U.S. patent application number 14/671506 was filed with the patent office on 2015-10-29 for polishing method and holder.
This patent application is currently assigned to FUJIMI INCORPORATED. The applicant listed for this patent is FUJIMI INCORPORATED. Invention is credited to Hiroshi Asano, SHINGO OTSUKI.
Application Number | 20150306727 14/671506 |
Document ID | / |
Family ID | 54269635 |
Filed Date | 2015-10-29 |
United States Patent
Application |
20150306727 |
Kind Code |
A1 |
OTSUKI; SHINGO ; et
al. |
October 29, 2015 |
POLISHING METHOD AND HOLDER
Abstract
A polishing method includes a polishing process of polishing a
surface to be polished of an object by relatively rotating a
holding fixture and a polishing pad with the surface to be polished
of the object held on the holding fixture being pressed against and
placed in contact with the polishing pad, while supplying a
polishing composition onto the polishing pad. During the polishing
process, the object held on the holding fixture turns around with
the surface to be polished of the object facing the polishing pad
to change the orientation of the object.
Inventors: |
OTSUKI; SHINGO; (Kiyosu-shi,
JP) ; Asano; Hiroshi; (Kiyosu-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIMI INCORPORATED |
Kiyosu-shi |
|
JP |
|
|
Assignee: |
FUJIMI INCORPORATED
Kiyosu-shi
JP
|
Family ID: |
54269635 |
Appl. No.: |
14/671506 |
Filed: |
March 27, 2015 |
Current U.S.
Class: |
451/59 ;
451/398 |
Current CPC
Class: |
B24B 37/30 20130101;
B24B 37/02 20130101 |
International
Class: |
B24B 37/02 20060101
B24B037/02; B24B 37/30 20060101 B24B037/30 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 1, 2014 |
JP |
2014-075649 |
Claims
1. A polishing method comprising a polishing process of polishing a
surface to be polished of an object by relatively rotating a
holding fixture and a polishing pad with the surface to be polished
of the object held on the holding fixture being pressed against and
placed in contact with the polishing pad, while supplying a
polishing composition onto the polishing pad, wherein during the
polishing process, the object held on the holding fixture turns
around with the surface to be polished of the object facing the
polishing pad to change the orientation of the object.
2. The polishing method according to claim 1, wherein the polishing
process includes temporarily stopping an operation to polish the
surface to be polished of the object to restart the operation to
polish the surface to be polished of the object after changing the
orientation of the object.
3. The polishing method according to claim 1, wherein the object is
one of a plurality of objects to be polished held on the holding
fixture.
4. The polishing method according to claim 1, wherein the surface
to be polished of the object is a curvilinear surface, and the
surface to be polished of the object is polished while pressing the
object against the polishing pad and deforming the polishing pad
into a shape conforming to the surface to be polished, which is the
curvilinear surface.
5. The polishing method according to claim 4, wherein the polishing
process is carried out by disposing a spacer between the holding
fixture and the object and placing the surface to be polished of
the object in a state of projecting toward the polishing pad.
6. The polishing method according to claim 1, wherein the surface
to be polished of the object is composed of a plurality of
surfaces, and the surface to be polished of the object is polished
while pressing the object against the polishing pad and deforming
the polishing pad into a shape conforming to the surface to be
polished, which is composed of the plurality of surfaces.
7. The polishing method according to claim 6, wherein the polishing
process is carried out by disposing a spacer between the holding
fixture and the object and placing the surface to be polished of
the object in a state of projecting toward the polishing pad.
8. A holding fixture used in a polishing method of polishing a
surface to be polished of an object by relatively rotating the
holding fixture and a polishing pad with the surface to be polished
of the object held on the holding fixture being pressed against and
placed in contact with the polishing pad, while supplying a
polishing composition onto the polishing pad, the holding fixture
comprising: a polishing head for holding the object; and a rotating
mechanism for turning around the object held on the polishing head
with the surface to be polished of the object facing the polishing
pad to change the orientation of the object.
9. The holding fixture according to claim 8, wherein the rotating
mechanism is provided with a rotating table onto which the object
is fixed.
10. The holding fixture according to claim 9, further comprising a
spacer disposed between the rotating table and the object to
project the surface to be polished of the object toward the
polishing pad.
11. The holding fixture according to claim 9, wherein the rotating
table is arranged so as to project from the polishing head toward
the polishing pad.
12. The holding fixture according to claim 8, wherein the polishing
head is configured to be able to hold a plurality of objects to be
polished.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a polishing method
including a polishing process of polishing a surface to be polished
of an object by relatively rotating a holding fixture and a
polishing pad with the surface to be polished of the object held on
the holding fixture being pressed against and placed in contact
with the polishing pad, while supplying a polishing composition
onto the polishing pad, and to the holding fixture used in the
polishing method.
[0002] Conventionally, there has been known a method for polishing
a surface to be polished of an object by relatively rotating a
holding fixture and a polishing pad with the surface to be polished
of the object held on the holding fixture being pressed against and
placed in contact with the polishing pad, while supplying a
polishing composition onto the polishing pad. This type of
polishing method is practiced using a single-sided polishing
apparatus or a double-sided polishing apparatus. For example,
Japanese Laid-Open Patent Publication No. 2011-253896 discloses a
method for polishing one surface of a semiconductor wafer using a
single-sided polishing apparatus. Japanese Laid-Open Patent
Publication No. 7-156061 discloses a method for simultaneously
polishing both surfaces of a computer disk substrate including
magnetic films on both sides using a double-sided polishing
apparatus.
[0003] Hereinafter, the configuration of a single-sided polishing
apparatus and a conventional polishing method using the
single-sided polishing apparatus will be described with reference
to FIGS. 12A and 12B. As illustrated in FIG. 12A, a single-sided
polishing apparatus 10 is provided with a surface plate 11 that
rotates around a rotational axis extending in the vertical
direction. A polishing pad 12 is attached to the upper surface of
the surface plate 11. A plurality of holding fixtures 13, each
being provided with a polishing head 14 that rotates around a
rotational axis P1 extending in the vertical direction, are
disposed on the polishing pad 12. As illustrated in FIG. 12B, a
plurality of (three) objects W are held on the lower surface of the
polishing head 14 of each holding fixture 13 with the surface to be
polished of each object W facing down. The objects W held on each
holding fixture 13 are arranged around the rotational axis P1 of
the corresponding polishing head 14 in the circumferential
direction thereof.
[0004] As illustrated in FIG. 12A, the surface plate 11 and the
polishing head 14 of each holding fixture 13 are rotated at
predetermined rotational speeds with an object W held on the lower
surface of the polishing head 14 of the holding fixture 13 being
pressed against and placed in contact with a polishing pad 12,
while supplying a polishing composition 15 onto the polishing pad
12. Consequently, the surface of the object W held on the holding
fixture 13 is polished by the polishing pad 12 and the polishing
composition 15.
SUMMARY OF THE INVENTION
[0005] Incidentally, polishing unevenness is caused in some cases
on a polished surface of the object when the above-described
conventional polishing method is used. Specifically, as illustrated
in FIG. 12B, the polished amount of a location A (location
positioned on the inner side of the object), which is close to the
rotational axis P1 of the polishing head 14 is smaller in some
cases than the polished amount of a location B (location positioned
on the outer side of the object), which is far away from the
rotational axis P1 of the polishing head 14.
[0006] This problem is considered to be attributable to the
polishing composition 15 supplied to the surface to be polished of
the object W. That is, since the polishing head 14 rotates around
the rotational axis P1 during polishing, the polishing composition
15 supplied onto the polishing pad 12 gets into between the object
W and the polishing pad 12 from the periphery of the polishing head
14 and flows inward in the radial direction of the polishing head
14. Accordingly, the location B of the object W, which is
positioned radially outward of the polishing head 14, is polished
using a fresh polishing composition 15. On the other hand, the
location A, which is positioned radially inward of the polishing
head 14, is polished using the polishing composition 15 that has
already been used to polish the location B and is, therefore, not
fresh since abrasive grains or the like of the composition are
worn-out. As described above, a difference in the degree of wear of
the polishing composition 15 (i.e., whether or not the polishing
composition 15 is fresh) used to polish the respective locations of
the object W is considered to be contributory to a
location-by-location variation in the amount of polishing. The
above-described problem of polishing unevenness occurs not only in
polishing methods using a single-sided polishing apparatus but also
in polishing methods using a double-sided polishing apparatus.
[0007] An objective of the present invention, which has been
accomplished in view of such circumstances as described above, is
to provide a polishing method and a holding fixture capable of
preventing the occurrence of polishing unevenness.
[0008] In order to achieve the objective described above and in
accordance with one aspect of the present invention, there is
provided a polishing method including a polishing process of
polishing a surface to be polished of an object by relatively
rotating a holding fixture and a polishing pad with the surface to
be polished of the object held on the holding fixture being pressed
against and placed in contact with the polishing pad, while
supplying a polishing composition onto the polishing pad. During
the polishing process, the object held on the holding fixture turns
around with the surface to be polished of the object facing the
polishing pad to change the orientation of the object.
[0009] The polishing process preferably includes temporarily
stopping an operation to polish the surface to be polished of the
object to restart the operation to polish the surface to be
polished of the object after changing the orientation of the
object.
[0010] The object is preferably one of a plurality of objects to be
polished held on the holding fixture.
[0011] The surface to be polished of the object may be a
curvilinear surface. In that case, the surface to be polished of
the object is preferably polished while pressing the object against
the polishing pad and deforming the polishing pad into a shape
conforming to the surface to be polished, which is the curvilinear
surface.
[0012] The surface to be polished of the object may be composed of
a plurality of surfaces. In that case, the surface to be polished
of the object is preferably polished while pressing the object
against the polishing pad and deforming the polishing pad into a
shape conforming to the surface to be polished, which is composed
of the plurality of surfaces.
[0013] The polishing process is preferably carried out by disposing
a spacer between the holding fixture and the object and placing the
surface to be polished of the object in a state of projecting
toward the polishing pad.
[0014] In order to achieve the objective described above and in
accordance with another aspect of the present invention, there is
provided a holding fixture used in a polishing method of polishing
a surface to be polished of an object by relatively rotating the
holding fixture and a polishing pad with the surface to be polished
of the object held on the holding fixture being pressed against and
placed in contact with the polishing pad, while supplying a
polishing composition onto the polishing pad. The holding fixture
is provided with a polishing head for holding the object; and a
rotating mechanism for turning around the object held on the
polishing head with the surface to be polished of the object facing
the polishing pad to change the orientation of the object.
[0015] The rotating mechanism is preferably provided with a
rotating table onto which the object is fixed.
[0016] The holding fixture is preferably further provided with a
spacer disposed between the rotating table and the object to
project the surface to be polished of the object toward the
polishing pad.
[0017] The rotating table is preferably arranged so as to project
from the polishing head toward the polishing pad.
[0018] The polishing head is preferably configured to be able to
hold a plurality of objects to be polished.
[0019] Other aspects and advantages of the invention will become
apparent from the following description taken in conjunction with
the accompanying drawings illustrating examples of the principles
of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIGS. 1A, 1B, and 1C are illustrations of surfaces to be
polished of objects;
[0021] FIG. 2 is a side view and a partial cross-sectional view of
a holding fixture;
[0022] FIG. 3 is a cross-sectional view illustrating a state of an
object to be polished being pressed against and placed in contact
with a polishing pad;
[0023] FIGS. 4A, 4B, 4C, and 4D are schematic views used to
describe the orientations of objects to be polished in a polishing
process;
[0024] FIG. 5 is an illustration of a holding fixture provided with
a rotating mechanism;
[0025] FIG. 6 is another illustration of a holding fixture provided
with a rotating mechanism;
[0026] FIG. 7 is an illustration of a holding fixture and a
spacer;
[0027] FIG. 8 is an illustration of a holding fixture provided with
a rotating mechanism and a spacer;
[0028] FIG. 9 is an illustration of a holding fixture provided with
a rotating mechanism;
[0029] FIGS. 10A, 10B, and 10C are illustrations of surfaces to be
polished of objects;
[0030] FIGS. 11A and 11B are illustrations of examples;
[0031] FIG. 12A is an illustration of a polishing method and a
single-sided polishing apparatus; and
[0032] FIG. 12B is a bottom view of a holding fixture.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] Hereinafter, one embodiment of the present invention will be
described.
[0034] First, a description will be made of an object W to be
polished using a polishing method of the present embodiment.
[0035] As the object W to be polished, it is possible to use an
object composed of metal, synthetic resin, ceramics, or a composite
thereof. Examples of the metal include magnesium, aluminum,
titanium, iron, nickel, cobalt, copper, zinc, manganese, and alloys
consisting primarily of at least one of these metals. Examples of
the synthetic resin include thermosetting resins, such as phenol
resin, epoxy resin, urethane resin, and polyimide, and
thermoplastic resins, such as polyethylene, polypropylene, and
acrylic resin. Examples of the ceramics include oxides, carbides,
nitrides, and borides of silicon, aluminum, zirconium, calcium, and
barium, in addition to pottery, glass, and fine ceramics.
[0036] The outer shape of the object W is not limited in particular
but may be polygonal, such as triangular and quadrangular,
circular, elliptical, or annular.
[0037] The object W includes, as one surface thereof, a surface to
be polished. The shape of the surface to be polished is not limited
in particular. Specifically, as illustrated in FIG. 1A, the object
W may include a flat surface W1 to be polished. Alternatively, as
illustrated in FIG. 1B, the object W may include a surface W2 to be
polished part or the entirety of which is a curvilinear surface.
The surface W2 may be curved so as to be convexed toward the outer
side thereof or so as to be convexed toward the inner side thereof,
or may have a shape combining these shapes. Yet alternatively, as
illustrated in FIG. 1C, the object W may include a surface W3 to be
polished composed of a plurality of surfaces W3a, W3b, and W3c. The
surface W3 may be polyhedrally shaped so as to be convexed toward
the outer side thereof or so as to be convexed toward the inner
side thereof, or may have a shape combining these shapes. One or
more of the surfaces constituting the surface W3 may be a
curvilinear surface. The surface W3 has only to be composed of two
or more surfaces.
[0038] Next, a description will be made of a polishing apparatus
used in the polishing method of the present embodiment.
[0039] Such a conventional single-sided polishing apparatus 10 as
illustrated in FIGS. 12A and 12B can be used in the polishing
method of the present embodiment. The single-sided polishing
apparatus 10 is provided with a surface plate 11 that rotates
around a rotational axis extending in the vertical direction. The
surface plate 11 is coupled with an unillustrated motor and rotates
in response to driving of the motor.
[0040] A polishing pad 12 is attached to the upper surface of the
surface plate 11. The polishing pad 12 can be of any type of
polishing pad suited to polish the surface to be polished of the
object W according to, for example, the material of the object W
and the shape of the surface to be polished of the object W. The
polishing pad 12 preferably has a surface shape capable of
uniformly coming into contact with the entire surface to be
polished of the object W. From a similar point of view, the
thickness and hardness of the polishing pad 12 are set as
appropriate.
[0041] Specific examples of the material of the polishing pad 12
include fabric, nonwoven, resinated nonwoven, synthetic leather,
synthetic resin foams, and composites of these materials. The
polishing pad 12 may be composed of only one of the specific
examples described above or may be composed of a combination of
some of the specific examples described above.
[0042] The hardness of the polishing pad 12 is not limited in
particular. The polishing pad 12 has a Shore A hardness of
preferably 5 or higher, however, if the surface to be polished of
the object W has a non-planar shape, for example, a curvilinear
surface or a polyhedral shape composed of a plurality of surfaces.
The Shore A hardness of the polishing pad 12 can be measured using
a rubber hardness meter (A-type) compliant with the Japanese
Industrial Standard JIS K6253 after the polishing pad 12 is left to
stand for 60 minutes or longer in a dry condition with a humidity
of 20 to 60% and at room temperature.
[0043] In the single-sided polishing apparatus 10 illustrated in
FIG. 12A, a plurality of holding fixtures 13, each being provided
with a polishing head 14 that rotates around a rotational axis P1
extending in the vertical direction, are disposed above the
polishing pad 12. The polishing head 14 is coupled with an
unillustrated motor and rotates in response to driving of the
motor.
[0044] As illustrated in FIG. 12B, a plurality of objects W are
held on the lower surface of each polishing head 14 with the
surface to be polished of each object facing down (outward). A
holding section that, though excluded from the drawings, includes
recesses into which the respective objects W are fitted and a
mechanism onto which the objects W are vacuum-adsorbed is provided
on the lower surface of each polishing head 14. The objects W are
thus held by the holding sections. The objects W held on the lower
surface of each polishing head 14 are arranged around the
rotational axis P1 of the polishing head 14 in the circumferential
direction thereof.
[0045] Next, the polishing method of the present embodiment will be
described. Here, a description will be made of a case where such an
object W as illustrated in FIG. 1B, specifically, an object W
having a square outer shape and including a curvilinear surface W2
to be polished is polished.
[0046] As illustrated in FIGS. 2 and 12B, three objects W are held
on the lower surface of a polishing head 14a of a holding fixture
13, so that the surface W2 to be polished of each object W faces
down. Then, the holding fixture 13 is moved down toward a polishing
pad 12 to press the surface W2 of the object W held on the lower
surface of the polishing head 14 against the polishing pad 12 and
place the surface W2 in contact therewith.
[0047] At this time, the polishing pad 12 deforms into a shape
conforming to the surface W2, as illustrated in FIG. 3, as the
result of the curvilinear surface W2 being pressed against the
polishing pad. Consequently, the entire surface W2 comes into
contact with the polishing pad 12. In other words, the holding
fixture 13 is moved down to apply a load (polishing load) until the
polishing pad 12 deforms into the shape conforming to the surface
W2 and comes into contact with the entire surface W2. In FIGS. 2
and 3, the surface plate 11 is excluded from the drawings.
[0048] Subsequently, as illustrated in FIG. 12A, the surface plate
11 and the polishing head 14 of each holding fixture 13 are rotated
at the respective predetermined rotational speeds, while supplying
a polishing composition 15 onto the polishing pad 12. In this way,
the polishing pad 12 attached onto the surface plate 11 and objects
W held on the polishing head 14 of each holding fixture 13
relatively rotate in close contact with each other. Thus, the
surface W2 of each object W is polished by the polishing pad 12 and
the polishing composition 15 (polishing process).
[0049] As the polishing composition 15, it is possible to use a
known polishing composition, specifically, a processing liquid,
such as a polishing liquid, a lapping liquid, and a grinding fluid,
primarily containing abrasive grains and water. Examples of the
abrasive grains include alumina, silica, ceria, diamond, and
silicon carbide. The polishing composition 15 may contain only one
type or more than one type of the abrasive grains described above.
The polishing composition 15 may contain other components, such as
a surfactant, a polymer material, a pH adjuster, an antiscattering
agent, a thickening agent, and a redox agent.
[0050] Various conditions used in the polishing process described
above are not limited in particular but may be set as appropriate
according to, for example, the material and shape of the object W.
For example, the flow rate of the polishing composition 15 supplied
onto the polishing pad 12 is preferably 10 ml/min or higher. The
rotational speed of the surface plate 11 and the rotational speed
of the polishing head 14 of the holding fixture 13 are preferably
such that a linear velocity is within the range from 10 m/min to
300 m/min on the surface to be polished of each object W. The
polishing load is preferably 0.05 kg/cm.sup.2 to 10 kg/cm.sup.2 per
a unit area of the surface to be polished of each object W.
[0051] Also in the polishing method of the present embodiment, both
temporarily stopping a polishing operation, i.e., an operation to
relatively rotate the objects W and the polishing head 14 while
supplying the polishing composition 15 onto the polishing pad 12,
and changing the orientations of the objects W held on the
polishing head 14 of each holding fixture 13 are performed during a
polishing process when a predetermined period of time elapses.
[0052] Specifically, as illustrated in FIGS. 4A and 4B, each object
W is rotated 90.degree. clockwise around an axial line P2 parallel
to the rotational axis P1 of each holding fixture 13, while
maintaining the state of the surface W2 facing the polishing pad
12. That is, each object W is changed from the holding condition
illustrated in FIG. 4A to the holding condition illustrated in FIG.
4B to change the orientation of the object W. For ease of
understanding, a star is put as a mark of a location of the surface
to be polished of each object W initially positioned close to the
rotational axis P1 of the holding fixture 13 in FIGS. 4A to 4D. The
changing of the orientation of each object W is performed by
temporarily detaching the objects W from the polishing head 14 of
each holding fixture 13, and then once again holding the objects W
on the polishing head 14 with the orientations of the objects W
changed.
[0053] After the objects W are changed in orientation, a polishing
operation is performed under the holding condition illustrated in
FIG. 4B. Thereafter, each object W is changed from the holding
condition illustrated in FIG. 4B to the holding condition
illustrated in FIG. 4C to change the orientation of the object W in
the same way as described above, when another period of the
above-mentioned predetermined time elapses. Then, a polishing
operation is performed under the holding condition illustrated in
FIG. 4C. Thereafter, each object W is changed from the holding
condition illustrated in FIG. 4C to the holding condition
illustrated in FIG. 4D to change the orientation of the object W
when yet another period of the above-mentioned predetermined time
elapses. Then, a polishing operation is performed for the
above-mentioned predetermined period of time under the holding
condition illustrated in FIG. 4D. Accordingly, in the present
embodiment, the objects W are polished under each of the four
holding conditions in which the orientation of each object W
differs in increments of 90.degree..
[0054] Next, the action of the present embodiment will be
described.
[0055] As illustrated in FIGS. 4A to 4D and in accordance with the
polishing method of the present embodiment, the orientations of
objects W held on the polishing head 14 of each holding fixture 13
are changed during a polishing process. Thus, polishing operations
are performed under respective holding conditions in which the
orientations of the objects W differ. Accordingly, during a
polishing process, a specific location of the surface to be
polished of each object W neither continues to be placed in a
position (position radially outward of the polishing head 14) to
which a fresh polishing composition 15 is supplied and in which the
amount of polishing is relatively large nor continues to be placed
in a position (position radially inward of the polishing head 14)
to which a non-fresh polishing composition 15 is supplied and in
which the amount of polishing is relatively small. This therefore
prevents the occurrence of polishing unevenness in which a specific
location of the surface to be polished of each object W is larger
or smaller in the amount of polishing than other locations.
[0056] Next, the advantageous effects of the present embodiment
will be described.
[0057] (1) The polishing method includes a polishing process of
polishing a surface to be polished of an object W by rotating a
holding fixture 13 and a polishing pad 12 with the surface to be
polished of the object W held on the holding fixture 13 being
pressed against and placed in contact with the polishing pad 12,
while supplying a polishing composition 15 onto the polishing pad
12. During the polishing process, the object W held on the holding
fixture 13 turns around with the surface W2 to be polished of the
object W facing the polishing pad 12 to change the orientation of
the object W. Accordingly, the polishing method prevents the
occurrence of polishing unevenness in which a specific location of
the surface to be polished of each object W is larger or smaller in
the amount of polishing than other locations.
[0058] (2) The orientation of each object W is changed so that each
location of the surface to be polished of the object W switches in
rotation among a position (position radially outward of the
polishing head 14) where the amount of polishing is relatively
large, a position (position radially inward of the polishing head
14) where the amount of polishing is relatively small, and a
position intermediate between those positions. If the location of
each object W marked with a star in FIGS. 4A to 4D is taken for
example, the location is placed in a position where the location is
relatively less likely to be polished under the condition
illustrated in FIG. 4A, the location is placed in a position where
the location is relatively more likely to be polished under the
condition illustrated in FIG. 4C, and the location is placed in a
position intermediate between those positions under the conditions
illustrated in FIGS. 4B and 4D.
[0059] Accordingly, the entire surface to be polished of each
object W is likely to be polished more uniformly, compared with a
case where each object W is rotated in increments of 180.degree.,
rather than 90.degree., to change the orientation of the object W,
so that the object W switches between a position where the amount
of polishing is relatively small and a position where the amount of
polishing is relatively large. As a result, the occurrence of
polishing unevenness is prevented more effectively.
[0060] (3) The polishing process includes temporarily stopping the
operation to polish the surface to be polished of the object W,
changing the orientation of the object W, and then restarting the
operation to polish the surface to be polished of the object W.
Accordingly, it is possible to use an existing single-sided
polishing apparatus 10 as is.
[0061] (4) The object W includes a curvilinear surface W2 to be
polished, and the surface W2 is polished while pressing the object
W against the polishing pad 12 to deform the polishing pad 12 into
a shape conforming to the surface W2 to be polished. In this case,
the area of contact of the polishing pad 12 with the surface W2
increases, and the polishing pad 12 comes into very close contact
with the surface W2. For this reason, a polishing composition 15
having got into between the object W and the polishing pad 12 has
difficulty in flowing therebetween and is less likely to be
supplied inward in the radial direction of the polishing head 14
during the polishing process. As a result, the problem in which the
amount of polishing of a location A (positioned radially inward of
the polishing head 14), which is close to the rotational axis P1 of
the polishing head 14 is smaller than the amount of polishing of a
location B (positioned radially outward of the polishing head 14),
which is far away from the rotational axis P1 of the polishing head
14 develops remarkably (see FIG. 12B).
[0062] Accordingly, the effect of suppressing polishing unevenness
by the polishing method of the present embodiment is especially
significant when the surface W2 is polished while deforming the
polishing pad 12 into a shape conforming to the surface W2. The
same effect is available in a case where the object W includes a
plurality of surfaces W3 to be polished, and the surfaces W3 are
polished while pressing the object W against the polishing pad 12
to deform the polishing pad 12 into a shape conforming to the
surfaces W3 to be polished.
[0063] The present embodiment can be modified as described below
and put into effect. [0064] The number of objects W held on each
holding fixture 13 is not limited in particular, but may be two or
less or four or more. In addition, the number of objects W may
differ for each holding fixture 13. [0065] In the embodiment
described above, each holding fixture 13 is rotated by means of
motor drive. Methods for rotating the holding fixture 13 are not
limited to this method, however. For example, holding fixtures 13
may be disposed on the polishing pad 12 with the polishing head 14
being rotatable, and then the polishing pad 12 may be rotated. In
this case, the polishing head 14 of each holding fixture 13 rotates
correspondingly with the rotation of the polishing pad 12. [0066]
In the embodiment described above, both the holding fixtures 13 and
the polishing pad 12 are rotated in the polishing process.
Alternatively, the embodiment may be configured to relatively
rotate the holding fixtures 13 and the polishing pad 12. That is,
only the holding fixtures 13 may be rotated without rotating the
polishing pad 12, or only the polishing pad 12 may be rotated
without rotating the holding fixtures 13.
[0067] The problem of polishing unevenness in objects W due to the
difference in the degree of wear of the polishing composition 15
(i.e., whether or not the polishing composition 15 is fresh) arises
also when only the polishing pad 12 is rotated without rotating the
holding fixtures 13. That is, if only the polishing pad 12 is
rotated, the polishing composition 15 supplied onto the polishing
pad 12 flows arcuately along the rotational direction of the
polishing pad 12 and between each object W held on the holding
fixture 13 and the polishing pad 12.
[0068] Here, assume that in the example illustrated in FIG. 12B,
the polishing composition 15 flows arcuately from the upper side of
the drawing toward the lower side thereof. At this time, the
location B of each object W positioned on the upper side is
polished using a fresh polishing composition 15, whereas the
location A is polished using a non-fresh polishing composition 15
that has been used to polish the location B, and therefore, the
abrasive grains and the like of which are worn-out.
[0069] Conversely, assume that the polishing composition 15 flows
arcuately from the lower side of the drawing toward the upper side
thereof. At this time, the location A of each object W positioned
on the upper side is polished using a fresh polishing composition
15, whereas the location B is polished using a non-fresh polishing
composition 15 that has been used to polish the location A, and
therefore, the abrasive grains and the like of which are
worn-out.
[0070] In this way, the degree of wear of the polishing composition
15 used to polish the respective locations of each object W differs
also when only the polishing pad 12 is rotated without rotating the
holding fixtures 13. Thus, polishing unevenness occurs in the
object W due to this difference. Such polishing unevenness caused
when only the polishing pad 12 is rotated can also be prevented
from occurring by changing the orientation of the object W during
the polishing process. [0071] In the embodiment described above,
the orientation of each object W is changed three times in
increments of 90.degree. in the polishing process. The orientation
angle of each object W changed at a time is not limited to
90.degree., however. The number of times with which the orientation
of the object W is changed is not limited to three times, either.
For example, the orientation of the object W may be changed twice
in increments of 120.degree., or may be changed by 180.degree. only
once.
[0072] An angle S by which the orientation of each object W is
changed at a time and the number of times T with which the
orientation of each object W is changed are preferably in the
relationship satisfying "S(T+1)=360". In this case, it is possible
to more effectively prevent the occurrence of polishing unevenness.
The angle by which the orientation of each object W is changed may
be varied for each operation to change the orientation of the
object W. [0073] In the embodiment described above, the surface to
be polished is polished while pressing each object W against the
polishing pad 12 to deform the polishing pad 12 into a shape
conforming to the surface to be polished. Alternatively, however,
the surface to be polished may be polished by pressing each object
W against the polishing pad 12 to the extent of not deforming the
polishing pad 12 and bringing the object W into contact therewith.
This polishing method is suited, for example, for such an object W
including a flat surface W1 to be polished as illustrated in FIG.
1A. [0074] In the embodiment described above, the orientation of
each object W is changed by temporarily detaching the objects W
from the polishing head 14 of each holding fixture 13, and then
once again holding the objects W on the polishing head 14 with the
orientations of the objects W changed. The orientation of the
object W may be changed by other methods, however. For example, a
holding fixture 13 provided with a rotating mechanism for changing
the orientation of each object W may be used and the orientation of
the object W may be changed by operating the rotating mechanism, as
illustrated in FIGS. 5 and 6.
[0075] In the example illustrated in FIG. 5, an insertion hole 21
vertically penetrating through the polishing head 14 of each
holding fixture 13 is formed in the polishing head 14, and a
circular housing recess 22 centered around the opening of the
insertion hole 21 is formed on the lower surface of the polishing
head 14. A rotational axis 23 is inserted through the insertion
hole 21. A circular plate-like rotating table 24 received in the
housing recess 22 is fixed on the lower end of the rotational axis
23 projecting into the housing recess 22. An operating member 25 is
fixed on the upper end of the rotational axis 23 projecting from
the upper surface of the polishing head 14. In this case, the
rotating mechanism is configured with the rotational axis 23, the
rotating table 24, and the operating member 25.
[0076] In the configuration of FIG. 5, an object W is held on the
lower surface of the rotating table 24. An operator turns around
the operating member 25 when changing the orientation of the object
W. Consequently, the rotating table 24 and the object W held
thereon turn around in conjunction with each other by way of the
rotational axis 23, thereby changing the orientation of the object
W. According to the configuration described above, the object W
need not be detached from the polishing head 14 of the holding
fixture 13 when changing the orientation of the object W. Thus, it
is possible to easily change the orientation of the object W.
[0077] In the example illustrated in FIG. 6, the circular housing
recess 22 is formed in the lower surface of the polishing head 14
and the circular plate-like rotating table 24 is received in the
housing recess 22. The rotational axis of a motor 26 fitted in the
polishing head 14 is fixed on the rotating table 24. The holding
fixture 13 is provided with a control unit (not illustrated) for
controlling the revolution of the motor 26. In this case, the
rotating mechanism is configured with the rotating table 24, the
motor 26, and the control unit.
[0078] In the configuration of FIG. 6, an object W is held on the
lower surface of the rotating table 24. The control unit rotates
the motor 26 when the orientation of the object W is changed.
Consequently, the rotating table 24 and the object W held thereon
turn around, thereby changing the orientation of the object W.
[0079] According to the configuration of FIG. 6, it is possible to
change the orientation of the object W while performing a polishing
operation when changing the orientation of the object W.
Accordingly, the polishing operation need not be stopped
temporarily, and therefore, it is possible to shorten the time
required for a polishing process. [0080] As illustrated in FIG. 7,
a polishing operation may be performed with a spacer 30 disposed
between the polishing head 14 of the holding fixture 13 and the
object W. That is, the polishing operation may be performed with
the object W held on the polishing head 14 through the spacer 30.
In this case, the object W largely projects toward the polishing
pad 12 due to the presence of the spacer 30. Accordingly, it is
easy to press the object W against the polishing pad 12 when
polishing a plurality of surfaces W3 or a curvilinear surface W2
(see FIG. 1B), even if the object W is small in thickness. It is
therefore easy to deform the polishing pad 12 into a shape
conforming to the surface to be polished.
[0081] The same holds true when a holding fixture 13 including a
rotating mechanism is used. As illustrated in FIG. 8, a polishing
operation may be performed with the spacer 30 disposed between the
rotating table 24 and the object W. The same effect is available by
using a holding fixture 13 on which the rotating table 24 is
mounted to project from the lower surface of the polishing head 14,
as illustrated in FIG. 9, instead of using the spacer 30. [0082] In
a double-sided polishing method for polishing both sides of an
object W using a double-sided polishing apparatus, an operation to
change the orientations of the objects W may be performed during a
polishing process in the same way as in the embodiment described
above.
[0083] In this case, such an object including surfaces to be
polished on both sides as illustrated in FIG. 10A, 10B, or 10C is
used as the object W. FIG. 10A illustrates an object W including
flat surfaces W1 to be polished on upper and lower sides. FIG. 10B
illustrates an object W including surfaces W2 to be polished, part
or the entirety of each of which is a curvilinear surface, on upper
and lower sides. FIG. 10C illustrates an object W including
surfaces W3 to be polished, each of which is composed of a
plurality of surfaces W3a, W3b, and W3c, on upper and lower sides.
Although both the upper and lower sides of each object W have the
same shape in the examples illustrated in FIG. 10A to FIG. 10C, the
upper and lower sides of each object W may differ in shape from
each other.
[0084] As the double-sided polishing apparatus, it is possible to
use such a known double-sided polishing apparatus as disclosed in
Japanese Laid-Open Patent Publication No. 7-156061. The
double-sided polishing apparatus is provided with a pair of
polishing pads oppositely disposed on the upper and lower sides of
the apparatus; and a holding fixture for holding an object W to be
polished between these polishing pads. The holding fixture is, for
example, a plate-like member including a holding hole corresponding
in shape to the outer shape of the object W. The object W is
inserted in the holding hole and held by means of interaction, such
as engagement, between the inner circumferential surface of the
holding hole and a side surface Ws of the object W (see FIGS. 10A
to 10C), with both surfaces to be polished of the object W
projecting to the upper and lower sides of the holding fixture.
[0085] In the double-sided polishing method, a polishing process of
polishing two surfaces of the object W is carried out by relatively
rotating the holding fixture and the polishing pads with both
surfaces of the object W held on the holding fixture being pressed
against and placed in contact with the upper and lower polishing
pads, while supplying a polishing composition onto the polishing
pads. The object W is temporarily detached from the holding hole of
the holding fixture in the course of this polishing process.
Thereafter, the object W is inserted in the holding hole with the
orientation of the object W changed, and is once again held on the
holding fixture, as illustrated in, for example, FIGS. 4A to 4D.
Then, the polishing operation is restarted. If an operation to
change the orientation of the object W is performed during the
polishing process, as described above, in the double-sided
polishing method, it is possible to prevent polishing unevenness
from occurring in both surfaces to be polished of the object W in
the same way as in the embodiment described above.
[0086] Next, the present invention will be described more
specifically by referring to Examples and Comparative Examples.
Examples
[0087] Using the single-sided polishing apparatus illustrated in
FIG. 12A, a surface to be polished of each object was polished by
rotating a holding fixture and a polishing pad (surface plate) with
the surface to be polished of the object held on the holding
fixture being pressed against and placed in contact with the
polishing pad, while supplying a polishing composition onto the
polishing pad. Specific polishing conditions are as shown in Table
1 below.
TABLE-US-00001 TABLE 1 Polishing machine Type of polishing machine:
Single-sided polishing (polishing machine apparatus) Surface plate
diameter: .phi.914 mm Holding fixture (polishing head) diameter:
360 mm Polishing pad Suede-based polishing pad to the underlying
layer of which a resin sponge is attached Polishing load 530
g/cm.sup.2 Rotating speed 30 rpm of surface plate Linear velocity
67 m/min Polishing Abrasive grains: CeO.sub.2 (particle diameter
2.1 .mu.m) composition Abrasive grain content: 100 g/L pH: 7.0
Polishing 80 ml/min composition supply rate
[0088] Such a flat glass plate (56 mm in depth.times.60 mm in
width.times.0.86 mm in thickness) including a curvilinear surface
to be polished as illustrated in FIG. 1B was used as the object to
be polished. The holding conditions of the object with respect to
the holding fixture are as illustrated in FIG. 11A. The object was
pressed against the polishing pad under a polishing load with which
the polishing pad deformed into a shape conforming to the surface
to be polished.
[0089] The rotation of the surface plate and the holding fixture
was stopped in six minutes after the start of polishing operation.
Then, the object held on a holding fixture was turned around
180.degree. and changed from the holding condition illustrated in
FIG. 11A to the holding condition illustrated in FIG. 11B, thereby
changing the orientation of the object. Then, polishing was
restarted, and finished after a lapse of another six minutes.
[0090] Thereafter, a surface roughness measurement was made for the
respective locations WA, WB, and WC of the polished surface of each
object illustrated in FIGS. 11A and 11B. The location WA is an edge
of the curvilinear surface of the object W and is a location
positioned radially inward of the holding fixture at the time of a
first polishing operation and positioned radially outward of the
holding fixture at the time of a second polishing operation. The
location WB is an edge of the curvilinear surface of the object W
and is a location positioned radially outward of the holding
fixture at the time of the first polishing operation and positioned
radially inward of the holding fixture at the time of the second
polishing operation. The location WC is a middle portion of the
curvilinear surface of the object W and is a location positioned
radially at the center of the holding fixture at the time of both
the first and second polishing operations.
[0091] Table 2 shows the results of surface roughness measurement
of the respective locations described above. For reference, Table 2
also shows the surface roughness of each location before polishing.
Surface roughness measurements were conducted using the SURFCOM
1500DX surface roughness measuring instrument made by Tokyo
Seimitsu Co., Ltd under the conditions of "standard: JIS'94, filter
cut off: 250 .mu.m, measurement length: 1 mm".
Comparative Examples
[0092] Polishing operation was performed under the same polishing
conditions of Examples using the same object as in Examples. In
Comparative Examples, however, polishing was finished after the
object was polished for 10 minutes under the holding condition
illustrated in FIG. 11A, without performing the operation to change
the orientation of the object. Thereafter, the surface roughness of
the respective locations WA, WB, and WC of the polished surface of
the object was measured in the same way as in Examples. Table 2
shows the results of the measurement.
TABLE-US-00002 TABLE 2 Measured Surface roughness [nm] location
Before polishing Examples Comparative Examples WA 579 25 575 WB 606
28 13 WC 130 1.4 1.5
[0093] As shown in Table 2, in accordance with Comparative
Examples, in which the operation to change the orientation of the
object was not performed, polishing of the location WA (location
positioned radially inward of the holding fixture) progressed less
compared with the location WB (location positioned radially outward
of the holding fixture). Thus, polishing unevenness occurred
between the location WA and the location WB. In contrast, in
accordance with Examples, in which the operation to change the
orientation of the object was performed, the location WA and the
location WB were substantially the same in surface roughness. Thus,
no polishing unevenness occurred between the location WA and the
location WB.
[0094] The foregoing description is intended to be illustrative and
not restrictive. For example, the above-described examples (or one
or a plurality of aspects thereof) may be used in combination with
each other. By examining the foregoing description, other
embodiments may be used by, for example, a person skilled in the
art. In the detailed description presented above, various
characteristic features may be grouped together in order to
simplify the disclosure. This should not be construed as unclaimed
characteristic features of the disclosure being intended to be
essential for any claims for patent. Rather, the subject matter of
the present invention may lie in less than all characteristic
features of the specific embodiments disclosed. Accordingly, the
appended claims are incorporated into the detailed description,
with each claim claiming itself as a separate embodiment. The scope
of the present invention should be defined by reference to the
appended claims for patent and along with the full range of
equivalents to which the appended claims are entitled.
* * * * *