U.S. patent number RE39,471 [Application Number 10/976,330] was granted by the patent office on 2007-01-16 for apparatus for and method for polishing workpiece.
This patent grant is currently assigned to Ebara Corporation. Invention is credited to Norio Kimura, Masamichi Nakashiba, Isamu Watanabe, Kaori Yoshida.
United States Patent |
RE39,471 |
Nakashiba , et al. |
January 16, 2007 |
**Please see images for:
( Certificate of Correction ) ** |
Apparatus for and method for polishing workpiece
Abstract
A polishing apparatus for polishing a workpiece such as a
semiconductor wafer has a turntable with a polishing surface, and a
top ring for holding a workpiece and pressing the workpiece against
the polishing surface under a first pressing. The polishing
apparatus has a pressurized fluid source for supplying pressurized
fluid, and a plurality of openings provided in the holding surface
of the top ring for ejecting the pressurized fluid supplied from
the pressurized fluid source. A plurality of areas each having the
openings are defined on the holding surface so that the pressurized
fluid is selectively ejectable from the openings in the respective
areas.
Inventors: |
Nakashiba; Masamichi (Mitaka,
JP), Kimura; Norio (Fujisawa, JP),
Watanabe; Isamu (Tokyo, JP), Yoshida; Kaori
(Tokyo, JP) |
Assignee: |
Ebara Corporation (Tokyo,
JP)
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Family
ID: |
35115438 |
Appl.
No.: |
10/976,330 |
Filed: |
October 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10142980 |
May 13, 2002 |
Re. 38854 |
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09589388 |
Jun 8, 2000 |
Re. 38826 |
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Reissue of: |
08807463 |
Feb 27, 1997 |
05762539 |
Jun 9, 1998 |
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Foreign Application Priority Data
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Feb 27, 1996 [JP] |
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65315/1996 |
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Current U.S.
Class: |
451/5; 451/285;
451/286; 451/287; 451/288; 451/289; 451/388; 451/41 |
Current CPC
Class: |
B24B
37/042 (20130101); B24B 37/30 (20130101); B24B
49/16 (20130101) |
Current International
Class: |
B24B
1/00 (20060101) |
Field of
Search: |
;451/41,286-289,5,398 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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401109966 |
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Apr 1989 |
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JP |
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401216768 |
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Aug 1989 |
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JP |
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404217456 |
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Aug 1992 |
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JP |
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6-333891 |
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Dec 1994 |
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JP |
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Other References
US. Pat. application Ser. No. 08/524,824, filed Sep. 7, 1995,
Kimura et al., entitled "Method and Apparatus for Polishing
Workpiece". cited by examiner.
|
Primary Examiner: Nguyen; George
Attorney, Agent or Firm: Wenderoth, Lind & Ponack,
L.L.P.
Parent Case Text
This .Iadd.is a Divisional Application of Reissue application Ser.
No. 10/142,980, filed May 13, 2002 RE 38854, which .Iaddend.is a
Continuation Application of Reissue application Ser. No. 09/589,388
RE 38826, filed Jun. 8, 2000, which is a Reissue of U.S. Pat. No.
5,762,539, issued Jun. 9, 1998.
Claims
What is claimed is:
.[.1. A polishing apparatus for polishing a surface of a workpiece
comprising: a turntable having a polishing surface thereon; a top
ring for supporting the workpiece to be polished and pressing the
workpiece against said polishing surface under a first pressing
force, said top ring having a holding surface for holding the
workpiece; a pressurized fluid source for supplying pressurized
fluid; a plurality of openings provided in said holding surface of
said top ring for ejecting said pressurized fluid supplied from
said pressurized fluid source, a plurality of areas each having
said openings being defined in said holding surface so that said
pressurized fluid is selectively ejectable from said openings in
said respective areas..].
.[.2. An apparatus according to claim 1, wherein said plurality of
areas comprises concentric annular areas..].
.[.3. An apparatus according to claim 1, wherein said plurality of
areas are defined by communicating with a plurality of chambers,
respectively formed in said top ring through said openings..].
.[.4. An apparatus according to claim 1, wherein said first
pressing force and a pressure of said pressurized fluid are
variable independently of each other..].
.[.5. An apparatus according to claim 1, wherein a pressure of said
pressurized fluid is variable in each of said areas..].
.[.6. An apparatus according to claim 1, further comprising: a
presser ring vertically movably disposed around said top ring; and
a pressing device for pressing said presser ring against said
polishing surface under a second pressing force which is
variable..].
.[.7. An apparatus according to claim 1, wherein said top ring has
a recess defined therein for accommodating the workpiece
therein..].
.[.8. A method of polishing a workpiece, comprising the steps of:
holding a workpiece between a polishing surface of a turntable and
a holding surface of a top ring disposed above said turntable;
pressing the workpiece by said top ring against said polishing
surface under a first pressing force; and ejecting pressurized
fluid from openings in a plurality of areas in said holding surface
of said top ring toward the workpiece held by said top ring, said
pressurized fluid being selectively ejectable from said openings in
said respective areas; and polishing the workpiece in such a state
that a pressing force applied to the workpiece by said pressurized
fluid is variable in a central portion and an outer circumferential
portion of the workpiece, respectively..].
.[.9. A method according to claim 8, further comprising the step
of: pressing a presser ring vertically movably disposed around said
top ring against said polishing surface around the workpiece under
a second pressing force which is determined based on said first
pressing force..].
.[.10. A method according to claim 8, said second pressing force is
determined on the basis of a pressure distribution on the workpiece
caused by said pressurized fluid ejected from said openings in said
respective areas..].
.[.11. A top ring for supporting the workpiece to be polished, for
use in a polishing apparatus, comprising: a holding surface for
holding the workpiece; and a plurality of openings, provided in
said holding surface, from which pressurized fluid is ejected, a
plurality of areas each having said openings being defined in said
holding surface so that said pressurized fluid is selectively
ejectable from said openings in said respective areas..].
.Iadd.12. A polishing apparatus for polishing a surface of a
workpiece, said polishing apparatus comprising: a turntable having
a polishing surface thereon; a top ring for supporting the
workpiece to be polished on a holding surface of said top ring and
pressing the workpiece against said polishing surface, said holding
surface having a plurality of openings formed therein; and a
pressurized fluid source for supplying a pressurized fluid to said
plurality of openings to form a pressure gradient progressively
changing from a central area of the workpiece to an outer
circumference area of the workpiece..Iaddend.
.Iadd.13. The polishing apparatus as recited in claim 12, wherein
the pressure gradient is formed such that a pressure applied to the
central area of the workpiece is larger than a pressure applied to
the outer circumferential area of the workpiece..Iaddend.
.Iadd.14. The polishing apparatus as recited in claim 12, wherein
the pressure gradient is formed such that a pressure applied to the
outer circumferential area of the workpiece is larger than a
pressure applied to the central area of the workpiece..Iaddend.
.Iadd.15. The polishing apparatus as recited in claim 12, wherein
said top ring comprises at least two pressurized chambers to which
the pressurized fluid is supplied, said at least two pressurized
chambers comprising a central circular chamber and an annular
chamber located outside of said central circular chamber, wherein
said circular chamber and said annular chamber are configured to
correspond the central area and the outer circumferential area of
the workpiece, respectively..Iaddend.
.Iadd.16. The polishing apparatus as recited in claim 12, wherein
the pressurized fluid comprises pressurized air..Iaddend.
.Iadd.17. The polishing apparatus as recited in claim 12, further
comprising a material disposed at said holding surface of said top
ring..Iaddend.
.Iadd.18. The polishing apparatus as recited in claim 17, wherein
said material comprises an elastic pad..Iaddend.
.Iadd.19. The polishing apparatus as recited in claim 18, wherein
said elastic pad comprises through holes therein for communication
with said plurality of openings in said holding
surface..Iaddend.
.Iadd.20. A polishing apparatus for polishing a surface of a
workpiece, said polishing apparatus comprising: a turntable having
a polishing surface thereon; a top ring for supporting the
workpiece to be polished on a holding surface of said top ring and
pressing the workpiece against said polishing surface; a presser
ring vertically movably disposed around said top ring, said presser
ring being movable with respect to said top ring; and a pressing
mechanism for providing polishing pressures on the workpiece by air
pressure, said polishing pressures having a gradient progressively
changing from a central area of the workpiece to an outer
circumferential area of the workpiece; wherein said top ring
comprises at least two pressurized chambers to which pressurized
fluid is supplied, said at least two pressurized chambers
comprising a central circular chamber and an annular chamber
located outside of said central circular chamber, and wherein said
central circular chamber and said annular chamber are configured to
correspond to the central area and the outer circumferential area
of the workpiece, respectively..Iaddend.
.Iadd.21. The polishing apparatus as recited in claim 20, wherein
the pressurized fluid comprises pressurized air..Iaddend.
.Iadd.22. A polishing apparatus for polishing a surface of a
workpiece, said polishing apparatus comprising: a turntable having
a polishing surface thereon; a top ring for supporting the
workpiece to be polished on a holding surface of said top ring and
pressing the workpiece against said polishing surface; a presser
ring vertically movably disposed around said top ring, said presser
ring being movable with respect to said top ring; and a pressing
mechanism for providing polishing pressures on the workpiece by air
pressure, said polishing pressures having a gradient progressively
changing from a central area of the workpiece to an outer
circumferential area of the workpiece; material disposed at said
holding surface of said top ring, wherein said material comprises
an elastic pad; wherein said holding surface of said top ring has a
plurality of openings formed therein, and wherein said elastic pad
comprises through holes therein for communication with said
plurality of openings in said holding surface..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for and a method of
polishing a workpiece such as a semiconductor wafer to a flat
mirror finish, and more particularly to an apparatus for and a
method of polishing a workpiece such as a semiconductor wafer which
can control the amount of a material removed from a desired area of
the workpiece by a polishing action.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands
smaller and smaller wiring patterns or interconnections and also
narrower spaces between interconnections which connect active
areas. One of the processes available for forming such
interconnection is photolithography. Though the photolighographic
process can form interconnections that are at most 0.5 .mu.m wide,
it requires that surfaces on which pattern images are to be focused
by a stepper be as flat as possible because the depth of focus of
the optical system is relatively small.
It is therefore necessary to make the surfaces of semiconductor
wafers flat for photolithography. One customary way of flattening
the surfaces of semiconductor wafers is to polish them with a
polishing apparatus.
Conventionally, a polishing apparatus has a turntable and a top
ring which rotate at respective individual speeds. A polishing
cloth is attached to the upper surface of the turntable. A
semiconductor wafer to be polished is placed on the polishing cloth
and clamped between the top ring and the turntable. An abrasive
liquid containing abrasive grains is supplied onto the polishing
cloth and retained on the polishing cloth. During operation, the
top ring exerts a certain pressure on the turntable, and the
surface of the semiconductor wafer held against the polishing cloth
is therefore polished to a flat mirror finish while the top ring
and the turntable are rotating.
The polishing apparatus is required to have such performance that
the surfaces of semiconductor wafers have a highly accurate
flatness. Therefore, it is preferable that the lower end surface
(the holding surface) of the top ring which holds a semiconductor
wafer and the contact surface of the polishing cloth which is held
in contact with the semiconductor wafer, and hence the surface of
the turntable to which the polishing cloth is attached, have a
highly accurate flatness, and those surfaces which are highly
accurately flat have been used in the art. The lower surface of the
top ring and the upper surface of the polishing cloth are parallel
to each other as in the ordinal cases.
It is known that the polishing action of the polishing apparatus is
affected not only by the configurations of the holding surface of
the top ring and the contract surface of the polishing cloth, but
also by the relative speed between the polishing cloth and the
semiconductor wafer, the distribution of pressure applied to the
surface of the semiconductor wafer which is being polished, the
amount of the abrasive liquid on the polishing cloth, and the
period of time when the polishing cloth has been used. It is
considered that the surface of the semiconductor wafer can be
highly accurately flat if the above factors which affect the
polishing action of the polishing apparatus are equalized over the
entire surface of the semiconductor wafer to be polished. The
larger the size of the semiconductor wafer is, the more difficult
the above factors are equalized.
However, some of the above factors can easily be equalized over the
entire surface of the semiconductor wafer, but the other factors
cannot be equalized. For example, the relative speed between the
polishing cloth and the semiconductor wafer can easily be equalized
by rotating the turntable and the top ring at the same rotational
speed and in the same direction. However, it is difficult to
equalize the amount of the abrasive liquid on the polishing cloth
because of a centrifugal forces imposed on the abrasive liquid.
The above approach which tries to equalize all the factors
affecting the polishing action, including the flatnesses of the
lower end surface of the top ring and the upper surface of the
polishing cloth on the turntable, over the entire surface of the
semiconductor wafer to be polished poses limitations on efforts to
make the polished surface of the semiconductor wafer flat, often
resulting in a failure to accomplish a desired degree of flatness
of the polished surface.
It has been customary to achieve a more accurate flatness by making
the holding surface of the top ring concave or convex to develop a
certain distribution of pressure on the surface of the
semiconductor wafer for thereby correcting irregularities of the
polishing action which are caused by an irregular entry of the
abrasive liquid and variations in the period of time when the
polishing cloth has been used.
However, various problems have arisen in the case where a specific
configuration is applied to the holding surface of the top ring.
Specifically, since the holding surface of the top ring is held in
contact with the semiconductor wafer at all times, the holding
surface of the top ring affects the polishing action continuously
all the time while the semiconductor wafer is being polished.
Because the configuration of the holding surface of the top ring
has direct effect on the polishing action, it is highly complex to
correct irregularities of the polishing action by intentionally
making the holding surface of the top ring concave or convex, i.e.,
non-flat. If the holding surface of the top ring which has been
made intentionally concave or convex is inadequate, the polished
surface of the semiconductor wafer may not be made as flat as
desired, or irregularities of the polishing action may not be
sufficiently corrected, so that the polished surface of the
semiconductor wafer may not be sufficiently flat.
In addition, inasmuch as the holding surface of the top ring is of
substantially the same size as the surface of the semiconductor
wafer to be polished, the holding surface of the top ring is
required to be made irregular in a very small area. Because such
surface processing is highly complex, it is not easy to correct
irregularities of the polishing action by means of the
configuration of the holding surface of the top ring.
The conventional polishing apparatuses, particularly those for
polishing semiconductor wafers, are required to polish workpiece
surfaces to higher flatness. There have not been available suitable
means and apparatus for polishing workpieces to shapes which are
intentionally not flat or for polishing workpieces such that
desired localized areas of workpiece surfaces are polished to
different degrees.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
polishing apparatus which can easily correct irregularities of a
polishing action on a workpiece such as a semiconductor wafer, and
polish a workpiece with an intensive polishing action on a desired
localized area thereof.
According to an aspect of the present invention, there is provided
a polishing apparatus for polishing a surface of a workpiece
comprising: a turntable having a polishing surface thereon; a top
ring for supporting the workpiece to be polished and pressing the
workpiece against the polishing surface under a first pressing
force, the top ring having a holding surface for holding the
workpiece; a pressurized fluid source for supplying pressurized
fluid; a plurality of openings provided in the holding surface of
the top ring for ejecting the pressurized fluid supplied from the
pressurized fluid source, a plurality of areas each having the
openings being defined in the holding surface so that the
pressurized fluid is selectively ejectable from the openings in the
respective areas.
According to another aspect of the present invention, there is
provided a method of polishing a workpiece, comprising the steps
of: holding a workpiece between a polishing surface of a turntable
and a holding surface of a top ring disposed above the turntable;
pressing the workpiece by the top ring against the polishing
surface under a first pressing force; and ejecting pressurized
fluid from openings in a plurality of areas in the holding surface
of the top ring toward the workpiece held by the top ring, the
pressurized fluid being selectively ejectable from the openings in
the respective areas; and polishing the workpiece in such a state
that a pressing force applied to the workpiece by the pressurized
fluid is variable in a central portion and an outer circumferential
portion of the workpiece, respectively.
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 preferred embodiments of the present
invention by way of example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary vertical cross-sectional view showing the
basic principles of the present invention;
FIGS. 2A, 2B, and 2C are enlarged fragmentary vertical
cross-sectional views showing the behavior of an polishing cloth
when the relationship between a pressing force applied by a top
ring and a pressing force applied by a presser ring is varied;
FIGS. 3A through 3C are graphs showing the results of an experiment
in which a semiconductor wafer was polished based on the basic
principles of the present invention;
FIGS. 4A through 4E are graphs showing the results of an experiment
in which a semiconductor wafer was polished based on the basic
principles of the present invention;
FIG. 5 is a vertical cross-sectional view of a polishing apparatus
according to a first embodiment of the present invention;
FIG. 6 is an enlarged vertical cross-sectional view showing details
of a top ring and a presser ring of the polishing apparatus
according to the first embodiment;
FIG. 7 is a cross-sectional view taken along line VII--VII of FIG.
6; and
FIG. 8 is an enlarged vertical cross-sectional view of a polishing
apparatus according to a second embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Like or corresponding parts are denoted by like or corresponding
reference numerals throughout views.
FIG. 1 shows the basic principles of the present invention. As
shown in FIG. 1, a top ring 1 has therein a circular first chamber
C.sub.1 at a central position thereof, an annular second chamber
C.sub.2 disposed at a radially outer side of the first chamber
C.sub.1, and an annular third chamber C.sub.3 disposed at a
radially outer side of the second chamber C.sub.2. The first
chamber C.sub.1 is connected to a pressurized fluid source through
a valve V.sub.1, the second chamber C.sub.2 is connected to a
pressurized fluid source through a valve V.sub.2, and the third
chamber C.sub.3 is connected to a pressurized fluid source through
a valve V.sub.3. The top ring 1 has a recess 1a defined in a lower
surface thereof for accommodating therein a semiconductor wafer 4
which is a workpiece to be polished. An elastic pad 2 of
polyurethane or the like is attached to the lower surface of the
top ring 1.
The top ring 1 and the elastic pad 2 have a plurality of openings
1o and 2o, respectively, which are in registry with each other.
Each of the openings 1o and 2o is communicated with any one of the
first chamber C.sub.1, the second chamber C.sub.2, and the third
chamber C.sub.3. That is, a plurality of openings each comprising
the openings 1o and 2o for ejecting pressurized fluid are provided
in a holding surface of the top ring 1 for holding the
semiconductor wafer 4 to be polished. Thus, three concentric
annular areas are defined on the holding surface of the top ring 1
by allowing the openings 1o and 2o to be communicated with any one
of the first, second and third chambers C.sub.1, C.sub.2 and
C.sub.3. The pressurized fluid is ejectable from the openings in
the respective annular areas, separately.
A presser ring 3 is disposed around the top ring 1 and is
vertically movable with respect to the top ring 1. A turntable 5
having an upper surface to which a polishing cloth 6 is attached is
provided below the top ring 1. The top ring 1 applies a pressing
force F.sub.1 (pressure per unit area, gf/cm.sup.2) to press the
semiconductor wafer 4 against the polishing cloth 6 on the
turntable 5, and the presser ring 3 applies a pressing force
F.sub.2 (pressure per unit area, gf/cm.sup.2) to press the
polishing cloth 6. These pressing forces F.sub.1, F.sub.2 are
variable independently of each other.
During polishing, pressurized fluid such as compressed air is
supplied to the first, second and third chambers C.sub.1, C.sub.2
and C.sub.3, selectively, and the supplied pressurized fluid is
ejected from the lower surface of the elastic pad 2 through the
openings 1o and 2o and is supplied between the holding surface of
the top ring 1 and the upper surface of the semiconductor wafer 4.
At this time, at least one of the first, second and third chambers
C.sub.1, C.sub.2 and C.sub.3 to which pressurized fluid is supplied
is selected, and hence at least one of the annular areas, from
which pressurized fluid is ejected, in the holding surface of the
top ring 1 is selected. For example, pressurized fluid is supplied
only to the first chamber C.sub.1, and is not supplied to the
second and third chambers C.sub.2 and C.sub.3, and thus the
pressurized fluid is ejected only from the central area of the
holding surface of the top ring 1. As a result, the semiconductor
wafer 4 is pressed against the polishing cloth 6 by the pressurized
fluid in such a state that the polishing pressure applied to the
central portion of the semiconductor wafer 4 is larger than the
polishing pressure applied to outer circumferential portion of the
semiconductor wafer 4. Thus, if the amount of a material removed
from the outer circumferential portion of the semiconductor wafer 4
is larger than the amount of a material removed from the central
portion of the semiconductor wafer 4, insufficient polishing action
at the central portion of the semiconductor wafer can be corrected
by utilizing the pressing action of the pressurized fluid.
On the other hand, if the amount of a material removed from the
central portion of the semiconductor wafer 4 is larger than the
amount of a material removed from the outer circumferential portion
of the semiconductor waiter 4, the pressurized fluid is supplied
only to the third chamber C.sub.3, and is not supplied to the first
and second chambers C.sub.1 and C.sub.2, and thus the pressurized
fluid is ejected only from the outer circumference area of the
holding surface of the top ring 1.
As a result, the polishing pressure applied to the outer
circumferential portion of the semiconductor wafer 4 is made larger
than the central portion of the semiconductor wafer 4. Thus,
insufficient polishing action at the outer circumferential portion
of the semiconductor wafer can be collected, and the entire surface
of the semiconductor wafer 4 can be uniformly polished.
The pressures of pressurized fluid supplied to the first chamber
C.sub.1, the second chamber C.sub.2 and the third chamber C.sub.3
are changed, respectively. That is, pressurized fluid having a
pressure of p.sub.1 gf/cm.sup.2 is supplied to the first chamber
C.sub.1, pressurized fluid having a pressure of P.sub.2 gf/cm.sup.2
is supplied to the second chamber C.sub.2, and pressurized fluid
having a pressure of p.sub.3 gf/cm.sup.2 is supplied to the third
chamber C.sub.3, respectively. In this manner, the pressures of
pressurized fluid ejected from the respective annular areas of the
holding surface of the top ring 1 are varied, and the fluid which
is supplied between the holding surface of the top ring 1 and the
upper surface of the semiconductor wafer 4 has pressure gradient so
as to be higher or lower progressively from the central area to the
outer circumferential area of the semiconductor wafer 4, and hence
the pressing force for pressing the semiconductor wafer 4 against
the polishing cloth 6 has gradient so as to be higher or lower
progressively from the central area to the outer circumferential
area of the semiconductor wafer 4. Thus, irregularities of the
polishing action can be sufficiently corrected, and the localized
area of the semiconductor wafer 4 is prevented from being polished
excessively or insufficiently.
In the present invention, the pressing force F.sub.1 (pressure per
unit area, gf/cm.sup.2) for pressing the semiconductor wafer 4
against the polishing cloth 6, and the pressing force F.sub.2
(pressure per unit area, gf/cm.sup.2) for pressing the polishing
cloth 6 are variable independently of each other. Therefore, the
pressing force F.sub.2 which is applied to the polishing cloth 6 by
the presser ring 3 can be changed depending on the pressing force
F.sub.1 which is applied by the top ring 1 to press the
semiconductor wafer 4 against the polishing cloth 6.
Theoretically, if the pressing force F.sub.1 which is applied by
the top ring 1 to press the semiconductor wafer 4 against the
polishing cloth 6 is equal to the pressing force F.sub.2 which is
applied to the polishing cloth 6 by the presser ring 3, then the
distribution of applied polishing pressures, which result from a
combination of the pressing forces F.sub.1, F.sub.2, is continuous
and uniform from the center of the semiconductor wafer 4 to its
peripheral edge and further to an outer circumferential edge of the
presser ring 3 disposed around the semiconductor wafer 4.
Accordingly, the peripheral portion of the semiconductor wafer 4 is
prevented from being polished excessively or insufficiently.
FIGS. 2A through 2C schematically show how the polishing cloth 6
behaves when the relationship between the pressing force F.sub.1
and the pressing force F.sub.2 is varied. In FIG. 2A, the pressing
force F.sub.1 is larger than the pressing force F.sub.2
(F.sub.1>F.sub.2). In FIG. 2B, the pressing force F.sub.1 is
nearly equal to the pressing force F.sub.2 (F.sub.1=F.sub.2). In
FIG. 2C, the pressing force F.sub.1 is smaller than the pressing
force F.sub.2 (F.sub.1<F.sub.2).
As shown in FIGS. 2A through 2C, when the pressing force F.sub.2
applied to the polishing cloth 6 by the presser ring 3 is
progressively increased, the polishing cloth 6 pressed by the
presser ring 3 is progressively compressed, thus progressively
changing its state of contact with the peripheral portion of the
semiconductor wafer 4, i.e., progressively reducing its area of
contact with the peripheral portion of the semiconductor wafer 4.
Therefore, when the relationship between the pressing force F.sub.1
and the pressing force F.sub.2 is changed in various patterns, the
distribution of polishing pressures on the semiconductor wafer 4
over its peripheral portion and inner region is also changed in
various patterns.
As shown in FIG. 2A, when the pressing force F.sub.1 is larger than
the pressing force F.sub.2 (F.sub.1>F.sub.2), the polishing
pressure applied to the peripheral portion of the semiconductor
wafer 4 is larger than the polishing pressure applied to the inner
region of the semiconductor wafer 47 so that the amount of a
material removed from the peripheral portion of the semiconductor
wafer 4 is larger than the amount of a material removed from the
inner region of the semiconductor wafer 4 while the semiconductor
wafer 4 is being polished.
As shown in FIG. 2B, when the pressing force F.sub.1 is
substantially equal to the pressing force F.sub.2
(F.sub.1=F.sub.2), the distribution of polishing pressures is
continuous and uniform from the center of the semiconductor wafer 4
to its peripheral edge and further to the outer circumferential
edge of the presser ring 3, so that the amount of a material
removed from the semiconductor wafer 4 is uniform from the
peripheral edge to the inner region of the semiconductor wafer 4
while the semiconductor wafer 4 is being polished.
As shown in FIG. 2C, when the pressing force F.sub.1 is smaller
than the pressing force F.sub.2 (F.sub.1<F.sub.2), the polishing
pressure applied to the peripheral portion of the semiconductor
wafer 4 is smaller than the polishing pressure applied to the inner
region of the semiconductor wafer 4, so that the amount of a
material removed from the peripheral edge of the semiconductor
wafer 4 is smaller than the amount of a material removed from the
inner region of the semiconductor wafer 4 while the semiconductor
wafer 4 is being polished.
The pressing force F.sub.1 and the pressing force F.sub.2 can be
changed independently of each other before polishing or during
polishing.
As described above, according to the present invention, pressurized
fluid is ejected from the holding surface of the top ring 1. At
this time, the areas from which the pressurized fluid is ejected
are suitably selected, and the pressing force applied to the
semiconductor wafer 4 by the pressurized fluid is changed in the
central portion and the outer circumferential portion of the
semiconductor wafer 4, respectively, during polishing.
In parallel with the above process, the pressing force F.sub.2 of
the presser ring 3 disposed around the top ring 1 is determined on
the basis of the pressing force F.sub.1 of the top ring 1, and the
semiconductor wafer 4 is polished while pressing the polishing
cloth 6 by the presser ring 3 under the pressing force F.sub.2
which has been determined. Further, the pressing force F.sub.2 is
determined on the basis of the pressure distribution which is
applied to the semiconductor wafer 4 by the pressurized fluid, and
the semiconductor wafer 4 is polished by a combination of an action
caused by the pressurized fluid and an action caused by the presser
ring 3. In this manner, insufficient polishing action in thus
localized area (for example, the central area or the outer
circumferential area) of the semiconductor wafer can be corrected,
and the localized area of the semiconductor wafer is prevented from
being polished excessively or insufficiently. In the case where the
polishing pressure applied to the central portion of the
semiconductor wafer 4 is made larger than the outer circumferential
portion of the semiconductor wafer 4 by supplying the pressurized
fluid, the pressing force F.sub.2 of the presser ring 3 is made
larger than the pressing force F.sub.1 of the top ring 1.
Conversely, in the case where the polishing pressure applied to the
outer circumferential portion of the semiconductor wafer 4 is made
larger than the central portion of the semiconductor wafer 4 by
supplying the pressurized fluid, the pressing force F.sub.2 of the
presser ring 3 is made smaller than the pressing force F.sub.1 of
the top ring 1.
FIGS. 3A through 3C show the results of an experiment in which a
semiconductor wafer was polished based on the basic principles of
supply of pressurized fluid according to the present invention. The
semiconductor wafer used in the experiment was an 8-inch
semiconductor wafer. In the experiment, the pressing force
(polishing pressure) applied to the semiconductor wafer by the top
ring was a constant level of 400 gf/cm.sup.2, and the supply of the
pressurized fluid was controlled. FIG. 3A shows the case in which
the pressurized fluid was not supplied. FIG. 3B shows the case in
which the pressurized fluid is supplied only to the first chamber
C.sub.1, and FIG. 3C shows the case in which the pressurized fluid
is supplied only to the third chamber C.sub.3. The pressure of the
pressurized fluid was 200 gf/cm.sup.2. In each of FIGS. 3A through
3C, the horizontal axis represents a distance (mm) from the center
of the semiconductor wafer, and the vertical axis represents a
thickness (.ANG.) of a material removed from a semiconductor
wafer.
As shown in FIGS. 3A through 3C, the thickness of the removed
material at the radial positions on the semiconductor wafer is
affected by controlling the supply of the pressurized fluid.
Specifically, when the pressurized fluid was not supplied, as shown
in FIG. 3A, the peripheral portion of the semiconductor wafer was
excessively polished. When the pressurized fluid is supplied only
to the first chamber C.sub.1 to press only the central portion of
the semiconductor wafer by the pressurized fluid, as shown in FIG.
3B, the peripheral portion of the semiconductor wafer was not
excessively polished and the central portion of the semiconductor
wafer was slightly excessively polished. When the pressurized fluid
was supplied only to the third chamber C.sub.3 to press only the
outer circumferential portion of the semiconductor wafer by the
pressurized fluid, as shown in FIG. 3C, the outer circumferential
portion of the semiconductor wafer was excessively polished and the
central portion of the semiconductor wafer was polished
insufficiently.
As described above, the experimental result shown in FIGS. 3A
through 3E indicate that the amount of the material removed from
the localized area of the semiconductor wafer can be adjusted by
controlling supply of the pressurized fluid.
FIGS. 4A through 4E show the results of an experiment in which a
semiconductor wafer was polished based on the basic principles of
the present invention. The semiconductor wafer used in the
experiment was an 8-inch semiconductor wafer. In the experiment,
the pressing force (polishing pressure) applied to the
semiconductor wafer by the top ring was a constant level of 400
gf/cm.sup.2, and the pressing force applied by the presser ring was
changed from 600 to 200 gf/cm.sup.2 successively by decrements of
100 gf/cm.sup.2. Specifically, the pressing force applied by the
presser ring was 600 gf/cm.sup.2 in FIG. 4A, 500 gf/cm.sup.2 in
FIG. 4B, 400 gf/cm.sup.2 in FIG. 4C, 300 gf/cm.sup.2 in FIG. 4D,
and 200 gf/cm.sup.2 in FIG. 4E. In each of FIGS. 4A through 4E, the
horizontal axis represents a distance (mm) from the center of the
semiconductor wafer, and the vertical axis represents a thickness
(.ANG.) of a material removed from the semiconductor wafer.
As shown in FIGS. 4A through 4E, the thickness of the removed
material at the radial positions on the semiconductor wafer is
affected when the pressing force applied by the presser ring was
changed. Specifically, when the pressing force applied by the
presser ring was in the range from 200 to 300 gf/cm.sup.2 as shown
in FIGS. 4D and 4E, the peripheral portion of the semiconductor
wafer was excessively polished. When the pressing force applied by
the presser ring was in the range from 400 to 500 gf/cm.sup.2, as
shown in FIGS. 4B and 4C, the peripheral portion of the
semiconductor wafer is substantially equally polished from the
peripheral edge to the inner region of the semiconductor wafer.
When the pressing force applied by the presser ring was 600
gf/cm.sup.2, as shown in FIG. 4A, the peripheral portion of the
semiconductor wafer was polished insufficiently.
The experimental results shown in FIGS. 4A through 4E indicate that
the amount of the material removed from the peripheral portion of
the semiconductor wafer can be adjusted by varying the pressing
force applied by the presser ring independently of the pressing
force applied by the top ring. From a theoretical standpoint, the
peripheral portion of the semiconductor wafer should be polished
optimally when the pressing force applied by the presser ring is
equal to the pressing force applied by the top ring. However, since
the polishing action depends on the type of the semiconductor wafer
and the polishing conditions, the pressing force applied by the
presser ring is selected to be of an optimum value based on the
pressing force applied by the top ring depending on the type of the
semiconductor wafer and the polishing conditions.
There are demands for the removal of a larger or smaller thickness
of material from the peripheral portion of the semiconductor wafer
than from the inner region of the semiconductor wafer depending on
the type of the semiconductor wafer. To meet such demands, the
pressing force applied by the presser ring is selected to be of an
optimum value based on the pressing force applied by the top ring
to intentionally increase or reduce the amount of the material
remove from peripheral portion of the semiconductor wafer.
FIGS. 5 through 7 show a polishing apparatus according to a first
embodiment of the present invention.
As shown in FIGS. 5 and 6, a top ring 1 has therein a circular
first chamber C.sub.1 at a central portion thereof, an annular
second chamber C.sub.2 disposed at a radially outer side of the
first chamber C.sub.1, and an annular third chamber C.sub.3
disposed at a radially outer side of the first chamber C.sub.2. The
first chamber C.sub.1 is connected to a compressed air source 24 as
a pressurized fluid source through a valve V.sub.1 and a regulator
R.sub.1, the second chamber C.sub.2 is connected to the compressed
air source 24 through a valve V.sub.2 and a regulator R.sub.2, and
the third chamber C.sub.3 is connected to the compressed air source
24 through a valve V.sub.3 and a regulator R.sub.3. The top ring 1
has a recess 1a defined in a lower surface thereof for
accommodating therein a semiconductor wafer 4 which is a workpiece
to be polished. An elastic pad 2 of the polyurethane or the like is
attached to the lower surface of the top ring 1.
The top ring 1 and the elastic pad 2 have a plurality of openings
1o and 2o, respectively, which are in registry with each other.
Each of the openings 1o and 2o is communicated with any one of the
first chamber C.sub.1, the second chamber C.sub.2, and the third
chamber C.sub.3. That is, a plurality of openings each comprising
the openings 1o and 2o for ejecting pressurized fluid are defined
on a holding surface of the top ring 1 for holding the
semiconductor wafer 4 to be polished. Thus, three concentric
annular areas A.sub.1, A.sub.2 and A.sub.3 are defined in the
holding surface of the top ring 1 by allowing the openings 1o and
2o to be communicated with any one of the first, second and third
chambers C.sub.1, C.sub.2 and C.sub.3. The compressed air having
different pressure from one another can be supplied to respective
annular areas A.sub.1, A.sub.2 and A.sub.3. Pressure gages or
pressure sensors G.sub.1, G.sub.2 and G.sub.3 are provided in the
respective pressurized fluid supply lines, and the pressure in the
respective chambers C.sub.1, C.sub.2 and C.sub.3 can be
independently controlled on the basis of the pressures detected by
the pressure gages G.sub.1, G.sub.2 and G.sub.3.
A pressure ring 3 is disposed around the top ring 1 and is
vertically movable with respect to the top ring 1. A turntable 5
with a polishing cloth 6 attached to an upper surface thereof is
disposed below the top ring 1.
The top ring 1 is connected to a vertical top ring shaft 8 whose
lower end is held against a ball 7 mounted on an upper surface of
the top ring 1. The top ring shaft 8 is operatively coupled to a
top ring air cylinder 10 fixedly mounted on an upper surface of a
top ring head 9. The top ring shaft 8 is vertically movable by the
top ring air cylinder 10 to press the semiconductor wafer 4
supported on the elastic pad 2 against the polishing cloth 6 on the
turntable 5.
The top ring shaft 8 has an intermediate portion extending through
and corotatably coupled to a rotatable cylinder 11 by a key (not
shown), and the rotatable cylinder 11 has a pulley 12 mounted on
outer circumferential surface thereof. The pulley 12 is operatively
connected by a timing belt 13 to a timing pulley 15 mounted on the
rotatable shaft of a top ring motor 14 which is fixedly mounted on
the top ring head 9. Therefore, when the top ring motor 14 is
energized, the rotatable cylinder 11 and the top ring shaft 8 are
integrally rotated through the timing pulley 15, the timing belt 13
and the timing pulley 12. Thus the top ring 1 is rotated. The top
ring head 9 is supported by a top ring head shaft 16 which is
vertically fixed on a frame (not shown).
The presser ring 3 is corotatably, but vertically movably, coupled
to the top ring 1 by a key 18. The presser ring 3 is rotatably
supported by a bearing 19 which is mounted on a bearing holder 20.
The bearing holder 20 is connected by vertical shafts 21 to a
plurality of (three in this embodiment) circumferentially spaced
presser ring air cylinders 22. The presser ring air cylinders 22
are secured to a lower surface of the top ring head 9.
The top ring air cylinder 10 and the pressure ring air cylinders 22
are pneumatically connected to the compressed air source 24 through
regulators R.sub.4 and R.sub.5, respectively. The regulator R.sub.4
regulates an air pressure supplied from the compressed air source
24 to the top ring air cylinder 10 to adjust the pressing force
which is applied by the top ring 1 to press the semiconductor wafer
4 against the polishing cloth 6. The regulator R.sub.5 also
regulates the air pressure supplied from the compressed air source
24 to the presser ring air cylinder 22 to adjust the pressing force
which is applied by the presser ring 3 to press the polishing cloth
6. The regulators R.sub.4 and R.sub.5 are controlled by a
controller (not shown in FIG. 5).
An abrasive liquid supply nozzle 25 is positioned above the
turntable 5 for supplying an abrasive liquid Q onto the polishing
cloth 6 on the turntable 5.
As shown in FIG. 6, the top ring 1 has an outer circumferential
annular flange 1s extending downwardly toward the turntable 5. The
lower surface of the top ring 1 and the annular flange is jointly
define a recess 1a for accommodating the semiconductor wafer 4
therein.
The polishing apparatus shown in FIGS. 5, 6 and 7 operates as
follow: The semiconductor wafer 4 to be polished is placed in the
recess 1a and held against the elastic pad 2, and the top ring air
cylinder 10 is actuated to lower the top ring 1 toward the
turntable 5 until the semiconductor wafer 4 is pressed against the
polishing cloth 6 on the upper surface of the rotating turntable 5.
The top ring 1 and the presser ring 3 are rotated by the top ring
motor 14 through the top ring shaft 8. Since the abrasive liquid Q
is supplied onto the polishing cloth 6 by the abrasive liquid
supply nozzle 25, the abrasive liquid Q is retained on the
polishing cloth 6. Therefore, the lower surface of the
semiconductor wafer 4 is polished with the abrasive liquid Q which
is present between the lower surface of the semiconductor wafer 4
and the polishing cloth 6.
During polishing, compressed air is supplied from the compressed
air source 24 to the first, second and third chambers C.sub.1,
C.sub.2 and C.sub.3 selectively, and the supplied compressed air is
ejected from the lower surface of the elastic pad 2 through the
openings 1o and 2o, and is supplied between the holding surface of
the top ring 1 and the upper surface of the semiconductor wafer 4.
At this time, at least one of the chambers C.sub.1, C.sub.2 and
C.sub.3 to which compressed air is supplied is selected, and at
least one of the annular areas A.sub.1, A.sub.2 and A.sub.3 from
which compressed air is ejected is selected. For example,
compressed air is supplied only to the first chamber C.sub.1, and
is not supplied to the second and third chambers C.sub.2 and
C.sub.3, whereby the semiconductor wafer 4 is pressed against the
polishing cloth 6 by the compressed air in such a state that the
polishing pressure applied to the central portion of the
semiconductor wafer 4 is larger than the polishing pressure applied
to outer circumferetial portion of the semiconductor wafer 4. Thus,
if the amount of a material removed from the outer circumferential
portion of the semiconductor wafer 4 is larger than the amount of a
material removed from the central portion of the semiconductor
wafer 4, insufficient polishing action at the central portion of
the semiconductor wafer can be corrected by utilizing the pressing
action of the pressurized fluid.
On the other hand, if the amount of a material removed from the
central portion of the semiconductor wafer 4 is larger than the
amount of a material removed from the outer circumferential portion
of the semiconductor wafer 4, the compressed air is supplied only
to the third chamber C.sub.3, and is not supplied to the first and
second chamber C.sub.1 and C.sub.2, whereby the polishing pressure
applied to the outer circumferential portion of the semiconductor
wafer 4 is larger than the polishing pressure applied to the
central portion of the semiconductor wafer 4. Thus, insufficient
polishing action at the outer circumferential portion of the
semiconductor wafer can be corrected, and the entire surface of the
semiconductor wafer 4 can be uniformly polished.
The pressures of compressed air supplied to the first chamber
C.sub.1, the second chamber C.sub.2 and the third chamber C.sub.3
are changed respectively, that is, compressed air having a pressure
of p.sub.1 gf/cm.sup.2 is supplied to the first chamber C.sub.1,
compressed air having a pressure of P.sub.2 gf/cm.sup.2 is supplied
to the second chamber C.sub.2, and compressed air having a pressure
of p.sub.3 gf/cm.sup.2 is supplied. In this manner, the compressed
air which is supplied between the holding surface of the top ring 1
and the upper surface of the semiconductor wafer 4 has pressure
gradient so as to be higher or lower progressively from the central
area to the outer circumferential area of the semiconductor wafer
4. That is, the pressing force for pressing the semiconductor wafer
4 against the polishing cloth 6 has gradient from the central area
to the outer circumferential area of the semiconductor wafer 4.
Thus, irregularities of the polishing action can be sufficiently
corrected and the localized area of the semiconductor wafer 4 is
prevented from being polished excessively or insufficiently.
Further, in the present invention, depending on the pressing force
applied by the top ring 1 actuated by the top ring air cylinder 10,
the pressing force applied to the polishing cloth 6 by the presser
ring 3 actuated by the presser ring air cylinders 22 is adjusted
while the semiconductor wafer 4 is being polished. During the
polishing process, the pressing force F.sub.1 (see FIG. 1) which is
applied by the top ring 1 to press the semiconductor wafer 4
against the polishing cloth 6 can be adjusted by the regulator
R.sub.1, and the pressing force F.sub.2 which is applied by the
presser ring 3 to press the polishing cloth 6 can be adjusted by
the regulator R.sub.2. Therefore, during the polishing process, the
pressing force F.sub.2 applied by the presser ring 3 to press the
polishing cloth 6 can be changed depending on the pressing force
F.sub.1 applied by the top ring 1 to press the semiconductor wafer
4 against the polishing cloth 6. By adjusting the pressing force
F.sub.2 with respect to the pressing force F.sub.1, the
distribution of polishing pressures is made continuous and uniform
from the center of the semiconductor wafer 4 to its peripheral edge
and further to the outer circumferential edge of the presser ring 3
disposed around the semiconductor wafer 4. Consequently, the
peripheral portion of the semiconductor wafer 4 is prevented from
being polished excessively or insufficiently. The semiconductor
wafer 4 can thus be polished to a high quality and with a high
yield.
If a larger or smaller thickness of material is to be removed from
the peripheral portion of the semiconductor wafer 4 than from the
inner region of the semiconductor wafer 4, then the pressing force
F.sub.2 applied by the presser ring 3 is selected to be of a
suitable value based on the pressing force F.sub.1 applied by the
top ring 1 to intentionally increase or reduce the amount of a
material removed from the peripheral portion of the semiconductor
wafer 4.
By controlling compressed air supplied to the first, second and
third chambers C.sub.1, C.sub.2 and C.sub.3, the semiconductor
wafer 4 is polished by a combination of a pressing action caused by
the compressed air and a pressing action caused by the presser ring
3. Thus, insufficient polishing action in the localized area (for
example, the central area or the outer circumferential area) of the
semiconductor wafer can be corrected. Further, the amount of the
material removed from the localized areas (for example, the central
area or the outer circumferential area) can be intentionally
increased or decreased. In this case, in the case where the
polishing pressure at the central portion of the semiconductor
wafer 4 is made larger than the polishing pressure at the outer
circumferential portion of the semiconductor wafer 4, the pressing
force F.sub.2 of the presser ring 3 is made larger than the
pressing force F.sub.1 of the top ring 1. Conversely, in the case
where the polishing pressure at the outer circumferential portion
of the semiconductor wafer 4 is made larger than the polishing
pressure at the central portion of the semiconductor wafer 4, the
pressing force F.sub.2 of the presser ring 3 is made smaller than
the pressing force F.sub.1 of the top ring 1.
In this embodiment, since the semiconductor wafer 4 is accommodated
in the recess 1a of the top ring 1 and protected by the annular
flange 1s, the outer circumferential surface of the semiconductor
wafer 4 at its peripheral edge is not rubbed by the presser ring 3
when the presser ring 3 is vertically moved with respect to the top
ring 1. Therefore, the presser ring 3 as it is vertically moved
with respect to the top ring 1 does not adversely affect the
polishing performance of the polishing apparatus during the
polishing process.
FIG. 8 shows a polishing apparatus according to a second embodiment
of the present invention. As shown in FIG. 8, a top ring 51
comprises a main body 52 and a ring member 54 detachably fixed by
bolts 53 to a lower outer circumferential surface of the main body
52. The top ring 51 has a recess 51a for accommodating the
semiconductor wafer 4. The recess 51a is defined by a lower surface
of the main body 52 and an inner circumferential surface of the
ring member 54. The semiconductor wafer 4 accommodated in the
recess 51a has an upper surface held by the lower surface of the
main body 52 and an outer circumferential surface held by the inner
circumferential surface of the ring member 54. The presser ring 3
is vertically movably disposed around the top ring 51.
The main body 52 of the top ring 51 has therein a circular first
chamber C.sub.1 at a central position thereof, an annular second
chamber C.sub.2 disposed at a radially outer side of the first
chamber C.sub.1, and an annular third chamber C.sub.3 disposed at a
radially outer side of the first chamber C.sub.2. The first chamber
C.sub.1, the second chamber C.sub.2 and the third chamber C.sub.3
are connected to the compressed air source (not shown) to allow
compressed air to be supplied thereto in the same manner as the
embodiment in FIGS. 5 through 7. The main body 52 of the top ring
51 has a plurality of openings 52o which are communicated with the
first chamber C.sub.1, the second chamber C.sub.2 and the third
chamber C.sub.3, respectively. An elastic pad 2 also has a
plurality of openings 2o which are in registry with the openings
52o. Thus compressed air can be applied to the upper surface of the
semiconductor wafer 4.
While the workpiece to be polished according to the present
invention has been illustrated as a semiconductor wafer, it may be
a glass product, a liquid crystal panel, a ceramic product, etc.
Further, as pressurized fluid, pressurized liquid may be used. The
top ring and the presser ring may be pressed by hydraulic cylinders
rather than the illustrated air cylinders. The presser ring may be
pressed by electric devices such as piezoelectric or
electromagnetic devices rather than the illustrated purely
mechanical devices.
As described above, the present invention offers the following
advantages:
The distribution of the previous force of the workpiece is
prevented from being nonuniform at the peripheral portion of the
workpiece during the polishing process, and the polishing pressures
can be uniformized over the entire surface of the workpiece.
Therefore, the peripheral portion of the semiconductor wafer is
prevented from being polished excessively or insufficiently. The
entire surface of workpiece can thus be polished to a flat mirror
finish. In the case where the present invention is applied to
semiconductor manufacturing processes, the semiconductor devices
can be polished to a high quality. Since the peripheral portion of
the semiconductor wafer can be used as products, yields of the
semiconductor devices can be increased.
In the case where there are demands for she removal of a larger or
smaller thickness of material from the peripheral portion of the
semiconductor wafer than from the inner region of the semiconductor
wafer depending on the type of the semiconductor wafer, the amount
of the material removed from the peripheral portion of the
semiconductor wafer can be intentionally increased or decreased.
Further, the amount of the material removed from not only the
peripheral portion of the semiconductor wafer but also the
localized area (for example, central portion or outer
circumferential portion) can be intentionally increased or
decreased.
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.
* * * * *