U.S. patent application number 10/899178 was filed with the patent office on 2005-02-03 for chemical mechanical polishing apparatus.
Invention is credited to Kim, Kyung-Hyun, Ko, Yong-Sun, Min, Chung-Ki.
Application Number | 20050022931 10/899178 |
Document ID | / |
Family ID | 34101737 |
Filed Date | 2005-02-03 |
United States Patent
Application |
20050022931 |
Kind Code |
A1 |
Min, Chung-Ki ; et
al. |
February 3, 2005 |
Chemical mechanical polishing apparatus
Abstract
The chemical mechanical polishing (CMP) apparatus includes an
insert pad that forms a local step on an upper surface of a
polishing pad assembly. The insert pad is interposed between a
rotatable platen and the polishing pad assembly.
Inventors: |
Min, Chung-Ki; (Suwon-si,
KR) ; Ko, Yong-Sun; (Suwon-si, KR) ; Kim,
Kyung-Hyun; (Seoul, KR) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 8910
RESTON
VA
20195
US
|
Family ID: |
34101737 |
Appl. No.: |
10/899178 |
Filed: |
July 27, 2004 |
Current U.S.
Class: |
156/345.12 |
Current CPC
Class: |
B24B 37/26 20130101;
B24B 37/22 20130101 |
Class at
Publication: |
156/345.12 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 28, 2003 |
KR |
2003-52091 |
Claims
What is claimed is:
1. A chemical mechanical polishing (CMP) apparatus comprising: a
rotatable platen; a polishing pad assembly disposed on the platen;
and an insert pad structure disposed between the platen and the
polishing pad assembly.
2. The apparatus of claim 1, wherein the polishing pad assembly is
a composite polishing pad formed of a soft polishing pad and a hard
polishing pad.
3. The apparatus of claim 1, wherein the insert pad structure is
0.5.about.300 mm thick.
4. The apparatus of claim 1, wherein the insert pad structure is
formed of plastic, ceramic, or metal.
5. The apparatus of claim 1, wherein the insert pad is adhered to
an upper surface of the platen by an adhesive.
6. The apparatus of claim 1, wherein the platen includes an upper
surface with an annular-shaped polishing area that corresponds to a
location where a wafer faces the polishing pad assembly during a
CMP process; the polishing area includes a central polishing area,
which is located under the polishing pad assembly and faces a
central portion of the wafer, and outer polishing areas, which are
located under the polishing pad assembly and face an outer portion
of the wafer.
7. The apparatus of claim 6, wherein the insert pad structure
includes an insert pad covering only the central polishing
area.
8. The apparatus of claim 7, wherein the insert pad is formed of an
annular-shaped film having inner and outer edges.
9. The apparatus of claim 8, wherein the insert pad has vertical
sidewalls at the inner and outer edges.
10. The apparatus of claim 9, wherein the insert pad is 0.5.about.2
mm thick.
11. The apparatus of claim 8, wherein the insert pad has sloped
sidewalls at the inner and outer edges.
12. The apparatus of claim 11, wherein the insert pad is
2.about.300 mm thick.
13. The apparatus of claim 6, wherein the insert pad structure
covers only the outer polishing areas.
14. The apparatus of claim 13, wherein the insert pad structure
comprises: a first insert pad that covers a central portion of the
upper surface of the platen and a second insert pad that covers an
outer portion of the upper surface of the platen.
15. The apparatus of claim 14, wherein the first insert pad is
formed of a circular or annular-shaped film.
16. The apparatus of claim 14, wherein the second insert pad is
formed of an annular-shaped film.
17. The apparatus of claim 14, wherein the first and second insert
pads are separated from each other at a distance corresponding to
the central polishing area.
18. The apparatus of claim 14, wherein the first and second insert
pads have a vertical sidewall at each edge thereof.
19. The apparatus of claim 18, wherein the insert pad is
0.5.about.2 mm thick.
20. The apparatus of claim 14, wherein the first and second insert
pads insert pads have at least one sloped sidewall at an edge
thereof.
21. The apparatus of claim 12, wherein the insert pad is
2.about.300 mm thick.
22. A chemical mechanical polishing apparatus, comprising: a
rotatable platen; and a polishing pad structure having a non-planar
surface disposed on the platen.
23. The apparatus of claim 22, wherein the polishing pad structure
has at least one thick portion and at least one thin portion, the
thick portion having a greater thickness than the thin portion.
24. The apparatus of claim 22, wherein the thick portion is over an
area of the platen corresponding to central portion of a wafer to
be polished.
25. The apparatus of claim 24, wherein the thin portions are over
an area of the platen corresponding to outer portions of the wafer
to be polished.
26. The apparatus of claim 23, wherein the thick portions are over
an area of the platen corresponding to output portions of a wafer
to be polished.
27. The apparatus of claim 26, wherein the thin portion is over an
area of the platen corresponding to a central portion of the wafer
to be polished.
28. The apparatus of claim 22, wherein the polishing pad structure
comprises: a polishing pad assembly; and an insert pad structure
disposed between the polishing pad assembly and the platen.
Description
BACKGROUND OF THE INVENTION
[0001] This application claims the priority of Korean Patent
Application No. 2003-52091, filed on Jul. 28, 2003, in the Korean
Intellectual Property Office, the disclosure of which is
incorporated herein in its entirety by reference.
[0002] 1. Field of the Invention
[0003] The present invention relates to a polishing apparatus for
polishing a wafer to form a semiconductor device, and more
particularly, to a chemical mechanical polishing (CMP)
apparatus.
[0004] 2. Description of the Related Art
[0005] In a semiconductor manufacturing process using chemical
mechanical polishing (CMP) technology, a wafer is polished by
rotating a wafer and rotating a polishing pad against one another
while a slurry is supplied. It is very difficult to uniformly
polish an area on a wafer and to planarize a die to a desired level
in a CMP process. A difference in uniformity occurs because of
different polishing rates applied to different portions of the
wafer. A polishing rate of the CMP process is a speed at which
polishing target material is removed from the wafer. Accordingly,
if the distribution of polishing rates is poor (i.e., not uniform),
then planarizing of the wafer is poor. As the degree of integration
of semiconductor devices increases, less and less deviations in the
distribution of polishing rates can be tolerated.
[0006] Therefore, it is required to exactly and flexibly control
the polishing rate. The planarity of the wafer is influenced by a
structure of a CMP apparatus, the slurry used, and an attritional
material, such as, a polishing pad used.
[0007] In particular, a polishing pad, which is generally used in
the CMP process, requires a proper balance between strength and
flexibility. Strength is necessary for obtaining uniformity in a
die, but sufficient flexibility is essential for obtaining
uniformity over the entire target on the wafer. Although a soft
polishing pad, which is now used commercially, is advantageously
elastically transformable and obtains a uniform polishing rate
regardless of whether a step exists on a wafer, it is difficult to
remove the step. On the other hand, a hard polishing pad can
guarantee excellent planarity regardless of steps on the wafer, but
it is difficult to remove a polishing target membrane with a
uniform polishing rate over the entire surface of the wafer.
Therefore, a composite polishing pad, in which soft and hard
polishing pads are sequentially deposited on a platen, is widely
used in order to obtain polishing characteristics of both the soft
and hard polishing pads together.
[0008] However, even if the composite polishing pad including
sequentially deposited soft and hard polishing pads is used, it is
extremely difficult to exactly and flexibly control the polishing
rate since the polishing rate.
[0009] In fact, the distribution of the polishing rate of the CMP
process is largely influenced by a structure of a polishing head,
chemical characteristics of a slurry, operating conditions of the
CMP apparatus, and characteristics of a polishing target membrane.
When an oxide layer is polished using a common silica slurry and a
CMP apparatus with a fixed retainer ring, that is, when a
mechanical element has a large influence on the polishing rate, the
polishing rate at an outer portion of the wafer is greater than a
central portion of a wafer. Accordingly, a poor distribution of the
polishing rate occurs. Yet, if a chemical element has a large
influence on the polishing rate, for example, a poly slurry or a
ceria slurry with a high selectivity is used, the polishing rate in
the central portion of the wafer is greater than the outer portion
of the wafer, and thus, a poor distribution of the polishing rate
occurs. As a consequence, a poor distribution of the polishing rate
on the wafer is very difficult to overcome by only adjusting
operating conditions of the CMP apparatus.
SUMMARY OF THE INVENTION
[0010] The present invention provides a chemical mechanical
polishing apparatus having a rotatable platen and a polishing pad
structure disposed on the rotatable platen. The polishing pad
structure has portions with different thickness. As such differing
amounts of stress will be applied to a wafer being polished such
that a more uniform distribution of polishing rates may be
achieved.
[0011] In one exemplary embodiment, the polishing pad structure
includes a polishing pad assembly and an insert pad structure
disposed between the polishing pad assembly and the platen.
[0012] In one embodiment, the insert pad structure includes an
insert pad disposed on an area of the platen corresponding to a
central area of the wafer to be polished. Here, the polishing pad
structure has a thick portion corresponding to the central area of
the wafer to be polished and thin portions corresponding to outer
areas of the wafer to be polished.
[0013] In another embodiment, the insert pad structure includes
insert pads disposed on areas of the platen corresponding to the
outer areas of the wafer to be polished. Here, the polishing pad
structure has thick portions corresponding to the outer areas of
the wafer to be polished and a thin portion corresponding to a
central area of the wafer to be polished.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The above and other features and advantages of the present
invention will become more apparent by describing in detail
exemplary embodiments thereof with reference to the attached
drawings in which:
[0015] FIG. 1 is a view of a polishing station and a polishing head
of a chemical mechanical polishing (CMP) apparatus according to an
embodiment of the present invention;
[0016] FIG. 2 is a top view of a platen included in the CMP
apparatus of FIG. 1;
[0017] FIG. 3 is an exploded perspective view of the CMP apparatus
of FIG. 1;
[0018] FIG. 4 is a plane view of an embodiment of an insert pad for
the CMP apparatus of FIG. 1;
[0019] FIG. 5 is a cross-sectional view of a wafer and the
polishing station of the CMP apparatus of FIG. 4;
[0020] FIG. 6A is a top view of another embodiment of an insert pad
installed in the CMP apparatus of FIG. 1;
[0021] FIG. 6B is a magnified cross-sectional view taken along the
line VIb-VIb' in FIG. 6A;
[0022] FIG. 7 is an exploded perspective view of main elements of a
CMP apparatus according to another embodiment of the present
invention;
[0023] FIG. 8 is a plane view of an insert pad of FIG. 7; and
[0024] FIG. 9 is a cross-sectional view of a wafer and a polishing
station of the CMP apparatus of FIG. 7.
DETAILED DESCRIPTION OF THE INVENTION
[0025] The present invention will now be described more fully with
reference to the attached drawings, in which exemplary embodiments
of the invention are shown. This invention may, however, be
embodied in many different forms and should not be construed as
being limited to the embodiments set forth herein; rather these
embodiments are provided so that this disclosure will be thorough
and complete, and will fully convey the concept of the invention to
those skilled in the art. In the drawings, the forms of elements
are exaggerated for clarity. To facilitate understanding, identical
reference numerals are used, where possible, to identify identical
elements throughout the figures.
[0026] FIG. 1 is a view of a polishing station 10 and a polishing
head 50 of a chemical mechanical polishing (CMP) apparatus
according to a first embodiment of the present invention.
[0027] Referring to FIG. 1, the polishing station 10 comprises a
platen 12, which is disk-shaped and can rotate, and a polishing pad
assembly 20, which is disposed on an upper surface of the platen
12. Any conventional polishing pad assembly may be used as the
polishing pad assembly 20. For example, the polishing pad assembly
20 may be a composite polishing pad which is formed of soft and
hard polishing pads.
[0028] The platen 12 is connected to a driver 15, such as a motor.
The platen 12 receives torque from the driver 15 during a CMP
process and rotates about a central axis X in a direction A. The
platen 12 may rotate in the direction A or in the opposite
direction.
[0029] An insert pad 30 is interposed between the platen 12 and the
polishing pad assembly 20 in order to form a local step in the
polishing pad assembly 20 to a thickness of 0.5.about.300 mm and is
formed of a film, which is made of a strong and hard material that
has no elasticity and flexibility. For instance, the insert pad 30
may be formed of hard plastic, such as an acryl resin, a
polyolefine series resin, a polybutyleneterephthalate (PBT) resin,
a polystyrene series resin, or a polycarbonate. Furthermore, the
insert pad 30 may be formed of ceramic or metal and is adhered to
the upper surface of the platen 12 by a bonding means, such as an
adhesive.
[0030] As illustrated in FIG. 1, the step formed by the insert pad
30 has a convex shape in a portion of the polishing pad assembly 20
that corresponds to a central portion of the wafer W. The structure
of the insert pad 30 will be explained in detail later. Together,
the insert pad 30 and the polishing pad assembly 20 form a
polishing pad structure.
[0031] As further shown in FIG. 1, a polishing head 50, which may
be formed of one or more components, is mounted above the polishing
station 10. The polishing head 50 comprises a vacuum device in
order to chuck or hold the wafer W in a stable state when a
polishing target on the wafer W faces the upper surface of the
polishing pad assembly 20.
[0032] In order to carry out the CMP process, the polishing head 50
applies pressure to the polishing pad assembly 20 and polishes the
polishing target on the wafer W when the wafer W is chucked. At
this time, the polishing head 50 and the wafer W rotate in the
direction of arrow B with a speed set by a polishing head
displacement device 52. However, the polishing head 50 and the
wafer W may rotate in the opposite direction to the direction
B.
[0033] A polishing slurry with a desirable composition is supplied
by a slurry supplying system 60 during the CMP process. Because the
insert pad 30 forms a step in the polishing pad assembly 20, a
relatively large pressure is applied to the central portion, as
compared to an outer portion, of the wafer W by the polishing pad
assembly 20 during a polishing process.
[0034] FIG. 2 is a top view of the platen 12, which is installed in
the CMP apparatus according to the first embodiment of the present
invention.
[0035] Referring to FIG. 2, the platen 12 rotates in the direction
A and the wafer W rotates in the same direction as the polishing
head 50, that is, in the direction B. An upper surface 12a of the
platen 12 has a polishing area 14, which is the area below the
wafer W when the polishing pad assembly 20 rotates during the CMP
process. The polishing area 14 has an annular shape with a first
width Wp in a radial direction. The polishing area 14 is divided
into a central polishing area 14a, which is located under the
polishing pad assembly 20 and faces a central portion of the wafer
W, and outer polishing areas 14b, which are located under the
polishing pad assembly 20 and faces an outer portion of the wafer
W. The central polishing area 14a has an annular or donut shape,
and the outer polishing areas 14b extend a radial distance
respectively from inner and outer circumferences of the central
polishing area 14a. A width or scope of the central and outer
polishing areas 14a and 14b may be adjusted according to a diameter
of the wafer W used in the CMP process.
[0036] FIG. 3 is an exploded perspective view of the CMP apparatus
according to the first embodiment of the present invention. FIG. 4
is a plane view of the insert pad 30 of the CMP apparatus.
[0037] Referring to FIGS. 3 and 4, the insert pad 30 is interposed
between the platen 12 and the polishing pad assembly 20 and covers
the central polishing area 14a of the upper surface 12a of the
platen 12. Therefore, the insert pad 30 has an annular shape almost
equal in size with the central polishing area 14a.
[0038] In FIG. 3, the polishing pad assembly 20 is a composite
polishing pad formed of a soft polishing pad 22 and a hard
polishing pad 24; however, any conventional polishing pads may be
used as the polishing pad assembly 20. In one embodiment, a groove
(not shown) is formed on an upper surface of the hard polishing pad
24, that faces the wafer W. With this structure, the slurry flows
into the groove in the CMP process, and thus, polishing efficiency
is enhanced.
[0039] In order to obtain the structure of the polishing station 10
in FIG. 3, the insert pad 30 is adhered to the platen 12, and the
soft polishing pad 22 and the hard polishing pad 24 are
sequentially deposited on the insert pad 30.
[0040] FIG. 5 is a cross-sectional view of the wafer W disposed on
the polishing station 10 of the CMP apparatus of FIG. 3. As shown,
since the insert pad 30 is interposed between the platen 12 and the
polishing pad assembly 20 and covers only the upper surface 12a of
the platen 12 in the central polishing area 14a, a step is formed
with a convex shape in the portion of the polishing pad assembly 20
that corresponds to the central portion of the wafer W. As will be
appreciated, the insert pad 30 causes the polishing pad structure
to have a thicker portion corresponding to the central portion of
the wafer W and thinner portions corresponding to outer portions of
wafer W. Stress is concentrated at this protruded portion more than
the other portions of the polishing pad assembly 20, and a
relatively large pressure is applied to the central portion of the
wafer W. Accordingly, the central portion of the wafer W is
polished at a higher rate.
[0041] Also, the insert pad 30 has a rectangular cross-section and
vertical sidewalls at the inner and outer radii of the insert pad
30. As shown, these sidewalls are exposed--not covered by the
polishing pad assembly 20. This structure of the insert pad is
particularly suitable when the desired step size is small. For
example, the insert pad 30 may have a thickness of less than 2
mm.
[0042] FIGS. 6A and 6B illustrate an example of an insert pad
installed in the CMP apparatus according to another embodiment of
the present invention. Specifically, FIG. 6A is a plane view of an
insert pad 40 and FIG. 6B is a magnified cross-sectional view taken
along the line VIb-VIb' of FIG. 6A.
[0043] Referring to FIGS. 6A and 6B, the insert pad 40 includes
inner and outer circumferential portions which have a slope. This
structure of the insert pad is suitable when a relatively large
step in the polishing pad assembly 20 is desired. For example, in
this embodiment, the insert pad 40 may have a thickness of
2.about.300 mm. If the insert pad 30, which has a rectangular shape
is too thick, the conformity of the polishing pad assembly 20 to
the insert pad 30 may be poor, and thus, an adhesive property
between the polishing pad assembly 20 and the insert pad 30 may be
degraded. However, if the insert pad 40 has the trapezoid sectional
shape as illustrated in FIG. 6, an excellent adhesive property
between the insert pad 40 and the polishing pad assembly 20 can be
maintained, even if the thickness of the insert pad 40 is
increased.
[0044] When the CMP apparatus according to the embodiments of the
present invention is used, the insert pad 30 covers only the
central polishing area 14a in the polishing area 14 on the platen
12. Pressure, which is applied to the central portion of the wafer
W, is increased along with the polishing speed of the central
portion of the wafer W. Consequently, the distribution of the
polishing rate on the wafer W is improved.
[0045] FIG. 7 is an exploded perspective view of a CMP apparatus
according to another embodiment of the present invention. FIG. 8 is
a plane view of the insert pad 130 of FIG. 7.
[0046] Referring to FIGS. 7 and 8, the insert pad structure 130 is
interposed between the platen 12 and the polishing pad assembly 20
and covers the upper surface 12a of the platen 12 on the outer
polishing areas 14b of the platen 12 (see FIG. 2). For this
purpose, the insert pad structure 130 comprises a first insert pad
130a that covers a central or inner circular portion of the platen
12 and a second insert pad 130b that covers an outer
circumferential portion of the platen 12. The first insert pad 130a
is illustrated with a circular shape in FIGS. 7 and 8. However, the
first insert pad 130a may be formed to have an annular shape that
covers only a central portion of the outer polishing area 14b
disposed towards the center of the platen 12. The second insert pad
130b has an annular shape as illustrated. The first and second
insert pads 130a and 130b are separated by the width of the central
polishing area 14a. The composition and shape of the first and
second insert pads 130a and 130b are not restricted to the
aforementioned case and they may be formed to have any shape that
covers only the outer polishing areas 14b of the polishing area 14.
That is, the first and second insert pads 130a and 130b do not
cover the central polishing area 14a.
[0047] FIG. 9 is a cross-sectional view of the wafer W disposed on
the polishing station 10 of the CMP apparatus of FIG. 7 according
to an embodiment of the present invention. More specifically, FIG.
9 is a cross-sectional view taken along the line IX-IX' of FIG.
8.
[0048] Referring to FIG. 9, the insert pads 130a and 130b are
interposed between the platen 12 and the polishing pad assembly 20
and cover only the outer polishing areas 14b in the polishing area
14, and thus, a step is formed to have a convex shape in a portion
corresponding to the outer portion of the wafer W among a portion
of the polishing pad assembly facing the wafer W. As will be
appreciated, the insert pads 130a and 130b forming the insert pad
structure cause the polishing pad structure to have thicker
portions corresponding to the outer portions of the wafer W and a
thinner portion corresponding to a central portion of the wafer W.
As a result, stress is concentrated on a high step area of the
polishing pad assembly 20 and relatively large pressure is applied
to the outer portion of the wafer W. This causes the polishing
speed of the outer portion of the wafer W to increase.
[0049] In FIG. 9, the insert pads 130a and 130b are illustrated
with a rectangular sectional shape and vertical sidewalls of the
insert pads 130a and 130b near the inner and outer radii of the
central polishing area 14a are exposed. This composition is
suitable when the insert pads 130a and 130b are formed of a
relatively thin film. However, the respective outer portions of
insert pads 130a 130b may be formed to have the cross-sectional
shape of FIG. 6 that the sidewalls of the insert pads 130a and 130b
near the inner and outer radii of the central polishing area 14a
are sloped.
[0050] Where a chemical element, for example, slurry that provides
a high selectivity has a large influence on a polishing rate, a
poor distribution of a polishing rate occurs since the polishing
rate of the central portion of the wafer W is greater than the
polishing rate of the outer portion of the wafer W. However, when
the CMP apparatus according to the this embodiment of the present
invention is used, the insert pad 130 covers only the outer
polishing areas 14b in the polishing area 14 on the platen 12, and
pressure applied to the outer portion of the wafer W and the
polishing speed of the outer portion of the wafer W increase.
Consequently, the distribution of the polishing rate of the wafer W
is improved.
[0051] As described above, the CMP apparatus according to the
example embodiments of the present invention includes an insert pad
that is formed of a hard material and is interposed between the
platen and the polishing pad assembly. When a poor distribution of
the polishing rate would occur due to a higher polishing rate at
the outer portion of the wafer than the central portion of the
wafer, the inclusion of the insert pad that covers only the central
polishing area increases the polishing speed in the central portion
of the wafer thereby improving the polishing rate distribution.
Furthermore, when a poor distribution of the polishing rate would
occur due to a higher polishing rate at the central portion of the
wafer than at the outer portion of the wafer, the inclusion of the
insert pad that covers only the outer polishing areas increases the
polishing speed in the outer portion of the wafer, thereby
improving the polishing rate distribution.
[0052] The distribution of the polishing rate is improved due to a
step that is formed on the polishing pad assembly. The step created
by the insert pad causes an increase in the pressure applied to the
wafer by the polishing pad at appropriate locations, thereby
compensating for the uneven polishing rate.
[0053] While the present invention has been particularly shown and
described with reference to exemplary embodiments thereof, it will
be understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the present invention as defined by
the following claims. For example, while the polishing pad
structure has been shown as formed of the polishing pad assembly
and one or more insert pads, an integral structure may be used.
* * * * *