U.S. patent application number 10/985940 was filed with the patent office on 2005-04-28 for method and apparatus for polishing workpiece.
Invention is credited to Kimura, Norio, Shimizu, Noburu.
Application Number | 20050090188 10/985940 |
Document ID | / |
Family ID | 27527776 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050090188 |
Kind Code |
A1 |
Shimizu, Noburu ; et
al. |
April 28, 2005 |
Method and apparatus for polishing workpiece
Abstract
A workpiece such as a semiconductor wafer is polished by
pressing the workpiece against a polishing surface under a
predetermined pressure. A polished surface of the workpiece is
processed by pressing the workpiece against a processing surface
under a predetermined pressure while the processing surface makes
circulatory translational motion along a predetermined path. The
processing surface comprises a surface of a polishing cloth or a
surface of an abrading plate, and the polished surface of the
workpiece is further polished or cleaned.
Inventors: |
Shimizu, Noburu;
(Kanagawa-ken, JP) ; Kimura, Norio; (Kanagawa-ken,
JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
27527776 |
Appl. No.: |
10/985940 |
Filed: |
November 12, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10985940 |
Nov 12, 2004 |
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10134513 |
Apr 30, 2002 |
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10134513 |
Apr 30, 2002 |
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09301718 |
Apr 29, 1999 |
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6413156 |
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09301718 |
Apr 29, 1999 |
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08857252 |
May 16, 1997 |
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5989107 |
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09301718 |
Apr 29, 1999 |
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08972012 |
Nov 17, 1997 |
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09301718 |
Apr 29, 1999 |
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PCT/JP98/05253 |
Nov 20, 1998 |
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Current U.S.
Class: |
451/36 ;
257/E21.23; 451/270; 451/41 |
Current CPC
Class: |
B24B 37/26 20130101;
B24B 27/0023 20130101; B24B 37/245 20130101; H01L 21/67173
20130101; B24B 37/042 20130101; H01L 21/68792 20130101; B24B 37/16
20130101; H01L 21/30625 20130101; B24B 37/345 20130101; H01L
21/68785 20130101; B08B 1/04 20130101; B24B 37/12 20130101; H01L
21/67219 20130101; B24B 37/105 20130101 |
Class at
Publication: |
451/036 ;
451/041; 451/270 |
International
Class: |
B24B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 16, 1996 |
JP |
146776/1996 |
Nov 15, 1996 |
JP |
321141/1996 |
Nov 21, 1997 |
JP |
338032/1997 |
Claims
1. A method for polishing a pattern surface of a semiconductor
wafer comprising: main polishing said pattern surface by pressing
said semiconductor wafer downwards against a main polishing surface
comprising abrasive grains and a binder binding said abrasive
grains; finish polishing the main polished surface of said
semiconductor wafer by pressing said semiconductor wafer downwards
against a finish polishing surface comprising a polishing cloth;
and cleaning said finish polished surface of said semiconductor
wafer, and then drying said cleaned finish polished surface of said
semiconductor wafer.
2. A method according to claim 1, wherein said main polishing,
finish polishing, cleaning and drying processes are carried out in
a single polishing apparatus.
3. A method according to claim 1, wherein said main polishing
surface is the surface of an abrading plate shaped as a circular
disc.
4. A method according to claim 1, wherein said main polished
semiconductor wafer is washed before said finish polishing.
5. A method according to claim 1, wherein said main polishing and
said finish polishing are carried out by holding said semiconductor
wafer by different top rings.
6. A method according to claim 1, wherein the pressing force on
said semiconductor wafer in said finish polishing process is equal
to or lower than that in said main polishing process.
7. A method according to claim 1, wherein said pattern surface
comprises a wiring pattern.
8. A method according to claim 2, wherein said cleaned and dried
semiconductor wafer is transferred to a cassette.
9. A method according to claim 1, wherein said abrading surface has
a groove defined in the upper surface thereof.
10. A method according to claim 1, wherein said abrasive grains
comprise CeO.sub.2.
11. A method according to claim 1, wherein said abrading surface
comprises holes on its upper surface.
12. A method according to claim 1, wherein said main polishing
process is longer than said finish polishing process.
13. A method according to claim 1, wherein said finish polished
semiconductor wafer is washed in one or more cleaning machines and
then dried.
14. A method according to claim 1, wherein said semiconductor wafer
is reversed before it is main polished.
15. A method according to claim 1, wherein a polishing liquid
containing abrasive grains is supplied to said finish polishing
surface.
16. A method for polishing a surface of a semiconductor wafer
comprising: delivering said semiconductor wafer from a cassette to
an abrading plate, said semiconductor wafer being reversed so as to
face said surface to be polished downwards while delivering; main
polishing said surface of said semiconductor wafer by pressing said
semiconductor wafer downwards against an abrading surface of an
abrading plate, said abrading plate comprising abrasive grains and
a binder binding said abrasive grains; and finish polishing the
polished surface of said semiconductor wafer by pressing said
semiconductor wafer downwards against a finish polishing
surface.
17. A method according to claim 16, wherein said semiconductor
wafer is delivered by using a robot.
18. A method according to claim 16, wherein said semiconductor
wafer is reversed by a reversing machine.
19. A method according to claim 16, wherein said semiconductor
wafer is a patterned semiconductor wafer.
20. A method according to claim 19, wherein said patterned
semiconductor wafer comprises a wiring pattern.
21. A method according to claim 16, further comprising cleaning and
then drying said finish polished surface of said semiconductor
wafer.
22. A method according to claim 16, wherein said main polished
semiconductor wafer is washed before said finish polishing.
23. A method according to claim 16, wherein said main polishing and
said finish polishing are carried out by holding said semiconductor
wafer by different top rings.
24. A method according to claim 16, wherein the pressing force on
said semiconductor wafer in said finish polishing is equal to or
lower than that in said main polishing.
25. A method according to claim 21, wherein said main polishing,
finish polishing, cleaning and drying processes are carried out in
a single polishing apparatus.
26. A method according to claim 25, wherein said semiconductor
wafer is supplied from and returned to the same cassette.
27. A method according to claim 16, wherein said abrading surface
has a groove defined in the upper surface thereof.
28. A method according to claim 16, wherein said abrasive grains
comprise CeO.sub.2.
29. A method according to claim 16, wherein said abrading surface
comprises holes on its upper surface.
30. A method according to claim 16, wherein said main polishing
process is longer than said finish polishing process.
31. A method according to claim 21, wherein said finish polished
semiconductor wafer is washed in one or more cleaning machines and
then dried.
32. A method according to claim 16, wherein said abrading plate is
a circular disc.
33. A method according to claim 16, wherein said finish polishing
surface is formed on a polishing cloth.
34. A method according to claim 16, wherein a polishing liquid
containing abrasive grains is supplied to said finish polishing
surface.
35. A method for polishing a surface of a semiconductor wafer
comprising: delivering said semiconductor wafer from a cassette to
a main polishing unit; main polishing said surface of said
semiconductor wafer by pressing said semiconductor wafer downwards
against an abrading surface of an abrading plate in said main
polishing unit, said abrading plate comprising abrasive grains and
a binder binding said abrasive grains; and finish polishing the
polished surface of said semiconductor wafer by pressing said
semiconductor wafer downwards against a finish polishing surface in
a finish polishing unit.
36. A method for polishing a pattern surface of a semiconductor
wafer comprising: polishing said pattern surface by pressing said
semiconductor wafer against a polishing surface comprising abrasive
grains and a binder binding said abrasive grains; and polishing the
polished surface of said semiconductor wafer by pressing said
semiconductor wafer against a polishing surface comprising a
polishing cloth while supplying deionized water to said polishing
surface comprising said polishing cloth.
37. A method for polishing a pattern surface of a semiconductor
wafer comprising: polishing said pattern surface by pressing said
semiconductor wafer against a polishing surface comprising abrasive
grains and a binder binding said abrasive grains; and polishing the
polished surface of said semiconductor wafer by pressing said
semiconductor wafer against a polishing surface comprising a
polishing cloth while supplying deionized water or a chemical to
said polishing surface comprising said polishing cloth.
38. A method for polishing a surface of a workpiece comprising:
polishing said surface by pressing the workpiece against a first
polishing surface comprising abrasive grains and a binder binding
said abrasive grains; and further processing said polished surface
of the workpiece while supplying deionized water.
39. A method according to claim 38, wherein said further processing
is a rubbing process comprising pressing said polished surface of
the workpiece against a rubbing surface.
40. A method according to claim 38, wherein said further processing
is finish polishing comprising pressing said polished surface of
the workpiece against a polishing cloth.
41. A method according to claim 38, wherein the workpiece comprises
a semiconductor wafer having a pattern surface thereon.
42. A method according to claim 41, wherein protruded regions of
the pattern surface of the semiconductor wafer can be selectively
removed to produce an overall flat surface of the polished
semiconductor wafer.
43. A method according to claim 38, wherein a pressing force
applied to the workpiece during said further processing is equal to
or lower than a pressing force for pressing the workpiece against
said first polishing surface.
44. A method according to claim 38, wherein a first polishing
process by said first polishing surface is longer than said further
processing.
45. A method according to claim 38, wherein the workpiece is washed
between said polishing process and said further processing
process.
46. A method according to claim 38, wherein the workpiece is turned
over before attachment to a top ring for holding the workpiece.
47. A method according to claim 38, further comprising several
cleaning steps for cleaning the workpiece after said further
processing.
48. A method according to claim 38, further comprising a drying
step for drying the polished workpiece.
49. A method for polishing a surface of a semiconductor wafer
comprising: delivering the wafer from a cassette to a first
polishing table; reversing the wafer; attaching the wafer to a top
ring, which holds the wafer during a polishing operation; rotating
and pressing the wafer by said top ring against a first polishing
surface of said first polishing table, said first polishing surface
comprising abrasive grains and a binder binding said abrasive
grains, while supplying a polishing solution; cleaning the first
polished wafer; delivering the wafer to a second polishing table;
further processing the polished surface of the wafer with the
second polishing table, having a polishing cloth, while supplying
deionized water or a chemical; cleaning and then drying the
polished wafer; reversing the wafer; and delivering the wafer to
the cassette.
50-64. (canceled)
Description
[0001] This is a continuation-in-part of application Ser. No.
08/857,252, filed May 16, 1997, of application Ser. No. 08/972,012,
filed Nov. 17, 1997 and of International Application No.
PCT/JP98/05253, filed Nov. 20, 1998.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method and an apparatus
for polishing a workpiece, and more particularly to a method and an
apparatus for polishing a workpiece such as a semiconductor wafer,
a glass substrate, or a liquid crystal panel which is required to
be highly cleaned.
[0004] 2. Description of the Related Art
[0005] As semiconductor devices become more highly integrated in
recent years, circuit interconnections become finer and the
distances between those interconnections also become smaller
Photolithographic processes for producing interconnections that are
0.5 .mu.m wide or smaller, particularly, require a flat
image-focusing plane for the stepper because the depth between
focal points is small. If a dust particle whose size is greater
than the distances between the interconnections is present on a
semiconductor substrate, then an undesirable short circuit tends to
occur between interconnections through the dust particle.
[0006] Therefore, it is important that the workpiece processing
must produce a flat and clean workpiece. These processing
requirements apply equally to other workpiece materials, such as
glass substrates for photo-masking or liquid crystal display
panels.
[0007] One conventional polishing apparatus is shown in FIG. 9 of
the accompanying drawings. As shown in FIG. 9, the conventional
polishing apparatus includes a polishing unit 10, a
loading/unloading unit 21, a feed robot 22, and two cleaning
machines 23a, 23b. As shown in FIG. 10 of the accompanying
drawings, the polishing unit 10 comprises a turntable 12 with a
polishing cloth 11 attached to an upper surface thereof, and a top
ring 13: for holding a workpiece 1 such as a semiconductor wafer
and pressing the workpiece 1 against the polishing cloth 11 on the
turntable 12.
[0008] In operation, the workpiece 1 is supported on the lower
surface of the top ring 13, and pressed by a lifting/lowering
cylinder against the polishing cloth 11 on the turntable 12 which
is being rotated. A polishing solution (abrasive solution) Q is
supplied from a polishing solution nozzle 14 onto the polishing
cloth 11 and retained by the polishing cloth 11. The lower surface
of the workpiece 1 is polished by the polishing cloth 11 while the
polishing solution Q is being present between the workpiece 1 and
the polishing cloth 11.
[0009] The turntable 12 and the top ring 13 rotate at respective
speeds that are independent of each other. The top ring 13 holds
the workpiece 1 with its edges being spaced distances "a", "b" from
the center and the circumferential edge of the turntable 12. Thus,
the entire lower surface of the workpiece 1 is uniformly polished
at a high polishing rate. The workpiece 1 has a diameter "d". The
turntable 12 has a diameter "D" which is selected to be at least
twice the diameter "d" of the workpiece 1, as indicated by the
following equation:
D=2(d+a+b)
[0010] After having been polished, the workpiece 1 is cleaned in
one or more cleaning processes and dried by the cleaning machines
23a, 23b, and then housed in a delivery cassette 24 of the
loading/unloading unit 21. When the workpiece 1 is cleaned, it may
be scrubbed by a brush of nylon, mohair or the like, or a sponge of
PVA (polyvinyl alcohol).
[0011] In the conventional polishing apparatus, since the relative
displacement between the turntable 12 and the top ring 13 is large,
and the relative sliding speed between them is also large, the
workpiece 1 can be polished efficiently to a flat finish. However,
the polished surface of the workpiece 1 tends to have large surface
roughness.
[0012] In order to produce a polished workpiece of better surface
quality, consideration may be given to using two turntables which
are operated by varying the surface roughnesses of the polishing
cloths, rotational speeds and types of polishing solutions.
However, as mentioned above, the diameter of the turntable is
larger than twice that of the workpiece diameter, and each
apparatus takes up a large floor space area which leads to higher
facility costs. These problems becomes more ignorable as the
semiconductor manufacturing industry seeks larger diameter
substrates.
[0013] While it is possible to use one turntable to produce a
superior surface quality by varying the type of polishing solution
and lowering the rotational speed of the turntable, it is obvious
that such an approach leads not only to a potential increase in the
cost of polishing solution but also to inevitable lowering in the
production efficiency due to a prolonged polishing operation.
[0014] In order to make the workpiece clean, there are some cases
where scrubbing process is carried out after the workpiece 1 has
been polished using the polishing solution Q. However, such
scrubbing process fails to remove submicron particles from the
polished surface of the workpiece 1, and is not effective enough to
clean the polished workpiece 1 if remaining particles are bonded to
the workpiece 1 by large bonding strength.
[0015] Further, the conventional polishing apparatus of the type
described above has an advantage that the entire surface of the
workpiece is polished uniformly, because the elasticity of the
polishing cloth 11 moderates the effects of undulation and bowing
in the workpiece. However, the workpiece such as a semiconductor
wafer is susceptible to edge wear caused by excessive polishing
around the peripheral edge of the wafer. Further, in order to
polish semiconductor wafers with printed wiring patterns, it is
required to obtain a polished surface having flatness of less than
1,000 angstrom by removing any micro-protrusions from uneven
surface of the semiconductor wafer. However, the polishing cloth 11
is unable to meet this requirement because the elasticity of the
polishing cloth allows the cloth itself to deform and the material
from recessed regions as well as from protruding regions is
removed.
SUMMARY OF THE INVENTION
[0016] It is therefore an object of the present invention to
provide a method and an apparatus for polishing a workpiece such as
a semiconductor wafer to a smooth flat finish with improved surface
roughness, while effectively removing minute particles from the
polished surface.
[0017] Another object of the present invention is to provide a
compact polishing apparatus to produce a high degree of flatness of
a workpiece such as a semiconductor wafer.
[0018] According to one aspect of the present invention, there is
provided a method for polishing a workpiece, comprising: polishing
a surface of the workpiece by pressing the workpiece against a
polishing surface; and processing a polished surface of the
workpiece by pressing the workpiece against a processing surface,
the processing surface making relative translational motion
relative to the workpiece.
[0019] According to another aspect of the present invention, there
is also provided an apparatus for polishing a workpiece,
comprising: a polishing unit for polishing a surface of the
workpiece by pressing the surface of the workpiece against a
polishing surface; a processing unit for processing a polished
surface of the workpiece by pressing the workpiece against a
processing surface, the processing surface making relative
translational motion relative to the workpiece.
[0020] According to the present invention, the relative
translational motion includes a relative motion of two surfaces of
many patterns. The typical pattern is circular or circulative i.e.,
repeating itself, and has a circular trace without respective
rotational motion. However, it may include a respective rotation of
a relatively large period of rotation compared to that of the
circulative translation between the two surfaces. The trace of
translation motion can be a linear translation pattern, a polygonal
pattern or an elliptical pattern, but from the practical standpoint
of polishing or processing efficiency and mechanical ease, a
circular pattern would be optimum. In the circulative translation
motion, all the regions of the workpiece are subjected to the same
pattern.
[0021] In the present invention, a high removal ratio and a high
flatness of the workpiece such as a semiconductor wafer is obtained
in the polishing step, by subjecting the workpiece to a high speed
material removal process with the polishing surface. In the
processing step, the surface processing is carried out by a
processing surface at a slow relative speed to attain a smooth
surface of the workpiece, and also any micro-particles which may be
adhered to the workpiece are removed. The surface of the workpiece
is treated with a solution appropriate to the application. That is,
in case that the processing step comprises a polishing step,
abrasive particles are used while purified water or a suitable
chemical solution is used in the processing step. In the processing
step, abrasive particles are normally not used, and if they are
used, a small amount of ultra-fine particles are used, and the
pressing pressure of the workpiece against the processing surface
is reduced compared to the polishing step.
[0022] Generally, a polishing apparatus of the circulatory
translational motion type may have a processing surface such as a
polishing cloth which is of relatively small dimensions. Then, the
relative speed between the surface being polished of a workpiece
and a polishing cloth is so small that sufficient polishing speed
cannot be achieved for polishing the workpiece. According to the
present invention, the processing surface which makes circulatory
translational motion can be used because no large processing speed
is required by the processing unit such as a cleaning unit.
[0023] In case that a surface of an abrading plate is used as a
polishing surface or a processing surface, such an apparatus can
satisfy a wide range of polishing needs, from rough grinding to
finish polishing, by choosing an abrasive grain size, a method of
supplying the polishing solution and a rotational speed to suit
each work. That is, to perform rough polishing, abrading surface is
made coarser and a relatively high speed and high pressing pressure
are used. On the other hand, to perform finish polishing, abrading
surface is made finer and a relatively low speed and low pressing
pressure are applied. Removal of micro-particles adhering to the
workpiece surface may also be performed during the finish polishing
by using a solution appropriate to the purpose. Specifically, for
rough polishing, abrasive grains are used while for finish
polishing, deionized water and solutions may be used. Abrading
grains are normally not used in finish polishing, but if they are
needed, a small amount of ultra-fine micro-grains is used.
[0024] The circulatory translational motion is defined as "a
relative motion between a first surface and a second surface facing
the first surface and a non-rotational motion which causes every
point on the first surface to describe a substantially identical
locus with respect to the second surface." The locus may be a
circle, an ellipse, a polygon, or any other regular shape. For a
better polishing ability and mechanical reasons, the circulatory
translational motion should preferably be made along a circular
path. The circulatory translational motion along the circular path
allows the confronting surfaces to move relatively to each other
uniformly in different areas thereof.
[0025] The circulatory translational motion of this invention has
the same meaning as orbital motion.
[0026] In preferred aspects, the polishing surface may comprise a
surface of a polishing cloth or a surface of an abrading plate. The
polishing surface may rotate about its rotating axis or make
relative translational motion relative to the workpiece. The
translational motion of the polishing surface may be provided only
by moving the polishing surface.
[0027] The processing may comprise polishing of the polished
surface of the workpiece or cleaning of the polished surface of the
workpiece. The processing surface may comprise a surface of a
polishing cloth or a surface of a wiping cloth or a surface of an
abrading plate. The relative translational motion of the processing
surface may be provided only by moving said processing surface.
[0028] The above and other objects, features, and advantages of the
present invention will become apparent from the following
description when taken in conjunction with the accompanying
drawings which illustrate a preferred embodiment of the present
invention by way of example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a plan view of a polishing apparatus according to
a first embodiment of the present invention;
[0030] FIG. 2 is a vertical cross-sectional view of a finish
polishing unit of the polishing apparatus shown in FIG. 1;
[0031] FIG. 3A is an enlarged plan view of a support structure on a
casing for supporting the edge of a surface plate of the finish
polishing unit shown in FIG. 2; and
[0032] FIG. 3B is a fragmentary cross-sectional view taken along
line A-A of FIG. 3A.
[0033] FIG. 4 is a perspective view of a modified embodiment of the
finish polishing unit;
[0034] FIG. 5 is a plan view of a polishing apparatus according to
a second embodiment of the present invention;
[0035] FIG. 6 is a vertical cross-sectional view of a cleaning unit
of the polishing apparatus shown in FIG. 5;
[0036] FIG. 7 is a plan view of a polishing apparatus according to
a third embodiment of the polishing apparatus;
[0037] FIG. 8 is a vertical cross-sectional view of a polishing
unit of the polishing apparatus shown in FIG. 7;
[0038] FIG. 9 is a perspective view of a conventional polishing
apparatus; and
[0039] FIG. 10 is a cross-sectional view of a conventional
polishing unit of the conventional polishing apparatus shown in
FIG. 9.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] Next, a polishing apparatus according to a first embodiment
of the present invention will be described with reference to FIGS.
1 through 3A and 3B.
[0041] As shown in FIG. 1, a polishing apparatus has a
loading/unloading unit 21 positioned at an end of an elongate
rectangular space for loading and unloading workpieces 1 (see FIG.
2) such as semiconductor wafers, and a main polishing unit 10
positioned at an opposite end of the elongate rectangular space for
polishing the workpieces 1. The loading/unloading unit 21 and the
main polishing unit 10 are interconnected by a workpiece delivery
line along which two feed robots 22a, 22b are movable between the
loading/unloading unit 21 and the main polishing unit 10. The
polishing apparatus also includes a reversing machine 25 disposed
on one side of the workpiece delivery line for reversing the
workpieces 1, a finish polishing unit (second polishing section) 30
and three cleaning units 23a, 23b, 23c disposed on the other side
of the workpiece delivery line. The cleaning units 23a, 23b, and
23c include rinsing machines or scrubbing machines using brushes,
sponges or the like.
[0042] The main polishing unit 10 comprises a turntable 12 and two
top rings 13, and is capable of parallel processing of two
workpieces simultaneously. Except for the two top rings 13, the
main polishing unit 10 is basically the same as the polishing unit
10 shown in FIGS. 9 and 10.
[0043] The finish polishing unit 30 will be described below with
reference to FIGS. 2 through 3A and 3B.
[0044] The finish polishing unit 30 comprises a translational table
section 31 which provides an abrading surface that makes
[0045] circulatory translational motion, and a top ring 32 for
holding a workpiece 1 with its lower surface facing downwardly and
pressing the workpiece 1 against the abrading surface with a given
pressure.
[0046] The translational table section 31 comprises a vertical
cylindrical casing 34 housing an electric motor 33 therein and
having an annular support flange 35 extending radially inwardly
from an upper peripheral edge of the casing 34. The support flange
35 has on its upper surface three or more circumferentially spaced
support structures 36 which carry a surface plate 37 thereon.
Specifically, as shown in FIG. 3B, the surface plate 37 has a
plurality of circumferentially equally spaced cavities 38 defined
in its lower surface, and the support flange 35 nas a plurality of
circumferentially equally spaced cavities 39 defined in its upper
surface. The cavities 38 and the cavities 39 are slightly
horizontally displaced from each other for reasons described below.
The support structures 36 comprise respective upper bearings 40
disposed in the respective cavities 38 and respective lower
bearings 41 disposed in the respective cavities 39. The upper and
lower bearings 40, 41 of each of the support structures 36 are
axially interconnected by a cranked joint 44 having upper and lower
shafts 42, 43 that are fitted respectively in the upper and lower
bearings 40, 41. The shafts 42, 43 and hence the upper and lower
bearings 40, 41 have respective axes horizontally spaced from each
other by a distance "e". The surface plate 37 is coupled to the
motor 33 as described below. When the motor 33 is energized, the
surface plate 37 that is coupled to the motor 33 and supported by
the support structures 36 can make translational motion along
circles each having a radius which is the same as the distance
"e".
[0047] The surface plate 37 has a tubular member projecting
downwardly from the lower surface thereof and defining a recess 48
therein. The motor 33 has a vertical shaft 45 having an upper end
connected to an eccentric drive shaft 46 that is rotatably mounted
in the recess 48 by a bearing 47. The eccentric driveshaft 46 has
its central axis Z2 spaced horizontally from a central axis Z1 of
the shaft 45 by a distance "e". The motor 33 is disposed in a motor
chamber 49 that is defined in the casing 34, and the shaft 45 is
rotatably supported in the casing 34 by upper and lower bearings
50, 51. Balancers 52a, 52b are attached respectively to upper and
lower ends of the shaft 45 for keeping the shaft 45 in a balanced
state while the shaft 45 is rotated in unison with the eccentric
drive shaft 46.
[0048] The surface plate 37 has a diameter which is slightly larger
than the sum of the diameter of the workpiece 1 to be polished and
the distance "e". The surface plate 37 comprises two plate members
53, 54 joined to each other with a space 55 defined therebetween
for allowing a polishing solution (abrasive liquid) to be supplied
to a polishing surface to pass therethrough. The space 55 is held
in communication with a supply port 56 defined in a side surface of
the surface plate 37 and also with a plurality of discharge ports
57 defined in the upper plate member 53 and opening upwardly. A
polishing cloth 59 is attached to the upper surface of the surface
plate 37, and has a plurality of discharge holes 58 defined therein
and aligned in registry with the respective discharge ports 57. The
upper surface of the polishing cloth 59 constitutes a polishing
surface. Usually, the discharge ports 57 and the discharge holes 58
are disposed substantially uniformly over the entire surface of the
surface plate 37. The polishing cloth 59 may have a grid-like
spiral, or radial pattern of fluid flow grooves defined in the
upper surface thereof, and the discharge holes 58 may be held in
communication with those grooves.
[0049] The top ring 32 is mounted on the lower end of a shaft 60 so
as to allow the top ring 32 to tilt upon changes in the inclination
of the polishing surface of the polishing cloth 59. Downward
pressing forces applied by an air cylinder (not shown) and rotative
forces from a drive motor (not shown) are transmitted through the
shaft 60 to the top ring 32. The top ring 32 is structurally
identical to the top ring 13 shown in FIGS. 9 and 10 except that
the top ring 32 rotates about its axis at a lower speed. The upper
end of the casing 34, the surface plate 37, and the top ring 32 are
horizontally surrounded by a reservoir 61 mounted on the upper end
of the casing 34 for collecting a polishing solution that is
supplied during polishing.
[0050] Operation of the polishing apparatus will be described below
A workpiece 1, typically a semiconductor wafer, in a delivery
cassette, identical to the delivery cassette 24 shown in FIG. 9, is
delivered by the feed robots 22a, 22b through the reversing machine
25, if necessary, to one of the top rings 13 of the main polishing
unit 10, and is attached to the top ring 13. The top ring 13
rotates about its own axis and presses the workpiece 1 against the
polishing cloth 11 (see FIG. 10) on the turntable 12. A first
polishing process is carried out by the actions of the high-speed
relative movement between the workpiece 1 and thc polishing cloth
11, and of the chemical effects produced by the polishing solution
supplied from the polishing solution nozzle 14 (see FIG. 10).
[0051] After having completed the first polishing process by the
main polishing unit 10, the workpiece 1 is, either directly or
after rough cleaning, transferred to the finish polishing unit 30
where the workpiece 1 is subject to a second polishing process.
Specifically, the motor 33 is energized to cause the surface plate
37 to make circulatory translational motion, and the workpiece 1
attached to the top ring 32 is pressed against the upper surface of
the polishing cloth 59 that is attached to the surface plate 37.
The surface of the polishing cloth 59 constitutes a processing
surface.
[0052] The workpiece 1 is then polished by a polishing solution
that is supplied to the surface to be polished of the workpiece 1
through the supply port 56, the space 55, the discharge ports 57,
and the discharge holes 58. The discharge ports 57 and the
discharge holes 58 allow the polishing solution to be supplied at a
sufficient rate to the entire area of the workpiece 1 including the
central area. Since small relative translational motion along
circles having the radius "e" occurs between the polishing cloth 59
and the workpiece 1, the workpiece 1 is uniformly polished over its
entire surface. If the polished surface of the workpiece 1 and the
polishing cloth 59 stay in the same relative positional
relationship, then the polished surface of the workpiece 1 would be
adversely affected by local irregularities of the polishing cloth
59. To avoid this drawback, the top ring 32 is rotated slowly about
its own axis so that the surface of the workpiece 1 is not polished
by the same local areas of the polishing cloth 59. Therefore, the
surface of the workpiece 1 is polished by successively different
areas of the polishing cloth 59, and hence is more uniformly
polished.
[0053] In the first polishing process carried out by the main
polishing unit 10, in order to obtain a given polishing rate, the
workpiece I and the polishing cloth 11 (see FIG. 10) are moved
relatively to each other at a high speed and pressed against each
other under relatively large forces. In the second polishing
process carried out by the finish polishing unit 30, since minute
particles need to be removed from the polished surface of the
workpiece 1 while the flatness and surface roughness of the
workpiece 1 are also required to be improved, the surface roughness
of the polishing cloth 59 is small, and the velocity of relative
motion between the workpiece 1 and the polishing cloth 59 and the
pressing force of the workpiece 1 against the polishing cloth 59
are smaller than those of the first polishing process. The
polishing solution is usually pure water, but may be a chemical or
a special slurry if necessary. For example, a chemical or a special
slurry depending on the material of the workpiece 1 may be supplied
between the workpiece 1 and the polishing cloth 59.
[0054] After the second polishing process of the workpiece 1 has
been completed by the finish polishing unit 30, the workpiece 1 is
cleaned by the cleaning machines 23a.about.23c in one or more
cleaning processes and then dried, and thereafter accommodated in
the delivery cassette 24.
[0055] In the polishing apparatus, the main polishing unit 10 has
two top rings 13. Therefore, if the time required for the second
polishing process is reduced to about half the time required for
the first polishing process, then the main polishing unit 10 and
the finish polishing unit 30 can be operated efficiently without a
loss time.
[0056] In this polishing apparatus, since the polishing process is
carried out in two stages which are being carried out
simultaneously, the time duration in the first polishing step can
be reduced, so that the process throughput is increased compared to
the rate obtainable with the conventional polishing apparatus shown
in FIGS. 9 and 10.
[0057] Since the polishing unit 30 is of the circulatory
translational motion type, the diameter of the surface plate 37 may
be slightly larger than the diameter of the workpiece 1 by the
distance "e".
[0058] Therefore, compared with a polishing apparatus having two
turntables of the same size as the main polishing unit 10, the
required floor space is reduced significantly. Further, because the
finish polishing unit 30 makes circulatory translational motion, it
is possible to support the surface plate 37 at several locations
along the peripheral edges of the surface plate 37, as shown in
FIG. 2, so that the workpiece can be polished to a higher flatness
than with the turntable which rotates at a high speed.
[0059] Examples of average conditions for the first polishing
process and the second polishing process are given as follows:
[0060] 1. First Polishing Process:
[0061] Polishing solution (Abrasive solution): Differs depending on
the material of the workpiece
[0062] Polishing cloth: Differs depending on the material of the
workpiece
[0063] Pressure applied to the workpiece: 200.about.500
g/cm.sup.2
[0064] Relative speed: 0.07.about.0.6 in/sec.
[0065] Polishing time: Differs depending on the amount of material
to be removed by polishing.
[0066] 2. Second Polishing Process:
[0067] Polishing solution: Water, a chemical, a slurry
[0068] Polishing cloth: Soft cloth (non-woven cloth, nap-like
material)
[0069] Pressure applied to the workpiece; 0.about.200
g/cm.sup.2
[0070] Relative speed: 0.07.about.0.6 m/sec.
[0071] Polishing time: 10.about.120 sec.
[0072] While the polishing cloth 59 makes circulatory translational
motion in the illustrated embodiment, the workpiece 1 may make
circulatory translational motion with respect to the polishing
cloth 59. In the illustrated embodiment, the surface plate 37 is
supported using the cranked joints 44 combined with the bearings
40, 41. However, the surface plate 37 may be supported by a
suitable support structure, such as magnetic bearings or
lubrication-free slide bearings, which allow the surface plate 37
to make circulatory translational motion while preventing it from
rotating about its own axis.
[0073] In the illustrated embodiment, the surface plate 37 is
caused to make circulatory translational motion by the eccentric
drive shaft 46 on the shaft 45 of the motor 33. However, the
surface plate 37 may be moved by a vector sum of motion in an X
direction and motion in a Y direction using an X-Y stage, or the
polishing cloth 59 and the workpiece 1 may jointly be moved to make
circulatory translational motion.
[0074] FIG. 4 shows an embodiment of a polishing apparatus of this
type comprising a top ring 100 for holding a workpiece on the lower
surface thereof, and a polishing tool 101 arranged beneath the top
ring 100 and attached to the X-Y stage. In this embodiment, an
electroplated grindstone is utilized as a polishing tool of a
relatively small abrasive grain size. The X-Y stage comprises an
X-stage 102, a Y-stage 103 and a fixing plate 104 which are piled
up in the order and mounted on a base 105. Between the X-stage 102
and the Y-stage 103, there are provided a linear guide mechanism
and a linear driving mechanism such as a feed screw so as to make
the X-stage 102 movable in the X direction. The same mechanisms are
provided between the Y-stage 103 and the fixing plate 104, and a
controlling device is provided for controlling these X- and
Y-direction driving mechanisms.
[0075] In the illustrated embodiment, by applying a displacement
having a sine-wave and a cosine-wave of the same phase to the
X-stage 102 and the Y-stage 103 respectively, the X-stage 102 will
make circulatory translational motion as a vector sum of both
directional movements. Thus, the polishing tool 101 makes
circulatory translational motion as in the first embodiment of the
invention. It is preferable to rotate the top ring 100 with a
period of rotation significantly in excess of a period of the
circulatory translational motion of the tool 101 in order to
eliminate the effect resulting from a local difference of surface
condition of the tool.
[0076] This embodiment, since a mechanical "eccentric" design is
not used, has an advantage that more degrees of freedom in changing
the trace (or locus) of the circulatory translational motion can be
obtained. For example, since it is possible to change the diameter
of the circulatory translational motion without stopping the
operation, the polishing motion during the polishing step of the
workpiece can be changed so as to polish the workpiece with a
smaller diameter in the starting and terminating periods than in
the usual polishing period. By applying such a control method, it
can avoid the deteriorative effects caused by the localized
conditional differences on the polishing tool surface, such as a
unidirectional scar, when repeating a simple circulative
motion.
[0077] The structure of this embodiment can create not only
circular translational motion but also any other type of
circulatory translational motion such as, an ellipsoidal motion, an
eight-shape (8) motion or an oscillating spiral motion, or any kind
of combination thereof.
[0078] Further, the structure of this embodiment can create not
only circulatory motion having a certain trace but also totally
random translational motion which is by no means circulatory. This
intentional randomization of the relative translational motion can
be performed by using a random number generation function of a
computer processor, for example. In this case, it is preferable to
retain a minimum radius of curvature of the trace in order to keep
a smooth motion.
[0079] According to the present invention, since the polishing
process is carried out in two stages, first and second polishing
steps, it is possible to produce a high degree of flatness and
smoothness of the workpiece. In the first polishing step, the
workpiece and the polishing tool are moved relative to each other
at relatively high speeds to produce flat surface of the workpiece.
This is followed by a second step to obtain smooth surface of the
workpiece by using a polishing tool having a lesser abrasive
quality and providing a relatively small degree of relative motion
between the workpiece and the polishing tool. The polishing process
is completed by removing micro-particles which may adhere to the
workpiece, to thus produce a workpiece having a high degree of
flatness, smoothness and cleanliness.
[0080] According to the present invention, since the second
polishing unit of the present invention makes circulatory
translational motion, the size of the apparatus can be slightly
larger than the workpiece by the distance of eccentricity, thus
enabling the apparatus to be compact. Additional benefit is that
the drive motor can be small and the occupied floor space is also
small The surface plate is supported at three locations or more
around the periphery of the surface plate so that the application
of the pressing force does not affect the stability of supporting
member and the flatness of the polished surface can be
maintained.
[0081] Next, a polishing apparatus according to a second embodiment
of the present invention will be described with reference to FIGS.
5 and 6.
[0082] As shown in FIG. 5, a polishing apparatus has a
loading/unloading unit 21 positioned at an end of an elongate
rectangular space for loading and unloading workpieces 1 (see FIG.
6) such as semiconductor wafers, and a main polishing unit 10
positioned at an opposite end of the elongate rectangular space for
polishing the workpieces 1. The loading/unloading unit 21 and the
main polishing unit 10 are interconnected by a workpiece delivery
line along which two feed robots 22a, 22b are movable between the
loading/unloading unit 21 and the main polishing unit 10. The
polishing apparatus also includes a reversing machine 25 disposed
on one side of the workpiece delivery line for reversing the
workpieces 1, a cleaning unit 130 and three cleaning units 23a,
23b, 23c disposed on the other side of the workpiece delivery line.
The cleaning units 23a, 23b, and 23c include rinsing machines or
scrubbing machines using brushes, sponges, or the like.
[0083] The main polishing unit 10 comprises a turntable 12 and two
top rings 13, and is capable of parallel processing of two
workpieces simultaneously. Except for the two top rings 13, the
main polishing unit 10 is basically the same as the polishing unit
10 shown in FIGS. 9 and 10.
[0084] As shown in FIG. 6, the cleaning unit 130 has the same
structure as the polishing unit 30 of the first embodiment shown in
FIG. 2.
[0085] Specifically, the cleaning unit 130 comprises a
translational table section 31 which provides an abrading surface
that makes circulatory translational motion, and a top ring 32 for
holding a workpiece 1 with its lower surface facing downwardly and
pressing the workpiece 1 against the abrading surface with a given
pressure.
[0086] Since the translational table section 31 has the same
structure as that of the first embodiment shown in FIG. 2, the
detailed structure will not be described.
[0087] In the second embodiment, a cleaning solution is supplied to
the surface to be cleaned of the workpiece through the supply port
56, the space 55, the discharge ports 57, and the discharge holes
58.
[0088] Operation of the polishing apparatus shown in FIGS. 5 and 6
will be described below.
[0089] A workpiece 1, typically a semiconductor wafer, in a
delivery cassette, identical to the delivery cassette 24 shown in
FIG. 9, is delivered by the feed robots 22a, 22b through the
reversing machine 25, if necessary, to one of the top rings 13 of
the main polishing unit 10, and is attached to the top ring 13. The
top ring 13 rotates about its own axis and presses the workpiece 1
against the polishing cloth 11 (see FIG. 10) on the turntable 12.
The workpiece 1 is polished by the polishing solution Q supplied
from the polishing solution nozzle 14 while the workpiece 1 and the
polishing cloth 11 are moving relatively to each other at a high
speed.
[0090] After having been polished by the main polishing unit 10,
the workpiece 1 is, either directly or after a rough cleaning,
transferred to the cleaning unit 130 where the workpiece 1 is
cleaned. Specifically, the motor 33 is energized to cause the
surface plate 37 to make circulatory translational motion, and the
workpiece 1 attached to the top ring 32 is pressed against the
upper surface of the polishing cloth 59 that is attached to the
surface plate 37.
[0091] The workpiece 1 is then cleaned by a cleaning solution that
is supplied to the surface of the workpiece 1 through the supply
port 56, the space 55, the discharge ports 57, and the discharge
holes 58. The discharge ports 57 and the discharge holes 58 allow
the cleaning solution to be supplied at a sufficient rate to the
entire area of the workpiece 1 including the central area. Since
small relative translational motion along circles having the radius
"e" occurs between the polishing cloth 59 and the workpiece 1, the
workpiece 1 is uniformly polished over its entire surface. If the
polished surface of the workpiece 1 and the polishing cloth 59 stay
in the same relative positional relationship, then the polished
surface of the workpiece 1 would be adversely affected by local
irregularities of the polishing cloth 59. To avoid this drawback,
the top ring 32 is rotated slowly about its own axis so that the
surface of the workpiece 1 will not be polished only by local areas
of the polishing cloth 59. Therefore, the surface of the workpiece
1 is polished by successively different areas of the polishing
cloth 59, and hence is more uniformly polished.
[0092] In the polishing process carried out by the main polishing
unit 10, since the workpiece 1 needs to be polished to a desired
surface finish or to be polished in a desired polishing speed, the
workpiece 1 and the polishing cloth 59 are moved relatively to each
other at a high speed and pressed against each other under
relatively large forces for thereby polishing the workpiece 1 to a
flat finish, or for thereby polishing the workpiece 1 in a high
polishing speed. In the cleaning process carried out by the
cleaning unit 130, since minute particles need to be removed from
the polished surface of the workpiece 1 while the flatness and
surface roughness of the workpiece 1 are also required to be
improved, the surface roughness of the polishing cloth 59 is small,
and the velocity of relative motion between the workpiece 1 and the
polishing cloth 59 and the pressing force of the workpiece 1
against the polishing cloth 59 are smaller than with the polishing
process. The cleaning solution is usually pure water, but may be a
chemical or a special slurry if necessary. For example, a chemical
or a special slurry depending on the material of the workpiece 1
may be supplied between the workpiece 1 and the polishing cloth 59.
In the polishing process, the polishing solution contains abrasive
particles. In the cleaning process, the cleaning solution usually
does not contain abrasive particles, but may contain fine abrasive
particles.
[0093] After the workpiece 1 has been cleaned by the cleaning unit
130, the workpiece 1 is further cleaned by the cleaning machines
23a.about.23c in one or more cleaning processes and then dried, and
thereafter accommodated in the delivery cassette 24.
[0094] In the polishing apparatus, the main polishing unit 10 has
two top rings 13. Therefore, if the time required for the cleaning
process is reduced to about half the time required for the
polishing process, then the main polishing unit 10 and the cleaning
unit 130 can be operated efficiently without a loss time.
[0095] Consequently, there is the advantage that the overall
throughput of the polishing apparatus is much higher than the
conventional polishing apparatus shown in FIGS. 9 and 10.
[0096] Since the cleaning unit 130 is of the circulatory
translational motion type, the diameter of the surface plate 37 may
be slightly larger than the diameter of the workpiece 1 by the
distance "e". Therefore, the motor 33 may be of a relatively small
size, and the polishing apparatus may take up a relatively small
space. These advantages manifest themselves when the workpiece 1
such as a semiconductor wafer is larger in size.
[0097] Inasmuch as the polishing cloth 59 in the cleaning unit 130
does not rotate about its own axis, the relative speed between the
workpiece 1 and the polishing cloth 59 remains in the same
condition at any position on the workpiece 1. Therefore, the
workpiece 1 can be processed to a flat finish even when it is
processed at a low speed, and can advantageously be processed to a
smooth surface finish. An installation space for the cleaning unit
130 may be comparatively small. Because the surface plate 37 of the
cleaning unit 130 makes circulatory translational motion, the
surface plate 37 can be supported at a plurality of positions along
its circumferential edge, as shown in FIG. 6. Therefore, even when
the surface plate 37 is subjected to large pressing forces, the
surface plate 37 can stably be supported, thus allowing the
workpiece 1 to be polished to a higher planar finish than with a
turntable which rotates at a high speed.
[0098] Examples of average conditions for the polishing and
cleaning processes are given as follows:
[0099] 1. Polishing Process:
[0100] Polishing solution: Differs depending on the material of the
workpiece
[0101] Polishing cloth: Differs depending on the material of the
workpiece
[0102] Pressure applied to the workpiece: 200.about.500
g/cm.sup.2
[0103] Relative speed: 0.07.about.0.6 m/sec.
[0104] Polishing time: Differs depending on the amount of material
to be removed by polishing.
[0105] 2. Cleaning Process:
[0106] Cleaning solution: Water, a chemical, a slurry
[0107] Polishing cloth: Soft cloth (non-woven cloth, nap-like
material)
[0108] Pressure applied to the workpiece: 0.about.200
g/cm.sup.2
[0109] Relative speed: 0.07.about.0.6 m/sec.
[0110] Cleaning time: 10.about.120 sec.
[0111] While the polishing cloth 59 makes circulatory translational
motion in the illustrated embodiment, the workpiece 1 may make
circulatory translational motion with respect to the polishing
cloth 59. In the illustrated embodiment, the surface plate 37 is
caused to make circulatory translational motion by the eccentric
drive shaft 46 on the shaft 45 of the motor 33. However, the
surface plate 37 may be moved by a vector sum of motion in an X
direction and motion in a Y direction using an X-Y stage, or the
polishing cloth 59 and the workpiece 1 may jointly be moved to make
circulatory translational motion. In the illustrated embodiment,
the surface plate 37 is supported using the cranked joints 44
combined with the bearings 40, 41. However, the surface plate 37
may be supported by a suitable support structure, such as magnetic
bearings or lubrication-free slide bearings, which allows the
surface plate 37 to make circulatory translational motion while
preventing it from rotating about its own axis.
[0112] Various changes and modifications may be made in the present
invention insofar as they have a polishing unit including a first
abrasive member rotatable about its own axis for polishing a
workpiece while the workpiece is being pressed against the first
abrasive member under a predetermined pressure, and a cleaning unit
including a second abrasive member made of a wiping cloth, a
non-woven cloth, or a cloth other than a non-woven cloth for
scrubbing the workpiece while being pressed against the polished
surface of the workpiece. For example, the polishing unit 10 with
the two top rings 13 as shown in FIG. 5 may be replaced with the
polishing unit 10 with the single top ring 13 as shown in FIG. 10,
and the cleaning unit 130 with the surface plate 37 making
circulatory translational motion may be replaced with a cleaning
unit with the turntable 12 and the single top ring 13 as shown in
FIG. 10. In such a modification, the polishing solution is used in
the polishing unit, whereas the cleaning solution such as water, a
chemical or a slurry is used in the cleaning unit, and the relative
speed between the workpiece and the abrasive member, the pressure
under which the workpiece and the abrasive member are pressed
against each other, and the surface roughness of the abrasive
member are set to different values in the polishing and cleaning
units.
[0113] The second abrasive member in the cleaning unit may comprise
a polishing cloth, a wiping cloth, or the like. The polishing cloth
is generally used to polish semiconductor wafers to a flat mirror
finish, and is available on the market. For example, the polishing
cloth may be a non-woven cloth of polyester, Suba 800 or IC-1000
manufactured by Rodel, Inc., Surf in xxx-5, Surfin 000 manufactured
by Fujimi Incorporated. The polishing cloths, Suba 800, Surfin
xxx-5, and Surfin 000 are made of fibers and put together by an
urethane resin, and the polishing cloth IC-1000 is made of foamed
polyurethane. The foamed polyurethane is porous and has a number of
minute recesses on its surface which are considered to be capable
of holding particles.
[0114] The polishing cloth is basically used to polish
semiconductor wafers and is of such a structure as to attract
abrasive particles contained in a polishing solution to its own
surface. When the polishing cloth is used for cleaning
semiconductor wafers, the polishing cloth is effective to easily
remove particles that strongly adheres to the semiconductor
wafers.
[0115] Because the cleaning unit uses a polishing cloth that is
originally used to polish a semiconductor wafer, the polishing
cloth can reduce the surface roughness of the semiconductor wafer,
and hence makes the surface of the semiconductor wafer flat and
smooth when the cleaning unit cleans the semiconductor wafer. This
effect of the polishing cloth was confirmed by way of
experimentation.
[0116] The wiping cloth is made of ultrafine fibers having a
diameter ranging from 1 to 2 .mu.m, and is commercially available
as miracle series (tradename) of Toray, Minimax (tradename) of
Kanebo, etc. Since these wiping cloths have 100.about.200 thousand
fibers per one square inch, they have many points of contact with a
workpiece to be wiped for thereby removing minute particles from
the workpiece.
[0117] Since the wiping cloth is a thin cloth, it may be attached
to the surface plate through a damper of sponge, rubber, or the
like so as not to damage the workpiece 1 while cleaning the
workpiece 1.
[0118] The principles of the present invention are applicable to
various workpieces including a glass substrate and a liquid crystal
panel which need to be highly cleaned.
[0119] The polishing apparatus shown in FIG. 5 may further be
modified such that the cleaning units 23a, 23b, 23c such as rinsing
machines or scrubbing machines may be positioned adjacent to the;
polishing unit 10 for removing relatively large particles from the
workpiece, and the cleaning unit 130 may be positioned adjacent to
the cleaning units 23a, 23b, 23c for removing submicron particles
that cannot be removed from the workpiece by a scrubbing action
using a brush or a sponge.
[0120] Next, a polishing apparatus according to a third embodiment
of the present invention will be described with reference to FIGS.
7 and 8.
[0121] As shown in FIG. 7, a polishing apparatus has a
loading/unloading unit 21 positioned at an end of an elongate
rectangular space for loading and unloading workpieces 1 (see FIG.
8) such as semiconductor wafers, and two main polishing units 230a,
230b positioned at an opposite end of the elongate rectangular
space for polishing the workpieces 1. The loading/unloading unit 21
and the main polishing units 230a, 230b are interconnected by a
workpiece delivery line along which two feed robots 22a, 22b are
movable between the loading/unloading unit 21 and the main
polishing units 230a, 230b. The polishing apparatus also includes a
reversing machine 25 disposed on one side of the workpiece delivery
line for reversing the workpieces 1, a finish polishing unit 230c
and three cleaning units 23a, 23b, 23c disposed on the other side
of the workpiece delivery line. The cleaning units 23a, 23b, 23c
include rinsing machines or scrubbing machines using brushes,
sponges, or the like.
[0122] The main polishing units 230a, 230b and the finish polishing
unit 230c are basically of the same structure, and are respectively
provided with a translational table section 31 which provides
circulatory translational motion of the abrading surface of a
polishing tool, and a top ring 32 for holding the workpiece 1 to be
polished and pressing the workpiece 1 against the abrading surface
with a given pressure.
[0123] The main and finish polishing units 230a, 230b and 230c have
the same structure as the finish polishing unit 30 of the first
embodiment shown in FIG. 2, except for an abrading plate.
[0124] To be more specific, an abrading plate 159 is attached to
the top surface of the surface plate 37 of the main polishing units
230a, 230b, and a polishing cloth 159a is attached to the surface
plate 37 of the finish polishing unit 230c. These abrading plate
159 and polishing cloth 159a are also provided with a plurality of
discharge holes 58 aligned in registry with the respective
discharge ports 57. The discharge ports and holes 57, 58 are
disposed substantially uniformly over the entire surface of the
surface plate 37, the abrading plate 159 and the polishing cloth
159a. The abrading plate 159 is bonded to the top surface of the
surface plate 37 in the main polishing units 230a, 230b, and the
polishing cloth 159a is bonded to the top surface of the surface
plate 37 in the finish polishing unit 230c.
[0125] The abrading plate 159 is a circular disc made of abrasive
grains of less than several micrometers (for example, CeO.sub.2)
and a resin serving as a binder for the abrasive grains. In order
to make the abrading surface flat, the material and manufacturing
process are selected so that the abrading plate 159 would not have
bowing and deformation during manufacturing and storage. The
abrading plate 159 has a grid-like, spiral, or radial pattern of
grooves defined in the upper surface to distribute the polishing
solution and to remove ground-off particles by polishing, and the
discharge holes 58 are aligned with the grooves. The particle size
of the abrasive grains contained in the polishing solution is
selected so that the particle size of the abrasive grains is
relatively large for the rough polishing units 230a, 230b, but is
relatively small in the finish polishing unit 230c.
[0126] The top ring 32 has the same structure as the top ring of
the first embodiment shown in FIG. 2 Operation of the polishing
apparatus in the third embodiment will be described below.
[0127] A workpiece 1, typically a semiconductor wafer, in a
delivery cassette, identical to the delivery cassette 24 shown in
FIG. 9, is delivered by the feed robots 22a, 22b through the
reversing machine 25, if necessary, to one of the top rings 13 of
the main polishing units 230a, 230b, and is attached to the top
ring 13. In the main polishing units 230a or 230b, rough polishing
is performed Roughly polished workpiece is transferred by the robot
22a, 22b to the cleaning machine 23a and cleaned therein, and then
finish polishing is performed in the finish polishing unit
230c.
[0128] Details of the polishing action will be explained further.
The surface plate 37 makes circulatory translational motion by the
action of the driving motor 33, and the workpiece 1 attached to the
top ring 32 is pressed against the surface of the abrading plate
159 bonded to the surface plate 37. The polishing solution is
supplied to the surface to be polished of the workpiece 1 through
the supply port 56, the space 55, the discharge ports and holes 57,
58, and the grooves of the abrading plate 159.
[0129] The action of the minute circular translational motion (of
motion radius "e") between the workpiece 1 and the rubbing surface
of the abrading plate 159 produces a uniform polish on the entire
surface of the workpiece 1.
[0130] If the polished surface of the workpiece 1 and the abrading
plate 159 stay in the same relative positional relationship, then
the polished surface of the workpiece 1 would be adversely affected
by local irregularities of the abrading plate 159. To avoid this
drawback, the top ring 32 is rotated slowly about its own axis so
that the surface of the workpiece 1 is not polished by the same
local areas of the abrading plate 159. Therefore, the surface of
the workpiece 1 is polished by successively different areas of the
abrading plate 159, and hence is more uniformly polished.
[0131] Finish polishing is basically the same process as rough
polishing. Here, in the main polishing process, polishing
conditions are such that the workpiece 1 and the polishing tool
(abrading plate) 159 are moved at a relatively fast speed, and that
the pressing force is relatively high and the polishing solution
contains relatively coarse abrasive grains to produce a given
amount of material removal. On the other hand, the purpose of the
finish polishing process is, in addition to producing further
leveling and smoothing of the surface of the workpiece, to remove
any adhered micro-particles from the surface of the workpiece.
Therefore, roughness of the polishing surface of the polishing tool
(cloth) 159a is finer, and the velocity of relative motion and
pressing force between the polishing tool and the workpiece are
lower than those in the main polishing process. The polishing
solution is usually deionized water, but occasionally a chemical or
a slurry may be used when necessary In case of using a slurry, the
use of abrasive grains of the same material as the abrading plate
in the slurry may produce good polishing results.
[0132] After the finish polishing process of the workpiece 1 has
been completed by the finish polishing units 230c, the workpiece 1
is cleaned by the cleaning machines 23a.about.23c in one or more
cleaning processes and then dried, and thereafter accommodated in
the delivery cassette 24.
[0133] In this polishing apparatus, two main polishing units 230a,
230b are provided to perform the main polishing process while one
finish polishing unit 230c is provided. This is because the
duration of the main polishing process is longer than that of the
finish polishing process. Thus, the main polishing units and the
finish polishing unit can be operated efficiently without a loss
time.
[0134] In the polishing apparatus, because the polishing process is
carried out in two stages in parallel, particle size of the
abrading plate 159 and the supply and discharge ports 57, 58 can be
selected to suit the condition of each polishing process.
Therefore, the duration of each polishing process is shortened.
Accordingly, the throughput in the overall apparatus is
significantly improved compared with the conventional polishing
apparatus shown in FIGS. 9 and 10.
[0135] Since the polishing units 230a.about.230c are of the
circulatory translational motion type, the diameter of the surface
plate 37 may be slightly larger than the diameter of the workpiece
1 by the distance "e". Therefore, compared with the conventional
polishing unit 10, the installation space is reduced significantly.
Additionally, it is easier to design a combined layout of units
including cleaning machines and inverters as well as to modify an
existing layout.
[0136] Furthermore, because the surface plate 37 makes circulatory
translational motion in the polishing units 230a.about.230c, the
surface plate 37 is supported at several location along the
peripheral edge of the surface plate 37 as shown in FIG. 8, so that
the workpiece can be polished to a higher flatness than with the
conventional polishing apparatus having a turntable which rotates
at a high speed.
[0137] Although the polishing cloth is used in the second polishing
process in the illustrated embodiment, an abrading plate may also
be used in the second polishing process. In this case, abrasive
grains of the abrading plate in the second polishing process are
finer than those in the first polishing process.
[0138] Examples of average conditions for the first polishing
process and the second polishing process are given as follows:
[0139] 1. First Polishing Process:
[0140] Polishing solution (Abrasive solution): Differs depending on
the material of the workpiece
[0141] Material of abrasive grains of the abrading plate:
CeO.sub.2
[0142] Grain size of the abrading plate: 0.1.about.10 .mu.m
[0143] Pressure applied to the workpiece: 200.about.500
g/cm.sup.2
[0144] Relative speed: 0.07.about.0.6 m/sec.
[0145] Polishing time: Differs depending on the amount of material
to be removed by polishing.
[0146] 2. Second Polishing Process:
[0147] Polishing solution: Water, a chemical, a slurry
[0148] Polishing cloth: Soft cloth (non-woven cloth, nap-like
material)
[0149] Pressure applied to the workpiece: 0.about.200
g/cm.sup.2
[0150] Relative speed: 0.07.about.0.6 m/sec.
[0151] Polishing time: 10.about.120 sec.
[0152] In the above embodiment, although the polishing tool makes
circulative translation motion, the workpiece may make the same
motion. In the illustrated embodiment, the surface plate 37 is
caused to make circulatory translational motion by the eccentric
drive shaft 46 on the shaft 45 of the motor 33. However, the
surface plate 37 may be moved by a vector sum of motion in an X
direction and motion in a Y direction using an X-Y stage. Also, the
circular translation motion is produced by an "eccentric" design
provided at the end of the drive shaft of the motor, but other
designs may be utilized. For example, circulative translation
motion of the surface plate may be created by the vector sum of
motions in the X- and Y-directions using the X-Y stage. Further,
the polishing tool and the substrate may jointly be moved to make
circulatory translational motion. Also, a crank type of support is
utilized to support the surface plate, but it is possible to use
other types of support such as magnetic bearings or
lubrication-free slide bearings, which allow the surface plate 37
to make circulatory translational motion while preventing it from
rotating about its own axis.
[0153] According to the third embodiment of the present invention,
because the size of the abrading plate needs to be slightly larger
than the workpiece size, it is easy to produce higher flatness over
the entire surface of the polishing tool, compared with the
conventional large polishing table. The polishing apparatus becomes
compact and the drives can also be small, and the installation
space of the polishing apparatus is minimized. The overall design
of the polishing apparatus, including the cleaning and reversing
machines, is simplified, and the changes of the layout can be made
readily. These advantages become more important as the size of the
workpiece to be processed increases. Because the polishing tool is
not rotated, the relative speed between the workpiece and the
polishing tool is uniform over the entire surface of the workpiece,
and hence it is possible to produce flatness of the workpiece even
at a low speed and to provide a smooth surface of a superior
quality.
[0154] Although a certain preferred embodiment of the present
invention has 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.
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