U.S. patent application number 12/992782 was filed with the patent office on 2011-03-24 for method for manufacturing polishing head and polishing apparatus.
This patent application is currently assigned to SHIN-ETSU HANDOTAI CO., LTD.. Invention is credited to Satoru Arakawa, Hiromasa Hashimoto, Hiromi Kishida, Hisashi Masumura, Kouji Morita.
Application Number | 20110070813 12/992782 |
Document ID | / |
Family ID | 41444210 |
Filed Date | 2011-03-24 |
United States Patent
Application |
20110070813 |
Kind Code |
A1 |
Masumura; Hisashi ; et
al. |
March 24, 2011 |
METHOD FOR MANUFACTURING POLISHING HEAD AND POLISHING APPARATUS
Abstract
A method for manufacturing a polishing head having an annular
rigid ring; a rubber film bonded to the rigid ring with uniform
tension; a mid plate joined to the rigid ring, forming a space
together with the rubber film and the rigid ring; and a mechanism
for changing pressure of the space, the method including performing
a tensile test on the rubber film according to JIS K6251 before
bonding the rubber film to the rigid ring, and selecting the rubber
film having a value of 10 MPa or less of an inclination obtained by
a linear approximation of a stress-strain curve within a strain
value of 5%; and bonding the selected rubber film having a value of
10 MPa or less of the inclination to the rigid ring to manufacture
the polishing head.
Inventors: |
Masumura; Hisashi;
(Nishishirakawa, JP) ; Hashimoto; Hiromasa;
(Nishishirakawa, JP) ; Morita; Kouji;
(Nishishirakawa, JP) ; Kishida; Hiromi; (Nagano,
JP) ; Arakawa; Satoru; (Nagano, JP) |
Assignee: |
SHIN-ETSU HANDOTAI CO.,
LTD.
Tokyo
JP
FUJIKOSHI MACHINERY CORP.
Nagano-shi, Nagano
JP
|
Family ID: |
41444210 |
Appl. No.: |
12/992782 |
Filed: |
June 2, 2009 |
PCT Filed: |
June 2, 2009 |
PCT NO: |
PCT/JP2009/002450 |
371 Date: |
November 15, 2010 |
Current U.S.
Class: |
451/360 ;
51/297 |
Current CPC
Class: |
B24B 37/32 20130101;
B24B 37/24 20130101; B24B 37/042 20130101 |
Class at
Publication: |
451/360 ;
51/297 |
International
Class: |
B24B 41/00 20060101
B24B041/00; B24D 18/00 20060101 B24D018/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 24, 2008 |
JP |
2008-164723 |
Claims
1. A method for manufacturing a polishing head having at least: an
annular rigid ring; a rubber film bonded to the rigid ring with a
uniform tension; a mid plate joined to the rigid ring, the mid
plate forming a space together with the rubber film and the rigid
ring; and a pressure adjustment mechanism for changing pressure of
the space, the polishing head holding a back surface of a workpiece
on a lower face portion of the rubber film and polishing the
workpiece by bringing a surface of the workpiece into sliding
contact with a polishing pad attached onto a turn table, the method
comprising the steps of: performing a tensile test on the rubber
film according to JIS K6251 before bonding the rubber film to the
rigid ring, and selecting the rubber film having a value of 10 MPa
or less of an inclination obtained by a linear approximation of a
stress-strain curve within a strain value of 5%; and bonding the
selected rubber film having a value of 10 MPa or less of the
inclination to the rigid ring to manufacture the polishing
head.
2. The method for manufacturing a polishing head according to claim
1, wherein the workpiece to be held is a silicon single crystal
wafer having a diameter of 300 mm or more.
3. A polishing apparatus having at least a polishing pad attached
onto a turn table, a polishing agent supply mechanism for supplying
a polishing agent onto the polishing pad, and a polishing head for
holding a workpiece, the polishing apparatus polishing a surface of
the workpiece while holding a back surface of the workpiece with
the polishing head, wherein the polishing head has at least: an
annular rigid ring; a rubber film bonded to the rigid ring with a
uniform tension; a mid plate joined to the rigid ring, the mid
plate forming a space together with the rubber film and the rigid
ring; and a pressure adjustment mechanism for changing pressure of
the space, the rubber film is formed by using a rubber material
having a value of 10 MPa or less of an inclination obtained by a
linear approximation of a stress-strain curve within a strain value
of 5%, the stress-strain curve being obtained as a result of
performing a tensile test on the rubber film according to JIS
K6251, the polishing pad has a young's modulus of 3.5 MPa or less,
the workpiece is polished by bringing a surface of the workpiece
into sliding contact with the polishing pad attached onto the turn
table with the pressure of the space controlled by the pressure
adjustment mechanism.
4. The polishing apparatus according to claim 3, wherein the
workpiece to be polished is a silicon single crystal wafer having a
diameter of 300 mm or more.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for manufacturing
a polishing head for holding a workpiece when a surface of the
workpiece is polished and a polishing apparatus provided with the
polishing head manufactured by the method, and more particularly to
a method for manufacturing a polishing head for holding the
workpiece on a rubber film and a polishing apparatus provided with
the manufactured polishing head.
BACKGROUND ART
[0002] As an apparatus for polishing a surface of a workpiece such
as a silicon wafer, there are a single-side polishing apparatus, in
which the workpiece is polished by each side, and a double-side
polishing apparatus, in which the both sides of the workpiece are
polished at the same time.
[0003] For example as shown in FIG. 9, a common single-side
polishing apparatus comprises a turn table 88 onto which a
polishing pad 89 is attached, a polishing agent supply mechanism
90, a polishing head 82 and the like. The polishing apparatus 81
polishes a workpiece W by holding the workpiece W with the
polishing head 82, supplying a polishing agent onto the polishing
pad 89 through the polishing agent supply mechanism 90, rotating
the turn table 88 and the polishing head 82 respectively, and
bringing a surface of the workpiece W into sliding contact with the
polishing pad 89.
[0004] As a method for holding the workpiece in the polishing head,
for example, there is a method of attaching the workpiece onto a
flat disk-shaped plate through an adhesive such as a wax. Other
than that, particularly as a holding method of suppressing rise or
sag on an outer circumferential portion of the workpiece and of
improving flatness of the whole workpiece, there is a so-called
rubber-chuck method in which a workpiece holding portion is made of
a rubber film, a pressurized fluid such as air is poured into a
back face of the rubber film, and the rubber film is inflated by a
uniform pressure so as to press the workpiece toward the polishing
pad (See Japanese Unexamined Patent Publication (Kokai) No.
H5-69310, for example).
[0005] An example of structure of a conventional polishing head by
a rubber-chuck method is schematically shown in FIG. 8. An
essential part of the polishing head 102 consists of an annular
rigid ring 104 made of SUS and the like, the rubber film 103 bonded
to the rigid ring 104, and a mid plate 105 joined to the rigid ring
104. A sealed space 106 is defined by the rigid ring 104, the
rubber film 103, and the mid plate 105. An annular template 114 is
provided concentrically with the rigid ring 104 in the periphery of
a lower face portion of the rubber film 103. The pressure of the
space is adjusted, for example, by supplying a pressurized fluid by
a pressure adjustment mechanism 107 in a center of the mid plate
105. A pressing means, not shown, for pressing the mid plate 105 in
the direction of the polishing pad 109 is provided.
[0006] As a material of the rubber film 103, there is a suggestion
of various rubber materials, such as a fluorinated rubber, a
urethane rubber, a silicon rubber, and an ethylene-propylene
rubber, having a rubber hardness ranging from 10 to 100, a tensile
strength ranging from 3 to 20 MPa, and a tensile elongation ranging
from 50 to 1000% in Japanese Unexamined Patent publication (Kokai)
No. 2005-7521.
[0007] With the polishing head 102 configured as above, the
workpiece W is held on a lower face portion of the rubber film 103
through a backing pad 113, an edge portion of the workpiece W is
held with the template 114, and the workpiece W is polished by
bringing it into sliding contact with the polishing pad 109
attached onto an upper face of the turn table 108 by pressing the
mid plate 105.
DISCLOSURE OF INVENTION
[0008] Polishing the workpiece W by using the polishing head 102 in
which the workpiece W is held on the rubber film 103, as described
above, may improve flatness and polishing stock removal uniformity
of the whole workpiece W in some cases. However, there is a problem
such that the flatness and the polishing stock removal uniformity
may decrease due to a difference of material of the rubber film 103
or a difference of the manufacturing lot even with regard to the
same materials and thus stable flatness of the workpiece W cannot
be obtained.
[0009] The present invention was accomplished in view of the
above-explained problems, and its object is to provide a method for
manufacturing a polishing head and a polishing apparatus that can
stably obtain constant flatness in polishing of the workpiece
W.
[0010] To achieve this object, the present invention provides a
method for manufacturing a polishing head having at least: an
annular rigid ring; a rubber film bonded to the rigid ring with a
uniform tension; a mid plate joined to the rigid ring, the mid
plate forming a space together with the rubber film and the rigid
ring; and a pressure adjustment mechanism for changing pressure of
the space, the polishing head holding a back surface of a workpiece
on a lower face portion of the rubber film and polishing the
workpiece by bringing a surface of the workplace into sliding
contact with a polishing pad attached onto a turn table, the method
comprising the steps of: performing a tensile test on the rubber
film according to JIS K6251 before bonding the rubber film to the
rigid ring, and selecting the rubber film having a value of 10 MPa
or less of an inclination obtained by a linear approximation of a
stress-strain curve within a strain value of 5%; and bonding the
selected rubber film having a value of 10 MPa or less of the
inclination to the rigid ring to manufacture the polishing
head.
[0011] In this manner, when the method comprises the steps of:
performing a tensile test on the rubber film according to JIS K6251
before bonding the rubber film to the rigid ring, and selecting the
rubber film having a value of 10 MPa or less of an inclination
obtained by a linear approximation of a stress-strain curve within
a strain value of 5%; and bonding the selected rubber film having a
value of 10 MPa or less of the inclination to the rigid ring to
manufacture the polishing head, the polishing head can be
manufactured which can suppress a variation in the polishing stock
removal uniformity that is generated between material types of
rubber film or material lots of the rubber film and which can
secure stably good flatness, in polishing of the workpiece.
[0012] In this case, the workpiece to be held can be a silicon
single crystal wafer having a diameter of 300 mm or more.
[0013] In this manner, even when the workpiece to be held is the
silicon single crystal wafer having a large diameter such as a
diameter of 300 mm or more, the polishing can be performed with
more uniform pressing force over the whole surface of the workpiece
and thereby good flatness can be secured, according to the present
invention.
[0014] Furthermore, the present invention provides a polishing
apparatus having at least a polishing pad attached onto a turn
table, a polishing agent supply mechanism for supplying a polishing
agent onto the polishing pad, and a polishing head for holding a
workpiece, the polishing apparatus polishing a surface of the
workpiece while holding a back surface of the workpiece with the
polishing head, wherein the polishing head has at least: an annular
rigid ring; a rubber film bonded to the rigid ring with a uniform
tension; a mid plate joined to the rigid ring, the mid plate
forming a space together with the rubber film and the rigid ring;
and a pressure adjustment mechanism for changing pressure of the
space, the rubber film is formed by using a rubber material having
a value of 10 MPa or less of an inclination obtained by a linear
approximation of a stress-strain curve within a strain value of 5%,
the stress-strain curve being obtained as a result of performing a
tensile test on the rubber film according to JIS K6251, the
polishing pad has a young's modulus of 3.5 MPa or less, the
workpiece is polished by bringing a surface of the workpiece into
sliding contact with the polishing pad attached onto the turn table
with the pressure of the space controlled by the pressure
adjustment mechanism.
[0015] In this manner, when the polishing head has at least: an
annular rigid ring; a rubber film bonded to the rigid ring with a
uniform tension; a mid plate joined to the rigid ring, the mid
plate forming a space together with the rubber film and the rigid
ring; and a pressure adjustment mechanism for changing pressure of
the space, the rubber film is formed by using a rubber material
having a value of 10 MPa or less of an inclination obtained by a
linear approximation of a stress-strain curve within a strain value
of 5%, the stress-strain curve being obtained as a result of
performing a tensile test on the rubber film according to JIS
K6251, the polishing pad has a young's modulus of 3.5 MPa or less,
the workpiece is polished by bringing a surface of the workpiece
into sliding contact with the polishing pad attached onto the turn
table with the pressure of the space controlled by the pressure
adjustment mechanism, a variation in the polishing stock removal
uniformity which is generated between material types of rubber film
or material lots of the rubber film can be suppressed, and the
workpiece can be polished with stably good flatness secured.
[0016] In this case, the workpiece to be polished can be a silicon
single crystal wafer having a diameter of 300 mm or more.
[0017] In this manner, even when the workpiece to be polished is
the silicon single crystal wafer having a large diameter such as a
diameter of 300 mm or more, the polishing can be performed with
more uniform pressing force over the whole surface of the workpiece
and thereby good flatness can be secured by holding it with the
polishing head according to the present invention to polish.
[0018] The method according to the present invention comprises the
steps of: performing a tensile test on the rubber film according to
JIS K6251 before bonding the rubber film to the rigid ring, and
selecting the rubber film having a value of 10 MPa or less of an
inclination obtained by a linear approximation of a stress-strain
curve within a strain value of 5%; and bonding the selected rubber
film having a value of 10 MPa or less of the inclination to the
rigid ring to manufacture the polishing head. Thereby, the
polishing head can be manufactured which can suppress a variation
in the polishing stock removal uniformity that is generated between
material types of rubber film or material lots of the rubber film
and which can secure stably good flatness, in polishing of the
workpiece.
[0019] Moreover, the polishing apparatus according to the present
invention has at least the polishing pad attached onto the turn
table, the polishing agent supply mechanism for supplying the
polishing agent onto the polishing pad, and the polishing head
manufactured by the above-described method for manufacturing
according to the present invention, the polishing pad has a young's
modulus of 3.5 MPa or less, and the workpiece is polished by
bringing a surface of the workpiece into sliding contact with the
polishing pad attached onto the turn table. Thereby, a variation in
the polishing stock removal uniformity that is generated between
material types of rubber film or material lots of the rubber film
can be suppressed, and the workpiece can be polished with stably
good flatness secured.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic view showing an example of the
polishing apparatus according to the present invention;
[0021] FIG. 2 are graphs showing an example of a stress-strain
curve obtained in the method for manufacturing a polishing head
according to the present invention, in which (A) shows the whole of
the stress-strain curve, and (B) shows the stress-strain curve
within a strain value of 5%;
[0022] FIG. 3 are graphs showing the stress-strain curve in the
step of selecting the rubber film in Example 1, in which (A) shows
the whole of the stress-strain curve, and (B) shows the
stress-strain curve within a strain value of 5%;
[0023] FIG. 4 is a view showing the results of a value of an
inclination obtained by a linear approximation of the stress-strain
curve within a strain value of 5% in the step of selecting the
rubber film in Example 1;
[0024] FIG. 5 is a view showing the results of the polishing
pressure distribution in Example 1 and Comparative Example.
[0025] FIG. 6 is a view showing the results of the polishing stock
removal uniformity in Example 1 and Comparative Example.
[0026] FIG. 7 is a view showing the results of the polishing stock
removal uniformity in Example 2 and Comparative Example.
[0027] FIG. 8 is a schematic view showing an example of a
conventional polishing head; and
[0028] FIG. 9 is a schematic view showing an example of a
conventional single-side polishing apparatus.
BEST MODE FOR CARRYING OUT THE INVENTION
[0029] Hereinafter, an embodiment of the present invention will be
explained, but the present invention is not restricted thereto.
[0030] In the event that the workpiece is polished while holding
the workpiece on the rubber film by using a conventional polishing
head, there arises a problem such that a variation in polishing
characteristics occurs due to a difference in the type of the
rubber, which is a material of the rubber film of the polishing
head, or due to a difference in the lot even though there is no
difference in the type, and thereby good flatness cannot be
obtained.
[0031] Moreover, such a variation in polishing characteristics is
difficult to be predicted based on physical properties such as the
hardness of a material lot of the rubber, which is a material of
the rubber film, or the tensile strength of the rubber.
[0032] In view of this, the present inventors keenly conducted
experiments and studies of the cause leading to the above-mentioned
problem.
[0033] As a result, the present inventors found out the
followings.
[0034] That is to say, good polishing stock removal uniformity can
be obtained by using a rubber material having a small stress for a
fine deformation of a strain of 5% or less, regardless of the type,
the hardness and the tensile strength of the rubber used as a
material of the rubber film. Specifically, when the rubber film
having a small stress at the time of finely deforming is used as
the rubber film of the polishing head to polish the workpiece,
polishing can be performed with uniform pressing force over the
whole surface of the workpiece. In addition, when the workpiece is
polished by using the polishing head having a template, pressure
distribution in an outer circumferential portion of the workpiece
that is caused by a small difference between a height of a lower
end face of the template and a height of a lower end face of the
workpiece can be alleviated, and the polishing stock removal
uniformity can be consequently good.
[0035] Accordingly, the present inventors further keenly conducted
experiments and studies to quantify the stress at the time of
finely deforming of rubber materials to be used as the rubber film,
investigated polishing characteristics of these rubber materials,
optimized, and brought the present invention to completion.
[0036] FIG. 1 shows an example of the polishing head and the
polishing apparatus according to the present invention.
[0037] As shown in FIG. 1, the polishing apparatus 1 has the
polishing head 2 and the turn table 8. The turn table 8 is of disk
shape, and the polishing pad 9 for polishing the workpiece W is
attached onto its upper face. A driving shaft 11 is vertically
connected to an lower portion of the turn table 8. The turn table 8
is configured to be rotated by a turn table rotating motor (not
shown) connected to an lower portion of the driving shaft 11.
[0038] The polishing head 2 is provided above the turn table 8. The
polishing head 2 has the annular rigid ring 4, the rubber film 3
that is bonded to the rigid ring 4 with a uniform tension and that
has a flat lower face, the mid plate 5 joined to the rigid ring 4,
for example, with bolts. A sealed space 6 is formed by the rigid
ring 4, the rubber film 3 and the mid plate 5.
[0039] The polishing head 2 is rotatable about its axis.
[0040] Here, a material of the rigid ring 4 is not restricted in
particular. For example, it can be a rigid material such as SUS
(stainless steel). A material and a shape of the mid plate is also
not restricted in particular as long as the space 6 can be
formed.
[0041] Moreover, a thickness of the rubber film 3 is not restricted
in particular. For example, it may be approximately 1 mm.
[0042] The rubber film used in the polishing head of the polishing
apparatus according to the present invention has the following
characteristics.
[0043] FIG. 2(A) shows an example of a stress-strain curve of the
rubber film, the stress-strain curve which is obtained as a result
of performing a tensile test according to JIS K6251. FIG. 2(B) is
an enlarged graph of a part within a strain value of 5% in the
stress-strain curve shown in FIG. 2(A). Here, a straight line
obtained by performing the linear approximation of the
stress-strain curve within a strain value of 5% using the least
squares method, as shown in FIG. 2(B), is expressed as
stress=a.times.strain+b.
[0044] In the present invention, the rubber film is used in which a
value of the inclination a of this straight line is 10 MPa or
less.
[0045] As shown in FIG. 1, the polishing apparatus has a polishing
slurry supply means 10 for supplying a polishing slurry to an upper
part of the turn table 8.
[0046] Moreover, an annular template 14 for holding an edge portion
of the workpiece W can be arranged in the periphery of the lower
face portion of the rubber film 3 to prevent the workpiece W from
coming off during polishing. In this case, the template 14 can be
arranged so as to be concentric with the rigid ring 4 and to
project downward along an outer circumferential portion of the
lower face portion of the rubber film 3.
[0047] Here, the height of the lower end face of the template 14
can be the same as the height of the lower end face of the held
workpiece W or can be such a height that the lower end face of the
template 14 slightly project downward, for example, by
approximately 10 .mu.m from the height of the lower end face of the
workpiece W.
[0048] The pressure distribution in the outer circumferential
portion of the workpiece can be alleviated by arranging the
template 14 as described above, thereby excessive polishing of the
outer circumferential portion of the workpiece can be prevented,
and the polishing stock removal uniformity of the workpiece can be
improved.
[0049] Moreover, the template 14 can be configured such that its
outer diameter is larger than at least an inner diameter of the
rigid ring 4 and its inner diameter is smaller than the inner
diameter of the rigid ring 4.
[0050] By this configuration, the polishing can be performed with
more uniform pressing force applied to the whole surface of the
workpiece.
[0051] Here, it is preferable that a material of the template 14 is
softer than the workpiece W so as not to contaminate the workpiece
W and to give a scratch or an impression and is a high abrasion
resistance material that is hard to wear due to sliding contact
with the polishing pad 9 during the polishing.
[0052] Moreover, as shown in FIG. 1, the polishing apparatus 1 has
the pressure adjustment mechanism 7 for changing the pressure of
the space 6 of the polishing head 2.
[0053] A through-hole 12 for pressure adjustment communicating with
the pressure adjustment mechanism 7 is provided at the center of
the mid plate 5, and the pressure of the space 6 can be adjusted,
for example, by supplying a pressurized fluid by the pressure
adjustment mechanism 7.
[0054] The polishing apparatus also has a means for pressing the
mid plate 5 toward the polishing pad 9 (not shown).
[0055] In this case, a backing pad 13 can be attached to be
provided on the lower face of the rubber film 3. The backing pad 13
is made to contain water so as to attach and to hold the workpiece
W on a workpiece holding face of the rubber film 3. Here, the
backing pad 13 can be made of, for example, foamed polyurethane. By
providing the above-described backing pad 13 and having it contain
water, the workpiece W can be surely held by surface tension of the
water contained in the backing pad 13.
[0056] A soft polishing pad having a young's modulus of 3.5 MPa or
less is used as the polishing pad 9 attached onto an upper face of
the turn table 8. When the polishing head 2 according to the
present invention is used in combination with the soft polishing
pad 9 having a young's modulus of 3.5 MPa or less, contact pressure
distribution between the workpiece W and the polishing pad 9 can be
more surely alleviated, and the polishing stock removal uniformity
of the workpiece W can be more surely improved.
[0057] It is to be noted that an embodiment of attaching the
template 14 directly onto the rubber film 3 is shown in FIG. 1, but
the present invention does not exclude a case of attaching the
template 14 onto the rubber film 3 through the backing pad 13 and
the like.
[0058] With the polishing apparatus 1 configured as described
above, the mid plate 5 is pressed toward the polishing pad 9
attached onto the turn table 8 by the means for pressing the mid
plate, not shown, and the surface of the workpiece W is polished by
bringing it into sliding contact with the polishing pad 9 while the
polishing agent is supplied through the polishing agent supply
mechanism 10. Here, the means for pressing the mid plate is
preferably able to press the mid plate 5 over the whole surface
with a uniform pressure, for example, by using an air cylinder.
[0059] In this way, when the workpiece W is polished by using the
polishing apparatus 1 according to the present invention, the
variation in the polishing stock removal uniformity that is
generated between the material types of the rubber film 3 or the
material lots of the rubber film 3 can be suppressed, and the
workpiece W can be polished with stably good flatness secured.
[0060] In addition, the pressure distribution in the outer
circumferential portion of the workpiece W that is caused by a
small difference between the height of the lower end face of the
template 14 and the height of the lower end face of the workpiece W
can be alleviated. The polishing can be thereby performed while the
pressing force applied to the workpiece W is kept uniform over the
whole surface, even though there are variations in thicknesses of
the workpiece W and the template 14 to a certain degree. As a
result, the workpiece W can be polished with good polishing stock
removal uniformity.
[0061] In this case, the workpiece to be polished can be a silicon
single crystal wafer having a diameter of 300 mm or more.
[0062] As described above, even when the workpiece to be polished
is the silicon single crystal wafer having a large diameter such as
a diameter of 300 mm or more, the polishing can be performed with
more uniform pressing force over the whole surface of the workpiece
by holding it with the polishing head according to the present
invention to polish, and thereby good flatness can be secured.
[0063] Next, the method for manufacturing a polishing head
according to the present invention will be explained.
[0064] For example as shown in FIG. 1, the polishing head
manufactured by the method for manufacturing according to the
present invention is configured to have at least: the annular rigid
ring 4; the rubber film 3 bonded to the rigid ring 4 with a uniform
tension; the mid plate 5 that is joined to the rigid ring 4 and
that forms the space 6 together with the rubber film 3 and the
rigid ring 4; and the pressure adjustment mechanism 7 for changing
the pressure of the space 6.
[0065] The method for manufacturing a polishing head according to
the present invention comprises at least the step of selecting the
rubber film 3 as follows.
[0066] First, the stress-strain curve as shown in FIG. 2(A) is
obtained by performing a tensile test on the rubber film 3
according to JIS K6251. Then, from this stress-strain curve, the
stress-strain curve within a strain value of 5% is extracted as
shown in FIG. 2(B), and a straight line is obtained by performing
the linear approximation of the extracted curve using the least
squares method. This straight line is expressed as
stress=a.times.strain+b.
[0067] Thereafter, the rubber film 3 having a value of 10 MPa or
less of the inclination a of the straight line is selected.
[0068] With the rubber film 3 selected as described above, it is
bonded to the rigid ring 4 with a uniform tension.
[0069] Here, the rubber film 3 can be selected at the stage of a
rubber material before forming the rubber film 3 itself, as long as
it is selected before bonding rubber film 3 to the rigid ring
4.
[0070] As described above, when the polishing head 2 is
manufactured by performing a tensile test on the rubber film 3
according to JIS K6251 before bonding the rubber film 3 to the
rigid ring 4, selecting the rubber film having a value of 10 MPa or
less of the inclination obtained by the linear approximation of the
stress-strain curve within a strain value of 5%, and bonding the
selected rubber film 3 having a value of 10 MPa or less of the
inclination to the rigid ring 4, the polishing head 2 can be
manufactured which can suppress the variation in the polishing
stock removal uniformity that is generated between the material
types of the rubber film 3 or the material lots of the rubber film
3 and which can secure stably good flatness, in polishing of the
workpiece W.
[0071] Next, the mid plate 5 is joined to the rigid ring 4, and the
space 6 is formed by the rigid ring 4, the mid plate 5 and the
rubber film 3 bonded to the rigid ring 4. The pressure adjustment
mechanism 7 is arranged above the mid plate 5. These steps can be
performed as with a conventional method.
[0072] Here, the annular template 14 for holding the edge portion
of the workpiece W can be arranged in the periphery of the lower
face portion of the rubber film 3 to prevent the workpiece W from
coming off during polishing. In this case, the template 14 can be
arranged so as to be concentric with the rigid ring 4 and to
project downward along the outer circumferential portion of the
lower face portion of the rubber film 3.
[0073] Here, the height of the lower end face of the template 14
can be the same as the height of the lower end face of the
workpiece W when the workpiece is held or can be such a height that
the lower end face of the template 14 slightly project downward,
for example, by approximately 10 .mu.m from the height of the lower
end face of the workpiece W.
[0074] The polishing head can alleviate excessive pressure
distribution applied to the outer circumferential portion of the
workpiece by arranging the template 14 as described above, and
thereby can improve the polishing stock removal uniformity of the
workpiece.
[0075] Moreover, the template 14 can be configured such that its
outer diameter is larger than at least an inner diameter of the
rigid ring 4 and its inner diameter is smaller than the inner
diameter of the rigid ring 4.
[0076] By this configuration, the polishing head can polish the
workpiece with more uniform pressing force applied to the whole
surface of the workpiece.
[0077] Here, it is preferable that the material of the template 14
is softer than the workpiece W so as not to contaminate the
workpiece W and to give a scratch or an impression and is a high
abrasion resistance material that is hard to wear due to sliding
contact with the polishing pad 9 during the polishing.
[0078] In this case, the backing pad 13, for example, made of
foamed polyurethane can be attached to be provided on the lower
face of the rubber film 3. By providing the above-described backing
pad 13 and having it contain water, the polishing head can surely
hold the workpiece W by surface tension of the water contained in
the backing pad 13.
[0079] In this case, the workpiece to be held can be the silicon
single crystal wafer having a diameter of 300 mm or more.
[0080] In this manner, even when the workpiece to be held is the
silicon single crystal wafer having a large diameter such as a
diameter of 300 mm or more, the polishing can be performed with
more uniform pressing force over the whole surface of the workpiece
and thereby good flatness can be secured, according to the present
invention.
[0081] Hereinafter, the present invention will be explained in more
detail based on Example, but the present invention is not
restricted thereto.
Example 1
[0082] The polishing heads as shown in FIG. 1 were manufactured by
the method for manufacturing according to the present invention.
Silicon single crystal wafers were polished with the polishing
apparatus having each manufactured polishing head, and the
polishing stock removal uniformity of each polished workpiece was
evaluated.
[0083] First, in order to select the rubber film, there were
prepared two types of lot A and lot B of ethylene-propylene-diene
rubber (EPDM) having a hardness standard of 80.degree., which is a
rubber hardness according to JIS K6253, (hereinafter, referred to
as EPDM 80.degree. A and EPDM 80.degree. B) and three types of
silicone rubber having a hardness standard of 70.degree.,
80.degree., and 90.degree. (hereinafter, referred to as silicone
70.degree., silicone 80.degree., and silicone 90.degree.), as a
rubber material of the rubber film. Tensile tests according to JIS
K6251 were performed on these 5 types of rubber materials, and the
stress-strain curves were measured each.
[0084] Table 1 shows the results of the tests. FIG. 3(A) shows the
obtained stress-strain curves. As shown in FIG. 3(B), the linear
approximation was performed, as stress=a.times.strain+b, using each
stress-strain curve within a strain value of 5% in FIG. 3(A), and a
value of each inclination a was calculated.
[0085] FIG. 4 shows the results of the values. As shown in FIG. 4,
it was revealed that even though the same type of rubber material
was used, the values of the inclination a were different due to the
difference of the lot, and in the rubber material of EPDM
80.degree. B, silicone 70.degree., and silicone 80.degree., the
values of the inclination a were 10 MPa or less.
[0086] After the rubber materials of the rubber films were selected
as described above, three polishing heads were manufactured using
EPDM 80.degree. B, silicone 70.degree., and silicone 80.degree.,
which had a value of 10 MPa or less of the inclination a, by the
following manner.
[0087] First, upper parts of the annular rigid rings that were made
of SUS and had an outer diameter of 360 mm were covered by the mid
plates respectively. The rubber films having a thickness of 1 mm
were bonded to the outer circumferences of the rigid rings with a
uniform tension, using three types of rubber materials (EPDM
80.degree. B, silicone 70.degree., and silicone 80.degree.), which
had a value of 10 MPa or less of the inclination a.
[0088] The backing pad was attached to be provided on the workpiece
holding face of the rubber film of each polishing head. A
commercial template assembly, in which a template made of glass
epoxy laminated sheet having an outer diameter of 355 mm and an
inner diameter of 302 mm was bonded, was adhered to a surface of
the backing pad by double-stick tape. In case of the rubber film
formed with silicone rubber, its surface was subjected to coating
processing with a thin polyurethane film having a thickness of
several .mu.m for the purpose of improving capability for adhering
to the double-stick tape. Moreover, the commercial template
assembly having a thickness of 787 .mu.m was used as the template
so that the position of the lower face of the template slightly
project downward from the position of the lower face of the
workpiece.
[0089] With the polishing apparatus having the polishing head
manufactured by the method for manufacturing a polishing head
according to the present invention as shown in FIG. 1, silicon
single crystal wafers having a diameter of 300 mm and a thickness
of 775 .mu.m, as a workpiece W, were polished. It is to be noted
that both surfaces of the used silicon single crystal wafers were
subjected to the first polishing in advance, and its edge portions
were also subjected to polishing. The turn table having a diameter
of 800 mm was used. The polishing pad of the type of containing
urethane in a nonwoven fabric was used, and its young's modulus was
2.2 MPa, which is 3.5 MPa or less.
[0090] During the polishing, an alkaline solution containing
colloidal silica was used as the polishing agent, and the polishing
head and the turn table were rotated at 31, and 29 rpm
respectively. A polishing load (pressing force) of the workpiece W
was set as 15 KPa. The polishing time was 3 minutes.
[0091] The polishing stock removal uniformity and the polishing
pressure distribution during polishing of the workpiece polished as
described above were evaluated. It is to be noted that the
polishing stock removal uniformity is obtained by measuring the
thickness of the workpiece before and after polishing in a region
excluding an outermost circumferential portion 2 mm width, as a
flatness quality area, with a flatness measurement instrument in a
diameter direction of the wafer and by taking a difference in the
thickness. It is represented by a formula of
polishing-stock-removal-uniformity (%)=(maximum
polishing-stock-removal in a diameter direction-minimum
polishing-stock-removal in a diameter direction)/average
polishing-stock-removal in a diameter direction.
[0092] The polishing pressure distribution of the wafer in the
range of 120 to 148 mm from its center in a diameter direction is
shown in FIG. 5, the wafer which was polished with the polishing
head using EPDM 80.degree. B as the rubber material of the rubber
film. The pressure distribution was measured by converting the
polishing stock removal at each position into
polishing-stock-removal/average
polishing-stock-removal.times.polishing-load (15 MPa) at each
position.
[0093] As shown in FIG. 5, it was revealed that a decrease in
pressure of the outer circumferential portion of the workpiece W
was more suppressed and uniformity of the polishing pressure
distribution was better in comparison with the polishing head using
the rubber film made of the rubber material having a value of over
10 MPa of an inclination a, which is used in later-explained
Comparative Example.
[0094] FIG. 6 shows the results of the polishing stock removal
uniformity.
[0095] As shown in FIG. 6, it was revealed that when polishing was
performed by the polishing apparatus having the polishing head
using the rubber film made of EPDM 80.degree. B, silicone
70.degree., and silicone 80.degree. respectively, the polishing
stock removal uniformity was improved in comparison with the result
of the later-explained Comparative Example, and that it was a good
result of 10% or less.
[0096] Accordingly, it can be confirmed that the variation in the
polishing stock removal uniformity that is generated between
material types of rubber film or material lots of the rubber film
can be suppressed and the stably good flatness can be secured
during polishing of the workpiece, by using the polishing apparatus
according to the present invention that has the polishing head
manufactured by the method for manufactured according to the
present invention.
Example 2
[0097] A polishing head using EPDM 80.degree. B as the rubber film
material was manufactured as with Example 1. A silicon single
crystal wafer was polished with the polishing apparatus having the
manufactured polishing head and the polishing stock removal
uniformity was evaluated as with Example 1 except for using the
polishing pad having a young's modulus of 3.2 MPa.
[0098] FIG. 7 shows the result of the polishing stock removal
uniformity. As shown in FIG. 7, it was revealed that the polishing
stock removal uniformity was improved in comparison with the result
of the later-explained Comparative Example, and that it was a good
result of 10% or less.
[0099] Moreover, as shown in FIG. 7, it was revealed that when the
young's modulus of the polishing pad was 3.5 MPa or less, the
polishing stock removal uniformity was a good result of 10% or
less.
Comparative Example
[0100] Silicon single crystal wafers were polished in the same
condition as Example 1 except that the polishing heads were
manufactured by using the rubber material having a value of over 10
MPa of the inclination a obtained, in Example 1, by the linear
approximation was performed, as stress=a.times.strain+b, using the
stress-strain curve within a strain value of 5%, that is, except
for using EPDM 80.degree. A and silicone 90.degree. as the rubber
film material, and the polishing stock removal uniformity and the
polishing pressure distribution during the polishing of each
polished wafer were evaluated.
[0101] FIG. 5 shows the results of the polishing pressure
distribution. As shown in FIG. 5, it was revealed that the decrease
in pressure of the outer circumferential portion of the workpiece
was more remarkable and uniformity of the polishing pressure
distribution was decreased in comparison with the result of Example
1 in which the rubber film having a value of 10 MPa or less of the
inclination a was selected.
[0102] FIG. 6 shows the results of the polishing stock removal
uniformity. As shown in FIG. 6, it was revealed that the polishing
stock removal uniformity was worse than the results of Example
1.
[0103] Accordingly, it was confirmed that when the workpiece was
polished with a conventional polishing apparatus, the variation in
the polishing stock removal uniformity occurred and stable flatness
of the workpiece was not obtained due to the differences of the
rubber film material and of the manufacturing lot even with regard
to the same materials.
[0104] Next, a silicon single crystal wafer was polished in the
same condition as Example 2 except for using the polishing pad
having a young's modulus of 4.5 MPa, and the polishing stock
removal uniformity of the polished wafer was evaluated.
[0105] FIG. 7 shows the result of the polishing stock removal
uniformity. As shown in FIG. 7, it was revealed that the polishing
stock removal uniformity was worse than the result of Example 2.
That is to say, the polishing head according to the present
invention that selects the rubber film having a value of 10 MPa or
less of the inclination obtained by the linear approximation of the
stress-strain curve within a strain value of 5% enables the
polishing stock removal uniformity to be improved, and when the
polishing apparatus is provided with the polishing head to polish,
the polishing pad attached onto the turn table needs to have a
young's modulus of 3.5 MPa or less.
TABLE-US-00001 TABLE 1 TENSILE TENSILE RUBBER STRENGTH ELONGATION
RUBBER MATERIAL HARDNESS (MPa) (%) EPDM RUBBER80.degree.A 75 10.78
219 EPDM RUBBER80.degree.B 77 12.57 405 SILICONE RUBBER70.degree.
73 7.19 127 SILICONE RUBBER80.degree. 75 7.32 148 SILICONE
RUBBER90.degree. 86 9.53 288
[0106] It is to be noted that the present invention is not
restricted 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.
[0107] For example, the polishing head manufactured by the method
for manufacturing according to the present invention is not
restricted to an embodiment shown in FIG. 1, and for example, a
shape and the like of the mid plate may be appropriately
designed.
[0108] Moreover, the structure of the polishing apparatus is also
not restricted to the embodiment shown in FIG. 1, and for example,
the polishing apparatus can be provided with a plurality of the
polishing head manufactured by the method for manufacturing
according to the present invention.
* * * * *