U.S. patent application number 11/912092 was filed with the patent office on 2009-03-19 for polishing pad, method of producing the same and method of producing semiconductor device by using the same.
This patent application is currently assigned to TOYO TIRE & RUBBER CO., LTD.. Invention is credited to Tsuyoshi Kimura, Yoshiyuki Nakai, Masahiro Watanabe.
Application Number | 20090075568 11/912092 |
Document ID | / |
Family ID | 36383723 |
Filed Date | 2009-03-19 |
United States Patent
Application |
20090075568 |
Kind Code |
A1 |
Kimura; Tsuyoshi ; et
al. |
March 19, 2009 |
POLISHING PAD, METHOD OF PRODUCING THE SAME AND METHOD OF PRODUCING
SEMICONDUCTOR DEVICE BY USING THE SAME
Abstract
The present invention provides a polishing pad used for
planarizing inter layer dielectrics and the like by CMP (chemical
mechanical polishing) in the manufacturing process of a
semiconductor device, a method of producing the polishing pad and a
method of producing a semiconductor device by using the polishing
pad. The present invention relates to a semiconductor wafer
polishing pad having grooves in a polishing surface and formed from
a foamed polyurethane, wherein a processed surface of the groove
comprising a side surface and a bottom surface has a surface
roughness Ra of not more than 10.
Inventors: |
Kimura; Tsuyoshi; (Osaka,
JP) ; Nakai; Yoshiyuki; (Osaka, JP) ;
Watanabe; Masahiro; (Osaka, JP) |
Correspondence
Address: |
MORRISON & FOERSTER LLP
1650 TYSONS BOULEVARD, SUITE 400
MCLEAN
VA
22102
US
|
Assignee: |
TOYO TIRE & RUBBER CO.,
LTD.
Osaka-shi
JP
|
Family ID: |
36383723 |
Appl. No.: |
11/912092 |
Filed: |
February 24, 2006 |
PCT Filed: |
February 24, 2006 |
PCT NO: |
PCT/JP2006/303454 |
371 Date: |
May 1, 2008 |
Current U.S.
Class: |
451/59 ; 451/527;
51/293 |
Current CPC
Class: |
Y10T 83/0304 20150401;
B24D 3/32 20130101; Y10T 409/304536 20150115; Y10T 29/49995
20150115; Y10T 409/303808 20150115; B24B 37/26 20130101 |
Class at
Publication: |
451/59 ; 451/527;
51/293 |
International
Class: |
B24D 11/00 20060101
B24D011/00; B24B 1/00 20060101 B24B001/00; B24D 18/00 20060101
B24D018/00; B24B 7/20 20060101 B24B007/20 |
Foreign Application Data
Date |
Code |
Application Number |
May 18, 2005 |
JP |
2005-145599 |
Claims
1. A semiconductor wafer polishing pad having grooves in a
polishing surface and formed from a foamed polyurethane, wherein a
processed surface of a groove formed in a side surface and a bottom
surface has a surface roughness Ra of not more than 10 .mu.m.
2. The polishing pad according to claim 1, wherein the processed
surface of the groove has a surface roughness Ra of 1 to 9
.mu.m.
3. A semiconductor wafer polishing pad comprising a polishing layer
formed from a porous material and having, a polishing surface of
the polishing layer with grooves formed therein, wherein at least
one portion of an inner surface of the groove has a non-porous
surface having a surface roughness Ra of 1.0 to 5.0 .mu.m.
4. (canceled)
5. The polishing pad according to claim 3, wherein the groove has a
depth of 0.5 to 1.5 mm.
6. The polishing pad according to claim 3 or 5, wherein the
polishing layer is formed from a porous material having an average
cell diameter of 20 to 70 .mu.m.
7. The polishing pad according to claim 3 or 5, wherein the
polishing layer has a specific gravity of 0.5 to 1.0
g/cm.sup.3.
8. The polishing pad according to claim 3 or 5, wherein the
polishing layer has a compressibility of 0.5 to 5.0%.
9. The polishing pad according to claim 3 or 5, wherein the
polishing layer has a hardness of 45 to 65.
10. The polishing pad according to claim 3 or 5, further comprising
a cushion layer, wherein the cushion layer has lower hardness than
the polishing layer.
11. A method of producing a semiconductor wafer polishing pad
comprising a step of mechanical cutting by stepwise varying a feed
speed and feed amount of a groove processing tool to form
concentric circular grooves having rectangle sectional shape on the
polishing surface.
12. The method according to claim 11, wherein the step of forming
the grooves comprises stopping the feed of the groove processing
tool for a certain time at the position that the groove processing
tool reaches a desired depth.
13. The method according to claim 11, wherein the feed speed and
feed amount of a groove processing tool are stepwise varied and
increased in order of precedence.
14. The method according to claim 11, wherein the polishing pad is
formed from a foamed polyurethane.
15. A method of producing a semiconductor device comprising at
least a step of polishing the surface of a semiconductor wafer by
using the polishing pad according to anyone of claims 1 to 3 and 5
to 10.
16. The polishing pad according to claim 6, wherein the polishing
layer has a specific gravity of 0.5 to 1.0 g/cm.sup.3.
17. The polishing pad according to claim 16, wherein the polishing
layer has a compressibility of 0.5 to 5.0%.
18. The polishing pad according to claim 16, wherein the polishing
layer has a hardness of 45 to 65.
19. The polishing pad according to claim 16, further comprising a
cushion layer, wherein the cushion layer has lower hardness than
the polishing layer.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polishing pad used for
polishing a material to be polished, a method of producing the
polishing pad and a method of producing a semiconductor device by
using the polishing pad. More particularly, it relates to a
polishing pad used for planarizing inter layer dielectrics and the
like by CMP (chemical mechanical polishing) in the manufacturing
process of a semiconductor device, a method of producing the
polishing pad and a method of producing a semiconductor device by
using the polishing pad.
BACKGROUND ART
[0002] Recently, in semiconductor integrated circuits, the device
size have been scale down and the integration has been improved,
and micro processing has been required. In addition, the device
structure has been complex and three-dimensional. The scale down
has been accomplished by the improvement of micro processing
technique in the manufacturing process of a semiconductor device,
particularly high resolution in photolithography process which
transfer a circuit pattern to photosensitive organic film (photo
resist) coated on a silicon wafer. In the photolithography process,
techniques of exposure by using a light source of shorter
wavelength have been developed. A method of compensating the
deficiency of the depth of focus to assure the resolution without
defocus of a micro pattern by reducing unevenness in the device
structure as possible has been attempted.
[0003] As a method of planarizing the unevenness in the device
structure, the CMP method, to which mirror surface processing of a
silicon wafer was applied, has been used. An apparatus for
generally using in the CMP method is shown by reference to FIG. 1.
The CMP apparatus used in the CMP method is provided with a
polishing platen 2 for supporting a polishing pad 1 and with a
supporting stand (polishing head) 5 for supporting a material to be
polished 4 (such as a semiconductor wafer). The polishing platen 2
and the supporting stand 5 are arranged such that the polished pad
1 and the material to be polished 4, both of which are supported by
them, are opposed to each other, and the polishing platen and the
supporting stand are constituted to be capable of rotating around
rotating shafts 6 and 7. The material to be polished 4 is stuck on
the supporting stand 5 which is provided with a pressing mechanism
for pushing the material to be polished 4 onto the polishing pad 1
at the time of polishing (not indicated). Abrasive (slurry)
3-feeding mechanism 8 is to feed an abrasive suspension having
abrasive grains such as silica particles dispersed in an alkali
solution to the polishing pad 1 on the polishing platen 2. In
addition, the CMP apparatus comprises dresser having abrasive
grains of diamond electrodeposited or melt bonded thereon to dress
the surface of the polishing pad (not indicated).
[0004] As an example of the method, there is a method of dressing
the polishing pad by dresser, rotating the shafts 6 and 7, pushing
the wafer 4 onto the polishing pad 1 by the pressing mechanism
while feeding an abrasive slurry from the abrasive slurry-feeding
mechanism 8 to the center portion of the polishing pad to polishing
the wafer. In the CMP method, micro scratches on the layer to be
polished such as the inter layer dielectrics of the wafer, the
dispersion of the abrasive rate and poor uniformity of the abrasive
amount within the surface of a silicon wafer are problem.
[0005] In order to restrain the formation of the micro scratches,
it is necessary that abrasive dust of the polishing pad and diamond
of the dresser formed during dressing of the polishing pad, inter
layer dielectrics, abrasive dust of the wafer and used abrasive
slurry (collectively, abrasive waste) are discharged to the
exterior of the polishing pad. In the conventional CMP apparatus,
the abrasive waste is discharged by continuously feeding the
abrasive slurry to the center portion of the polishing pad in a
sufficient amount. In case of forming a dressed layer on the
polishing pad by dressing and then polishing the wafer while
feeding the abrasive slurry described above, the abrasive slurry is
pushed out by centrifugal force from the rotation of the polishing
pad and by pushing the wafer onto the polishing pad. Therefore, the
abrasive slurry is almost discharged to the exterior of the
polishing pad without concerning the polishing to consume excess
abrasive slurry, which is expensive.
[0006] In order to dissolve the problems, various attempts have
been made in the polishing method to improve the abrasive
properties of the material to be polished. Among them, there have
been various attempts with respect with grooves for remaining
abrasive slurry on the polishing surface and discharging it.
[0007] In Japanese Patent No. 2647046, a polishing pad comprising
grooves for flowing abrasive formed in the inner portion and the
outer portion of the surface of the polishing pad, and a plurality
of pores for retaining the abrasive formed on the surface of the
polishing pad other than the portion that the grooves are formed,
is disclosed. As one embodiment of the polishing pad, the polishing
pad comprising lattice pattern groove formed in the center portion
and the peripheral portion of the surface of the polishing pad, and
pores formed in a portion between center portion and the peripheral
portion, is described in FIG. 1. The pores are formed in broad area
at once by using punches arranged in a line or a few lines. It is
difficult to form the pores by using a processing apparatus
generally used for that purpose. The technical effects of reducing
the unusual retainment of the abrasive slurry based on the balance
between feeding and discharging the abrasive slurry are not
particularly disclosed. The term "unusual retainment" used herein
means that the retainment of the abrasive slurry is in largely
non-uniform state on the polishing surface of the polishing pad,
which has a bad effect on polishing a material to be polished.
[0008] In Japanese Patent Kokai Publication No. 249710/1998, a
polishing pad comprising grooves formed such that the groove shape
geometrically having a center is eccentric to the polishing pad. It
is described to dissolve a problem of transferring the groove shape
to a silicon wafer processed to degrade the uniformity by the
eccentricity of concentric circular groove to the polishing pad.
However, it is difficult to prevent the abrasive rate in the center
portion of the wafer from degrading. In addition, the technical
effects of reducing of the unusual retainment of the abrasive
slurry based on the balance between feeding and discharging the
abrasive slurry are not particularly disclosed.
[0009] In Japanese Patent Kokai Publication No. 70463/1999, a
polishing pad comprising a first zone having plural concentric
circular grooves and a second zone having a second pitch. It is
described that the polishing pad has two zones having a different
groove pitch to improve the uniformity of the polishing. However,
the technical effects of reducing of the unusual retainment of the
abrasive slurry based on the balance between feeding and
discharging the abrasive slurry are not particularly disclosed, and
it is difficult to improve the uniformity of the polishing.
[0010] In Japanese Patent Kokai Publication No. 198061/2000, a
polishing pad comprising plural loop grooves and plural
stream-lined grooves is disclosed. In the polishing pad, it is
attempted to positively control the flow of the abrasive slurry by
forming the grooves into the stream-lined shape. However, in the
polishing pad, it is problem that the abrasive slurry necessary to
polishing flows out along the stream-lined grooves. In addition,
the technical effects of reducing of the unusual retainment of the
abrasive slurry based on the balance between feeding and
discharging the abrasive slurry are not particularly disclosed, and
the uniformity of the polishing is not sufficiently obtained.
[0011] In Japanese Patent Kokai Publication No. 224950/2002, a
polishing pad comprising grooves having arc shaped bottom to
prevent the abrasive slurry from stagnating. In the polishing pad,
it is attempted to control the flow of the abrasive slurry smoothly
by forming the grooves into the arc bottom shape. In the polishing
pad, the shape of the groove and the surface roughness thereof are
considered. However, it is different from the present invention in
view that the polishing surface material is round graphite cast
iron. In addition, it is different from the present invention in
view that the material to be polished is bare wafer or glass
substrate. Moreover, the unusual retainment of the abrasive slurry
based on the balance between feeding and discharging the abrasive
slurry are not discussed in case of using porous material as the
polishing layer as described in the present invention.
[0012] In Japanese Patent Kokai Publication No. 9156/2004, a
polishing pad comprising grooves, of which the inner surface has a
surface roughness of not more than 20 .mu.m, on the polishing
surface. In the polishing pad, the surface roughness of the inner
surface of the groove is considered. The surface roughness of the
groove is obtained for the groove formed by cutting the polishing
surface material or molding it in a mold. It has been found from an
additional test by the present inventors that it is difficult for
the inner surface of the groove to have the surface roughness of
not more than 20 .mu.m in case of forming the groove on the pore
material by the above method. Therefore, a main object of the
invention is the select of the polishing layer material rather than
a method of forming grooves, which is different from the present
invention. In addition, the unusual retainment of the abrasive
slurry based on the balance between feeding and discharging the
abrasive slurry are not discussed in case of using porous material
as the polishing layer as described in the present invention.
[0013] In order to dissolve the problems, a polishing pad for
processing semiconductor device that concentric circular grooves
having right-angle edge are formed at the upper edge portion of the
groove and groove processing tool are disclosed in Japanese Patent
Kokai Publication Nos. 181649/2001 and 184730/2002, and a fine
groove processing machine, processing tool and method of processing
for forming concentric circular grooves or lattice pattern groove
on semiconductor polishing pad for CMP processing are disclosed in
Japanese Patent Kokai Publication No. 11630/2002.
[0014] In the polishing pad disclosed in Japanese Patent Kokai
Publication Nos. 181649/2001 and 184730/2002, it is easy to control
the flow of the abrasive slurry between the device surface to be
polished and the upper surface of the pad by forming concentric
circular grooves having right-angle edges at the upper corner
portion in cross section and adjusting the width, depth and pitch
of the groove to specified ranges, and it is expected that
hydroplaning is restrained and the soft metal surface of the device
is effectively planarized by the CMP processing method. However,
the cross section shape of the groove is not stable, and the
flowability of the abrasive slurry varies every pad. Therefore,
stable abrasive properties are not sufficiently obtained.
[0015] In the polishing pad comprising fine grooves formed by the
groove processing tool disclosed in Japanese Patent Kokai
Publication No. 11630/2002, the cross section shape of the groove
is not stable, and the flowability of the abrasive slurry varies
every pad. Therefore, scratches are easily formed, and stable
abrasive properties are not sufficiently obtained.
[0016] In the above polishing pad disclosed in Japanese Patent
Kokai Publications Nos. 181649/2001, 184730/2002 and 11630/2002,
edges at the corner portion in cross section of the groove is
right-angle by specifying the shape of the cutting edge of the
groove processing tool, thereby it is attempted to restrain the
occurrence of dulled edge and burr on the wall surface of the
groove. Stable abrasive properties are not sufficiently obtained
only by specifying the shape of the cutting edge of the groove
processing tool.
DISCLOSURE OF INVENTION
Objects of the Invention
[0017] A main object of the present invention is to dissolve
problems at the same time, such as the occurrence of scratches, the
non-uniformity or deterioration of the abrasive rate, the
non-uniformity within wafer of the abrasive amount, the consumption
of excess abrasive slurry and the suitable retainment of the
abrasive slurry between the material to be polished and the
polishing pad in a polishing pad used for planarizing inter layer
dielectrics and the like by CMP (chemical mechanical polishing) in
the manufacturing process of a semiconductor device, a method of
producing the polishing pad and a method of producing a
semiconductor device by using the polishing pad.
[0018] By dissolving the problems at the same time, the present
invention provides a polishing pad used for planarizing inter layer
dielectrics and the like by CMP (chemical mechanical polishing) in
the manufacturing process of a semiconductor device, a method of
producing the polishing pad and a method of producing a
semiconductor device by using the polishing pad.
[0019] The polishing pad of the present invention is suitably used
as a polishing pad used for planarizing a material to be polished
by CMP (chemical mechanical polishing) in order to dissolve
problems at the same time, such as the occurrence of scratches, the
non-uniformity or deterioration of the abrasive rate, the
non-uniformity within wafer of the abrasive amount, the consumption
of excess abrasive slurry and the suitable retainment of the
abrasive slurry between the material to be polished and the
polishing pad. In order to dissolve the problems at the same time,
the polishing pad of the present invention is a polishing pad
comprising grooves on a polishing surface and formed from a foamed
polyurethane, of which a processed surface of the groove comprising
a side surface and a bottom surface has a surface roughness Ra of
not more than 10.
[0020] The present invention relates to a semiconductor wafer
polishing pad comprising grooves on a polishing surface and formed
from a foamed polyurethane, wherein a processed surface of the
groove comprising a side surface and a bottom surface has a surface
roughness Ra of not more than 10.
[0021] In order to put the present invention into a more suitable
practical application, it is preferable that the processed surface
of the groove have a surface roughness Ra of 1 to 9.
[0022] In another embodiment, the present invention relates to a
semiconductor wafer polishing pad comprising a polishing layer,
wherein the polishing layer is formed from a porous material, a
polishing surface of the polishing layer has grooves, and at least
one portion of the inner surface of the groove has a non-porous
surface.
[0023] In order to put the present invention into a more suitable
practical application, it is preferable that: [0024] the non-porous
surface have a center line average roughness Ra of a roughness
curve of 1.0 to 5.0 .mu.m; [0025] the groove have a depth of 0.5 to
1.5 mm; [0026] the polishing layer be formed from a porous material
having an average cell diameter of 20 to 70 .mu.m; [0027] the
wherein the polishing layer have a specific gravity of 0.5 to 1.0
g/cm.sup.3; [0028] the polishing layer have a compressibility of
0.5 to 5.0%; [0029] the polishing layer have a hardness of 45 to
65; and [0030] the polishing pad further comprise a cushion layer
and the cushion layer have lower hardness than the polishing
layer.
[0031] In further embodiment, the present invention relates to a
method of producing a semiconductor wafer polishing pad comprising
a step of mechanical cutting by stepwise varying a feed speed and
feed amount of a groove processing tool to form concentric circular
grooves having rectangle sectional shape on the polishing
surface.
[0032] In order to put the present invention into a more suitable
practical application, it is preferable that: [0033] the step of
forming the grooves comprise stopping the feed of the groove
processing tool for a certain time at the position that the groove
processing tool reaches a desired depth; [0034] the feed speed and
feed amount of a groove processing tool are stepwise varied and
increased in order of precedence; and [0035] the polishing pad be
formed from a foamed polyurethane.
[0036] In yet further embodiment, the present invention relates to
a method of producing a semiconductor device comprising a step of
polishing the surface of a semiconductor wafer by using the
polishing pad of the present invention.
[0037] In the polishing of the semiconductor wafer and the like by
using the polishing pad of the present invent, it is possible to
dissolve problems at the same time, such as the non-uniformity or
deterioration of the abrasive rate, the non-uniformity within wafer
of the abrasive amount, the consumption of excess abrasive slurry
and the suitable retainment of the abrasive slurry between the
material to be polished and the polishing pad; and particularly it
is effective to reduce the occurrence of scratches because the
polishing pad has good balance between feeding and discharging the
abrasive slurry during polishing to reduce the unusual retainment
of the abrasive slurry in the grooves during polishing. Therefore,
the polishing pad is effective to the manufacturing process of a
semiconductor device, such as CMP of a semiconductor wafer.
BRIEF DESCRIPTION OF DRAWINGS
[0038] The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawing which is given by way of illustration only, and thus are
not limitative of the present invention, and wherein:
[0039] FIG. 1 is a schematic cross section illustrating a polishing
apparatus generally used for CMP process.
[0040] FIG. 2 is a schematic cross section illustrating groove
having rectangular cross section shape.
[0041] FIG. 3 is a schematic cross section illustrating one
embodiment of the groove formed on the polishing layer of the
polishing pad of the present invention.
[0042] FIG. 4 is a schematic cross section illustrating the groove
formed on the polishing layer of the conventional polishing
pad.
[0043] FIG. 5 is an enlarged schematic diagram illustrating one
embodiment of the cutting edge of the groove processing tool used
for the method of producing the polishing pad of the present
invention [(a) front elevational view, (b) side elevational
view].
[0044] FIG. 6 is an enlarged schematic diagram illustrating the
cutting edge of the groove processing tool used for the method of
producing the conventional polishing pad [(a) front elevational
view, (b) side elevational view].
[0045] FIG. 7 is an enlarged schematic diagram of the corner
portion of the cutting edge of the groove processing tool before
and after polishing illustrating the test method of the wear of the
groove processing tool.
DESCRIPTION OF NOTATIONS
[0046] 1: Polishing pad [0047] 2: Polishing platen [0048] 3:
Abrasive slurry [0049] 4: Material to be polished [0050] 5:
Supporting stand [0051] 6,7: Rotating shaft [0052] 8: Abrasive
slurry-feeding mechanism [0053] 10,20: Groove [0054] 11,21: Side
surface of processed surface of groove [0055] 12,22: Bottom surface
of processed surface of groove [0056] 13: Depth of groove [0057]
14: Width of groove [0058] 15: Pitch of groove [0059] 23:
Blister
BEST MODE FOR CARRYING OUT THE INVENTION
[0060] The polishing pad of the present invention comprises grooves
on a polishing surface and formed from a foamed polyurethane,
wherein a processed surface of the groove comprising a side surface
and a bottom surface has a surface roughness Ra of not more than
10. In another embodiment, the polishing pad of the present
invention comprises a polishing layer, wherein the polishing layer
is formed from a porous material, a polishing surface of the
polishing layer has grooves, and at least one portion of the inner
surface of the groove has a non-porous surface. In addition, the
method of producing the polishing pad of the present invention
comprises a step of mechanical cutting by stepwise varying a feed
speed and feed amount of a groove processing tool to form
concentric circular grooves having rectangle sectional shape on the
polishing surface. The polishing pad of the present invention and
the method of producing the same will be explained with reference
to the accompanying drawing in detail. FIG. 3 is a schematic cross
section illustrating one embodiment of the groove formed on the
polishing layer of the polishing pad of the present invention. FIG.
4 is a schematic cross section illustrating the groove formed on
the polishing layer of the conventional polishing pad. The drawings
are schematic cross sections illustrating the groove formed on the
polishing layer of the polishing pad, and the size is not exactly
shown.
[0061] As shown in FIG. 3, in the polishing pad of the present
invention, it is required for the processed surface of the groove
comprising the side surface 11 and bottom surface 12 to have a
surface roughness Ra of not more than 10, preferably 1 to 9, more
preferably 1 to 5. When the surface roughness Ra is larger than 10,
the flowability of the abrasive slurry is degraded, and cohesion
thereof easily occurs or the clogging of abrasive waste easily
occurs, which causes the formation of scratches.
[0062] It is desired that defects having a depth of not less than
100 .mu.m (100 to 500 .mu.m) or burrs having a length of 200 .mu.m
(200 to 1000 .mu.m) are not more than 2 per one cross section in
the groove in the polishing surface of the polishing pad of the
present invention. When the number of the defects or burrs are
larger than 2, the flowability of the abrasive slurry is degraded,
and cohesion thereof easily occurs or the clogging of abrasive
waste easily occurs, which causes the formation of scratches. The
number of the defect and burr are measured by observing the groove
cross section of a sample formed by dividing the polishing pad into
five pieces in the radius direction to count the number of defects
having the above depth and burrs having the above length.
[0063] FIG. 5 is an enlarged schematic diagram illustrating one
embodiment of the cutting edge of the groove processing tool used
for the method of producing the polishing pad of the present
invention. FIG. 6 is an enlarged schematic diagram illustrating the
cutting edge of the groove processing tool used for the method of
producing the conventional polishing pad. As shown in FIG. 5, in
the method of the polishing pad of the present invention, the
grooves are formed by mechanical cutting with the groove processing
tool and the concentric circular groove having rectangle sectional
shape are formed on the polishing surface. It is desired that the
sectional shape of the cutting edge of the groove processing tool
used for the method of producing the polishing pad of the present
invention be rectangle without the side relief angle c in the
conventional groove processing tool shown in FIG. 6. When the
groove processing tool having the side relief angle c is used, the
width of the groove formed is small by the wear of the groove
processing tool (FIG. 4), and the non-uniformity of the retaining
amount of the abrasive slurry is not sufficiently obtained, which
causes the non-uniformity and deterioration of the abrasive rate.
In the side shape of the cutting edge of the groove processing
tool, when the groove processing tool having the rake angle d in
the conventional groove processing tool shown in FIG. 6 is used,
the contact area of the groove processing tool with the polishing
surface to be processed varies by the wear of the groove processing
tool, and the desired surface roughness Ra of the groove processed
surface is not sufficiently obtained (FIG. 4). Therefore, it is
desired for the groove processing tool used for the method of
producing the polishing pad of the present invention to have the
cutting edge shape without the side relief angle c and the rake
angle d as shown in FIG. 5.
[0064] In the method of producing the polishing pad of the present
invention, it is required to mechanically cut while stepwise
varying a feed speed and feed amount of a groove processing tool.
The wording "stepwise varying" a feed speed and feed amount of a
groove processing tool used herein refers to stepwise vary the feed
speed and feed amount while forming one of concentric circular
grooves. The value of the feed speed and the like at every step may
be increased in order of precedence, decreased in order of
precedence, or increased or decreased. The time at every step may
be the same or different.
[0065] It is desired for the feed speed of a groove processing tool
to be within the range of 0.01 to 0.10 m/min, preferably 0.01 to
0.08 m/min, more preferably 0.01 to 0.05 m/min and to be varied at
1 to 2 steps, preferably 2 to 3 steps, more preferably 2 to 5 steps
while forming one of concentric circular grooves. When the feed
speed is smaller than 0.01 m/min, the processing time is increased
and the wear of the groove processing tool is accelerated. On the
other hand, when the feed speed is larger than 0.10 m/min, the
occurrence of the burr is increased, the load applied to the groove
processing tool is increased and the groove shape is not
stable.
[0066] When forming the groove at a constant low feed speed, the
wear of the groove processing tool is large and the processing time
is increased. Therefore, it is desired that the feed speed is
increased in order of precedence. In addition, it is desired that
there be a time of stopping the feed of the groove processing tool,
that is, a time that the feed speed is zero at the position of
reaching the groove processing tool to the deepest portion, that
is, the desired groove depth. It is desired for the time of
stopping the feed of the groove processing tool to be within the
range of 0.5 to 5 seconds, preferably 1.0 to 3.0 seconds. When the
time is longer than 5 seconds, the wear of the groove processing
tool is large. On the other hand, when the time is shorter than 0.5
seconds, it is difficult to maintain the stable groove shape and
surface state.
[0067] The feed amount of the groove processing tool is stepwise
varied by stepwise varying the feed speed as described above. In
addition, it is desired to stepwise vary the total feed amount of
the groove processing tool, which varies depending on the desired
groove depth, as the same as the feed speed.
[0068] As described above, in the method of producing the polishing
pad of the present invention, the processed surface of the groove
can have low surface roughness Ra of not more than 10 and the burr
formed on the surface of the polishing pad by the groove processing
is reduced to form concentric circular grooves having the desired
rectangle sectional shape. When the roughness Ra of the processed
surface of the groove is large, the flowability of the abrasive
slurry and abrasive waste is degraded, which causes the formation
of scratches as described above. As shown in FIG. 3, the burr
formed on the surface of the polishing pad by groove processing is
reduced to obtain grooves having right-angle edge at the upper edge
portion of the groove using the method of producing the polishing
pad of the present invention. In addition, the angle between the
side surface 11 and bottom surface 12 is right-angle, and it is
possible to stably form the grooves having precise rectangle
sectional shape. Therefore, in the polishing pad obtained by the
method of producing the polishing pad of the present invention, the
shape of the groove formed on the polishing surface is stable, and
the retaining amount of the abrasive slurry is stable. Therefore,
the problems, such as the non-uniformity or deterioration of the
abrasive rate, the non-uniformity within wafer of the abrasive
amount and the consumption of excess abrasive slurry, are
dissolved. In addition, the suitable retainment of the abrasive
slurry between the material to be polished and the polishing pad
can be obtained.
[0069] In the polishing pad of the present invention, the width,
depth and pitch of the groove are not limited as long as the
grooves having precise rectangle sectional shape are stably formed,
but the groove may have a width of 0.2 to 5.0 mm, a depth of 0.2 to
4.0 mm and a pitch of 0.5 to 6.0 mm, which may be suitably selected
from the ranges depending on the material to be polished, the
method of polishing and polishing condition. In the present
invention, the concentric circular grooves preferably have the same
width, the same depth and the same pitch, respectively. In case of
using such polishing pad, it is easy to control the abrasive rate,
and it is convenient during producing the polishing pad.
[0070] The polishing pad of the present invention may be a
single-layered polishing pad, which has been conventionally used,
or a laminated polishing pad comprising at least two layers of
polishing layer (hard surface layer) contact with the material to
be polished, such as a semiconductor wafer and an cushion layer
(elastic supporting layer) positioned between the polishing layer
and a polishing platen, or a multi-layered polishing pad.
[0071] In the laminated polishing pad, the polishing layer and
cushion layer are separately formed. It is desired for the
polishing layer to have a hardness of 45 to 65. When the hardness
of the polishing layer is lower than 45, the planarity of the
material to be polished is degraded. On the other hand, when the
hardness of the polishing layer is higher than 65, the planarity is
good, but the uniformity of the material to be polished is
degraded. The hardness of the polishing layer was measured
according to JIS K6253-1997. The material for the polishing layer
was cut into a size of 2 cm.times.2 cm (a proper thickness) as a
sample for measuring the hardness, and the sample was left at a
temperature of 23.degree. C..+-.2.degree. C. and humidity of
50%.+-.5% for 16 hours. The hardness of the polishing layer was
measured by using a stack of the samples having a thickness of not
less than 6 mm with a hardness meter (Asker D hardness meter
manufactured by Kobunshi Keiki Co., Ltd.). It is desired for the
cushion layer to have a hardness of 25 to 100, preferably 30 to 85.
The hardness of the cushion layer was measured with a hardness
meter (Asker A hardness meter manufactured by Kobunshi Keiki Co.,
Ltd.) according to JIS K6253-1997. It is desired for the polishing
layer to have a thickness of 0.2 to 4.0 mm, preferably 0.8 to 3.0
mm. It is desired for the cushion layer to have a thickness of 0.5
to 2.5 mm, preferably 1.0 to 2.0 mm.
[0072] In the single-layered polishing pad, the thickness is 1.0 to
5.0 mm and the material thereof may be suitably selected and used
from the material used for the polishing layer and cushion
layer.
[0073] In the laminated polishing pad, a material for the polishing
layer is not limited as long as it satisfies the above hardness
range, but the polishing layer is preferably formed from porous
material. Examples of the porous materials include, for example,
polyurethane resin, polyester resin, polyamide resin, acrylic
resin, polycarbonate resin, halogen-based resin (such as polyvinyl
chloride, polytetrafluoroethylene, and polyvinylidene fluoride),
epoxy resin, photosensitive resin and the like. The porous material
may be used alone, but the porous material may be used in
combination with at least one of the other porous material.
[0074] In the present invention, particularly preferred is foamed
polyurethane resin as the material for the polishing layer, because
the polyurethane resin has excellent wear resistance and polymer
having a desired physical properties can be easily obtained by
varying a composition of raw material.
[0075] A method of foaming the polyurethane resin is not limited,
but includes chemical foaming method using a foaming agent,
mechanical foaming method, a method of adding hollow micro beads or
precursor forming hollow micro beads by heating, or combinations
thereof. Micro foam used for the polishing pad of the present
invention is formed by the foaming method.
[0076] The polyurethane resin comprises isocyanate-terminated
urethane prepolymer and chain extender. The isocyanate-terminated
urethane prepolymer comprises polyisocyanate, low molecular weight
polyol and high molecular weight polyol.
[0077] Examples of the polyisocyanates, which are not limited,
include 2,4- and/or 2,6-diisocyanato toluene, 2,2'-, 2,4'- and/or
4,4'-diisocyanato diphenylmethane, 1,5-naphthalene diisocyanate, p-
and m-phenylene diisocyanate, dimeryl diisocyanate, xylylene
diisocyanate, diphenyl-4,4'-diisocyanate, 1,3- and
1,4-tetramethylxylydene diisocyanate, tetramethylene diisocyanate,
1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate,
cyclohexane-1,3- and 1,4-diisocyanate,
1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane
(=isophorone diisocyanate), bis-(4-isocyanatocyclohexyl)methane
(=hydrogenated MDI), 2- and
4-isocyanatocyclohexyl-2'-isocyanatocyclohexylmethane, 1,3- and
1,4-bis-(isocyanatomethyl)-cyclohexane,
bis-(4-isocyanato-3-methylcyclohexyl)methane and the like. These
may be used alone or in combination of two or more thereof. The
polyisocyanate may be suitably selected depending on the desired
pot-life during casting and molding.
[0078] Examples of the high molecular weight polyols include
hydroxy-terminated polyester, polycarbonate, polyester carbonate,
polyether, polyether carbonate, polyesteramide and the like.
Preferred are polyether and polycarbonate in view of good
hydrolysis resistance, and preferred is polyether in view of cost
and melt viscosity. Examples of the polyether polyols include
reaction products of starting compound having a reactive hydrogen
atom with alkylene oxide, such as ethylene oxide, propylene oxide,
butylene oxide, styrene oxide, tetrahydrofuran, epichlorohydrin, or
mixtures of these alkylene oxides. Examples of the starting
compounds having a reactive hydrogen atom include water, bisphenol
and divalent alcohol for preparing polyester polyol described
later.
[0079] Examples of polycarbonates having a hydroxy group include
reaction products of diols, such as 1,3-propanediol,
1,4-butanediol, 1,6-hexanediol, diethylene glycol, polyethylene
glycol, polypropylene glycol and/or polytetramethylene glycol, with
phosgene, diallyl carbonate (such as diphenyl carbonate) or cyclic
carbonate (propylene carbonate). Examples of polyester polyols
include reaction products of divalent alcohol with dibasic
dicarboxylic acid, but it is desired to have larger distance
between ester bonds in order to improve hydrolysis resistance. It
is preferable that both the divalent alcohol and dibasic
dicarboxylic acid have longer chain component.
[0080] Examples of divalent alcohols, which are not limited,
include ethylene glycol, 1,3- and 1,2-propylene glycol, 1,4- and
1,3- and 2,3-butylene glycol, 1,6-hexane glycol, 1,8-octane glycol,
neopentyl glycol, cyclohexanedimethanol,
1,4-bis-(hydroxymethyl)-cyclohexane, 2-methyl-1,3-propanediol,
3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol,
diethylene glycol, dipropylene glycol, triethylene glycol,
tripropylene glycol, dibutylene glycol and the like.
[0081] Examples of the dibasic dicarboxylic acids include
aliphatic, cycloaliphatic, aromatic and/or heterocyclic dibasic
dicarboxylic acid, but preferred is aliphatic or cycloaliphatic
dibasic dicarboxylic acid because it is required that the resulting
NCO terminated prepolymer is liquid or low melt viscosity. If
aromatic dibasic dicarboxylic acid is applied, it is preferable to
use in combination with aliphatic or cycloaliphatic dibasic
dicarboxylic acid. Examples of the dicarboxylic acids, which are
not limited, include succinic acid, adipic acid, suberic acid,
azelaic acid, sebacic acid, phthalic acid, isophthalic acid,
terephthalic acid, naphthalene dicarboxylic acid, cyclohexane
dicarboxylic acid (o-, m-, p-), dimeric fatty acid (such as oleic
acid) and the like. The polyester polyol may have a portion of
carboxyl terminated group. Lactones, such as .di-elect
cons.-caprolactone, or polyester of hydroxycarboxylic acid, such as
.di-elect cons.-hydroxycapronic acid may be also used.
[0082] Number average molecular weight of the high molecular weight
polyol is not limited, but is preferably within the range of 500 to
2,000 in view of the elastic properties of the resulting
polyurethane. When the number average molecular weight is lower
than 500, the elastic properties of the resulting polyurethane
resin is not sufficiently obtained, which is brittle resin.
Therefore, the polishing layer prepared from the polyurethane resin
is hard and brittle, which causes the formation of scratches on the
polishing surface of the material to be polished. The polishing pad
from the polyurethane resin is easily worn, and it is not suitable
in view of life of the polishing pad. On the other hand, when the
number average molecular weight is higher than 2,000, the resulting
polyurethane resin is soft, and the polishing layer prepared from
the polyurethane resin tends to have poor planarity.
[0083] Examples of low molecular weight polyols include divalent
alcohols for preparing polyester polyol described above. As the low
molecular weight polyols used for the present invention, it is
preferable to use at least one selected from the group consisting
of diethylene glycol, 1,3-butylene glycol, 3-methyl-1,5-pentanediol
and 1,6-hexamethylene glycol, or mixtures thereof. If ethylene
glycol or 1,4-butylene glycol as low molecular weight polyols other
than those used for the present invention is used, the reactivity
is too high during casting and molding, or the hardness of the
resulting polyurethane molded polishing material is too high, and
the polishing material of the present invention is brittle or the
surface of IC is easy to damage. On the other hand, if divalent
alcohols having longer chain than 1,6-hexamethylene glycol are
used, suitable reactivity during casting and molding, or suitable
hardness of the resulting polyurethane molded polishing material is
sometimes obtained. However, the cost is too high, and it is not
useful to use the divalent alcohols.
[0084] Since it is necessary to select the isocyanate component
depending on the desired pot-life during casting and molding and to
lower the melt viscosity of the resulting NCO terminated
prepolymer, the isocyanate component is applied alone or in
combination with two or more. Examples thereof, which are not
limited, include 2,4- and/or 2,6-diisocyanato toluene, 2,2'-, 2,4'-
and/or 4,4'-diisocyanato diphenylmethane, 1,5-naphthalene
diisocyanate, p- and m-phenylene diisocyanate, dimeryl
diisocyanate, xylylene diisocyanate, diphenyl-4,4'-diisocyanate,
1,3- and 1,4-tetramethylxylydene diisocyanate, tetramethylene
diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene
diisocyanate, cyclohexane-1,3- and 1,4-diisocyanate,
1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane
(=isophorone diisocyanate), bis-(4-isocyanatocyclohexyl)methane
(=hydrogenated MDI), 2- and
4-isocyanatocyclohexyl-2'-isocyanatocyclohexylmethane, 1,3- and
1,4-bis-(isocyanatomethyl)-cyclohexane,
bis-(4-isocyanato-3-methylcyclohexyl)methane and the like.
[0085] A ratio of the high molecular weight polyol to the low
molecular weight polyol is determined depending on the performance
requirement of the polishing layer prepared by using these
polyols.
[0086] Examples of the chain extenders used for the present
invention include, for example, organic diamine compounds. Examples
of the organic diamine compounds, which are not limited, include
4,4'-methylene-bis(o-chloroaniline),
2,6-dichloro-p-phyenylenediamine,
4,4'-methylene-bis(2,3-dichloroaniline),
3,3'-dichloro-4,4'-diaminodiphenylmethane, chloroaniline-modified
dichlorodiaminodiphenylmethane, 1,2-bis(2-aminophenylthio)ethane,
trimethylene glycol-di-p-aminobenzoate,
3,5-bis(methylthio)-2,6-toluene diamine and the like. The low
molecular weight polyols described above can be used as the chain
extenders. They may be used alone or in combination with two or
more.
[0087] The ratio of the organic isocyanate, polyol and chain
extender during preparing polyurethane resin can suitably change
depending on molecular weight of each component and the desired
properties of the polishing layer formed therefrom. In order to
obtain the polishing layer having excellent abrasive properties, it
is desired that a ratio of number of isocyanate group in the
organic isocyanate to the total number of functional groups
(hydroxyl group and amino group) in the polyol and chain extender
be within the range of 0.95 to 1.15, preferably 0.99 to 1.10.
[0088] The polyurethane resin of the present invention can be
produced by known urethane-making techniques. The polyurethane
resin may optionally contain stabilizers such as antioxidants,
surfactants, lubricants, pigments, fillers, antistatic agents, and
the other additives.
[0089] In the polishing pad of the present invention, it is desired
for the foamed polyurethane for the polishing layer (that is, the
porous material for the polishing layer or micro fine foam for the
polishing zone) to have an average cell diameter of not more than
70 .mu.m, preferably 20 to 70 .mu.m, more preferably 30 to 50
.mu.m. When the average cell diameter is out of the range, the
planarity is not sufficiently obtained. The planarity means
smoothness in micro structure of the material to be polished, such
as a semiconductor wafer. As a method of measuring the average cell
diameter in the foamed polyurethane, for example, there is a method
of measuring the diameter of the cells at a specified area by using
an image processing unit.
[0090] In the polishing pad of the present invention, it is desired
for the foamed polyurethane for the polishing layer to have a
specific gravity of 0.5 to 1.0 g/cm.sup.3. When the specific
gravity is lower than 0.5 g/cm.sup.3, the strength of the surface
of the polishing layer (polishing zone) is reduced, and the
planarity of the material to be polished, such as a semiconductor
wafer is degraded. On the other hand, when the specific gravity is
higher than 1.0 g/cm.sup.3, the number of the micro pore in the
polishing layer (polishing zone) is reduced, and the planarity is
good, but the abrasive rate tends to be degraded. The specific
gravity is a ratio of a mass of a sample to a mass of pure water
having the same volume as the sample at a pressure of 1.01 bars and
a temperature of 4.degree. C. The specific gravity can be measured
according to JIS Z8807.
[0091] In the polishing pad of the present invention, it is desired
for the foamed polyurethane for the polishing layer (polishing
zone) to have a hardness of 45 to 65, preferably 40 to 60. When the
hardness is lower than 45, the planarity of the material to be
polished is degraded. On the other hand, when the hardness is
higher than 65, the planarity is good, but the uniformity within
wafer tends to be degraded. The uniformity means the uniformity of
abrasive amount within the surface of a silicon wafer.
[0092] In the polishing pad of the present invention, it is desired
for the foamed polyurethane for the polishing layer (polishing
zone) to have a compressibility of 0.5 to 5.0%, preferably 0.5 to
3.0%. When the compressibility is within the above range, both the
planarity and uniformity can be sufficiently obtained. The
compressibility is determined by using the following formula:
Compressibility(%)=[(T.sub.1-T.sub.2)/T.sub.1].times.100
[0093] wherein T.sub.1 represents the thickness of a sample after
application of 30 kPa (300 g/cm.sup.2) stress for 60 seconds to the
sample, and T.sub.2 represents the thickness of the sample after
application of 180 kPa (1,800 g/cm.sup.2) stress for 60 seconds to
the sample in the state T.sub.1.
[0094] In the polishing pad of the present invention, it is desired
for the foamed polyurethane for the polishing layer (polishing
zone) to have a compressibility recovery of 50 to 100%. When the
compressibility recovery is out of the above range, the thickness
of the polishing layer is largely changed by repeated loading from
the material to be polished, and the stability of the abrasive
properties is degraded.
[0095] In the polishing pad of the present invention, it is desired
for the foamed polyurethane for the polishing layer (polishing
zone) to have a storage elastic modulus of not less than 200 MPa as
measured by dynamic viscoelastic measurement at a temperature of
40.degree. C. and a frequency of 1 Hz. When the storage elastic
modulus is less than 200 MPa, the strength of the surface of the
polishing layer is reduced, and the planarity of the material to be
polished, such as a semiconductor wafer is degraded. The storage
elastic modulus means elastic modulus measured by applying sine
wave vibration to the foam polyurethane as a sample with a tensile
mode folder of a dynamic viscoelasticity spectrometer.
[0096] The method of preparing closed-cell type foamed polyurethane
suitably used in the polishing layer for the polishing pad of the
present invention will be explained in detail hereinafter. The
method of preparing the foamed polyurethane comprises the following
steps (a) to (c).
[0097] (a) Stirring to prepare a cell dispersion of an
isocyanate-terminated prepolymer;
A silicone-based surfactant is added to an isocyanate-terminated
prepolymer and stirred in an inert gas, and the inert gas is
dispersed as fine cells to form a cell dispersion. When the
isocyanate-terminated prepolymer is in a solid form at ordinary
temperatures, the prepolymer is melted by pre-heating to a suitable
temperature.
[0098] (b) Mixing a curing agent (chain extender);
A chain extender is added to, and mixed with, the cell dispersion
under stirring.
[0099] (c) Curing step
The isocyanate-terminated prepolymer mixed with the chain extender
is cast in a mold, and heat-cured.
[0100] The inert gas used in production of the polyurethane resin
foam is used for forming fine cells, and it is preferably not
combustible. Examples of the gases include nitrogen, oxygen, a
carbon dioxide gas, a rare gas such as helium and argon, and a
mixed gas thereof, and the air dried to remove water is most
preferable in view of cost.
[0101] As a stirrer for dispersing the inert gas in the
silicone-based surfactant-containing isocyanate-terminated
prepolymer to form fine cells, well known stirrers can be used
without particular limitation, and examples thereof include a
homogenizer, a dissolver, a twin-screw planetary mixer and the
like. The shape of an agitator of the stirrer is not particularly
limited either, but a whipper-type agitator is preferably used to
form fine cells.
[0102] In a preferable embodiment, different stirrers are used in
stirring for forming a cell dispersion in the stirring step and in
stirring for mixing an added chain extender in the mixing step,
respectively. In particular, stirring in the mixing step may not be
stirring for forming cells, and a stirrer not generating large
cells is preferably used. Such a stirrer is preferably a planetary
mixer. The same stirrer may be used in the stirring step and the
mixing step, and stirring conditions such as revolution rate of the
agitator are preferably adjusted as necessary.
[0103] In the method of preparing the foamed polyurethane, heating
and post-curing of the foam obtained by casting the cell dispersion
in a mold and reacting it until the dispersion lost fluidity are
effective in improving the physical properties of the foam, and are
extremely suitable. The cell dispersion may be cast in a mold and
immediately post-cured in a heating oven, and even under such
conditions, heat is not immediately conducted to the reactive
components, and thus the diameters of cells are not increased. The
curing reaction is preferably conducted at normal pressures to
stabilize the shape of cells.
[0104] In the preparation of the polyurethane resin, a well known
catalyst accelerating polyurethane reaction, such as tertiary
amine-based catalysts, organotin-based catalysts, may be used. The
type and amount of the catalyst added are determined depending on
flow time in casting in a predetermined shape mold after the mixing
step.
[0105] The production of the foamed polyurethane may be in a batch
system where each component is weighed and introduced into a
vessel, or in a continuous production system where each component
and an inert gas are continuously supplied to and stirred in a
stirring device and the resulting cell dispersion is provided to
produce molded articles.
[0106] The polishing layer used for the polishing pad of the
present invention can be produced by cutting a sheet of the foamed
polyurethane resin prepared as described above into a predetermined
size.
[0107] In the polishing pad of the present invention, it is desired
for the polishing layer to have a thickness, which is not limited,
of 0.6 to 3.5 mm. Examples of the methods of preparing the
polishing layer having the above thickness include a method of
processing the foam block produced by the method described above to
a given thickness by a slicer of band saw type or planer type; a
method of casting resin in a mold comprising a cavity having a
given thickness to cure it; a method of using coating technique or
sheet molding technique; and the like.
[0108] It is desired for the polishing layer to have a variability
of thickness of not more than 100 .mu.m, preferably not more than
50 .mu.m. When the variability of thickness is larger than 100
.mu.m, the polishing layer has large crinkle, and portions having
different contact state with the material to be polished are
formed, which degrades the abrasive performance. In order to
dissolve the variability of thickness of the polishing layer, the
surface of the polishing layer is dressed by dresser having
abrasive grains of diamond electrodeposited or melt bonded thereon
at initial stage of polishing. However, when the variability of
thickness is larger than the upper limit, dressing time is long,
which reduces the productive efficiency.
[0109] In addition, in order to restrain the variability of the
thickness of the polishing layer, the surface of the polishing
layer (zone) adjusted to a given thickness may be buffing treated.
The buffing treatment is preferably conducted stepwise by using
abrasive sheets having different particle size.
[0110] In the polishing layer formed from the foamed polyurethane
of the present invention, it is required to provide grooves on the
polishing surface (polishing zone) contact with a material to be
polished to polish the material. The abrasive slurry provided
during polishing the semi-conductor device is effectively retained
by the presence of the grooves. The grooves also have a function of
uniformly distributing the abrasive slurry on the polishing
surface. In addition, the grooves also have a function of a path
for briefly retaining abrasive waste, such as abrasive dust, used
abrasive slurry, and smoothly discharging it to the exterior
thereof. The grooves also prevent the material to be polished from
breaking by the absorption of the material to be polished to the
polishing layer.
[0111] The grooves on the surface of the polishing layer, of which
the cross section shape is not particularly limited, includes, for
example, rectangular groove comprising side surfaces and bottom
surface, U-shaped groove, V-shaped groove and the like. FIG. 2 is a
schematic cross section illustrating grooves having rectangular
cross section shape. The side surface 11 and bottom surface 12 of
the groove 10 shown in FIG. 2 are inner surface of the groove. The
term "inner surface of groove" used herein refers to at least one
surface of side surface and bottom surface of the groove. In case
of U-shaped groove, it is difficult to distinguish between the side
surface and bottom surface as the inner surface of the groove. In
case of V-shaped groove, the inner surface of the groove comprises
only the side surface.
[0112] In the polishing pad of the present invention, it is not
necessary for the whole inner surface of the groove to be
non-porous surface. In case of the groove having small depth and
rectangular cross section shape, even if only the bottom surface of
the groove is non-porous surface, it is considered that the
technical effects accomplished by the present invention are
sufficiently obtained. However, it is more preferable that the
inner surface of the groove, which is at least one surface of the
side surface and bottom surface of the groove, is a non-porous
surface in whole, because more excellent technical effects can be
obtained.
[0113] The shape of the groove on the polishing surface of the
polishing layer is not particularly limited, but includes, for
example, round loop, polygonal loop (such as triangle loop, square
loop, pentagon loop), oval loop, and the like. The number of the
groove is not particularly limited as long as it is not less than
2. The arrangement of the grooves is not particularly limited, but
includes, for example, loop grooves concentrically arranged, loop
grooves eccentrically arranged, loop grooves comprising one loop
groove and the other grooves positioned in a portion surrounded by
the loop groove on the polishing surface and the like.
[0114] Among the loop grooves described above, loop grooves
arranged in the form of concentric circles are preferable in view
of abrasive performance and easiness of processing the groove.
[0115] There may be grooves having the other shape or recesses on
the polishing surface in addition to the loop grooves. The grooves
having the other shape may be, for example, linear grooves arranged
in the direction of the diameter on the polishing layer. The linear
grooves may be arranged in a lattice pattern. There may be
perforations penetrated from the polishing surface to the backside
of the polishing layer in addition to the grooves described
above.
[0116] It is desired for the groove on the surface of the polishing
layer to have a width of 0.05 to 2.0 mm, preferably 0.20 to 0.50
mm. When the width of the groove is smaller than 0.05 mm, it is
difficult to enter the abrasive slurry in the groove, and the
technical effects of functioning as a flow path of the abrasive
slurry are sufficiently obtained, which degrades the abrasive rate.
In addition, it is very difficult to process the grooves having a
width of smaller than 0.05 mm, and productivity is degraded. On the
other hand, when the width of the groove is larger than 2.0 mm, the
polishing effective area of the polishing surface of the polishing
layer contact with the material to be polished is reduced, and the
abrasive rate is reduced. The abrasive rate is a parameter used for
evaluating the abrasive properties.
[0117] In the present invention, it is desired for the groove to
have a pitch of 0.1 to 20 mm. The pitch 15 is distance between the
groove 14 formed and the other groove 14 as shown in FIG. 2. When
the pitch of the groove is smaller than 0.1 mm, many grooves are
formed on the polishing pad, and the polishing effective area of
the polishing surface of the polishing layer contact with a
semiconductor wafer as the material to be polished is reduced,
which reduces the abrasive rate. On the other hand, when the pitch
of the groove is larger than 20 mm, the area of the polishing
surface of the polishing layer contact with the material to be
polished is increased, and the frictional resistance between the
material to be polished and the polishing pad. Therefore, the
material to be polished removes from the polishing head (which is
so-called "dechucking"). The pitch of the groove means a shortest
distance between adjacent grooves.
[0118] It is desired for the groove to have a depth of not less
than 0.5 mm, which is a distance from the polishing surface to the
deepest portion of the bottom surface. When the depth of the groove
is less than 0.5 mm, the balance between feeding and discharging
the abrasive slurry is not sufficiently obtained, which is not
preferable for polishing. The depth of the groove is preferably not
more than 0.85 of the thickness of the polishing layer having the
polishing surface in view of the strength of the polishing pad.
FIG. 2 is also a schematic cross section for illustrating the width
14, pitch 15 and depth 13 of the groove 10.
[0119] A method of forming the groove is not limited, but includes
a method of mechanical cutting using, for example, a cutting tool
of a predetermined size, a method of casting resin in a mold having
a given surface shape and curing it, a method of pressing resin
using a press plate having a given surface shape, a method of
forming the grooves by photolithography, a method of forming the
grooves by printing, a method of forming the grooves by laser light
using carbon dioxide laser and the like. Preferred is the method of
mechanical cutting.
[0120] The polishing pad formed from a porous material, such as
foamed polyurethane is excellent to polishing the semi-conductor
device. In case of forming the grooves on the porous material by
the mechanical cutting, "burr" or open pore is formed by cutting
the pore portion are formed on the inner surface, such as the side
surface and bottom surface, of the groove. The used abrasive slurry
and abrasive dust are easily remained and accumulated by the
presence of the hangnail or open pore on the inner surface of the
groove. Thereby the groove is stopped up, and the abrasive rate is
reduced, a scratch occurs and the uniformity of polishing is not
sufficiently obtained. Such polishing pad is not durable to long
time polishing.
[0121] In order to solve the problems described above, it is
considered to use methods of forming the groove, for example, by
heat pressing, embossing, laser processing. The inner surface of
the groove formed by the methods is smooth surface without burr,
but the inner surface has a drawback to easily cause heat
deterioration. The heat deterioration causes swelling of the
groove, thermal hardening of the surface and the like, which cause
scratches. On the other hand, in case of forming the polishing
layer by non-foamed material, the groove having smooth inner
surface can be also formed by cutting and the like. However, the
polishing layer formed from the non-foamed material tends to have
poor retainability of the abrasive slurry. In addition, since the
non-foamed material has no pore formed by foaming, the abrasive
slurry and abrasive dust have no escape, which increases the
formation of scratches.
[0122] The polishing pad of the present invention comprises the
polishing layer formed from a porous material and the inner surface
of the groove formed on the surface of the polishing layer has a
non-porous surface. The wording "the inner surface of the groove
formed on the surface of the polishing layer has a non-porous
surface" means that the polishing layer is formed from a porous
material, but the inner surface of the groove formed on the
polishing layer has smooth surface, which does not have any pores.
In case that the inner surface of the groove has a non-porous
surface, it is desired for the non-porous surface to have a center
line average roughness Ra of a roughness curve of 1.0 to 5.0 .mu.m,
preferably 1.5 to 3.0 .mu.m as a surface roughness. When the center
line average roughness Ra of a roughness curve is larger than 5.0
.mu.m, the technical effects of reducing of the unusual retainment
of the abrasive slurry are not sufficiently obtained. On the other
hand, it is difficult to prepare the non-porous surface having a
center line average roughness Ra of a roughness curve of less than
1.0 .mu.m based on the present technical level.
[0123] In the polishing pad of the present invention, since the
polishing surface has grooves and the inner surface of the groove
has the non-porous surface, it is possible to effectively restrain
the clogging of the groove from the residual abrasive slurry and
the retainment of the abrasive dust even if the polishing layer is
formed from porous material. Therefore, it is possible to restrain
the unusual retainment of the abrasive slurry, and it is possible
to prepare the polishing pad having excellent long-term
usability.
[0124] "A center line average roughness Ra of a roughness curve"
used herein is a parameter according to JIS B 0601. The center line
average roughness Ra of a roughness curve can be measured with an
optical type surface roughness tester, such as a three-dimensional
surface profiler, laser scanning microscope, electron beam surface
profiler; a contact type surface roughness tester, such as a
surface roughness tester with contact stylus; and the like.
[0125] A method of making the inner surface of the groove on the
polishing layer a non-porous surface includes a method of forming
the groove by cutting and the like, and then processing the inner
surface of the groove to the non-porous surface by post processing.
Examples of methods of post processing include a method of
irradiating a laser beam to the surface portion of the inner
surface of the groove by a laser processing machine to melt it; a
method of thinly applying a resin to the surface portion of the
inner surface of the groove to level it; a method of applying a
resin to the groove portion, and then newly forming a groove; and
the like.
[0126] Examples of the resins used for the post processing include
resins that can be used for preparing the polishing layer. The
inner surface of the groove can be treated to form the non-porous
surface by applying the resin to the groove portion without the
foaming treatment described above. Examples of methods of applying
the resin to the groove portion include a method of coating the
resin thermally melted thereto; a method of preparing a resin
solution by dissolving or dispersing the resin in a solvent, and
then coating or spraying the resin solution thereto; a method of
applying polymerizable resin to the groove portion by coating or
spraying, and then post curing it; and the like.
[0127] The polishing layer of the polishing pad of the present
invention is formed from the porous material. Therefore, in the
polishing effective area portion, which is the polishing surface
other than the groove portion, that is, the groove pitch portion of
the polishing layer, the porous surface is exposed. That is, the
polishing surface has micro pores.
[0128] The polishing pad of the present invention may be a
single-layered polishing pad, which is composed of only a polishing
layer, or a laminated polishing pad comprising at least two layers
of the polishing layer and a cushion layer positioned between the
polishing layer and a polishing platen.
[0129] The polishing pad is preferably the laminated polishing pad
comprising the polishing layer and the cushion layer. The cushion
layer plays a role in compensating the properties of the polishing
layer. The cushion layer is required in order to accomplish both
the planarity and uniformity within wafer, which are relation of a
trade-off in the CMP. The planarity means smoothness in a pattern
portion when a material to be polished having micro unevenness
formed during forming the pattern is polished, the uniformity
within wafer means uniformity in the whole material to be polished.
The planarity is improves by the properties of the polishing layer,
the uniformity within wafer is improves by the properties of the
cushion layer.
[0130] The hardness of the cushion layer is preferably lower than
that of the polishing layer, which improves the adaptability of the
polishing layer to the whole wafer, and the uniformity of the
polishing layer is improved. It is desired for the cushion layer to
have an Asker A hardness of 20 to 40, preferably 25 to 35.
[0131] Examples of materials for forming the cushion layer, which
are not limited, but include a nonwoven fibrous fabric, such as
polyester nonwoven fabric, nylon nonwoven fabric, acrylic nonwoven
fabric; a resin impregnated nonwoven fabric, such as polyester
nonwoven fabric impregnated with polyurethane; polymer resin foam,
such as polyurethane foam, polyethylene foam; rubbery resin, such
as butadiene rubber, isoprene rubber; photosensitive resin; and the
like.
[0132] A method of laminating the polishing layer to the cushion
layer include, for example, a method of interposing a double-coated
tape between the polishing layer and the cushion, and then pressing
it.
[0133] The double-coated tape comprises adhesive layers on the both
surface of a substrate, such as nonwoven fabric and film. It is
desired to use the film as a substrate in order to prevent the
abrasive slurry from penetrating into the cushion layer. In
addition, examples of the compositions for the adhesive layer
include rubber-based adhesive, acrylic-based adhesive and the like.
In view of the metal ion content, preferred is the acrylic-based
adhesive, because it has small content of the metal ion. Since the
composition of the polishing layer may be different from that of
the cushion layer, each adhesive layer of the double-coated tape
can have different composition and adjust the adhesion of the each
adhesive layer to suitable range.
[0134] The polishing pad obtained as described above is mounted on
the polishing platen by bonding with a double-coated tape, and the
surface of semi-conductor wafer can be polished. The double-coated
tape comprises adhesive layers on the both surface of a substrate,
such as nonwoven fabric and film as described in the double-coated
tape for bonding the polishing layer to the cushion layer. Since
the polishing pad is removed from the platen after polishing, it is
desired to use the film for the substrate, because it is possible
to prevent the tape from remaining on the polishing platen. The
same compositions for the adhesive layer as that of the
double-coated tape for bonding the polishing layer to the cushion
layer can be used.
[0135] Semi-conductor device is produced through the step of
polishing the surface of semi-conductor wafer by using the
polishing pad of the present invention. The semi-conductor wafer is
generally formed by depositing wire metal and oxide film on silicon
wafer. A method of polishing the semi-conductor wafer and polishing
apparatus used for the method are not limited, but the method is
conducted by using the polishing apparatus comprising, for example,
a polishing platen for supporting a polishing pad, a supporting
stand (polishing head) for supporting a material to be polished
(such as a semi-conductor wafer), a backing for uniformly applying
pressure to the wafer and an abrasive slurry-feeding mechanism. The
polishing pad is mounted on the polishing platen by bonding with a
double-coated tape. The polishing platen and supporting stand are
positioned such that the polishing pad and semi-conductor wafer
supported by the platen and the stand respectively are opposed to
each other, and have an axis of revolution respectively. At the
side of the supporting stand, a pressing mechanism for pushing the
semi-conductor wafer onto the polishing pad is provided. During
polishing, the semi-conductor wafer is pushed onto the polishing
pad while rotating the polishing platen and supporting stand, and
the polishing is conducted while feeding the abrasive slurry. Feed
of the abrasive slurry, polishing load, revolution number of the
polishing platen and revolution number of the semi-conductor wafer,
which are not limited, are adjusted to suitable range.
[0136] Thereby, a projective portion on the surface of the material
to be polished, such as the semi-conductor wafer, is smoothly
polished. After the polishing, dicing, bonding, packaging and the
like are conducted, and semi-conductor device is produced. The
semi-conductor device is used for processor, memory and the
like.
EXAMPLES
[0137] Hereinafter, the present invention is described in more
detail by reference to the Examples, but the present invention is
not limited by the Examples.
[0138] (Average Cell Diameter)
[0139] In measurement of average cell diameter, the material, such
as the polishing layer was cut into a thickness of about 1 mm
parallel to the layer with a microtome cutter as a sample for
measuring the average cell diameter. The sample was mounted on a
slide glass, and the diameter of the all cells was measured at an
optional 0.2 mm.times.0.2 mm square area by using an image
processing unit (Image Analyzer V10 manufactured by TOYOBO Co.,
Ltd.) to calculate the average cell diameter.
[0140] (Specific Gravity)
[0141] The specific gravity was measured according to JIS
Z8807-1976. The material, such as the polishing layer was cut into
a strip sized of 4 cm.times.8.5 cm (a proper thickness) as a sample
for measuring the specific gravity, and the sample was left at a
temperature of 23.degree. C..+-.2.degree. C. and humidity of
50%.+-.5% for 16 hours. The specific gravity was measured by using
a hydrometer (Sartorius K.K.).
[0142] (Hardness)
[0143] (1) Hardness of Polishing Layer
[0144] The hardness was measured according to JIS K6253-1997. The
material for the polishing layer was cut into a size of 2
cm.times.2 cm (a proper thickness) as a sample for measuring the
hardness, and the sample was left at a temperature of 23.degree.
C..+-.2.degree. C. and humidity of 50%.+-.5% for 16 hours. The
hardness was measured by using a stack of the samples having a
thickness of not less than 6 mm with a hardness meter (Asker D
hardness meter manufactured by Kobunshi Keiki Co., Ltd.).
[0145] (2) Hardness of Cushion Layer
[0146] The hardness was measured according to JIS K6253-1997. The
material for the cushion layer was cut into a size of 2 cm.times.2
cm (a proper thickness) as a sample for measuring the hardness, and
the sample was left at a temperature of 23.degree. C..+-.2.degree.
C. and humidity of 50%.+-.5% for 16 hours. The hardness was
measured by using a stack of the samples having a thickness of not
less than 6 mm with a hardness meter (Asker A hardness meter
manufactured by Kobunshi Keiki Co., Ltd.).
[0147] (Compressibility)
[0148] The material for the polishing layer, which cut into disk
having a diameter of 7 mm (a proper thickness), was used as a
sample for measuring the compressibility, the sample was left at a
temperature of 23.degree. C..+-.2.degree. C. and humidity of
60%.+-.10% for 40 hours. The compressibility was measured by using
TMA (SS6000; manufactured by Seiko Instruments). The
compressibility is determined by using the following formula:
Compressibility(%)=[(T.sub.1-T.sub.2)/T.sub.1].times.100
[0149] wherein T.sub.1 represents the thickness of a sample after
application of 30 kPa (300 g/cm.sup.2) stress for 60 seconds to the
sample, and
[0150] T.sub.2 represents the thickness of the sample after
application of 180 kPa stress for 60 seconds to the sample in the
state T.sub.1.
[0151] (Compression Recovery)
[0152] The material for the polishing layer, which cut into disk
having a diameter of 7 mm (a proper thickness), was used as a
sample for measuring the compression recovery, the sample was left
at a temperature of 23.degree. C..+-.2.degree. C. and humidity of
60%.+-.10% for 40 hours. The compressibility was measured by using
TMA (SS6000; manufactured by Seiko Instruments). The
compressibility is determined by using the following formula:
Compression
recovery(%)=(T.sub.3-T.sub.2)/(T.sub.1-T.sub.2).times.100
[0153] wherein T.sub.1 represents the thickness of a sample after
application of 30 kPa (300 g/cm.sup.2) stress for 60 seconds to the
sample,
[0154] T.sub.2 represents the thickness of the sample after
application of 180 kPa stress for 60 seconds to the sample in the
state T.sub.1, and
[0155] T.sub.3 represents the thickness of the sample after no
loaded state for 60 seconds and then application of 30 kPa (300
g/cm.sup.2) stress for 60 seconds to the sample in the state
T.sub.2.
[0156] (Storage Elastic Modulus)
[0157] A 3 mm.times.40 mm rectangular sample (a proper thickness)
was cut out and used as a sample for measurement of dynamic
viscoelasticity. The accurate width and thickness of each sheet
after cutting were measured using a micro-meter. For measurement, a
dynamic viscoelasticity spectrometer (manufactured by Iwamoto
Seisakusho, now IS Giken) was used to determine storage elastic
modulus E'. Measurement conditions are as follows:
[0158] measurement temperature, 40.degree. C.;
[0159] applied strain, 0.03%;
[0160] initial loading, 20 g; and
[0161] frequency, 1 Hz.
[0162] [Evaluation of Abrasive Properties]
[0163] As the polishing apparatus, SPP600S manufactured by Okamoto
Machine Tool Works, Ltd. was used in evaluation of abrasive
properties of the resulting polishing pad.
[0164] (Abrasive Rate)
[0165] The abrasive rate was determined by the calculation from a
time until polishing 0.5 .mu.m thickness of an oxide film from the
oxide film formed on silicon wafer having a diameter of 8 inches.
The thickness of an oxide film was measured by an interference film
thickness measuring device manufactured by Otsuka Denshisha. The
polishing conditions were as follows: silica slurry SemiSperse-12
(manufactured by Cabot) was dropped at a flow rate of 150 mL/min.,
the polishing loading was 350 g/cm.sup.2, the number of revolutions
of the polishing platen was 35 rpm, and the number of revolutions
of the wafer was 30 rpm.
[0166] (Planarity)
[0167] For evaluation of planarity, a 0.5 .mu.m thermal-oxide film
was deposited on a 8-inch silicon wafer and subjected to
patterning, and a 1 .mu.m oxide film p-TEOS (tetraethoxy silane)
was further deposited thereon, to prepare a wafer having a pattern
with an initial difference in level of 0.5 .mu.m. This wafer was
polished under the above-described conditions, and each difference
in level was measured to evaluate the planarity. The planarity was
determined by measuring the two differences in level. One is a
local difference in level, which is level difference in the pattern
where lines having a width of 270 .mu.m were spaced at 30 .mu.m,
that is, the difference in level after 1 minute from polishing. The
other is the abrasive amount in 270 .mu.m space when the global
difference in level between tops of lines in two patterns, which
are a pattern where lines having a width of 270 .mu.m is spaced at
30 .mu.m and a pattern where lines having a width of 30 .mu.m is
spaced at 270 .mu.m, was reduced to 2000 .ANG. or less was measured
to evaluate the planarity. The smaller the local difference in
level, the higher the speed of planarizing unevenness of the oxide
film formed depending to the pattern on the wafer within a certain
time. The smaller the abrasive amount in the space, the smaller the
abrasive amount of the portion not to be polished, and it is shown
that the planarity is excellent.
[0168] (Uniformity within Wafer)
[0169] After polishing, the thickness of the film was measured at
25 points on the polished surface of a silicon wafer. The maximum
thickness Tmax and minimum thickness Tmin of the film were used to
calculate uniformity (%) according to the following equation:
Uniformity Within Wafer(%)=(Tmax-Tmin)/(Tmax+Tmin)..times.100
The smaller the value of the uniformity is, the higher the
uniformity within the surface of the silicon wafer is.
[0170] (Number of Scratch)
[0171] Number of scratches of not less than 0.5 .mu.m on the wafer
after polishing was measured with a wafer surface analyzer WM2500
manufactured by Topcon Corporation
[0172] (Surface Roughness Ra)
[0173] The inner surface portion of the groove formed on the
polishing surface of the polishing layer was cut out as a test
piece. The test piece adhered on the glass platen with a wax. The
center line average roughness Ra of a roughness curve of the test
piece on the glass platen was measured as surface roughness
according to JIS B 0633 with a surface profiler P-15 manufactured
by Tencor Corporation at the following measuring condition. [0174]
Scan length: 2500 .mu.m [0175] Scan speed: 20 .mu.m/sec [0176]
Stylus force: 2 mg [0177] Stylus radius: 2.0 .mu.m [0178] Cone
angle of stylus tip: 60 degree Further 4 test pieces were prepared
as described above, and the center line average roughness Ra was
measured as described above. The average of the resulting 5
measured values was determined, and the average is shown as the
center line average roughness Ra of a roughness curve as the
surface roughness Ra.
[0179] (Sectional Shape of Groove)
[0180] The sectional shape of the groove was evaluated by using the
following evaluation criteria.
[0181] Evaluation Criteria
[0182] .smallcircle.: An average of the groove width measured at
three points in the depth direction when observing the sectional
shape of the groove is within the target range and the deviation of
the three measuring points is not more than 30 .mu.m or not more
than 10% of the target range. Therefore, rectangle sectional shape
is obtained.
[0183] .DELTA.: The average of the groove width is within the
target range, but the deviation is larger than 30 .mu.m. Burrs is
largely formed only at one portion. The rectangle sectional shape
is generally obtained and the deviation of the three measuring
points is not more than 30 .mu.m, but the average of the groove
width is slightly out of the target range.
[0184] x: The average of the groove width is out of the target
range and rectangle sectional shape is not entirely obtained.
[0185] (Surface Burr)
[0186] Burr from the groove to the surface in the sectional
surface, in which the sectional shape of the groove was measured,
was evaluated by using the following evaluation criteria.
[0187] Evaluation Criteria
[0188] .smallcircle.: Not more than 80 .mu.m
[0189] .DELTA.: From 80 to 100 .mu.m
[0190] x: Not less than 100 .mu.m
[0191] (Wear of Groove Processing Tool)
[0192] After processing the groove by using the groove processing
tool, of which the cutting edge was newly polished, the wear state
of the cutting edge of the groove processing tool was evaluated.
The R of the corner portion of the cutting edge shown in FIG. 7 was
measured (by using a scanning electron microscopy SEM or
microscope), and the wear of the groove processing tool was
evaluated by using the following evaluation criteria.
[0193] Evaluation Criteria
[0194] .smallcircle.: R=0 to 0.20 mm and the corner portion of the
cutting edge is not nicked.
[0195] .DELTA.: R=0.20 to 0.30 mm and the corner portion of the
cutting edge is slightly nicked.
[0196] x: R=not less than 0.30 mm and the corner portion of the
cutting edge is largely nicked.
Example 1
Preparation of Polishing Layer
[0197] 100 parts by weight of a polyether-based urethane prepolymer
(Adiprene L-325 manufactured by Uniroyal, NCO content: 2.22 meq/g)
filtered and 3 parts by weight of a silicone-based nonionic
surfactant (SH192 manufactured by Toray Dow Corning Silicone Co.,
Ltd.) were introduced into a fluorine coated vessel and mixed, and
the temperature was maintained to 80.degree. C. The mixture was
vigorously stirred for about 4 minutes at about 900 rpm by using a
fluorine coated stirrer with introducing air into reaction process.
26 parts by weight of 4,4'-methylene-bis(o-chloroaniline) (Ihara
Cuamine MT manufactured by Ihara Chemical Industry) previously
melted at 120.degree. C. and filtered was introduced thereto. After
stirring for about 1 minute, the mixed reaction solution was
introduced into a fluorine coated pan-type open mold. When the
reaction solution did not flow, the mold was put in an oven and
post-cured at 110.degree. C. for 6 hours to produce a foamed
polyurethane resin block. This foamed polyurethane resin block was
sliced by a slicer of band saw type (manufactured by Fecken) to
obtain a foamed polyurethane resin sheet.
[0198] The sheet was buffing treated with a buff (manufactured by
Amitec) to form a sheet having the desired thickness (sheet
thickness: 1.27 mm). The buffing treated sheet for the polishing
layer had an average cell diameter of 45 .mu.m, a specific gravity
of 0.86, a hardness of 53, a compressibility of 1.0%, a compression
recovery of 65.0% and a flexural modulus of 275 MPa. The buffing
treated sheet was punched into a disk having a diameter of 24
inches (610 mm), and concentric circular grooves having a depth of
0.8 mm, width of 0.25 mm and pitch of 1.5 mm were formed on the
surface of the sheet by using a surface groove processing machine
(Toho Engineering).
[0199] The resin used for the foamed polyurethane resin sheet was
prepared as described above without stirring with introducing air
into reaction process, and then the resin was vacuum defoamed to
prepare a resin used for post processing. The resulting resin was
coated on the groove portion in the uncured state, and cured by
heat treatment. The cured resin portion was then cut as described
above to form grooves again (post processing). The cutting was
attentively conducted without cutting all the coated resin. As a
result, the polishing layer, of which both the side surface and
bottom surface as the inner surface of the groove were non-porous
surface, was prepared.
[0200] The inner surface of the groove before post processing had a
center line average roughness Ra of a roughness curve of 7 to 20
.mu.m, and the inner surface of the groove after post processing
had a center line average roughness Ra of a roughness curve of 0.6
to 1.0 .mu.m.
[0201] A double-coated tape (double-tack tape manufactured by
Sekisui Chemical Co., Ltd.) adhered to the opposite side of the
groove processed surface of the polishing layer sheet by using a
laminator.
[0202] Production of Polishing Pad
[0203] A polyethylene foam (Toray PEF manufactured by Toray
Industries, Inc.) (thickness, 0.8 mm) having a surface brushed with
a buff and subjected to corona treatment as a cushion layer was
laminated to the adhesive surface of the double-coated tape on the
polishing layer by using a laminator. In addition, a double-coated
tape adhered to the opposite side of the cushion layer by using a
laminator to prepare a polishing pad.
[0204] The abrasive properties of the resulting polishing pad were
measured or evaluated. As a result, a silicon wafer polished by
using the polishing pad had a few scratches and good uniformity,
and the polishing pad had good stability of polishing the silicon
wafer for a long time of not less than 40 hours such that abrasive
dust and abrasive slurry were not unusually remained in the
grooves.
Comparative Example 1
[0205] 100 parts by weight of a polyether-based urethane prepolymer
(Adiprene L-325 manufactured by Uniroyal, NCO content: 2.22 meq/g)
filtered and 3 parts by weight of a silicone-based nonionic
surfactant (SH192 manufactured by Toray Dow Corning Silicone Co.,
Ltd.) were introduced into a fluorine coated vessel and mixed, and
the temperature was maintained to 80.degree. C. The mixture was
vigorously stirred for about 4 minutes at about 900 rpm by using a
fluorine coated stirrer with introducing air into reaction process.
26 parts by weight of 4,4'-methylene-bis(o-chloroaniline) (Ihara
Cuamine MT manufactured by Ihara Chemical Industry) previously
melted at 120.degree. C. and filtered was introduced thereto. After
stirring for about 1 minute, the mixed reaction solution was
introduced into a fluorine coated pan-type open mold. When the
reaction solution did not flow, the mold was put in an oven and
post-cured at 110.degree. C. for 6 hours to produce a foamed
polyurethane resin block. This foamed polyurethane resin block was
sliced by a slicer of band saw type (manufactured by Fecken) to
obtain a foamed polyurethane resin sheet.
[0206] The sheet was buffing treated with a buff (manufactured by
Amitec) to form a sheet having the desired thickness (sheet
thickness: 1.27 mm). The buffing treated sheet for the polishing
layer had an average cell diameter of 45 .mu.m, a specific gravity
of 0.86, a hardness of 53, a compressibility of 1.0%, a compression
recovery of 65.0% and a flexural modulus of 275 MPa. The buffing
treated sheet was punched into a disk having a diameter of 24
inches (610 mm), and concentric circular grooves having a depth of
0.8 mm, width of 0.25 mm and pitch of 1.5 mm were formed on the
surface of the sheet by using a surface groove processing machine
(Toho Engineering) to prepare the polishing layer sheet having
groove processed polishing surface.
[0207] The inner surface of the groove (without post processing)
had a center line average roughness Ra of a roughness curve of 7 to
20 .mu.m.
[0208] A double-coated tape (double-tack tape manufactured by
Sekisui Chemical Co., Ltd.) adhered to the opposite side of the
groove processed surface of the polishing layer sheet by using a
laminator.
[0209] Production of Polishing Pad
[0210] A polyethylene foam (Toray PEF manufactured by Toray
Industries, Inc.) (thickness, 0.8 mm) having a surface brushed with
a buff and subjected to corona treatment as a cushion layer was
laminated to the adhesive surface of the double-coated tape on the
polishing layer by using a laminator. In addition, a double-coated
tape adhered to the opposite side of the cushion layer by using a
laminator to prepare a polishing pad.
[0211] The abrasive properties of the resulting polishing pad were
measured or evaluated. As a result, a silicon wafer polished by
using the polishing pad had scratches after polishing for 15 hours,
and the abrasive dust and abrasive slurry were unusually remained
in the grooves.
Example 2
[0212] 100 parts by weight of a polyether-based urethane prepolymer
(Adiprene L-325 manufactured by Uniroyal, NCO content: 2.22 meq/g)
filtered and 3 parts by weight of a silicone-based nonionic
surfactant (SH192 manufactured by Toray Dow Corning Silicone Co.,
Ltd.) were introduced into a fluorine coated vessel and mixed, and
the temperature was maintained to 80.degree. C. The mixture was
vigorously stirred for about 4 minutes at about 900 rpm by using a
fluorine coated stirrer with introducing air into reaction process.
26 parts by weight of 4,4'-methylene-bis(o-chloroaniline) (Ihara
Cuamine MT manufactured by Ihara Chemical Industry) previously
melted at 120.degree. C. and filtered was introduced thereto. After
stirring for about 1 minute, the mixed reaction solution was
introduced into a fluorine coated pan-type open mold. When the
reaction solution did not flow, the mold was put in an oven and
post-cured at 110.degree. C. for 6 hours to produce a foamed
polyurethane resin block. This foamed polyurethane resin block was
sliced by a slicer of band saw type (manufactured by Fecken) to
obtain a foamed polyurethane resin sheet. The sheet was buffing
treated with a buff (manufactured by Amitec) to form a sheet having
the desired thickness (sheet thickness: 1.27 mm). The buffing
treated sheet for the polishing layer had an average cell diameter
of 45 .mu.m, a specific gravity of 0.86, a hardness of 53, a
compressibility of 1.0%, a compression recovery of 65.0% and a
flexural modulus of 275 MPa.
[0213] The buffing treated sheet was punched into a disk having a
diameter of 24 inches (610 mm), and concentric circular grooves
having a width of 0.25 mm, depth of 0.40 mm and pitch of 1.5 mm
were formed on the surface of the polishing layer sheet by using a
surface groove processing machine. A feed speed of a groove
processing tool was No. 1 shown in the following Table 2. The
surface roughness of the resulting groove processing surface was
measured, and the shape of the groove, surface burr and wear of the
groove processing tool were evaluated. The results are shown in the
following Table 1 and Table 2. A double-coated tape (double-tack
tape manufactured by Sekisui Chemical Co., Ltd.) adhered to the
opposite side of the groove processed surface of the polishing
layer sheet by using a laminator. A cushion sheet (polyethylene
foam, Toray PEF manufactured by Toray Industries, Inc., thickness:
0.8 mm) having a surface brushed with a buff and subjected to
corona treatment was laminated to the adhesive surface of the
double-coated tape on the polishing layer by using a laminator. In
addition, a double-coated tape adhered to the opposite side of the
cushion layer by using a laminator to prepare a polishing pad.
Example 3
[0214] The polishing pad was prepared as described in Example 2
except that the feed speed of a groove processing tool was No. 4
shown in the following Table 2. The surface roughness of the
resulting groove processing surface was measured, and the shape of
the groove, surface burr and wear of the groove processing tool
were evaluated. The results are shown in the following Table 1 and
Table 2.
Comparative Example 2
[0215] The polishing pad was prepared as described in Example 2
except that the feed speed of a groove processing tool was No. 11
shown in the following Table 2. The surface roughness of the
resulting groove processing surface was measured, and the shape of
the groove, surface burr and wear of the groove processing tool
were evaluated. The results are shown in the following Table 1 and
Table 2.
[0216] The abrasive properties of the polishing pads of Examples 2
to 3 and Comparative Example 2 were evaluated. The results are
shown in the following Table 1.
TABLE-US-00001 TABLE 1 Comparative Example No. Example No. 1 2 1
Surface 5.57 8.59 12.54 roughness Ra Abrasive rate 2300 2300 2350
(.ANG./min) Number of 53 76 178 scratches (per a wafer)
TABLE-US-00002 TABLE 2 Feed speed of groove processing tool (m/min)
T.sub.s Groove No. 1 2 3 4 (sec) shape Burr W 1 0.01 0.03 0.05 1.00
1.00 .DELTA. .smallcircle. .DELTA. 2 0.01 0.03 0.05 0.08 --
.smallcircle. .smallcircle. .smallcircle. 3 0.01 0.03 0.05 -- --
.smallcircle. .smallcircle. .smallcircle. 4 0.01 0.03 -- -- --
.smallcircle. .smallcircle. .smallcircle. 5 0.03 0.05 0.08 1.00 --
.smallcircle. .DELTA. .smallcircle. 6 0.03 0.05 0.08 -- --
.smallcircle. .DELTA. .smallcircle. 7 0.03 0.05 -- -- --
.smallcircle. .DELTA. .smallcircle. 8 0.01 -- -- -- --
.smallcircle. .smallcircle. x 9 0.03 -- -- -- -- .DELTA. .DELTA.
.smallcircle. 10 0.05 -- -- -- -- x x .smallcircle. 11 0.08 -- --
-- -- x x .smallcircle. 12 1.00 -- -- -- -- x x .smallcircle. 13
2.00 -- -- -- -- x x .DELTA. T.sub.s: Stop time of groove
processing tool W: Wear of groove processing tool
[0217] As apparent from the results of Table 1, the polishing pads
of Examples 2 to 3 had smaller surface roughness of the groove
processing surface and smaller number of scratches than the
polishing pad of Comparative Example 2. The polishing pads of
Examples 2 to 3 had excellent abrasive properties as compared with
the polishing pad of Comparative Example 2.
[0218] On the other hand, in the polishing pad of Comparative
Example 2 produced without the method of producing the polishing
pad of the present invention, the abrasive rate was not reduced,
but the number of scratches was very large and the burr on the
surface of the pad from groove processing was largely degraded.
[0219] As described above, the feed speed of a groove processing
tool in the polishing pads of Examples 2 to 3 and Comparative
Example 2 are No. 1, No. 4 and No. 11 shown in Table 2,
respectively. The feed speed of the groove processing tool is
stepwise varied in No. 1 and No. 4, stepwise increased in No. 4,
and increased or decreased in No. 1. In No. 1, there is a time that
the feed speed is zero at the position of reaching the groove
processing tool to the desired groove depth.
[0220] On the other hand, No. 11 is a conventional method of
producing the polishing pad that the feed speed of the groove
processing tool is constant in the groove processing step. In the
polishing pads of Examples 2 and 3, the grooves having precise
rectangle sectional shape and a few surface burr on the groove
processed surface are obtained by stepwise varying the feed speed
of the groove processing tool as shown in No. 1 and No. 4. On the
other hand, in the polishing pad of Comparative Example 2, since
the feed speed is constant as shown in No. 11, the sectional shape
of the groove is not precise rectangle and the groove has many
surface burrs on the groove processed surface.
* * * * *