U.S. patent application number 09/938345 was filed with the patent office on 2002-03-14 for polishing pad, polishing method, and polishing machine for mirror-polishing semiconductor wafers.
This patent application is currently assigned to Shin-Estu Handotai Co., Ltd.. Invention is credited to Fukami, Teruaki, Kobayashi, Makoto, Masumura, Hisashi, Okada, Mamoru, Takaku, Tsutomu.
Application Number | 20020031990 09/938345 |
Document ID | / |
Family ID | 26370783 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020031990 |
Kind Code |
A1 |
Masumura, Hisashi ; et
al. |
March 14, 2002 |
Polishing pad, polishing method, and polishing machine for
mirror-polishing semiconductor wafers
Abstract
There is disclosed a polishing pad for mirror-polishing a
semiconductor wafer, especially in a finish polishing process, by
use of a polishing machine which includes a turn table on which a
polishing pad is attached, a unit for feeding a polishing agent
onto a surface of the polishing pad, and a mechanism for pressing a
semiconductor wafer onto the surface of the polishing pad. The
polishing pad includes a top layer formed of a porous soft
material, a bottom layer formed of a rubber elastomer, and an
intermediate layer formed of a hard plastic sheet. The hard plastic
sheet is disposed between the top layer and the bottom layer and is
bonded to the bottom layer. In the polishing pad, undulation
produced in the bottom layer due to a horizontal force generated
during polishing is prevented from being transferred to the top
layer of the polishing pad, and unevenness in polishing stock
removal stemming from warpage or undulation of a wafer itself can
be mitigated.
Inventors: |
Masumura, Hisashi;
(Fukushima-ken, JP) ; Kobayashi, Makoto;
(Fukushima-ken, JP) ; Fukami, Teruaki;
(Fukushima-ken, JP) ; Takaku, Tsutomu;
(Fukushima-ken, JP) ; Okada, Mamoru; (Nagano-ken,
JP) |
Correspondence
Address: |
HOGAN & HARTSON L.L.P.
500 S. GRAND AVENUE
SUITE 1900
LOS ANGELES
CA
90071-2611
US
|
Assignee: |
Shin-Estu Handotai Co.,
Ltd.
|
Family ID: |
26370783 |
Appl. No.: |
09/938345 |
Filed: |
August 23, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09938345 |
Aug 23, 2001 |
|
|
|
09237881 |
Jan 27, 1999 |
|
|
|
6306021 |
|
|
|
|
Current U.S.
Class: |
451/287 |
Current CPC
Class: |
B24B 37/24 20130101;
B24B 37/22 20130101 |
Class at
Publication: |
451/287 |
International
Class: |
B24B 005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 29, 1998 |
JP |
10-32241 |
Aug 27, 1998 |
JP |
10-259411 |
Claims
What is claimed is:
1. A polishing pad for mirror-polishing a semiconductor wafer by
use of a polishing machine comprising a turn table on which a
polishing pad is attached, a unit for feeding a polishing agent
onto a surface of the polishing pad, and a mechanism for pressing a
semiconductor wafer onto the surface of the polishing pad, wherein
the polishing pad comprises: a top layer formed of a porous soft
material; a bottom layer formed of a rubber elastomer; and a hard
plastic sheet disposed between the top layer and the bottom layer
and bonded to the bottom layer.
2. A polishing pad for mirror-polishing a semiconductor wafer
according to claim 1, wherein the tensile strength of the hard
plastic sheet is 1 MPa or more.
3. A polishing pad for mirror-polishing a semiconductor wafer
according to claim 1, wherein the material of the hard plastic
sheet is selected from the group of polyethylene terephthalate,
polyimide, polyethylene, and polyurethane.
4. A polishing pad for mirror-polishing a semiconductor wafer
according to claim 2, wherein the material of the hard plastic
sheet is selected from the group of polyethylene terephthalate,
polyimide, polyethylene, and polyurethane.
5. A polishing pad for mirror-polishing a semiconductor wafer
according to claim 1, wherein the thickness of the hard plastic
sheet is 0.02 to 0.2 mm.
6. A polishing pad for mirror-polishing a semiconductor wafer
according to claim 2, wherein the thickness of the hard plastic
sheet is 0.02 to 0.2 mm.
7. A polishing pad for mirror-polishing a semiconductor wafer
according to claim 3, wherein the thickness of the hard plastic
sheet is 0.02 to 0.2 mm.
8. A polishing pad for mirror-polishing a semiconductor wafer
according to claim 4, wherein the thickness of the hard plastic
sheet is 0.02 to 0.2 mm.
9. A polishing pad for mirror-polishing a semiconductor wafer
according to claim 1, wherein the t op layer formed of a porous
soft material has an Asker C hardness of 80 or less.
10. A polishing pad for mirror-polishing a semiconductor wafer
according to claim 1, wherein the bottom layer formed of a rubber
elastomer has an Asker C hardness of 15 to 40.
11. A polishing pad for mirror-polishing a semiconductor wafer in a
finish polishing process by use of a polishing machine comprising a
turn table on which a polishing pad is attached, a unit for feeding
a polishing agent onto a surface of the polishing pad, and a
mechanism for pressing a semiconductor wafer onto the surface of
the polishing pad, wherein the polishing pad comprises: a top layer
formed of a suede-type polishing cloth; a bottom layer formed of a
rubber elastomer; and a hard plastic sheet disposed between the top
layer and the bottom layer and bonded to the bottom layer.
12. A polishing pad for mirror-polishing a semiconductor wafer
according to claim 11, wherein the thickness of the hard plastic
sheet is 0.1 to 0.4 mm.
13. A polishing pad for mirror-polishing a semiconductor wafer
according to claim 11, wherein the bottom layer formed of a rubber
elastomer has an Asker C hardness of 20 to 60 .
14. A polishing pad for mirror-polishing a semiconductor wafer
according to claim 11, wherein the thickness of the nap layer of
the top layer formed of a suede-type polishing cloth is 400 to 800
.mu.m.
15. A mirror-polishing method for a semiconductor wafer, wherein a
semiconductor wafer is mirror-polished by use of a polishing pad
for mirror-polishing a semiconductor wafer according to claim
1.
16. A mirror-polishing method for a semiconductor wafer, wherein a
semiconductor wafer is finish-polished by use of a polishing pad
for mirror-polishing a semiconductor wafer according to claim
11.
17. A mirror-polishing machine for a semiconductor comprising a
turn table on which a polishing pad is attached, a unit for feeding
a polishing agent onto a surface of the polishing pad, and a
mechanism for pressing a semiconductor wafer onto the surface of
the polishing pad, wherein a mirror-polishing pad according to
claim 1 is attached to the turn table.
18. A mirror-polishing machine for a semiconductor comprising a
turn table on which a polishing pad is attached, a unit for feeding
a polishing agent onto a surface of the polishing pad, and a
mechanism for pressing a semiconductor wafer onto the surface of
the polishing pad, wherein a polishing pad according to claim 11 is
attached to the turn table.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a polishing pad for
mirror-polishing semiconductor wafers, and to a mirror-polishing
method and a mirror-polishing machine which use the polishing
pad.
[0003] 2. Background Art
[0004] Conventionally, in a semiconductor-device fabrication
process, thin films such as oxide film, metal film, or polycrystal
silicon film are layered on a semiconductor wafer in order to form
elements thereon. In such a process, when a plurality of wiring
layers are formed, the surfaces thereof become uneven, resulting in
occurrence of a problem that focusing cannot be performed properly
when a fine pattern is exposed and printed on the surface. In order
to solve the problem, a so-called CMP (Chemical Mechanical
Polishing) technique has been proposed. In relation to the CMP
technique, use of a polishing pad having a two-layer structure has
been proposed in order to maintain a constant distribution of
thickness of films and eliminate fine unevenness on the films (see
(Junji Watanabe et al. "The Structure of a Polishing Pad for
Polishing while the Surface is Used as a Reference," papers of
Spring Meeting, The Japan Society for Precision Engineering, 183
(1997)). In the two-layer polishing pad, the bottom layer is formed
of a rubber elastomer in order to remove nonuniformity of polishing
stock removal caused by warpage or a large undulation of a wafer
itself; and a top layer is formed of hard cloth in order to
eliminate unevenness on the wafer surface generated in a
semiconductor device fabricating process, to thereby obtain a flat
surface.
[0005] Meanwhile, in the production of mirror-polished wafers for
semiconductor devices, mirror-polishing is performed in order to
obtain a desired flatness and surface roughness. In the
conventional polishing process, one surface of a semiconductor is
rough-polished by use of a hard single-layer polishing pad in order
to obtain a desired flatness, and the surface is then
finish-polished by use of a single-layer soft polishing pad in
order to obtain a desired roughness.
[0006] In general, mirror-polishing is performed in a single stage
or multiple stages, and a so-called suede-type polishing pad is
used in the final or finish polishing. In the suede-type polishing
pad, polyurethane is layered on a substrate sheet formed of
polyurethane-impregnated polyester felt or the like, a foam layer
is grown in the polyurethane, and the surface portion of the foam
layer is removed in order to form fluffy openings in the foam
layer. When the surface of a semiconductor wafer is removed by an
amount of a few to a few hundreds of nano-millimeters through use
of such a suede-type polishing pad, surface roughness having a
period of a few to a few tens of nano-millimeters (hereinafter may
be referred to as "haze") can be improved to a sufficient
degree.
[0007] By the way, with a recent increase in the degree of
integration of semiconductor devices, the requirement for the
flatness of wafers has become more strict. Therefore, a
conventional polishing method for semiconductor mirror-polished
wafers cannot achieve a flatness required for production of
state-of-the-art semiconductor devices. Therefore, there has arisen
a requirement to maintain a flatness obtained through
flatness-improving machining, such as double-side polishing or
surface grinding, until completion of final or finish
polishing.
[0008] Further, since improvement of surface roughness--which is a
purpose of finish polishing--can be achieved by finish polishing in
which the polishing stock removal has been set to a very small
amount as described above, the degradation of flatness due to the
finish polishing has been considered ignorable.
[0009] In general, the above-described CMP technique is employed in
order to achieve uniform polishing stock removal. However, when a
two-layer polishing pad having a hard top layer that has
conventionally been used in the CMP technique is used, a polished
wafer will have a degraded surface roughness. Especially, when such
a two-layer polishing pad is used for finish polishing, improvement
in the haze level, which is the purpose of the finish polishing,
becomes difficult. Further, when a two-layer polishing pad having a
top layer formed of a suede-type polishing pad that has
conventionally been used for finish polishing is used, undulation
is generated in the bottom layer made of rubber elastomer, due to a
horizontal force generated during polishing, and the undulation is
transferred to the top layer of the polishing pad, resulting in
occurrence of a problem that a wafer is polished unevenly in terms
of polishing stock removal. Especially, this problem tends to
become remarkable in the vicinity of the edge portion of a wafer.
Since the top layer is softer than the top layer that has been used
in conventional two-layer polishing pads, the top layer exhibits
excessively high performance of following undulation of the bottom
layer, resulting in degradation in uniformity of polishing stock
removal at the peripheral portion of a wafer, which causes a
variation in flatness before and after finish polishing.
[0010] The inventors of the present invention investigated
variations in flatness caused by finish polishing, and found that
the flatness can be degraded to a large degree even by finish
polishing in which stock removal is very small. Accordingly, the
inventors considered that there must be developed a finish
polishing method that does not degrade flatness or that can secure
uniform polishing stock removal.
SUMMARY OF THE INVENTION
[0011] The present invention has been accomplished to solve the
above-mentioned problems, and an object of the present invention is
to provide a polishing pad for mirror-polishing, in which
undulation produced in a bottom layer made of rubber elastomer due
to a horizontal force generated during polishing is prevented from
being transferred to a top layer of the polishing pad, and which
mitigates unevenness in polishing stock removal stemming from
warpage or undulation of a wafer itself, as well as a polishing
method and a polishing machine which utilize the polishing pad.
[0012] Another object of the present invention is to provide a
polishing pad for finish mirror-polishing which has the same
features as those of the above-described polishing pad for
mirror-polishing, as well as a polishing method and a polishing
machine for finish polishing which utilize the polishing pad.
[0013] In order to achieve the above object, the present invention
provides a polishing pad for mirror-polishing a semiconductor wafer
by use of a polishing machine comprising a turn table on which a
polishing pad is attached, a unit for feeding a polishing agent
onto a surface of the polishing pad, and a mechanism for pressing a
semiconductor wafer onto the surface of the polishing pad, wherein
the polishing pad comprises a top layer formed of a porous soft
material, a bottom layer formed of a rubber elastomer, and a hard
plastic sheet disposed between the top layer and the bottom layer
and bonded to the bottom layer.
[0014] Since the polishing pad has a three-layer structure
including a top layer formed of a porous soft material, an
intermediate layer formed of a hard plastic sheet, and a bottom
layer formed of a rubber elastomer, and the hard plastic sheet
serving as the intermediate layer has sufficient stiffness,
undulation produced in a bottom layer made of rubber elastomer due
to a horizontal force generated during polishing is prevented from
being transferred to a top layer of the polishing pad. In addition,
unevenness in polishing stock removal stemming from warpage or
undulation of a wafer itself is mitigated, so that semiconductor
wafers having a desired flatness and surface roughness can be
produced.
[0015] In this case, the tensile strength of the hard plastic sheet
is preferably 1 MPa or more; the material of the hard plastic sheet
is preferably selected from the group of polyethylene terephthalate
(PET), polyimide, polyethylene, and polyurethane; and the thickness
of the hard plastic sheet is preferably 0.02 to 0.2 mm.
[0016] When the tensile strength of the hard plastic sheet serving
as the intermediate layer is less than 1 MPa, a sufficient degree
of stiffness cannot be obtained. Therefore, a material having a
tensile strength of 1 MPa or more is preferably selected for the
intermediate layer.
[0017] When the material of the hard plastic sheet is selected from
the above-described materials, physical properties required in the
present invention are obtained.
[0018] When the thickness of the hard plastic sheet is less than
0.02 mm, the stiffness becomes insufficient, so that the plastic
sheet cannot absorb undulation generated in the bottom layer and
generates resonance. When the thickness of the hard plastic sheet
exceeds 0.2 mm, the stiffness becomes excessively high, so that
warpage or undulation of the hard plastic sheet itself affects
uniformity in polishing stock removal. Therefore, the thickness of
the hard plastic sheet is preferably set to fall within the range
of 0.02 to 0.2 mm.
[0019] Further, the top layer formed of a porous soft material
preferably has an Asker C hardness of 80 or less, and the bottom
layer formed of a rubber elastomer preferably has an Asker C
hardness of 15 to 40.
[0020] When the hardnesses of the top layer and the bottom layer
are set in the above-described manner, the characteristics of the
polishing pad having a three-layer structure can be utilized to a
sufficient degree, with the result that a mirror polished wafer
having a desired flatness and surface roughness can be obtained.
When the Asker C hardness of the top layer exceeds 80, the surface
roughness is undesirably degraded. Therefore, the Asker C hardness
of the top layer is preferably set to 80 or less. When the Asker C
hardness of the bottom layer is less than 15, the bottom layer
becomes excessively soft, resulting in generation of large
undulation. When the Asker C hardness of the bottom layer exceeds
40, the hardness becomes excessively high, so that warpage or
undulation of the bottom layer itself affects uniformity in
polishing stock removal. Therefore, the hardness of the bottom
layer is preferably set to fall within the range of 15 to 40.
[0021] The present invention also provides a multi-layer polishing
pad for mirror-polishing the surface of a semiconductor wafer in a
finish polishing process by use of a polishing machine comprising a
turn table on which a polishing pad is attached, a unit for feeding
a polishing agent onto a surface of the polishing pad, and a
mechanism for pressing a semiconductor wafer onto the surface of
the polishing pad, wherein the multi-layer polishing pad comprises
a top layer formed of a suede-type polishing cloth, a bottom layer
formed of a rubber elastomer, and a hard plastic sheet disposed
between the top layer and the bottom layer and bonded to the bottom
layer.
[0022] Since the polishing pad has a three-layer structure
including a top layer formed of suede-type polishing cloth, an
intermediate layer formed of a hard plastic sheet, and a bottom
layer formed of a rubber elastomer, and the hard plastic sheet
serving as the intermediate layer has sufficient stiffness,
undulation produced in a bottom layer made of rubber elastomer due
to a horizontal force generated during finish polishing is
prevented from being transferred to the top layer of the polishing
pad. In addition, unevenness in polishing stock removal stemming
from warpage or undulation of a wafer itself is mitigated, so that
semiconductor wafers having excellent surfaces of a desired
flatness and haze level can be produced.
[0023] In this finish polishing, the thickness of the hard plastic
sheet is preferably 0.1 to 0.4 mm.
[0024] When the thickness of the hard plastic sheet used in the
polishing pad for finish polishing is set to fall within the
above-described range, the hard plastic sheet has a proper
stiffness, so that the plastic sheet can sufficiently absorb the
undulation generated in the bottom layer and does not generate
resonance. Further, warpage or undulation of the hard plastic sheet
itself does not affect uniformity in polishing stock removal.
[0025] In this case, the bottom layer formed of a rubber elastomer
preferably has an Asker C hardness of 20 to 60.
[0026] When the hardness of the bottom layer is set to fall within
the above-described range, the bottom layer does not become
excessively soft, so that no large undulation is generated.
Further, since the bottom layer does not become excessively hard,
warpage or undulation of the bottom layer itself does not affect
uniformity in polishing stock removal.
[0027] Moreover, the thickness of the nap layer of the top layer
formed of the above-described suede-type polishing cloth is
preferably 400 to 800 .mu.m.
[0028] The nap layer refers to the surface-layer portion of the
suede-type polishing cloth, which is formed by the process of
growing a foam layer and removing the surface portion of the foam
layer in order to form openings in the foam layer.
[0029] When the nap layer of the top layer of the polishing pad
used for finish polishing has a thickness of the above-described
range, the foam diameter at the openings decreases, so that the
haze level is improved. Further, the friction resistance between a
wafer and the polishing pad decreases, with the result that the
degree of undulation of the bottom layer formed of a rubber
elastomer decreases. Therefore, the degree of undulation that is
transmitted to the top surface via the intermediate layer can be
decreased.
[0030] The present invention further provides a mirror-polishing
method for a semiconductor wafer, wherein a semiconductor wafer is
mirror-polished by use of a polishing pad for mirror polishing
according to the present invention.
[0031] According to the method of the present invention, undulation
produced in a bottom layer made of rubber elastomer due to a
horizontal force generated during polishing is absorbed by the
intermediate layer, with the result that uniformity in polishing
stock removal and surface roughness are improved.
[0032] The present invention also provides a mirror-polishing
method for a semiconductor wafer, wherein a semiconductor wafer is
finish-polished by use of a multi-layer polishing pad for finish
polishing according to the present invention.
[0033] According to the method of the present invention, in the
finish polishing, a haze level comparable to that obtained through
use of a single-layer polishing pad is obtained without impairment
of a high degree of uniformity in polishing stock removal.
[0034] Moreover, the present invention provides a mirror-polishing
machine for a semiconductor comprising a turn table on which a
polishing pad is attached, a unit for feeding a polishing agent
onto a surface of the polishing pad, and a mechanism for pressing a
semiconductor wafer onto the surface of the polishing pad, wherein
the mirror-polishing pad according to the present invention is
attached to the turn table.
[0035] In the polishing machine in which the polishing pad having a
three-layer structure according to the present invention is
attached to the turn table, due to the stiffness of the hard
plastic sheet serving as the intermediate layer, undulation
produced in a bottom layer made of rubber elastomer due to a
horizontal force generated during polishing is prevented from being
transferred to a top layer of the polishing pad. In addition,
unevenness in polishing stock removal stemming from warpage or
undulation of a wafer itself is mitigated, so that semiconductor
wafers having a desired flatness and surface roughness can be
produced. Moreover, since the polishing machine can cope with a
recent increase in the degree of integration in a device
fabrication process, the productivity and yield of semiconductor
devices can be improved considerably.
[0036] The present invention also provides a mirror-polishing
machine for a semiconductor comprising a turn table on which a
polishing pad is attached, a unit for feeding a polishing agent
onto a surface of the polishing pad, and a mechanism for pressing a
semiconductor wafer onto the surface of the polishing pad, wherein
the multi-layer polishing pad for finish polishing according to the
present invention is attached to the turn table.
[0037] In the polishing machine in which the polishing pad having a
three-layer structure according to the present invention is
attached to the turn table, due to the stiffness of the hard
plastic sheet serving as the intermediate layer, undulation
produced in a bottom layer made of rubber elastomer due to a
horizontal force generated especially during finish polishing is
prevented from being transferred to a top layer of the polishing
pad. In addition, unevenness in polishing stock removal stemming
from warpage or undulation of a wafer itself is mitigated, so that
semiconductor wafers having a desired flatness and haze level can
be produced. Moreover, since the polishing machine can cope with a
recent increase in the degree of integration in a device
fabrication process, the productivity and yield of semiconductor
devices can be improved considerably.
[0038] As described above, in the present invention, undulation
produced in the rubber elastomer serving as the bottom layer of the
polishing pad due to a horizontal force generated during mirror
polishing is prevented from being transferred to the top layer of
the polishing pad. In addition, unevenness in polishing stock
removal stemming from warpage or undulation of a wafer itself is
mitigated, so that a produced wafer will have a mirror-finished
surface having an excellent flatness and improved surface
roughness. Therefore, it becomes possible to cope with an increase
in the degree of integration in a device fabrication process, while
improving the productivity and yield of semiconductor devices.
Especially, during final or finish polishing, a desirable haze
level is maintained and the uniformity in flatness is improved
through polishing in which the stock removal is set to a relatively
small amount.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 is a view schematically showing the structure of a
single-side polishing machine to which a polishing pad for
mirror-polishing according to the present invention is attached;
and
[0040] FIGS. 2A and 2B are explanatory views for comparison between
a three-layer polishing pad according to the present invention and
a conventional two-layer polishing pad in terms of action and
effect, wherein FIG. 2A shows the three-layer polishing pad
according to the present invention, and FIG. 2B shows the
conventional two-layer polishing pad.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0041] An embodiment of the present invention will now be
described; however, the present invention is not limited
thereto.
[0042] The present inventors found that when semiconductor wafers
are mirror-polished by use of a two-layer polishing pad that has
been used in the CMP technique, in some cases, a sufficient degree
of uniformity in terms of polishing stock removal cannot be
obtained and surface roughness does not reach an acceptable level.
The inventors investigated the causes of the above problem and
found that due to a horizontal force generated during polishing,
undulation is generated in rubber elastomer serving as a bottom
layer, the undulation becomes large especially in the vicinity of
the edge of a wafer, and such a large undulation is transferred to
the top layer of the polishing pad.
[0043] Through investigations and studies on the material and
structure of the polishing pad performed for finding a measure for
preventing generation of undulation in the bottom layer of the
polishing pad, the present inventors found that the above-described
problem can be solved by inserting a hard plastic sheet between the
top layer and the bottom layer of the above-described two-layer
polishing pad. The present invention was achieved on the basis of
this finding and through thorough investigation of other
conditions.
[0044] First, with reference to the drawings, there will be
described a single-side polishing machine in which a polishing pad
for mirror-polishing according to the present invention is
used.
[0045] As shown in FIG. 1, the single-side polishing machine is
constructed to polish one side of a semiconductor wafer. That is,
the polishing machine 10 includes a turn table 12, a wafer holder
13, and a polishing agent supply unit 14. A polishing pad 16 is
bonded to the top face of the turn table 12. The turn table 12 is
rotated at a predetermined rotary speed via a rotary shaft 17.
[0046] The wafer holder 13 holds a wafer W at the bottom surface
thereof by means of vacuum suction or the like, and is rotated via
a rotary shaft 18. The wafer holder 13 presses the wafer W against
the polishing pad 16 with a predetermined load. The polishing agent
supply unit 14 supplies polishing agent 19 onto the polishing pad
16 at a predetermined flow rate. The polishing agent 19 enters the
space between the wafer W and the polishing pad 16, so that the
wafer W is polished.
[0047] Next, a three-layer polishing pad of the present invention
will be described.
[0048] The polishing pad according to the present invention is used
for mirror-polishing a semiconductor wafer by use of a polishing
machine including at least a turn table on which a polishing pad is
attached, a unit for feeding a polishing agent onto a surface of
the polishing pad, and a mechanism for pressing a semiconductor
wafer onto the surface of the polishing pad, and comprises a top
layer formed of a porous soft material, a bottom layer formed of a
rubber elastomer, and a hard plastic sheet disposed between the top
layer and the bottom layer and bonded to the bottom layer.
[0049] Since the polishing pad has a three-layer structure
including a top layer formed of a porous soft material, an
intermediate layer formed of a hard plastic sheet, and a bottom
layer formed of a rubber elastomer, due to the stiffness of the
hard plastic sheet serving as the intermediate layer, undulation
produced in a bottom layer made of rubber elastomer due to a
horizontal force generated during polishing is prevented from being
transferred to a top layer of the polishing pad. In addition,
unevenness in polishing stock removal stemming from warpage or
undulation of a wafer itself is mitigated, so that semiconductor
wafers having a desired flatness and surface roughness can be
produced.
[0050] FIGS. 2A and 2B are explanatory views for comparison between
a three-layer polishing pad according to the present invention and
a conventional two-layer polishing pad, in terms of action and
effect.
[0051] FIG. 2A shows the case of a three-layer polishing pad 20
according to the present invention; and indicates that due to the
rigidity of the hard plastic sheet 22 serving as an intermediate
layer, undulation of the bottom layer 23 formed of rubber elastomer
is suppressed and is prevented from being transmitted to the top
layer 21.
[0052] FIG. 2B shows the case of a conventional two-layer polishing
pad 25; and indicates that since the polishing pad 25 is formed of
a top layer 21 and a bottom layer 23 with no intermediate layer
disposed therebetween, undulation is generated in the bottom layer
23 at a position corresponding to the forward end of the wafer W
with respect to the direction of relative rotation thereof, and the
thus-generated undulation is transmitted to the top layer 21, and
that such a phenomenon occurs remarkably at the periphery of the
wafer W.
[0053] The material of the hard plastic sheet that is used in the
present invention and that provides the above-described excellent
performance is preferably a plastic that is categorized as a
relatively hard plastic such as PET, polyimide, polyethylene, or
polyurethane.
[0054] The hard plastic sheet preferably has a thickness in the
range of 0.02 to 0.2 mm. When the thickness of the hard plastic
sheet is less than 0.02 mm, the stiffness becomes insufficient, so
that the plastic sheet cannot absorb undulation generated in the
bottom layer and generates resonance. When the thickness of the
hard plastic sheet exceeds 0.2 mm, the stiffness becomes
excessively high, so that warpage or undulation of the hard plastic
sheet itself undesirably affects uniformity in polishing stock
removal.
[0055] The tensile strength of the hard plastic sheet is preferably
1 MPa or more, because a sufficient degree of stiffness cannot be
obtained when the tensile strength of the hard plastic sheet is
less than 1 MPa.
[0056] Examples of the porous soft material used as the top layer
of the three-layer polishing pad include velour-type artificial
leather formed of urethane-impregnated nonwoven fabric and
suede-type artificial leather formed of foamed polyurethane, which
are generally used for mirror-polishing of semiconductor wafers. No
limitation is imposed on the material of the top layer, except for
the surface hardness. The top layer preferably has an Asker C
hardness of 80 or less. When the Asker C hardness of the top layer
exceeds 80, the surface roughness is undesirably degraded.
[0057] Examples of the rubber elastomer used as the bottom layer of
the three-layer polishing pad include foamed silicone rubber,
foamed urethane rubber, and other sponge-like rubber elastomers.
The rubber elastomer preferably has an Asker C hardness of 15 to
40. When the Asker C hardness of the bottom layer is less than 15,
the bottom layer becomes excessively soft, resulting in generation
of large undulation. When the Asker C hardness of the bottom layer
exceeds 40, the hardness becomes excessively high, so that warpage
or undulation of the bottom layer itself affects uniformity in
polishing stock removal. Therefore, the hardness of the bottom
layer is preferably set to fall within the range of 15 to 40.
[0058] As described above, when the polishing pad is formed into a
three layer structure through use of materials that have physical
properties suitable for the respective layers, the properties of a
mirror-polishing pad can be brought into full play, so that
mirror-polished wafers having a desired flatness and surface
roughness can be obtained.
[0059] Next, there will be described a three-layer polishing pad
suitable for final or finish polishing among various kinds of
mirror-polishing processes. The three-layer polishing pad suitable
for final or finish polishing improves uniformity in flatness while
maintaining a good haze level through polishing involving a small
amount of stock removal among the above-described three-layer
polishing pads for mirror polishing. The structure of this
polishing pad is basically the same as that of the above-described
three-layer polishing pad, and a description will be given of only
the points that have been improved for finishing polishing.
[0060] As the top layer of the polishing pad applied for finish
polishing, there is used a so-called suede-type polishing pad which
is formed by a method in which polyurethane is layered on a
substrate sheet formed of polyurethane-impregnated polyester felt;
a foam layer is grown in the polyurethane; and the surface portion
of the foam layer is removed in order to form openings in the foam
layer.
[0061] The suede-type top layer preferably has an Asker C hardness
of 80 or less. In this case, since the surface roughness having a
longer period becomes better than the level of haze having a
shorter period, great change in flatness is prevented.
[0062] Further, the nap layer serving as an opening portion
preferably has a thickness of 400 to 400 .mu.m. When the nap layer
has a thickness of the above-described range, the foam diameter
decreases, so that the haze level is improved. Further, the
friction resistance between a wafer and the polishing pad
decreases, with the result that the degree of undulation of the
bottom layer formed of a rubber elastomer decreases. Therefore, the
degree of undulation that is transmitted to the top surface via the
intermediate layer can be decreased.
[0063] The action and effect of the hard plastic sheet serving as
the intermediate layer are the same as the action and effect of the
hard plastic sheet used in the above-described three-layer
polishing pad for mirror polishing. The material of the hard
plastic sheet according to the present invention that provides the
above-described excellent performance is preferably a plastic that
is categorized as a relatively hard plastic such as PET, polyimide,
polyethylene, or polyurethane.
[0064] The hard plastic sheet preferably has a thickness in the
range of 0.1 to 0.4 mm. In the finish polishing, the hard plastic
sheet has a proper stiffness when the thickness of the hard plastic
sheet is set to the above-described range, so that the plastic
sheet sufficiently absorbs undulation generated in the bottom layer
formed of a rubber elastomer and does not generate resonance.
Further, warpage or undulation of the hard plastic sheet itself
does not affect uniformity in polishing stock removal in the final
polishing.
[0065] The tensile strength of the hard plastic sheet is preferably
1 MPa or more, in order to secure a sufficient degree of
stiffness.
[0066] Examples of the rubber elastomer used as the bottom layer of
the three-layer polishing pad include foamed silicone rubber,
foamed urethane rubber, and other sponge-like rubber elastomers.
The rubber elastomer preferably has an Asker C hardness of 20 to
60. When the hardness of the bottom layer is set to fall within the
above-described range, the bottom layer does not become excessively
soft, so that no large undulation is generated. Further, since the
bottom layer does not become excessively hard, warpage or
undulation of the bottom layer itself does not affect uniformity in
polishing stock removal.
[0067] As described above, when the polishing pad is formed into a
three layer structure through use of materials that have physical
properties suitable for the respective layers, the properties of a
finish-polishing pad can be brought into full play, so that
mirror-polished wafers having a desired flatness and haze level can
be obtained. The reason why the physical properties of the
polishing pad are slightly changed for finish polishing is that
stock removal is set to a small amount in the finish polishing, and
polishing conditions, such as polishing pressure and roughness of
abrasive grains, in the finish polishing differ from those of other
polishing processes.
EXAMPLES
[0068] The present invention will next be described in detail by
way of examples; however, the invention is not limited only to
these examples.
[0069] Asker C hardness indicating the hardness of the top layer
and bottom layer will first be explained.
[0070] Asker C hardness is measured in accordance with JIS K 6301
and by use of a C-type spring hardness tester, in which a needle is
protruded by a spring force through a center hole formed in a
pressing surface. The pressing surface of the tester is brought
into contact with a surface of a sample rubber, and a distance
which the pressing needle is pushed back by the rubber surface is
measured as a hardness. The C-type tester vertically presses the
samples under a load of 5000 g.
Example 1
[0071] (1) Three-layer polishing pad
[0072] top layer: SUBA400 (trade name, by Rodel Nitta K.K., a
velour type polishing pad made of nonwoven fabric impregnated with
urethane resin. Asker C hardness: 76);
[0073] bottom layer: SE-200 (trade name, by Sun Polymer K.K.,
foamed silicone rubber sheet, Asker C hardness: 16);
[0074] intermediate layer: PET sheet (thickness: 50 .mu.m)
[0075] (2) Polishing agent: colloidal silica (particle size: a few
nm, silica concentration: 2.5 wt. %, pH: 10.5)
[0076] (3) Polishing conditions: single-side polishing, load: 300
g/cm.sup.2, relative polishing speed: 50 m/min, polishing time: 13
minutes)
[0077] (4) Sample to be polished: silicon single-crystal wafer
(thickness: 735 .mu.m)
[0078] Mirror-polishing was performed under the above-mentioned
conditions (1) to (4), and thickness distribution over the entire
surface of the wafer before and after polishing was measured by use
of a capacitance type thickness meter. Uniformity of the polishing
stock removal was calculated by dividing the difference between the
maximum stock removal and the minimum stock removal in the wafer
plane (namely the maximum variation in stock removal) by the
average stock removal. The average stock removal was 11 .mu.m and
the uniformity in stock removal was 2.6%. Further, the surface
micro roughness of the polished wafer was measured by use of an
optical interferometric surface roughness meter to obtain an Rrms
(root mean square roughness) of 0.25 nm. In this regard, the target
Rrms was 0.35 nm.
Example 2
[0079] (1) Three-layer polishing pad:
[0080] top layer: SUBA400 (as described above, Asker C hardness:
76);
[0081] bottom layer: SE-200 (as described above, Asker C hardness:
20, 25, 43 (3 levels));
[0082] intermediate layer: PET sheet (thickness: 50 .mu.m)
[0083] (2) Polishing agent: colloidal silica (as described
above)
[0084] (3) Polishing conditions: single-side polishing, load: 300
g/cm.sup.2, relative polishing speed: 50 m/min, polishing stock
removal: 10 .mu.m
[0085] (4) Sample to be polished: silicon single-crystal wafer
(thickness: 735 .mu.m)
[0086] Mirror-polishing was performed under the above-mentioned
conditions (1) to (4), and the uniformity of polishing stock
removal was measured to obtain the following results:
1 Asker C hardness Uniformity of stock removal of bottom layer by
polishing (%) 20 2.3 25 1.8 43 8.2 16* 2.6* *: Example 1
[0087] As is apparent from the above results, a uniformity in stock
removal of not greater than 5% is obtained when the hardness C of
the rubber elastomer serving as the bottom layer is within the
range of layer of 15 to 40.
Example 3
[0088] (1) Three-layer polishing pad:
[0089] top layer: SUBA400 (as described above, Asker C hardness:
76);
[0090] bottom layer: SE-200 (as described above, Asker C hardness:
16);
[0091] intermediate layer: polyimide sheet (thickness: 0.0125,
0.05, 0.1, 0.3 mm (4 levels))
[0092] (2) Polishing agent: colloidal silica (as described
above)
[0093] (3) Polishing conditions: single-side polishing, load: 300
g/cm.sup.2, relative polishing speed: 50 m/min, polishing stock
removal: 10 .mu.m
[0094] (4) Sample to be polished: silicon single-crystal wafer
(thickness: 735 .mu.m)
[0095] Mirror-polishing was performed under the above-mentioned
conditions (1) to (4), and the uniformity of polishing stock
removal was measured to obtain the following results:
2 Thickness of Uniformity of stock removal intermediate layer by
polishing (%) 0.0125 5.8 0.05 2.4 0.1 3.6 0.3 7.6
[0096] As is apparent from the above results, when the hard plastic
sheet serving as the intermediate layer is excessively thin, the
function as the intermediate layer is lost, resulting in poor
uniformity in stock removal. When the hard plastic sheet serving as
the intermediate layer is excessively thick, the function of the
rubber elastomer serving as the bottom layer is lost, resulting in
poor uniformity in stock removal. Therefore, excellent uniformity
in stock removal is obtained when the thickness of the intermediate
layer falls in the range of 0.02 to 0.2 mm.
Example 4
[0097] (1) Three-layer polishing pad:
[0098] top layer: SUBA400 (as described above, Asker C hardness:
76);
[0099] bottom layer: SE-200 (as described above, Asker C hardness:
16);
[0100] intermediate layer: the following four sheets:
[0101] polyurethane B (thickness: 0.1 mm, tensile strength: 2.5
MPa)
[0102] polyurethane A (thickness: 0.1 mm, tensile strength: 0.5
Mpa, product of low degree of polymerization)
[0103] polyimide (thickness: 0.1 mm, tensile strength: 82 MPa)
[0104] PET (thickness: 0.1 mm, tensile strength: 135 MPa)
[0105] (2) Polishing agent: colloidal silica (as described
above)
[0106] (3) Polishing conditions: single-side polishing, load: 300
g/cm.sup.2, relative polishing speed: 50 m/min, polishing stock
removal: 10 .mu.m
[0107] (4) Sample to be polished: silicon single-crystal wafer
(thickness: 735 .mu.m)
[0108] Mirror-polishing was performed under the above-mentioned
conditions (1) to (4), and the uniformity of polishing stock
removal was measured to obtain the following results:
3 Intermediate layer Uniformity of Thickness Tensile strength stock
removal Material (mm) (MPa) by polishing (%) polyurethane A 0.1 0.5
6.5 polyurethane B 0.1 2.5 4.5 polyimide 0.1 82 3.6 PET 0.1 135
3.2
[0109] As is apparent from the above results, when the hard plastic
sheet serving as the intermediate layer has a tensile strength of 1
MPa or higher, excellent uniformity in stock removal of 5% or less
is obtained.
Example 5
[0110] (1) Three-layer polishing pad:
[0111] top layer: SUBA400 (Asker C hardness: 76), SUBA600 (Asker C
hardness: 85);
[0112] bottom layer: SE-200 (as described above, Asker C hardness:
16);
[0113] intermediate layer: PET sheet (thickness: 50 .mu.m)
[0114] (2) Polishing agent: the same as in Example 1
[0115] (3) Polishing conditions: the same as in Example 1
[0116] (4) Sample to be polished: the same as in Example 1
[0117] Mirror-polishing was performed at the average polishing
stock removal of 9.2 .mu.m, and the uniformity in stock removal was
measured to obtain the following results:
4 Asker C hardness Uniformity of stock removal of the top layer by
polishing (%) 76 2.6 85 5.5
[0118] As is apparent from the above results, when the top layer
has an Asker C hardness of 80 or less, excellent uniformity in
stock removal of 5% or less is obtained.
Comparative Example 1
[0119] (1) Single-layer polishing pad: only SUBA 400 (as described
above, Asker C hardness: 76);
[0120] (2) Polishing agent: the same as Example 1
[0121] (3) Polishing condition: the same as Example 1
[0122] (4) Sample to be polished: the same as Example 1
[0123] Mirror-polishing was performed at the average polishing
stock removal of 5.2 .mu.m. The uniformity in stock removal of the
polished wafer was 32.2%.
Comparative Example 2
[0124] (1) Two-layer polishing pad: two-layer polishing pad
composed of a top layer and a bottom layer and obtained through
omission of the hard plastic sheet serving as the intermediate
layer from the three-layer polishing pad of Example 1.
[0125] (2) Polishing agent: the same as Example 1
[0126] (3) Polishing condition: the same as Example 1
[0127] (4) Sample to be polished: the same as Example 1
[0128] Mirror-polishing was performed at the average polishing
stock removal of 11 .mu.m. The uniformity in stock removal of the
polished wafer was 6.5% .
[0129] As is apparent from the above Comparative examples,
uniformity in stock removal degrades remarkably when
mirror-polishing is performed through use of a single-layer
polishing pad including only a top layer formed of a porous soft
material or through use of a two-layer polishing pad obtained
through omission of the hard plastic sheet serving as the
intermediate layer from the three-layer polishing pad of the
present invention.
Example 6
[0130] (1) Three-layer polishing pad:
[0131] top layer: CIEGAL 7355 (trade name, by Daiich Lace K.K.,
suede-type polishing pad, Asker C hardness: 73);
[0132] bottom layer: HN-400 (trade name, by Tigers Polymer K.K.,
foamed nitrile rubber sheet, Asker C hardness: 43);
[0133] intermediate layer: PET sheet (thickness: 300 .mu.m)
[0134] (2) Polishing agent: colloidal silica (particle size: a few
nm, silica concentration: 0.5 wt. %, pH: 9.5)
[0135] (3) Polishing condition: single-side polishing, load: 200
g/cm.sup.2, relative polishing speed: 50 m/min, polishing time: 6
minutes)
[0136] (4) Sample to be polished: silicon single-crystal wafer
(thickness: 735 .mu.m)
[0137] Mirror-polishing was performed under the above-mentioned
conditions (1) to (4), and GBIR (Grobal Back-side Ideal Range) as
indices for evaluation of flatness before and after polishing was
compared.
[0138] GBIR is an index for evaluating thickness variation in the
wafer plane and standardized by SEMI (Semiconductor Equipment and
Materials Institute) standard M1 etc. The evaluation was performed
by use of a capacitance type thickness meter. A measurement error
was about .+-.0.05 .mu.m. Mirror-polishing was performed at the
average polishing stock removal of 0.6 .mu.m. The amount of change
in GBIR was 0.03 .mu.m.
[0139] A haze level of polished wafer was measured by use of a
light scattering surface roughness meter. A measured haze level was
37 bit. In this regard, the target of the level was 40 bit. The
smaller the bit value is, the better the haze level is.
Example 7
[0140] (1) Three-layer polishing pad:
[0141] top layer: CIEGAL 7355 (as described above, Asker C
hardness: 73);
[0142] bottom layer: HN-400 (as described above, Asker C hardness:
15 , 25, 65 (3 levels));
[0143] intermediate layer: PET sheet (thickness: 300 .mu.m)
[0144] (2) Polishing agent: colloidal silica (as described
above)
[0145] (3) Polishing condition: single-side polishing, load: 200
g/cm.sup.2, relative polishing speed: 50 m/min, polishing time: 6
minutes, polishing stock removal: 0.6 .mu.m
[0146] (4) Sample to be polished: silicon single-crystal wafer
(thickness: 735 .mu.m)
[0147] Finish-polishing was performed under the above-mentioned
conditions (1) to-(4), and the amount of change in GBIR was
measured to obtain the following results.
5 Asker C hardness Amount of change of the bottom layer in GBIR
(.mu.m) 15 0.13 25 0.02 65 0.16 43* 0.03* *: Example 6
[0148] As is apparent from the above results, the amount of change
in GBIR can be suppressed within the range of the measurement
error, when the rubber elastomer serving as the bottom layer has an
Asker C hardness in the range of 20 to 60.
Example 8
[0149] (1) Three-layer finish-polishing pad:
[0150] top layer: CIEGAL 7355 (as described above, Asker C
hardness: 73);
[0151] bottom layer: HN-400 (as described above, Asker C hardness:
43);
[0152] intermediate layer: PET sheet (thickness: 0.05, 0.1, 0.3,
0.5 mm (4 levels))
[0153] (2) Polishing agent: colloidal silica (as described
above)
[0154] (3) Polishing condition: single-side polishing, load: 200
g/cm.sup.2, relative polishing speed: 50 m/min, polishing time: 6
minutes, polishing stock removal: 0.6 .mu.m
[0155] (4) Sample to be polished: silicon single-crystal wafer
(thickness: 735 .mu.m)
[0156] Finish-polishing was performed under the above-mentioned
conditions (1) to (4), and the amount of change in GBIR was
measured to obtain the following results.
6 Thickness of the Amount of change intermediate layer (mm) in GBIR
(.mu.m) 0.05 0.14 0.1 0.04 0.3 0.03 0.5 0.10
[0157] As is apparent from the above results, the amount of change
in GBIR can be suppressed within the range of the measurement error
when the hard plastic sheet serving as the intermediate layer has a
thickness in the range of 0.1 to 0.4 mm.
Example 9
[0158] (1) Three-layer finish-polishing pad:
[0159] top layer: CIEGAL 7355 (as described above, Asker C
hardness: 73);
[0160] bottom layer: HN-400 (as described above, Asker C hardness:
43);
[0161] intermediate layer: the following four sheets:
[0162] polyurethane A (thickness: 0.3 mm, tensile strength: 0.5
MPa)
[0163] polyurethane B (thickness: 0.3 mm, tensile strength: 2.5
MPa)
[0164] polyimide (thickness: 0.3 mm, tensile strength: 82 MPa)
[0165] PET (thickness: 0.3 mm, tensile strength: 135 MPa)
[0166] (2) Polishing agent: colloidal silica (as described
above)
[0167] (3) Polishing condition: single-side polishing, load: 200
g/cm.sup.2, relative polishing speed: 50 m/min, polishing time: 6
minutes, polishing stock removal: 0.6 .mu.mm
[0168] (4) Sample to be polished: silicon single-crystal wafer
(thickness: 735 .mu.m)
[0169] Finish-polishing was performed under the above-mentioned
conditions (1) to (4), and the amount of change in GBIR was
measured to obtain the following results:
7 Intermediate layer Amount of Thickness Tensile strength change in
Material (mm) (MPa) GBIR (.mu.m) polyurethane A 0.3 0.5 0.15
polyurethane B 0.3 2.5 0.04 polyimide 0.3 82 0.03 PET 0.3 135
0.03
[0170] As is apparent from the above results, the amount of change
in GBIR can be suppressed within the range of the measurement
error, when the hard-plastic-sheet intermediate layer has a tensile
strength of 1 MPa or more.
Example 10
[0171] (1) Three-layer finish-polishing pad:
[0172] top layer: two kinds of suede type polishing pads having
different Asker C hardnesses that were produced by impregnating
urethane into felt by use of different methods. (Asker C hardness:
73, 85);
[0173] bottom layer: HN-400 (as described above, Asker C hardness:
43); intermediate layer: PET sheet (thickness: 300 .mu.m)
[0174] (2) Polishing agent: the same as Example 7
[0175] (3) Polishing condition: the same as Example 7
[0176] (4) Sample to be polished: the same as Example 7
[0177] Finish-polishing was performed under the above-mentioned
conditions (1) to (4), and the amount of change in GBIR was
measured to obtain the following results:
8 Asker C hardness Amount of change of the top layer in GBIR
(.mu.m) 73 0.03 85 0.12
[0178] As is apparent from the above results, the amount of change
in GBIR can be suppressed within the range of the measurement
error, when the top layer has an Asker C hardness of 80 or
less.
Example 11
[0179] (1) Three-layer finish-polishing pad:
[0180] top layer: four kinds of polishing pads having different nap
layer thickness (Asker C hardness: 73, nap layer thickness: 350,
500, 700, 900 .mu.m);
[0181] bottom layer: HN-400 (as described above, Asker C hardness:
43);
[0182] intermediate layer: PET sheet (thickness: 300 .mu.m)
[0183] (2) Polishing agent: the same as Example 7
[0184] (3) Polishing condition: the same as Example 7
[0185] (4) Sample to be polished: the same as Example 7
[0186] Finish-polishing was performed under the above-mentioned
conditions (1) to (4), and the amount of change in GBIR and the
haze level were measured to obtain the following
9 Nap layer thickness Amount of change (.mu.m) Haze level (Bit) in
GBIR (.mu.m) 350 48 0.02 500 38 0.03 700 38 0.02 900 36 0.12
[0187] As is apparent from the above results, the amount of change
in GBIR can be suppressed within the range of the measurement error
without making the haze level worse when the top layer has a nap
layer thickness within the range of 400 to 800 .mu.m.
Comparative Example 3
[0188] (1) Singe-layer finish-polishing pad: CIEGAL (as described
above, Asker C hardness: 73);
[0189] (2) Polishing agent: the same as Example 1
[0190] (3) Polishing condition: the-same as Example 1
[0191] (4) Sample to be polished: the same as Example 1
[0192] Finish-polishing was performed at the average polishing
stock removal of 0.6 .mu.m to obtain the following results:
10 Haze level Amount of change Structure of Polishing pad (Bit) in
GBIR (.mu.m) Single-layer finish-polishing 38 0.51 pad Three-layer
finish- 38 0.03 polishing pad
Comparative Example 4
[0193] (1) Two-layer finish-polishing pad: two-layer polishing pad
composed of a top layer and a bottom layer and obtained through
removal of the hard plastic sheet serving as the intermediate layer
from the three-layer polishing pad of Example 6.
[0194] (2) Polishing agent: the same as Example 6
[0195] (3) Polishing condition: the same as Example 6
[0196] (4) Sample to be polished: the same as Example 6
[0197] Finish-polishing was performed at the average polishing
stock removal of 0.6 .mu.m to obtain the following results:
11 Haze level Amount of change Structure of Polishing pad (Bit) in
GBIR .mu.m) Single-layer finish-polishing 38 0.18 pad Three-layer
finish- 38 0.03 polishing pad
[0198] As is apparent from the-above Comparative examples,
uniformity of polishing stock removal degrades considerably, when
finish-polishing is performed through use of a single-layer
polishing pad having only a top layer formed of suede-type
finish-polishing pad or through use of a two-layer finish-polishing
pad obtained through removal of the intermediate layer from the
three-layer polishing pad of the present invention.
[0199] The present invention is not limited to the above-described
embodiments. The above-described embodiments are mere examples, and
those having the substantially same structure as that described in
the appended claims and providing the similar action and effects
are included in the scope of the present invention.
[0200] In the above-described embodiments of the present invention,
descriptions are given with reference to single-side polishing.
However, needless to say, the invention can be applied to
double-side polishing.
* * * * *