U.S. patent application number 10/153317 was filed with the patent office on 2002-11-28 for polishing head of a chemical and mechanical polishing apparatus for polishing a wafer.
This patent application is currently assigned to Samsung Electronics Co., Ltd.. Invention is credited to Han, Myoung-Sik, Hong, Chang-Ki.
Application Number | 20020177395 10/153317 |
Document ID | / |
Family ID | 19709828 |
Filed Date | 2002-11-28 |
United States Patent
Application |
20020177395 |
Kind Code |
A1 |
Han, Myoung-Sik ; et
al. |
November 28, 2002 |
Polishing head of a chemical and mechanical polishing apparatus for
polishing a wafer
Abstract
Disclosed is a polishing head of a chemical and mechanical
polishing apparatus uniformly polishing a wafer. The polishing head
has a body defining at least one air passage therein through which
air is introduced into and exhausted from the polishing head. The
body is movable upward and downward. An air pressure distributing
member is mounted to a lower portion of the body for distributing a
pressure of the air supplied through the air passage. A membrane is
mounted to enclose a lower surface of the air pressure distributing
member so as to be expanded and shrunk by the pressure of the air
supplied through the air pressure distributing member. A surface of
the air pressure distributing member makes contact with a back
surface of a wafer. An air pressure compensating member makes
uniformly the pressure that is applied to central and edge portions
of the wafer which makes contact with the membrane. Since the air
pressure compensating member applies to the edge portion of the
wafer, the air pressure is compensated so that the uniform air
pressure is applied to the wafer. Thus, the wafer is uniformly
polished.
Inventors: |
Han, Myoung-Sik; (Suwon-si,
KR) ; Hong, Chang-Ki; (Suwon-si, KR) |
Correspondence
Address: |
Frank Chau, Esq.
F. CHAU & ASSOCIATES, LLP
Suite 501
1900 Hempstead Turnpike
East Meadow
NY
11554
US
|
Assignee: |
Samsung Electronics Co.,
Ltd.
|
Family ID: |
19709828 |
Appl. No.: |
10/153317 |
Filed: |
May 22, 2002 |
Current U.S.
Class: |
451/398 ;
451/288 |
Current CPC
Class: |
B24B 37/30 20130101 |
Class at
Publication: |
451/398 ;
451/288 |
International
Class: |
B24B 005/00; B24B
029/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 23, 2001 |
KR |
2001-28360 |
Claims
What is claimed is:
1. A polishing head of a chemical and mechanical polishing
apparatus for polishing a wafer, said polishing head comprising: a
body having at least one air passage therein, through which air is
introduced into the body and exhausted from the body; an air
pressure distributing unit mounted to a lower portion of the body
for distributing air pressure supplied through the air passage; a
membrane for enclosing a lower surface of the air pressure
distributing unit, the membrane having a lower surface for making
contact with a back surface of the wafer, the membrane being
expanded and shrunk by the pressure of the air supplied through the
air pressure distributing unit; and an air pressure compensating
unit for distributing pressure to selected portions of the surface
of the wafer contacting the membrane.
2. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 1, wherein the selected portions of
the surface of the wafer contacting membrane include a center
portion and an edge portion of the wafer.
3. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 1, wherein the air pressure
compensating unit is disposed between the air pressure distributing
unit and the membrane and an upper surface and a lower surface of
the air pressure compensating unit are respectively fixed to edge
of the lower surface of the air pressure distributing unit and edge
of an upper surface of the membrane.
4. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 3, wherein the air pressure
compensating unit has a ring shape, which is adhered to edges of
the air pressure distributing unit and the membrane.
5. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 4, wherein the air pressure
compensating unit has a cross-sectional shape of which an upper
side and a lower side are parallel with each other, an inner side
is inclined and an outer side is vertical to the upper and lower
sides.
6. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 5, wherein the inner side of the air
pressure compensating unit is inclined in a direction to a center
of the membrane so as to compensate a space between the membrane
and an edge of the wafer when the membrane is expanded by the air
pressure.
7. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 5, wherein the air pressure
compensating unit has a thickness enough to compensate an expanding
difference between the edge portion and the center portion of the
membrane when the membrane is expanded by the air pressure.
8. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 1, wherein the air pressure
compensating unit has a ring shape, disposing under the membrane
and an edge of the membrane.
9. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 8, wherein the air pressure
compensating unit is inclined in a direction to a center of the
membrane.
10. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 1, wherein the air pressure
compensating unit is comprised of resilient material.
11. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 10, wherein the resilient material is
a rubber or a silicon resin.
12. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 1, wherein the air pressure
distributing unit is formed as a disc shape having a predetermined
diameter, in which a plurality of thru-holes are formed at portions
within a range of a predetermined radius from a center of the disc
shape.
13. A polishing head of a chemical and mechanical polishing
apparatus for polishing a wafer, said polishing head comprising: a
body having a plurality of air passages therein, through which air
is introduced into and exhausted from the polishing head, and a
retainer ring for securing the wafer, said body being movable
upwardly and downwardly; an air pressure distributing plate mounted
to a lower portion of the body for distributing air pressure
supplied through the air passages; an air cushion connected with an
end portion of one of the air passages so as to close the end
portion and make contact with an edge portion of an upper surface
of the air pressure distributing plate, the air cushion being
resiliently expanded and shrunk during introducing and venting of
the air through the air passages for applying pressure to the edge
portion of the upper surface of the air pressure distributing
plate; a membrane mounted to enclose a lower surface of the air
pressure distributing unit for being expanded and shrunk by the
pressure of the air supplied through the air pressure distributing
plate, a lower surface of the membrane making contact with a back
side of the wafer; and an air pressure compensating member for
uniformly distributing the pressure that is applied at central and
edge portions of the wafer which makes contact with the
membrane.
14. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 13, wherein the air pressure
compensating member is disposed between the air pressure
distributing plate and the membrane so that an upper surface and a
lower surface of the air pressure compensating member are
respectively fixed to an edge on the lower surface of the air
pressure distributing plate and an edge of an upper surface of the
membrane.
15. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 13, wherein the air pressure
compensating member has a ring shape, which is adhered to edges of
the air pressure distributing plate and the membrane.
16. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 15, wherein the air pressure
compensating member has a cross-sectional shape in which an upper
side and a lower side are in parallel with each other, an inner
side is inclined and an outer side is vertical to the upper and
lower sides.
17. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 16, wherein the inner side of the air
pressure compensating member is inclined in a direction to a center
of the polishing he ad so as to compensate a space between the
membrane and an edge of the wafer when the membrane is expanded by
the air pressure.
18. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 16, wherein the air pressure
compensating member has a thickness enough to compensate an
expanding difference between the edge portion and the center
portion of the membrane when the membrane is expanded by the air
pressure.
19. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 13, wherein the air pressure
compensating member has a ring shape, disposing under the membrane
and an edge of the membrane.
20. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 19, wherein the air pressure
compensating member is inclined in a direction to a center of the
membrane.
21. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 13, wherein the air pressure
compensating member is comprised of resilient material.
22. The polishing heads of a chemical and mechanical polishing
apparatus as claimed in claim 21, wherein the resilient material is
a rubber or a silicon resin.
23. The polishing head of a chemical and mechanical polishing
apparatus as claimed in claim 13, further comprising a dividing
plate between the body and the air pressure distributing member for
reducing a space between the body and the air pressure distributing
plate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a chemical and mechanical
polishing apparatus, and more particularly to a polishing head of a
chemical and mechanical polishing apparatus capable of uniformly
polishing a wafer.
[0003] 2. Description of the Related Art
[0004] In a semiconductor device manufacture process, a surface of
a semiconductor wafer is polished, using chemical and mechanical
components such as abrasive supplied between the wafer and a
polishing pad. This process is commonly known as a chemical and
mechanical polishing (CMP).
[0005] CMP has developed into an integral component of the
manufacture and yield of cost effective semiconductor products. In
general, a CMP apparatus for planarizing surface of the wafer
includes a polishing head for supporting and pressing the wafer, a
polishing platen rotatively operating and having a polishing pad, a
slurry supplying device, and a conditioner for conditioning the
polishing pad.
[0006] When the CMP apparatus performs the polishing process, the
surface of the wafer being polished must be uniformly polished
throughout. Therefore, the polishing pressure applied to a
respective region of the wafer, the amount of slurry, and the
condition of the polishing pad which come in contact with the wafer
must be regularly controlled.
[0007] FIG. 1 is a cross sectional view of a conventional polishing
head of a CMP apparatus.
[0008] Referring to FIG. 1, when a wafer is polished, a surface of
the wafer W contacts with a polishing pad 10 and a polishing head
12 contacts with the other surface of the wafer for applying a
pressure to the wafer W. The polishing pad 10 and the polishing
head 12 rotate in the same direction or opposite direction,
respectively.
[0009] The polishing head 12 includes a body 14 capable of moving
upward and downward. The body 14 includes air passages 16 for
receiving and discharging air and a retainer ring 18 for securing
the wafer W and preventing it from separating from the body 14.
[0010] A perforated plate 20 is disposed on a lower portion of the
body 14 for distributing a pressure of air supplied through the air
passages 16. A plurality of thru-holes 20a are formed in the
perforated plate 20 for uniformly distributing the air
pressure.
[0011] A membrane 22 is attached to the body 14 to enclose a lower
portion of the perforated plate 20.
[0012] FIG. 2 is a perspective view showing the membrane 22 mounted
to the polishing head 12 shown in FIG. 1.
[0013] The membrane 22 is resiliently expanded and shrunk by the
air pressure supplied through the plurality of thru-holes 20a (in
FIG. 1).
[0014] Referring again to FIG. 1 for describing the polishing
process of the wafer, the air is exhausted through the air passages
16 from the body 14, so that the body 14 is in a vacuum state at a
certain portion thereof. Due to the vacuum state in the body 14,
the wafer W adheres to the lower surface of the membrane 22, which
contacts with the polishing pad 10. Air is then introduced through
the air passages 16 into the body 14 to expand the membrane 22. The
expanded membrane 22 presses the wafer W. A problem with this
process is that the membrane 22 is non-uniformly expanded at a
center portion and an edge portion thereof.
[0015] FIG. 3 is a partially enlarged cross sectional view showing
the edge portion A of the expanded membrane of the polishing
apparatus shown in FIG. 1.
[0016] Referring to FIG. 3, the membrane 22 is inclined at the edge
portion during the expansion. When the membrane 22 is expanded, a
gap 22a is formed between the edge portion of the membrane 22 and
the edge portion of the wafer W so that the membrane 22 does not
contact with the wafer W at the edge portion thereof. As a result,
the pressure is not applied to the edge portion of the wafer W.
[0017] Accordingly, the wafer W has a different polishing rate
between the edge portion and portions other than the edge portion
during the polishing. Due to the different polishing rate, the
wafer W has a non-uniform profile at the edge portion thereof.
[0018] U.S. Pat. No. 6,116,992 (issued to Prince on Sep. 12, 2000)
discloses a CMP apparatus having a retainer ring of which a bottom
surface is projected to help the polishing of the wafer W. However,
nonuniformity in a polished wafer still exists in the CMP
apparatus, if the membrane has uneven expansion
characteristics.
[0019] Accordingly, there is a problem in that a process error is
found in chips formed on the edge portion of the wafer as the edge
portion of the wafer is non-uniformly polished, resulting in
decreased yield and reliability of the semiconductor devices.
SUMMARY OF THE INVENTION
[0020] The present invention has been made to solve the
above-mentioned problem, and accordingly it is an object of the
present invention to provide a CMP apparatus capable of uniformly
polishing a wafer.
[0021] A polishing head of a chemical and mechanical polishing
apparatus for polishing a wafer is provided, the polishing head
includes: a body having at least one air passage therein, through
which air is introduced into the body and exhausted from the body;
an air pressure distributing unit mounted to a lower portion of the
body for distributing air pressure supplied through the air
passage; a membrane for enclosing a lower surface of the air
pressure distributing unit, the membrane having a lower surface for
making contact with a back surface of the wafer, the membrane being
expanded and shrunk by the pressure of the air supplied through the
air pressure distributing unit; and an air pressure compensating
unit for distributing pressure to selected portions of the surface
of the wafer connecting the membrane.
[0022] According to an embodiment of the present invention, the
selected portions of the surface of the wafer include a center
portion and an edge portion of the wafer. The air pressure
compensating unit is disposed between the air pressure distributing
unit and the membrane and an upper surface and a lower surface of
the air pressure compensating unit are respectively fixed to edge
of the lower surface of the air pressure distributing unit and edge
of an upper surface of the membrane. The air pressure compensating
unit has a ring shape, which is adhered to edges of the air
pressure distributing unit and the membrane. The air pressure
compensating unit has a cross-sectional shape of which an upper
side and a lower side are parallel with each other, an inner side
is inclined and an outer side is vertical to the upper and lower
sides. The inner side of the air pressure compensating unit is
inclined in a direction to a center of the membrane so as to
compensate a space between the membrane and an edge of the wafer
when the membrane is expanded by the air pressure. The air pressure
compensating unit has a thickness enough to compensate an expanding
difference between the edge portion and the center portion of the
membrane when the membrane is expanded by the air pressure. The air
pressure compensating unit has a ring shape, disposing under the
membrane and an edge of the membrane. The air pressure compensating
unit is inclined in a direction to a center of the membrane. The
air pressure compensating unit is comprised of resilient material.
The resilient material is a rubber or a silicon resin. The air
pressure distributing unit is formed as a disc shape having a
predetermined diameter, in which a plurality of thru-holes are
formed at portions within a range of a predetermined radius from a
center of the disc shape.
[0023] A polishing head of a chemical and mechanical polishing
apparatus for polishing a wafer is also provided, the polishing
head includes: a body having a plurality of air passages therein,
through which air is introduced into and exhausted from the
polishing head, and a retainer ring for securing the wafer, said
body being movable upwardly and downwardly; an air pressure
distributing plate mounted to a lower portion of the body for
distributing air pressure supplied through the air passages; an air
cushion connected with an end portion of one of the air passages so
as to close the end portion and make contact with an edge portion
of an upper surface of the air pressure distributing plate, the air
cushion being resiliently expanded and shrunk during introducing
and venting of the air through the air passages for applying
pressure to the edge portion of the upper surface of the air
pressure distributing plate; a membrane mounted to enclose a lower
surface of the air pressure distributing unit for being expanded
and shrunk by the pressure of the air supplied through the air
pressure distributing plate, a lower surface of the membrane making
contact with a back side of the wafer; and an air pressure
compensating member for uniformly distributing the pressure that is
applied at central and edge portions of the wafer which makes
contact with the membrane.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The above and other objects and advantages of the present
invention will become readily apparent by reference to the
following detailed description when considered in conjunction with
the accompanying drawings wherein:
[0025] FIG. 1 is a cross sectional view showing a conventional
polishing head of a CMP apparatus;
[0026] FIG. 2 is a perspective view showing a membrane mounted on
the CMP apparatus shown in FIG. 1;
[0027] FIG. 3 is a partially enlarged cross sectional view showing
an edge of the membrane of the CMP apparatus, in which the membrane
is expanded to apply pressure to a wafer;
[0028] FIG. 4 is a cross sectional view showing a polishing head of
a CMP apparatus according to a preferred embodiment of the present
invention;
[0029] FIG. 5 is a perspective view showing a membrane mounted on
the CMP apparatus as shown in FIG. 4;
[0030] FIG. 6 is a plan view showing the membrane mounted on the
CMP apparatus shown in FIG. 4; and
[0031] FIG. 7 is a partially enlarged cross sectional view showing
an edge of the membrane of the CMP apparatus shown in FIG. 4, in
which the membrane is expanded to apply pressure to a wafer.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0032] Hereinafter, preferred embodiments of the present invention
will be described in detail with reference to the accompanying
drawings.
[0033] FIG. 4 is a cross sectional view showing a polishing head of
a CMP apparatus according to an embodiment of the present
invention.
[0034] Referring to FIG. 4, when a wafer W is polished, a surface
of the wafer W is in contact with a polishing pad 30 and the other
surface of the wafer W is in contact with a polishing head 32 so
that pressure is applied to the wafer W. A polishing pad 30 and the
polishing head 32 rotates in the same direction or opposite
direction.
[0035] The polishing head 32 includes a body 34 that is capable of
being rotated and moving upwardly and downwardly. The body 34
includes a housing 36, a base 38 for supporting the housing 36, and
a retainer ring 40 mounted on edges of a lower portion of the base
38 for securing the wafer W and preventing it from being separated
from the body 34.
[0036] The housing 36 is connected with a driving section (not
shown), which is upwardly and downwardly moved in a vertical
direction to a surface of the polishing pad 30 by the driving
section. Further, the housing 36 rotates about a rotation axis that
is in a vertical direction to the surface of the polishing pad 30.
The housing 36 having upper and lower surfaces in a disc shape
includes a plurality of tubes 42a, 42b, and 42c for supplying and
exhausting air to/from the CMP apparatus first tube 42a. The first
tube 42a passes through a center portion from the upper surface to
the lower surface. Second and third tubes 42b and 42c spaced apart
from the first tube 42a in the radial direction of the housing 36
pass through from the upper surface of the housing 36 to the lower
surface of the housing 36. The second and third tubes 42b and 42c
are preferably disposed symmetricly about the first tube 42a.
[0037] The base 38 is connected with a certain portion of the lower
surface of the housing 36 for supporting the housing 36. The base
38 has upper and lower surfaces in a disc shape. The first tube 42a
of the housing 36 is extended into the base 38 so that the first
tube 42a passes through a center portion of the base 38. Further,
the second tube 42b is also extended to pass through the base
38.
[0038] The housing 36 and the base 38 are connected with each other
by means of a connecting member 60. The connecting member 60
includes an outer clamp (not shown) to be connected to the lower
surface of the housing 36, an inner clamp (not shown) fixed to an
upper surface of the base 38 by means of screws (not shown) and an
annular resilient sheet (not shown) connecting the housing 36 to
the base 38.
[0039] When the housing 36 is connected with the base 38 by means
of the connecting member 60, a first chamber 44 is formed between
the housing 36 and the base 38. The first chamber 44 is defined by
the housing 36, the base 38, and the connecting member. The third
tube 42c passing through the housing 36 connects with the first
chamber 44 and defines a passage for introducing and exhausting air
to and from the first chamber 44. Therefore, when the air is
introduced into the first chamber 44 through the third tube 42c,
the air pressure increases in the first chamber 44 to downwardly
push the base 38. Conversely, when the air is exhausted through the
third tube 42c from the first chamber 44, the first chamber 44 is
vacuumed to generate a vacuum pressure. As a result, the base 38 is
upwardly moved to the housing 36 by the vacuum pressure.
[0040] The retainer ring 40 has a ring shape, which is fixed along
an edge of the lower surface of the base 38. The retainer ring 40
is preferably fixed to the base 38 by screws (not shown) for
preventing the wafer W from being departed from the polishing head
32 during the polishing process.
[0041] A perforated plate 46 is mounted on a lower portion of the
body 34 for evenly distributing air pressure supplied through the
first tube 42a. Preferably, the perforated plate 46 is mounted on
the lower surface of the base 38 and inside of the retainer ring
40. The perforated plate 46 is formed as a disc shape having a
predetermined diameter, in which a plurality of thru-holes 46a are
formed in a predetermined range of radius from a center of the
perforated plate 46. The air pressure is distributed through the
thru-holes 46a of the perforated plate 46 toward the lower
direction. That is, the air is introduced in and exhausted from a
space between the base 38 and the perforated plate 46 through the
first tube 42a, and the air is distributed through the thru-holes
46a of the perforated plate 46 toward the lower direction.
[0042] A dividing plate 48 is further disposed between the base 38
and the perforated plate 46 to support the lower portion of the
base 38. The dividing plate 48 is formed as a disc shape having a
predetermined thickness, in which a pipe 48a passes through the
center portion of the dividing plate 48 to connect with the
perforated plated 46. The pipe 48a is disposed substantially at the
center of the dividing plate 48 and is extended upward.
[0043] Accordingly, the air is introduced in and exhausted from the
space between the dividing plate 48 and the perforated plate 46.
Since the dividing plate 48 is disposed between the base 38 and the
perforated plate 46, the space for distributing the air which is
supplied through the first tube 42a can be reduced and the air
pressure increases in the space.
[0044] At an edge of an upper surface of the perforated plate 46,
an air cushion 50 is connected with an end position of the second
tube 42b so as to close an end part of the second tube 42b. The air
is introduced into or exhausted from the air cushion 50 through the
second tube 42b, therefore the air cushion 50 is resiliently
expanded or shrunk. Accordingly, when air is introduced into the
air cushion 50, the air cushion 50 is expanded to apply the
pressure to the edge portion of the perforated plate 46.
[0045] The polishing head 32 further includes a membrane 52 that
encloses a substantially lower portion of the perforated plate
46.
[0046] FIG. 5 is a perspective view showing the membrane 52 mounted
on the CMP apparatus as shown in FIG. 4. FIG. 6 is a plan view
showing the membrane 52 mounted on the CMP apparatus as shown in
FIG. 4.
[0047] Referring to FIGS. 5 and 6, the membrane 52 is comprised of
a resilient material, an elastic material, or a rubbery material,
which can be resiliently expanded and shrunk by the air pressure
supplied through the perforated plated 46. According to an
embodiment of the present invention, the membrane 52 includes a
pressure compensating member 54 at an inside edge of the membrane
52. The details related to the pressure compensating member 54 will
be described below.
[0048] The membrane 52 is in contact with a back surface of the
wafer W. As the membrane 52 is expanded, the pressure is applied to
the back surface of the wafer W during polishing of the wafer W.
The membrane 52 continuously encloses the lower surface, the side
and the edge of the upper surface of the perforated plate 46 (in
FIG. 4) having a disk shape, and the membrane 52 is adhesively
fixed to the side of the perforated plate 46 and the edge of the
upper surface of the perforated plate 46.
[0049] When air is introduced through the perforated plate 46, the
membrane 52 is expanded downwardly due to the air pressure.
Furthermore, when air is exhausted through the perforated plate 46,
the membrane 52 is in close contact with the perforated plate 46,
and some portions of the membrane 52 are sucked into the thru-holes
46a of the perforated plate 46. During polishing of the wafer W,
the membrane 52 is in contact with a back surface of the wafer
W.
[0050] Hereinafter, an operation of the polishing head according to
a preferred embodiment of the present invention will be described
in detail.
[0051] Referring again to FIG. 4, air is exhausted through the
first tube 42a from the space between the dividing plate 48 and the
perforated plate 46 to provide vacuum. When the space between the
perforated plate and the dividing plate 48 is under vacuum
pressure, the back surface of the wafer W is stuck to the lower
surface of the membrane 52. Then, the body 34 is moved downwardly
so as to allow the front surface of the wafer W to make contact
with the polishing pad 30. When the front surface of the wafer W is
in contact with the polishing pad 30, the air is introduced between
the perforated plate 46 and the dividing plate 48 to expand the
membrane 52. The lower surface of the membrane 52 applies the
pressure to the wafer W as the membrane 52 is expanded. The
polishing pad 30 and the polishing head 32 are respectively rotated
to polish the wafer W.
[0052] FIG. 7 is a partially enlarged cross sectional view showing
an edge B of the membrane 52, in which the membrane 52 as shown in
FIG. 4 is expanded to apply the pressure to the wafer W.
[0053] Air introduced through the first tube 42a between the
perforated plate 46 and the dividing plate 48 applies air pressure
to the membrane 52 through the perforated plate 46. Since the
perforated plate 46 has the disc shape, in which the plurality of
the thru-holes 46a are formed in the range of the predetermined
radius from the center axis thereof, air pressure cannot be
uniformly applied to the whole surface of the membrane 52 through
the perforated plate 46. That is, the edge portion of the
perforated plate 46 has a few thru-holes so that a small amount of
air is introduced into the edge portion of the perforated plate 46.
Therefore, the membrane 52 is greatly expanded at the center
portion rather than the edge portion thereof. In addition, the edge
portion of the membrane 52 that is expanded is inclined toward the
center portion so that the edge portion of the membrane 52 does not
make contact with the wafer W. As a result, the pressure is not
applied to the edge portion of the wafer W.
[0054] According to an embodiment of the present invention, the
pressure compensating member 54 in the polishing head 32
compensates the air pressure at the edge of the membrane 52 so as
to make uniform the pressure applied to the wafer W in contact with
the membrane 52. The pressure compensating member 54 is provided
between the membrane 52 and the perforated plate 46. Preferably, an
upper surface of the pressure compensating member 54 is fixedly
adhered to the edge of the lower surface of the perforated plate 46
and the lower surface of the pressure compensating member 54 is
fixedly adhered to the edge of the inner surface of the membrane 52
that faces the edge of the lower surface of the perforated plate
46. The pressure compensating member 54 has the ring shape, the
upper surface and the lower surface of the pressure compensating
member 54 are respectively and continuously adhered to the edges of
the perforated plate 46 and the membrane 52.
[0055] In the cross-sectional view, an upper side and a lower side
of the pressure compensating member 54 are in parallel with each
other. Furthermore, an inner side of the pressure compensating
member 54 is inclined in a direction to the center of the membrane
46 and an outer side of the pressure compensating member 54 is
vertical to the upper side and the lower side of the pressure
compensating member 54.
[0056] The inner side of the compensating member 54 has a desired
gradient enough to compensate the space between the edge of the
wafer W and the membrane 52 when the membrane 52 is expanded due to
the air pressure. Preferably, the membrane 52 is inclined at a
predetermined angle from the edge to the center axis thereof while
being expanded by the pressure of the air supplied through the
thru-holes 46a of the perforated plate 46. Therefore, when the
membrane 52 is expanded, the pressure compensating member 54
functions as filling material between the wafer W and the membrane
52, depending on the gradient of the edge of the membrane 51 to
uniformly polish the center portion and the edge portion of the
wafer W during the polishing of the wafer W. Accordingly, the inner
side of the pressure compensating member 52 must have the gradient
enough to allow the membrane 52 to make close contact with the
wafer W. Further, the pressure compensating member 54 has a
thickness enough to compensate for any expansion due to air
pressure between the edge portion and the center portion of the
membrane 52.
[0057] According to an embodiment of the present invention, the
pressure compensating member 54 is also disposed under the membrane
52 and an edge of the membrane 52, and is inclined in a direction
to a center of the membrane 52.
[0058] According to an embodiment of the present invention, the
pressure compensating member 54 is preferably comprised of
resilient material such as a rubber and a silicon resin, of which
the edge portion is resiliently bent by the air pressure.
[0059] When the membrane 52 is expanded and presses the wafer W,
the pressure compensating member 54 pushes the edge portion of the
membrane 52 to remove the space between the edge portions of the
membrane 52 and the wafer W. Therefore, the pressure that is
supplied for the edge portion and the center portion of the wafer W
can be uniform. Accordingly, the edge portion and the center
portion of the wafer W are uniformly polished and a polishing
profile of the wafer W is improved. Furthermore, since the process
failure caused at the edge portion of the wafer W is reduced, the
yield and the reliability of the semiconductor device is
improved.
[0060] Further, the pressure compensating member 54 uniformly
applied pressure to the edge portion and the center portion of the
wafer W while preventing the wafer from being dropped downwardly
when the wafer W is stuck to the membrane 52. Particularly, when
the polishing of the wafer W is finished or temporarily stopped,
the wafer W is stuck to the membrane 52 as the air is exhausted
through the first tube 42a from the space between the dividing
plate 48 and the perforated plate 46. When the wafer W is stuck to
the membrane 52, the wafer W is somewhat bent in a state that the
center portion of the wafer W is concaved downwardly as the
pressure compensating member 54 is disposed at the edge of the
membrane 52. When the wafer W is stuck to the membrane 52 in the
state of being bent, the membrane 52 is sucked into the thru-holes
46a of the perforated plate 46 while the wafer W maintains a close
contact with the membrane 52. As a result, the vacuum pressure
increases in the space between the membrane 52 and the wafer W so
as to prevent the wafer W from being dropped downwardly.
[0061] Although preferred embodiments of the present invention have
been described, it is understood that the present invention should
not be limited to these preferred embodiments but various changes
and modifications can be made by one skilled in the art within the
spirit and scope of the present invention as hereinafter
claimed.
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