U.S. patent application number 12/386139 was filed with the patent office on 2009-08-13 for carrier for holding an object to be polished.
This patent application is currently assigned to Speedfam Co., Ltd.. Invention is credited to Toshikuni Shimizu, Akira Yoshida.
Application Number | 20090203300 12/386139 |
Document ID | / |
Family ID | 34824559 |
Filed Date | 2009-08-13 |
United States Patent
Application |
20090203300 |
Kind Code |
A1 |
Yoshida; Akira ; et
al. |
August 13, 2009 |
Carrier for holding an object to be polished
Abstract
The present invention provides a diamond-like carbon coated
carrier for holding an object to be polished used for double-sided
polishing, and a manufacturing method therefor. The carrier for
holding a workpiece according to the present invention has a
substrate whose entire surface is coated with diamond-like carbon.
The method of the present invention includes coating the entire
carrier surface with diamond-like carbon using a surface coating
apparatus using plasma CVD.
Inventors: |
Yoshida; Akira; (Ayase-city,
JP) ; Shimizu; Toshikuni; (Ayase-city, JP) |
Correspondence
Address: |
FLYNN THIEL BOUTELL & TANIS, P.C.
2026 RAMBLING ROAD
KALAMAZOO
MI
49008-1631
US
|
Assignee: |
Speedfam Co., Ltd.
|
Family ID: |
34824559 |
Appl. No.: |
12/386139 |
Filed: |
April 14, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11074481 |
Mar 8, 2005 |
|
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12386139 |
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Current U.S.
Class: |
451/398 ;
451/548 |
Current CPC
Class: |
B24B 41/067
20130101 |
Class at
Publication: |
451/398 ;
451/548 |
International
Class: |
B24B 41/06 20060101
B24B041/06; B24D 3/00 20060101 B24D003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 9, 2004 |
JP |
2004-066013 |
Claims
1. A carrier for holding an object to be polished, used for a
double-sided polishing apparatus, comprising a substrate which has
been subjected to lapping and/or polishing to provide the substrate
with a uniform thickness and then coating the entire surface of the
substrate with diamond-like carbon.
2. The carrier for holding an object to be polished used for a
double-sided polishing apparatus of claim 1, wherein the relative
standard deviation of the substrate thickness is no more than
0.4%.
3. The carrier for holding an object to be polished used for a
double-sided polishing apparatus of claim 1, wherein the
diamond-like carbon is formed into a film having a thickness of
from 0.10 .mu.m to 20 .mu.m.
4. The carrier for holding an object to be polished used for a
double-sided polishing apparatus of claim 1, wherein the substrate
is made of a material selected from the group consisting of
stainless steel, steel, aluminum, an aluminum alloy, a resin, a
fiber-reinforced resin, and a composite thereof.
5. The carrier for holding an object to be polished used for a
double-sided polishing apparatus of claim 1, wherein the carrier
has a holding hole for holding the object and resinous portion
surrounding the holding hole.
Description
[0001] This is a continuation of Ser. No. 11/074,481, filed Mar. 8,
2005, which corresponds to Japanese Application No. 2004-066013,
filed Mar. 9, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a carrier for holding a
workpiece which is used in a double-sided polishing apparatus that
simultaneously polishes both surfaces of the workpiece by holding
the workpiece between upper and lower platens covered with abrasive
cloth with the platens and the workpiece being in pressure contact
with each other, and rotating at least one of the platens and the
workpiece, the surface of the carrier being coated with
diamond-like carbon, and to a method of manufacturing the carrier,
and a method of polishing a workpiece using the carrier. In
particular, the invention relates to a diamond-like carbon coated
carrier for holding a workpiece used for polishing both surfaces of
a silicon wafer, a method of manufacturing the carrier, and a
polishing method using the carrier.
[0004] 2. Description of the Related Art
[0005] In polishing a silicon wafer, a compound semiconductor
wafer, an aluminum-made magnetic disk substrate, a glass-made
magnetic disk substrate, or a workpiece that is made of photomask
glass, a crystal oscillator, metal, or the like, the workpiece is
held by a carrier cut into a shape where a holding hole is formed
in conformity to a shape of the workpiece and peripheral (outer)
gear teeth are arranged at an outer edge so as to mesh with an
internal gear and sun gear of a double-sided polishing machine. The
workpiece is driven together with the carrier. The carrier is
mainly used as a member of a polishing apparatus for lapping or
polishing both surfaces of a silicon wafer, a magnetic disk
substrate, or the like at a time. Hence, the thickness of the
carrier member is set slightly smaller than that of the workpiece
such as a wafer.
[0006] Up to now, the following method has been generally used for
producing such carriers. That is, glass cloth woven out of a metal
material such as steel or stainless steel and glass fibers, or
organic fiber cloth is impregnated with an epoxy resin, a phenol
resin, or other such thermosetting resins. Then, several cloths are
stacked into a desired thickness, pressed with a pressing machine,
and cured with heat. The resultant material, for example, a
so-called FRP is used as a raw material and cut into a size
sufficient to hold the workpiece in accordance with the intended
use. In addition, its peripheral portion is cut in conformity with
a gear shape.
[0007] Those carriers are rotated together with a silicon wafer, a
magnetic disk substrate, etc. in the polishing apparatus, and
forcedly driven by an internal gear and a sun gear through its
peripheral gear teeth. Hence, the surface is polished to some
degree to lower its strength or accuracy of form, resulting in a
reduction in durability over time. Also, a gear portion is worn to
cause the carrier to come off from the polishing apparatus or to
destabilize polishing conditions. This requires replacement with
new carriers each time or periodically. Accordingly, there is an
increasing demand for development of carriers having a high
durability that secures as long a service life as possible. To meet
such a demand, there is proposed an FRP-based carrier as disclosed
in JP 2001-038609 A, for example. Furthermore, as the purity of a
silicon wafer is increased, there has arisen a problem of
contamination of the wafer with a trace amount of heavy metals
eluting from a metal-made carrier, albeit being a negligible amount
in a conventional technique.
[0008] In the conventional technique, regarding the silicon wafer
or compound wafer, the thickness is adjusted by lapping or
grinding, and the wafer is etched with an acid or alkali etchant,
followed by polishing to attain a mirror-finished surface on one or
both of the front and rear sides of the wafer. With a view to
increasing the surface accuracy or preventing house dust
contamination, some workpieces, which include the silicon wafer,
undergo double-sided polishing, in which the polishing was hitherto
performed on only one side. To that end, a demand for double-sided
polishing is growing. An indispensable condition for double-sided
polishing is to use a carrier for holding a workpiece. In this
case, what is important are an abrasion resistance and durability
of a carrier itself, and whether or not a heavy metal in the
carrier causes any contamination.
[0009] A carrier made of, for example, a hard resin or a nonmetal
material such as FRP is inferior in abrasion resistance and
durability, and thus falls short of practical applicability.
Meanwhile, a carrier made of a metal material such as steel or
stainless steel has a problem of heavy metal contamination. Hence,
there is a growing demand for the development of carriers that will
overcome all the above problems.
[0010] As one possible method of preventing heavy metal
contamination on the assumption that a metal material having
superior abrasion resistance and durability is used as a substrate,
the substrate surface is coated with any material. As an example
thereof, there is proposed a ceramic-coated metal carrier as
disclosed in JP 04-026177 A. Although exhibiting an extremely high
performance regarding abrasion resistance, the carrier has a
problem in that ceramic particles adhering to the surface drop out
of the surface, and the workpiece is scratched thereby. Also, JP
2002-018707 A discloses an SK steel-made carrier whose surface is
plated with metal. This offers by no means a solution to the
problem in that the workpiece is contaminated with heavy metal, in
particular, in polishing the semiconductor wafer. Further, JP
11-010530 A discloses a carrier given a dressing function, which is
prepared by welding the ceramic particles to uneven upper and lower
surfaces and in addition, coating the uneven surfaces with
diamond-like carbon. The document describes that the durability and
the abrasion resistance are improved by the effect of the
diamond-like carbon. The carrier is devised for the purpose of
preventing the ceramic particles functioning to dress the target
from coming off from the surface, and thus differs from the carrier
for holding the workpiece which is used for double-sided
polishing.
[0011] The inventors of the present invention have made extensive
studies with an aim to solve the problems regarding the durability,
abrasion resistance, and heavy metal contamination in polishing
both surfaces of a semiconductor material such as a silicon wafer.
As a result, the inventors presupposed that the above-mentioned
problems may be solved by coating an ordinary carrier with
diamond-like carbon on its surface with a high surface smoothness,
and have worked on its development and research. As has been known
in the art, a feature of the diamond-like carbon (hereinafter,
referred to as "DLC") resides in its structure, albeit an amorphous
carbon structure, in which a diamond structure (SP.sup.3 bond) and
a graphite structure (SP bond) coexist, and which has as a high
hardness as diamond, and attains a high surface smoothness and low
friction coefficient unlike diamond. The DLC can be easily formed
into a thin film by plasma CVD etc. as disclosed in JP 10-046344 A.
The inventors of the present invention have concluded that a
carrier produced by uniformly and firmly laminating the DLC thin
film having the above-described performance thereon and a
manufacturing method therefor would solve the above-mentioned
problems.
[0012] The inventors of the present invention have found, as a
result of extensive studies on the problem inherent in the
aforementioned conventional double-sided polishing carrier, all or
part of the carrier surface is coated with a uniform DLC thin film
having a highly smooth surface, whereby it is possible to
remarkably improve the abrasion resistance and durability of the
carrier, to prevent heavy metals from eluting from the carrier to
cause contamination, and to protect the surface to be polished
against any scratches resulting from a coating material coming off
from the carrier surface.
SUMMARY OF THE INVENTION
[0013] It is therefore an object of the present invention to
provide a carrier having a high durability and abrasion resistance
and causing as few scratches on a workpiece and as little heavy
metal contamination as possible. Another object of the present
invention is to provide a manufacturing method for the carrier.
Still another object of the present invention is to provide a
double-sided polishing method using the carrier.
[0014] The aforementioned objects can be attained by a carrier for
holding a workpiece, the carrier including a substrate whose entire
surface is coated with DLC. A polishing apparatus, in which the
carrier of the present invention is used, is a so-called
double-sided polishing apparatus for polishing both surfaces of the
workpiece at a time by holding the workpiece between upper and
lower platens covered with an abrasive cloth, the platens and the
workpiece being in pressure contact with each other, and rotating
at least one of the upper and lower platens and the workpiece.
[0015] Further, according to the other object of the present
invention, a manufacturing method for a DLC-coated carrier for
holding a workpiece relates to a manufacturing method for a carrier
holding a workpiece, including: providing a surface coating
apparatus using a plasma CVD method in which an anode electrode and
a cathode electrode are arranged face to face in a vacuum chamber,
a carrier substrate is interposed between the anode electrode and
the cathode electrode, and RF power is applied between the anode
electrode and the cathode electrode while supplying a material gas
to form a diamond-like carbon film on the substrate surface;
interposing a substrate between the anode electrode and the cathode
electrode; and shifting a supporting position of the substrate
during formation of the diamond-like carbon film or between current
formation and next formation. In other words, in the manufacturing
method, a so-called plasma CVD method is used, and the supporting
position of the substrate is shifted as appropriate to thereby
leave substantially no uncoated area.
[0016] The still other object of the present invention is attained
by a polishing method for polishing both surfaces of a workpiece,
including: mounting a carrier for holding a workpiece according to
the present invention, between upper and lower platens covered with
abrasive cloth; holding the workpiece in a holding hole in the
carrier for holding the workpiece; rotating at least one of the
upper and lower platens and the workpiece while supplying an
abrasive slurry to a surface to be processed to polish both
surfaces of the workpiece, wherein the abrasive cloth is made of
one selected from the group consisting of sueded synthetic leather,
polyurethane, and a composite prepared by binding non-woven cloth
with polyurethane.
[0017] According to the present invention, it is possible to
provide a carrier for holding a workpiece with ease, which is
superior in durability and abrasion resistance and free of heavy
metal contamination. In other words, the carrier of the present
invention overcomes all the problems inherent in the conventional
carrier.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] Hereinafter, an embodiment of the present invention will be
described. In the present invention, a carrier is shaped into a
disk-like thin plate, and has a peripheral gear at its outermost
edge and a holding hole for holding a workpiece in its inner
position, and optionally a lightening hole. The carrier size varies
depending on the apparatus model but ranges from several
centimeters to several ten centimeters; some carriers exceed 1 m in
size by the model. A carrier somewhat thinner than the polishing
object is used. For example, a silicon wafer has a thickness of
about several hundred micrometers. Accordingly, the entire surface
of a carrier substrate corresponds to the front and rear surfaces
and a side surface (section along its thickness direction). In the
present invention, an area to be coated with DLC includes the side
surface. In particular, the carrier is thin in section along its
thickness direction, and besides, meshes with an internal gear and
sun gear of an apparatus or contacts the workpiece at the side
surface portion. Hence, such a portion is most likely to receive a
local stress and a large frictional force, and thus is more fragile
than other portions. Even if not cracked, this portion will cause
minute cracks and heavy metal contamination resulting from wear.
Upon polishing, a workpiece is held between upper and lower platens
covered with abrasive cloth and polished while spraying an abrasive
such as colloidal silica slurry. As a result, although the front
and rear surfaces of the carrier are not directly applied with
pressure, they are polished to a slight extent, leading to wear and
considerable reduction in durability.
[0019] In the present invention, a material of a substrate used for
a carrier is not particular limited but is preferably any of steel,
stainless steel, aluminum, an aluminum alloy, a resin, a
fiber-reinforced resin, and a composite thereof. In particular, in
polishing a silicon wafer of 300 mm in diameter, it is preferable
to use a metal material such as steel, stainless steel, or an
aluminum alloy as the material of the substrate.
[0020] In the present invention, it is indispensable to completely
cover the front and rear surfaces and side surface (section along
the thickness direction) of the carrier with a DLC thin film. As
mentioned above, a feature of the DLC resides in its structure in
which a diamond structure (SP.sup.3 bond) and a graphite structure
(SP.sup.2 bond) coexist, and which has a hardness of 1,000 to 4,000
kgf/mm.sup.2 in terms of Vickers hardness, that is, a high hardness
comparable with superhard ceramics or diamond. Meanwhile, the DLC
is amorphous, not microcrystalline, unlike diamond or superhard
ceramics, and thus is featured by its ability to form a uniform and
highly smooth surface. To elaborate, a feature of the DLC resides
in a high hardness equivalent to diamond as well as a high surface
smoothness and low friction coefficient, unlike diamond, in short,
its extremely high sliding property. Accordingly, a feature of the
carrier for holding a workpiece whose entire surface is coated with
the DLC according to the present invention resides in less wear and
damage in a sliding portion, and still less wear of the surface. In
addition, the entire surface of the carrier of the present
invention is coated with the DLC as a nonmetal material, so even
with a substrate made of a metal, for example, steel, the carrier
is free from elution due to a chemical reaction with an acid or
alkali in the abrasive composition, which enables protection
against heavy metal contamination.
[0021] As a manufacturing method for the carrier for holding the
workpiece according to the present invention, plasma CVD is
employed as discussed above. With this method, the entire structure
is exposed to the plasma, making it possible to cover the entire
surface with the uniform and dense DLC coating film. The DLC
coating film thickness can be controlled based on coating
conditions and time. The carrier of the present invention is
relatively large when taking into account a material size treatable
with conventional plasma CVD methods. It is necessary to support
the carrier with any holding jig during the treatment, so the
supported portion is not exposed to the plasma during the
treatment. As a result, part of the substrate surface remains
untreated. Accordingly, a supporting position is shifted as
appropriate, which leaves substantially no uncoated area, and the
substantially uniform DLC thin film with the uniform thickness can
be formed.
[0022] In manufacturing the carrier for holding the workpiece of
the present invention, it is preferable to make the substrate
thickness uniform in advance of the DLC coating on the substrate
surface. If the substrate thickness is not uniform, the wear
proceeds concentratedly in the thick portion and a coating on this
portion peels off. A relative standard deviation of the thickness
is preferably 0.4% or less, more preferably 0.2% or less. As a
method of uniformizing the substrate thickness, lapping, cutting,
or polishing may be adopted without any particular limitations;
alternatively, those may be carried out in turn stepwise.
[0023] In the present invention, the DLC coating film thickness
preferably ranges from 0.1 .mu.m to 20 .mu.m. With the thickness
smaller than 0.1 .mu.m, its frictional strength is a little
inferior, while the thickness exceeding 20 .mu.m requires too much
time to form the film and is disadvantageous in terms of cost
performance. Also, for the purpose of protecting end surfaces of
the workpiece during processing, a resin may be applied to surround
the holding hole for holding the workpiece in the DLC coated
carrier.
[0024] Hereinafter, the method of the present invention will be
described in more detail based on examples and comparative
examples, but the present invention is not limited by those
examples. A polishing apparatus and conditions used in the examples
of the present invention and comparative examples are summarized in
Tables 1 and 3 below. As the polishing apparatus, a double-sided
polishing apparatus (DSM-9B, available from SPEEDFAM Co., Ltd.) was
used. As the abrasive cloth, SUBA 800 (available from Rodel Co.,
Ltd.) was used. An abrasive, Rodel 12371 (available from Rodel Co.,
Ltd.) was prepared by adding 10 parts of pure water per part of
concentrate solution.
Example 1
Production of DLC Coated Carrier
[0025] An SUS-made carrier substrate, which had been lapped into
the thickness of 550 .mu.m in advance, was coated with DLC of a
thickness of 2.5 .mu.m. After the substrate was coated with the DLC
up to 1.0 .mu.m under the film formation temperature set to
150.degree. C., the supporting position was shifted to resume the
deposition by 1.5 .mu.m.
[0026] (Wear Test and Durability Test)
[0027] The resultant DLC coated carrier was polished under the
conditions of Table 1 without holding the workpiece. The diluted
abrasive was recycled. A wear rate was determined by calculating a
difference between the thicknesses measured before and after the
polishing with a micrometer. The durability was examined based on a
visual test.
Comparative Examples 1 to 3
[0028] As a carrier, three types of carriers of an SUS-made
carrier, a glass epoxy-resin-made (EG-made) carrier, and an
FR-vinylon-made resin were used, none of which were coated with the
DLC.
[0029] The three types of carriers all had the thickness of about
550 .mu.m. The carriers were polished under the conditions of Table
1 without holding a workpiece as in Example 1. The diluted abrasive
was recycled. Polishing test results of Example 1 and Comparative
Examples 1 to 3 are listed in Table 2 below.
TABLE-US-00001 TABLE 1 item processing time processing condition
DSM - 9B platen rotational speed 100 rpm contact pressure 70
g/cm.sup.2 PAD suba 800 slurry Rodel 2371 processing time DLC: 10
hours others: 1 hour
TABLE-US-00002 TABLE 2 Comparative mate- Example Comparative
Comparative Example 3 rial 1 Example 1 Example 2 FR- item unit
DLC*.sup.1 SUS EG*.sup.2 vinylon wear rate .mu.m/hr <0.1 4.2 4.7
0.9 visual -- .largecircle. .largecircle. .largecircle. X*.sup.3
test *.sup.1The SUS-made carrier surface is coated with DLC with a
thickness of 2.5 .mu.m. *.sup.2glass epoxy resin *.sup.3Cracks
occur at the base of gear teeth.
TABLE-US-00003 TABLE 3 item processing condition processing
condition DSM - 9B platen rotational speed 100 rpm contact pressure
70 g/cm.sup.2 PAD suba 800
Example 2
[0030] The DLC coated carrier produced in Example 1 was polished
under the conditions of Table 3 with the carrier holding a 6-inch
silicon wafer as a workpiece. In Example 2, the diluted abrasive
was not recycled.
Comparative Examples 4 to 6
[0031] The three types of carriers used in Comparative Examples 1
to 3, that is, the SUS-made carrier, the glass-epoxy-resin-made
(EG-made) carrier, and the FR-vinylon-made carrier were employed.
Similar to Example 2, the carriers were polished under the
conditions of Table 3, with the carriers holding the 6-inch silicon
wafer. In Comparative Examples 1 to 3, the diluted abrasive was not
recycled. Polishing test results of Example 2 and Comparative
Examples 4 to 6 are listed in Table 4 below.
TABLE-US-00004 TABLE 4 Comparative Comparative Comparative item
Example 1 Example 1 Example 2 Example 3 DLC*.sup.1 SUS EG*.sup.2
FR-vinylon Fe 5 or lower 45 5 or lower 5 or lower Cu 5 or lower 8 5
or lower 5 or lower Cr 5 or lower 13 5 or lower 5 or lower
Comparison Between Examples and Comparative Examples
[0032] As a result of comparing Example 1 with Comparative Examples
1 to 3, the wear rate is remarkably low in Example 1, and the
carrier made of FR-vinylon (Comparative Example 3) prepared by
binding glass fibers with vinylon shows the next lower wear rate.
After the test, a visual test was carried out to examine how far
cracks occur in each carrier. As a result, the carrier of Example 1
subjected to the visual test over 10 hours showed no change. The
carriers of Comparative Examples 1 and 2 subjected to the same test
over 1 hour showed no change, but cracks occurred at the base of
gear teeth of the carrier of Comparative Example 3.
Evaluation of Example 2 and Comparative Examples 4 to 6
[0033] The silicon wafer surface polished in Example 2 and
Comparative Examples 4 to 6 was rinsed with pure water, after which
a mixture of nitric acid and hydrofluoric acid was used to dissolve
the surface portion of the silicon wafer. Then, heavy metal in the
solution was subjected to quantitative analysis with an ICP mass
spectroscope to measure a contamination level of the silicon wafer
surface with iron, copper, and chromium. As apparent from the
results shown in Table 4, the carrier of Example 2 and carriers
made of a nonmetal material involved less contamination with a
heavy metal. In other words, the carrier produced by coating the
metal substrate with DLC is comparable with nonmetal carriers in
terms of the contamination with heavy metal.
[0034] As has been described so far, in Comparative Example 1, the
wear rate is high and contamination with a heavy metal is observed.
In Comparative Example 2, the durability and contamination with a
heavy metal fall within an allowable range, while the wear rate is
high. In Comparative Example 3, the durability and contamination
with a heavy metal fall within an allowable range, while the cracks
occur at the base of gear teeth during the test over 1 hour. This
reveals that its durability is far from practical.
[0035] The DLC coated carrier of the present invention as explained
in Examples 1 and 2 excels in every item: wear resistance,
durability, and heavy metal contamination.
[0036] As mentioned above, the use of the DLC coated carrier
according to the present invention can improve the durability and
wear resistance of the carrier as expendables and significantly
prolong the carrier's service life, so the carrier produces
beneficial effects from the economical and qualitative points of
view. Furthermore, the metal surface is coated throughout, whereby
even in polishing, heavy metal neither elutes nor spatters, which
is highly advantageous for polishing a workpiece such as a silicon
wafer which is extremely weak against contamination with heavy
metal and actually producing the same.
* * * * *