer. Here,
"nonporous" signifies a state in which there are substantially no
voids (closed pores) as would exist in porous or sponge-like
(referred to below simply as "porous") polymeric elastomers.
Concretely, this means, for example, that it is not a polymeric
elastomer having many tiny pores as would be obtained by
coagulating a solvent-based polyurethane. In cases where the
polymeric elastomer for bundling or binding is nonporous, because
the polishing stability increases and slurry debris and pad debris
do not readily accumulate in the voids during polishing, the
polishing pad is less subject to wear, enabling a high polishing
rate to be maintained for an extended period of time. In addition,
because the adhesive strength with respect to the ultrafine fibers
is high, the occurrence of scratches that arise from the shedding
of fibers can be suppressed. Moreover, because a higher stiffness
can be achieved, a polishing pad having an excellent planarization
performance is obtained.
[0086] The polishing pad in the present embodiment preferably has a
water absorption ratio when swollen to saturation with 50.degree.
C. water, of preferably 10 to 80 mass %, and more preferably 15 to
70 mass %. At such a water absorption ratio of at least 10 mass %,
the abrasive slurry is easily retained, as a result of which the
polishing rate increases and the polishing uniformity tends to
improve. At such a water absorption ratio of 80 mass % or less, a
high polishing rate is achieved. Moreover, because properties such
as hardness do not readily change during polishing, the stability
over time in the planarization performance tends to be
outstanding.
[0087] By subjecting the polishing pad of the present embodiment to
a pad-flattening treatment by buffing or the like, a seasoning
treatment (conditioning treatment) using a pad dressing such as a
diamond prior to polishing, or a dressing treatment at the time of
polishing, the ultrafine fiber bundles present near the surface can
be separated or fibrillated, enabling the ultrafine fibers to be
formed at the surface of the polishing pad. The fiber density of
the ultrafine fibers at the polishing pad surface is preferably at
least 600 fibers/mm.sup.2, more preferably at least 1,000
fibers/mm.sup.2, and most preferably at least 2,000
fibers/mm.sup.2. If the fiber density is too low, the retention of
the abrasive slurry will tend to be insufficient. From the
standpoint of manufacturability, the upper limit in the fiber
density, although not subject to any particular limitation, is
about 1,000,000 fibers/mm.sup.2. The ultrafine fibers at the
surface of the polishing pad may or may not stand upright. In cases
where the ultrafine fibers stand upright, the surface of the
polishing pad becomes softer, further increasing the
scratch-reducing effect. On the other hand, in cases where the
degree of uprightness of the ultrafine fibers is low, this is
advantageous for applications in which importance is placed on the
micro-flatness. It is preferable in this way to suitably select the
surface state according to the intended application.
[0088] Method for Manufacturing the Polishing Pad
[0089] Next, an example of a method for manufacturing the polishing
pad of the present embodiment is described in detail.
[0090] The polishing pad of the embodiment can be obtained by a
manufacturing method which includes, for example, a web fabricating
step which fabricates a filament web composed of islands-in-the-sea
type composite fibers obtained by melt spinning a water-soluble
thermoplastic resin and a water-insoluble thermoplastic resin; a
web entangling step which forms an entangled web sheet by stacking
together a plurality of the filament webs and entangling the webs;
a wet heat shrinkage treatment step which shrinks the entangled web
sheet to a surface area shrinkage ratio of at least 30% by
subjecting the sheet to wet heat shrinkage; an ultrafine
fiber-entangled body-forming step which forms an ultrafine
fiber-entangled body composed of ultrafine fibers by dissolving the
water-soluble thermoplastic resin within the entangled web sheet in
hot water; and a polymeric elastomer filling step which impregnates
the ultrafine fiber-entangled body with an aqueous liquid of a
polymeric elastomer and dry-coagulates the elastomer.
[0091] In the above manufacturing method, by passing through the
step wherein the entangled web sheet containing filaments is
subjected to wet heat shrinkage, the entangled web sheet can be
shrunk to a considerable degree compared with a case in which an
entangled web sheet containing staple fibers is subjected to wet
heat shrinkage, thereby increasing the fiber density of the
ultrafine fibers. Moreover, by dissolving and extracting the
water-soluble thermoplastic resin in the entangled web sheet, an
ultrafine fiber-entangled body composed of ultrafine fiber bundles
is formed. At this time, voids are formed in the areas where the
water-soluble thermoplastic resin has been dissolved and extracted.
Next, by thoroughly impregnating a high-concentration aqueous
liquid of the polymeric elastomer into these voids and by
dry-coagulating the elastomer, the ultrafine fibers making up the
ultrafine fiber bundles converge together, and the ultrafine fiber
bundles also mutually converge. In this way, there can be obtained
the polishing pad which has a high fiber density, a low void volume
and, because the ultrafine fibers have been made to converge as
bundles, a high stiffness.
[0092] By controlling the shrinkage treatment and adjusting the
amount of polymeric elastomer impregnated into the voids so as to
set the void volume of the polishing pad to 50% or more, the
polishing pad suitable for use on bare silicon wafers can be
obtained, in which the polishing pad has an appropriate stiffness
and both an improved abrasive-slurry retention and an improved
cushionability.
[0093] Each of the manufacturing steps is described below in
greater detail.
[0094] (1) Web Fabricating Step
[0095] In this step, first a filament web composed of
islands-in-the-sea type composite fibers obtained by melt spinning
a water-soluble thermoplastic resin and a water-insoluble
thermoplastic resin is produced.
[0096] The islands-in-the-sea type composite fibers are obtained by
respectively melt spinning a water-soluble thermoplastic resin and
a water-insoluble thermoplastic resin having a low compatibility
with the water-soluble thermoplastic resin, then by combining the
two. Ultrafine fibers are then formed by dissolving and removing,
or decomposing and removing, the water-soluble thermoplastic resin
from the islands-in-the-sea type composite fibers. From an
industrial standpoint, it is preferable for the size of the
islands-in-the-sea type composite fibers to be from 0.5 to 3
dtex.
[0097] In the embodiment, islands-in-the-sea type composite fibers
are described in detail as the composite fibers employed to form
ultrafine fibers. However, in place of islands-in-the-sea type
fibers, other known ultrafine fiber-generating fibers such as
fibers having a multilayer laminated cross-section can be also
used.
[0098] As the water-soluble thermoplastic resin, a thermoplastic
resin which can be dissolved and removed or decomposed and removed
using, for example, water, an alkaline aqueous solution or an
acidic aqueous solution, and which is melt-spinnable may be
advantageously used. Examples of such water-soluble thermoplastic
resins include polyvinyl alcohol resins (PVA resins) such as
polyvinyl alcohol and polyvinyl alcohol copolymers; modified
polyesters containing polyethylene glycol and/or an alkali metal
salt of sulfonic acid as the copolymerizing ingredients; and
polyethylene oxide. Of these, the use of a PVA resin is especially
preferred for the following reasons.
[0099] When islands-in-the-sea type composite fibers using a PVA
resin as the water-soluble thermoplastic resin component are
employed, the ultrafine fibers formed by dissolving the PVA resin
undergo a considerable degree of crimping. As a result, an
ultrafine fiber-entangled body having a higher fiber density is
obtained. Alternatively, in cases where islands-in-the-sea type
composite fibers in which a PVA resin serves as the water-soluble
thermoplastic resin component are used, when the PVA resin is
dissolved, because the formed ultrafine fibers and the polymeric
elastomer substantially do not decompose or dissolve, the physical
properties of the ultrafine fibers and the polymeric elastomer do
not readily decline. Moreover, the burden on the environment is
also low.
[0100] The PVA resin can be obtained by saponifying a copolymer in
which vinyl ester units serve as a primary component. Illustrative
examples of vinyl monomers for forming the vinyl ester units
include vinyl acetate, vinyl formate, vinyl propionate, vinyl
valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl
benzoate, vinyl pivalate and vinyl versatate. These may be used
singly or as combinations of two or more thereof. Of these, vinyl
acetate is preferred from an industrial standpoint.
[0101] The PVA resin may be a homo-PVA composed only of vinyl ester
units, or may be a modified PVA containing as constituent units
copolymerizable monomer units other than vinyl ester units. In
terms of the ability to control the melt spinnability, the water
solubility and the physical properties of the fibers, the modified
PVA is more preferred. Illustrative examples of copolymerizable
monomer units other than the vinyl ester units include
.alpha.-olefins having 4 or fewer carbons, such as ethylene,
propylene, 1-butene and isobutene; and vinyl ethers such as methyl
vinyl ether, ethylene vinyl ether, n-propyl vinyl ether, isopropyl
vinyl ether and n-butyl vinyl ether. The content of copolymerizable
monomer units other than vinyl ester units is in a range of
preferably from 1 to 20 mol %, more preferably from 4 to 15 mol %,
and even more preferably from 6 to 13 mol %. Of these, an
ethylene-modified PVA containing from 4 to 15 mol %, and especially
from 6 to 13 mol %, of the ethylene units is preferred because the
resulting islands-in-the-sea type composite fibers have higher
physical properties.
[0102] From the standpoint of forming a stable islands-in-the-sea
structure, exhibiting a melt viscosity with excellent melt spinning
properties, and having a rapid dissolution rate during dissolution,
it is desirable for the PVA resin to have a viscosity-average
degree of polymerization in a range of from 200 to 500, preferably
from 230 to 470, and most preferably from 250 to 450. The above
degree of polymerization is measured in general accordance with
JIS-K6726. That is, the viscosity-average degree of polymerization
is calculated according to the following formula from the intrinsic
viscosity [.eta.] measured in 30.degree. C. water after the PVA
resin is re-saponified and purified.
Viscosity-average degree of polymerization
P=([.eta.].times.103/8.29)(1/0.62)
[0103] The degree of saponification of the PVA resin is preferably
from 90 to 99.99 mol %, more preferably from 93 to 99.98 mol %,
even more preferably from 94 to 99.97 mol %, and most preferably
from 96 to 99.96 mol %. When the degree of saponification is in
such a range, a PVA resin having an excellent water solubility,
good thermal stability, excellent melt spinnability and excellent
biodegradability can be obtained.
[0104] From the standpoint of having excellent mechanical
properties and thermal stability, and also from the standpoint of
having an excellent melt spinnability, it is desirable for the
melting point of the above PVA resin to be in a range of from 160
to 250.degree. C., preferably 170 to 227.degree. C., more
preferably from 175 to 224.degree. C., and most preferably from 180
to 220.degree. C. When the melting point of the PVA resin is too
high, the melting point and the degradation temperature become
similar, as a result of which the melt spinnability tends to
decrease due to the occurrence of decomposition during melt
spinning.
[0105] Also, when the melting point of the PVA resin is too much
lower than the melting point of the above-mentioned water-insoluble
thermoplastic resin, this is undesirable because the melt
spinnability decreases. From this standpoint, the melting point of
the PVA resin is preferably not more than 60.degree. C. lower, and
more preferably not more than 30.degree. C. lower, than the melting
point of the water-insoluble thermoplastic resin.
[0106] The water-insoluble thermoplastic resin is preferably a
thermoplastic resin which is not dissolved and removed, or
decomposed and removed, by water, an alkaline aqueous solution, an
acid aqueous solution or the like, and which is capable of being
melt spun.
[0107] Illustrative examples of the water-insoluble thermoplastic
resin include various types of the above-described thermoplastic
resins that can be used to form the ultrafine fibers making up the
polishing pad.
[0108] The water-insoluble thermoplastic resin may contain various
additives. Examples of such additives include catalysts,
discoloration inhibitors, heat stabilizers, flame inhibitors,
lubricants, stain blockers, fluorescent whiteners, delusterants,
colorants, gloss enhancers, antistatic agents, fragrances,
deodorants, antimicrobial agents, miticides and inorganic fine
particles.
[0109] Next, the method for melt spinning the above water-soluble
thermoplastic resin and the above water-insoluble thermoplastic
resin to form an islands-in-the-sea type composite fiber, and for
forming a filament web from the resulting islands-in-the-sea type
composite fibers, is described in detail.
[0110] The filament web can be obtained by, for example,
melt-spinning and thereby combining the water-soluble thermoplastic
resin and the water-insoluble thermoplastic resin, then by drawing
and subsequently depositing the fibers using a spunbonding process.
By forming a web using a spunbonding process in this way, there can
be obtained a filament web composed of islands-in-the-sea type
composite fibers which does not shed many fibers and has a high
fiber density and good shape stability. As used herein, "filament"
refers to a fiber which has been manufactured without passing
through such a cutting step as a case in the manufacture of a
staple fiber.
[0111] In the manufacture of the islands-in-the-sea type composite
fibers, the water-soluble thermoplastic resin and the
water-insoluble thermoplastic resin are separately melt-spun, and
are combined. The mass ratio of the water-soluble thermoplastic
resin and the water-insoluble thermoplastic resin is in a range of
preferably from 5/95 to 50/50, and more preferably from 10/90 to
40/60. When the mass ratio of the water-soluble thermoplastic resin
and the water-insoluble thermoplastic resin is in this range, an
ultrafine fiber-entangled body having a high density can be
obtained, and the ultrafine fiber formability is also
excellent.
[0112] After the water-soluble thermoplastic resin and the
water-insoluble thermoplastic resin have been combined by melt
spinning, a filament web is formed by spunbonding as described
below.
[0113] First, the water-soluble thermoplastic resin and the
water-insoluble thermoplastic resin are each melt-mixed in separate
extruders, and strands of the molten resins are simultaneously
discharged from the respective differing spinnerets. Next, the
discharged strands are combined in a combining nozzle, then
discharged from the nozzle orifices in the spinning head to form an
islands-in-the-sea type composite fiber. To obtain fiber bundles
having low individual fiber fineness and a high fiber density, it
is desirable for the number of islands in the islands-in-the-sea
type composite fiber during molten composite spinning to be
preferably from 4 to 4,000 islands/fiber, and more preferably from
10 to 1,000 islands/fiber.
[0114] The above islands-in-the-sea type composite fiber is cooled
in a cooling device, following which a suction apparatus such as an
air jet nozzle is used to draw the fiber with a high-speed stream
of air at a velocity equivalent to the take-up speed of 1,000 to
6.000 m/min in such a way as to achieve the target fineness. Next,
the drawn composite fibers are deposited onto a movable collecting
surface, thereby forming a filament web. At this time, if
necessary, the deposited filament web may be subjected to localized
pressure bonding. A basis weight for the fiber web in a range of
from 20 to 500 g/m.sup.2 enables a uniform ultrafine
fiber-entangled body to be obtained, and is also desirable from an
industrial standpoint.
[0115] (2) Web Entangling Step
[0116] Next, the web entangling step in which a sheet of entangled
webs is formed by stacking and entangling a plurality of the above
filament webs is described.
[0117] An entangled web sheet is formed by using a known nonwoven
fabric manufacturing process such as needlepunching or
hydroentanglement to carry out an entangling treatment on the
filament webs. By way of illustration, a description is given below
of the entangling treatment by needlepunching.
[0118] First, a silicone finish or a mineral oil finish, such as a
needle break preventing finish, an antistatic finish or an
entanglement enhancing finish, is applied to the filament web. To
reduce variations in the basis weight, the finish may be applied
after superimposing two or more fiber webs in a crosslapped
manner.
[0119] Next, the entangling treatment is carried out in which the
fibers are three-dimensionally entangled by needlepunching. By
carrying out the needlepunching treatment, an entangled web sheet
which has a high fiber density and does not readily shed fibers can
be obtained. The basis weight of the entangled web sheet is
suitably selected in accordance with the thickness and other
properties of the target polishing pad. For example, a basis weight
in a range of 100 to 1500 g/m.sup.2 is desirable from the
standpoint of excellent handleability.
[0120] The type and amount of the finish, and the needle conditions
(e.g., needle shape, needle depth, punch density) in needlepunching
are suitably selected in such a way as to give the entangled web
sheet a high delamination strength between the layers of the sheet.
The higher number of barbs is preferable within a range where
needle breakage does not arise. By way of illustration, the number
of barbs may be selected from among 1 to 9 barbs. The needle depth
is preferably set in such a way that the barbs penetrate to the
surface of the stacked webs and within a range where the pattern
after needlepunching does not emerge strongly on the web surface.
Also, the needle punch density is adjusted according to such
factors as the shape of the needles and the type and amount of the
finish used, although a density of from 500 to 5,000
punches/cm.sup.2 is preferred. Carrying out the entangling
treatment in such a way that the ratio of the basis weight
following the entangling treatment to the basis weight before the
entangling treatment is 1.2 or more, and especially 1.5 or more, is
preferable from the standpoint of obtaining an ultrafine
fiber-entangled body having a high fiber density and reducing the
shedding of fibers. The upper limit is not subject to any
particular limitation, although the ratio of 4 or less is
preferable to avoid increased production costs due to a decrease in
throughput.
[0121] If the polishing pad is to be used for polishing bare
silicon wafers, it is preferable to set the void volume of the
polishing pad to at least 50%. For this reason, the amount of
polymeric elastomer filled into the polishing pad may be adjusted
depending on whether the fiber density is to be increased or
decreased.
[0122] A delamination strength for the entangled web sheet of at
least 2 kg/2.5 cm, and especially at least 4 kg/2.5 cm, is
desirable for obtaining an ultrafine fiber-entangled body which has
a good shape retention, sheds few fibers, and has a high fiber
density. The delamination strength serves as an indicator of the
degree of three-dimensional entangling. In cases where the
delamination strength is too low, the ultrafine fiber-entangled
body will not have a sufficiently high fiber density. The upper
limit in the delamination strength of the entangled nonwoven fabric
is not subject to any particular limitation; however, from the
standpoint of the entangling treatment efficiency, it is preferably
not more than 30 kg/2.5 cm.
[0123] For the purpose of adjusting the hardness of the polishing
pad, it is possible, insofar as the advantageous effects of the
invention are attainable, to use as the sheet of entangled webs a
laminated structure such as an entangled nonwoven fabric that has
been entangled and thereby united with a knit or woven fabric
(e.g., knit or woven fabric/entangled nonwoven fabric, entangled
nonwoven fabric/knit or woven fabric/entangled nonwoven fabric).
Such a laminated structure is obtained by carrying out an
entangling treatment wherein a knit or woven fabric composed of
ultrafine fibers is additionally superimposed on the sheet of
entangled webs (a nonwoven fabric) obtained as described above and
subjected to needlepunching and/or hydroentanglement.
[0124] The ultrafine fibers making up such a knit or woven fabric
are not subject to any particular limitation. Specifically,
examples preferably used include polyester fibers formed from
polyethylene terephthalate (PET), polytrimethylene terephthalate,
polybutylene terephthalate (PBT) or a polyester elastomer;
polyamide fibers formed from polyamide 6, polyamide 66, aromatic
polyamides or polyamide elastomers; and urethane polymers, olefin
polymers and acrylonitrile polymers. Of these, fibers formed of
PET, PBT, polyamide 6, polyamide 66 or the like are preferred from
an industrial standpoint.
[0125] Specific examples of the component removed from the
islands-in-the-sea type composite fibers which form the above knit
or woven fabric include polystyrene and copolymers thereof,
polyethylene, PVA resins, copolymeric polyester and copolymeric
polyamide. Of these, the use of a PVA resin is preferred on account
of the large shrinkage that arises at the time of removal by
dissolution.
[0126] (3) Wet Heat Shrinkage Treatment Step
[0127] Next, the wet heat shrinkage treatment step for increasing
the fiber density and degree of entanglement in the sheet of
entangled webs by subjecting the sheet to wet heat shrinkage is
described. In this step, subjecting the entangled web sheet
containing filaments to wet heat shrinkage enables a considerable
shrinkage compared with when an entangled web sheet containing
staple fibers is subjected to wet heat shrinkage, thereby resulting
in a particularly high fiber density for the ultrafine fibers.
[0128] The wet heat shrinkage treatment is preferably carried out
by steam heating. The steam heating conditions preferably entail a
heat treatment at an ambient temperature in a range of 60 to
130.degree. C. and a relative humidity of at least 75%, more
preferably at least 90%, for a period of 60 to 600 seconds. Such
heating conditions are preferable because the entangled web sheet
can be shrunk at a high shrinkage ratio. If the relative humidity
is too low, water in contact with the fibers will rapidly dry, as a
result of which shrinkage may be inadequate.
[0129] It is desirable for the wet heat shrinkage treatment to
shrink the entangled web sheet by a surface area shrinkage ratio of
at least 30%, preferably at least 35%, and more preferably at least
400/o. By inducing the shrinkage at such a high shrinkage ratio, a
high fiber density can be achieved. The upper limit in the surface
area shrinkage ratio is not subject to any particular limitation.
However, from the standpoint of the shrinkage limit and the
treatment efficiency, a shrinkage ratio of up to about 80% is
preferred.
[0130] The surface area shrinkage ratio (%) is calculated from the
following formula (1):
[(surface area of sheet side before shrinkage treatment-surface
area of sheet side after shrinkage treatment)/surface area of sheet
side before shrinkage treatment].times.100 (1)
This surface area refers to the average surface area obtained from
the surface area of the front side of the sheet and the surface
area of the back side of the sheet.
[0131] The ratio of the void volume of the entangled web sheet that
has been subjected to the wet heat shrinkage treatment in this way
can be adjusted by hot rolling or hot pressing the sheet at or
above the heat distortion temperature of the islands-in-the-sea
type composite fiber. By making the hot pressing conditions
stronger, it is possible to increase the fiber density and achieve
greater compactness.
[0132] It is desirable for the change in the basis weight of the
entangled web sheet before and after the wet heat shrinkage
treatment to be such that the basis weight following shrinkage
treatment, as compared with the basis weight before shrinkage
treatment, is at least 1.2 times (mass ratio), and more preferably
at least 1.5 times, but not more than 4 times, and more preferably
not more than 3 times.
[0133] (4) Fiber Bundle-Binding Step
[0134] Prior to carrying out an ultrafine fiber-forming treatment
on the entangled web sheet, for the purpose of increasing the shape
stability of the entangled web sheet, or for the purpose of
adjusting or reducing the void volume of the resulting polishing
pad, if necessary, the fiber bundles may be bonded beforehand by
impregnating the shrinkage-treated entangled web sheet with an
aqueous liquid of the polymeric elastomer and dry coagulating the
elastomer.
[0135] In this step, the polymeric elastomer is filled into the
entangled web sheet by impregnating the shrinkage-treated entangled
web sheet with an aqueous liquid of the polymeric elastomer and dry
coagulating the elastomer. Because the aqueous liquid of the
polymeric elastomer has a low viscosity even at high
concentrations, and also has an excellent penetrability during
impregnation, a high degree of filling at the interior of the
entangled web sheet is easily achieved. It also has an excellent
adherence to the fibers. Therefore, by carrying out this step, it
is possible to tightly restrain the islands-in-the-sea type
composite fibers.
[0136] As used herein, "aqueous liquid of elastomeric polymer"
refers to an aqueous solution obtained by dissolving the polymeric
elastomer-forming ingredients in an aqueous solvent, or an aqueous
dispersion obtained by dispersing the polymeric elastomer-forming
ingredients in an aqueous medium. Here, "aqueous dispersion"
includes suspension type dispersions and emulsion type dispersions.
The use of the aqueous dispersion is especially preferred on
account of the excellent water resistance.
[0137] The method of preparing the polyurethane resin as the
aqueous solution or the aqueous dispersion is not subject to any
particular limitation. Use may be made of a known method, such as a
method wherein the polyurethane resin is imparted with
dispersibility in an aqueous medium by including therein a monomer
unit having a hydrophilic group such as a carboxylic group, a
sulfonic acid group or a hydroxyl group, or a method wherein a
surfactant is added to the polyurethane resin so as to emulsify or
suspend the resin. Because such aqueous polymeric elastomers have
an excellent water-wettability, they have an excellent ability to
retain the abrasive, both uniformly and in a large amount.
[0138] Illustrative examples of surfactants that may be used in
such emulsification or suspension include anionic surfactants such
as sodium lauryl sulfate, ammonium lauryl sulfate, sodium
polyoxyethylene tridecyl ether acetate, sodium dodecylbenzene
sulfonate, sodium alkyldiphenyl ether disulfonate and sodium
dioctylsulfosuccinate; and nonionic surfactants such as
polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl
ether, polyoxyethylene lauryl ether, polyoxyethylene stearyl ether
and polyoxyethylene-polyoxypropylene block copolymer. Moreover, a
so-called reactive surfactant which has reactivity may also be
used. It is also possible, by suitably selecting the cloud point of
the surfactant, to impart thermosensitive gelling properties to the
polyurethane resin. However, when a large amount of surfactants is
used, this sometimes has adverse effects on the polishing
performance and the polishing stability over time. Hence, it is
preferable to keep the amount of surfactants used to the minimum
required.
[0139] By setting the solids concentration of the aqueous liquid of
the polymeric elastomer to at least 10 mass %, and preferably at
least 15 mass %, the void volume ratio can be reduced.
[0140] Examples of methods for impregnating the aqueous liquid of
the polymeric elastomer into the entangled web sheet include
methods involving the use of a knife coater, bar coater or roll
coater, and dipping methods.
[0141] The polymeric elastomer may then be coagulated by drying the
entangled web sheet into which the aqueous liquid of the polymeric
elastomer has been impregnated. Examples of drying methods include
methods which involve a heat treatment in a drying device at 50 to
200.degree. C., and methods wherein infrared heating is followed by
a heat treatment in a drying device.
[0142] In cases where the entangled web sheet is dried after the
aqueous liquid of the polymeric elastomer has been impregnated into
the entangled web sheet, a uniform filled state sometimes cannot be
achieved on account of migration of the aqueous liquid to the
surface layer of the entangled web sheet. In such cases, the
migration can be suppressed by, for example, adjusting the particle
size of the polymeric elastomer in the aqueous liquid; adjusting
the type and amount of ionic groups on the polymeric elastomer, or
adjusting the stability thereof by means of the pH or the like; or
lowering the water dispersion stability at about 40 to 100.degree.
C. through the concomitant use of a monovalent or divalent alkali
metal salt or alkaline earth metal salt, a nonionic emulsifying
agent, an associative water-soluble thickening agent, an
associative thermosensitive gelling agent such as a water-soluble
silicone compound, a water-soluble polyurethane compound, or an
organic or inorganic substance which changes the pH under the
effect of heating. If necessary, the migration may be induced so
that the polymeric elastomer is preferentially distributed in the
surface.
[0143] (5) Ultrafine Fiber-Forming Step
[0144] Next, the ultrafine fiber-forming step, which is a step in
which ultrafine fibers are formed by dissolving the water-soluble
thermoplastic resin in hot water, is described.
[0145] This is a step in which ultrafine fibers are formed by
removing the water-soluble thermoplastic resin. At this time, voids
are formed in areas where the water-soluble thermoplastic resin in
the entangled web sheet has been dissolved and extracted. The
polymeric elastomer is filled into these voids in the subsequent
polymeric elastomer filling step, as a result of which the
ultrafine fibers converge as bundles, and the bundles of ultrafine
fibers are restrained.
[0146] The ultrafine fiber-forming treatment is a treatment in
which the entangled web sheet, or a composite of the entangled web
sheet with the polymeric elastomer, is subjected to hot-water heat
treatment with water, an alkaline aqueous solution, an acidic
aqueous solution or the like so as to dissolve and remove, or
decompose and remove, the water-soluble thermoplastic resin.
[0147] In a preferred example of the hot-water heat treatment
conditions, a first stage consisting of 5 to 300 seconds of
immersion in 65 to 90.degree. C. hot water is followed by a second
stage consisting of 100 to 600 seconds of treatment in 85 to
100.degree. C. hot water. Also, to increase the dissolution
efficiency, if necessary, nipping treatment with rollers,
high-pressure water jet treatment, ultrasonic treatment, shower
treatment, agitation treatment, rubbing treatment or the like may
be carried out.
[0148] In this step, when the water-soluble thermoplastic resin
dissolves from the islands-in-the-sea type composite fibers to form
the ultrafine fibers, the ultrafine fibers undergo considerable
shrinkage. Because the fiber density rises through such shrinkage,
the ultrafine fiber-entangled body having a high-density is
obtained.
[0149] (6) Polymeric Elastomer Filling Step
[0150] Next, a step is described wherein, by filling the polymeric
elastomer into the interior of the ultrafine fiber bundles formed
of the ultrafine fibers, the ultrafine fibers are made to converge
as bundles, in addition to which the individual ultrafine fiber
bundles are restrained and, moreover, the ultrafine fiber bundles
are bound to each other.
[0151] In the ultrafine fiber-forming step (5), by subjecting the
islands-in-the-sea type composite fibers to ultrafine fiber-forming
treatment, the water-soluble thermoplastic resin was removed,
resulting in the formation of voids at the interior of the
ultrafine fiber bundles. In the present step, by suitably filling
such voids with the polymeric elastomer, the ultrafine fibers are
made to converge as bundles, in addition to which the individual
ultrafine fiber bundles are restrained and the ultrafine fiber
bundles are bound to each other, which makes it possible to set the
void volume ratio in the polishing pad to, for example, 50% or
less. Also, by filling with the polymeric elastomer to a sufficient
degree, the void volume ratio is lowered, making it possible to
give the polishing pad a dense structure. Moreover, when the
ultrafine fibers are formed into ultrafine fiber bundles, the
aqueous fluid of the polymeric elastomer readily impregnates
therein by way of a capillary effect, further facilitating the
convergence of the ultrafine fibers into bundles and the restraint
of the ultrafine fiber bundles.
[0152] The aqueous liquids of the polymeric elastomer that may be
used in this step are the same as the aqueous liquids of polymeric
elastomers that were mentioned above in the fiber bundle-binding
step (4).
[0153] A method similar to that used in the fiber bundle-binding
step (4) may be suitably used in the present step as the method of
filling the polymeric elastomer into the interior of the ultrafine
fiber bundles formed of ultrafine fibers. In addition, the void
volume ratio may be adjusted to the desired value by suitably
combining the fiber bundle-binding step (4) and the polymeric
elastomer filling step (6). In this way, the polishing pad is
formed.
[0154] Post-Treatment of Polishing Pad
[0155] If necessary, the polishing pad obtained may be subjected to
a post-treatment, such as molding, flattening, napping, lamination,
surface treatment and washing.
[0156] The molding and flattening are treatments wherein the
polishing pad obtained is hot-press molded to a given thickness, or
is cut to a given outside shape by grinding. The polishing pad is
preferably ground to a thickness of about 0.5 to 3 mm.
[0157] The napping refers to a treatment in which a mechanical
frictional force or abrasive force is applied to the surface of the
polishing pad by means of sandpaper, card clothing, a diamond
dresser or the like so as to separate the ultrafine fibers that
have been made to converge into bundles. By the napping, the fiber
bundles existing in the polishing pad surface are fibrillated to
form a large number of ultrafine fibers on the surface.
[0158] The lamination refers to a treatment in which the stiffness
is adjusted by superimposing and laminating the resulting polishing
pad on a backing material. For example, by laminating the polishing
pad together with an elastomer sheet having a low hardness, the
global planarity of the surface being polished (the planarity of
the overall substrate being polished) can be further increased.
Adhesion during such lamination may be melt adhesion or adhesion
using a non-pressure-sensitive adhesive or a pressure-sensitive
adhesive. Illustrative examples of such backing materials include
sheet-like backing materials, such as elastic sponge bodies
obtained from polyurethane or the like; nonwoven fabrics
impregnated with polyurethane (such as the product available from
Nitta Haas Inc. under the trade name Suba 400); elastomeric resin
films composed of a rubber such as natural rubber, nitrile rubber,
polybutadiene rubber or silicone rubber, or a thermoplastic
elastomer such as polyester thermoplastic elastomer, polyamide
thermoplastic elastomer or fluorinated thermoplastic elastomer;
foamed plastics; and knit fabrics or woven fabrics.
[0159] The surface treatment refers to a treatment in which grooves
or holes in the form of a grid, concentric circles or spirals are
formed on the surface of the polishing pad in order to adjust the
ability to retain and the ability to discharge the abrasive
slurry.
[0160] The cleaning refers to a treatment of cleaning away
impurities such as particles and metal ions which adhere to the
resulting polishing pad by using cold water or warm water, or to a
cleaning treatment with an aqueous solution or solvent containing
an additive which has a cleansing action, such as a surfactant.
[0161] The polishing pad of the present embodiment is preferably
used for polishing silicon wafers, compound semiconductor wafers,
semiconductor wafers, semiconductor devices, liquid crystal
members, optical components, quartz, optical substrates, electronic
circuit substrates, electronic circuit mask substrates, multilayer
wiring substrates, hard disks, and microelectromechanical system
(MEMS) substrates. Because the polishing pad of the embodiment has
the void volume ratio that has been set to at least 50%, it is
particularly effective for polishing bare silicon wafers.
[0162] Specific examples of semiconductor wafers and semiconductor
devices include dielectric films made of silicon, silicon oxide,
silicon oxyfluoride and organic polymers; wiring metal films made
of copper, aluminum or tungsten; and barrier metal films made of
tantalum, titanium, tantalum nitride or titanium nitride.
[0163] In polishing, the polishing pad may be used in any polishing
step, such as primary polishing, secondary polishing (adjustment
polishing), finish polishing and mirror polishing. Portions to be
polished may be the front, rear or end surface of a substrate.
EXAMPLES
[0164] The invention is illustrated more concretely below with
examples, although the invention is not limited in any way by the
examples.
Example 1
[0165] Islands-in-the-sea type composite fibers were formed by
discharging a water-soluble thermoplastic polyvinyl alcohol resin
(abbreviated below as "PVA resin") and an isophthalic acid-modified
polyethylene terephthalate having a degree of modification of 6 mol
% (having a water absorption ratio when saturated with water at
50.degree. C. of 1 mass % and a glass transition temperature of
77.degree. C.; abbreviated below as "modified PET") in a mass ratio
of 20:80 from a spinneret for melt spinning composite fibers. The
spinneret produced composite fibers having 50 islands/fiber, and
the spinneret temperature was 260.degree. C. The ejector pressure
was adjusted so as to give a spinning speed of 4,000 m/min, and
filaments having an average fineness of 2.0 dtex was collected on a
net, thereby giving a spunbonded sheet (filament web) with a basis
weight of 40 g/m.sup.2.
[0166] Twelve of the resulting spunbonded sheets were superimposed
in a crosslapped arrangement to produce a stack of webs having a
total basis weight of 480 g/m.sup.2. A needle break-preventing oil
agent was then sprayed onto the resulting stacked webs. Next, using
1-barb 42-gauge needles and 6-barb 42-gauge needles, the stacked
webs were entangled by needlepunching at 1800 punches/cm.sup.2,
thereby giving a sheet of entangled webs. The entangled web sheet
thus obtained had a basis weight of 750 g/m.sup.2. The surface area
shrinkage due to the needlepunching treatment was 35%.
[0167] Next, the resulting entangled web sheet was steam-treated
for 90 seconds at 70.degree. C. and 90% RH. The surface area
shrinkage at this time was 40%. The sheet was then dried in a
140.degree. C. oven and subsequently hot pressed at 140.degree. C.
to give an entangled web sheet having a basis weight of 1,250
g/m.sup.2, an apparent density of 0.65 g/cm.sup.3 and a thickness
of 1.9 mm. The entangled web sheet had a thickness after hot
pressing which was 0.80 times as thick as the sheet prior to hot
pressing.
[0168] Next, the hot-pressed entangled web sheet was impregnated
with an aqueous dispersion of polyurethane elastomer A (solids
concentration, 20 mass %) as the first polyurethane elastomer.
Polyurethane elastomer A was a noncrystalline polycarbonate-based
non-yellowing-type polyurethane resin which was prepared by
polymerizing 55 mass % of, as the soft component, a polyol
component obtained by mixing a noncrystalline polycarbonate polyol
(a copolymeric polyol composed of 3-methyl-1,5-pentylene carbonate
and hexamethylene carbonate) and a polyalkylene glycol having 2 to
3 carbons in a molar ratio of 99.7:0.3 and adding to the mixture
1.5 mass % of a carboxylic group-containing monomer
(2,2-bis(hydroxymethyl)propionic acid), with
4,4'-dicyclohexylmethane diisocyanate, a short-chain polyamine and
a short-chain polyol as the hard components. The water absorption
ratio of polyurethane elastomer A was 3 mass %, the storage modulus
at 23.degree. C. was 300 MPa, the storage modulus at 50.degree. C.
was 150 MPa, the glass transition temperature was -20.degree. C.
and the average particle size of the aqueous dispersion was 0.03
.mu.m. The amount of adherent solids of the aqueous dispersion at
this time was 10 mass % with respect to the mass of the entangled
web sheet. The entangled web sheet impregnated with the aqueous
dispersion was subjected to dry coagulation treatment at 90.degree.
C. and 50% RH, then dried at 140.degree. C. The dried sheet was
then hot-pressed at 140.degree. C., giving a sheet having a basis
weight of 1,370 g/m.sup.2, an apparent density of 0.76 g/cm.sup.3
and a thickness of 1.8 mm.
[0169] Next, the entangled web sheet filled with polyurethane
elastomer A was treated with nip rollers, then immersed for 10
minutes in 95.degree. C. hot water while being subjected to
high-pressure water jet treatment so as to dissolve and remove the
PVA resin. This was followed by drying, thereby giving a composite
of polyurethane elastomer A with an ultrafine fiber-entangled body,
in which the composite was composed of ultrafine fibers having an
average fineness of 0.05 dtex, and had a basis weight of 1,220
g/m.sup.2, an apparent density of 0.66 g/cm.sup.3 and a thickness
of 1.85 mm.
[0170] This composite was then impregnated with an aqueous
dispersion of polyurethane elastomer B (solid concentration, 30
mass %) as the second polyurethane elastomer. Polyurethane
elastomer B was a polyurethane resin prepared by using 100 parts by
mass of a polycarbonate-based non-yellowing-type polyurethane
resin, adding 5 parts by mass of a carbodiimide crosslinking agent,
and heat treating so as to form a crosslinked structure, in which
the polycarbonate-based non-yellowing-type polyurethane resin was
obtained by polymerizing 50 mass % of the soft component obtained
by mixing a noncrystalline polycarbonate polyol (a copolymeric
polyol composed of hexamethylene carbonate and pentamethylene
carbonate) and a polyalkylene glycol having 2 to 3 carbons in a
molar ratio of 99.9:0.1, and adding to the mixture 1.5 mass % of a
carboxylic group-containing monomer
(2,2-bis(hydroxymethyl)propionic acid), with
4,4'-dicyclohexylmethane diisocyanate, a short-chain amine and a
short-chain diol as the hard components. The water absorption ratio
for polyurethane elastomer B was 2 mass %, the storage modulus at
23.degree. C. was 450 MPa, the storage modulus at 50.degree. C. was
300 MPa, the glass transition temperature was -25.degree. C. and
the average particle size of the aqueous dispersion was 0.05 .mu.m.
The amount of adherent solids of the aqueous dispersion at this
time was 15 mass % with respect to the mass of the composite. Next,
the composite impregnated with the aqueous dispersion was subjected
to coagulation treatment at 90.degree. C. and 50% RH, then to
drying treatment at 140.degree. C. The dried composite was then
hot-pressed at 140.degree. C., giving a polishing pad precursor.
The resulting polishing pad precursor had a basis weight of 1,390
g/m.sup.2, an apparent density of 0.80 g/cm.sup.3 and a thickness
of 1.75 mm.
[0171] In the polishing pad precursor thus obtained, all 50 fibers
of the ultrafine fibers making up each fiber bundle converged as a
bundle. Moreover, the polymeric elastomer was present at the
interior of the ultrafine fiber bundles, and restrained the
bundles.
[0172] The resulting polishing pad precursor was subjected to
grinding treatment to flatten the surface, thereby giving a
flattened pad having a basis weight of 1,120 g/m.sup.2, an apparent
density of 0.80 g/cm.sup.3 and a thickness of 1.4 mm. In addition,
the pad was cut into circular shapes having a diameter of 51 cm,
following which grooves having a width of 2.0 mm and a depth of 1.0
mm were formed in a grid at 15.0 mm intervals on the surface,
thereby giving circular polishing pads. The mass ratio of the
ultrafine fiber-entangled body to the polyurethane elastomer was
76/24, and the ratio of polymeric elastomer A to polymeric
elastomer B was 40/60. The resulting polishing pads were evaluated
by the below-described methods. The results are shown in Table
1.
Example 2
[0173] The same procedure as in Example 1 was carried out up to the
production of the entangled web sheet. After being hot-pressed
without being impregnated with polyurethane elastomer A, the
entangled web sheet was then immersed for 10 minutes in 95.degree.
C. hot water and the PVA resin was dissolved and removed, thereby
giving an ultrafine fiber-entangled body composed of bundles of
ultrafine fibers. The resulting ultrafine fiber-entangled body was
then impregnated with an aqueous dispersion of polyurethane
elastomer B (solids concentration, 40 mass %). At this time, the
amount of adherent solids of the aqueous dispersion was 20 mass %
with respect to the mass of the ultrafine fiber-entangled body.
Next, the ultrafine fiber-entangled body impregnated with the
aqueous dispersion was coagulated at 90.degree. C. and 50% RH. This
was followed by drying treatment at 140.degree. C., then hot
pressing at 140.degree. C. thereby giving a polishing pad
precursor. The resulting polishing pad precursor was post-treated
in the same way as in Example 1, giving a flattened pad having a
basis weight of 1,080 g/m.sup.2, an apparent density of 0.77
g/cm.sup.3 and a thickness of 1.4 mm. Following a treatment to form
grooves, circular polishing pads were obtained. In the resulting
polishing pads, all 50 fibers of the ultrafine fibers making up
each fiber bundle converged as a bundle. Moreover, the polymeric
elastomer was present at the interior of the ultrafine fiber
bundles, and restrained the bundles. The resulting polishing pads
were evaluated by the below-described methods. The results are
shown in Table 1.
Example 3
[0174] Aside from not carrying out the hot pressing treatment
before the impregnation of polyurethane elastomer A and also not
carrying the hot pressing treatment after impregnation and drying,
polishing pads were obtained in the same way as in Example 1.
[0175] The polishing pad precursor thus obtained had a basis weight
of 1,360 g/m.sup.2, an apparent density of 0.62 g/cm.sup.3 and a
thickness of 2.2 mm, in addition to which the mass ratio of the
ultrafine fiber-entangled body to the polyurethane elastomer was
70/30. In the resulting polishing pad precursor, all 50 fibers of
the ultrafine fibers making up each fiber bundle converged as a
bundle. Moreover, the polymeric elastomer was present at the
interior of the ultrafine fiber bundles, and restrained the
bundles. Polishing pads obtained by carrying out flattening and
groove-forming treatment in the same way as in Example 1 were
evaluated by the below-described methods. The results are shown in
Table 1.
Example 4
[0176] Aside from the use as the first polyurethane elastomer of,
instead of polyurethane elastomer A, a polycarbonate-based
non-yellowing-type polyurethane elastomer C (water absorption
ratio, 4%; storage modulus at 23.degree. C., 250 MPa; storage
modulus at 50.degree. C., 100 MPa; glass transition temperature,
-30.degree. C.; average particle size of aqueous dispersion, 0.03
.mu.m) obtained by polymerizing 58 mass % of, as the soft
component, a polyol component composed of a polyether-based
polyalkylene glycol mixed with a polycarbonate polyol in a molar
ratio of 88:12 and additionally containing 1.2 mass % of a
carboxylic group-containing monomer
(2,2-bis(hydroxymethyl)propionic acid), with isophorone
diisocyanate, a short-chain polyamine and a short-chain polyol as
the hard components; and aside from the use as the second
polyurethane elastomer of, instead of polyurethane elastomer B, a
polyurethane elastomer D (water absorption ratio, 4%; storage
modulus at 23.degree. C., 300 MPa, storage modulus at 50.degree.
C., 125 MPa; glass transition temperature, -30.degree. C.; average
particle size of aqueous dispersion, 0.05 .mu.m) obtained by
increasing the polyol component of polyurethane elastomer B by 10
mass % to set the amount of the polyol component relative to the
polyurethane elastomer at 60 mass %, polishing pads were produced
in the same way as in Example 1. In the resulting polishing pads,
all 50 fibers of the ultrafine fibers making up each fiber bundle
converged as a bundle. Moreover, the polymeric elastomer was
present at the interior of the ultrafine fiber bundles, and
restrained the bundles. The resulting polishing pads were evaluated
by the below-described methods. The results are shown in Table
1.
Example 5
[0177] Aside from carrying out melt spinning by discharging a PVA
resin and a modified PET in a mass ratio of 20:80 from a spinneret
having 9 islands/fiber, polishing pads were obtained in the same
way as in Example 1. The average fineness of the ultrafine fibers
was 0.28 dtex. In the resulting polishing pads, all 9 fibers of the
ultrafine fibers making up each bundle converged as a bundle.
Moreover, the polymeric elastomer was present at the interior of
the ultrafine fiber bundles, and restrained the bundles. The
resulting polishing pads were evaluated by the below-described
methods. The results are shown in Table 1.
Example 6
[0178] Aside from changing as follows the polishing conditions in
the below-described polishing pad evaluations, the polishing
performance was evaluated in the same way using the polishing pads
obtained in Example 1. The polishing conditions were as
follows.
[0179] (1) Aside from changing the silicon wafer having an oxide
film to a bare silicon wafer and changing the slurry used in
polishing to Glanzox 1103, available from Fujimi Incorporated,
evaluation was carried out in the same way.
[0180] (2) Aside from changing the slurry used in polishing to the
polishing slurry GPL-C1010, available from Showa Denko KK, and
changing the slurry flow rate to 200 mL, evaluation was carried out
in the same way.
[0181] (3) Aside from changing the wafer to a tungsten wafer and
changing the slurry used in polishing to W-2000, available from
Cabot Corporation (34 g of hydrogen peroxide added per 1,030 g of
slurry), evaluation was carried out in the same way.
[0182] (4) Aside from changing the wafer to a GaAs wafer, changing
the slurry used in polishing to INSEC-FP, available from Fujimi
Incorporated, and changing the polishing pressure to 20 kPa,
evaluation was carried out in the same way.
[0183] The results are shown in Table 3.
Example 7
[0184] The same procedure as in Example 1 was carried out up to the
impregnation of polyurethane elastomer A to the interior of a
hot-pressed entangled web sheet (basis weight, 1,280 g/m.sup.2;
apparent density, 0.56 g/cm.sup.3; thickness, 2.3 mm) and the
subsequent dry-coagulation. A sheet having a basis weight of 1,340
g/m.sup.2, an apparent density of 0.69 g/cm.sup.3 and a thickness
of 1.95 mm was obtained without carrying out hot pressing.
[0185] Next, the entangled web sheet filled with polyurethane
elastomer A was treated with nip rollers, then immersed in
95.degree. C. hot water for 10 minutes while being
high-pressure-water jet treated so as to dissolve and remove the
PVA resin, and subsequently dried, thereby giving a composite of
polyurethane elastomer A and an ultrafine fiber-entangled body in
which the composite had the average fineness of the ultrafine
fibers of 0.05 dtex, a basis weight of 1.050 g/m.sup.2, an apparent
density of 0.57 g/cm.sup.3 and a thickness of 1.85 mm.
[0186] This composite was then impregnated with polyurethane
elastomer B as the second polyurethane elastomer, following which
the elastomer was dry-coagulated, and hot pressing was not carried
out, thereby giving a polishing pad precursor. The polishing pad
precursor had a basis weight of 1,170 g/m.sup.2, an apparent
density of 0.60 g/cm.sup.3 and a thickness of 1.95 mm.
[0187] The polishing pad precursor was then subjected to grinding
treatment for surface flattening, thereby giving a flattened pad
having a basis weight of 1,000 g/m.sup.2, an apparent density of
0.57 g/cm.sup.3 and a thickness of 1.75 mm. This pad was cut into
circular shapes having a diameter of 51 cm, and grooves with a
width of 2.0 mm and a depth of 1.0 mm were formed in a grid on the
surface at intervals of 15.0 mm, thereby giving circular polishing
pads. The mass ratio of the ultrafine fiber-entangled body to the
polyurethane elastomer was 76/24, and the ratio of polymeric
elastomer A to polymeric elastomer B was 40/60. The resulting
polishing pads were evaluated by the below-described methods. The
results are shown in Table 1.
Example 8
[0188] Aside from changing in the same way in (1) to (3) of Example
6 the polishing conditions in the below-described polishing pad
evaluations, the polishing performance was evaluated in the same
way using the polishing pads obtained in Example 7.
[0189] The results are shown in Table 4.
Comparative Example 1
[0190] Ny filaments having an average fineness of 2 dtex were
melt-spun by melt-spinning Ny 6. The resulting filaments were
collected on a net, thereby giving a spunbonded sheet (filament
web) having a basis weight of 30 g/m.sup.2.
[0191] Stacked webs were formed in the same way as in Example 2
from the resulting spunbonded sheet. Next, the resulting stacked
webs were entangled by needlepunching in the same way as in Example
1, thereby giving an entangled web sheet. The resulting entangled
web sheet had a basis weight of 800 g/m.sup.2. Hot pressing at
140.degree. C. was then carried out, thereby giving an entangled
web sheet having an apparent density of 0.42 g/cm.sup.3 and a
thickness of 1.9 mm.
[0192] Next, an aqueous dispersion of polyurethane elastomer B
(solids concentration, 30 mass %) was impregnated into the
hot-pressed entangled web sheet. The amount of adherent solids of
the aqueous dispersion at this time was 20 mass % with respect to
the mass of the entangled web sheet. The entangled web sheet
impregnated with the aqueous dispersion was then subjected to
coagulation treatment at 90.degree. C. and 90% RH, and also
subjected to drying treatment at 140.degree. C., after which hot
pressing treatment was carried out at 140.degree. C., thereby
giving a polishing pad precursor having a basis weight of 920
g/m.sup.2, an apparent density of 0.54 g/m.sup.2 and a thickness of
1.7 mm. Buffing treatment was then carried out to flatten the front
and back faces, thereby giving a polishing pad. The resulting
polishing pad was evaluated by the below-described methods. The
results are shown in Table 2.
Comparative Example 2
[0193] Instead of using an aqueous dispersion of polyurethane
elastomer A to form a polyurethane elastomer, an aqueous dispersion
of polyurethane elastomer E (solids concentration, 20 mass %) was
impregnated as the polymeric elastomer. Polyurethane elastomer E
was a non-yellowing-type polyurethane resin obtained by
polymerizing a polyol (60 mass % relative to the polyurethane
elastomer) composed of polyethylene glycol and polytetramethylene
glycol in a 15/85 mixture with isophorone diisocyanate, a
short-chain polyamine and a short-chain polyol as the hard
components. Polyurethane elastomer E had a water absorption ratio
of 12 mass %, a storage modulus at 23.degree. C. of 200 MPa, a
storage modulus at 50.degree. C. of 80 MPa, a glass transition
temperature of -48.degree. C., and an average particle size in the
aqueous dispersion of 0.4 .mu.m. Aside from this, polishing pads
were produced in the same way as in Example 2. The resulting
polishing pads were evaluated by the below-described methods. The
results are shown in Table 2.
Comparative Example 3
[0194] Aside from using polyurethane elastomer F (water absorption
ratio, 8%; storage modulus at 23.degree. C., 80 MPa, storage
modulus at 50.degree. C., 30 MPa; glass transition temperature,
-32.degree. C.; average particle size of aqueous dispersion, 0.02
.mu.m) obtained by increasing the polyol component of polyurethane
elastomer B to 65 mass %, polishing pads were produced in the same
way as in Example 2. The resulting polishing pads were evaluated by
the below-described methods. The results are shown in Table 2.
Comparative Example 4
[0195] Aside from the use of polyurethane elastomer G (water
absorption ratio, 1%; storage modulus at 23.degree. C., 1,000 MPa,
storage modulus at 50.degree. C., 200 MPa; glass transition
temperature, 0.degree. C.; average particle size of aqueous
dispersion, 0.08 m) obtained by changing the polyol component of
polyurethane elastomer B to hexamethylene carbonate diol, using 30
mass % of the soft (polyol) component and polymerizing this with
4,4'-dicyclohexylmethane diisocyanate, a short-chain amine and a
short-chain diol as the hard components, polishing pads were
produced in the same way as in Example 2. The resulting polishing
pads were evaluated by the below-described methods. The results are
shown in Table 2.
[0196] The polishing pads obtained were evaluated by the following
methods.
[0197] Evaluation Methods
[0198] (1) Average Fineness of Ultrafine Fibers, and Verification
of Converging State of Ultrafine Fibers of Fiber Bundles
[0199] The polishing pad obtained was cut in the thickness
direction with a cutter blade, thereby forming a cut face in the
thickness direction. The cut face was dyed with osmium oxide, then
examined at a magnification of 500 to 1,000.times. with a scanning
electron microscope (SEM), and the image was photographed. The
cross-sectional area of the ultrafine fibers present in the cut
face was then determined from the resulting image. This was
calculated from the average cross-sectional surface area obtained
by averaging the cross-sectional areas at 100 randomly selected
places and from the density of the resin making up the fibers. In
addition, the image obtained was observed. When not only ultrafine
fibers making up the outside edge of the fiber bundle but also
ultrafine fibers at the interior were bonded and integrally united
to each other by the polymeric elastomer, the ultrafine fibers were
judged to be "converging". When little or no polymeric elastomer
was present at the interior of the fiber bundles and the ultrafine
fibers were in a substantially unbonded and un-united state, the
ultrafine fibers were judged to be "non-converging".
[0200] (2) Storage Moduli of Polymeric Elastomer at 23.degree. C.
and 50.degree. C.
[0201] The polymeric elastomer used in the polishing pad was
prepared as film samples having a length of 4 cm, a width of 0.5 cm
and a thickness of 400 .mu.m.+-.100 .mu.m. Next, the sample
thickness was measured with a micrometer, following which a dynamic
viscoelastic analyzer (DVE Rheospectra, manufactured by Rheology
Co., Ltd.) was used to measure the dynamic viscoelastic moduli at
23.degree. C. and 50.degree. C. under the following conditions:
frequency, 11 Hz; temperature ramp-up rate, 3.degree. C./min. The
storage moduli were computed from the measured results. In cases
where two types of polymeric elastomer were used, samples of each
were prepared and measured, and the sum of the values obtained by
multiplying by the respective mass ratio was used as the storage
modulus for the polymeric elastomers.
[0202] (3) Glass Transition Temperature of Polymeric Elastomer
[0203] The polymeric elastomer used in the polishing pad was
prepared as a film having a length of 4 cm, a width of 0.5 cm and a
thickness of 400 .mu.m.+-.100 .mu.m. The sample thickness was
measured with a micrometer, following which the dynamic
viscoelasticity was measured at a frequency of 11 Hz and a
temperature ramp-up rate of 3.degree. C./min using a dynamic
viscoelastic analyzer (DVE Rheospectra, manufactured by Rheology
Co., Ltd.), and the main dispersion peak temperature of the loss
modulus was treated as the glass transition temperature. In cases
where two types of polymeric elastomer were used, samples of each
were prepared and measured, and the sum of the values obtained by
multiplying by the respective weight ratio was used as the storage
modulus for the polymeric elastomers.
[0204] (4) Water Absorption Ratio of Polymeric Elastomer upon
Saturation with Water at 50.degree. C.
[0205] A 200 .mu.m thick film obtained by drying the polymeric
elastomer at 50.degree. C. was heat-treated at 130.degree. C. for
30 minutes, then held for 3 days at 20.degree. C. and 65% RH to
form a dry sample which was immersed in 50.degree. C. water for two
days. The sample was then removed from the 50.degree. C. water,
immediately after which excess water droplets, etc. on the topmost
surface of the film were wiped off with a JK Wiper 150-S(Nippon
Paper Crecia Co., Ltd.), thereby giving a water-swollen sample. The
weights of the dry sample and the water-swollen sample were
measured, and the water absorption ratio was determined according
to the following formula.
Water absorption ratio (mass %)=[(mass of water-swollen sample-mass
of dry sample)/(mass of dry sample)].times.100
In cases where two types of polymeric elastomer were used, samples
of each were prepared and measured, and the sum of the values
obtained by multiplying by the respective weight ratio was used as
the storage modulus for the polymeric elastomers.
[0206] (5) Water Absorption Ratio of Ultrafine Fibers upon
Saturation with Water at 50.degree. C. (water absorption ratio of
thermoplastic resin making up ultrafine fibers upon saturation with
water at 50.degree. C.)
[0207] A 200 m thick film obtained by hot-pressing the
thermoplastic resin making up the ultrafine fibers at a temperature
of the melting point+20 to 100.degree. C. was heat-treated at
130.degree. C. for 30 minutes, then held for 3 days at 20.degree.
C. and 65% RH to form a dry sample, which was subsequently immersed
in 50.degree. C. water for two days. The sample was then removed
from the water, immediately after which excess water droplets, etc.
on the topmost surface of the film were wiped off with a JK Wiper
150-S(Nippon Paper Crecia Co., Ltd.), thereby giving a
water-swollen sample. The weights of the dry sample and the
water-swollen sample were measured, and the water absorption ratio
was determined according to the following formula.
Water absorption ratio (mass %)=[(mass of water-swollen sample-mass
of dry sample)/(mass of dry sample)].times.100
[0208] (6) Average Particle Size of Aqueous Polyurethane
[0209] The average particle size of the water-dispersed polymeric
elastomer was determined through measurement by dynamic light
scattering using a ELS-800 system (Otsuka Chemical Co., Ltd.) and
analysis by the cumulant method (described in Koroido kagaku
[Colloidal chemistry] Vol. IV: Koroido kagaku jikken-h
[Experimental methods in colloidal chemistry], published by Tokyo
Kagaku Dojin). In cases where two types of polymeric elastomer were
used, samples of each were measured, and the sum of the values
obtained by multiplying by the respective weight ratio was used as
the storage modulus for the polymeric elastomers.
[0210] (7) Apparent Density of Polishing Pad and Void Volume Ratio
of Polishing Pad (Volumetric Ratio of Void Areas in Polishing
Pad)
[0211] The apparent density of the polishing pad was measured in
general accordance with JIS L1096. At the same time, the
theoretical density of the composite of the ultrafine
fiber-entangled body with the polymeric elastomer in the absence of
voids was calculated from the compositional ratios of the
respective components in the polishing pad and the densities of
each of these components. In addition, the ratio of the apparent
density to the theoretical density was treated as the volumetric
ratio of the filled areas in the polishing pad, and [1-(ratio of
apparent density to theoretical density)].times.100(%) was treated
as the void volume ratio of the polishing pad (volumetric ratio of
void areas in the polishing pad). The densities of the components
used in Example 1 were as follows: modified PET, 1.38 g/cm.sup.3;
polyurethane elastomer, 1.05 g/cm.sup.3; PVA resin, 1.25
g/cm.sup.3.
[0212] (8) Evaluation of Polishing Performance by Polishing Pad
[0213] A pressure-sensitive adhesive tape was bonded to the back
side of a circular polishing pad, following which the pad was
mounted on a CMP polisher (PP0-60S, manufactured by Nomura Machine
Tool Works. Ltd.). Next, using a 200-grit diamond dresser (MEC
200L, available from Mitsubishi Materials Corporation),
conditioning (seasoning) was carried out by grinding the surface of
the polishing pad for 18 minutes at a pressure of 177 kPa and a
dresser rotational speed of 110 rpm under a flow of distilled water
at a rate of 120 mL/min.
[0214] Next, a 6-inch diameter silicon wafer having an oxide film
surface was polished for 100 seconds at a platen speed of 50 rpm, a
head speed of 49 rpm and a polishing pressure of 35 kPa while
supplying an abrasive slurry (SS 12, available from Cabot
Corporation) at a rate of 120 mL/min. The thickness after polishing
at 49 randomly selected points in the plane of the silicon wafer
having an oxide film surface was measured, and the polishing rate
(nm/min) was determined by dividing the polished thickness at each
point by the polishing time. In addition, the polishing rate (R)
was calculated as the average value of the polishing rates at the
49 points, and the standard deviation (.sigma.) was determined.
[0215] The planarity was then evaluated from the following formula.
A smaller planarity value indicates a better planarization
performance.
Planarity (%)=(.sigma./R).times.100
[0216] Next, the polishing pad used in the above polishing
operation was held in a wet state at 25.degree. C. for 24 hours,
then the polishing pad was seasoned and used again to carry out
polishing, following which the polishing rate (R) and planarity
were determined.
[0217] Seasoning and polishing were alternately repeated in this
way 300 times, and the polishing rate (R) and planarity after 300
polishing cycles were determined.
[0218] The number of scratches at least 0.16 .mu.m in size present
on the surface of the silicon wafer having an oxide film after each
polishing operation was determined using a wafer surface inspection
system (Surfscan SPI, available from KLA-Tencor), based on which
the tendency for scratching to occur was evaluated.
[0219] (9) Evaluation of Polishing Performance by Polishing Pad in
Bare Silicon Wafer Polishing
[0220] A pressure-sensitive adhesive tape was bonded to the back
side of a circular polishing pad, following which the pad was
mounted on a CMP polisher (PP0-60S, manufactured by Nomura Machine
Tool Works. Ltd.). Next, using a 200-grit diamond dresser (MEC
200L, available from Mitsubishi Materials Corporation),
conditioning (seasoning) was carried out by grinding the surface of
the polishing pad for 18 minutes at a pressure of 177 kPa and a
dresser rotational speed of 110 rpm under a flow of distilled water
at a rate of 120 mL/min.
[0221] Next, a 6-inch diameter silicon wafer was polished for 100
seconds at a platen speed of 50 rpm, a head speed of 49 rpm and a
polishing pressure of 35 kPa while supplying Glanzox 1103 (Fujimi
Incorporated) at a rate of 120 mL/min. The thickness after
polishing at 49 randomly selected points in the plane of the
silicon wafer was measured, and the polishing rate (nm/min) was
determined by dividing the polished thickness at each point by the
polishing time. In addition, the polishing rate (R) was calculated
as the average value of the polishing rates at the 49 points, and
the standard deviation (.sigma.) was determined.
[0222] The planarity was then evaluated from the following formula.
A smaller planarity value indicates a better planarization
performance.
Planarity (%)=(.sigma./R).times.100
[0223] Next, the polishing pad used in the above polishing
operation was held in a wet state at 25.degree. C. for 24 hours,
then the polishing pad was seasoned and used again to carry out
polishing, following which the polishing rate (R) and planarity
were determined.
[0224] Seasoning and polishing were alternately repeated in this
way 300 times, and the polishing rate (R) and planarity after 300
polishing cycles were determined.
[0225] The results for Examples 1 to 5 and 7 are shown in Table 1,
the results for Example 6 are shown in Table 3, the results for
Example 8 are shown in Table 4, and the results for Comparative
Examples 1 to 4 are shown in Table 2.
TABLE-US-00001 TABLE 1 Example No. 1 2 3 4 5 7 Average fineness of
ultrafine fibers dtex 0.05 0.05 0.05 0.05 0.05 0.05 Number of
ultrafine fibers of fiber number 50 50 50 50 9 50 bundles
Converging state of ultrafine fibers -- converging converging
converging converging converging converging of fiber bundles Type
of thermoplastic resin in isophthalate- isophthalate- isophthalate-
isophthalate- isophthalate- isophthalate- ultrafine fibers modified
modified modified modified modified modified polyethylene
polyethylene polyethylene polyethylene polyethylene polyethylene
terephthalate terephthalate terephthalate terephthalate
terephthalate terephthalate Glass transition temperature of
.degree. C. -23 -25 -23 -30 -23 -23 polymeric elastomer Water
absorption ratio of polymeric mass % 2.4 2 2.4 4 2.4 2.4 elastomer
upon saturation (50.degree. C.) Storage modulus of polymeric MPa
390 450 390 280 390 390 elastomer at 23.degree. C. Storage modulus
of polymeric MPa 240 300 240 115 240 240 elastomer at 50.degree. C.
Ratio of storage moduli at 23.degree. C. -- 1.6 1.5 1.6 2.4 1.6 1.6
and 50.degree. C. of polymeric elastomer Polycarbonate ratio in
polyol % >99 >99 >99 95 >99 >99 component of
polymeric elastomer Average particle size of aqueous .mu.m 0.04
0.05 0.04 0.04 0.04 0.04 polyurethane Ultrafine fiber-entangled
body/polymeric 76/24 83/17 70/30 76/24 76/24 76/24 elastomer (mass
ratio) Apparent density of polishing pad g/cm.sup.3 0.8 0.77 0.62
0.8 0.8 0.57 Void volume ratio of polishing pad vol % 38 42 52 38
38 56 Polishing rate (initial) nm/min 190 200 210 200 210 210
(after 24 hours) 200 200 220 210 220 220 (after 300 polishing
cycles) 200 200 210 200 220 210 Planarity (initial) % 6 6 7 6 7 7
(after 24 hours) 5 5 6 6 7 6 (after 300 polishing cycles) 5 6 6 7 6
7 Scratches (initial) number 12 10 8 10 15 10 (after 24 hours)
number 10 10 10 10 12 10 (after 300 cycles) number 8 11 10 14 12
8
TABLE-US-00002 TABLE 2 Comparative Examples 1 to 4 1 2 3 4 Average
fineness of ultrafine fibers dtex 1 0.05 0.05 0.05 Number of
ultrafine fibers of fiber bundles number 1 50 50 50 Converging
state of ultrafine fibers of -- -- converging converging converging
fiber bundles Type of thermoplastic resin in ultrafine fibers Ny6
isophthalate-modified isophthlate-modified isophthalate-modified
polyethylene polyethylene polyethylene terephthalate terephthalate
terephthalate Glass transition temperature of polymeric .degree. C.
-25 -48 -32 0 elastomer Water absorption ratio of polymeric
elastomer mass % 2 12 8 1 upon saturation (50.degree. C.) Storage
modulus of polymeric elastomer at 23.degree. C. MPa 450 200 80 1000
Storage modulus of polymeric elastomer at 50.degree. C. MPa 300 80
30 200 Ratio of storage moduli at 23.degree. C. and -- 1.5 2.5 2.7
5 50.degree. C. of polymeric elastomer Polycarbonate ratio in
polyol component % >99 0 >99 >90 of polymeric elastomer
Average particle size of aqueous polyurethane .mu.m 0.05 0.4 0.02
0.08 Ultrafine fiber-entangled body/polymeric 83/17 83/17 76/24
76/24 elastomer (mass ratio) Apparent density of polishing pad
g/cm.sup.3 0.54 0.8 0.8 0.8 Void volume ratio of polishing pad vol
% 52 40 38 38 Polishing rate (initial) 160 200 210 210 (after 24
hours) nm/min 160 180 220 230 (after 300 polishing cycles) 170 150
220 230 Planarity (initial) % 8 8 14 6 (after 24 hours) 9 10 16 6
(after 300 polishing cycles) 10 15 20 1.0 Scratches (initial)
number 15 8 10 50 (after 24 hours) number 40 20 18 80 (after 300
cycles) number 60 40 25 140
TABLE-US-00003 TABLE 3 Type of polishing pad Polishing pad of
Example 1 Polishing Conditions (1) (2) (3) (4) Polishing rate
(initial) nm/min 580 540 150 780 (after 24 hours) 620 560 140 800
(after 300 polishing cycles) 630 560 140 780 Planarity (initial) %
7 7 7 8 (after 24 hours) 7 8 7 9 (after 300 polishing cycles) 8 8 8
9 Scratches (initial) number -- 15 -- -- (after 24 hours) number --
12 -- -- (after 300 polishing cycles) number -- 12 -- --
TABLE-US-00004 TABLE 4 Polishing pad Type of polishing pad of
Example 7 Polishing Conditions (1) (2) (3) Polishing rate (initial)
nm/min 720 620 140 (after 24 hours) 756 630 150 (after 300
polishing cycles) 760 610 160 Planarity (initial) % 6 7 7 (after 24
hours) 7 6 8 (after 300 polishing cycles) 6 7 9
[0226] As explained above, one aspect of the invention relates to a
polishing pad which comprises an ultrafine fiber-entangled body
formed of ultrafine fibers having an average fineness of 0.01 to
0.8 dtex, and a polymeric elastomer, wherein the polymeric
elastomer has a glass transition temperature of -10.degree. C. or
below, storage moduli at 23.degree. C. and 50.degree. C. of 90 to
900 MPa, and a water absorption ratio, when saturated with water at
50.degree. C., of 0.2 to 5 mass %.
[0227] According to this arrangement, there can be obtained a
polishing pad which is capable of carrying out, with long-term
stability, polishing that achieves a high planarity while
suppressing the occurrence of scratches.
[0228] It is preferable for the ultrafine fiber-entangled body to
be composed of bundles of 5 to 70 ultrafine fibers, and for the
polymeric elastomer to be present inside the ultrafine fiber
bundles.
[0229] According to this arrangement, the polymeric elastomer makes
the ultrafine fibers converge as bundles and also restrains the
ultrafine fiber bundles, thereby increasing the stiffness of the
polishing pad and enabling the planarization performance, polishing
uniformity and stability over time to be enhanced.
[0230] It is preferable for the ultrafine fibers be formed of
polyester fibers because this enables the ultrafine fiber-entangled
body that is compact and has a high density to be formed.
[0231] It is preferable for the ultrafine fibers to be formed of a
thermoplastic resin having a water absorption ratio, when saturated
with water at 50.degree. C., of 0.2 to 2 mass %.
[0232] This arrangement enables the polishing pad to be obtained
which suppresses the decrease over time in the planarization
performance and undergoes little fluctuation in polishing rate and
polishing uniformity.
[0233] It is preferable that the polymeric elastomer is a
polyurethane resin obtained by using a polyol, a polyamine and a
polyisocyanate, and that 60 to 100 mass % of the polyol is a
noncrystalline polycarbonate diol.
[0234] According to this arrangement, the resistance to the slurry
used in polishing is high, enabling a good stability over time to
be maintained during polishing.
[0235] It is preferable for the polymeric elastomer to be a
polyurethane resin obtained by using as the polyol a noncrystalline
polycarbonate diol together with a carboxylic group-containing
diol, and by using an alicyclic diisocyanate as the
polyisocyanate.
[0236] According to this arrangement, the polymeric elastomer can
easily be adjusted to the glass transition temperature of
-10.degree. C. or less, the storage moduli at 23.degree. C. and
50.degree. C. of 90 to 900 MPa, and the water absorption ratio,
when saturated with water at 50.degree. C. of 0.2 to 5 mass/0%.
[0237] It is preferable that the polymeric elastomer has a ratio of
the storage modulus at 23.degree. C. to the storage modulus at
50.degree. C. (storage modulus at 23.degree. C./storage modulus at
50.degree. C.) being 4 or less.
[0238] According to this arrangement, even when a temperature
change occurs during polishing, the storage moduli do not readily
change, as a result of which the stability over time during
polishing can be enhanced.
[0239] It is preferable for the polymeric elastomer to be an
aqueous polyurethane having an average particle size of 0.01 to 0.2
.mu.m because a good water resistance is achieved and the fiber
bundle restraining force increases.
[0240] It is preferable for the mass ratio of the ultrafine
fiber-entangled body and the polymeric elastomer (ultrafine
fiber-entangled body/polymeric elastomer) to be from 55/45 to 95/5
because the polishing efficiency is enhanced and the pad wear
during polishing decreases.
[0241] It is preferable for void areas in the polishing pad to have
a volume ratio of at least 50%.
[0242] According to this arrangement, because the polishing pad has
both good slurry retention and suitable stiffness and
cushionability it can be advantageously used for polishing bare
silicon wafers.
[0243] Another aspect of the invention relates to a method for
manufacturing a polishing pad, the method comprising a step of
filling the interior of bundles of ultrafine fibers which have an
average fineness of from 0.01 to 0.8 dtex with a polymeric
elastomer having a glass transition temperature of -10.degree. C.
or below, storage moduli at 23.degree. C. and 50.degree. C. of 90
to 900 MPa. and a water absorption ratio, when saturated with water
at 50.degree. C., of 0.2 to 5 mass %.
[0244] According to this arrangement, the polishing pad which has a
high stiffness and high abrasive slurry retention and which do not
readily form scratches on the substrate being polished can be
obtained.
[0245] In the method for manufacturing the polishing pad, it is
preferable for the polymeric elastomer to be filled into the
interior of an ultrafine fiber-entangled body composed of the
bundles of the ultrafine fibers in such a way that void areas in
the polishing pad have a volume ratio of at least 50%.
[0246] According to this arrangement, by adjusting the amount of
the polymeric elastomer filled into the ultrafine fiber-entangled
body so as to make the void volume ratio in the polishing pad of at
least 50%, the polishing pad for polishing bare silicon wafers
which has a suitable stiffness and an improved abrasive slurry
retention and cushionability can be obtained.
INDUSTRIAL APPLICABILITY
[0247] The polishing pad according to the present invention can be
used as a polishing pad for polishing various devices, substrates
and other products on which planarization or mirror polishing are
carried out, examples of which include semiconductor substrates,
semiconductor devices, compound semiconductor devices, compound
semiconductor substrates, compound semiconductor products, LED
substrates, LED products, silicon wafers, hard disk substrates,
glass substrates, glass products, metal substrates, metal products,
plastic substrates, plastic products, ceramic substrates and
ceramic products.
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