U.S. patent application number 10/548645 was filed with the patent office on 2006-08-03 for polishing tool and polishing apparatus.
Invention is credited to Katsuya Okumura, Manabu Tsujimura.
Application Number | 20060172665 10/548645 |
Document ID | / |
Family ID | 32984674 |
Filed Date | 2006-08-03 |
United States Patent
Application |
20060172665 |
Kind Code |
A1 |
Okumura; Katsuya ; et
al. |
August 3, 2006 |
Polishing tool and polishing apparatus
Abstract
A polishing tool is used for polishing a workpiece (13) such as
a semiconductor wafer to a flat mirror finish. The polishing tool
has a polishing table (10) and a polishing pad (11) attached to an
upper surface of the polishing table (10). The polishing pad (11)
has a plurality of polishing pad pieces (111) attached to the
polishing table (10). It is possible to facilitate adjustment of
polishing performance over a surface of the workpiece (13) and
replacement of a polishing pad (10).
Inventors: |
Okumura; Katsuya; (Tokyo,
JP) ; Tsujimura; Manabu; (Tokyo, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
32984674 |
Appl. No.: |
10/548645 |
Filed: |
March 12, 2004 |
PCT Filed: |
March 12, 2004 |
PCT NO: |
PCT/JP04/03378 |
371 Date: |
February 13, 2006 |
Current U.S.
Class: |
451/6 ; 451/285;
451/41 |
Current CPC
Class: |
B24B 37/24 20130101 |
Class at
Publication: |
451/006 ;
451/041; 451/285 |
International
Class: |
B24B 49/00 20060101
B24B049/00; B24B 7/30 20060101 B24B007/30; B24B 29/00 20060101
B24B029/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2003 |
JP |
2003-070894 |
Claims
1. A polishing tool for polishing a workpiece, said polishing tool
comprising: a polishing table; and a polishing pad attached to an
upper surface of said polishing table, said polishing pad having a
plurality of polishing pad pieces attached to said polishing
table.
2. The polishing tool as recited in claim 1, wherein said polishing
table has a plurality of recesses for receiving said plurality of
polishing pad pieces.
3. The polishing tool as recited in claim 2, wherein said plurality
of recesses has the same shape as said plurality of polishing pad
pieces.
4. The polishing tool as recited in claim 1, wherein said polishing
table includes a holding plate having a plurality of through-holes
for receiving said plurality of polishing pad pieces.
5. The polishing tool as recited in claim 4, wherein said plurality
of through-holes has the same shape as said plurality of polishing
pad pieces.
6. The polishing tool as recited in claim 1, wherein at least one
of said polishing pad pieces is attached to said polishing table by
a thermo-sensitive adhesive which is softened and lowered in
adhesive strength under a high temperature while it is hardened and
increased in adhesive strength under a room temperature.
7. The polishing tool as recited in claim 6, wherein the
thermo-sensitive adhesive comprises a liquid crystal material or a
hot-melt adhesive.
8. The polishing tool as recited in claim 6, wherein said polishing
table has a rough surface onto which the thermo-sensitive adhesive
is applied.
9. A polishing tool for polishing a workpiece, said polishing tool
comprising: a polishing table; a plurality of pedestals attached to
an upper surface of said polishing table; and a polishing pad
having a plurality of polishing pad pieces attached to said
plurality of pedestals.
10. The polishing tool as recited in claim 9, wherein said
polishing table has a plurality of recesses for receiving said
plurality of pedestals.
11. The polishing tool as recited in claim 10, wherein said
plurality of recesses has the same shape as said plurality of
pedestals.
12. The polishing tool as recited in claim 9, wherein said
polishing table includes a holding plate having a plurality of
through-holes for receiving said plurality of pedestals.
13. The polishing tool as recited in claim 12, wherein said
plurality of through-holes has the same shape as said plurality of
pedestals.
14. The polishing tool as recited in claim 9, wherein at least one
of said pedestals is attached to said polishing table by a
thermo-sensitive adhesive which is softened and lowered in adhesive
strength under a high temperature while it is hardened and
increased in adhesive strength under a room temperature.
15. The polishing tool as recited in claim 14, wherein the
thermo-sensitive adhesive comprises a liquid crystal material or a
hot-melt adhesive.
16. The polishing tool as recited in claim 14, wherein said
plurality of pedestals has a rough surface onto which the
thermo-sensitive adhesive is applied.
17. The polishing tool as recited in claim 9, wherein said
plurality of pedestals is attached to said polishing table by
vacuum attraction.
18. The polishing tool as recited in claim 9, wherein said
polishing table is made of a material having a high thermal
conductivity, wherein said plurality of pedestals is made of a
material having a low thermal conductivity.
19. The polishing tool as recited in claim 1, wherein said
polishing pad pieces are arranged so as to form gaps between
adjacent polishing pad pieces.
20. The polishing tool as recited in claim 19, further comprising
at least one weir disposed in said gaps.
21. The polishing tool as recited in claim 1, wherein each of said
polishing pad pieces has a size smaller than the workpiece.
22. The polishing tool as recited in claim 1, wherein said
polishing pad pieces have the same material properties and surface
shape.
23. The polishing tool as recited in claim 1, wherein said
plurality of polishing pad pieces comprises: at least one first
polishing pad piece; and at least one second polishing pad piece
having different material properties or surface shape than material
properties or surface shape of said at least one first polishing
pad piece.
24. A method of polishing a workpiece, said method comprising:
pressing the workpiece against the polishing tool as recited in
claim 1; supplying a polishing liquid to an upper surface of the
polishing tool; and moving the polishing tool and the workpiece
relative to each other to polish the workpiece.
25. A method of attaching a polishing pad to a polishing table,
said method comprising: applying a thermo-sensitive adhesive
between the polishing table and the polishing pad, the
thermo-sensitive adhesive being softened and lowered in adhesive
strength under a high temperature while being hardened and
increased in adhesive strength under a room temperature; heating
the thermo-sensitive adhesive when the polishing pad is disposed on
the polishing table; and cooling the thermo-sensitive adhesive
after said heating to bond the polishing pad to the polishing
table.
26. The method as recited in claim 25, wherein the polishing pad
has a plurality of polishing pad pieces attached to the polishing
table.
27. The method as recited in claim 25, wherein said heating
comprising introducing a heating medium adjusted in temperature
into the polishing table.
28. The method as recited in claim 25, wherein said cooling
comprising introducing a cooling medium adjusted in temperature
into the polishing table.
29. The method as recited in claim 25, wherein said heating
comprising heating the thermo-sensitive adhesive by a heating
device provided near an unbonded surface of the polishing pad.
30. The method as recited in claim 25, wherein said cooling
comprising cooling the thermo-sensitive adhesive by a cooling
device provided near an unbonded surface of the polishing pad.
31. A polishing apparatus for polishing a workpiece, said polishing
apparatus comprising: a polishing table; a polishing pad attached
to an upper surface of said polishing table, said polishing pad
having a plurality of polishing pad pieces attached to said
polishing table; a top ring for pressing the workpiece against said
polishing pad; a light source provided in said polishing table for
emitting light to a surface of the workpiece through an opening
formed between adjacent polishing pad pieces; and a light-receiving
portion provided in said polishing table for receiving light
reflected from the workpiece.
32. A polishing apparatus for polishing a workpiece, said polishing
apparatus comprising: a polishing table; a plurality of pedestals
attached to an upper surface of said polishing table; a polishing
pad having a plurality of polishing pad pieces attached to said
plurality of pedestals; a top ring for pressing the workpiece
against said polishing pad; a light source provided in said
polishing table for emitting light to a surface of the workpiece
through an opening formed between adjacent polishing pad pieces;
and a light-receiving portion provided in said polishing table for
receiving light reflected from the workpiece.
33. A polishing apparatus for polishing a workpiece, said polishing
apparatus comprising: a polishing table; a polishing pad attached
to an upper surface of said polishing table, said polishing pad
having at least one light-transmissive piece and a plurality of
polishing pad pieces attached to said polishing table; a top ring
for pressing the workpiece against said polishing pad; a light
source provided in said polishing table for emitting light to a
surface of the workpiece through said at least one
light-transmissive piece; and a light-receiving portion provided in
said polishing table for receiving light reflected from the
workpiece.
34. A polishing apparatus for polishing a workpiece, said polishing
apparatus comprising: a polishing table; a plurality of pedestals
attached to an upper surface of said polishing table; a polishing
pad having at least one light-transmissive piece and a plurality of
polishing pad pieces attached to said plurality of pedestals; a top
ring for pressing the workpiece against said polishing pad; a light
source provided in said polishing table for emitting light to a
surface of the workpiece through said at least one
light-transmissive piece; and a light-receiving portion provided in
said polishing table for receiving light reflected from the
workpiece.
35. A polishing apparatus for polishing a workpiece, said polishing
apparatus comprising: a polishing table; a polishing pad attached
to an upper surface of said polishing table, said polishing pad
having a plurality of polishing pad pieces attached to said
polishing table; a top ring for pressing the workpiece against said
polishing pad; a light source provided in said polishing table for
emitting light to a surface of the workpiece through at least one
through-hole formed in at least one of said plurality of polishing
pad pieces; a light-receiving portion provided in said polishing
table for receiving light reflected from the workpiece; a fluid
supply passage aligned with said at least one through-hole for
supplying measurement fluid; and a fluid discharge passage aligned
with said at least one through-hole for discharging the measurement
fluid.
36. A polishing apparatus for polishing a workpiece, said polishing
apparatus comprising: a polishing table; a plurality of pedestals
attached to an upper surface of said polishing table; a polishing
pad having a plurality of polishing pad pieces attached to said
plurality of pedestals; a top ring for pressing the workpiece
against said polishing pad; a light source provided in said
polishing table for emitting light to a surface of the workpiece
through at least one through-hole formed in at least one of said
plurality of polishing pad pieces and at least one through-hole
formed in at least one of said plurality of pedestals; a
light-receiving portion provided in said polishing table for
receiving light reflected from the workpiece; a fluid supply
passage for supplying measurement fluid, said fluid supply passage
being aligned with said at least one through-hole formed in said at
least one of said plurality of polishing pad pieces and said at
least one through-hole formed in said at least one of said
plurality of pedestals; and a fluid discharge passage for
discharging the measurement fluid, said fluid discharge passage
being aligned with said at least one through-hole formed in said at
least one of said plurality of polishing pad pieces and said at
least one through-hole formed in said at least one of said
plurality of pedestals.
37. A polishing apparatus for polishing a workpiece, said polishing
apparatus comprising: a polishing table; a polishing pad attached
to an upper surface of said polishing table, said polishing pad
including: a groove in said upper surface of said polishing pad for
allowing a polishing liquid to pass therethrough; and a weir
provided in said groove to disturb flow of the polishing liquid;
and a top ring for pressing the workpiece against said polishing
pad.
38. A polishing apparatus for polishing a workpiece, said polishing
apparatus comprising: a polishing table; a polishing pad bonded to
an upper surface of said polishing table by an adhesive made of a
liquid crystal material; and a top ring for pressing the workpiece
against said polishing pad.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polishing tool, and more
particularly to a polishing tool for polishing a workpiece such as
a semiconductor wafer to a flat mirror finish. The present
invention also relates to a polishing apparatus having such a
polishing tool and a method of a polishing a workpiece with such a
polishing apparatus. Further, the present invention is concerned
with a method of attaching a polishing pad to a polishing
table.
BACKGROUND ART
[0002] As semiconductor devices have become more highly integrated
in recent years, circuit interconnections have become finer and
distances between those circuit interconnections have become
smaller. In the case of photolithography, which can form
interconnections that are at most 0.5 .mu.m wide, it is required
that surfaces on which pattern images are to be focused by a
stepper should be as flat as possible because the depth of focus of
an optical system is relatively small. In order to planarize such a
semiconductor wafer, there has been used a polishing apparatus for
performing chemical mechanical polishing (CMP).
[0003] This type of polishing apparatus comprises a polishing table
having a polishing pad (polishing cloth) attached on an upper
surface of the polishing table, and a top ring for holding a
workpiece to be polished, such as a semiconductor wafer. The
polishing table and the top ring are rotated at independent
rotational speeds, respectively. The top ring presses the workpiece
against the polishing pad at a predetermined pressure. A polishing
liquid is supplied from a polishing liquid supply nozzle onto the
polishing pad. Thus, a surface of the workpiece is polished to a
flat mirror finish.
[0004] In such a polishing apparatus, polyurethane foam is mainly
used as a material for the polishing pad mounted on the polishing
table. Such a polishing pad is generally formed by cutting a molded
block-like compact. Polishing performance is influenced by
hardness, cross-link density, and foaming density of the polishing
pad. Hardness is determined by a compounding ratio of a prepolymer
and a hardener. Cross-link density is determined by a curing
temperature after compounding. Foaming density is determined by a
compounding ratio of polymeric fine materials.
[0005] The particularly important factors are cross-link density
and foaming density in view of polishing performance. For example,
if the cross-link density of the polishing pad is low, a workpiece
tends to be polished at a high polishing rate and to have a good
flatness on a polished surface thereof. Further, when the foaming
density of the polishing pad is high, a high polishing rate can be
achieved. When a polishing pad has a cross-link density and a
foaming density in predetermined ranges, stable polishing
performance can be achieved. However, it is not easy to produce a
polishing pad having a uniform cross-link density and a uniform
foaming density because it is difficult to uniformly diffuse
compounding materials in a compact in a molding process and to
uniformly control temperatures in the compact.
[0006] For example, a temperature gradient is produced between a
central area and a peripheral area of a compact when the compact is
heated for molding. Thus, a difference of the cross-link density is
produced between the central area and the peripheral area of the
compact. As a result, the block-like compact has variations in
cross-link density and foaming density. When a polishing pad
produced by cutting such a compact is used for polishing a
workpiece, polishing rates become non-uniform over a surface of the
workpiece, and polishing performance becomes unstable. Further,
polishing pads produced by cutting different portions of a compact
have different polishing performance. Accordingly, polishing
performance may vary each time a polishing pad is replaced with
another one.
[0007] In order to solve the above drawbacks, there have been made
efforts to maintain uniformity of compounding materials in a
compact or a uniform temperature distribution in the compact when
the compact is heated for molding.
[0008] However, a polishing pad used for polishing 8-inch wafers
has a diameter of about 600 mm, and a polishing pad used for
polishing 12-inch wafers has a diameter of at least 700 mm.
Accordingly, a block-like compact becomes large in size. Thus, it
becomes more difficult to eliminate non-uniformity of properties of
the compact. Thus, it is difficult to achieve stable polishing
performance and adjust polishing performance over a surface of a
workpiece.
DISCLOSURE OF INVENTION
[0009] The present invention has been made in view of the above
drawbacks. It is, therefore, a first object of the present
invention to provide a polishing tool which can achieve stable
polishing performance and facilitate adjustment of polishing
performance over a surface of a workpiece and replacement of a
polishing pad.
[0010] A second object of the present invention is to provide a
method of polishing a workpiece which achieve stable polishing
performance.
[0011] A third object of the present invention is to provide a
method of attaching a polishing pad to a polishing table which can
facilitate adjustment of polishing performance over a surface of a
workpiece and replacement of a polishing pad.
[0012] A fourth object of the present invention is to provide a
polishing apparatus which can achieve stable polishing performance
and facilitate adjustment of polishing performance over a surface
of a workpiece and replacement of a polishing pad.
[0013] In order to achieve the first object, according to a first
aspect of the present invention, there is provided a polishing tool
for polishing a workpiece. The polishing tool has a polishing table
and a polishing pad attached to an upper surface of the polishing
table. The polishing pad has a plurality of polishing pad pieces
attached to the polishing table.
[0014] According to a second aspect of the present invention, there
is provided a polishing tool for polishing a workpiece. The
polishing tool has a polishing table, a plurality of pedestals
attached to an upper surface of the polishing table, and a
polishing pad having a plurality of polishing pad pieces attached
to the plurality of pedestals.
[0015] In order to produce a polishing pad having uniform
properties, it is desirable to cut only a particular portion (or
area) having uniform properties in a compact. When a produced
polishing pad has a large area, properties have variations over a
surface of the polishing pad. Thus, it is desirable to cut a
compact with a possible smallest area. When small polishing pads
thus produced, which are hereinafter referred to as polishing pad
pieces, are attached onto a polishing table for polishing a
workpiece such as a semiconductor wafer, a surface of the workpiece
is polished more uniformly, and stable polishing performance can
also be achieved.
[0016] As described above, when a compact is large in size,
properties of the compact are likely to be non-uniform. Therefore,
it is also effective to use a small compact for molding. When a
compact is small in size, a temperature gradient becomes small
between a central area and a peripheral area of the compact. Thus,
variations of properties are unlikely to be produced in the
compact, and a polishing pad having uniform properties can be
obtained. When small polishing pads thus produced are attached onto
the polishing table for polishing the workpiece, a surface of the
workpiece is polished more uniformly, and stable polishing
performance can be achieved.
[0017] A semiconductor wafer to be actually polished may have
non-uniform thickness of films formed on a surface of the
semiconductor wafer. When such a semiconductor wafer is polished,
areas having larger thickness should be polished at a higher
polishing rate and areas having smaller thickness should be
polishing at a lower polishing rate so as to uniformize the
thickness of films remaining on the surface of the semiconductor
wafer after polishing. In order to meet such demands, it is
desirable to change properties and surface shapes of the respective
small polishing pads through which wafers pass, instead of to
uniformize properties and surface shapes of the small polishing
pads. Specifically, it is desirable that a polishing pad is divided
into possible smallest polishing pad pieces so as to accurately
control polishing performance over a surface of a semiconductor
wafer.
[0018] According to the present invention, when the plurality of
polishing pad pieces has the same material properties including
foaming density, cross-link density, and hardness, and the same
surface shapes including grooves and holes, a workpiece can be
polished at a uniform polishing rate over a surface thereof. On the
other hand, when the plurality of polishing pad pieces includes at
least one polishing pad piece having different material properties
including foaming density, cross-link density, and hardness, or
different surface shapes including grooves and holes than those of
other polishing pad pieces, a polishing rate distribution can be
adjusted over a surface of a workpiece to be polished.
[0019] According to a preferred aspect of the present invention,
the polishing table has a plurality of recesses for receiving the
plurality of polishing pad pieces or the plurality of pedestals.
The plurality of recesses should preferably have the same shape as
the plurality of polishing pad pieces or the plurality of
pedestals. With this arrangement, it is possible to facilitate
positioning of the polishing pad pieces or the pedestals when the
polishing pad pieces or the pedestals are attached to the polishing
table.
[0020] According to a preferred aspect of the present invention,
the polishing table includes a holding plate having a plurality of
through-holes for receiving the plurality of polishing pad pieces
or the plurality of pedestals. The plurality of through-holes
should preferably have the same shape as the plurality of polishing
pad pieces or the plurality of pedestals. With this arrangement, it
is not necessary to form the recesses for receiving the plurality
of polishing pad pieces or the plurality of pedestals in the upper
surface of the polishing table. The shape and the arrangement of
the through-holes can arbitrarily be selected by changing holding
plates.
[0021] According to a preferred aspect of the present invention, at
least one of the polishing pad pieces or at least one of the
pedestals is attached to the polishing table by a thermo-sensitive
adhesive which is softened and lowered in adhesive strength under a
high temperature while it is hardened and increased in adhesive
strength under a room temperature.
[0022] Small polishing pads require a considerably long period of
time to be attached onto an upper surface of a polishing table.
Generally, an adhesive is applied in advance onto surfaces of the
polishing pads. Since the adhesive used has a large adhesive
strength, it is difficult to remove the polishing pads once they
have been bonded to the upper surface of the polishing table. On
the other hand, once the polishing pads have been removed from the
upper surface of the polishing table, they cannot be bonded again
to the upper surface of the polishing table. Therefore, when
polishing pad pieces into which a conventional polishing pad having
an adhesive thereon is divided are used, it is necessary to
carefully position and attach each piece onto the polishing table.
Thus, a considerably long period of time is required to replace a
polishing pad with another one. Since the polishing apparatus is
stopped during replacement of the polishing pad, the number of lots
produced per hour is reduced. In order to improve the number of
lots produced, it is desired to attach polishing pad pieces onto a
polishing table at a time, instead of to attach each polishing pad
piece onto a polishing table.
[0023] According to the present invention, since a portion or all
of the polishing pad pieces or the pedestals is bonded to the
polishing table by a thermo-sensitive adhesive, a portion or all of
the polishing pad pieces or the pedestals can readily be attached
to and removed from the upper surface of the polishing table.
[0024] When a thermo-sensitive adhesive is used as an adhesive, the
polishing pad piece or pedestal can be bonded to the polishing
table as follows. The thermo-sensitive adhesive is applied between
the polishing pad piece or pedestal and the polishing table and
heated so as to be softened and lowered in adhesive strength. At
that time, the polishing pad piece or pedestal is pressed against
the upper surface of the polishing table so as to produce no air
bubbles between the polishing pad piece or pedestal and the
polishing table. Then, the thermo-sensitive adhesive is cooled to a
room temperature so as to bond the polishing pad piece or pedestal
to the polishing table. The polishing pad piece or pedestal can be
removed or separated from the polishing table as follows. The
thermo-sensitive adhesive is heated so as to be softened and
lowered in adhesive strength. At that time, the polishing pad piece
or pedestal can be removed or separated from the polishing
table.
[0025] The thermo-sensitive adhesive should preferably comprise a
liquid crystal material or a hot-melt adhesive. The liquid crystal
material and the hot-melt adhesive have characteristics that they
are softened and lowered in adhesive strength under a high
temperature while they are hardened and increased in adhesive
strength under a room temperature. Thus, with a liquid crystal
material or a hot-melt adhesive, it is possible to bond the
polishing pad piece or pedestal to the polishing table, or remove
the polishing pad piece or pedestal from the polishing table.
[0026] The polishing table may have a rough surface onto which the
thermo-sensitive adhesive is applied. The plurality of pedestals
may have a rough surface onto which the thermo-sensitive adhesive
is applied. Specifically, a surface onto which the thermo-sensitive
adhesive is applied may be roughened by sandblasting or the like to
form a rough surface. With such a rough surface, it is possible to
enhance the adhesive strength of the adhesive.
[0027] According to a preferred aspect of the present invention,
the plurality of pedestals is attached to the polishing table by
vacuum attraction. Thus, the pedestals may be attached to the
polishing table by vacuum attraction. In this case, when the vacuum
attraction is stopped and vacuum is released to the atmosphere, the
pedestals can be removed or separated from the polishing table.
[0028] According to a preferred aspect of the present invention,
the polishing pad pieces are arranged so as to form gaps between
adjacent polishing pad pieces. With this arrangement, a polishing
liquid can be supplied uniformly. Thus, the polishing rate
distribution can effectively be uniformized over the surface of the
workpiece. It is also possible to arbitrary change the polishing
rate distribution. Further, it is possible to efficiently supply
the polishing liquid to a polishing interface, i.e. between the
workpiece and the polishing pad. As a result, it is possible to
reduce the amount of polishing liquid, which is expensive, and
hence to reduce operating cost.
[0029] It is desirable that the polishing tool also has at least
one weir disposed in the gaps. With such a weir, the flow of the
polishing liquid is disturbed in the gap. Thus, the polishing
liquid overflowing the weir in the gap can efficiently be
introduced into the polishing interface, i.e. between the workpiece
and the polishing pad. Accordingly, it is possible to further
reduce the amount of polishing liquid supplied.
[0030] It is desirable that each of the polishing pad pieces has a
size smaller than the workpiece. Since each of the polishing pad
pieces has a size smaller than the workpiece, such polishing pad
pieces can have uniform material properties and surface shape.
Thus, it is possible to further facilitate the uniformity of the
polishing rate over the surface of the workpiece or adjustment of
the polishing rate distribution over the surface of the
workpiece.
[0031] According to a preferred aspect of the present invention,
the polishing pad pieces have the same material properties and
surface shape. With this arrangement, since the plurality of
polishing pad pieces has the same material properties including
foaming density, cross-link density, and hardness, and the same
surface shapes including grooves and holes, a workpiece can be
polished at a uniform polishing rate over a surface thereof.
[0032] According to another preferred aspect of the present
invention, the plurality of polishing pad pieces includes at least
one first polishing pad piece and at least one second polishing pad
piece having different material properties or surface shape than
material properties or surface shape of the at least one first
polishing pad piece. With this arrangement, since the plurality of
polishing pad pieces includes at least one polishing pad piece
having different material properties including foaming density,
cross-link density, and hardness, or different surface shapes
including grooves and holes than those of other polishing pad
pieces, a polishing rate can be adjusted over a surface of a
workpiece to be polished.
[0033] According to a preferred aspect of the present invention,
the polishing table is made of a material having a high thermal
conductivity, and the plurality of pedestals is made of a material
having a low thermal conductivity. Thus, the polishing table may be
made of a material having a high thermal conductivity such as SiC,
and the plurality of pedestals may be made of a material having a
low thermal conductivity such as resin. With this configuration,
the polishing pad pieces and the pedestals can effectively be
attached to and removed from the polishing table.
[0034] In order to achieve the second object, according to a third
aspect of the present invention, there is provided a method of
polishing a workpiece. According to this method, the workpiece is
pressed against the aforementioned polishing tool. At that time, a
polishing liquid is supplied to an upper surface of the polishing
tool, and the polishing tool and the workpiece are moved relative
to each other to polish the workpiece. This method can achieve the
same advantageous effects as described above in connection with the
polishing tool.
[0035] In order to achieve the third object, according to a fourth
aspect of the present invention, there is provided a method of
attaching a polishing pad to a polishing table. According to this
method, a thermo-sensitive adhesive is applied between the
polishing table and the polishing pad. The thermo-sensitive
adhesive is softened and lowered in adhesive strength under a high
temperature while it is hardened and increased in adhesive strength
under a room temperature. The thermo-sensitive adhesive is heated
when the polishing pad is disposed on the polishing table. Then,
the thermo-sensitive adhesive is cooled to bond the polishing pad
to the polishing table. The polishing pad may have a plurality of
polishing pad pieces attached to the polishing table.
[0036] A heating medium adjusted in temperature may be introduced
into the polishing table to heat the thermo-sensitive adhesive.
Alternatively, the thermo-sensitive adhesive may be heated by a
heating device provided near an unbonded surface of the polishing
pad. A cooling medium adjusted in temperature may be introduced
into the polishing table to cool the thermo-sensitive adhesive.
Alternatively, the thermo-sensitive adhesive may be cooled by a
cooling device provided near an unbonded surface of the polishing
pad.
[0037] With this method, a portion or all of the polishing pad
pieces can readily be attached to the polishing table in a short
term. In order to prevent change of properties from being caused to
the polishing pad, the heating temperature should preferably be at
most 200.degree. C., more preferably at most 100.degree. C.
[0038] In order to achieve the fourth object, according to a fifth
aspect of the present invention, there is provided a polishing
apparatus for polishing a workpiece. The polishing apparatus has a
polishing table, a polishing pad attached to an upper surface of
the polishing table, and a top ring for pressing the workpiece
against the polishing pad. The polishing pad has a plurality of
polishing pad pieces attached to the polishing table. The polishing
apparatus includes a light source provided in the polishing table
for emitting light to a surface of the workpiece through an opening
formed between adjacent polishing pad pieces. The polishing
apparatus also includes a light-receiving portion provided in the
polishing table for receiving light reflected from the
workpiece.
[0039] According to a sixth aspect of the present invention, there
is provided a polishing apparatus for polishing a workpiece. The
polishing apparatus has a polishing table, a plurality of pedestals
attached to an upper surface of the polishing table, and a
polishing pad having a plurality of polishing pad pieces attached
to the plurality of pedestals. The polishing apparatus also has a
top ring for pressing the workpiece against the polishing pad. The
polishing apparatus includes a light source provided in the
polishing table for emitting light to a surface of the workpiece
through an opening formed between adjacent polishing pad pieces.
The polishing apparatus also includes a light-receiving portion
provided in the polishing table for receiving light reflected from
the workpiece.
[0040] According to a seventh aspect of the present invention,
there is provided a polishing apparatus for polishing a workpiece.
The polishing apparatus has a polishing table and a polishing pad
attached to an upper surface of the polishing table. The polishing
apparatus also has a top ring for pressing the workpiece against
the polishing pad. The polishing pad has at least one
light-transmissive piece and a plurality of polishing pad pieces
attached to the polishing table. The polishing apparatus includes a
light source provided in the polishing table for emitting light to
a surface of the workpiece through the at least one
light-transmissive piece. The polishing apparatus also includes a
light-receiving portion provided in the polishing table for
receiving light reflected from the workpiece.
[0041] According to an eighth aspect of the present invention,
there is provided a polishing apparatus for polishing a workpiece.
The polishing apparatus has a polishing table, a plurality of
pedestals attached to an upper surface of the polishing table, and
a polishing pad having at least one light-transmissive piece and a
plurality of polishing pad pieces attached to the plurality of
pedestals. The polishing apparatus also has a top ring for pressing
the workpiece against the polishing pad. The polishing apparatus
includes a light source provided in the polishing table for
emitting light to a surface of the workpiece through the at least
one light-transmissive piece. The polishing apparatus also includes
a light-receiving portion provided in the polishing table for
receiving light reflected from the workpiece.
[0042] With these arrangements, light can be emitted from the
polishing table to a surface of the workpiece through an opening
formed between adjacent polishing pad pieces or through the at
least one light-transmissive piece. The light reflected from the
workpiece is received in the polishing table. Thus, it is possible
to measure the film thickness of the surface of the workpiece
during polishing or detect an end point of the polishing process.
Accordingly, the polishing process can be adjusted so as to control
excessive polishing or insufficient polishing. As a result,
productivity can be improved.
[0043] According to a ninth aspect of the present invention, there
is provided a polishing apparatus for a polishing a workpiece. The
polishing apparatus has a polishing table, a polishing pad attached
to an upper surface of the polishing table, and a top ring for
pressing the workpiece against the polishing pad. The polishing pad
has a plurality of polishing pad pieces attached to the polishing
table. At least one of the polishing pad pieces has at least one
through-hole formed therein. The polishing apparatus includes a
light source provided in the polishing table for emitting light to
a surface of the workpiece through the through-hole, and a
light-receiving portion provided in the polishing table for
receiving light reflected from the workpiece. The polishing
apparatus also includes a fluid supply passage aligned with the at
least one through-hole for supplying measurement fluid, and a fluid
discharge passage aligned with the at least one through-hole for
discharging the measurement fluid.
[0044] According to a tenth aspect of the present invention, there
is provided a polishing apparatus for a polishing a workpiece. The
polishing apparatus has a polishing table, a plurality of pedestals
attached to an upper surface of the polishing table, and a
polishing pad having a plurality of polishing pad pieces attached
to the plurality of pedestals. The polishing apparatus includes a
top ring for pressing the workpiece against the polishing pad. At
least one of the polishing pad pieces has at least one through-hole
formed therein. At least one of the pedestals has at least one
through-hole formed therein. The polishing apparatus also includes
a light source provided in the polishing table for emitting light
to a surface of the workpiece through the through-holes formed in
the at least one of the polishing pad pieces and the at least one
of the pedestals. The polishing apparatus has a light-receiving
portion provided in the polishing table for receiving light
reflected from the workpiece. The polishing apparatus also includes
a fluid supply passage for supplying measurement fluid and a fluid
discharge passage for discharging the measurement fluid. The fluid
supply passage is aligned with the through-holes formed in the at
least one of the polishing pad pieces and the at least one of the
pedestals. The fluid discharge passage is aligned with the
through-holes formed in the at least one of the polishing pad
pieces and the at least one of the pedestals.
[0045] According to an eleventh aspect of the present invention,
there is provided a polishing apparatus for polishing a workpiece.
The polishing apparatus has a polishing table and a polishing pad
attached to an upper surface of the polishing table. The polishing
apparatus also has a top ring for pressing the workpiece against
the polishing pad. The polishing pad includes a groove formed in
the upper surface of the polishing pad for allowing a polishing
liquid to pass therethrough, and a weir provided in the groove to
disturb flow of the polishing liquid.
[0046] With such a groove formed in the upper surface of the
polishing pad, the polishing liquid can effectively be introduced
into a polishing interface, i.e. between the workpiece and the
polishing pad. As a result, it is possible to reduce the amount of
polishing liquid, which is expensive, and hence to reduce operating
cost. With the weir provided in the groove to disturb the flow of
the polishing liquid, since the flow of the polishing liquid in the
groove is disturbed by the weir, the polishing liquid can more
effectively be introduced into the polishing interface.
[0047] According to a twelfth aspect of the present invention,
there is provided a polishing apparatus for polishing a workpiece.
The polishing apparatus has a polishing table and a polishing pad
bonded to an upper surface of the polishing table by an adhesive
made of a liquid crystal material. The polishing apparatus also has
a top ring for pressing the workpiece against the polishing
pad.
[0048] As described above, a liquid crystal material has
characteristics that it is softened and lowered in adhesive
strength under high temperatures while it is hardened and increased
in adhesive strength under a room temperature. Therefore, the
polishing pad can easily be bonded to and removed from the
polishing table.
[0049] The above and other objects, features, and advantages of the
present invention will be apparent from the following description
when taken in conjunction with the accompanying drawings which
illustrate preferred embodiments of the present invention by way of
example.
BRIEF DESCRIPTION OF DRAWINGS
[0050] FIG. 1A is a side view showing a polishing apparatus
according to an embodiment of the present invention;
[0051] FIG. 1B is a plan view of FIG. 1A;
[0052] FIG. 2A is a plan view showing a polishing pad in the
polishing apparatus shown in FIG. 1A;
[0053] FIG. 2B is a plan view showing a variation of the polishing
pad shown in FIG. 2A;
[0054] FIG. 3A is a plan view showing a polishing pad according to
another embodiment of the present invention;
[0055] FIG. 3B is a plan view showing a polishing pad according to
still another embodiment of the present invention;
[0056] FIG. 4A is a plan view showing a polishing pad according to
still another embodiment of the present invention;
[0057] FIG. 4B is an enlarged view of a portion A in FIG. 4A;
[0058] FIG. 5A is a plan view showing a polishing pad according to
another embodiment of the present invention;
[0059] FIG. 5B is a plan view showing a polishing pad according to
still another embodiment of the present invention;
[0060] FIG. 6A is a cross-sectional view showing an attachment
structure of a polishing tool according to an embodiment of the
present invention;
[0061] FIG. 6B is a cross-sectional view showing an attachment
structure of a polishing tool according to another embodiment of
the present invention;
[0062] FIG. 7A is a plan view showing a portion of a polishing pad
according to another embodiment of the present invention;
[0063] FIG. 7B is a plan view showing a portion of a polishing pad
according to still another embodiment of the present invention;
[0064] FIG. 8A is a plan view showing a modification of the
polishing pad shown in FIG. 7A;
[0065] FIG. 8B is a cross-sectional view of FIG. 8A;
[0066] FIG. 9A is a plan view showing a portion of a polishing pad
according to another embodiment of the present invention;
[0067] FIG. 9B is a partial cross-sectional view of FIG. 9A;
[0068] FIG. 9C is a plan view showing a variation of the polishing
pad shown in FIG. 9A;
[0069] FIGS. 10A through 10C are cross-sectional views showing
examples of a light-transmissive plate shown in FIG. 9B;
[0070] FIG. 11A is a plan view showing a portion of a polishing pad
according to another embodiment of the present invention;
[0071] FIG. 11B is a partial cross-sectional view of FIG. 11A;
[0072] FIG. 11C is a plan view showing a variation of the polishing
pad shown in FIG. 1A;
[0073] FIGS. 12A through 12C are cross-sectional views showing a
polishing tool according to other embodiments of the present
invention;
[0074] FIGS. 13A through 13D are schematic views showing a method
of attaching a polishing pad to a polishing table according to an
embodiment of the present invention;
[0075] FIGS. 14A through 14C are schematic views showing a method
of attaching a polishing pad to a polishing table according to
another embodiment of the present invention;
[0076] FIGS. 15A through 15C are schematic views showing a method
of attaching a polishing pad to a polishing table according to
still another embodiment of the present invention;
[0077] FIGS. 16A through 16D are schematic views showing a method
of removing a polishing pad from a polishing table according to an
embodiment of the present invention;
[0078] FIGS. 17A through 17C are schematic views showing a method
of removing a polishing pad from a polishing table according to
another embodiment of the present invention;
[0079] FIGS. 18A through 18C are schematic views showing a method
of removing a polishing pad from a polishing table according to
still another embodiment of the present invention;
[0080] FIGS. 19A through 19C are schematic views showing a method
of removing a polishing pad from a polishing table according to
still another embodiment of the present invention;
[0081] FIGS. 20A through 20D are cross-sectional views showing a
polishing tool according to embodiments of the present invention;
and
[0082] FIGS. 21A and 21B are cross-sectional views showing a
polishing pad according to the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0083] Embodiments of the present invention will be described below
with reference to FIGS. 1A through 21B. Like or corresponding parts
are denoted by like or corresponding reference numerals throughout
drawings, and will not be described below repetitively.
[0084] FIG. 1A is a side view showing a polishing apparatus
according to an embodiment of the present invention, and FIG. 1B is
a plan view of FIG. 1A. As shown in FIGS. 1A and 1B, this polishing
apparatus has a polishing table 10 having a polishing pad 11
(polishing cloth) attached on an upper surface of the polishing pad
11, and a top ring 12 for holding a workpiece 13 to be polished,
such as a semiconductor wafer. The polishing table 10 and the top
ring 12 are rotated at independent rotational speeds, respectively.
The top ring 12 presses the workpiece 13 against the polishing pad
11 at a predetermined pressure. A polishing liquid Q is supplied
from a polishing liquid supply nozzle 14 onto the polishing pad 11.
Thus, a surface of the workpiece 13 is polished to a flat mirror
finish.
[0085] Generally, a polishing pad which has the same size as a
polishing table is attached onto an upper surface of the polishing
table. A pressure sensitive adhesive sheet for bonding is attached
to a rear face of the polishing pad. The pressure sensitive
adhesive sheet is protected by a protective film. At the time of
use, the protective film is peeled so as to expose the pressure
sensitive adhesive sheet. Then, the pressure sensitive adhesive
sheet is pressed against the upper surface of the polishing table
so as to be bonded to the upper surface of the polishing table. At
that time, the pressure sensitive adhesive sheet should carefully
be bonded so as not to produce air between the pressure sensitive
adhesive sheet and the polishing table. If air is produced between
the pressure sensitive adhesive sheet and the polishing table, then
the pressure sensitive adhesive sheet is raised at points where air
is formed, so that polishing pressures are not maintained at proper
values at those points. Further, the pressure sensitive adhesive
sheet has a large adhesive strength, it is difficult to remove the
polishing pad once it has been bonded to the upper surface of the
polishing table. On the other hand, once the polishing pad has been
removed from the upper surface of the polishing table, it cannot be
bonded again to the upper surface of the polishing table.
Therefore, when the polishing pad is attached onto the polishing
table, it is necessary to carefully position the polishing pad on
the polishing table.
[0086] FIG. 2A is a plan view showing the polishing pad 11 in the
polishing apparatus shown in FIG. 1A. As shown in FIG. 2A, the
polishing pad 11 is divided into a plurality of polishing pad
pieces 111. In order to produce a polishing pad 11 having uniform
properties including density and hardness, it is desirable to
select and use polishing pad pieces 111 having the same properties.
The sizes of the polishing pad pieces 111 are not limited to the
illustrated example. For example, as shown in FIG. 2B, the
polishing pad 11 may be divided into a plurality of polishing pad
pieces 111 having sizes larger than those of the polishing pad
pieces shown in FIG. 2A. In these cases, the sizes of the polishing
pad pieces 111 should preferably be smaller than the workpiece 13.
If the polishing pad pieces 111 have a large area, properties of
the polishing pad pieces 111 are likely to have variations on
surfaces thereof. Thus, it is desirable that the polishing pad
pieces 111 should have an area as small as possible. When the
polishing pad pieces 111 have a size smaller than the workpiece 13,
a surface of the workpiece 13 can be polished more uniformly, and
uniform polishing performance can be maintained on the surface of
the workpiece 13.
[0087] As shown in FIGS. 2A and 2B, the polishing pad pieces 111
should preferably have a hexagonal shape because the small
polishing pad pieces 111 can be disposed efficiently without any
gaps on a circular upper surface of the polishing table 10.
However, the shapes of the polishing pad pieces 111 are not limited
to hexagonal shapes. As shown in FIG. 3A, a circular polishing pad
21 may be divided concentrically and radially into elongated
arcuate pieces 211. Alternatively, as shown in FIG. 3B, a circular
polishing pad 31 may be divided into rectangular pieces 311.
Polishing pad pieces having different shapes, such as regular
hexagons and rectangles, may be combined with each other, which are
not shown.
[0088] FIG. 4A is a plan view showing a polishing pad 41 according
to another embodiment of the present invention, and FIG. 4B is an
enlarged view showing a portion A in FIG. 4A. As shown in FIGS. 4A
and 4B, the polishing pad 41 is divided into polishing pad pieces
411. Since the polishing pad pieces 411 can be attached and
detached individually, material properties and surface shapes of
the polishing pad pieces 411 can arbitrarily be selected.
[0089] FIG. 5A is a plan view showing a polishing pad 51 according
to still another embodiment of the present invention. The polishing
pad 51 is divided into polishing pad pieces 511 having the same
material properties including foaming density, cross-link density,
and hardness, and the same surface shapes including grooves and
holes in the polishing pad 51. As the polishing pad pieces 511 are
smaller in size, properties of the polishing pad pieces 511 become
uniform. Thus, when each of the polishing pad pieces 511 has a size
smaller than the diameter of the workpiece 13 such as a
semiconductor wafer and the same material properties and surface
shapes as those of the workpiece 13, polishing rates become more
uniform over a surface of the workpiece 13.
[0090] FIG. 5B is a plan view showing a polishing pad 61 according
to still another embodiment of the present invention. The polishing
pad 61 includes polishing pad pieces 611 and polishing pad pieces
612 having different material properties including foaming density,
cross-link density, and hardness, or different surface shapes
including grooves and holes than those of the polishing pad pieces
611. Thus, in the present embodiment, polishing rates at a
peripheral portion of a workpiece 13 is different from those at a
central portion of the workpiece 13. The workpiece 13 may have
non-uniform thickness of films formed on a surface of the workpiece
13. For example, the workpiece 13 may have a large thickness at the
peripheral portion of the workpiece 13 and a small thickness at the
central portion of the workpiece 13. Since a workpiece should have
a uniform film thickness after polishing, the peripheral portion of
the workpiece 13 should be polished at a higher polishing rate when
the workpiece 13 is polished.
[0091] For these purpose, as shown in FIG. 5B, the polishing pad
pieces 612 having properties to achieve a higher polishing rate as
compared to the polishing pad pieces 611 are arranged at the
central area of the polishing table 10. The polishing pad pieces
612 arranged at the central area of the polishing table 10 affect
only the peripheral portion of the workpiece 13. With such a
polishing pad 61, the peripheral portion of the workpiece 13, which
has a larger thickness, can be polished at a higher polishing rate.
Thus, the workpiece 13 can be polished so as to have a uniform film
thickness.
[0092] The arrangement of the polishing pad pieces 612 having
different material properties or surface shapes and the polishing
pad pieces 611 is not limited to the illustrated example. The
polishing pad pieces 612 and the polishing pad pieces 611 may be
arranged in various manners according to intended purpose and the
shape of the polishing pad 61. For example, polishing pad pieces
having different material properties or surface shapes may be
disposed at a peripheral area of the polishing table 10.
Alternatively, polishing pad pieces having different material
properties or surface shapes may be disposed at areas through which
the center of the workpiece 13 passes over the polishing table
10.
[0093] FIG. 6A is a cross-sectional view showing an attachment
structure of a polishing tool according to an embodiment of the
present invention. As shown in FIG. 6A, the polishing table 10 has
a plurality of recesses 101 formed on an upper surface thereof. The
recesses have the same shape as polishing pad pieces 711 so as to
easily position the polishing pad pieces 711 on the upper surface
of the polishing table 10. Typically, an adhesive layer 151 is
formed on a rear face of each polishing pad piece 711. If the
polishing pad pieces 711 are attached and bonded to the upper
surface of the polishing table 10 without the recesses 101, then
the polishing pad pieces 711 may deviate from proper positions
because the adhesive layers 151 have viscosity. If each polishing
pad piece 711 is carefully positioned, a considerably long period
of time would be required to attach a large number of polishing pad
pieces 711. In the present embodiment, as shown in FIG. 6A, since
the polishing table 10 has the recesses 101 in the upper surface
thereof, each polishing pad piece 711 can properly be positioned
without deviation. Thus, the polishing pad pieces 711 can readily
be attached to the upper surface of the polishing table 10 in a
short term.
[0094] FIG. 6B is a cross-sectional view showing an attachment
structure of a polishing tool according to another embodiment of
the present invention. As shown in FIG. 6B, instead of the recesses
101 shown in FIG. 6A, the polishing table 10 has a holding plate 76
for the same purpose as the recesses 101. Specifically, the holding
plate 76 has a plurality of through-holes 761 having the same shape
as the polishing pad pieces 711. The holding plate 76 is placed on
the upper surface of the polishing table 10. The polishing pad
pieces 711 are disposed and positioned in the through-holes 761 of
the holding plate 76. Thus, the polishing pad pieces 711 are
attached and bonded to the polishing table 10. In this manner, it
is not necessary to form the recesses 101 in the polishing table as
shown in FIG. 6A. The shape and the arrangement of the
through-holes 761 can arbitrarily be selected by changing holding
plates 76.
[0095] FIG. 7A is a plan view showing a portion of a polishing pad
81 according to another embodiment of the present invention. As
shown in FIG. 7A, the polishing pad 81 has hexagonal polishing pad
pieces 811 arranged with gaps 87 formed between adjacent polishing
pad pieces 811 and 811. The gaps 87 communicate with each other so
as to form grooves through which a polishing liquid flows as shown
by arrows 88. When a large number of polishing pad pieces 811 are
arranged in this manner, a polishing liquid easily flows through
the grooves formed by the gaps 87. Thus, it is possible to
efficiently supply the polishing liquid to a polishing interface
between a workpiece and the polishing pad 81. As a result, it is
possible to reduce the amount of polishing liquid, which is
expensive, and hence to reduce operating cost.
[0096] FIG. 7B is a plan view showing a portion of a polishing pad
91 according to another embodiment of the present invention. As
shown in FIG. 7B, the polishing pad 91 has rectangle polishing pad
pieces 911 arranged with gaps 97 formed between adjacent polishing
pad pieces 911 and 911. The gaps 97 communicate with each other so
as to form grooves through which a polishing liquid flows as shown
by arrows 98. When a large number of polishing pad pieces 911 are
arranged in this manner, a polishing liquid easily flows through
the grooves formed by the gaps 97. Thus, it is possible to
efficiently supply the polishing liquid to a polishing interface
between a workpiece and the polishing pad 91. As a result, it is
possible to reduce the amount of polishing liquid, which is
expensive, and hence to reduce operating cost.
[0097] When the polishing pad has deep grooves, a polishing liquid
may be discharged to the exterior of the polishing pad without
overflowing the grooves. In order to prevent such a phenomenon, it
is desirable to arrange the polishing pad pieces so as to form
refracted grooves as shown in FIG. 7A. With this arrangement, a
polishing liquid hits walls of the grooves at refracted portions of
the grooves and overflows the walls of the grooves. Thus, the
polishing liquid can be supplied to the polishing interface. In
order to enhance this effect, as shown in FIG. 8A, it is desirable
to provide weirs 89 located in the grooves 87. With such weirs 89,
when a polishing liquid flows through the grooves 87, it overflows
the weirs 89 as shown by arrows 88 in FIG. 8B. Thus, it is possible
to efficiently supply the polishing liquid to a polishing
interface. Such weirs 89 are also applicable to any polishing pad
having grooves in a polishing surface.
[0098] The weirs 89 should preferably be made of the same material
as the polishing pad pieces 811 or a material that is more likely
to be worn than the polishing pad pieces 811. The pattern of the
formed grooves and the arrangement of the weirs 89 are not limited
to the illustrated example. The grooves may be formed in various
patterns, and the weirs 89 may be arranged in various manners. For
example, not all of the grooves may communicate with each other,
and some of the grooves may be blocked. The grooves may have
different widths. Specifically, the gaps 87 between the polishing
pad pieces 811 and 811 may have different widths. The gap 87 may
not be formed in part between the polishing pad pieces 811 and
811.
[0099] FIG. 9A is a plan view showing a portion of a polishing pad
101 according to another embodiment of the present invention, and
FIG. 9B is a partial cross-sectional view of FIG. 9A. As shown in
FIG. 9A, a polishing pad 101 has hexagonal polishing pad pieces
1011 arranged with gaps 107 formed between adjacent polishing pad
pieces 1011 and 1011. As shown in FIGS. 9A and 9B, the polishing
table 100 has an opening 110, extending through the polishing table
100, in the groove between the polishing pad pieces 1011 and 1011.
Light 114 is emitted through the opening 110 to a surface 13a of a
workpiece 13 from a light source 112 provided in the polishing
table 100. Reflected light 115 is received by a light-receiving
portion 113 provided in the polishing table 100. FIG. 9A shows that
an opening 110 is formed in the groove 107 between the polishing
pad pieces 1011 and 1011. However, as shown in FIG. 9C, the opening
110 may be disposed in a space between a small polishing pad piece
1012 and a polishing pad piece 1011. In either case, the polishing
table 100 has a space for the opening 110 extending through the
polishing table 100. Therefore, it is possible to emit light 114
from the polishing table 100 to the surface 13a of the workpiece 13
and then receive reflected light 115 in the polishing table
100.
[0100] As shown in FIG. 9B, a light-transmissive plate 111 may be
provided on the upper surface of the polishing table 100 to prevent
a polishing liquid from entering the interior of the polishing
table 100. The light-transmissive plate may have a flat shape 11a
as shown in FIG. 10A, or a curved shape 111b or 111c facing the
workpiece as shown in FIG. 10B or 10C. When the light-transmissive
plate has an upper curved surface, a polishing liquid is less
likely to accumulate on the top of the upper surface. In such a
case, the light transmittance is not lowered.
[0101] FIG. 11A is a plan view showing a portion of a polishing pad
121 according to another embodiment of the present invention, and
FIG. 11B is a partial cross-sectional view of FIG. 11A. As shown in
FIG. 11A, the polishing pad 121 has polishing pad pieces 1211
including at least one light-transmissive piece 120. As shown in
FIG. 11B, light 114 is emitted from a light source 112 provided in
the polishing table 10 through the light-transmissive piece 120,
and reflected light 115 is received by a light-receiving portion
113 provided in the polishing table 10. It is desirable to position
an upper surface of the light-transmissive piece 120 at the same
height as an upper surface of the polishing pad pieces 1211.
[0102] Material of the light-transmissive piece 120 is not limited
to a specific one, but should preferably be a material that allows
light having a wavelength of at least 300 nm to pass therethrough.
For example, the light-transmissive piece 120 may include the same
material as the polishing pad pieces 1211, e.g. polyurethane.
Alternatively, the light-transmissive piece 120 may comprise a
material that is worn to the same degree as the polishing pad
pieces 1211 or is more likely to be worn than the polishing pad
pieces 1211, quartz glass, or liquid crystal material. Further, the
light-transmissive piece 120 may be formed by a combination of the
above materials in a piled manner.
[0103] The formation of the opening 110 and the arrangement of the
light-transmissive piece 120 are not limited to the illustrated
examples. The opening 110 may be formed in various manners, and the
light-transmissive piece 120 may be arranged in various manners.
For example, all of the polishing pad pieces 1211 may comprise a
light-transmissive piece 120. FIG. 11C shows another variation of
the polishing pad 121 shown in FIG. 11A.
[0104] With the above configuration, it is possible to monitor
states of the workpiece 13 during polishing, such as film thickness
or exposure of different materials. Thus, end point detection of
the polishing process can readily be performed. Accordingly, the
polishing process can be adjusted so as to control excessive
polishing or insufficient polishing. As a result, productivity can
be improved.
[0105] A stream-type measurement device may be used as a substrate
measuring device for the above purposes. The stream-type
measurement device has a water supply passage and a water discharge
passage provided in a polishing table. A supply port of the fluid
supply passage and a discharge port of the fluid discharge passage
are provided in the polishing table. One of the polishing pad
pieces, or one of the polishing pad pieces and one of the pedestals
have a through-hole aligned with the supply port of the fluid
supply passage and the discharge port of the fluid discharge
passage. Pure water is ejected through the fluid supply passage and
the through-hole or the through-holes to the substrate. Two optical
fibers are disposed in a stream of the pure water. These optical
fibers are connected to a light source and a light-receiving
portion. Measurement light is emitted through one of the optical
fibers to the substrate from the light source, and reflected light
is received through the other of the optical fibers from the
substrate by the light-receiving portion. Thus, the film thickness
or exposure of different materials can be monitored based on the
reflected light.
[0106] With such an arrangement, the measurement fluid such as pure
water is supplied through the fluid supply passage and discharged
through the fluid discharge passage. Accordingly, the through-hole
or the through-holes are filled with transparent pure water, and
hence polishing slurry is prevented from entering the through-hole
or the through-holes, thus allowing measurement with use of
transmitted light to be performed.
[0107] FIGS. 12A through 12C are cross-sectional views showing a
polishing tool according to other embodiments of the present
invention. As shown in FIGS. 12A through 12C, polishing pad pieces
711 are attached onto an upper surface of the polishing table 10.
In FIG. 12A, the polishing pad pieces 711 are attached directly to
recesses 101 in the polishing table 10 by thermo-sensitive adhesive
layers 151. Specifically, the adhesive layer 151 is softened and
lowered in adhesive strength under high temperatures while it is
hardened and increased in adhesive strength under a room
temperature.
[0108] In FIG. 12B, the polishing pad pieces 711 are attached to
recesses 101 in the polishing table 10 by upper thermo-sensitive
adhesive layers 151, pedestals 251, and lower thermo-sensitive
adhesive layers 152. Specifically, the upper and lower adhesive
layers 151 and 152 are softened and lowered in adhesive strength
under high temperatures while they are hardened and increased in
adhesive strength under a room temperature. Each polishing pad
piece 711 is attached to each pedestal 251, and each pedestal 251
is attached to recess 101 in the polishing table 10 by the lower
thermo-sensitive adhesive layer 152.
[0109] In FIG. 12C, the polishing pad pieces 711 are attached to a
recess 102 in the polishing table 10 by upper thermo-sensitive
adhesive layers 151, a pedestal 261, and a lower thermo-sensitive
adhesive layer 152. Specifically, a plurality of polishing pad
pieces 711 is attached to the pedestal 261, and the pedestal 261 is
attached to the recess 102 in the polishing table 10 by the lower
thermo-sensitive adhesive layer 152.
[0110] In FIGS. 12A through 12C, the recesses 101 and 102 are
formed in the polishing table 10 to facilitate positioning of the
polishing pad pieces 711, and the pedestals 251 and 261. However, a
holding plate 76 as shown in FIG. 6B may be used for positioning
instead of the recesses 101 and 102 formed in the upper surface of
the polishing table 10. The thermo-sensitive adhesive layers may
comprise a liquid crystal material or a hot-melt adhesive.
[0111] The liquid crystal material is an organic material as
follows. The liquid crystal material has no long-range order with
respect to positions of molecules and is fluidic. However, the
liquid crystal material has a long-range order with respect to
orientation (mainly uniaxial orientation) and is elastic in a
liquid crystal state. A liquid crystal material includes a
thermotropic liquid crystal, which shows a liquid crystal state as
an intermediate state between a crystal and an isotropic liquid,
and a lyotropic liquid crystal, which has an order of orientation
in a solution state. The above embodiments employ a thermotropic
liquid crystal as an adhesive.
[0112] The hot-melt adhesive is an adhesive including resin, wax,
plasticizer, tackifier, antioxidant, and filler. The resin in the
hot-melt adhesive should preferably comprise resin mainly including
a copolymer of ethylene and vinyl acetate, or resin including one
of polyethylene, polyamide, and polyester. The thermo-sensitive
adhesive should preferably have a softening and melting temperature
of 200.degree. C. or lower, at which properties of the polishing
pad pieces 711 are not changed. More specifically, the
thermo-sensitive adhesive should preferably have a softening and
melting temperature of 100.degree. C. or lower, more preferably
70.degree. C. or lower.
[0113] FIGS. 13A through 13D are schematic views showing a method
of attaching a polishing pad to a polishing table 10 according to
an embodiment of the present invention. FIGS. 13A through 13D show
processes in which polishing pad pieces 711 are attached directly
onto the recesses 101 in the polishing table 10. As shown in FIG.
13A, an adhesive is applied onto rear faces of a plurality of
polishing pad pieces 711 to form adhesive layers 151. As shown in
FIG. 13B, the polishing pad pieces 711 are disposed within the
recesses 101 in the polishing table 10. Unbonded surfaces of the
polishing pad pieces 111, which are opposite to the adhesive layers
151, are pressed by a device 127. At that time, the adhesive layers
151 are heated to a high temperature (at most 200.degree. C.,
preferably at most 100.degree. C., more preferably at most
70.degree. C.) by the device 127 to attach the polishing pad pieces
711 onto bottom surfaces of the recesses 101. Then, the polishing
pad pieces 711 are cooled to a room temperature. Thus, as shown in
FIG. 13C, the polishing pad pieces 711 are attached directly to the
recesses 101.
[0114] Alternatively, there may be used a pressing device 128 for
pressing the unbonded surfaces of the polishing pad pieces 711 and
a heating and cooling device 129 disposed within the polishing
table 10 for heating and cooling the adhesive layers 151.
Specifically, as shown in FIG. 13A, an adhesive is applied onto
rear faces of a plurality of polishing pad pieces 711 to form
adhesive layers 151. As shown in FIG. 13D, the polishing pad pieces
711 are disposed within the recesses 101 in the polishing table 10.
While the polishing pad pieces 711 are pressed by the pressing
device 128, the adhesive layers 151 are heated to a high
temperature (at most 200.degree. C., preferably at most 100.degree.
C., more preferably at most 70.degree. C.) by the heating and
cooling device 129 provided in the polishing table 10 to thereby
attach the polishing pad pieces 711 onto the bottom surfaces of the
recesses 101. Then, the polishing pad pieces 711 are cooled to a
room temperature. Thus, as shown in FIG. 13C, the polishing pad
pieces 711 are attached directly to the recesses 101.
[0115] For example, the device 127 employs a high-temperature fluid
or other heating media, which are adjusted in temperature, to heat
the polishing pad pieces 711, and also employs a low-temperature
fluid or other cooling media, which are adjusted in temperature, to
cool the polishing pad pieces 711. For example, the heating and
cooling device 129 introduces a high-temperature fluid or other
heating media, which are adjusted in temperature, into the interior
of the polishing table 10 to heat the polishing pad pieces 711, and
also introduces a low-temperature fluid or other cooling media,
which are adjusted in temperature, into the interior of the
polishing table 10 to cool the polishing pad pieces 711.
[0116] With the above processes as shown in FIGS. 13A through 13D,
a plurality of polishing pad pieces 711 can be attached directly to
a plurality of recesses 101 formed in the upper surface of the
polishing table 10 at a time.
[0117] FIGS. 14A through 14C are schematic views showing a method
of attaching a polishing pad to a polishing table 10 according to
another embodiment of the present invention. FIGS. 14A through 14D
show processes in which polishing pad pieces 711 are attached via
pedestals 251 mounted onto recesses 101 in the polishing table 10.
As shown in FIG. 14A, the pedestals 251 are attached via adhesive
layers 152 onto a plurality of recesses 101 in the polishing table
10. An adhesive is applied onto rear faces of a plurality of
polishing pad pieces 711 to form adhesive layers 151. The adhesive
layer 151 comprises an adhesive that is softened and lowered in
adhesive strength under high temperatures while it is hardened and
increased in adhesive strength under a room temperature. The
adhesive layer 152 comprises a general adhesive. As shown in FIG.
14B, the polishing pad pieces 711 are placed on the pedestals 251.
While the polishing pad pieces 711 are pressed by a device 127, the
adhesive layers 151 are heated to a high temperature (at most
200.degree. C., preferably at most 100.degree. C., more preferably
at most 70.degree. C.) by the device 127 to attach the polishing
pad pieces 711 onto upper surfaces of the pedestals 251. Then, the
polishing pad pieces 711 are cooled to a room temperature. Thus, as
shown in FIG. 14C, the polishing pad pieces 711 are attached via
the pedestals 251 to the recesses 101.
[0118] FIGS. 15A through 15C are schematic views showing a method
of attaching a polishing pad to a polishing table 10 according to
still another embodiment of the present invention. FIGS. 15A
through 15C show processes in which polishing pad pieces 711 are
attached via pedestals 251 onto recesses 101 in the polishing table
10. As shown in FIG. 15A, the pedestals 251 are attached via
adhesive layers 151 onto rear faces of the polishing pad pieces
711. An adhesive is applied onto rear faces of the pedestals 251 to
form adhesive layers 152. The adhesive layer 152 comprises an
adhesive that is softened and lowered in adhesive strength under
high temperatures while it is hardened and increased in adhesive
strength under a room temperature. The adhesive layer 151 comprises
a general adhesive. As shown in FIG. 15B, while the polishing pad
pieces 711 are pressed by a pressing device 128, the adhesive
layers 152 are heated to a high temperature (at most 200.degree.
C., preferably at most 100.degree. C., more preferably at most
70.degree. C.) by a heating and cooling device 129 in the polishing
table 10 to thereby attach the pedestals 251 onto bottom surfaces
of the recesses 101. Then, the pedestals 251 are cooled to a room
temperature. Thus, as shown in FIG. 15C, the polishing pad pieces
711 are attached via the pedestals 251 to the recesses 101.
[0119] With the above processes as shown in FIGS. 15A through 15C,
a plurality of polishing pad pieces 711 can be attached via
pedestals 251 to a plurality of recesses 101 formed in an upper
surface of the polishing table 10 at a time.
[0120] FIGS. 16A through 16D are schematic views showing a method
of removing a polishing pad from a polishing table 10 according to
an embodiment of the present invention. FIGS. 16A through 16D show
processes in which polishing pad pieces 711 are removed from
recesses 101 in the polishing table 10. As shown in FIG. 16A, the
polishing pad pieces 711 are bonded to the recesses 101 in the
polishing table 10 by an adhesive layers 151. As shown in FIG. 16B,
the adhesive layers 151 are heated to a high temperature by a
heating device 131 provided near unbonded surfaces of the polishing
pad pieces 711 so as to reduce an adhesive strength of the adhesive
layers 151. Then, as shown in FIG. 16C, the polishing pad pieces
711 are removed (or separated) from the recesses 101.
Alternatively, as shown in FIG. 16D, the adhesive layers 151 may be
heated to a high temperature by a heating device 132 provided
within the polishing table 10 so as to reduce an adhesive strength
of the adhesive layers 151. Then, as shown in FIG. 16C, the
polishing pad pieces 711 may be removed (or separated) from the
recesses 101.
[0121] FIG. 17A through 17C are schematic views showing a method of
removing a polishing pad from a polishing table 10 according to
another embodiment of the present invention. FIGS. 17A through 17C
show processes in which polishing pad pieces 711 attached via
pedestals 251 to the recesses 101 are removed from the pedestals
251. As shown in FIG. 17A, the polishing pad pieces 711 are
attached via the pedestals 251 to the recesses 101 in the polishing
table 10. Adhesive layers 151 between the polishing pad pieces 711
and the pedestals 251 comprise an adhesive that is softened and
lowered in adhesive strength under high temperatures while it is
hardened and increased in adhesive strength under a room
temperature. Adhesive layers 152 between the pedestals 251 and the
recesses 101 comprise a general adhesive.
[0122] As shown in FIG. 17B, the adhesive layers 151 are heated to
a high temperature by a heating device 131 provided near unbonded
surfaces of the polishing pad pieces 711 so as to reduce an
adhesive strength of the adhesive layers 151. Then, as shown in
FIG. 17C, the polishing pad pieces 711 are removed (or separated)
from the pedestals 251.
[0123] FIG. 18A through 18C are schematic views showing a method of
removing a polishing pad from a polishing table 10 according to
still another embodiment of the present invention. FIGS. 18A
through 18C show processes in which polishing pad pieces 711
attached via pedestals 251 to recesses 101 are removed from the
recesses 101 in the polishing table 10 together with the pedestals
251. As shown in FIG. 18A, the polishing pad pieces 711 are
attached via the pedestals 251 to the recesses 101 in the polishing
table 10. Adhesive layers 151 between the polishing pad pieces 711
and the pedestals 251 comprise a general adhesive. Adhesive layers
152 between the pedestals 251 and the recesses 101 comprise an
adhesive that is softened and lowered in adhesive strength under
high temperatures while it is hardened and increased in adhesive
strength under a room temperature.
[0124] As shown in FIG. 18B, the adhesive layers 152 are heated to
a high temperature by a heating device 132 provided within the
polishing table 10 so as to reduce an adhesive strength of the
adhesive layers 152. Then, as shown in FIG. 18C, the polishing pad
pieces 711 are removed (or separated) from the recesses 101
together with the pedestals 251 attached to the rear surfaces of
the polishing pad pieces 711.
[0125] FIG. 19A through 19C are schematic views showing a method of
removing a polishing pad from a polishing table 10 according to
still another embodiment of the present invention. FIGS. 19A
through 19C show processes in which a portion of polishing pad
pieces 711 attached to pedestals 251 by adhesive layers 151 is
removed from the pedestals 251 bonded to the recesses 101 in the
polishing table 10 by adhesive layers 152. As shown in FIG. 19A,
the polishing pad pieces 711 are attached to the pedestals 251
bonded to the recesses 101 in the polishing table 10. The adhesive
layers 151 between the polishing pad pieces 711 and the pedestals
251 comprise an adhesive that is softened and lowered in adhesive
strength under high temperatures while it is hardened and increased
in adhesive strength under a room temperature. As shown in FIG.
19B, the adhesive layer 151 of a portion of the polishing pad
pieces 711 is heated to a high temperature by a heating device 131
provided near unbonded surfaces of the polishing pad pieces 711 so
as to reduce an adhesive strength of the adhesive layer 151. Then,
as shown in FIG. 19C, the polishing pad piece 711 are removed (or
separated) from the pedestal 251.
[0126] FIGS. 20A through 20D are cross-sectional views showing a
polishing tool according to embodiments of the present invention.
FIGS. 20A through 20D show examples of bonding arrangement of the
polishing pad pieces 711 and the pedestals 251. In FIG. 20A, a
bottom surface of the recess in a polishing table 10 is roughened
by sandblasting or the like to form a rough surface 101a. An
adhesive layer 151 is applied between the rough surface 101a and
the polishing pad piece 711 to attach the polishing pad piece 711
onto the recess 101. The adhesive layer 151 comprises an adhesive
that is softened and lowered in adhesive strength under high
temperatures while it is hardened and increased in adhesive
strength under a room temperature. With this arrangement, the
adhesive layer 151 can have a larger adhesive strength.
[0127] In FIG. 20B, a pedestal 251 is attached to a recess 101 of a
polishing table 10 by an adhesive layer 152 of a general adhesive.
An upper surface of the pedestal 251 is roughened by sandblasting
or the like to form a rough surface 251a. An adhesive layer 151 is
applied between the rough surface 251a and the polishing pad piece
711 to attach the polishing pad piece 711 onto the pedestal 251.
The adhesive layer 151 comprises an adhesive that is softened and
lowered in adhesive strength under high temperatures while it is
hardened and increased in adhesive strength under a room
temperature. With this arrangement, the adhesive layer 151 can have
a larger adhesive strength.
[0128] In FIG. 20C, a bottom surface of a recess 101 in a polishing
table 10 is roughened by sandblasting or the like to form a rough
surface 101a. An adhesive layer 152 is applied between the rough
surface 101a and the pedestal 251 to attach the pedestal 251 onto
the recess 101. The adhesive layer 152 comprises an adhesive that
is softened and lowered in adhesive strength under high
temperatures while it is hardened and increased in adhesive
strength under a room temperature. The polishing pad piece 711 is
attached to an upper surface of the pedestal 251 by an adhesive
layer 151 of a general adhesive. With this arrangement, the
adhesive layer 152 can have a larger adhesive strength.
[0129] In FIG. 20D, a bottom surface of a recess 101 in a polishing
table 10 is roughened by sandblasting or the like to form a rough
surface 101a. An adhesive layer 152 is applied between the rough
surface 101a and the pedestal 251 to attach the pedestal 251 onto
the recess 101. The adhesive 152 comprises an adhesive that is
softened and lowered in adhesive strength under high temperatures
while it is hardened and increased in adhesive strength under a
room temperature. An upper surface of the pedestal 251 is roughened
by sandblasting or the like to form a rough surface 251a. An
adhesive layer 152 is applied between the rough surface 251a and
the polishing pad piece 711 to attach the polishing pad piece 711
onto the pedestal 251. The adhesive layer 152 comprises an adhesive
that is softened and lowered in adhesive strength under high
temperatures while it is hardened and increased in adhesive
strength under a room temperature.
[0130] As described above, the bottom surface of the recess 101 to
which the polishing pad piece 711 is to be attached (FIG. 20A), the
upper surface of the pedestal 251 to which the polishing pad piece
711 is to be attached (FIG. 20B), the bottom surface of the recess
101 to which the pedestal 251 is to be attached (FIG. 20C), and the
bottom surface of the recess 101 to which the pedestal 251 is to be
attached and the upper surface of the pedestal 251 to which the
polishing pad piece 711 is to be attached (FIG. 20D) are roughened
by sandblasting or the like so as to form rough surfaces. In these
cases, it is possible to enhance an adhesive strength of an
adhesive.
[0131] In the above examples, an adhesive is used to bond the
pedestal 251, to which the polishing pad piece 711 is attached, to
the polishing table 10. However, the pedestal 251 may be bonded to
the polishing table 10 in various manners. For example, the
pedestal 251 may be fixed to the polishing table 10 by vacuum
attraction. FIGS. 21A and 21B show an example in which pedestals
2511, 2512, and 2513 each having a polishing pad piece 1111, 1112,
and 1113 attached thereon are fixed to a polishing table 10 by
vacuum attraction. As shown in FIGS. 21A and 21B, valves V11, V12,
and V13 for vacuum are provided in vacuum lines, and valves V21,
V22, and V23 for the atmosphere are provided in vacuum lines. The
valves V11, V12, and V13 are connected to a vacuum source 134
through vacuum lines 133.
[0132] As shown in FIG. 21A, the valves V11, V12, and V13 are
opened, and the valves V21, V22, and V23 are closed to attract the
respective pedestals 1511, 1512, and 1513 so as to fix the
polishing pad pieces 1111, 1112, and 1113 to the polishing table
10. In this state, as shown in FIG. 21B, the valve V12 is closed,
and the valve V22 is opened (or released to the atmosphere) while
the valves V11 and V13 are opened and the valves V21 and V23 are
closed. As a result, only the pedestal 2512 having the polishing
pad piece 1112 attached thereon can be removed or separated from
the polishing table 10. When the pedestal 2512 having the polishing
pad piece 1112 is attached again to the polishing table, the valve
22 is closed and the valve V12 is opened.
[0133] The valves V11, V12, V13, V21, V22, and V23 are not limited
to specific types of valves, but should preferably comprise a
solenoid valve capable of opening and closing based on electric
signals. In the example shown in FIGS. 21A and 21B, the pedestals
2511, 2512, and 2513 are individually attached to and removed from
the polishing table 10. However, the attachment and removal of the
pedestals 2511, 2512, and 2513 are not limited to this example. For
example, a plurality of pedestals 2511, 2512, and 2513 may
simultaneously be replaced by simultaneously releasing vacuum for
the pedestals 2511, 2512, and 2513, and may simultaneously be
attracted under vacuum. Alternatively, after simultaneously
releasing vacuum for a plurality of pedestals, part of the
pedestals may simultaneously be replaced and then attracted under
vacuum.
[0134] For example, the polishing table 10 as described above is
made of a material having a high thermal conductivity such as SiC,
and the pedestals 2511, 2512, and 2513 may be made of a material
having a low thermal conductivity such as resin. With this
configuration, the polishing pad pieces 1111, 1112, and 1113 and
the pedestals 2511, 2512, and 2513 can be attached to and removed
from the polishing table 10 effectively.
[0135] In the polishing apparatus according to the present
invention, a polishing pad to be attached to an upper surface of a
polishing table may have an upper surface with grooves for allowing
a polishing liquid to pass therethrough. Further, weirs may be
provided in the grooves to disturb the flow of the polishing
liquid. With this arrangement, the polishing liquid can effectively
be introduced into a polishing interface, i.e. between a workpiece
and the polishing pad. As a result, it is possible to reduce the
amount of polishing liquid, which is expensive, and hence to reduce
operating cost. With the weirs provided in the grooves to disturb
the flow of the polishing liquid, since the flow of the polishing
liquid in the grooves is disturbed by the weirs, the polishing
liquid can more effectively be introduced into the polishing
interface.
[0136] In the polishing apparatus according to the present
invention, a polishing pad may be bonded and fixed to an upper
surface of a polishing table by an adhesive of a liquid crystal
material. As described above, the liquid crystal material is
softened and lowered in adhesive strength under high temperatures
at which properties of the polishing pad are not changed while it
is hardened and increased in adhesive strength under a room
temperature. Therefore, the polishing pad can easily be bonded to
and removed from the polishing table.
[0137] Although certain preferred embodiments of the present
invention have been shown and described in detail, it should be
understood that various changes and modifications may be made
therein without departing from the scope of the appended
claims.
INDUSTRIAL APPLICABILITY
[0138] The present invention is suitable for use in a polishing
tool for polishing a workpiece such as a semiconductor wafer to a
flat mirror finish.
* * * * *