U.S. patent application number 16/123383 was filed with the patent office on 2019-01-03 for workpiece polishing apparatus.
This patent application is currently assigned to SHIN-ETSU HANDOTAI CO., LTD.. The applicant listed for this patent is SHIN-ETSU HANDOTAI CO., LTD.. Invention is credited to Hiromasa HASHIMOTO, Masanao SASAKI.
Application Number | 20190001463 16/123383 |
Document ID | / |
Family ID | 64735186 |
Filed Date | 2019-01-03 |
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United States Patent
Application |
20190001463 |
Kind Code |
A1 |
HASHIMOTO; Hiromasa ; et
al. |
January 3, 2019 |
WORKPIECE POLISHING APPARATUS
Abstract
A workpiece polishing apparatus including a polishing pad to
polish a workpiece, a polishing agent supplying mechanism to supply
a polishing agent, and a polishing head to hold the workpiece such
that a back surface of the workpiece is held by a backing pad and
an edge of the workpiece is held by an annular template. This
apparatus polishes the workpiece by pressing the workpiece and the
template against the polishing pad and thereby bringing the
workpiece into sliding contact with the polishing pad. The template
is made of a resin containing filler or woven fabric and has fine
depressions created by filler or woven fabric exposed on the
surface on the side that presses the polishing pad. This apparatus
can stabilize the polishing rate of the outer circumferential
portion of the workpiece and thereby polish the workpiece into a
very flat workpiece.
Inventors: |
HASHIMOTO; Hiromasa;
(Nishigo-mura, JP) ; SASAKI; Masanao;
(Nishigo-mura, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SHIN-ETSU HANDOTAI CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
SHIN-ETSU HANDOTAI CO.,
LTD.
Tokyo
JP
|
Family ID: |
64735186 |
Appl. No.: |
16/123383 |
Filed: |
September 6, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14787659 |
Oct 28, 2015 |
|
|
|
PCT/JP2014/002066 |
Apr 10, 2014 |
|
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16123383 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24B 37/20 20130101;
B24B 37/32 20130101 |
International
Class: |
B24B 37/20 20060101
B24B037/20; B24B 37/32 20060101 B24B037/32 |
Foreign Application Data
Date |
Code |
Application Number |
May 16, 2013 |
JP |
2013-103719 |
Claims
1. A workpiece polishing apparatus comprising: a polishing pad
configured to polish a workpiece; a polishing agent supplying
mechanism configured to supply a polishing agent; and a polishing
head including a backing pad and an annular template configured to
hold the workpiece such that a back surface of the workpiece is
held by the backing pad and an edge of the workpiece is held by the
template; the apparatus being configured to polish the workpiece by
pressing the workpiece and the template against the polishing pad
and thereby bringing the workpiece into sliding contact with the
polishing pad, wherein the template is made of a resin containing
filler and has fine depressions on a surface on a side that presses
the polishing pad, the fine depressions being created by the filler
exposed on the surface on the side that presses the polishing pad,
and a surface coverage of the depressions on the surface of the
template on the side that presses the polishing pad ranges from 5%
to 85%.
2. The workpiece polishing apparatus according to claim 1, wherein
each of the depressions has a depth of 0.05 mm or more.
3. The workpiece polishing apparatus according to claim 1, wherein
each of the depressions has an opening with a width of 5 mm or
less, and pitches among the depressions are 10 mm or less.
4. The workpiece polishing apparatus according to claim 2, wherein
each of the depressions has an opening with a width of 5 mm or
less, and pitches among the depressions are 10 mm or less.
5. The workpiece polishing apparatus according to claim 1, wherein
a contact angle between each of the depressions and the polishing
pad is 90.degree. or less.
6. The workpiece polishing apparatus according to claim 2, wherein
a contact angle between each of the depressions and the polishing
pad is 90.degree. or less.
7. The workpiece polishing apparatus according to claim 3, wherein
a contact angle between each of the depressions and the polishing
pad is 90.degree. or less.
8. The workpiece polishing apparatus according to claim 4, wherein
a contact angle between each of the depressions and the polishing
pad is 90.degree. or less.
9. The workpiece polishing apparatus according to claim 1, wherein
the surface coverage of the depressions on the surface of the
template on the side that presses the polishing pad is more than
25% and 85% or less.
Description
[0001] This is a Continuation-in-Part of application Ser. No.
14/787,659 filed Oct. 28, 2015, which is a National Stage Entry of
PCT/JP2014/002066 filed Apr. 10, 2014, which claims priority to JP
2013-103719 filed May 16, 2013. The disclosure of the prior
applications is hereby incorporated by reference herein in its
entirety.
TECHNICAL FIELD
[0002] The present invention relates to a workpiece polishing
apparatus.
BACKGROUND ART
[0003] In production of semiconductor wafers such as silicon
wafers, a polishing process to improve surface roughness and
flatness of a wafer is one of important processes.
[0004] As the precision of devices has recently been increased,
there is an increasing need for more precisely flattened
semiconductor wafers for use in device fabrication. According to
this need, chemical mechanical polishing (CMP) is used as a
technique to flatten a surface of semiconductor wafers.
[0005] Apparatuses for polishing surfaces of a wafer such as a
silicon wafer may be classified into two types: a single-side
polishing apparatus that polishes one side of a workpiece at a time
and a double-side polishing apparatus that polishes both sides
simultaneously.
[0006] As shown in FIG. 7, for example, a common single-side
polishing apparatus is constituted of a turn table 104 to which a
polishing pad 107 is attached, a polishing agent supplying
mechanism 108, a polishing head 102, and other components. The
polishing apparatus 101 of this type holds a workpiece W by the
polishing head 102, supplies a polishing agent 109 to the polishing
pad 107 through the polishing agent supplying mechanism 108,
rotates the turn table 104 and the polishing head 102, and bring a
surface of the workpiece W into sliding contact with the polishing
pad 107 to polish the workpiece W.
[0007] There are plural methods to hold a workpiece, such as a
method of attaching the workpiece to a flat disc-like plate by an
adhesive such as wax, a method of attaching the workpiece to a soft
pad (a baking material) by water, and a method of attaching the
workpiece by vacuum suction.
[0008] In the polishing head 102 shown in FIG. 7, an elastic pad (a
baking pad) 105 such as a polyurethane pad is stack on the lower
surface of a disc-like holding plate 106 made of, for example,
ceramics. The workpiece W is held by a surface tension of wafer
absorbed by this elastic pad 105. A guide ring 103 to prevent the
workpiece W from coming off the holding plate 106 during polishing
is also provided around the holding plate 106.
[0009] This polishing apparatus 101 is easily affected by the
precision of the flatness of the holding plate 106, variation in
dimension due to deformation occurring when a pressure is applied
to the holding plate 106, and the precision of the thickness of the
backing pad 105, because the polishing apparatus 101 indirectly
presses the workpiece W through the holding plate 106. It is
difficult to polish the entire surface of the workpiece with very
high precision. In addition, an outer circumferential portion of
the workpiece tends to be polished in a larger amount, and the
so-called outer circumferential sag is easy to occur. This
apparatus therefore cannot be used when the entire surface of the
workpiece is needed to have very high precision of flatness.
[0010] In view of these problems, Patent Document 1 suggests a
polishing head that uniformly presses the entire surface of a
workpiece against a polishing surface to uniformly polish this
entire surface so that the outer circumferential sag of the
workpiece can be prevented and the flatness of the workpiece
surface can be improved. This polishing head is shown in FIG. 8 and
FIG. 9. FIG. 8 shows a schematic diagram of the whole polishing
head. FIG. 9 shows an enlarged view of a part of this conventional
polishing head.
[0011] The polishing head 117 includes a head 120 having a hollow
that forms a holding part with an opening facing downward, a holder
121 disposed inside the hollow of the head 120, an elastic body 110
having an outer end fixed to a wall of the head 120 and an inner
end fixed to the holder 121 that hangs the holder 121 while
allowing a minute amount of vertical and horizontal movement of the
holder, a first pressure chamber 111 defined by the holder 121 and
the elastic body in the interior of the head 120, a thin elastic
film 112 having an outer end fixed to the outer side of the holder
121 and an outer surface capable of contacting the workpiece W and
pressing the workpiece W against the polishing surface of the turn
table, and a second pressure chamber 113 defined by an outer
surface 116a of the holding plate 116 and an inner surface 112a of
the thin elastic film. A first fluid supplying means 122 supplies
fluid to the first pressure chamber 111 with a given pressure. A
second fluid supplying means 123 supplies fluid to the second
pressure chamber 113 with a given pressure.
[0012] The thin elastic film 112 is fixed to the outer surface of
the holding plate 116 such that its outer end 112b is put between a
fixing ring 115 and the holding plate 116 and screwed by bolts (not
shown). This thin elastic film 112 is provided so as to be capable
of contacting the workpiece W on its outer surface side and
uniformly pressing the workpiece W against the polishing surface of
the turn table like an action of an airbag. The workpiece W is
surely attached to the surface of the thin elastic film 112 by the
surface tension of liquid such as wafer.
[0013] A template 114 that is an annular disc is mounted on the
side of the outer surface (the lower surface) of the thin elastic
film 112, and formed so as to be capable of surrounding the
workpiece W and thereby preventing the workpiece W from skidding.
An inner circumferential portion of the template 114, together with
an outer circumferential portion of the workpiece W, is pressed by
the thin elastic film 112. The thickness of the template 114 is
determined to be the same as the thickness of the workpiece W. This
enables the outer circumferential portion of the workpiece W to
receive a uniform load and prevent the occurrence of its sag.
CITATION LIST
Patent Literature
[0014] Patent Document 1: Japanese Unexamined Patent publication
(Kokai) No. H09-29618
[0015] Patent Document 2: Japanese Unexamined Patent publication
(Kokai) No. H11-90820
SUMMARY OF INVENTION
Technical Problem
[0016] A polishing process with the polishing head 117 disclosed in
Patent Document 1, however, may degrade the flatness of a
workpiece. The present inventors considered the reason and found
the following.
[0017] Uniformly pressing the inner circumferential portion of the
template 114 reduces a gap between the template 114 and the
polishing pad 107, thereby making it difficult to supply a
polishing agent to the gap between the template 114 and the
polishing pad 107. This makes unstable the amount of the polishing
agent supplied to the gap between the polishing pad and the outer
circumferential portion of the workpiece, thereby causing variation
in concentration of abrasive grains of the polishing agent.
[0018] The inventors further investigated the relation between the
concentration of abrasive grains of the polishing agent and
variation in stack removal of a polished workpiece. The polishing
head shown in FIG. 8 was used as a polishing head. A
mirror-polished silicon wafer with a diameter of 300 mm was used as
a wafer to be polished. The cross-sectional shape of the thickness
of the wafer was measured in advance with WaferSight made of
KLA-Tencor. A laminating plate composed of a commercially available
glass woven fabric impregnated with epoxy resin was used as a
template. A commercially available colloidal silica slurry was used
as a polishing agent. Colloidal silica having an average diameter
of 35 nm to 70 nm was used as abrasive grains. This colloidal
silica was deluded with pure water. Potassium hydroxide was added
to the resultant slurry such that pH was 10.5.
[0019] A commercially available nonwoven fabric was used as a
polishing pad. In polishing, the polishing head and the polishing
turn table were rotated at 30 rpm. The polishing pressure (the
pressure of the fluid) against the wafer was 150 g/cm.sup.2. In
polishing processes of three silicon wafers, the dilution ratio of
the polishing agent was changed to change the concentration of
abrasive grains. After the polished wafers were cleaned, the
cross-sectional shape of their thickness was measured with
WaferSight made of KLA-Tencor as in before the polishing. The
difference in thickness between before and after the polishing was
calculated to evaluate the stock removal of the wafers. As shown in
FIG. 4, it was revealed that there is a correlative relationship
between the concentration of abrasive grains and the stock removal
of the wafers; as the concentration of abrasive grains becomes
higher, the stock removal of the wafers shifts to a sag side.
[0020] It can accordingly be said that when a polishing agent is
supplied to the gap between the polishing pad and the outer
circumferential portion of a workpiece during polishing of the
workpiece, the occurrence of variation in the abrasive grains
concentration of this polishing agent increases the instability of
the shape of the outer circumference of the workpiece; the flatness
of the workpiece is thus degraded.
[0021] It has been known that a template is provided with a channel
penetrating from its outer circumferential end to its inner
circumferential end such as a groove, a hole, or a concave passage
so that a polishing agent is sufficiently supplied to the gap
between the template and the polishing pad (See Patent Document 2).
This countermeasure has the problem in that the density of the
polishing agent affects the outer circumferential portion of the
workpiece because of the groove or hole, creating a winding shape
in a circumferential direction; the flatness of the workpiece is
thus degraded.
[0022] Providing a groove on a surface of a polishing pad is known
as a countermeasure of a polishing pad side. This countermeasure
however produces a finely roughened surface of a polished workpiece
due to the groove.
[0023] In addition, there is a patent in which a template is used
also as a dressing body for the polishing pad surface that has a
dressing surface with irregularities for dressing on the polishing
pad side of the template. This template however is not practical
because when the polishing surface of the polishing pad is
roughened during polishing, shavings are created, thereby making
scratches on the wafer surface during polishing at a fraction
defective more than 10%. In examples of this dressing body, fine
irregularities of embossment, fine gentle hollows of dimples, or
irregularities radially formed about the center of the dressing
surface (including an annular surface) are formed. The size of
these irregularities is, for example, about 500 .mu.m.
[0024] The present invention was accomplished in view of the
above-described problems. It is an object of the present invention
to provide a workpiece polishing apparatus that can stabilize the
amount of a polishing agent supplied to a gap between the polishing
pad and the outer circumferential portion of a workpiece through a
gap between the template and the polishing pad, and inhibit
variation in concentration of abrasive grains of the polishing
agent. This workpiece polishing apparatus can therefore stabilize a
polishing rate of the outer circumferential portion of the
workpiece and polish the workpiece into a very flat workpiece.
Solution to Problem
[0025] To achieve this object, the present invention provides a
workpiece polishing apparatus comprising: a polishing pad
configured to polish a workpiece; a polishing agent supplying
mechanism configured to supply a polishing agent; and a polishing
head configured to hold the workpiece such that a back surface of
the workpiece is held by a backing pad and an edge of the workpiece
is held by an annular template; the apparatus being configured to
polish the workpiece by pressing the workpiece and the template
against the polishing pad and thereby bringing the workpiece into
sliding contact with the polishing pad, wherein the template is
made of a resin containing filler or woven fabric and has fine
depressions on a surface on a side that presses the polishing pad,
the fine depressions being created by the filler or woven fabric
exposed on the surface on the side that presses the polishing
pad.
[0026] In the workpiece polishing apparatus of this type, the
polishing agent is easy to pass through a gap between the template
and the polishing pad because of the fine depressions lying on a
pressing surface of the template; the amount of polishing agent
supplied to a gap between the polishing pad and the outer
circumferential portion of the workpiece is stabilized; and the
polishing agent is supplied to the workpiece surface and the
polishing pad surface with a uniform abrasive grains concentration.
The shape of the outer circumferential portion of the workpiece can
consequently be made flat and a very flat workpiece can be
obtained. In addition, since the template is made of the resin
containing filler or woven fabric that is exposed on the surface on
the side that presses the polishing pad, the fine uniform
depressions can be readily formed. These depressions create no
shaving of the polishing pad and make no scratch on the wafer.
[0027] The surface coverage of the exposed filler or woven fabric
on the surface of the template on the side that presses the
polishing pad preferably ranges from 5% to 85%.
[0028] When the surface coverage of the filler or woven fabric is
5% or more, it is more certain that the polishing agent is easy to
pass uniformly through the gap between the template and the
polishing pad, and variation in concentration of abrasive grains of
the polishing agent can be inhibited. Consequently, the flatness of
the workpiece can more reliably be made high. When this surface
coverage is 85% or less, a workpiece having a low fraction
defective (scratch) can reliably be obtained.
[0029] Each of the depressions preferably has a depth of 0.05 mm or
more.
[0030] In such an apparatus, it is more certain that the polishing
agent is easy to pass through the gap between the template and the
polishing pad; the amount of the polishing agent supplied to the
gap between the polishing pad and the workpiece is stabilized; and
the variation in concentration of abrasive grains of the polishing
agent between the polishing pad and the outer circumferential
portion of the workpiece can effectively be inhibited. The
polishing rate, particularly at the outer circumferential portion
of the workpiece is consequently stabilized to polish the workpiece
into a very flat workpiece.
[0031] Each of the depressions preferably has an opening with a
width of 5 mm or less. The pitches among the depressions are
preferably 10 mm or less.
[0032] Such an apparatus can inhibit a winding shape created in a
circumferential direction of the workpiece, thereby enabling
acquisition of a workpiece having higher flatness.
[0033] The contact angle between each of the depressions and the
polishing pad is preferably 90.degree. or less.
[0034] Such an apparatus can polish the workpiece without damaging
the polishing pad, thereby enabling acquisition of a workpiece
having a low fraction defective (scratch).
Advantageous Effects of Invention
[0035] The inventive polishing apparatus includes the template that
is made of a resin containing filler or woven fabric and has fine
depressions created by the filler or woven fabric exposed on a
surface on a side that presses the polishing pad. This apparatus
can thereby make it easy to pass the polishing agent uniformly
through the gap between the template and the polishing pad because
of the depressions of the template, stabilize the amount of the
polishing agent supplied to the gap between the polishing pad and
the workpiece, particularly the outer circumferential portion, and
supply the polishing agent to the surface of the outer
circumferential portion of the workpiece and the surface of the
polishing pad with a uniform abrasive grains concentration. The
shape of the outer circumferential portion of the workpiece can
consequently be made flat and a very flat workpiece can be
obtained. In addition, since the template is made of the resin
containing filler or woven fabric, and the filler or woven fabric
is exposed on the surface on the side that presses the polishing
pad, the fine uniform depressions can be readily formed, and a
winding shape and a scratch are scarcely created on the polished
workpiece.
BRIEF DESCRIPTION OF DRAWINGS
[0036] FIG. 1 is a schematic diagram showing an exemplary polishing
apparatus according to the present invention;
[0037] FIG. 2 is an enlarged view showing an example of the
vicinity of a template having an added filler of a polishing head
of the inventive polishing apparatus;
[0038] FIG. 3 is an enlarged view showing an example of the
vicinity of a template having an added woven fabric of a polishing
head of the inventive polishing apparatus;
[0039] FIG. 4 is a diagram showing the relationship between the
concentration of abrasive grains of a polishing agent and variation
in stock removal of a polished workpiece;
[0040] FIG. 5 is a diagram showing the relationship between the
surface flatness of a workpiece and a surface coverage of
depressions on the surface of a template on a side that presses a
polishing pad in examples 1 and 2 and comparative example;
[0041] FIG. 6 is a diagram showing the relationship between a
fraction defective (scratch) of a surface of a workpiece and the
surface coverage of depressions on the surface of a template on the
side that presses the polishing pad in examples 1 and 2 and
comparative example;
[0042] FIG. 7 is a schematic diagram showing an example of a
conventional polishing apparatus;
[0043] FIG. 8 is a schematic diagram showing an exemplary polishing
head of a conventional polishing apparatus; and
[0044] FIG. 9 is an enlarged view of a part of the polishing head
of the conventional polishing apparatus.
DESCRIPTION OF EMBODIMENTS
[0045] An embodiment of the present invention will hereinafter be
described, but the present invention is not limited to this
embodiment.
[0046] In polishing of a workpiece, uniformly pressing an inner
circumferential portion of a template makes it difficult to supply
a polishing agent to a gap between the template and a polishing pad
and to a gap between the polishing pad and an outer circumferential
portion of the workpiece, thereby making it easy to cause variation
in concentration of abrasive grains of the polishing agent supplied
to the gap between the polishing pad and the workpiece, as
described previously. This variation in the abrasive grains
concentration increases the instability of the shape of the
workpiece, particularly the outer circumference, resulting in the
degradation of the flatness of the workpiece.
[0047] In view of this problem, the inventors diligently considered
how a very flat workpiece can be obtained in a workpiece polishing
process. The inventors consequently thought of a polishing
apparatus including a template that is made of a resin containing
filler or woven fabric and has fine depressions created by the
filler or woven fabric exposed on the surface on the side that
presses the polishing pad. The apparatus of this type can readily
pass the polishing agent uniformly through the gap between the
template and the polishing pad over the depressions, stabilize the
amount of the polishing agent supplied to the gap between the
polishing pad and the outer circumferential portion of the
workpiece and supply the polishing agent to the surface of the
workpiece and the surface of the polishing pad with a uniform
abrasive grains concentration. The shape of the workpiece,
particularly the outer circumferential portion, can consequently be
made flat and a very flat workpiece can be obtained. The inventors
made these findings, thereby brought the invention to
completion.
[0048] The inventive workpiece polishing apparatus will now be
described in detail with reference to the drawings, but the
invention is not limited thereto.
[0049] As shown in FIG. 1, the inventive polishing apparatus 1 is
constituted of a polishing pad 4 used to polish a workpiece, a
polishing agent supplying mechanism 7 used to supply a polishing
agent 8, and a polishing head 2 used to hold the workpiece W. The
polishing pad 4 is attached to a turn table 3. The polishing head 2
has a baking pad 5 to hold the back surface of the workpiece W and
an annular template 6 to hold the edge of the workpiece W.
[0050] This polishing apparatus 1 holds the back surface of the
workpiece W by the backing pad 5 and the edge of the workpiece W by
the template 6, and presses the workpiece W and the template 6
against the polishing pad 4 thereby to bring the workpiece W into
sliding contact with the polishing pad 4 while supplying the
polishing agent 8 to the polishing pad 4 through the polishing
agent supplying mechanism 7 and rotating the turn table 3 and the
polishing head 2, so that the workpiece W is polished.
[0051] FIG. 2 and FIG. 3 each show schematically an example of an
enlarged periphery 9 of the polishing head. As shown in FIG. 2, the
template 6 is made of a resin containing filler 10. Because the
surface configured to press the polishing pad 4 exposes the filler
10, the template 6 has fine depressions 12 on this pressing
surface. Alternatively, as shown in FIG. 3, the template 6 is made
of a resin containing woven fabric 11. Because the surface
configured to press the polishing pad 4 exposes the woven fabric
11, the template 6 has fine depressions 12 on this pressing
surface.
[0052] Other components of the polishing head 2 are not
particularly limited; any configuration may be acceptable, provided
the backing pad and the template having the depressions can hold
the back surface and edge of the workpiece respectively.
[0053] The polishing apparatus 1 can readily pass the polishing
agent 8 uniformly through the gap between the template 6 and the
polishing pad 4 because of the interposition of the depressions 12
of the template 6, stabilize the amount of polishing agent 8
supplied to the gap between the polishing pad 4 and the outer
circumferential portion of the workpiece W and supply the polishing
agent 8 to the surface of the workpiece W and the surface of the
polishing pad 4 with a uniform abrasive grains concentration. The
polishing rate of the workpiece W, particularly at the outer
circumferential portion, is consequently stabilized within the
circumference, so the shape of this outer circumferential portion
can be made flat. A very flat workpiece W can thus be obtained.
Since the template 6 having a proper thickness is made of the resin
containing filler 10 or woven fabric 11, and the filler 10 or woven
fabric 11 is exposed on the surface configured to press the
polishing pad 4, the fine depressions 12 can therefore be readily
formed uniformly. The formation of the fine depressions 12 needs no
complicated processing apparatus nor processing method, so the cost
can be reduced to a lower level.
[0054] The surface coverage of the exposed filler 10 or woven
fabric 11 on the surface of the template 6 on the side that presses
the polishing pad 4 preferably ranges from 5% to 85%, more
preferably to 80%.
[0055] When the surface coverage of the filler 10 or woven fabric
11 is 5% or more, the amount of polishing agent 8 supplied to the
gap between the polishing pad 4 and the outer circumferential
portion of the workpiece W can be stabilized, and the polishing
agent 8 supplied to the gap between the polishing pad 4 and the
outer circumferential portion of the workpiece W can be inhibited
from varying its abrasive grains concentration, so the flatness of
the workpiece W can more reliably be improved. When this surface
coverage is 85% or less, the surface of the template 6 on the side
that presses the polishing pad 4 can be inhibited from wearing
down, and the occurrence of shavings can be inhibited.
Consequently, a workpiece W having a low fraction defective can
reliably be obtained.
[0056] The depth of the depressions 12 is preferably 0.05 mm or
more.
[0057] In this manner, the depressions 12 can be maintained for a
long period of time even when the surface of the template 6 is also
polished during polishing of the workpiece, so the lifetime of the
template can be improved.
[0058] Moreover, the depth of the opening of each depression 12 is
preferably 5 mm or less. The pitch among each depression 12 is
preferably 10 mm or less.
[0059] In this manner, the outer circumferential portion of the
workpiece can be inhibited from being affected by the density of
the polishing agent 8, so the occurrence of a winding shape in a
circumferential direction of the workpiece W can be inhibited. A
flatter workpiece W can consequently be obtained.
[0060] The contact angle between each depression 12 and the
polishing pad 4 is preferably 90.degree. or less.
[0061] In this manner, the workpiece W can be polished without
damaging the polishing pad 4 by the depressions 12. A workpiece W
with a lower fraction defective can consequently be obtained.
EXAMPLE
[0062] The present invention will be more specifically described
below with reference to examples and a comparative example, but the
invention is not limited to these examples.
Example 1
[0063] A workpiece was polished with the inventive workpiece
polishing apparatus to evaluate the flatness of the polished
workpiece and the scratch fraction defective.
[0064] The polishing apparatus shown in FIG. 1 was used in example
1. The polishing head shown in FIG. 2 was used in this polishing
apparatus. This polishing head was the same as the polishing head
shown in FIG. 8 except for the template. The template used herein
was produced in the following manner. A bisphenol A based epoxy
resin containing a glass filler having a maximum dimension of 2 mm
and an adjusted concentration was prepared. This resin was applied
by spraying to produce an epoxy resin prepreg containing glass
fiber. This prepreg was stacked such that the prepreg was disposed
on the side configured to press the polishing pad. The resultant
was formed into an annular shape under pressure. The thickness of
the template was 750 .mu.m. The surface coverage of the exposed
filler on the surface on the side configured to press the polishing
pad was 25%.
[0065] A 300-mm-diameter silicon wafer was used as a subject to be
polished. A commercially available slurry of colloidal silica that
was deluded with pure water and contained potassium hydroxide so as
to have a pH of 10.5 was used as the polishing agent. The average
diameter of abrasive grains of this colloidal silica was in the
range from 35 nm to 70 nm. The polishing pad used was a
commercially available nonwoven fabric. In the polishing, the
polishing head and the polishing turn table were rotated at 30 rpm.
The polishing pressure (the pressure of fluid) against the wafer
was 150 g/cm.sup.2. After the wafer was polished, the wafer was
cleaned. The flatness of the wafer was then measured with
WaferSight made by KLA-Tencor to evaluate SFQRmax. The fraction
defective on the surface was also evaluated with SP-1 made by
KLA-Tencor.
Example 2
[0066] A workpiece was polished under the same conditions as
example 1 except that the template differed in the following
points. The flatness and the fraction defective of the polished
workpiece were evaluated. In this example, the template was
produced in the following manner. A flat fabric type of glass fiber
cloth with a thickness of 0.18 mm and a horizontal and vertical
pitch of 0.5 mm was impregnated with a bisphenol A based epoxy
resin. The resultant was dried to produce a prepreg for a front
surface. This prepreg was stacked such that the prepreg was
disposed configured to press the polishing pad. The resultant was
formed into an annular shape with a thickness of 760 .mu.m under
pressure. The surface configured to press the polishing pad was
then polished to expose the glass fiber in a netlike form. The
template had a 16% surface coverage of the exposed glass fiber
cloth on the surface configured to press the polishing pad.
Comparative Example
[0067] A workpiece was polished under the same conditions as
example 1 except that a conventional template having no depression
unlike the present invention was used. The flatness and the
fraction defective of the polished workpiece were evaluated. In
this comparative example, the template was produced by using a
commercially available epoxy resin disc containing glass fiber. The
thickness of the template was 750 .mu.m. The template had no
depression created by an exposed filler or glass fiber cloth on the
surface configured to press the polishing pad. In other words, the
surface coverage of depressions was 0%.
[0068] In examples 1 and 2, polishing was repeated in the same
manner except that the surface coverage of the depressions was
changed to 40%, 60%, 80%, and 85%. The result is shown in FIG. 5
and FIG. 6. FIG. 5 shows the correlation between the surface
coverage of the depressions on the surface of the template on the
side configured to press the polishing pad and SFQRmax. Comparing
the flatness in examples 1 and 2 with that in comparative example,
examples 1 and 2 demonstrated that the shape of the outer
circumference of the wafer was flat or a weak sag and SFQRmax was
good; comparative example demonstrated that many wafers had a
strong rise shape at their outer circumferential portion and
SFQRmax was degraded.
[0069] FIG. 6 shows the correlation between the surface coverage of
the depressions on the surface of the template on the side
configured to press the polishing pad and the fraction defective.
The measurement of the fraction defective in examples 1 and 2 and
comparative example revealed that when the surface coverage of the
depressions was 40%, 60%, or 80%, a wafer that was substantially
free of scratches was obtained. When the surface coverage of the
depressions was 85%, the fraction defective was somewhat increased,
but still a lower level than a fraction defective more than 10%
that was exhibited by the conventional apparatus.
[0070] It is to be noted that the present invention is not limited
to the foregoing embodiment. The embodiment is just an
exemplification, and any examples that have substantially the same
feature and demonstrate the same functions and effects as those in
the technical concept described in claims of the present invention
are included in the technical scope of the present invention.
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