U.S. patent application number 14/767115 was filed with the patent office on 2016-01-07 for hard sheet and method for producing the same.
This patent application is currently assigned to KURARAY CO., LTD.. The applicant listed for this patent is KURARAY CO., LTD.. Invention is credited to Koichi HAYASHI, Masasi MEGURO, Rei NAGAYAMA, Nobuo TAKAOKA.
Application Number | 20160002835 14/767115 |
Document ID | / |
Family ID | 51353810 |
Filed Date | 2016-01-07 |
United States Patent
Application |
20160002835 |
Kind Code |
A1 |
MEGURO; Masasi ; et
al. |
January 7, 2016 |
HARD SHEET AND METHOD FOR PRODUCING THE SAME
Abstract
Provided is a hard sheet including a non-woven fabric of
ultrafine fibers and elastic polymer added into the non-woven
fabric. JIS-D hardness of the sheet is 45 degrees or more. R %
thereof calculated by R (%)=(D hardness maximum-D hardness
minimum)/D hardness average.times.100 is 0 to 20%, when a sectional
surface of the sheet extending in the thickness direction thereof
is evenly divided into three parts corresponding to a first outer
layer, an intermediate layer, and a second outer layer in order
from any one surface side of the sheet; JIS-D hardness measurements
are made at six points being three arbitrary points each on the
first outer layer and on the intermediate layer; and then the JIS-D
hardnesses obtained are used for the calculation. In the sheet, the
total content of ions capable of changing the pH of water is 400
.mu.g/cm.sup.3 or less.
Inventors: |
MEGURO; Masasi;
(Okayama-shi, JP) ; NAGAYAMA; Rei; (Okayama-shi,
JP) ; TAKAOKA; Nobuo; (Kurashiki-shi, JP) ;
HAYASHI; Koichi; (Kurashiki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KURARAY CO., LTD. |
Kurashiki-shi, Okayama |
|
JP |
|
|
Assignee: |
KURARAY CO., LTD.
Kurashiki-shi
JP
|
Family ID: |
51353810 |
Appl. No.: |
14/767115 |
Filed: |
February 5, 2014 |
PCT Filed: |
February 5, 2014 |
PCT NO: |
PCT/JP2014/000616 |
371 Date: |
August 11, 2015 |
Current U.S.
Class: |
15/209.1 ;
264/257 |
Current CPC
Class: |
D06N 3/14 20130101; D06N
3/0004 20130101; B24B 37/24 20130101; D06M 2200/35 20130101; D06M
15/564 20130101; B24B 37/22 20130101; D04H 1/4382 20130101; D06N
3/0011 20130101; D06N 2211/08 20130101 |
International
Class: |
D04H 1/4382 20060101
D04H001/4382; B24B 37/24 20060101 B24B037/24; B24B 37/22 20060101
B24B037/22; D06M 15/564 20060101 D06M015/564 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2013 |
JP |
2013-024525 |
Claims
1. A hard sheet comprising: a non-woven fabric comprising ultrafine
fibers having a fineness of 0.0001 to 0.5 dtex; and an elastic
polymer added into the non-woven fabric, the hard sheet having: a
JIS-D hardness of 45 degrees or more; a R % calculated by an
equation of R (%)=(D hardness maximum-D hardness minimum)/D
hardness average.times.100 of 0 to 20%, when a sectional surface of
the hard sheet extending in a thickness direction of the hard sheet
is evenly divided into three parts corresponding to a first outer
layer, an intermediate layer, and a second outer layer in order
from any one surface side; JIS-D hardness measurements are made at
a total of six points being three arbitrary points on the first
outer layer and three arbitrary points on the intermediate layer;
and then the JIS-D hardnesses obtained at the six points are used
for the calculation; and a total content of ions capable of causing
a pH change in water, of 400 .mu.g/cm.sup.3 or less.
2. The hard sheet of claim 1, wherein the total content of the ions
is from 1 to 100 .mu.g/cm.sup.3.
3. The hard sheet of claim 1, wherein the ultrafine fibers are long
fibers and form fiber bundles.
4. The hard sheet of claim 3, wherein an apparent density of the
non-woven fabric is from 0.35 to 0.90 g/cm.sup.3.
5. The hard sheet of claim 3, wherein, on the sectional surface of
the hard sheet extending in the thickness direction of the hard
sheet, the ultrafine fibers forming the fiber bundles are,
partially at least, bundled together by the elastic polymer.
6. The hard sheet of claim 5, wherein, on the sectional surface of
the hard sheet extending in the thickness direction of the hard
sheet, the fiber bundles are, partially at least, bound together by
the elastic polymer.
7. The hard sheet of claim 3, wherein half or more of the ultrafine
fibers forming the fiber bundles are bound together by the elastic
polymer.
8. The hard sheet of claim 7, wherein on the sectional surface of
the hard sheet extending in the thickness direction of the hard
sheet, half or more of the fiber bundles are bound together by the
elastic polymer.
9. The hard sheet of claim 1, wherein the elastic polymer is a
non-porous elastic polymer.
10. The hard sheet of claim 1, wherein a mass ratio of the
non-woven fabric to the elastic polymer (non-woven fabric/elastic
polymer) is from 90/10 to 55/45.
11. The hard sheet of claim 10, wherein an apparent density is from
0.50 to 1.2 g/cm.sup.3.
12. The hard sheet of claim 1, wherein the second outer layer has a
JIS-D hardness of 45 degrees or more, and the R % calculated by the
equation of R (%)=(D hardness maximum-D hardness minimum)/D
hardness average.times.100 is 0 to 20%, when JIS-D hardness
measurements are made at a total of six points being three
arbitrary points on the second outer layer and three arbitrary
points on the intermediate layer, and then the JIS-D hardnesses
obtained at the six points are used for the calculation.
13. A polishing pad comprising the hard sheet of claim 1 as a
polishing layer.
14. A production method for producing a hard sheet, the method
comprising: (1) preparing an entangled fiber sheet comprising long
fibers of ultrafine-fiber-forming fibers, the entangled fiber sheet
being capable of forming a non-woven fabric with an apparent
density of 0.35 g/cm.sup.3 or more comprising ultrafine fibers with
a fineness of 0.5 dtex or less, by subjecting
ultrafine-fiber-forming treatment; (2) impregnating the entangled
fiber sheet with a first emulsion comprising an elastic polymer and
a gelling agent comprising ions capable of causing a pH change in
water, then allowing the first emulsion to gelate, and then
solidifying the elastic polymer by heating and drying; (3) forming
a first composite body comprising the non-woven fabric and the
elastic polymer by subjecting the ultrafine-fiber-forming fibers to
ultrafine-fiber-forming treatment; (4) forming a second composite
body by impregnating the first composite body with a second
emulsion including an elastic polymer and a gelling agent and then
solidifying the elastic polymer by heating and drying, the second
composite body having a difference in porosity between a first
outer layer and an intermediate layer of 5% or less, when the
second composite body formed is evenly divided into three parts in
a thickness direction of the second composite body, the three parts
corresponding to the first outer layer, the intermediate layer, and
a second outer layer in order from any one surface side; (5) water
washing the second composite body such that a total content of the
ions becomes 400 .mu.g/cm.sup.3 or less to obtain a hard sheet; and
(6) hot pressing at least one selected from the group consisting of
the first composite body, the second composite body, and the hard
sheet, such that a surface hardness of the hard sheet becomes 45
degrees or more in JIS-D hardness.
15. The production method of claim 14, wherein the total content of
the ions is from 1 to 100 .mu.g/cm.sup.3.
16. The production method of claim 14, wherein the
ultrafine-fiber-forming fibers are sea-island-type conjugated
fibers comprising a water-soluble thermoplastic polyvinyl
alcohol-based resin as a sea component and a water-insoluble
thermoplastic resin as island components; and the
ultrafine-fiber-forming treatment in the forming (3) is a process
whereby the water-soluble thermoplastic polyvinyl alcohol-based
resin is dissolved in hot water and selectively removed.
Description
TECHNICAL FIELD
[0001] The present invention relates to a hard sheet favorably used
as a polishing pad, specifically, as a polishing layer of a
polishing pad for polishing semiconductor wafers, semiconductor
devices, silicon wafers, hard disks, glass substrates, optical
products, various metals, or the like.
BACKGROUND ART
[0002] Integrated circuits formed on semiconductor wafers are
highly integrated and have multilayer wiring. Such semiconductor
wafers require a high degree of planarity.
[0003] Chemical mechanical polishing (CMP) has been known as a
polishing method for polishing semiconductor wafers. CMP is a
method wherein the surface of a member to be polished is polished
with a polishing pad, while a polishing slurry (hereafter also
simply referred to as slurry) containing abrasive grains is dropped
to the surface.
[0004] Patent Literatures 1 to 4 listed below each disclose a
polishing pad formed of a polymeric foam having a closed cell
structure, which is for use in CMP. A polymeric foam is made by
foam casting a curable-type two-component liquid polyurethane. A
polishing pad made of a polymeric foam has greater rigidity
compared to a polishing pad of a non-woven fabric type that will be
described later; and is therefore preferably used for polishing
semiconductor wafers which require a high degree of planarity.
[0005] A polishing pad made of a polymeric foam has high rigidity.
Therefore, load is selectively applied to the protrusions on the
member to be polished. As a result, a relatively high polishing
rate is obtained. However, when there is an aggregate of abrasive
grains on the surface to be polished, load is also selectively
applied to the aggregate of abrasive grains. Therefore, scratches
tend to occur easily on the surface to be polished. Particularly,
in the case of polishing a member having copper wiring or a
low-dielectric material having weak adherence at the interface,
scratches or boundary separation tend to occur easily (e.g., see
Non-Patent Literature 1) . Moreover, in foam casting, the elastic
polymer tends to foam unevenly easily; therefore, for the member to
be polished, the planarity and the polishing rate during polishing
tend to become uneven easily. Furthermore, since abrasive grains
and polishing dust gradually clog the separate pores in the
polymeric foam, the polishing rate gradually lowers.
[0006] Patent Literatures 5 to 14 listed below each disclose a
non-woven-fabric-type polishing pad obtained by impregnating a
non-woven fabric with porous polyurethane that has undergone wet
coagulation. A non-woven-fabric-type polishing pad has excellent
flexibility and tends to deform easily. Therefore, since load is
unlikely to be selectively applied to the abrasive grains that are
aggregated on the surface to be polished, scratches are unlikely to
occur. However, due to the flexibility of the non-woven-fabric-type
polishing pad, the polishing rate is low. Moreover, a
non-woven-fabric-type polishing pad deforms in conformity with the
surface shape of the member to be polished; therefore planarization
performance, i.e., the ability to planarize the member to be
polished, is low.
[0007] Moreover, Patent Literatures 15 to 18 listed below each
disclose a polishing pad comprising a non-woven fabric of ultrafine
fibers that is capable of high planarization performance. For
example, Patent Literature 15 discloses a polishing pad as a
sheet-like product comprising: a non-woven fabric formed by
entanglement of ultrafine polyester fiber bundles with an average
fineness of 0.0001 to 0.01 dtex; and an elastic polymer mainly
composed of polyurethane included in the non-woven fabric via
impregnation. This reference discloses that such polishing pad
achieves a polishing work with higher precision than in the
past.
[0008] In common polishing pads that have used a non-woven fabric
comprising ultrafine fibers, there has been used a non-woven fabric
obtained by needle punching short ultrafine fibers. Such non-woven
fabric has had low apparent density, high porosity, and thus low
rigidity. Therefore, due to such non-woven fabric deforming in
conformity with the surface shape of the surface to be polished,
planarization performance was low.
[0009] Patent Literature 19 discloses a polishing pad comprising:
an entangled fiber body formed of a fiber bundle of individual
ultrafine fibers; and an elastic polymer, wherein one part of the
elastic polymer is present in the fiber bundle to bundle together
the individual ultrafine fibers, and the volume percent of the part
excluding the pores falls within the range of 55 to 95%.
[0010] Moreover, Patent Literature 20 discloses a polishing pad
having a polishing layer and a base layer, wherein an intermediate
layer with a water absorption of 1% or less is interposed between
the polishing layer and the base layer, and the difference between
the D hardness of the polishing layer and the D hardness of the
intermediate layer is 20 degrees or less.
PRIOR ART
Patent Literatures
[0011] [Patent Literature 1] Japanese Laid-Open Patent Publication
No. 2000-178374 [0012] [Patent Literature 2] Japanese Laid-Open
Patent Publication No. 2000-248034 [0013] [Patent Literature 3]
Japanese Laid-Open Patent Publication No. 2001-89548 [0014] [Patent
Literature 4] Japanese Laid-Open Patent Publication No. Hei
11-322878 [0015] [Patent Literature 5] Japanese Laid-Open Patent
Publication No. 2002-9026 [0016] [Patent Literature 6] Japanese
Laid-Open Patent Publication No. Hei 11-99479 [0017] [Patent
Literature 7] Japanese Laid-Open Patent Publication No. 2005-212055
[0018] [Patent Literature 8] Japanese Laid-Open Patent Publication
No. Hei 3-234475 [0019] [Patent Literature 9] Japanese Laid-Open
Patent Publication No. Hei 10-128674 [0020] [Patent Literature 10]
Japanese Laid-Open Patent Publication No. 2004-311731 [0021]
[Patent Literature 11] Japanese Laid-Open Patent Publication No.
Hei 10-225864 [0022] [Patent Literature 12] Japanese Unexamined
Patent Publication No. 2005-518286 [0023] [Patent Literature 13]
Japanese Laid-Open Patent Publication No. 2003-201676 [0024]
[Patent Literature 14] Japanese Laid-Open Patent Publication No.
2005-334997 [0025] [Patent Literature 15] Japanese Laid-Open Patent
Publication No. 2007-54910 [0026] [Patent Literature 16] Japanese
Laid-Open Patent Publication No. 2003-170347 [0027] [Patent
Literature 17] Japanese Laid-Open Patent Publication No.
2004-130395 [0028] [Patent Literature 18] Japanese Laid-Open Patent
Publication No. 2002-172555 [0029] [Patent Literature 19] Japanese
Laid-Open Patent Publication No. 2008-207323 [0030] [Patent
Literature 20] Japanese Laid-Open Patent Publication No.
2011-200984
Non-Patent Literature
[0030] [0031] [Non-Patent Literature 1] "CMP No Saiensu (The
Science of CMP)"; Science Forum Inc.; Aug. 20, 1997; pp.
113-119
SUMMARY OF INVENTION
Technical Problem
[0032] An object of the present invention is to provide a polishing
pad with a high polishing rate that is unlikely to change with
time.
Solution to Problem
[0033] One aspect of the present invention relates to a hard sheet
including:
[0034] a non-woven fabric of ultrafine fibers having a fineness of
0.0001 to 0.5 dtex; and
[0035] an elastic polymer added into the non-woven fabric,
[0036] the hard sheet having:
[0037] a JIS-D hardness of 45 degrees or more;
[0038] a R % calculated by an equation of R (%)=(D hardness
maximum-D hardness minimum)/D hardness average.times.100 of 0 to
20%, when a sectional surface of the hard sheet extending in a
thickness direction of the hard sheet is evenly divided into three
parts corresponding to a first outer layer, an intermediate layer,
and a second outer layer in order from any one surface side; JIS-D
hardness measurements are made at a total of six points being three
arbitrary points on the first outer layer and three arbitrary
points on the intermediate layer; and then the JIS-D hardnesses
obtained at the six points are used for the calculation, and
[0039] a total content of ions capable of causing a pH change in
water, of 400 .mu.g/cm.sup.3 or less.
[0040] Moreover, another aspect of the present invention relates to
a polishing pad including the foregoing hard sheet as a polishing
layer.
[0041] Moreover, still another aspect of the present invention
relates to a production method of hard sheet including:
[0042] (1) a step of preparing an entangled fiber sheet including
long fibers of ultrafine-fiber-forming fibers, the entangled fiber
sheet being capable of forming a non-woven fabric with an apparent
density of 0.35 g/cm.sup.3 or more including ultrafine fibers with
a fineness of 0.5 dtex or less, by subjecting
ultrafine-fiber-forming treatment;
[0043] (2) a step of impregnating the entangled fiber sheet with a
first emulsion including an elastic polymer and a gelling agent
containing ions capable of causing a pH change in water, then
allowing the first emulsion to gelate, and then solidifying the
elastic polymer by heating and drying;
[0044] (3) a step of forming a first composite body including the
non-woven fabric and the elastic polymer by subjecting the
ultrafine-fiber-forming fibers to ultrafine-fiber-forming
treatment;
[0045] (4) a step of forming a second composite body by
impregnating the first composite body with a second emulsion
including an elastic polymer and a gelling agent and then
solidifying the elastic polymer by heating and drying, the second
composite body having a difference in porosity between a first
outer layer and an intermediate layer of 5% or less, when the
second composite body formed is evenly divided into three parts in
a thickness direction of the second composite body, the three parts
corresponding to the first outer layer, the intermediate layer, and
a second outer layer in order from any one surface side;
[0046] (5) a step of water washing the second composite body such
that a total content of the ions becomes 400 .mu.g/cm.sup.3 or less
to obtain a hard sheet; and
[0047] (6) a step of hot pressing at least one selected from the
first composite body, the second composite body, and the hard
sheet, such that a surface hardness of the hard sheet becomes 45
degrees or more in JIS-D hardness.
Advantageous Effects of Invention
[0048] There is obtained a hard sheet for obtaining a polishing pad
having a high polishing rate that is unlikely to change with
time.
BRIEF DESCRIPTION OF DRAWING
[0049] FIG. 1 is schematic sectional illustration of one embodiment
of a hard sheet.
DESCRIPTION OF EMBODIMENT
[0050] An embodiment of a hard sheet according to the present
invention will now be described in detail. FIG. 1 is a schematic
sectional view of a hard sheet 10 of the present embodiment. In
FIG. 1, the circled area schematically depicts an enlarged view of
a portion of the sectional view.
[0051] As in FIG. 1, the hard sheet 10 includes: a non-woven fabric
1 being an entangled body of ultrafine fibers 1a; and an elastic
polymer 2 added into the non-woven fabric 1. The hard sheet 10 has
a JIS-D hardness of 45 degrees or more; and has a R % calculated by
the equation of R (%)=(D hardness maximum among six points-D
hardness minimum among six points)/D hardness average of six
points.times.100 of 0 to 20%, when the hard sheet 10 is evenly
divided into three parts in the sheet thickness direction and the
three parts correspond to a first outer layer 3, an intermediate
layer 4, and a second outer layer 5 in order from the sheet surface
side; JIS-D hardness measurements are made at a total of six points
being three arbitrary points in the first outer layer 3 and at
three arbitrary points in the intermediate layer 4; and then R % is
calculated using the D hardnesses obtained at the six points.
Moreover, the R % calculated by the above equation is preferably
also 0 to 20%, when JIS-D hardness measurements are made at a total
of six points being three arbitrary points in the second outer
layer 5 and at three arbitrary points in the intermediate layer 4,
and the D hardnesses obtained at the six points are used for the
calculation. Furthermore, the total content of ions capable of
causing a pH change in water, is 400 .mu.g/cm.sup.3 or less.
[0052] In the hard sheet 10, regarding the ultrafine fibers 1a
which form the non-woven fabric 1, a plurality of the ultrafine
fibers 1a form a fiber bundle 1b. Moreover, the fiber bundles 1b
are bound together with the elastic polymer 2. Preferably, half or
more of the fiber bundles 1b are bound together with the elastic
polymer 2. Furthermore, the ultrafine fibers 1a which form each of
the fiber bundles 1b are also bound together with the elastic
polymer 2. Preferably, half or more of the ultrafine fibers 1a are
bound together with the elastic polymer 2. Such composite body
comprising the non-woven fabric 1 and the elastic polymer 2
corresponds to the hard sheet 10 that is closely-packed, with a
small amount of pores and a high degree of hardness. Such hard
sheet 10 has high rigidity due to the reinforcing effect by the
fiber bundles 1b and the high packing rate (i.e., low porosity) of
the hard sheet.
[0053] The hard sheet 10 comprises the non-woven fabric 1 of the
ultrafine fibers which form the fiber bundles. The fiber bundles in
the non-woven fabric that are present at the surface separate into
individual fibers or become fibrillated during polishing. As a
result, the ultrafine fibers with a high fiber density become
exposed at the polishing surface. These exposed ultrafine fibers
come in contact with the member to be polished, over a wide area;
and also can retain large amounts of slurry. Furthermore, since the
exposed ultrafine fibers soften the surface of the polishing pad,
selective load application to aggregates of abrasive grains is
suppressed. As a result, occurrence of scratches is suppressed.
[0054] Moreover, the hard sheet 10 has a JIS-D hardness of 45
degrees or more; and is adjusted to be uniform in the thickness
direction such that R % calculated by the equation of R (%)=(D
hardness maximum-D hardness minimum)/D hardness average.times.100
by using the JIS-D hardnesses measured at a total of six points,
i.e., three points in the first outer layer 3 and three points in
the intermediate layer 2, is 0 to 20%. Moreover, preferably, the
hard sheet 10 is adjusted to be uniform in the thickness direction
such that R % calculated by using the JIS-D hardnesses measured at
a total of six points, i.e., three points in the second outer layer
5 and three points in the intermediate layer 2, also becomes 0 to
20%. As such, by adjusting to obtain a uniform degree of hardness,
a uniform degree of polishing becomes possible.
[0055] Furthermore, the hard sheet 10 is adjusted such that the
total content of ions capable of causing a pH change in water
becomes 400 .mu.g/cm.sup.3 or less. In order for the elastic
polymer to be uniformly added into the hard sheet in the thickness
direction as described above, typically, a gelling agent is used.
Ions in the hard sheet may change the pH of the slurry during
polishing. When the pH of the slurry changes, the polishing rate
tends to lower and abrasive grains tend to aggregate easily. In
such case, by reducing ionizable compounds in the hard sheet by
water washing or the like, lowering of the polishing rate caused by
a pH change in the slurry can be suppressed. Note that the ions
capable of causing a pH change in water correspond to all ions
capable of changing the pH of water when dissolved therein.
[0056] As will be described in detail below, the hard sheet of the
present embodiment is produced by adding an elastic polymer into a
closely-packed non-woven fabric of the ultrafine fibers via
impregnation, uniformly and in large proportions in the thickness
direction. Moreover, in such production of the hard sheet, in order
to add large proportions of the elastic polymer into the non-woven
fabric via impregnation, an emulsion of elastic polymer containing
a gelling agent is preferably used. Furthermore, production is made
possible by water washing the non-woven fabric in the production
process, such that the total content of ions in the gelling agent
that are capable of causing a pH change in water becomes 400
.mu.g/cm.sup.3 or less.
[0057] The components of the hard sheet of the present embodiment
will now be described in further detail.
[0058] The non-woven fabric in the present embodiment is formed of
ultrafine fibers, and the ultrafine fibers preferably form fiber
bundles.
[0059] The ultrafine fibers has a fineness of 0.0001 to 0.5 dtex
and preferably 0.001 to 0.01 dtex. When the fineness of the
ultrafine fibers is less than 0.0001 dtex, the ultrafine fibers in
the vicinity of the surface are unlikely to sufficiently separate
into individual fibers during polishing, resulting in decrease in
the amount of the slurry retained. When the fineness of the
ultrafine fibers exceeds 0.5 dtex, the surface becomes too rough,
thereby causing a lower polishing rate; and also, abrasive grains
tend to aggregate easily on the surface of the ultrafine
fibers.
[0060] The ultrafine fibers are preferably long fibers (filaments),
and specifically, have an average fiber length of preferably 100 mm
or more and further preferably 200 mm or more. The upper limit of
the average fiber length is not particularly limited; and fibers
with a length of, for example, several meters, several hundred
meters, several kilometers, or a higher value may be included, if
not cut during the entanglement process as will be described below.
When the ultrafine fibers are long fibers, fiber density can be
increased, and therefore, rigidity of the hard sheet is increased.
Moreover, the long fibers are unlikely to become detached during
polishing. Note that when the ultrafine fibers are short fibers,
fiber density cannot be easily increased, and therefore, a high
rigidity cannot be obtained for the hard sheet. Moreover, the short
fibers tend to become detached easily during polishing.
[0061] Regarding the ultrafine fibers which form the non-woven
fabric, it is preferable that a plurality thereof bundled together
form a fiber bundle. The average sectional area of the fiber bundle
present on a sectional surface of the hard sheet extending in the
thickness direction thereof is preferably 80 .mu.m.sup.2 or more,
further preferably 100 .mu.m.sup.2 or more, and particularly
preferably 120 .mu.m.sup.2 or more, in terms of obtaining a hard
sheet with a particularly high rigidity.
[0062] Moreover, regarding the fiber bundles present on the
sectional surface of the hard sheet extending in the thickness
direction thereof, the proportion of the fiber bundles with a
sectional area of 40 .mu.m.sup.2 or more is preferably 25% or more,
relative to a predetermined total number of the fiber bundles on
the sectional surface of the hard sheet extending in the thickness
direction thereof. When the hard sheet is used in polishing pads
for silicon wafers, semiconductor wafers, and semiconductor devices
which all require a particularly high degree of planarity, the
proportion of the fiber bundles with a sectional area of 40
.mu.m.sup.2 or more is preferably 40% or more, further preferably
50% or more, and particularly preferably 100%. When the proportion
of the fiber bundles of 40 .mu.m.sup.2 or more is too low,
polishing rate tends to lower and planarization performance tends
to degrade.
[0063] Moreover, in the hard sheet of the present embodiment, the
bundle density of the fiber bundles per unit area of the sectional
surface of the hard sheet extending in the thickness direction
thereof is preferably 600 bundles/mm.sup.2 or more, and further
preferably 1000 bundles/mm.sup.2 or more, and moreover, preferably
4000 bundles/mm.sup.2 or less and further preferably 3000
bundles/mm.sup.2 or less. In case of such bundle density, during
polishing, the fiber bundles at the surface separate into
individual fibers or become fibrillated, and ultrafine fibers
become formed in large amounts, thereby increasing the amount of
the slurry retained. Moreover, by such separation or fibrillation
of the fiber bundles, the polishing surface becomes soft and thus
suppresses occurrence of scratches. When the bundle density is too
low, the fiber density of the ultrafine fibers formed on the
polishing surface lowers; and therefore, polishing rate tends to
lower or planarization performance tends to degrade. Moreover, when
the fiber bundle density is too high, the polishing surface becomes
too closely-packed and tends to cause reduction in the amount of
the slurry retained and in the polishing rate. Note that in the
hard sheet of the present embodiment, variations in the fiber
bundle density are preferably small in the thickness direction and
the planar direction, in terms of improving polishing
stability.
[0064] The ultrafine fibers are preferably formed of a
thermoplastic resin with a glass transition temperature (T.sub.g)
of preferably 50.degree. C. or more and further preferably
60.degree. C. or more. When T.sub.g of the thermoplastic resin is
too low, during polishing, planarization performance tends to
degrade due to insufficient rigidity, and also, polishing stability
and polishing uniformity tend to lower due to lowering of rigidity
with time. The upper limit of T.sub.g is not particularly limited,
and is preferably 300.degree. C. and further preferably 150.degree.
C., considering that production is industrial. Note that since the
ultrafine fibers will be water-absorbable in the polishing process,
T.sub.g is still further preferably 50.degree. C. or more, when
measured on the ultrafine fibers that remain wet after having
undergone treatment with warm water at 50.degree. C. Moreover,
water absorption of the thermoplastic resin is preferably 4 mass %
or less and further preferably 2 mass % or less. When water
absorption exceeds 4 mass %, during polishing, the ultrafine fibers
gradually absorb water in the slurry and thereby cause rigidity to
lower with time. In such case, planarization performance tends to
degrade easily with time, or, polishing rate and polishing
uniformity tend to vary easily. Water absorption is preferably 0 to
2 mass %.
[0065] Specific examples of the thermoplastic resin include:
aromatic polyester-based resins such as polyethylene terephthalate
(PET, T.sub.g: 77.degree. C., water absorption: 1 mass %),
isophthalic acid-modified polyethylene terephthalate (T.sub.g: 67
to 77.degree. C., water absorption: 1 mass %), sulfoisophthalic
acid-modified polyethylene terephthalate (T.sub.g: 67 to 77.degree.
C., water absorption: 1 to 4 mass %) , polybutylene naphthalate
(T.sub.g: 85.degree. C., water absorption: 1 mass %), and
polyethylene naphthalate (T.sub.g: 124.degree. C., water
absorption: 1 mass %); and semi-aromatic polyamide-based resins
such as copolymerizable nylon comprising terephthalic acid,
nonanediol, and methyl octanediol (T.sub.g: 125 to 140.degree. C.,
water absorption: 1 to 4 mass %). These may be used singly or in a
combination of two or more. Among these, polyethylene terephthalate
(PET), isophthalic acid-modified polyethylene terephthalate,
polybutylene naphthalate, and polyethylene naphthalate are
preferred, in terms of being capable of sufficiently maintaining
rigidity, water resistance, and wear resistance. Particularly, PET
and modified PET such as isophthalic acid-modified PET become
crimped to a considerable degree in the wet heat treatment process
as will be described below, wherein ultrafine fibers are formed
from a sheet of entangled web comprising sea-island-type conjugated
fibers; and are therefore preferred in terms of being capable of
forming a closely-packed, highly-dense body of entangled fibers; of
tending to easily increase rigidity of the hard sheet; of tending
not to easily cause progressive change in the hard sheet due to
moisture, during polishing; and the like.
[0066] Moreover, to the extent of not adversely affecting the
effects of the present invention, as necessary, the ultrafine
fibers may contain ultrafine fibers formed of another thermoplastic
resin. Examples of such thermoplastic resin for combined use
include: aromatic polyesters, aliphatic polyesters, and copolymers
thereof, such as polylactic acid, polybutylene terephthalate,
polyhexamethylene terephthalate, polyethylene succinate,
polybutylene succinate, polybutylene succinate adipate, and
polyhydroxybutyrate-polyhydroxyvalerate copolymer; aliphatic nylons
and copolymers thereof, such as nylon 6, nylon 66, nylon 10, nylon
11, and nylon 12; polyolefins such as polyethylene and
polypropylene; modified polyvinyl alcohols containing 25 to 70 mol
% of ethylene units; and elastomers such as polyurethane-based
elastomer, nylon-based elastomer, and polyester-based
elastomer.
[0067] The hard sheet includes an elastic polymer that is added
into the non-woven fabric of the ultrafine fibers.
[0068] Specific examples of the elastic polymer include
polyurethane, polyamide-based elastomers, (meth)acrylic ester-based
elastomers, (meth)acrylic ester-styrene-based elastomers,
(meth)acrylic ester-acrylonitrile-based elastomers, (meth)acrylic
ester-olefin-based elastomers, (meth)acrylic ester-(hydrogenated)
isoprene-based elastomers, (meth)acrylic ester-butadiene-based
elastomers, styrene-butadiene-based elastomers,
styrene-hydrogenated isoprene-based elastomers,
acrylonitrile-butadiene-based elastomers,
acrylonitrile-butadiene-styrene-based elastomers, vinyl
acetate-based elastomers, (meth)acrylic ester-vinyl acetate-based
elastomers, ethylene-vinyl acetate-based elastomers,
ethylene-olefin-based elastomers, silicone-based elastomers,
fluorine-based elastomers, and polyester-based elastomers.
[0069] The elastic polymer is preferably non-porous. Note that
being non-porous means that there are substantially no pores (no
closed cells) as those in porous or sponge-like elastic polymer.
For example, it means that the elastic polymer is not of the kind
having a plurality of closed cells as in an elastic polymer
obtained by solidifying a solvent-based polyurethane.
[0070] When the elastic polymer is non-porous, high polishing
stability is obtained, wearing is unlikely, and residues of the
slurry and of the pad are unlikely to remain in the pores.
Therefore, a high polishing rate can be maintained for long hours.
Moreover, since the elastic polymer has high adhesion to the
ultrafine fibers, the ultrafine fibers are unlikely to fall out.
Furthermore, since a high degree of rigidity is obtained,
planarization performance is excellent.
[0071] Water absorption of the elastic polymer is preferably 0.5 to
8 mass % and further preferably 1 to 6 mass %. When water
absorption of the elastic polymer is too low, slurry wettability
thereof lowers. As a result, polishing rate, polishing uniformity,
and polishing stability tend to lower and abrasive grains tend to
aggregate easily. When water absorption of the elastic polymer is
too high, rigidity of the hard sheet lowers with time during
polishing and planarization performance degrades. Moreover,
polishing rate and polishing uniformity becomes varied easily. Note
that water absorption of the elastic polymer corresponds to water
absorption when a film of the elastic polymer after drying
treatment is immersed in water at room temperature for saturation
and swelling. Note that when two or more kinds of elastic polymers
are included, water absorption is theoretically calculated by
multiplying water absorption of each kind of the elastic polymer by
its mass fraction and then adding together the obtained values.
[0072] Water absorption of the elastic polymer can be adjusted by
introducing a hydrophilic functional group or by adjusting the
degree of crosslinkage. Examples of the hydrophilic functional
group include a carboxyl group, a sulfonic acid group, and a
polyalkylene glycol group with three or less carbon atoms. The
hydrophilic group can be introduced by copolymerization of monomers
having the hydrophilic group. For copolymerization, the proportion
of the monomer units having the hydrophilic group is preferably 0.1
to 20 mass % and further preferably 0.5 to 10 mass %.
[0073] Regarding the elastic polymer, the storage elastic modulus
at 150.degree. C. [E' (150.degree. C., dry)] is preferably 0.1 to
100 MPa and further preferably 1 to 80 MPa. The storage elastic
modulus of the elastic polymer can be adjusted by adjusting the
degree of crosslinkage. Note that when two or more kinds of elastic
polymers are included, the storage elastic modulus is theoretically
calculated by multiplying the storage elastic modulus [E'
(150.degree. C., dry)] of each kind of the elastic polymer by its
mass fraction and then adding together the obtained values.
[0074] Regarding the elastic polymer, one may be used singly or two
or more may be used in a combination. Among those given in above,
polyurethane is preferred in terms of having excellent ability to
bind to the ultrafine fibers.
[0075] The ultrafine fibers that form the fiber bundles are
preferably bundled together by the elastic polymer; and half or
more of the ultrafine fibers are further preferably bundled
together by the elastic polymer.
[0076] Moreover, the fiber bundles are preferably bound together by
the elastic polymer present on the outer side of the fiber bundles;
and half or more of these fiber bundles are further preferably
bound together by the elastic polymer and are thus present in bulk
form. By the fiber bundles being bound together, structural
stability of the hard sheet improves and polishing stability thus
improves. By bundling together the ultrafine fibers and also
binding together the fiber bundles by the elastic polymer, the hard
sheet with a uniform and high degree of hardness is obtained.
[0077] When the ultrafine fibers that form the fiber bundles are
not bundled together, since the ultrafine fibers obtain
flexibility, it becomes difficult to obtain excellent planarization
performance. Moreover, the ultrafine fibers tend to fall out easily
during polishing, and abrasive grains tend to aggregate on the
ultrafine fibers that have fallen out, thereby easily causing
scratches. To have the ultrafine fibers bundled together by the
elastic polymer, means that the ultrafine fibers present in the
fiber bundle adhere and bond to one another via the elastic polymer
present in the fiber bundle.
[0078] The ratio between the non-woven fabric and the elastic
polymer (non-woven fabric/elastic polymer) in the resin sheet is
preferably 90/10 to 55/45 and further preferably 85/15 to 65/35, in
mass ratio. When the ratio between the non-woven fabric and the
elastic polymer falls within the above range, the rigidity of the
hard sheet can be easily increased. Moreover, the density of the
ultrafine fibers that are exposed at the surface of the hard sheet
can be sufficiently increased. As a result, polishing stability,
polishing rate, and planarization performance can be sufficiently
improved.
[0079] The apparent density of the hard sheet is preferably 0.5 to
1.2 g/cm.sup.3 and further preferably 0.6 to 1.2 g/cm.sup.3, in
terms of maintaining high rigidity.
[0080] The JIS-D hardness of the hard sheet of the present
embodiment is 45 degrees or more; and the R % calculated by the
equation of R (%)=(D hardness maximum-D hardness minimum)/D
hardness average of six points.times.100 is 0 to 20%, when a
sectional surface of the hard sheet extending in the thickness
direction thereof is evenly divided into three parts corresponding
to a first outer layer, an intermediate layer, and a second outer
layer in order from any one surface side of the hard sheet, JIS-D
hardness measurements are made at a total of six points, i.e.,
three arbitrary points on the first outer layer and three arbitrary
points on the intermediate layer, and the D hardnesses obtained at
the six points are used for the calculation. Moreover, the R %
calculated by the above equation by using D-hardnesses measured at
a total of six points, i.e., three arbitrary points on the second
outer layer and three arbitrary points on the intermediate layer,
is also preferably 0 to 20%.
[0081] The JIS-D hardness of the hard sheet is 45 degrees or more,
preferably 45 to 75 degrees, and further preferably 50 to 70
degrees. By adjusting the hardness of the first outer layer to 45
degrees or more in JIS-D hardness, excellent planarization
performance is obtained. When the JIS-D hardness is too high,
scratches tend to occur easily. Note that regarding the hard sheet
of the present embodiment, since the ultrafine fibers exposed at
the sheet surface have high fiber density, despite the sheet being
hard, the sheet surface is soft. Therefore, scratches are unlikely
to occur.
[0082] The R % calculated by the above equation using the
D-hardnesses measured at a total of six points, i.e., three
arbitrary points on the first outer layer and three arbitrary
points on the intermediate layer, is 0 to 20% and preferably 0 to
15%. When the R % of the first outer layer and the intermediate
layer falls within the above range, when the hard sheet is used as
a polishing pad, the change in the polishing rate at the first
outer layer and the intermediate layer becomes small and a stable
polishing performance is obtained. When the R % exceeds 20%, the
change in the polishing rate thereat becomes large during polishing
and a stable polishing performance is not obtained. Note that
arbitrary points for JIS-D hardness measurement mean that points
for measurement on each of the layers are selected arbitrarily, and
that regardless of the positions of the points measured uniformly,
the R % obtained would be 0 to 20%. In such case, there will be no
deviation in hardness, not only in the thickness direction but also
in the width direction; and therefore, there will be a uniform
polishing rate and thus a stable polishing performance in the
planar direction as well. Similarly, the R % calculated by the
above equation using D-hardnesses measured at a total of six
points, i.e., three arbitrary points on the second outer layer and
three arbitrary points on the intermediate layer, is preferably 0
to 20% and further preferably 0 to 15%.
[0083] In the hard sheet of the present embodiment, the total
content of ions that cause a pH change in water is 400
.mu.g/cm.sup.3 or less. As will be described below, the hard sheet
of the present embodiment is produced, for example, by impregnating
a non-woven fabric with an emulsion of an elastic polymer and then
solidifying the elastic polymer by heating and drying, thereby to
add the elastic polymer into the non-woven fabric. In such process,
water in the emulsion in the non-woven fabric via impregnation
starts drying from the fabric surface. Therefore, as evaporation of
the water progresses, there occurs migration of the emulsion from
inside the non-woven fabric to the outer layer of the non-woven
fabric. When migration occurs, the elastic polymer is unevenly
distributed to the vicinity of the outer layer of the non-woven
fabric, the amount of the elastic polymer in the vicinity of the
intermediate layer becomes small, and voids tend to easily remain
in the vicinity of the intermediate layer. Such migration is
suppressed by adding a gelling agent into the emulsion, so that the
emulsion would gelate before drying. The present inventors found
that when ions included in the gelling agent that are capable of
causing a pH change in water remain in predetermined amounts or
more in the hard sheet, the polishing rate lowered during
polishing.
[0084] In the hard sheet, the total content of the ions capable of
causing a pH change in water is 400 .mu.g/cm.sup.3 or less,
preferably 350 .mu.g/cm.sup.3 or less, and further preferably 100
.mu.g/cm.sup.3 or less. Moreover, the total content of the ions is
preferably 0 .mu.g/cm.sup.3, but is preferably about 1 to 100
.mu.g/cm.sup.3 and further preferably about 10 to 50
.mu.g/cm.sup.3, in terms of efficiency in industrial water washing.
When the total content of the ions capable of causing a pH change
in water in the hard sheet exceeds 400 .mu.g/cm.sup.3, a pH change
occurs in the slurry and the polishing rate lowers, and
furthermore, abrasive grains tend to aggregate easily.
[0085] Note that the ions that causes a pH change in water
correspond to all kinds of ions that change the pH of water when
dissolved therein. Specifically, for example, there are ions
included in a common gelling agent, such as sulfate ions, nitrate
ions, carbonate ions, ammonium ions, sodium ions, calcium ions, and
potassium ions.
[Production Method of Polishing Pad]
[0086] A detailed description of an example of a hard sheet
production method will now be given. A hard sheet can be produced,
for example, by following steps given below.
(1) Step of Preparing an Entangled Fiber Sheet Comprising Long
Fibers of Ultrafine-Fiber-Forming Fibers
[0087] In the present step, an entangled fiber sheet of long fibers
of ultrafine-fiber-forming fibers will be prepared. The entangled
fiber sheet of long fibers of ultrafine-fiber-forming fibers can be
produced, for example, as follows.
[0088] First, a web of long fibers formed of sea-island-type
conjugated fibers comprising a water-soluble thermoplastic resin as
the sea component and a water-insoluble thermoplastic resin as the
island components, will be produced. Such sea-island-type
conjugated fibers correspond to ultrafine-fiber-forming fibers
capable of forming ultrafine fibers which comprise the resin of the
island components, by dissolution of the sea component. Although
the example described for the present embodiment uses the
sea-island-type conjugated fibers as the ultrafine-fiber-forming
fibers, in place of such sea-island-type conjugated fibers,
well-known ultrafine-fiber-forming fibers such as
multilayer-stack-section fibers may be used.
[0089] The water-soluble thermoplastic resin corresponds to a
thermoplastic resin that can be removed by dissolution or
decomposition by using water, an alkaline aqueous solution, an
acidic aqueous solution, or the like. Specific examples of the
water-soluble thermoplastic resin include: PVA-based resins such as
polyvinyl alcohol (PVA) and PVA copolymers; modified polyesters
containing polyethylene glycol and/or alkali metal salt of sulfonic
acid as copolymerizable components; and polyethylene oxide. Among
these, PVA-based resins are preferred.
[0090] When PVA-based resin included as the sea component in the
sea-island-type conjugated fibers is dissolved therefrom, the
ultrafine fibers, i.e., the island components, become crimped to a
considerable degree. As a result, a non-woven fabric with a high
fiber density is obtained. Moreover, when the PVA-based resin is
dissolved from the sea-island-type conjugated fibers including the
PVA-based resin, since the ultrafine fibers, i.e., the island
components and an elastic polymer are neither decomposed nor
dissolved, physical properties of the ultrafine fibers and the
elastic polymer are unlikely to degrade.
[0091] For the PVA-based resin, an ethylene-modified PVA containing
preferably 4 to 15 mol % and further preferably 6 to 13 mol % of
ethylene units is preferred, in terms of improving the physical
properties of the sea-island-type conjugated fibers.
[0092] The viscosity-average degree of polymerization of the
PVA-based resin is preferably 200 to 500, further preferably 230 to
470, and particularly preferably 250 to 450. Moreover, the melting
point of the PVA-based resin is preferably 160 to 250.degree. C.,
further preferably 175 to 224.degree. C., and particularly
preferably 180 to 220.degree. C., in terms of excellent mechanical
characteristics and excellent thermal stability, and thus,
excellent melt spinning ability.
[0093] For the water-insoluble thermoplastic resin which forms the
island components, a thermoplastic resin that cannot be removed by
dissolution or decomposition by using water, an alkaline aqueous
solution, an acidic aqueous solution, or the like; and that can
undergo melt spinning, is used. As specific examples of the
water-insoluble thermoplastic resin, the various resins capable of
forming ultrafine fibers as given above, preferably thermoplastic
resins with Tg of 50.degree. C. or more and water absorption of 4
mass % or less, are used.
[0094] Moreover, the water-insoluble thermoplastic resin may
contain additives such as a catalytic agent, an anti-coloring
agent, a heat resistance modifier, a flame retardant, a lubricant,
a stain inhibitor, a fluorescent whitening agent, a delustering
agent, a coloring agent, a gloss enhancer, an anti-static agent, an
aroma modifier, a deodorizing agent, an anti-bacterial agent, a
tick repellent, and inorganic particulates.
[0095] The sea-island-type conjugated fibers can be produced by a
conjugate spinning method wherein the water-soluble thermoplastic
resin and the water-insoluble thermoplastic resin having low
compatibility with the water-soluble thermoplastic resin are each
melt spun and then conjugated. Thereafter, the sea-island-type
conjugated fibers, remaining in long fiber form, are preferably
converted into a web.
[0096] The web of the long fibers of the sea-island-type conjugated
fibers is obtained, for example, by a spunbonding method wherein
the water-soluble thermoplastic resin and the water-insoluble
thermoplastic resin are each melt spun and then conjugated, and the
resultant is drawn and then deposited. Note that the long fibers
correspond to continuous fibers that are produced without
undergoing a cutting process as in production of short fibers. A
detailed description will now be given of a production method of a
web of long fibers of sea-island-type conjugated fibers, in one
example.
[0097] First, the water-soluble thermoplastic resin and the
water-insoluble thermoplastic resin are each melted and kneaded by
separate extruders, and are then ejected at once from separate
spinnerets, as molten resin strands. Then, the ejected strands are
conjugated by a composite nozzle; and thereafter, the resultant is
ejected from a nozzle opening of a spinning head, thereby to form a
sea-island-type conjugated fiber.
[0098] The mass ratio between the water-soluble thermoplastic resin
and the water-insoluble thermoplastic resin in the sea-island-type
conjugated fibers is not particularly limited, and is preferably
5/95 to 50/50 and further preferably 10/90 to 40/60. It is
favorable that the mass ratio between the water-soluble
thermoplastic resin and the water-insoluble thermoplastic resin
falls within the above range, in terms of obtaining a high-density
non-woven fabric and securing excellent ultrafine fiber
formability. Moreover, in conjugate melt spinning, the number of
islands in the sea-island-type conjugated fibers is preferably 4 to
4000 islands/fiber and further preferably 10 to 1000 islands/fiber.
Moreover, fineness of the sea-island-type conjugated fiber is not
particularly limited, and is preferably about 0.5 to 3 dtex from an
industrial perspective.
[0099] The sea-island-type conjugated fibers are cooled by using a
cooling device; and then drawn by a high-speed air flow at a rate
corresponding to a take-up speed of 1000 to 6000 m/min such that a
target fineness is obtained, by using a suction device such as an
air-jet nozzle. Thereafter, the conjugated fibers that have been
drawn are deposited on top of a mobile capturing surface, thereby
to form a web of long fibers. At that time, the deposited web of
the long fibers may be partially pressure bonded as necessary.
[0100] Subsequently, plural sheets of the web are overlapped and
entangled. Entanglement of the sheets of the web can be conducted
by needle punching or high-pressure water jetting. As a typical
example, an entanglement treatment by needle punching will be
described in detail.
[0101] First, a silicone-based oiling agent such as an
anti-needle-breakage oiling agent, an anti-static oiling agent, or
an entanglement-enhancing oiling agent, or a mineral-oil-based
oiling agent is added into the web. Then, the web is entangled by
needle punching. The mass per unit area of the entangled web
preferably falls within the range of 100 to 1500 g/m.sup.2, in
terms of excellent handling characteristics.
[0102] Subsequently, the entangled web of the long fibers is shrunk
to increase fiber density. By shrinking the web of the long fibers,
shrinking is allowed to a greater extent compared to when shrinking
a web of short fibers. Shrinkage treatment is preferably conducted
by a wet heat shrinkage treatment such as steam heating. Regarding
steam heating conditions, for example, a condition of heating for
60 to 600 seconds at an ambient temperature of 60 to 130.degree. C.
and at a relative humidity of preferably 75% or more and further
preferably 90% or more, can be given.
[0103] The wet heat shrinkage treatment preferably causes the
entangled web of the long fibers to shrink such that the area
shrinkage becomes preferably 35% or more and further preferably 40%
or more. By allowing such high degree of shrinkage, fiber density
increases significantly. The upper limit of the area shrinkage is
preferably about 80% or less, in terms of shrinkage limit and
treatment efficiency. Note that the area shrinkage (%) is
calculated by the following equation:
(Area of entangled web before shrinkage treatment-Area of entangled
web after shrinkage treatment)/Area of entangled web before
shrinkage treatment.times.100.
[0104] The entangled web that has undergone the wet heat shrinkage
treatment as above may further be hot rolled or hot pressed,
thereby to further increase fiber density. Regarding the change in
mass per unit area of the entangled web before and after the wet
heat shrinkage treatment, the mass per unit area thereafter
compared to the mass per unit area therebefore (mass ratio) is
preferably 1.2 times or more and further preferably 1.5 times or
more, and preferably 4 times or less and further preferably 3 times
or less. As such, a web of long fibers of sea-island-type
conjugated fibers (hereafter referred to as entangled fiber sheet)
is obtained.
[0105] Such entangled fiber sheet becomes converted to a non-woven
fabric with an apparent density of 0.35 to 0.90 g/cm.sup.3, due to
the sea-island-type conjugated fibers subsequently forming
ultrafine fibers.
[0106] Compared to an entangled web comprising short fibers, the
entangled web comprising the long fibers shrinks to a more
considerable extent by wet heating, due to formation of the
ultrafine fibers. Therefore, the fiber density of the ultrafine
fibers is of a higher degree. Subsequently, the water-soluble
thermoplastic resin in the sea-island-type conjugated fibers is
removed selectively, thereby to form a non-woven fabric comprising
fiber bundles of the ultrafine fibers. At that time, voids are
created at portions from which the water-soluble thermoplastic
resin has been extracted by dissolution. By adding large
proportions of elastic polymer into the voids, the ultrafine fibers
that form the fiber bundles are bundled together, and also, the
fiber bundles are bound together. As such, a hard sheet with high
fiber density, low porosity, and high rigidity is obtained.
(2) Step of Impregnating the Entangled Fiber Sheet with a First
Emulsion Comprising a Gelling Agent and an Elastic Polymer, the
Gelling Agent Containing Ions that Cause a pH Change in Water;
Allowing the First Emulsion to Gelate; and Then Solidifying the
Elastic Polymer by Heating and Drying
[0107] In the present step, an elastic polymer is packed in the
entangled fiber sheet, uniformly in the sheet thickness direction.
Since an emulsion of elastic polymer is highly concentrated, low in
viscosity, and excellent in permeability via impregnation, the
entangled fiber sheet can be easily filled with large proportions
of the emulsion. Moreover, by including a gelling agent in the
emulsion of elastic polymer, it is possible to suppress migration
of the emulsion which causes uneven distribution thereof in the
sheet thickness direction when dried.
[0108] In contrast to when a conventional and typical solution of
elastic polymer is used, when the emulsion of elastic polymer is
used, a non-porous elastic polymer can be formed.
[0109] For the elastic polymer, elastic polymer capable of hydrogen
bonding is preferable in terms of high adhesion to fibers. Elastic
polymers capable of hydrogen bonding correspond to, for example,
elastomers comprising a polymer capable of crystallization or
aggregation by hydrogen bonding, as with polyurethanes,
polyamide-based elastomers, polyvinyl alcohol-based elastomers, and
the like.
[0110] A detailed description of when polyurethane is used as the
elastic polymer will now be given in a typical example.
[0111] Examples of the polyurethane include various kinds thereof
obtained by reacting polymeric polyol having an average molecular
weight of 200 to 6000, organic polyisocyanate, and a
chain-elongating agent, in a predetermined molar ratio.
[0112] Specific examples of the polymeric polyol include:
polyether-based polyols such as polyethylene glycol, polypropylene
glycol, polytetramethylene glycol, and poly(methyl
tetramethylene)glycol, and copolymers thereof; polyester-based
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, and
polycaprolactone diol, and copolymers thereof; polycarbonate-based
polyols such as polyhexamethylene carbonate diol,
poly(3-methyl-1,5-pentylene carbonate)diol, polypentamethylene
carbonate diol, and polytetramethylene carbonate diol, and
copolymers thereof; and polyester carbonate polyols. Moreover, as
necessary, these maybe used in a combination with 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. Such polymeric polyols may be
used singly or in a combination of two or more. Particularly,
amorphous polycarbonate-based polyol, alicyclic polycarbonate-based
polyol, linear polycarbonate-based polyol, a mixture of any one of
these polycarbonate-based polyols and polyether-based polyol, and
polyester-based polyol are preferred in terms of obtaining a hard
sheet that is excellent in durability characteristics such as
hydrolysis resistance and oxidation resistance. Moreover,
polyurethane having a polyalkylene glycol group with five carbon
atoms or less and particularly three carbon atoms or less is
preferred, in terms of water wettability becoming particularly
favorable.
[0113] Specific examples of the organic polyisocyanate include:
non-yellowing diisocyanates such as aliphatic or alicyclic
diisocyanates, e.g., hexamethylene diisocyanate, isophorone
diisocyanate, norbornene diisocyanate, and 4,4'-dicyclohexylmethane
diisocyanate; and aromatic diisocyanates such as 2,4-tolylene
diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane
diisocyanate, and xylylene diisocyanate polyurethane. Moreover, as
necessary, these may be used in a combination with a
multifunctional isocyanate such as a trifunctional isocyanate or a
tetrafunctional isocyanate. Such organic polyisocyanates may be
used singly or in a combination of two or more. Among these,
4,4'-dicyclohexylmethane diisocyanate, 2,4-tolylene diisocyanate,
2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and
xylylene diisocyanate are preferred, in terms of high adhesion to
fibers and of obtaining a hard sheet with a high degree of
hardness.
[0114] Specific examples of the chain-elongating agent include:
diamines such as hydrazine, ethylenediamine, propylenediamine,
hexamethylenediamine, nonamethylenediamine, xylylenediamine,
isophoronediamine, piperazine and derivatives thereof, adipic
dihydrazide, and isophthalic dihydrazide; triamines such as
diethylenetriamine; tetramines such as triethylenetetramine; diols
such as ethylene glycol, propylene glycol, 1,4-butanediol,
1,6-hexanediol, 1,4-bis(.beta.-hydroxyethoxy)benzene, and
1,4-cyclohexanediol; triols such as trimethylolpropane; pentanols
such as pentaerythritol; and amino alcohols such as aminoethyl
alcohol and aminopropyl alcohol. These may be used singly or in a
combination of two or more. Among these, two or more from
hydrazine, piperazine, hexamethylenediamine, isophoronediamine or a
derivative thereof, and a triamine such as ethylenetriamine are
preferably used in a combination, in terms of completing a curing
reaction in a short time. Moreover, monoamines such as ethylamine,
propylamine, or butylamine; monoamine compounds having a carboxyl
group such as 4-aminobutanoic acid and 6-aminohexanoic acid; or
monools such as methanol, ethanol, propanol, or butanol, may be
used in a combination with the chain-elongating agent at the time
of chain-elongation reaction.
[0115] Moreover, a compound such as a diol having a carboxyl group,
or the like, such as 2,2-bis(hydroxymethyl)propionic acid,
2,2-bis(hydroxymethyl)butanoic acid, or
2,2-bis(hydroxymethyl)valeric acid, can be used in a combination
with the polyurethane, thereby to introduce an ionic group such as
a carboxyl group into the polyurethane skeleton. This can further
improve water wettability.
[0116] Moreover, in order to control water absorption and storage
elastic modulus of the polyurethane, a crosslinking agent having
molecules that contain two or more of a functional group capable of
reacting with a functional group included in monomer units that
form polyurethane, or a self-crosslinking compound such as a
polyisocyanate-based compound or a polyfunctional blocked
isocyanate-based compound, is added, thereby to form a crosslinked
structure.
[0117] Examples of the combination of the functional group with
monomer units and the functional group in the crosslinking agent,
include: a carboxyl group and an oxazoline group; a carboxyl group
and a carbodiimide group; a carboxyl group and an epoxy group; a
carboxyl group and a cyclocarbonate group; a carboxyl group and an
aziridine group; and a carbonyl group and a hydrazine or hydrazide
derivative. Among these, a combination of monomer units having a
carboxyl group and a crosslinking agent having an oxazoline group,
a carbodiimide group, or an epoxy group; a combination of monomer
units having a hydroxyl group or an amino group and a crosslinking
agent having a blocked isocyanate group; and a combination of
monomer units having a carbonyl group and a hydrazine or hydrazide
derivative, are particularly preferred in terms of allowing easy
formation of crosslinks as well as excellent rigidity and wear
resistance of the hard sheet. Note that the crosslinked structure
is preferably formed in the heat treatment process conducted after
the polyurethane is added into the entangled fiber sheet, in terms
of being able to maintain stability of the emulsion of elastic
polymer. Among the above, a carbodiimide group and/or an oxazoline
group that allow excellent crosslinking performance and pot life of
the emulsion, and that are problem-free in regard to safety, are
particularly preferred. Examples of the crosslinking agent having a
carbodiimide group include water-dispersion carbodiimide-based
compounds such as "CARBODILITE E-01", "CARBODILITE E-02", and
"CARBODILITE V-02" all available from Nisshibo Industries, Inc.
Moreover, examples of the crosslinking agent having an oxazoline
group include water-dispersion oxazoline-based compounds such as
"EPOCROS K-2010E", "EPOCROS K-2020E", and "EPOCROS WS-500" all
available from Nippon Shokubai Co., Ltd. Regarding the amount of
the crosslinking agent added into the polyurethane, effective
components of the crosslinking agent relative to the polyurethane
is preferably 1 to 20 mass %, further preferably 1.5 to 1 mass %,
and still further preferably 2 to 10 mass %.
[0118] Moreover, in terms of increasing adhesion to the ultrafine
fibers so as to increase rigidity of the fiber bundles, the content
of the components of the polymeric polyol in the polyurethane is
preferably 65 mass % or less and further preferably 60 mass % or
less. Moreover, the content thereof in the polyurethane is
preferably 40 mass % or more and further preferably 45 mass % or
more, in terms of being able to suppress occurrence of scratches
due to imparting of moderate elasticity.
[0119] The method for preparing an emulsion of the polyurethane is
not particularly limited and a known method can be used.
Specifically, for example, a method for imparting an ability of
self-emulsification in water to the polyurethane, by using monomers
having a hydrophilic group such as a carboxyl group, a sulfone
group, or a hydroxyl group, as copolymerizable components; or a
method for emulsifying the polyurethane by adding a surfactant
thereto, can be given. An elastic polymer that include monomeric
units having a hydrophilic group as copolymerizable components have
excellent water wettability and therefore can retain large amounts
of slurry.
[0120] Specific examples of the surfactant used for emulsification
include: anionic surfactants such as sodium lauryl sulfate,
ammonium lauryl sulfate, polyoxyethylene tridecyl ether sodium
acetate, sodium dodecylbenzenesulfonate, sodium
alkyldiphenyletherdisulfonate, and sodium dioctylsulfosuccinate;
and non-ionic surfactants such as polyoxyethylene nonylphenyl
ether, polyoxyethylene octylphenyl ether, polyoxyethylene lauryl
ether, polyoxyethylene stearyl ether, and
polyoxyethylene-polyoxypropylene block copolymer. Moreover, a
surfactant having reactivity, i.e., a reactive surfactant maybe
used. Moreover, by arbitrarily selecting the clouding point of the
surfactant, a thermosensitive gelation ability also can be imparted
to the emulsion.
[0121] The solidifying concentration of the emulsion is preferably
15 to 40 mass % and further preferably 25 to 35 mass %, in terms of
being able to pack the entangled fiber sheet with the elastic
polymer, highly and uniformly in the sheet thickness direction.
Moreover, the particle size of the emulsion is preferably 0.01 to 1
.mu.m and further preferably 0.03 to 0.5 .mu.m.
[0122] A first emulsion includes a gelling agent containing ions
that cause a pH change in water. The gelling agent is used in order
to allow gelation of the emulsion particles by heating, by causing
change in the pH of the emulsion. The water in the emulsion
included in the non-woven fabric via impregnation starts drying
from the surface of the non-woven fabric. Therefore, as evaporation
of the water progresses, migration of the emulsion from inside the
non-woven fabric to the outer layer of the non-woven fabric tends
to easily occur. When migration of the emulsion inside the
non-woven fabric occurs, the elastic polymer is unevenly
distributed to the vicinity of the outer layer of the non-woven
fabric, the amount of the elastic polymer in the vicinity of the
intermediate layer becomes small, and voids tend to easily remain
in the vicinity of the intermediate layer. When voids remain in the
vicinity of the intermediate layer, hardness at the intermediate
layer lowers and also becomes non-uniform. Such migration is
suppressed by adding the gelling agent into the emulsion, so that
the emulsion would gelate before drying.
[0123] For the gelling agent, any kind can be used without
particular limitation, as long as the gelling agent is a
water-soluble salt capable of changing the pH of the emulsion to
the extent that the emulsion particles would gelate by heating.
Specific examples of the gelling agent include monovalent or
bivalent inorganic salts such as sodium sulfate, ammonium sulfate,
sodium carbonate, calcium chloride, calcium sulfate, calcium
nitrate, zinc oxide, zinc chloride, magnesium chloride, potassium
chloride, potassium carbonate, sodium nitrate, and lead
nitrate.
[0124] The proportion of the gelling agent in the first emulsion is
preferably 0.5 to 5 parts by mass and further preferably 0.6 to 4
parts by mass, relative to 100 parts by mass of the elastic
polymer, in terms of being able to moderately impart a gelation
ability.
[0125] The first emulsion may further contain a penetrating agent,
an antifoam, a lubricant, a water repellant, an oil repellant, a
viscous agent, an extender, a curing accelerator, an antioxidant,
an ultraviolet absorber, a fluorescing agent, an antifungal agent,
a foaming agent, a water-soluble polymeric compound such as
polyvinyl alcohol or carboxymethyl cellulose, a dye, a pigment,
inorganic particulates, or the like.
[0126] The method for impregnating the entangled fiber sheet with
the first emulsion is not particularly limited, and for example, a
method of dipping and nipping, knife coating, bar coating, or roll
coating can be used.
[0127] Subsequently, after the entangled fiber sheet is impregnated
with the first emulsion, heating is conducted to allow the first
emulsion to gelate inside the entangled fiber sheet. Regarding
heating conditions for such gelation, for example, a condition of
holding heating for about 0.5 to 5 minutes at preferably 40 to
90.degree. C. and further preferably 50 to 80.degree. C., is
preferably used. Moreover, heating is preferably conducted with
steam, in terms of being able to uniformly heat the inner layer,
while also suppressing migration of the emulsion that is due to
rapid evaporation of water from the outer layer.
[0128] Then, after the first emulsion gelates, heating and drying
is conducted to solidify the elastic polymer.
[0129] For heating and drying, for example, a method for heating
and drying in a dryer such as a hot-air dryer, or a method for
heating and drying in the dryer after conducting infrared heating,
can be given. Regarding heating and drying conditions, for example,
a condition of heating in 2 to 10 minutes such that the maximum
temperature becomes preferably 130 to 160.degree. C. and further
preferably 135 to 150.degree. C., can be given. By heating and
drying, the water in the first emulsion evaporates, resulting in
even aggregation of the elastic polymer. Therefore, the elastic
polymer is able to be uniformly added into the entangled fiber
sheet, also in the sheet thickness direction.
(3) Step of Subjecting the Ultrafine-Fiber-Forming Fibers to an
Ultrafine-Fiber-Forming Treatment, Thereby to Form a First
Composite Body Comprising a Non-Woven Fiber of the Ultrafine Fibers
and the Elastic Polymer Included therein
[0130] The sea-island-type conjugated fibers included in the
entangled fiber sheet into which the elastic polymer has been added
via impregnation, are subjected to an ultrafine-fiber-forming
treatment, thereby to form a first composite body comprising a
non-woven fabric of the ultrafine fibers and the elastic polymer
included therein.
[0131] The present step involves forming ultrafine fibers by an
ultrafine-fiber-forming treatment whereby the water-soluble
thermoplastic resin is removed from the sea-island-type conjugated
fibers which comprise the water-soluble thermoplastic resin as the
island components and the water-insoluble thermoplastic resin as
the sea component.
[0132] The ultrafine-fiber-forming treatment is a treatment whereby
the entangled fiber sheet comprising the sea-island-type conjugated
fibers undergoes hot water heat treatment by using water, alkaline
aqueous solution, acidic aqueous solution, or the like, thereby to
remove the water-soluble thermoplastic resin forming the sea
component, by dissolution or decomposition.
[0133] To give a specific example of a method preferably used for
hot water heat treatment, at the first stage, the entangled fiber
sheet is immersed in hot water at 65 to 90.degree. C. for 5 to 300
seconds; and then, at the second stage, the entangled fiber sheet
is immersed in hot water at 85 to 100.degree. C. for 100 to 600
seconds. Moreover, in order to improve dissolution efficiency, as
necessary, a treatment such as nipping with rollers, high-pressure
water jetting, ultrasonication, showering, stirring, rubbing, or
the like may be conducted.
[0134] By subjecting the entangled fiber sheet to hot water heat
treatment, the water-soluble thermoplastic resin dissolves from the
sea-island-type conjugated fibers, resulting in formation of
ultrafine fibers. Note that when formed, the ultrafine fibers
become crimped to a considerable degree. Such crimping causes the
ultrafine fibers to have a higher fiber density. Moreover, due to
the removal of the water-soluble thermoplastic resin from the
sea-island-type conjugated fibers, voids are created at portions
where the water-soluble thermoplastic resin had been present. These
voids are packed with the elastic polymer by a subsequent process.
Moreover, by subjecting the entangled fiber sheet to hot water heat
treatment, the gelling agent included in the sheet is also removed
by dissolution in hot water. As such, a first composite body is
formed.
(4) Step of Forming a Second Composite Body by Impregnating the
First Composite Body with a Second Emulsion Comprising a Gelling
Agent and an Elastic Polymer; Allowing the Second Emulsion to
Gelate; and then Solidifying the Elastic Polymer by Heating and
Drying
[0135] As described above, in the first composite body formed by
removal of the water-soluble thermoplastic resin from the
sea-island-type conjugated fibers, voids are created at portions
where the water-soluble thermoplastic resin had been present. In
order to obtain the hard sheet of the present embodiment having a
uniform and high degree of hardness, the voids in the first
composite body are packed with the elastic polymer, thereby to bind
the ultrafine fibers together.
[0136] By packing the voids created by removal of the water-soluble
thermoplastic resin, with the elastic polymer, the ultrafine fibers
are bundled together and the porosity of the hard sheet can thus be
lowered. When the ultrafine fibers form fiber bundles, the emulsion
tends to permeate easily due to capillary action.
[0137] A second emulsion is selected from those listed for the
first emulsion. Note that the second emulsion and the first
emulsion may have the same composition or different
compositions.
[0138] In the present step, it is preferable that the second
emulsion is added and undergoes gelation, such that when the second
composite body formed is evenly divided into three parts in the
thickness direction thereof and the three parts correspond to a
first outer layer, an intermediate layer, and a second outer layer
in order from any one surface side thereof, the difference in
porosity between the first outer layer and the intermediate layer
is preferably 5% or less and further preferably 3% or less. By
adjusting as such, a hard sheet with a uniform and high degree of
hardness is obtained.
[0139] Note that the difference in porosity between the first outer
layer and the intermediate layer is calculated by the following
equation:
Difference in porosity between first outer layer and intermediate
layer (%)=Absolute value (Porosity of intermediate layer
(%)-Porosity of first outer layer (%)).
[0140] The porosity of each of the layers is obtained as follows.
An image of a sectional surface of the second composite body
extending in the thickness direction thereof, magnified 30.times.,
is taken by a scanning electron microscope. Then, by using an image
analysis software Popimaging (available from Digital being
kids.Co), the image obtained is binarized by dynamic thresholding
to determine the void portions. Then, a circle is inscribed in each
of the void portions; and the total area of the inscribed circles
is referred to as the total amount of voids in all of the layers in
total. Then, by using the image, 1/3 of the second composite body
in the thickness direction, from one surface, is determined as the
first outer layer; 1/3 thereof in the thickness direction, from the
other surface, is determined as the second outer layer; and the
remaining layer is determined as the intermediate layer; and the
total area of the inscribed circles is obtained for each of the
layers and referred to as the amount of the voids in each of the
layers. Then, porosity of each of the layers is obtained by the
following equation:
Porosity of each layer=Amount of voids in each layer/Amount of
voids in layers in total.times.100 (%).
[0141] Regarding the method for impregnating the first composite
body with the second emulsion and the methods for gelation and for
heating and drying of the second emulsion, those similar to the
method for impregnating the first composite body with the first
emulsion and the methods for gelation and for heating and drying of
the first emulsion, are used. As such, a second composite body is
formed.
(5) Step of Water Washing Such that the Total Content of Ions that
Cause a pH Change in the Second Composite Body Becomes 400
.mu.g/cm.sup.3 or Less
[0142] As described above, the hard sheet of the present embodiment
used the emulsion containing the gelling agent, in order to
suppress migration of the emulsion to the outer layer at the time
of adding the elastic polymer into the non-woven fabric. The
present inventors found that when considerable amounts of ions that
had been in the gelling agent remained in the hard sheet obtained,
the polishing rate lowered at the time of polishing. Moreover, they
found that by conducting water washing and making the remaining
amount of the ions 400 .mu.g/cm.sup.3 or less, lowering of the
polishing rate was able to be suppressed.
[0143] The process of water washing is such that the total content
of the ions that cause a pH change in water included in the hard
sheet becomes 400 .mu.g/cm.sup.3 or less, preferably 350
.mu.g/cm.sup.3 or less, and further preferably 100 .mu.g/cm.sup.3
or less. As the water washing method, for example, heated water
washing treatment is preferable in terms of excellent water washing
efficiency. Regarding specific conditions, for example, a condition
of immersing the second composite body in hot water at 80.degree.
C. or more, can be given. In detail, for example, at the first
stage, the second composite body is immersed in hot water at 65 to
90.degree. C. for 5 to 300 seconds; and then, at the second stage,
the second composite body is immersed in hot water at 85 to
100.degree. C. for 100 to 600 seconds. Moreover, in order to
improve water washing efficiency, as necessary, a treatment such as
nipping with rollers, high-pressure water jetting, ultrasonication,
showering, stirring, rubbing, or the like may be conducted.
(6) Step of Hot Pressing at Least One Selected from the First
Composite Body, the Second Composite Body, and the Hard Sheet, in
Order to Make the Surface Hardness of the Hard Sheet 45 Degrees or
More in JIS-D Hardness
[0144] The voids present in the hard sheet lower the degree of
hardness as well as hardness uniformity of the sheet. In the
present step, the first composite body, the second composite body,
and/or the hard sheet as described above are hot pressed to reduce
the number of voids. By reducing the number of voids as such, the
apparent density of the hard sheet increases, the degree of
hardness as well as hardness uniformity increases, and the rigidity
thus increases. Regarding hot pressing conditions, a preferable
condition is of pressing at a linear pressure of 30 to 100 kg/cm by
using metal rollers heated to, for example, 160 to 180.degree. C.
as the temperature not allowing decomposition of the ultrafine
fibers and the elastic polymer.
[0145] By following the steps as above, the hard sheet of the
present embodiment is obtained. The hard sheet of the present
embodiment is preferably used as a polishing layer of a polishing
pad. Specifically, the hard sheet can be processed as desired as
necessary to form a polishing layer. For example, the hard sheet is
subjected to a napping treatment by using sandpaper, card clothing,
diamond, or the like, or to a brushing by reverse sealing, hot
press treatment, or emboss processing. Moreover, grooves in a grid
pattern, a concentric pattern, a spiral pattern, or the like, or
holes may be formed on the surface of the hard sheet.
[0146] Moreover, as necessary, an elastic layer such as that of a
knitted fabric, a woven fabric, a non-woven fabric, an elastic
resin film, or an elastic sponge-like body, may be stacked on the
hard sheet serving as the polishing layer. Examples of such elastic
film and such elastic sponge-like body include: non-woven fabrics
impregnated with a kind of polyurethane currently widely used
(e.g., "SUBA400" (available from Nitta Haas Incorporated)); rubbers
such as natural rubber, nitrile rubber, polybutadiene rubber, and
silicone rubber; thermoplastic elastomers such as polyester-based
thermoplastic elastomer, polyamide-based thermoplastic elastomer,
and fluorine-based thermoplastic elastomer; foamed plastic; and
polyurethane. By stacking the elastic layer as such, local
planarity of the surface to be polished (local planarity of wafer)
can also be improved. Note that regarding the polishing pad, in
addition to the kind comprising the polishing layer and the elastic
layer directly joined to each other by fusion bonding or the like,
there are also the kind comprising such two layers adhering to each
other via an adhesive, a double-sided adhesive tape, or the like;
and furthermore, the kind comprising such two layers with another
layer further interposed therebetween.
[0147] The polishing pad which uses the hard sheet of the present
embodiment can be used for chemical mechanical polishing (CMP)
wherein the surface to be polished and the polishing pad are
brought in contact with each other under pressure at a certain rate
for a certain amount of time, via a slurry, by using a known CMP
equipment. The slurry contains, for example, a liquid medium such
as water, oil, or the like; an abrading agent such as silica,
aluminum oxide, cerium oxide, zirconium oxide, silicon carbide or
the like; and a component such as a base, an acid, a surfactant, or
the like. Moreover, in conducting CMP, as necessary, a lubricant, a
coolant, or the like may be used in a combination with the
slurry.
[0148] The product for polishing is not particularly limited and
examples include crystal, silicon, glass, optical substrates,
electronic circuit boards, multilayer wiring boards, and hard
disks. Particularly, for polishing, silicon wafers and
semiconductor wafers are preferred. Specific examples of
semiconductor wafers include those having on the surface, for
example, an insulating film of silicon oxide, silicon fluoride
oxide, organic polymer, or the like; a film comprising metal for
wiring material such as copper, aluminum, tungsten, or the like; or
a barrier film of metal such as tantalum, titanium, tantalum
nitride, titanium nitride, or the like.
EXAMPLES
[0149] The present invention will now specifically described by way
of Examples. The following Examples, however, are not to be
construed as limiting in anyway the scope of the present
invention.
[0150] First, evaluation methods used for the present Examples will
be described on the whole as follows.
[Apparent Density of Hard Sheet]
[0151] The value obtained by dividing the mass per unit area
(g/cm.sup.2) of the hard sheet by the thickness (cm) thereof was
referred to as the apparent density (g/cm.sup.3). Moreover,
apparent density measurements were made at ten arbitrary points in
the hard sheet, and the arithmetic average of the obtained values
was calculated as the apparent density. Note that the thickness was
measured with an applied load of 240 gf/cm.sup.2 in compliance with
JISL1096.
[JIS-D Hardness Measurements of Surface, First Outer Layer, and
Intermediate Layer of Hard Sheet, and Calculation of R %]
[0152] D hardness measurements were made on the surface, the first
outer layer, and the intermediate layer of the hard sheet in
compliance with JIS K 7311. Specifically, for the D hardness of the
surface of the hard sheet, eight hard sheets each with a thickness
of about 1.25 mm were overlapped and D hardness measurements were
made at three points at regular intervals in the width direction;
and the average of the obtained values was referred to as the D
hardness of the surface of the hard sheet.
[0153] Moreover, for the D hardness of the first outer layer, a
hard sheet with a thickness of about 1.25 mm was abraded starting
from the second outer layer side, thereby obtaining a 0.40 mm-thick
sheet for the first outer layer. Then, 25 sheets of the sheet for
the first outer layer thus obtained were overlapped and hardness
measurements were made at three points at regular intervals in the
width direction; and the average of the obtained values was
referred to as the JIS-D hardness of the first outer layer.
Furthermore, for the D-hardness of the intermediate layer, a hard
sheet was abraded starting from the first outer layer side and the
second outer layer side, evenly, thereby obtaining a 0.40 mm-thick
sheet for the intermediate layer. Then, 25 sheets of the sheet for
the intermediate layer thus obtained were overlapped and hardness
measurements were made at three points at regular intervals in the
width direction; and the average of the obtained values was
referred to as the hardness of the intermediate layer. Thereafter,
by using the values of the JIS-D hardnesses obtained at the total
of six points being the three points in the first outer layer and
the three points in the second outer layer, R (%) was obtained from
the following equation:
R (%)=(D hardness maximum-D hardness minimum)/D hardness
average.times.100.
[Total Content of Ions Capable of Causing pH Change in Water]
[0154] A piece of the hard sheet cut into a rectangle and 10 mL of
water were put in a screw-cap test tube. Then, the screw-cap test
tube was heated at 90.degree. C. for 2 hours with a block heater,
thereby to extract water-soluble substances in the hard sheet by
hot water extraction. Then, ion components in the liquid extract
were detected by ion chromatography (ICS-1600). The total content
of sulfate ions and ammonium ions, i.e., ions capable of causing a
pH change in water, was measured and then converted to the amount
of the ions included per unit volume of the hard sheet.
[Polishing Rate]
[0155] The hard sheet was cut into a 51 cm-diameter circle, and a
grid pattern of 1.0 mm-wide, 0.5 mm-deep grooves spaced 15.0 mm
apart from one another was created on the surface, thereby to
produce a polishing pad. Then, after an adhesive tape was attached
to the back surface of the polishing pad, the back surface was
attached to a CMP polishing machine ("PPO-60S" available from
Nomura Machine Tool Works, Ltd.). Next, under the conditions of a
platen rotation of 70 rotations/min, ahead rotation of 69
rotations/min, and a polishing pressure of 40 g/cm.sup.2, a 4-inch
diameter synthetic quartz was polished for 3 hours, while a slurry
(SHOROXA-31 available from Showa Denko K.K.) was fed thereto at a
rate of 100 ml/min. Then, thickness measurements were made at 25
arbitrary points within the surface of the polished synthetic
quartz; and then, the average of polished-off thicknesses at those
points was divided by the polishing time, thereby to obtain the
polishing rate (nm/min).
[0156] Note that polishing rate measurements were made on the first
outer layer of a hard sheet about 1.25 mm thick, and also on a hard
sheet 0.70 mm thick with the intermediate layer exposed.
Example 1
[0157] Water-soluble PVA was used as a sea component, and
isophthalic acid-modified PET with a degree of modification of 6
mol % was used as island components. The water-soluble PVA and the
isophthalic acid-modified PET were ejected from a spinneret for
conjugate melt spinning (number of islands: 25 islands/fiber) at
260.degree. C., such that the water-soluble PVA and the isophthalic
acid-modified PET would be 25/75 (mass ratio) . Then, the ejector
pressure was adjusted so that the spinning rate would be 3700
m/min, long fibers with a fineness of 3 dtex were captured on a
net, and a web with a mass per unit area of 35 g/m.sup.2 was
obtained.
[0158] Sixteen layers of the web were overlapped by cross lapping
to produce overlapped webs with a total mass per unit area of 480
g/m.sup.2. Then, an anti-needle-breakage oiling agent was sprayed
to the overlapped webs. Then, a 42 count needle with 1 barb and a
42 count needle with 6 barbs were used to treat the overlapped webs
by needle punching at 3150 punches/cm.sup.2, thereby to obtain an
entangled web. The entangled web had a mass per unit area of 770
g/m.sup.2 and a delamination strength of 9.6 kg/2.5 cm. The area
shrinkage due to the needle punching treatment was 25.8%.
[0159] Subsequently, the entangled web was treated with steam for
70 seconds under the conditions of 110.degree. C. and 23.5% RH. The
area shrinkage at that time was 44%. Then, the entangled web was
dried in an oven at 90 to 110.degree. C. and then hot pressed at
115.degree. C., thereby to obtain an entangled fiber sheet with a
mass per unit area of 1312 g/m.sup.2, an apparent density of 0.544
g/cm.sup.3, and a thickness of 2.41 mm.
[0160] Subsequently, the entangled fiber sheet was impregnated with
a polyurethane emulsion serving as a first emulsion. Note that the
polyurethane was a non-yellowing polyurethane including: a polyol
component being a mixture of polycarbonate-based polyol and
polyalkylene glycol with 2 to 3 carbon numbers in a molar ratio of
99.8:0.2; and 1.5 mass % of carboxyl group-containing monomers.
Moreover, the polyurethane was a non-porous polyurethane capable of
forming a crosslinked structure by heat treatment. The first
emulsion was prepared so as to contain 4.6 parts by mass of a
carbodiimide-based crosslinking agent and 1.8 parts by mass of
ammonium sulfate as a gelling agent, both relative to 100 parts by
mass of the polyurethane; and also so that the solidifying content
in the polyurethane would be 20%.
[0161] The entangled fiber sheet impregnated with the first
emulsion was heated at 90.degree. C. in a 30% RH atmosphere to
allow the first emulsion to gelate; and this was followed by drying
treatment at 150.degree. C. Then, the entangled fiber sheet was hot
pressed at 140.degree. C., thereby to adjust the mass per unit area
to 1403 g/m.sup.2, the apparent density to 0.716 g/cm.sup.3, and
the thickness to 1.96 mm.
[0162] Subsequently, nipping treatment and high-pressure water
jetting treatment were used to immerse the entangled fiber sheet
with the polyurethane added therein in hot water at 95.degree. C.
for 10 minutes, thereby to dissolve and thus remove the
water-soluble PVA, thereby to convert ultrafine fibers with a
fineness of 0.09 dtex; and this was followed by drying. As such, a
first composite body with a mass per unit area of 1009 g/m.sup.2,
an apparent density of 0.538 g/cm.sup.3, and a thickness of 1.87 mm
was obtained.
[0163] Subsequently, the first composite body was impregnated with
a polyurethane emulsion (solid content: 30 mass %) serving as a
second emulsion. Note that the polyurethane was of the same kind as
the one used for the previous impregnation. The second emulsion was
prepared so as to contain 4.6 parts by mass of a carbodiimide-based
crosslinking agent and 1.0 part by mass of ammonium sulfate, both
relative to 100 parts by mass of the polyurethane; and also so that
the solidifying content in the polyurethane would be 30%.
[0164] The first composite body impregnated with the second
emulsion was heated at 90.degree. C. in a 60% RH atmosphere, to
allow the second emulsion to gelate; and this was followed by
drying treatment at 150.degree. C. As such, a second composite body
with a mass per unit area of 1245 g/m.sup.2, an apparent density of
0.748 g/cm.sup.3, and a thickness of 1.66 mm was obtained. The
difference in porosity between the first outer layer and the
intermediate layer in the second composite body was 1.8%.
[0165] Subsequently, nipping treatment and high-pressure water
jetting treatment were used to water wash the second composite body
by immersion in hot water at 95.degree. C. for 10 minutes. This was
followed by drying at 180.degree. C. Then, the second composite
body was hot pressed under the conditions of a linear pressure of
100 kg/cm and 160.degree. C., thereby to obtain an intermediary
body for a hard sheet, with a mass per unit area of 1212 g/m.sup.2,
an apparent density of 0.795 g/cm.sup.2, and a thickness of 1.53
mm.
[0166] The outer layer on both sides of the intermediary body for a
hard sheet was abraded with a #100 paper to reduce the outer layer
thicknesses by 0.15 mm each, thereby finishing to obtain a hard
sheet with a mass per unit area of 994 g/m.sup.2, an apparent
density of 0.788 g/cm.sup.3, and a thickness of 1.26 mm. JIS-D
hardness of the hard sheet was 52 degrees. R % of the JIS-D
hardness was 11.3%. In the hard sheet, the total content of sulfate
ions and ammonium ions, i.e., ions capable of causing a pH change,
was 26.9 .mu.g/cm.sup.3.
[0167] The evaluation results are shown in Table 1.
TABLE-US-00001 TABLE 1 Example No. Comp Comp Comp Comp 1 2 3 Ex. 1
Ex. 2 Ex. 3 Ex. 4 D hardness 52 53 51 53 55 50 50 R (%) 11.3 6.6
19.6 14.6 30.2 19.6 19.6 Total ion content 26.9 28.0 300 939 9.6
404 504 (.mu.g/cm.sup.3) Initial polishing rate 128 129 125 93 133
122 121 at first layer (nm/min) Polishing After 89.3 100 96.1 89
89.6 91.6 92.1 rate in 0.5 hrs percentage at After 97.7 96.9 88.8
93 88.7 82.8 81.8 intermediate 3 hrs layer/first After 99.2 -- 85.3
-- -- 76.4 77.0 layer (%) 5 hrs Average 95.4 98.5 90.1 91.0 89.2
83.6 83.6
Example 2
[0168] Except that the first composite body before addition of the
second emulsion was hot pressed under the conditions of a linear
pressure of 100 kg/cm and 160.degree. C., a hard sheet was produced
as in Example 1 and then evaluated. Note that the hard sheet
obtained had a mass per unit area of 996 g/m.sup.2, an apparent
density of 0.808 g/cm.sup.3, and a thickness of 1.23 mm. The
results are shown in Table 1.
Example 3
[0169] Except that the second composite body was water washed to a
lesser degree, a hard sheet was produced as in Example 1 and then
evaluated. In the hard sheet, the total content of sulfate ions and
ammonium ions, i.e., ions capable of causing a pH change, was 300
.mu.g/cm.sup.3. The results are shown in Table 1.
Comparative Example 1
[0170] Except that the second composite body was not water washed
instead of being water washed by immersion in hot water at
95.degree. C. for 10 minutes, a hard sheet was produced as in
Example 1 and then evaluated. The results are shown in Table 1.
Comparative Example 2
[0171] Except that the first composite body was further hot pressed
under the conditions of a linear pressure of 100 kg/cm and
160.degree. C.; and that the first composite body was impregnated
with an emulsion with a similar composition as the second emulsion
but not including the gelling agent, instead of being impregnated
with the second emulsion including the gelling agent, a hard sheet
was produced as in Example 1 and then evaluated. Note that the hard
sheet obtained had a mass per unit area of 969 g/m.sup.2, an
apparent density of 0.817 g/cm.sup.3, and a thickness of 1.19 mm.
The results are shown in Table 1.
Comparative Example 3
[0172] Except that the second composite body was water washed to a
lesser degree, a hard sheet was produced as in Example 1 and then
evaluated. In the hard sheet, the total content of sulfate ions and
ammonium ions, i.e., ions capable of causing a pH change, was 404
.mu.g/cm.sup.3. The results are shown in Table 1.
Comparative Example 4
[0173] Except that the second composite body was water washed to a
lesser degree, a hard sheet was produced as in Example 1 and then
evaluated. In the hard sheet, the total content of sulfate ions and
ammonium ions, i.e., ions capable of causing a pH change, was 504
.mu.g/cm.sup.3. The results are shown in Table 1.
[0174] As showing the results in Table 1, the polishing pads
according to the present invention which used the hard sheets
obtained in Example 1, 2 and 3, respectively, wherein the JIS-D
hardnesses were 45 degrees or more, the R %s were 0 to 20%, and the
total contents of the ions capable of causing a pH change in water
were 400 .mu.g/cm.sup.3 or less, each exhibited a polishing rate at
the first outer layer, i.e., the initial polishing rate, of 120
nm/min; and maintained 90% or more of the initial polishing rate
based on the average thereof of until after five hours. In
contrast, regarding the polishing pad which used the hard sheet of
Comparative Example 1 wherein the gelling agent was added into the
second emulsion and the second composite body was not sufficiently
water washed, the polishing rate at the first outer layer was
significantly low, being 93 nm/min. Moreover, regarding the hard
sheet of Comparative Example 2, an effort was made to uniformly
pack the hard sheet with the elastic polymer by hot pressing,
instead of doing so by adding the gelling agent into the second
emulsion. In the polishing pad with respect to Comparative Example
2, the total content of the ions was small but the R % was 30.2%,
thus exhibiting non-uniformity. As a result, only 89% of the
initial polishing rate based on the average thereof of until after
five hours, was able to be maintained. Moreover, regarding
Comparative Examples 3 and 4 wherein the total contents of the ions
were 404 .mu.g/cm.sup.3 and 504 .mu.g/cm.sup.3, respectively, only
about 84% of each of the initial polishing rates based on the
averages thereof of until after five hours, were able to be
maintained.
EXPLANATION OF REFERENCE NUMERALS
[0175] 1 non-woven fabric
[0176] 1a ultrafine fiber
[0177] 1b fiber bundle
[0178] 2 elastic polymer
[0179] 3 first outer layer
[0180] 4 intermediate layer
[0181] 5 second outer layer
* * * * *