U.S. patent application number 12/682458 was filed with the patent office on 2010-08-19 for polishing head and polishing apparatus.
This patent application is currently assigned to SHIN-ETSU HANDOTAI CO., LTD.. Invention is credited to Satoru Arakawa, Hiromi Kishida, Koji Kitagawa, Hisashi Masumura, Kouji Morita.
Application Number | 20100210192 12/682458 |
Document ID | / |
Family ID | 40667190 |
Filed Date | 2010-08-19 |
United States Patent
Application |
20100210192 |
Kind Code |
A1 |
Masumura; Hisashi ; et
al. |
August 19, 2010 |
POLISHING HEAD AND POLISHING APPARATUS
Abstract
The present invention is a polishing head having at least: an
approximately discoid mid plate; a rubber film covering at least a
lower face portion and a side face portion of the mid plate; and a
space portion surrounded by the mid plate and the rubber film; in
which pressure of the space portion can be changed by a pressure
adjustment mechanism, a back surface of a workpiece is held on a
lower face portion of the rubber film and a front surface of the
workpiece is brought into sliding contact with a polishing pad
attached onto a turn table for performing polishing; wherein the
mid plate and the rubber film do not contact one another to have a
gap at least throughout a whole of the lower face portion of the
mid plate. As a result, there is provided a polishing head etc by a
rubber chuck method in which a uniform polishing load is applied
over the workpiece without influence of stiffness or flatness of
the mid plate.
Inventors: |
Masumura; Hisashi;
(Nishishirakawa, JP) ; Kitagawa; Koji;
(Nishishirakawa, JP) ; Morita; Kouji;
(Nishishirakawa, JP) ; Kishida; Hiromi; (Nagano,
JP) ; Arakawa; Satoru; (Nagano, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
SHIN-ETSU HANDOTAI CO.,
LTD.
Tokyo
JP
FUJIKOSHI MACHINERY CORP.
Nagano-shi, Nagano
JP
|
Family ID: |
40667190 |
Appl. No.: |
12/682458 |
Filed: |
November 20, 2007 |
PCT Filed: |
November 20, 2007 |
PCT NO: |
PCT/JP2007/001271 |
371 Date: |
April 9, 2010 |
Current U.S.
Class: |
451/177 |
Current CPC
Class: |
B24B 41/002 20130101;
B24B 57/02 20130101; B24B 37/30 20130101 |
Class at
Publication: |
451/177 |
International
Class: |
B24B 7/00 20060101
B24B007/00 |
Claims
1. A polishing head having at least: an approximately discoid mid
plate; a rubber film covering at least a lower face portion and a
side face portion of the mid plate; and a space portion surrounded
by the mid plate and the rubber film; in which pressure of the
space portion can be changed by a pressure adjustment mechanism, a
back surface of a workpiece is held on a lower face portion of the
rubber film and a front surface of the workpiece is brought into
sliding contact with a polishing pad attached onto a turn table for
performing polishing; wherein the mid plate and the rubber film do
not contact one another to have a gap at least throughout a whole
of the lower face portion of the mid plate.
2. The polishing head according to claim 1, wherein the gap between
the mid plate and the rubber film is less than 1 mm.
3. The polishing head according to claim 1, wherein the mid plate
and the rubber film also do not contact one another to have a gap
throughout a whole of the side face portion of the mid plate.
4-7. (canceled)
8. The polishing head according to claim 2, wherein the mid plate
and the rubber film also do not contact one another to have a gap
throughout a whole of the side face portion of the mid plate.
9. The polishing head according to claim 1, wherein an inner
diameter of the portion covering the side face portion of the mid
plate in the rubber film is larger than a flatness quality area of
the workpiece.
10. The polishing head according to claim 2, wherein an inner
diameter of the portion covering the side face portion of the mid
plate in the rubber film is larger than a flatness quality area of
the workpiece.
11. The polishing head according to claim 3, wherein an inner
diameter of the portion covering the side face portion of the mid
plate in the rubber film is larger than a flatness quality area of
the workpiece.
12. The polishing head according to claim 4, wherein an inner
diameter of the portion covering the side face portion of the mid
plate in the rubber film is larger than a flatness quality area of
the workpiece.
13. The polishing head according to claim 1, wherein the polishing
head has a backing pad on the face of the rubber film, the face
holding the workpiece.
14. The polishing head according to claim 2, wherein the polishing
head has a backing pad on the face of the rubber film, the face
holding the workpiece.
15. The polishing head according to claim 3, wherein the polishing
head has a backing pad on the face of the rubber film, the face
holding the workpiece.
16. The polishing head according to claim 4, wherein the polishing
head has a backing pad on the face of the rubber film, the face
holding the workpiece.
17. The polishing head according to claim 5, wherein the polishing
head has a backing pad on the face of the rubber film, the face
holding the workpiece.
18. The polishing head according to claim 6, wherein the polishing
head has a backing pad on the face of the rubber film, the face
holding the workpiece.
19. The polishing head according to claim 7, wherein the polishing
head has a backing pad on the face of the rubber film, the face
holding the workpiece.
20. The polishing head according to claim 8, wherein the polishing
head has a backing pad on the face of the rubber film, the face
holding the workpiece.
21. The polishing head according to claim 9, wherein a diameter of
the backing pad is larger than that of the workpiece.
22. A polishing apparatus used for polishing a surface of a
workpiece at least comprising: a polishing pad attached onto a turn
table; a polishing agent supply mechanism for providing a polishing
agent to the polishing pad; and a polishing head for holding the
workpiece, which is the polishing head according to claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polishing head for
holding a workpiece when a surface of the workpiece is polished and
a polishing apparatus having it, and more particularly to a
polishing head for holding the workpiece on a rubber film and a
polishing apparatus having it.
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 93 onto which a
polishing pad 94 is attached, a polishing agent supply mechanism
96, a polishing head 92 and the like. The polishing apparatus 91
polishes a workpiece W by holding the workpiece W with the
polishing head 92, supplying the polishing agent 95 to the
polishing pad 94 through the polishing agent supply mechanism 96,
rotating the turn table 93 and the polishing head 92 respectively,
and bringing the surface of the workpiece W into sliding contact
with the polishing pad 94.
[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, as a method for improving flatness over the 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 surface of the rubber film, and the
rubber film is inflated by a uniform pressure so as to press the
workpiece to the polishing pad (See Japanese Patent Application
Laid-open (kokai) No. H05-69310, Japanese Patent Application
Laid-open (kokai) No. 2005-313313, etc.).
[0005] An example of structure of a conventional polishing head by
a rubber chuck method is schematically shown in FIG. 8 (a) and an
enlarged diagram of a peripheral portion of the polishing head is
shown in FIG. (b). An essential part of the polishing head 71
consists of an approximately discoid mid plate 72 and a rubber film
73 fixed by fitting it with the mid plate 72. The rubber film 73 is
supported by a peripheral portion 72c of an upper face, a side face
portion 72b and a peripheral portion of a lower face portion 72a of
the mid plate. A projecting portion 72d is formed in the peripheral
portion of the lower face portion 72a of the mid plate in order to
form a space portion 74 between the rubber film 73 and the mid
plate. A through hole 76 for pressure adjustment communicating with
a pressure adjustment mechanism 75 is provided at the center of the
mid plate 72 and pressure of the space portion 74 is adjusted, for
example, by supplying a pressurized fluid with the pressure
adjustment mechanism 75. In addition, the polishing head comprises
a pressing means, not shown, for pressing the mid plate 72 toward
the polishing pad 94.
[0006] Besides, there is the case where a polishing head having the
structure as described in Japanese Patent Application Laid-open
(kokai) No. 2005-313313 is used and it is provided with a mechanism
for uniformly applying pressure to the mid plate, a mechanism for
applying pressure to a retainer ring placed in a periphery of a
workpiece holding portion and the like, in addition to a mechanism
for applying pressure to the rubber film.
[0007] The workpiece W is held on the lower face portion of the
rubber film 73 through a backing pad 77 and is brought into sliding
contact with the polishing pad 94 attached onto an upper face of
the turn table 93 by pressing the mid plate for performing
polishing using the polishing head configured as described
above.
[0008] It is described that polishing the workpiece using the
polishing head by a rubber chuck method as described above enables
obtaining the workpiece having a relatively good polishing stock
removal uniformity. However, there is a problem that a polishing
sag or the like occurs particularly on an outer peripheral portion.
Thus, the polishing stock removal uniformity is required to further
improve.
DISCLOSURE OF INVENTION
[0009] In view of the above-explained problems, it is a main object
of the present invention to provide a polishing head by a rubber
chuck method in which a uniform polishing load can be applied over
the workpiece without influence of stiffness or flatness of the mid
plate.
[0010] In order to accomplish the above object, the present
invention provides a polishing head having at least: an
approximately discoid mid plate; a rubber film covering at least a
lower face portion and a side face portion of the mid plate; and a
space portion surrounded by the mid plate and the rubber film; in
which pressure of the space portion can be changed by a pressure
adjustment mechanism, a back surface of a workpiece is held on a
lower face portion of the rubber film and a front surface of the
workpiece is brought into sliding contact with a polishing pad
attached onto a turn table for performing polishing; wherein the
mid plate and the rubber film do not contact one another to have a
gap at least throughout a whole of the lower face portion of the
mid plate.
[0011] When the workpiece is polished using the polishing head in
which the mid plate and the rubber film do not contact one another
to have a gap at least throughout a whole of the lower face portion
of the mid plate as described above, since there is the gap between
the lower face portion of the mid plate and the rubber film, the
workpiece can be polished while a uniform polishing load is applied
over the workpiece without the influence of stiffness or flatness
of the mid plate. As a result, the workpiece can be polished with
maintaining a high flatness throughout a whole of the workpiece,
particularly in the outer peripheral portion.
[0012] In this case, it is preferable that the gap between the mid
plate and the rubber film is less than 1 mm.
[0013] In this manner, when the gap between the mid plate and the
rubber film is less than 1 mm, the workpiece can be polished with
the pressure of the space portion more stabilized.
[0014] In addition, it is preferable that the mid plate and the
rubber film also do not contact one another to have a gap
throughout a whole of the side face portion of the mid plate.
[0015] In this manner, when the mid plate and the rubber film also
do not contact one another to have a gap throughout a whole of the
side face portion of the mid plate, since the side face of the mid
plate also does not contact with the rubber film, the influence of
the stiffness or the shape of the side face portion of the mid
plate on the rubber film can be further reduced and thus the
workpiece can be polished while the back surface of the workpiece
is more effectively pressed with a uniform polishing load. As a
result, the workpiece can be polished with more effectively
maintaining a high flatness of the front surface of the
workpiece.
[0016] In addition, it is preferable that an inner diameter of the
portion covering the side face portion of the mid plate in the
rubber film is larger than a flatness quality area of the
workpiece.
[0017] In this manner, when an inner diameter of the portion
covering the side face portion of the mid plate in the rubber film
is larger than a flatness quality area of the workplace, the
influence of the stiffness of the portion covering the side face
portion of the mid plate in the rubber film on a workpiece holding
face of the rubber film can be reduced and the polishing stock
removal uniformity can be more effectively improved while the
workpiece is polished.
[0018] In addition, the polishing head can have a backing pad on
the face of the rubber film, the face holding the workpiece. In
this case, it is preferable that a diameter of the backing pad is
larger than that of the workpiece.
[0019] In this manner, even if the polishing head has a backing pad
in order to surely hold the workpiece in the polishing head and to
prevent an occurrence of a scratch and the like on the back
surface, when a diameter of the backing pad is larger than that of
the workplace, the influence of a limit to inflation of the rubber
film due to the backing pad on the workpiece can be reduced. As a
result, the workpiece can be pressed with a more uniform polishing
load.
[0020] Furthermore, the present invention provides a polishing
apparatus used for polishing a surface of a workpiece at least
comprising: a polishing pad attached onto a turn table; a polishing
agent supply mechanism for providing a polishing agent to the
polishing pad; and a polishing head for holding the workpiece,
which is the polishing head according to the present invention.
[0021] In this manner, when the workpiece is polished using the
polishing apparatus including the polishing head according to the
present invention, the workpiece can be polished while a uniform
polishing load is applied over the workpiece. As a result, the
workpiece can be polished with maintaining a high flatness
throughout a whole surface of the workpiece, particularly in the
outer peripheral portion.
[0022] When the workpiece is polished using the polishing head
according to the present invention, the workpiece can be polished
while a uniform pressing force is applied throughout the whole of
the front surface of the workpiece. As a result, the polishing
stock removal uniformity can be improved throughout the whole
surface of the workpiece and the surface flatness of the polished
workplace can be made to be good.
BRIEF DESCRIPTION OF DRAWINGS
[0023] FIG. 1 are schematic sectional views showing a first
embodiment of the polishing head according to the present
invention, wherein (a) is a schematic sectional view showing the
whole of the polishing head and (b) is an enlarged view showing the
peripheral portion thereof.
[0024] FIG. 2 are schematic sectional views showing a second
embodiment of the polishing head according to the present
invention, wherein (a) is a schematic sectional view showing the
whole of the polishing head and (b) is an enlarged view showing the
peripheral portion thereof.
[0025] FIG. 3 is a schematic constitutional view showing an example
of the polishing apparatus comprising the polishing head according
to the present invention.
[0026] FIG. 4 are explanatory views showing a positional
relationship between the portion covering the side face portion of
the mid plate in the rubber film (a rubber film side portion) and
the outermost peripheral portion of the workpiece.
[0027] FIG. 5 is a graph showing the polishing stock removal
uniformities of the workpiece polished in Example 1, Example 2, and
Comparative Example.
[0028] FIG. 6 is a graph showing the polishing stock removal
uniformities of the workpiece in the case that an inner diameter of
the portion covering the side face portion of the mid plate in the
rubber film (a rubber film side portion) is changed.
[0029] FIG. 7 is a graph showing the polishing stock removal
uniformities of the workpiece in the case that an outer diameter of
the backing pad is changed.
[0030] FIG. 8 are schematic sectional views showing an example of
structure of a conventional polishing head by a rubber chuck
method, wherein (a) is a schematic sectional view showing the whole
of the polishing head and (b) is an enlarged view showing the
peripheral portion thereof.
[0031] FIG. 9 is a schematic constitutional view showing an example
of a single-side polishing apparatus.
[0032] FIG. 10 is a schematic sectional view showing an example of
the case where the polishing head according to the present
invention comprises a retainer ring.
[0033] FIG. 11 are explanatory views showing a positional
relationship among the workpiece, the backing pad and the rubber
film in the polishing head according the present invention.
BEST MODES FOR CARRYING OUT THE INVENTION
[0034] Hereinafter, the present invention will be explained more
specifically.
[0035] As described above, in the case of holding a workpiece with
the polishing head by a rubber chuck method and polishing the
surface of the workpiece, the surface flatness of the polished
workpiece is required to be a still higher level. However,
conventionally there is a problem that a polishing sag and the like
occurs particularly in the peripheral portion.
[0036] In order to solve the problem, the present inventors have
conducted experiments and studies.
[0037] The present inventors found as follows through them. As
shown in FIG. 8, conventionally there is the case that a part (a
projecting portion) 72d where a lower face portion 72a of a mid
plate 72 and a rubber film 73 contact one another is provided. In
this case, even if the projecting portion 72d does not adhered to
the rubber film 73 and they are in free condition due to a
pressurized fluid during polishing the workpiece, the mid plate is
pressed toward a polishing pad 94 at the time of pressing the whole
of the polishing head 71 and then a workpiece holding portion of
the rubber film 73 is affected by stiffness of the mid plate 72,
flatness of the lower face portion 72a (a lower face of the
projecting portion 72d) or the like, at the time of polishing. As a
result, its shape or pressing force becomes nonuniform and thereby
a shape of the workpiece W that is held on the workpiece holding
face of the rubber film 73 and polished deteriorates.
[0038] In particular, in the case of the polishing head configured
such that a retainer ring is placed outside the workpiece holding
face of the rubber film 73 and an edge portion of the workpiece W
is held by the retainer ring, the workpiece W is held up to the
almost outermost peripheral portion of the lower face portion of
the rubber film 73. There is consequently a great influence of a
contact portion between the rubber film 73 and the projecting
portion 72d formed in the peripheral portion of the lower face
portion 72a of the mid plate. In addition, in the case that the
workpiece W is not held just below the contact portion between the
rubber film 73 and the projecting portion 72d of the mid plate
unlike described above but is held more inside, the workpiece
holding face of the rubber film 73 is not a little affected by
existence of the contact portion between the rubber film 73 and the
projecting portion 72d of the mid plate such as an occurrence of
pressure distribution.
[0039] The present inventors studied measures to solve the
above-mentioned problems. As a result, the present inventors found
as follows. It was conventionally considered that structure was
essential in which the projecting portion 72d was provided so as to
support the rubber film 73 in the peripheral portion of the mid
plate 72. However, the present inventors found that the structure
was not essential. That is, the present inventors found that the
problems can be solved by configuring in such a manner that the mid
plate and the rubber film do not contact one another to provide a
gap between them throughout the whole surface of the lower face
portion of the mid plate and that the shape of the rubber film can
be stably maintained, and thereby bringing the present invention to
completion.
[0040] Hereinafter, a polishing head and a polishing apparatus
according to the present invention will be explained specifically
referring to the attached figures. However, the present invention
is not limited thereto.
[0041] FIG. 1 show an example of the polishing head according to
the present invention (a first embodiment). The polishing head 11
comprises an approximately discoid mid plate 12 and a rubber film
(an elastic film) 13 covering at least a lower face portion 12a and
a side face portion 12b of the mid plate 12. The rubber film 13 is
fixed to the mid plate 12 on the peripheral portion 12c of the
upper face of the mid plate. The rubber film can be fixed on a
peripheral portion 12c of an upper face of the mid plate, for
example, in such a manner that the rubber film is adhered using an
adhesive, is pinched with a back plate 18 and is fixed using a
screw and the like. In this case, the mid plate 12 and the rubber
film 13 do not contact one another to have a gap 14a at least
throughout the whole of the lower face portion 12a. The rubber film
can be formed by a conventionally known method to prepare the
rubber film 13 having the shape as described above. A thickness of
the rubber film is not particularly restricted and a suitable
thickness can be appropriately selected. For example, it can be a
thickness of about 1 mm.
[0042] A space portion 14 is thus defined between the mid plate 12
and the rubber film 13, at least between the lower face portion 12a
of the mid plate and the rubber film 13. A pressure adjustment
mechanism 15 is further provided to adjust the pressure of the
space portion 14. The pressure of the space portion 14 is adjusted,
for example, by supplying a pressurized fluid through a
through-hole 16 provided in the mid plate 12.
[0043] It is preferable to configure the polishing head 31 in such
a manner that the mid plate and the rubber film 13 also do not
contact one another to have a gap 14b throughout the whole surface
of the side face portion 12b of the mid plate, like a second
embodiment of the polishing head according to the present invention
in which a schematic sectional view of the whole of the polishing
head is shown in FIG. 2 (a) and an enlarged view is shown in FIG. 2
(b). In this case, the rubber film 13 contacts with only the
peripheral portion 12c of the upper face of the mid plate and is
fixed. In this case, the rubber film can also be formed by a
conventionally known method.
[0044] It is to be noted that it is desirable that both of them are
not fixed by adhering and the like, as the case where there is not
the gap between the side face portion 12b of the mid plate and the
rubber film 13 and they contact one another unlike the polishing
head in which the mid plate and the rubber film 13 do not contact
one another to have the gap 14b throughout the whole surface of the
side face portion 12b of the mid plate as shown in FIG. 2.
[0045] Besides, a backing pad 17 can be attached to be provided on
the workpiece holding face of the rubber film 13 so as to more
surely hold the workpiece W. The backing pad 17 is made to contain
water so as to attach and to hold the workpiece W on the workpiece
holding face of the rubber film 13. The backing pad 17 can be made
of, for example, foamed polyurethane. By providing such backing pad
17 and having it contain water, the workpiece W can be surely held
by surface tension of the water contained in the backing pad
17.
[0046] In addition, the polishing head 11, 31 comprises a means for
pressing the mid plate 12 (or the whole of the polishing head 11,
31) (not shown).
[0047] With the polishing head 11, 31 configured as described
above, the mid plate 12 is pressed toward the polishing pad 22
attached onto the turn table 21 by the means for pressing the mid
plate, which not shown, and the workpiece W is brought into sliding
contact with the polishing pad 22 for polishing the workpiece
surface. The means for pressing the mid plate is preferably able to
press the mid plate throughout the whole face with a uniform
pressure.
[0048] As an example is shown in FIG. 10 regarding the case of the
first embodiment (the polishing head 11), the polishing head 11, 31
can comprise a retainer ring 19 that is placed along the peripheral
portion of the lower face portion of the rubber film 13 and that is
capable of pressing the polishing pad 22 working with or being
independent from the workpiece holding face of the rubber film 13.
The retainer ring 19 can be configured, for example, such that a
guide ring 19a, which holds the edge portion of the workpiece W,
and a dress ring 19b, which is placed outside the guide ring 19a
and that performs dressing of the polishing pad 22.
[0049] It is desirable that the distance of the gap 14a between the
lower face portion 12a of the mid plate and the rubber film 13 is
sufficient so that the lower face portion 12a of the mid plate and
the rubber film 13 do not contact one another during polishing. Its
limit is desirably less than 1 mm. When the distance is less than 1
mm, the pressure of the space portion 14 can be easily controlled
to be stably uniform throughout the whole surface. Also, in the
case of the second embodiment shown in FIG. 2, the same settings
are applied to the distance of the gap 14a between the lower face
portion 12a of the mid plate and the rubber film 13, but the
distance of the gap 14b between the side face portion 12b of the
mid plate and the rubber film 13 is not particularly restricted.
However, it is desirable that the distance that makes the shape of
the rubber film 13 unstable is avoided. For example, it is
desirably about 2 mm or less.
[0050] The structure of the polishing head 11, 31 as described
above enables adjusting the shape and the pressure distribution of
the rubber film 13 by the pressure of the space portion 14. In
addition to this, since the lower face portion 12a of the mid plate
and the rubber film 13 do not contact one another, the stiffness of
the mid plate, the shape of the mid plate or the like has no affect
on the rubber film 13 and consequently the workpiece W can be
polished with a uniform polishing pressure.
[0051] The structure of the polishing head 31 in which the side
face portion 12b of the mid plate and the rubber film 13 do not
contact one another as the second embodiment described above
enables preventing not only the influence of the lower face portion
12a of the mid plate on the rubber film 13 but also the influence
of the side face portion 12c on the rubber film 13.
[0052] In the present invention, in the case of holding the
workpiece W on the approximately whole of the lower face portion of
the rubber film 13, for example the retainer ring 19, which holds
the edge portion of the workpiece W, is placed outside the
workpiece holding face of the rubber film 13 and the workpiece W is
held on the approximately whole of the lower face portion of the
rubber film 13, a particularly high effect of improving the
polishing stock removal uniformity is achieved by the structure
such that there is not a contact portion between the lower face
portion 12a of the mid plate and the rubber film 13 as well as a
conventional polishing head. However, the present invention is not
restricted thereto. When the workpiece is held in state where an
outer diameter of the workpiece is located inside the peripheral
portion of the rubber film 13, the present invention can also
completely dissolve the influence of the pressure distribution
conventionally occurring on the workpiece holding face of the
rubber film 13 due to existence of the contact portion between the
lower face portion 12a of the mid plate and rubber film 13, and can
consequently improve the polishing stock removal uniformity in
comparison with a conventional polishing head.
[0053] The present invention can completely dissolve the influence
of the stiffness and the shape of the lower face portion 12a of the
mid plate on the workpiece holding portion of the rubber film 13.
In contrast, when the workpiece is held on the whole of the lower
face portion of the rubber film 13, for example in the case that
the retainer ring 19, which holds the edge portion of the workplace
W, is placed outside the workpiece holding portion of the rubber
film 13 and the workpiece W is held on the approximately whole of
the lower face portion of the rubber film 13, the influence of the
stiffness of the portion (hereinafter also referred to as a rubber
film side portion) covering the side face portion 12b of the mid
plate in the rubber film 13 remains on the rubber film 13. The
influence of the stiffness of the rubber film side portion is minor
than the influence of the mid plate 12. However, the influence is
preferably suppressed as much as possible to further improve the
polishing stock removal uniformity of the workpiece W.
[0054] FIG. 4 show enlarged views the peripheral portion of the
polishing head for reducing the influence of the rubber film side
portion. FIG. 4 (a) shows the case of the first embodiment and FIG.
4 (b) shows the case of the second embodiment. As shown in FIGS. 4
(a) and (b), it is preferable that an outer diameter of the portion
(the rubber film side portion) 13b covering the side face portion
12b of the mid plate in the rubber film 13 is larger than that of
the workpiece W. However, for example, in the case that the
retainer ring, which holds the edge portion of the workplace W, is
placed outside the workpiece holding face of the rubber film 13 and
the workpiece W is held on the approximately whole of the lower
face portion of the rubber film 13, by reason that a size of the
retainer ring is set beforehand etc., it can be difficult to
configure such that an inner diameter of the rubber film side
portion 13b is larger than an outer diameter of the workpiece W. In
this case, the inner diameter of the rubber film side portion 13b
can be larger than at least a flatness quality area of the
workpiece W.
[0055] The flatness quality area of the workpiece is an area where
a prescribed flatness is guaranteed in the whole surface of the
workpiece. It is determined by specifications. For example in the
case of a silicon single crystal wafer having a diameter of 300 mm,
it is normally the area except about 1 to 2 mm of the outermost
periphery.
[0056] The structure and the placement of the mid plate 12 and
rubber film 13 for the workpiece W enable reducing the influence of
the stiffness of the rubber film side portion 13b on the workpiece
holding face of the rubber film 13 and further improving the
polishing stock removal uniformity while the polishing is
performed.
[0057] As described above, the backing pad 17 can be attached to be
provided on the lower face of the rubber film 13 to hold the
workpiece W on the workpiece holding face of the rubber film 13. In
this case, as shown FIG. 11, it is preferable that a diameter of
the backing pad 17 is larger than a diameter of the workpiece W. It
is noted to be that FIG. 11 (a) shows the case of the first
embodiment and FIG. 11 (b) shows the case of the second embodiment.
These structures bring about reducing the influence on the
polishing pressure or the polishing shape that occurs by reason
that the inflation of the rubber film 13 itself is restricted by
the backing pad 17 in the adhering boundary between the baking pad
17 and rubber film 13.
[0058] However, of course, the diameter of the backing pad 17 needs
to be equal to that of the lower face portion of the rubber film 13
on which the backing pad 17 is attached to be provided or to be
less than that. In particular, in the case that the retainer ring,
which holds the edge portion of the workpiece W, is placed outside
the workpiece holding face of the rubber film 13 and the workpiece
W is held on the approximately whole of the lower face portion of
the rubber film 13, a size of the backing pad cannot be made to be
so large. For example, when a silicon wafer having a diameter of
300 mm as the workpiece is polished, the inner diameter of the
retainer ring is about 302 mm. In this case, when the diameter of
the lower face portion of the rubber film 13 is 301.5 mm or less,
the diameter of the baking pad is also 301.5 mm or less.
[0059] However, as described above, when the diameter of the baking
pad 17 is even slightly larger than that of the workpiece W, the
polishing stock removal uniformity of the workpiece W can be more
effectively improved.
[0060] FIG. 3 shows an outline of a polishing apparatus 61 provided
with the polishing head 11 described above. The polishing apparatus
61 comprises a polishing pad 22 attached onto a turn table 21 and a
polishing agent supply mechanism 66 for providing a polishing agent
65 onto the polishing pad 22 in addition to the polishing head
11.
[0061] When the workpiece W is polished using the polishing
apparatus 61, first the workpiece W is held on the rubber film 13.
In the case that the backing pad 17 is attached to be provided on
the rubber film 13, the back surface of the workpiece W can be held
on the rubber film 13 by attaching the workpiece W onto the backing
pad 17 containing water. In the case that the retainer ring is
placed in the periphery of the rubber film 13, the edge of the
workpiece W is held by the retainer ring.
[0062] Then, the polishing agent 65 is supplied onto the polishing
pad 22 through the polishing agent supply mechanism 66, and while
the polishing head 11 and the turn table 21 are rotated in
predetermined directions respectively, the workpiece W is brought
into sliding contact with the polishing pad 22. The front surface
of the workpiece W can be polished by pressing the workpiece W held
by the rubber film 13 toward the polishing pad 22 on the turn table
21 with a predetermined pressing force while rotating it.
[0063] When the workpiece W is polished using the polishing
apparatus 61 provided with the polishing head 11 as described
above, the shape and the pressure distribution of the rubber film
13 can be adjusted by the pressure of the space portion 14. In
addition to that, since the lower face portion 12a of the mid plate
and the rubber film 13 do not contact one another, the stiffness,
the shape of the mid plate or the like has no affect on the rubber
film 13 and consequently the workpiece W can be polished with a
uniform polishing pressure.
[0064] The polishing apparatus in which the polishing head 11 shown
in FIG. 3 is replaced with the polishing head 31 shown in FIG. 2
can achieve the same effects.
[0065] Hereinafter, Examples and Comparative Example of the present
invention are explained.
Example 1
[0066] The polishing head 11 configured as shown in FIG. 1 was
manufactured as follows.
[0067] The rubber film 13 having a thickness of 1 mm of which a
diameter of the lower face portion is 300 mm was fit with the mid
plate 12 having a outer diameter of 298 mm, and was pinched with
the back plate 18 to fix using a screw so that the gap 14a between
the lower face portion 12a of the mid plate and rubber film 13 was
0.5 mm. The backing pad 17 having a diameter of 298 mm was attached
to be provided on the lower face portion of the rubber film 13. The
retainer ring having an inner diameter of 302 mm was placed in the
periphery of the rubber film 13.
[0068] A silicon single crystal wafer having a diameter of 300 mm
and a thickness of 775 .mu.m as the workpiece W was polished using
the polishing apparatus provided with the polishing head 11
described above as follows. The used silicon single crystal wafer
was subjected to first polishing on its both surfaces in advance
and its edge portion was also polished. The turn table 21 having a
diameter of 800 mm and a usual polishing pad 22 were used.
[0069] At the polishing, an alkaline solution containing colloidal
silica was used as the polishing agent, and the polishing head 11
and the turn table 21 were rotated at 42 rpm and 44 rpm
respectively. A polishing load (pressing force) of the workpiece W
was set as the pressure of the space portion 14 were 28, 29 and 30
kPa and the two workpieces were polished with each polishing load
respectively. The polishing time was 80 seconds.
[0070] The polishing stock removal uniformity of the workpiece W
polished as described above was evaluated.
[0071] It is to be noted that the polishing stock removal
uniformity is obtained by measuring the thickness of the workpiece
before and after the polishing in a region excluding an outermost
circumference portion 2-mm width as a flatness quality area in a
plane by a flatness measurement instrument and by taking a
difference in the polishing stock removal and represented by a
formula of polishing stock removal uniformity (%)=(maximum
polishing stock removal in the plane-minimum polishing stock
removal in the plane)/average polishing stock removal in the
plane.
[0072] The polishing stock removal uniformity of the workpiece
obtained from the result is shown in FIG. 5. The obtained polishing
stock removal uniformity was about 25 to 30% and was good.
Example 2
[0073] The polishing head 31 as shown in FIG. 2 was manufactured as
with Example 1 except that the mid plate 12 having an outer
diameter of 296 mm was used and the gap 14b between the lower face
portion 12b of the mid plate and rubber film 13 was 1 mm.
[0074] Silicon single crystal wafers were polished using the
polishing head 31 as with Example 1.
[0075] The polishing stock removal uniformity of the workpiece
obtained from the result is shown in FIG. 5. The obtained polishing
stock removal uniformity was about 15 to 25% and was further
improved in comparison with Example 1.
Comparative Example
[0076] As with Example 1, silicon single crystal wafers were
polished using the conventional polishing head 71 as shown in FIG.
8.
[0077] The polishing stock removal uniformity of the workpiece
obtained from the result is shown in FIG. 5. The obtained polishing
stock removal uniformity, which had variation though, was about 50
to 80% and became worse than Examples 1 and 2.
[0078] From the results described above, in Example 1 and 2 having
the structure of the polishing head according to the present
invention, the polishing stock removal uniformity of the workpiece
is improved in comparison with the conventional polishing head and
the effect of the present invention is clearly achieved.
Example 3
[0079] As with Example 2 described above, except of using the
polishing head 31 manufactured in such a manner that the inner
diameter of the rubber film side portion 13b was varied in the
range of 296.9 to 299.5 mm, a silicon single crystal wafer having a
diameter of 300 mm was used as the workpiece W and the one
workpiece was polished respectively with the polishing load of 30
kPa. The outer diameter of the rubber film side portion and the
lower portion of the rubber film were 298.9 to 301.5 mm since the
thickness of the rubber film was 1 mm. The flatness quality area of
the workpiece W was 298 mm in the case of excepting a width of the
workpiece outermost peripheral portion of 1 mm and it was 296 mm in
the case of excepting a width of the workpiece outermost peripheral
portion of 2 mm.
[0080] The polishing stock removal uniformity of the workpiece
obtained from the result is shown in FIG. 6. There is a tendency
that the larger the inner diameter of the rubber film side portion
13b is, the more the polishing stock removal uniformity
improve.
Example 4
[0081] As with Example 2 described above, except that the inner
diameter of the rubber film side portion 13b was 299.5 mm, the
polishing load was 30 kPa and the diameter of the backing pad 17
was varied in the range of 298 to 300.4 mm, a silicon single
crystal wafer having a diameter of 300 mm was used as the workpiece
W and the one workpiece was polished respectively.
[0082] The polishing stock removal uniformity of the workpiece
obtained from the result is shown in FIG. 7. The polishing stock
removal uniformity was further improved in the case that the
diameter of the backing pad 17 is larger than 300 mm, which is the
same as the diameter of the workpiece W in this case.
[0083] 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 influences as those in the technical concept
described in claims of the present invention are included in the
technical scope of the present invention.
[0084] For example, the polishing head according to the present
invention is not restricted to the embodiments shown in FIGS. 1 and
2. The shape and the like of the polishing head can be designed as
far as the whole of the lower face portion of the mid plate and the
rubber film do not contact one another.
[0085] The feature of the polishing apparatus is not also
restricted to one shown in FIG. 3. The polishing apparatus can
comprise a plurality of the polishing heads according to the
present invention.
* * * * *