Information
-
Patent Grant
-
6277008
-
Patent Number
6,277,008
-
Date Filed
Monday, April 12, 199925 years ago
-
Date Issued
Tuesday, August 21, 200122 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Hail, III; Joseph J.
- Nguyen; G
Agents
- Hutchins, Wheeler & Dittmar
-
CPC
-
US Classifications
Field of Search
-
International Classifications
-
Abstract
A polishing apparatus includes a polishing pad, a substrate holder, and a retainer ring. The polishing pad is adhered to a polishing table. The substrate holder urges, while it holds a substrate as a polishing target, a polishing target surface of the substrate against the polishing pad. The retainer ring is formed on a holding surface of the substrate holder to correspond to the circumference of the substrate. The retainer ring has a resin portion formed on its surface which is to come into contact with the polishing pad, and an annular resin holding portion for holding the resin portion and made of a material having a higher mechanical strength than the resin portion.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a polishing apparatus used in, e.g., chemical-mechanical polishing (CMP).
A technique for planarizing a substrate surface by polishing has been employed in many fields including the semiconductor substrate fabrication process. In recent years, CMP for planarizing the unevenness of a surface, e.g., the unevenness of the surface of an interlevel insulating film, formed during the fabrication by polishing is used in a process of fabricating devices on a semiconductor substrate.
In CMP, hard polishing cloth made of a material such as foamed polyurethane, different from relatively soft polishing cloth comprised of unwoven fabric used for polishing the surface of the semiconductor substrate, is used to planarize the insulating film. To obtain the polishing uniformity within the substrate surface, an elastic cushion layer is generally formed under a hard pad.
FIGS. 4A and 4B
show the arrangement of a conventional polishing apparatus.
As shown in
FIG. 4A
, the conventional polishing apparatus is constituted by a substrate holder
409
for holding a polishing target, a polishing table
410
to which a polishing pad
402
is adhered, an abrasive supply member
411
, and a conditioning mechanism
413
on which a diamond pellet
412
is mounted. Mechanisms provided to the substrate holder
409
and conditioning mechanism
413
to rotate, swing, and press them, and a rotational mechanism provided to the polishing table
410
are not illustrated.
As shown in
FIG. 4B
, a retainer ring
401
is set on a surface of the substrate holder
409
which opposes a substrate
405
, to correspond to the circumference of the substrate
405
. The retainer ring
401
holds the substrate
405
and prevents lateral shift of the substrate
405
. As the material of the retainer ring
401
, a hard plastic such as polyethylene terephthalate is used. An air cushion
407
applies a downward load to the retainer ring
401
. An elastic layer called an insert pad
403
is formed on the surface of the substrate holder
409
inside the retainer ring
401
.
By using the polishing arrangement having the above arrangement, for example, the surface of an interlevel insulating layer in the multilevel interconnection structure of an LSI is planarized.
During polishing, the retainer ring
401
prevents not only lateral shift of the substrate
405
but also abnormal polishing of the outer peripheral portion of the substrate
405
. More specifically, during polishing, the substrate
405
is urged against the polishing table
410
by the polishing pad
402
consisting of an upper hard layer and a lower soft layer. The contact pressure is the maximum at the outer peripheral portion of the substrate
405
.
At this time, as shown in
FIG. 5A
, the polishing pad
402
is deformed by the pressing force of the substrate
405
for several mm from the outer peripheral portion of the substrate
405
, and the pressure acting on the outer peripheral portion of the substrate
405
decreases. As a result, the polishing amount on the outer peripheral portion of the substrate
405
decreases. In particular, depending on the modulus of elasticity of the insert pad
403
and other polishing conditions, a deformation region
501
of the polishing pad
402
sometimes extends for several cm from the outer peripheral portion of the substrate
405
.
In the conventional polishing apparatus, abnormal polishing is suppressed in the following manner. First, the surfaces of the retainer ring
401
and substrate
405
that are to come into contact with the polishing pad
402
are set to be flush. The width of the retainer ring
401
with which the retainer ring
401
is to come into contact with the polishing pad
402
is set to be equal to or more than the deformation region described above of the polishing pad
402
. This suppresses a deformation region
502
from extending over the outer peripheral portion of the substrate
405
, as shown in FIG.
5
B.
A load is applied to the retainer ring
401
by the air cushion
407
independently of applying a load to the substrate
405
. This makes the pressure that presses the retainer ring
401
against the polishing pad
402
independent and constant. For example, the retainer ring
401
is brought into contact with the polishing pad
402
with a load of about 500 g/cm
2
(≈7 psi).
For this reason, during polishing, the retainer ring
401
is also polished by the polishing pad
402
, and the material of the retainer ring
401
generated by grinding spreads over the polishing pad
402
as impurities. In this case, if an alloy material such as stainless steel is used to form the retainer ring
401
, the metal component generated by grinding spreads over the polishing pad
402
to adversely affect the characteristics of devices formed on the substrate
405
. Also, the cutting chips of the alloy material damage the polishing surface of the polishing pad
402
. To solve these problems, a plastic is used as the material of the conventional retainer ring
401
.
As the process amount increases, the plastic retainer ring
401
deforms, and the specified performance is not maintained.
In this case, even if a hard plastic is used to suppress deformation, its mechanical strength is limited and inferior to that of a metal alloy material such as stainless steel. Even a conventional retainer ring using a hard plastic deforms when the number of polishing processes increases, and the capability of the retainer to press the polishing pad degrades. As a result, in the conventional polishing apparatus, when the number of polishing processes increases, an abnormality in polishing amount occurs on the outer peripheral portion of the substrate as a polishing target.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a polishing apparatus in which, even if the number of polishing processes increases, occurrence of an abnormality in polishing amount on the outer peripheral portion of the substrate as a polishing target is suppressed.
In order to achieve the above object, according to the present invention, there is provided a polishing apparatus comprising a polishing pad adhered to a polishing table, a substrate holder for urging, while holding a substrate as a polishing target, a polishing target surface of the substrate against the polishing pad, and a retainer ring formed on a holding surface of the substrate holder to correspond to a circumference of the substrate, the retainer ring having a resin portion formed on a surface thereof which is to come into contact with the polishing pad, and an annular resin holding portion for holding the resin portion and made of a material having a higher mechanical strength than the resin portion.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A
is a front view of a polishing apparatus according to an embodiment of the present invention, and
FIG. 1B
is a sectional view of the main part of the substrate holder shown in
FIG. 1A
;
FIG. 2
is a graph showing the polishing characteristics;
FIGS. 3A and 3B
are views each showing deformation of the retainer ring shown in
FIG. 1B
;
FIG. 4A
is a front view of a conventional polishing apparatus, and
FIG. 4B
is a sectional view of the main part of the substrate holder shown in
FIG. 4A
; and
FIGS. 5A and 5B
are views each showing deformation of the polishing pad.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will be described in detail with reference to the accompanying drawings.
FIG. 1
schematically shows a polishing apparatus according to an embodiment of the present invention. As shown in
FIG. 1A
, the polishing apparatus according to this embodiment is constituted by a substrate holder
109
for holding a substrate as a polishing target, a polishing table
110
to which a polishing pad
102
is adhered, an abrasive supply member
111
, and a conditioning mechanism
113
on which a diamond pellet
112
is mounted.
The polishing pad
102
has a two-layered structure constituted by an upper hard layer and a lower soft layer. Mechanisms provided to the substrate holder
109
and conditioning mechanism
113
to rotate, swing, and press them, and a rotational mechanism provided to the polishing table
110
are not illustrated.
As shown in
FIG. 1B
, a retainer ring
101
is set on a surface (holding surface) of the substrate holder
109
which opposes a substrate
105
, to correspond to the circumference of the substrate
105
. The retainer ring
101
holds the substrate
105
and prevents lateral shift of the substrate
105
. An air cushion
107
biases the retainer ring
101
toward the polishing table
110
. An elastic layer called an insert pad
103
is formed on the surface of the substrate holder
109
inside the retainer ring
101
.
To perform polishing, the polishing target surface of the substrate
105
is pressed against the polishing pad
102
through the insert pad
103
. For example, part of the multilevel interconnection structure of an LSI is formed on the polishing target surface of the substrate
105
, and an interlevel insulating film is formed on the uppermost layer of the multilevel interconnection structure. An unevenness formed by a lower wiring layer or the like is present on the surface of the interlevel insulating film. The polishing apparatus of this embodiment planarizes this unevenness by cutting and polishing in accordance with CMP.
As shown in
FIG. 1B
, the retainer ring
101
is constituted by a lower resin portion
101
a
made of a hard plastic such as polyethylene terephthalate, and an upper metal portion
101
b
made of, e.g., SUS
316
(stainless steel). The metal portion
101
b
serving as a resin holding portion, and the resin portion
101
a
are firmly bonded to each other with an adhesive. A surface of the resin portion
101
a
of the retainer ring
101
which is to come into contact with the polishing pad
102
is set to be flush with that of the polishing target surface of the substrate
105
.
The retainer ring
101
is biased by using the air cushion
107
independently of controlling a load to the substrate
105
. This makes the pressure that presses the retainer ring
101
against the polishing pad
102
independent and constant. For example, the retainer ring
101
is brought into contact with the polishing pad
102
with a biasing force (pressure) of about 500 g/cm
2
(≈7 psi).
According to this embodiment, the retainer ring
101
has a two-layered structure constituted by the resin portion
101
a
and metal portion
101
b
. As a result, compared to a conventional case wherein the whole retainer ring is formed of a hard plastic, the mechanical strength of the retainer ring
101
increases considerably.
Of the retainer ring
101
, only its resin portion
101
a
comes into contact with the polishing pad
102
, and its metal portion
101
b
does not. Therefore, no metal component will spread over the polishing pad
102
to adversely affect the characteristics of devices formed on the substrate
105
. Also, the polishing surface of the polishing table will not be damaged by the cutting chips of the metal material.
A practical example of polishing apparatus of this embodiment will be described.
In the polishing apparatus using the retainer ring
101
, an 8-inch diameter silicon substrate formed with an oxide film on its surface was employed as a sample. The oxide film was removed by CMP. The thickness of the oxide film to be removed by polishing was set to about 650 nm. Under these conditions, 25 substrates were polished. When the 26th substrate was polished, a region where the polishing film thickness was smaller by about 20 nm to 30 nm was formed at a region of about 3 mm from the outer peripheral portion of the silicon substrate, as indicated by a curve (a) of FIG.
2
.
In contrast to this, the same process was performed by using the conventional retainer ring
401
(
FIG. 4B
) formed of only a hard plastic. As a result, a region where the polishing film thickness was small was formed at a region of about 5 mm or more from the outer peripheral portion of the silicon substrate, as indicated by a curve (b) of FIG.
2
.
In this manner, when the retainer ring
101
of this embodiment is used, even if the polishing process amount increases, abnormal polishing occurring on the outer peripheral portion of the substrate as the polishing target can be suppressed.
In the embodiment, the resin portion
101
a
and metal portion
101
b
of the retainer ring
101
have almost the same shape. However, the present invention is not limited to this. For example, as shown in
FIG. 3A
, a stepped resin portion
301
a
may be formed, and the shapes of the resin portion
301
a
and a metal portion
301
b
may be different from each other. When a retainer ring
301
is formed in this manner, its mechanical strength and its contact area with the polishing pad
102
of the polishing table
110
can be designed freely.
As shown in
FIG. 3B
, a retainer ring
311
may be formed such that its resin portion
311
a
covers its annular metal portion
311
b
. When the retainer ring
311
is formed in this manner, the resin portion
311
a
and metal portion
311
b
need not be brought into tight contact with each other through an adhesive or the like. As a result, even when the resin portion
311
a
cannot be adhered to the metal portion
311
b
depending on combinations of the materials, the retainer ring
311
can be fabricated.
In the above embodiment, stainless steel is used to form the metal portion, and polyethylene terephthalate is used to form the resin portion. However, the present invention is not limited to this, but the following engineering plastics may be used instead. More specifically, examples are polycarbonate, polyamide, polybutylene terephthalate, polysulfone, polyether sulfone, polyether ether ketone, polyamide imide, polyether imide, a chlorotrifluoroethylene-ethylene copolymer, and the like.
The material of the metal portion is not limited to stainless steel, but a metal having a resistance to corrosion and a high mechanical strength, or its alloy may be used.
As has been described above, according to the present invention, since a resin is used to form only a surface of the retainer ring which is to come into contact with the polishing pad, a higher mechanical strength than that obtained when the entire retainer ring is made of only a resin can be obtained. As a result, even when the number of polishing processes increases, the retainer ring does not substantially deform, and occurrence of an abnormality in polishing amount on the outer peripheral portion of the substrate as the polishing target can be suppressed.
Claims
- 1. A polishing apparatus comprising:a polishing pad adhered to a polishing table; a substrate holder for holding a substrate as a polishing target, while urging a polishing target surface of the substrate against said polishing pad; and a retainer ring formed on a holding surface of said substrate holder to correspond to a circumference of the substrate, said retainer ring having a resin portion formed on a surface thereof which is to come into contact with said polishing pad, and an annular holding portion for holding said resin portion and made of a material having a higher mechanical strength than said resin, wherein said retainer ring resin holding portion is encapsulated with said resin portion.
- 2. A polishing apparatus comprising:a polishing pad adhered to a polishing table; a substrate holder for holding a substrate as a polishing target, while urging a polishing target surface of the substrate against said polishing pad; and a retainer ring formed on a holding surface of said substrate holder to correspond to a circumference of the substrate, said retainer ring having a stepped resin portion formed on a surface thereof, a smaller diameter upper portion of said stepped resin portion disposed to come into contact with said polishing pad, and an annular holding portion for holding said resin portion and made of steel.
Priority Claims (1)
Number |
Date |
Country |
Kind |
10-099231 |
Apr 1998 |
JP |
|
US Referenced Citations (4)
Foreign Referenced Citations (5)
Number |
Date |
Country |
1352932 |
May 1974 |
GB |
7-227757 |
Aug 1995 |
JP |
9-139366 |
May 1997 |
JP |
9-155730 |
Jun 1997 |
JP |
10-0267597 |
Jul 2000 |
JP |