U.S. patent application number 11/433843 was filed with the patent office on 2006-11-23 for apparatus for polishing wafer and process for polishing wafer.
This patent application is currently assigned to Sumco Corporation. Invention is credited to Tomohiro Hashii, Sakae Koyata, Katsuhiko Murayama, Kazushige Takaishi.
Application Number | 20060264158 11/433843 |
Document ID | / |
Family ID | 36808329 |
Filed Date | 2006-11-23 |
United States Patent
Application |
20060264158 |
Kind Code |
A1 |
Hashii; Tomohiro ; et
al. |
November 23, 2006 |
Apparatus for polishing wafer and process for polishing wafer
Abstract
An apparatus for polishing wafers and a process for polishing
wafers are provided. The apparatus for polishing a wafer which
polishes the wafer W held by a carrier plate which rotates around
an axis, by pressing and rubbing the wafer to a polishing pad
disposed to a polishing platen 12 which rotates around another axis
which differs from said axis, in which the polishing pad 11 is
equipped with plural areas including a first area 11a and a second
area 11b having hardness different from each other, each of the
first 11a area and second area 11b being formed at a distribution
and/or an area ratio such that the rate of the time or distance
that the wafer W passes through the first area 11a during polishing
to the time or distance that the wafer W passes through the second
area 11b during polishing becomes a predetermined value.
Inventors: |
Hashii; Tomohiro;
(Imari-shi, JP) ; Murayama; Katsuhiko; (Takeo-shi,
JP) ; Koyata; Sakae; (Ogi-shi, JP) ; Takaishi;
Kazushige; (Takeo-shi, JP) |
Correspondence
Address: |
KOLISCH HARTWELL, P.C.
200 PACIFIC BUILDING
520 SW YAMHILL STREET
PORTLAND
OR
97204
US
|
Assignee: |
Sumco Corporation
|
Family ID: |
36808329 |
Appl. No.: |
11/433843 |
Filed: |
May 11, 2006 |
Current U.S.
Class: |
451/41 ;
451/285 |
Current CPC
Class: |
B24B 37/20 20130101;
B24B 37/042 20130101 |
Class at
Publication: |
451/041 ;
451/285 |
International
Class: |
B24B 7/30 20060101
B24B007/30; B24B 29/00 20060101 B24B029/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 18, 2005 |
JP |
2005-145611 |
Claims
1. An apparatus for polishing a wafer which polishes the wafer held
by a carrier plate which rotates around an axis, by pressing and
rubbing the wafer to a polishing pad disposed to a polishing platen
which rotates around another axis which differs from said axis,
wherein said polishing pad is equipped with plural areas including
a first area and a second area having hardness different from each
other, each of said first area and second area being formed at a
distribution and/or an area ratio such that the rate of the time or
distance that said wafer passes through said first area during
polishing to the time or distance that said wafer passes through
said second area during polishing becomes a predetermined
value.
2. The apparatus for polishing a wafer as set forth in claim 1,
wherein each of said first area and said second area is shaped into
a planar sector, and said first area and said second area are
arranged alternately to constitute said plural areas.
3. The apparatus for polishing a wafer as set forth in claim 1,
wherein each of said first area and said second area is shaped into
a planar spiral, and said first area and said second area are
arranged alternately to constitute said plural areas.
4. A process for polishing a wafer comprising rotating a polishing
pad equipped with plural areas including a first area and a second
area having hardness different from each other, and pressing and
rubbing a wafer which rotates to said polishing pad thereby
polishing surface of said wafer.
Description
[0001] Priority is claimed on Japanese Patent Application No.
2005-145611, filed May 18, 2005, the content of which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an apparatus for polishing
wafers such as integrated circuits and a process for polishing
wafers.
[0004] 2. Description of Related Art
[0005] Generally, as for the silicon wafer of which the surface is
etched, polish is performed to the surface in a polishing process.
In the conventional polishing process, by performing the first
polishing process which removes the coarse unevenness on the
surface of a wafer using a wafer polishing apparatus which is
equipped with a hard polishing pad, and makes the surface flat, and
the second polishing process eliminating the minute pit on the
surface of a wafer using a wafer polishing apparatus equipped with
a soft polishing pad, the surface of wafer is finished to be a flat
and strain-free surface. It should be noted that since the kind of
polishing pad used in the first polishing process and the second
polishing process differs from each other, a wafer polishing
apparatus for exclusive use is used in the first polishing process
and the second polishing process, respectively.
[0006] FIGS. 7A and 7B are figures showing a schematic view of a
wafer polishing apparatus used in the conventional polishing
method, and FIG. 7A is a plan view thereof, and FIG. 7B is a side
view thereof (for example, refer to Patent document 1).
[0007] A conventional wafer polishing apparatus consists of a
rotation disk 31, a polishing pad 32 which is stuck on
approximately whole surface of the rotation disk, plural rotation
holders 33 disposed upward the rotation disk 31, and a wafer
attachment plate 35 fixed to each rotation holders 33. The rotation
holder 33 is constituted so that it can be driven up and down and
rotated through a shaft 34. Plural wafers 36 are attached in the
wafer attachment plate 35. It should be noted that the mark 37
denotes a pouring pipe, and it is also possible to polish wafers
while supplying a rinsing liquid or a polishing liquid 38 through
the pouring pipe 37, if needed.
[0008] [Patent document 1] Japanese Unexamined Patent Application,
First Publication No. S64-78758 official report
[0009] However, there is a problem in that the manufacturing cost
of wafers becomes expensive due to increasing of the equipment for
polishing wafers and polishing materials in the conventional
polishing method, because each of the first polishing process and
the second polishing process is performed using a wafer polishing
apparatus and a polishing pad for exclusive use. Moreover, since
two polishing processes are performed while changing the wafer
polishing equipment to be used, there is a problem in that the
polishing process becomes complicated and it takes a long time for
performing polishing process.
[0010] The present invention was made in view of the above
circumstances, and it is an object of the present invention to
provide an apparatus for polishing wafers which can reduce
equipments for polishing wafers and materials for polishing, and
which can simplify the polishing process and shorten the time for
polishing, and a process for polishing wafers.
[0011] In order to solve the above problems, the inventors of the
present invention have researched and repeated experiments
thoroughly, and as a result, they have found that the coarseness
component of the surface of wafer before being polished consists of
a component with a large (for example, a wavelength over 10 .mu.m)
wavelength and a component with a small (a wavelength under 10
.mu.m) wavelength in terms of the PSD (power spectral density)
analysis as shown in FIG. 1.
[0012] Moreover, it turned out that when the wafer surface is
polished using a conventional hard polishing pad which is made of a
foaming urethane with hardness of 90, as shown in the curve A in
FIG. 2A, the component with a large wavelength can be removed in a
short time (i.e. a convergence constant is large), whereas the
convergence constant of a component with a short wavelength is
small. Moreover, it turned out that when the wafer surface is
polished using a conventional soft polishing pad which is made of
suede with hardness of 68, as shown in the curve B of FIG. 2A, the
component with a small wavelength can be removed in a short time
(i.e. a convergence constant is large), whereas the convergence
constant of a component with a large wavelength is small.
[0013] It should be noted that the convergence constant in the
above is an inverse of time until the wafer surface is converted
into a mirror surface, and the more the convergence constant is,
the shorter the time until the wafer surface is converted into a
mirror surface becomes, and the better the coefficient of polishing
becomes.
[0014] Moreover, the hardness of the above polishing pad is the
value measured by the spring type hardness meter (JIS-A type).
[0015] Furthermore, the inventors of the present invention have
researched and repeated experiments thoroughly, and as a result,
they have found that if the surface of a wafer is polished using a
polishing pad (it may be referred as "a mixed pad") having both an
area made of a hard polishing material and an area made of a soft
polishing material, then the convergence constant of the component
with a large wavelength becomes much greater than that of a
conventional soft polishing pad, although the convergence constant
of the component with a large wavelength becomes slightly smaller
than that of a conventional hard polishing pad, as shown by the
curve C in FIG. 2A, whereas the convergence constant of the
component with a small wavelength becomes much greater than that of
a conventional hard polishing pad, although the convergence
constant of the component with a small wavelength becomes slightly
smaller than that of a conventional soft polishing pad, and that
both a coarseness component with a large wavelength and a
coarseness component with a small wavelength on the surface of a
wafer can be removed efficiently using one apparatus for polishing
wafer, thereby finishing to be a smooth and strain-free mirror
surface, and thus they have completed the present invention. It
should be noted that a graphic chart demonstrating the correlation
between wavelength and coarseness component of wafer surface is
shown in FIG. 2B.
SUMMARY OF THE INVENTION
[0016] The present invention provides an apparatus for polishing a
wafer which polishes the wafer held by a carrier plate which
rotates around an axis, by pressing and rubbing the wafer to a
polishing pad disposed to a polishing platen which rotates around
another axis which differs from said axis, wherein said polishing
pad is equipped with plural areas including a first area and a
second area having hardness different from each other, each of said
first area and second area being formed at a distribution and/or an
area ratio such that the rate of the time or distance that said
wafer passes through said first area during polishing to the time
or distance that said wafer passes through said second area during
polishing becomes a predetermined value.
[0017] Moreover, in the apparatus for polishing a wafer of the
present invention, each of said first area and said second area may
be shaped into a planar sector, and said first area and said second
area may be arranged alternately to constitute said plural
areas.
[0018] Moreover, in the apparatus for polishing a wafer of the
present invention, each of said first area and said second area may
be shaped into a planar spiral, and said first area and said second
area may be arranged alternately to constitute said plural
areas.
[0019] The process for polishing a wafer of the present invention
comprises rotating a polishing pad equipped with plural areas
including a first area and a second area having hardness different
from each other, and pressing and rubbing a wafer which rotates to
said polishing pad thereby polishing surface of said wafer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a graphic chart which shows the PSD analysis
result of the coarseness of the surface of the wafer before being
polished.
[0021] FIG. 2A is a graphic chart which shows the relation between
a polishing pad and a convergence constant
[0022] FIG. 2B is a diagrammatic chart which shows the relation
between the component of the coarseness of the surface of the wafer
and a wavelength.
[0023] FIG. 3 is a principal part expanded sectional view of the
apparatus for polishing a wafer of the preferred embodiment of the
present invention.
[0024] FIG. 4 is a plan view of a polishing platen and a career
plate disposed to the apparatus for polishing a wafer of FIG.
1.
[0025] FIG. 5 is a plan view of the polishing pad disposed to the
apparatus for polishing a wafer of FIG. 1.
[0026] FIG. 6 is a graphic chart which shows polishing time of
Comparative Example.
[0027] FIG. 7A is a plan view which shows a schematic constitution
of a conventional wafer polishing apparatus.
[0028] FIG. 7B is a side view which shows a schematic constitution
of a conventional wafer polishing apparatus.
[0029] FIG. 8 is a plan view showing another example of the
polishing pad disposed to the apparatus for polishing a wafer of
the present invention.
[0030] FIG. 9 is a plan view showing another example of the
polishing pad disposed to the apparatus for polishing a wafer of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0031] Hereafter, embodiments of the apparatus for polishing a
wafer of the present invention will be explained, based on
drawings.
[0032] FIG. 3 is a principal part expanded sectional view of the
apparatus for polishing a wafer of this embodiment, FIG. 4 is a
plan view which shows the polishing platen disposed to the
apparatus for polishing a wafer of FIG. 1 and a career plate, and
FIG. 5 is a plan view of the polishing pad disposed to the
apparatus for polishing a wafer of FIG. 1.
[0033] The apparatus for polishing a wafer 10 of this embodiment is
equipped with a polishing platen 12 to the surface of which a
planar circular polishing pad 11 consisting of plural areas is
disposed, and plural (four in the drawing) polishing heads 13
disposed upwardly.
[0034] Each polishing head 13 is disposed rotatably around an axis.
The career plate 14 is disposed to the surface opposed to the
polishing platen of each polishing head 13, such that when the
polishing head 13 rotates, the carrier plate 14 which is disposed
to the polishing head 13 will also rotate around the axis. In this
carrier plate 14, each of plural (i.e., 5 pieces in the drawing)
silicon wafers is held at a predetermined interval (i.e., at
72.degree. angular interval) around the center of the head. Silicon
wafer W is, for example, one which was subjected to etching after
being sliced or wrapped, and which necessitates to be subjected to
be polishing process of polishing the surface to be mirror. As for
the dimension of the silicon wafer W, one having a diameter of 300
mm and a thickness of 0.75 mm is used suitably, for example.
[0035] The polishing pad 11 is constituted from plural areas
including a first area 11a and a second area 11b each of which
hardness differs from each other.
[0036] The first area 11a and the second area 11b are formed at a
distribution and/or an area ratio, such that the time or distance
that wafer W passes through the first area 11a and the time or
distance that wafer W passes through the second area 11b when
polishing a wafer with the polishing pad 11 becomes a predetermined
rate.
[0037] Specifically, as it will be mentioned later, it is possible
to set each of the first area 11a being hard and the second area
11b being soft, such that the length of trajectory formed when each
of the first area 11a and the second area 11b passes a minute
portion of wafer W during polishing process will be proportioned to
the inverse of the hardness of each areas of 11a and 11b, for
example, it is possible to set such that the formula (length of the
first area 11a):(length of the second area 11b)=(hardness of the
second area):(hardness of the first area) is satisfied,
alternatively, the formula (time that the first area 11a passes
through):(time that the second area 11b passes through)=(hardness
of the second area):(hardness of the first area) is satisfied.
[0038] Alternatively, it is possible to set each of the first area
11a being hard and the second area 11b being soft, such that the
length that the first area 11a passes through a certain portion of
wafer W will be equivalent to the length that the second area 11b
passes through the certain portion of wafer W during the polishing
process, for example, it is possible to set such that the following
formula [length of passing through the hard area]:[length of
passing through the soft area]=1:1 can be satisfied.
[0039] In this embodiment, as shown in FIG. 5, each of the planar
sector-shaped first area 11a and the planar sector-shaped second
area 11b is arranged alternately, thereby constituting a planar
circular polishing pad 11. That is, the polishing pad 11 is divided
into plural (i.e. eight pieces in the drawing) areas.
[0040] As for the first area 11a, material with hardness larger
than that of the second area 11b is used, for example, the foaming
urethane of hardness 90 is used.
[0041] As for the second area 11b, material with hardness smaller
than that of the first area 11a, for example, suede and the
nonwoven fabric of hardness 68 are used.
[0042] The hardness of the polishing pad 11 on which each of the
first area 11a and the second area 11b is arranged alternately
ranges from 68 to 90.
[0043] Although FIG. 5 shows the case in which the area ratio of
the first area 11a and the second area 11b is 1:1, it is possible
to make the area of the second area 11a having a small hardness
larger than the area of the first area 11a having a large
hardness.
[0044] In this case, it is possible to elongate the time or
distance that the component with a small wavelength, which takes a
time to be removed, of the coarseness component of the surface of
the silicon wafer, passes through the second area 11b when
polishing silicon wafer W with the polishing pad 11, and hence the
removal efficiency of the coarseness component with a small
wavelength can be increased.
[0045] The polishing platen 12 is disposed rotatably centering
around another axis which is different from the above axis. The
rotating direction of the polishing platen 12 is set to be the same
as in each of the polishing head 13. It should be noted that the
moving method of the polishing head 13 is not restricted to this
embodiment.
[0046] The method for attaching the silicon wafer W to the career
plate 14 may be either a wax adhering or a wax-less mounting
method.
[0047] Next, a process for polishing silicon wafer W using this
apparatus for polishing 10 will be explained.
[0048] As shown in FIGS. 3 and 4, at first, each of plural pieces
(i.e. 5 pieces in the drawing) of silicon wafers W is stuck with
wax at a predetermined interval (i.e. at 72.degree. angular
interval in the drawing) to each carrier plate 14, and then each
carrier plate 14 is fixed to the lower surface of the polishing
head 13 corresponding thereto.
[0049] And each polishing head 13 is lowered, thereby pressing each
silicon wafer W to a polishing surface of the polishing pad 11
disposed to the polishing platen 12. The polishing platen 12 is
rotated in the direction indicated by a solid line arrow of FIG. 4,
while maintaining this state and supplying polish liquid to the
polishing pad 11. Simultaneously, while rotating each polishing
head 13 in the direction indicated by an
alternate-long-and-two-short-dashes-line arrow of FIG. 4, each
silicon wafer W is pressed and rubbed to the polishing pad 11,
thereby polishing wafer W. In this polishing operation, the time or
distance that the polished surface (surface) of wafer W passes
through the first area 11a and the time or distance that the
polished surface (surface) of wafer W passes through the second
area 11b becomes a predetermined rate. For example, when the area
ratio of the first area 11a to the second area 11b of the polishing
pad 11 is 1:1, the ratio of the time or distance that the surface
of the wafer W passes through the first area 11a to the time or
distance that the surface of the wafer W passes through the second
area 11b is 1:1. When the area of the second area 11b is larger
than the area of the first area 11a, the time or distance that the
surface of wafer W passes through the second area 11b becomes
larger than the time or distance that the surface of wafer W passes
through the first area 11a.
[0050] Thereby, the polished surface (surface) of each silicon
wafer W is polished, and coarseness with a large (periodic time is
large) wavelength and coarseness with a small (periodic time is
small) wavelength existed on the wafer surface before being
polished can be converged using one pad.
[0051] In the apparatus for polishing a wafer 10 in this
embodiment, each of the first area 11a and the second area 11b
differing in hardness is disposed alternately to the polishing pad
11 at a distribution and/or area ratio, such that the time or
distance that the silicon wafer W passes through the first area 11a
and the time or distance that the silicon wafer W passes through
the second area 11b when polishing becomes a predetermined rate,
and hence if polishing of wafer W is performed using this apparatus
for polishing a wafer 10, then both coarse unevenness and minute
pit on the surface of the wafer can be efficiently removed, thereby
finishing into a smooth and strain-free mirror surface. That is, in
accordance with the polishing using the apparatus for polishing a
wafer in this embodiment, both coarse unevenness and minute pit
(i.e. both a coarse component with a large wavelength and a coarse
component with a small wavelength) on the surface of a wafer can be
removed in the same process using one apparatus for polishing a
wafer, and hence it is not necessary to change the apparatus for
polishing a wafer and the polishing pad corresponding to the case
of removing coarse unevenness and the case of eliminating minute
pit as usual, and it is possible to reduce equipment for polishing
a wafer and polishing material, thereby simplifying the polishing
process and shortening the polishing period of a wafer, and as a
result, a wafer can be efficiently polished.
[0052] Moreover, in accordance with the process for polishing a
wafer in this embodiment, the polishing pad 11 which is equipped
with plural areas including the first area 11a and the second area
11b each of which differs in hardness is rotated, and a rotating
silicon wafer W is pressed and rubbed to the polishing pad 11,
thereby removing both coarse unevenness and minute pit on the
surface of the wafer with the polishing pad 11, and hence it is not
necessary to change the apparatus for polishing a wafer and the
polishing pad corresponding to the case of removing coarse
unevenness and the case of eliminating minute pit as usual, and it
is possible to reduce equipment for polishing a wafer and polishing
material, thereby simplifying the polishing process and shortening
the polishing period of a wafer, and as a result, a wafer can be
efficiently polished.
[0053] Specifically, the processing time in the case (i.e. in the
case of performing a first polishing process using a hard polishing
pad, and a second polishing process using a soft polishing pad, as
Comparative Example) of polishing by changing apparatus for
polishing a wafer which is used in the case of removing the coarse
unevenness on the surface of a wafer and the polishing pad which is
used in the case of removing a minute pit, as usual takes
approximately 1650 seconds, as shown in FIG. 6. On the other hand,
it is revealed that the processing time in the case of polishing
the surface of wafer W using the apparatus for polishing a wafer 10
of the embodiment which is equipped with the polishing pad (i.e.
mixed pad) 11 to which each of the first area 11a and the second
area 11b which differs in hardness is disposed alternately takes
approximately 800 seconds as shown in FIG. 6, it is possible to
make the time required for polishing a wafer 1/2 or less of that of
Comparative Example, and that wafer can be polished
efficiently.
[0054] In accordance with this embodiment, by performing processing
corresponding to each coarseness component on one axis, the time
required for polishing can be reduced to be half, an equipment
therefor can also be reduced to be half, the polishing pad can also
be reduced to be half, and the cost can be reduced.
[0055] It should be noted that although it is explained about the
case in which the apparatus for polishing a wafer in the above
embodiment is equipped with the polishing pad 11 which is
constituted from eight areas in which each of the first area 11a
being planar sector-shaped and the second area 11b being planar
sector-shaped is disposed alternately, as for the polishing pad,
any other polishing pad may be used as long as it consists of each
of the first area and the second area which differs in hardness and
arranged alternately, for example, the polishing pad may be
constituted from two areas of a first area 11a which is planar
semicircle-shaped and a second area 11b which is planar
semicircle-shaped.
[0056] Moreover, as shown in FIG. 8, the polishing pad 21 may be
constituted from plural areas consisting of the first area 21a and
the second area 21b, each of which has planar spiral-shape, differs
in hardness and is arranged alternately.
[0057] Moreover, as shown in FIG. 9, the polishing pad 21 may be
constituted from plural areas consisting of the first area 31a and
the second area 31b, each of which has planar pinwheel-shape,
differs in hardness and is arranged alternately.
[0058] In the apparatus for polishing a wafer in this embodiment,
each of the first area and the second area differing in hardness is
disposed alternately to the polishing pad at a distribution and/or
area ratio, such that the time or distance that the silicon wafer
passes through the first area and the time or distance that the
silicon wafer passes through the second area when polishing becomes
a predetermined rate, and hence if polishing of wafer is performed
using this apparatus for polishing a wafer, then both coarse
unevenness and minute pit on the surface of the wafer can be
efficiently removed, thereby finishing into a smooth and
strain-free mirror surface. That is, in accordance with the
polishing using the apparatus for polishing a wafer in this
embodiment, both coarse unevenness and minute pit (i.e. both a
coarse component with a large wavelength and a coarse component
with a small wavelength) on the surface of a wafer can be removed
in the same process using one apparatus for polishing a wafer, and
hence it is not necessary to change the apparatus for polishing a
wafer and the polishing pad corresponding to the case of removing
coarse unevenness and the case of eliminating minute pit as usual,
and it is possible to reduce equipment for polishing a wafer and
polishing material, thereby simplifying the polishing process and
shortening the polishing period of a wafer, and as a result, a
wafer can be efficiently polished.
[0059] Moreover, in accordance with the process for polishing a
wafer in this embodiment, the polishing pad which is equipped with
plural areas including the first area and the second area each of
which differs in hardness is rotated, and a rotating silicon wafer
is pressed and rubbed to the polishing pad, thereby removing both
coarse unevenness and minute pit on the surface of the wafer with
the polishing pad, and hence it is not necessary to change the
apparatus for polishing a wafer and the polishing pad corresponding
to the case of removing coarse unevenness and the case of
eliminating minute pit as usual, and it is possible to reduce
equipment for polishing a wafer and polishing material, thereby
simplifying the polishing process and shortening the polishing
period of a wafer, and as a result, a wafer can be efficiently
polished.
[0060] While preferred embodiments of the invention have been
described and illustrated above, it should be understood that these
are exemplary of the invention and are not to be considered as
limiting. Additions, omissions, substitutions, and other
modifications can be made without departing from the spirit or
scope of the present invention. Accordingly, the invention is not
to be considered as being limited by the foregoing description, and
is only limited by the scope of the appended claims.
* * * * *