Information
-
Patent Grant
-
6676497
-
Patent Number
6,676,497
-
Date Filed
Friday, September 8, 200024 years ago
-
Date Issued
Tuesday, January 13, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 384 193
- 384 194
- 384 206
- 384 228
- 451 41
- 451 285
- 451 286
- 451 287
- 451 288
- 451 289
- 451 290
- 451 385
- 451 398
-
International Classifications
-
Abstract
A carrier head for chemical mechanical polishing, includes a base, a support structure attached to the base having a surface for contacting a substrate, and a retaining structure attached to the base to prevent the substrate from moving along the surface. The retaining structure and the surface define a cavity for receiving the substrate. The retaining structure includes an upper portion in contact with the base, a lower portion, and a vibration damper separating the upper portion and the lower portion. The vibration damper, the vibration damper includes a material that does not rebound to its original shape when subjected to a deformation.
Description
TECHNICAL FIELD
This invention relates generally to chemical mechanical polishing systems and processes.
BACKGROUND
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After a layer is deposited, a photoresist coating is applied on top of the layer. A photolithographic apparatus, which operates by focusing a light image on the coating, is used to remove predetermined portions of the coating, leaving the photoresist coating on areas where circuitry features are to be formed. The substrate is then etched to remove the uncoated portions of the layer, leaving the desired circuitry features.
As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, becomes increasingly non-planar. This non-planar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Specifically, the photolithographic apparatus may not be able to focus the light image on the photoresist layer if the maximum height difference between the peaks and valleys of the non-planar surface exceeds the depth of focus of the apparatus. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. Chemical mechanical polishing typically requires mechanically abrading the substrate in a slurry that contains a chemically reactive agent. During polishing, the substrate is typically held against a rotating polishing pad by a carrier head. The carrier head may also rotate and move the substrate relative to the polishing pad. As a result of the motion between the carrier head and the polishing pad, abrasives, which may either be embedded in the polishing pad or contained in the polishing slurry, planarize the non-planar substrate surface by abrading the surface.
The polishing process generates vibrations that may reduce the quality of the planarization or damage the polishing apparatus.
SUMMARY
In general, one aspect of the invention relates to a carrier head for chemical mechanical polishing. The carrier head has a base, a support structure attached to the base, and a retaining structure attached to the base. The support structure has a surface for contacting a substrate while the retaining structure prevents the substrate from moving along the surface. The retaining structure and the surface define a cavity for receiving the substrate. The retaining structure includes an upper portion in contact with the base, a lower portion, and a vibration damper separating the upper portion and the lower portion. The vibration damper includes a material that does not rebound to its original shape when subjected to a deformation.
In general, a second aspect of the invention relates to a chemical mechanical polishing apparatus that includes a polishing pad to polish a substrate and the carrier ahead described above.
Implementations of the first and second aspects of the invention may include one or more of the following features. The lower portion of the retaining structure may be thicker than the substrate to prevent the vibration damper and the upper portion from contacting the substrate. The lower portion of the retaining structure may define the walls of the cavity for receiving the substrate, and the vibration damper may reduce the transmission of vibration energy from the substrate through the lower portion to the upper portion. The lower portion may contact a polishing pad during polishing, while the vibration damper may reduce the transmission of vibration energy from the polishing pad through the lower portion to the upper portion. The retaining structure may be an annular wall around a periphery of the surface, and the vibration damper may be an annular ring separating the annular upper portion from the annular lower portion. The vibration damper may be mounted on the first portion and the second portion using a pressure sensitive adhesive. The lower portion may include a wearable member for contacting the polishing pad, and a support member may be mounted on the wearable member to add rigidity to the wearable member. The vibration damper may be mounted on the support member.
In general, a third aspect of the invention relates to a polishing station that includes a platen, a vibration damper mounted on the platen, and a substrate polishing pad mounted on the vibration damper. The vibration damper includes a material that does not rebound to its original shape when subjected to a deformation.
In general, a fourth aspect of the invention relates to a chemical mechanical polishing apparatus including the polishing station described above and a carrier head to press a substrate on the polishing pad when the substrate is being polished.
Implementations of the third and fourth aspect of the invention may include one or more of the following features. The vibration damper may be substantially disc shaped and may be mounted on the platen and the substrate polishing pad using a pressure sensitive adhesive. The polishing station may include a protective layer for mounting the polishing pad on the vibration damper. The protective layer may include a Teflon sheet, aluminum, or stainless steel, and the protective layer may be adhered to the vibration damper and the polishing pad using a pressure sensitive adhesive.
In general, a fifth aspect of the invention relates to a carrier head for positioning a substrate on a polishing surface. The carrier head includes a structure having a surface for contacting a substrate, a housing connectable to a drive shaft to rotate with the drive shaft about a rotation axis, and a gimbal mechanism between the structure and the housing to preventing the structure from moving out of the rotation axis. The gimbal mechanism prevents the structure from moving laterally while permitting the structure to gimbal relative to the housing. The gimbal has a top coupled to the housing, a bottom coupled to the structure, and a vibration damper separating the top from the bottom. The vibration damper includes a material that does not rebound to its original shape when subjected to a deformation.
In general, a sixth aspect of the invention relates to a chemical mechanical polishing apparatus that includes a polishing pad and the carrier head just described above.
Implementations of the fifth and sixth aspect of the invention may include one or more of the following features. The vibration damper may be mounted to the top and the bottom using a pressure sensitive adhesive. The housing may define a bushing, and the top may include a gimbal rod that extends into the bushing to couple the top to the housing, and a gimbal ring that is coupled to the gimbal rod. The bushing may allows the gimbal rod to move along the rotation axis while preventing the gimbal rod from moving out of the rotation axis. The vibration damper may be mounted on the gimbal ring using a pressure sensitive adhesive. The gimbal mechanism may include a substantially planar flexure ring that flexes in a direction perpendicular to the plane of the flexure ring to gimbal the structure to the housing. The damping material may be mounted on the flexure ring using a pressure sensitive adhesive.
Implementations of all the general aspects of the invention may include one or more of the following features. The damping material may rebound by less than ten percent of the deformation, preferably less than six percent of the deformation. The damping material may include a soft plastic or a visco-elastomer, such as an isodamp C-1000 series isolation damping material (e.g. C-1002 material).
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
DESCRIPTION OF DRAWINGS
FIG. 1
shows a polishing machine having three polishing stations and four carrier heads;
FIG. 2
is a cross-sectional view of a carrier head of
FIG. 1
, which includes a retaining ring;
FIG. 3A
is a more detailed cross-sectional view of the retaining ring of
FIG. 2
during polishing; and
FIG. 3B
is a cross-sectional view of the polishing station of FIG.
1
.
Like reference symbols in the various drawings indicate like elements.
DETAILED DESCRIPTION
Referring to
FIG. 1
, a chemical mechanical polishing (CMP) apparatus
1
embodying the invention will be described. The CMP apparatus
1
is used for polishing a substrate
10
. A more detailed description of a similar CMP apparatus may be found in U.S. Pat. No. 5,738,574, the entire disclosure of which is hereby incorporated by reference.
The CMP apparatus
1
includes a lower machine base
22
and a multi-head carousel
60
. The lower machine base
22
has three polishing stations
25
a
,
25
b
, and
25
c
on a tabletop
23
. Each polishing station
25
a
-
25
c
includes a circular polishing pad
32
, which is adhered to a circular platen
30
, of about the same diameter as the polishing pad
32
, using a pressure sensitive adhesive (PSA) (not shown). Platen
30
is a stainless steel plate connected by a stainless steel platen drive shaft (not shown) to a platen drive motor (also not shown), which is located inside machine base
22
. The polishing pad
32
is a fixed abrasive polishing pad, manufactured by 3M Superabrasives and Microfinishing Systems Division, St.Paul, Minn., Tel. (651) 737-1785. The fixed-abrasive polishing pad
32
contains abrasive particles, such as silica, embedded in a resin. The resin slowly disintegrates during use revealing new abrasive particles for polishing. Because the apparatus
1
is used for polishing “eight-inch” or “twelve-inch” substrates, the diameter of the polishing pad
32
and the platen
30
is between twenty and thirty inches.
A slurry arm
52
provides slurry to the polishing pad
32
through several spray nozzles (not shown). The slurry contains a reactive agent and a chemically reactive catalyzer. To polish an oxide substrate, deionized water is used as the reactive agent and potassium hydroxide is used as the catalyzer. The slurry arm
52
also provides fluid for rinsing the substrate.
The carousel
60
is positioned above the lower machine base
22
. Carousel
60
includes four carrier head systems
70
a
-
70
d
that are spaced at equal angular intervals about an axis
64
of symmetry of the carousel. Each carrier head system
70
a
-
70
d
has a circular carrier head
100
for holding a substrate
10
. The carrier head
100
is mounted on a drive shaft
74
, which extends through a slot
72
to connect the carrier head to a carrier head rotation motor
76
. The carrier head rotation motor
76
is supported on a slider (not shown).
During polishing, a pneumatic system (described below) lowers the carrier head
100
onto a polishing pad
32
to press the substrate
10
against the polishing pad
32
with a pre-determined loading force. The platen drive motor rotates the platen, thereby causing the polishing pad
32
to rotate. At the same time, the rotation motor
76
rotates the substrate
10
by rotating the carrier head
100
, while the slider (not shown) linearly drives the rotation motor
76
back and forth along the slot
72
to oscillate the carrier head
100
and the substrate
10
laterally on the surface of the polishing pad. Thus the apparatus moves the substrate
10
relative to the polishing pad
32
, thereby abrading the surface of the substrate against abrasives contained within the polishing pad. The slurry arm
52
provides slurry
50
, which contains a reactive agent (as previously described), to facilitate the polishing of the substrate. The loading and motion of the carrier head against the polishing pad, and the rotation speed of the polishing pad are carefully controlled to maintain a desired rate and quality of polishing.
We will describe three embodiments of the polishing apparatus
10
according to the invention. The embodiments use a vibration damping material at different locations to significantly reduce the transfer of vibrational energy from one part of the polishing apparatus adjacent to the damping material to another adjacent part of the polishing system and thereby reducing or preventing vibration during polishing. Generally, the damping material has significantly better vibration damping characteristics than both adjacent parts of the polishing apparatus, which are typically made from stiff materials, e.g., metals. The damping material is a visco-elastomer with little or no memory so as to provide good vibration damping characteristics, such as the commercially available, isolation damping material, C-1002, which is manufactured by E-A-R specialty composites of 7911 Zionesville Rd, Indianapolis, Ind. 46268.
Referring to
FIG. 2
, a first embodiment that has the vibration damping material in the carrier head
100
will be described. Carrier head
100
includes a housing
102
, a base
104
, a gimbal mechanism
106
, a retaining ring
110
, and a substrate backing assembly
112
. The housing
102
is substantially cylindrical and can be connected to a drive shaft
74
using a set of bolts (not shown). The drive shaft rotates the housing about an axis
107
. A passage
126
extends through the housing for pneumatic control of the carrier head, as will be described below. The housing
102
has a cylindrical bushing
122
fitted into a vertical bore
124
, which, runs vertically through the housing.
Gimbal mechanism
106
has a gimbal rod
150
, which is fitted into the bushing
122
so that the rod
150
is free to move vertically within the bore. The bushing
122
prevents lateral motion of the gimbal rod
150
. A gimbal ring
220
is attached to the gimbal rod
150
. A flexure ring
152
is attached to the gimbal ring
220
through a damping material
230
, to prevent or reduce the transmission of vibration energy from the flexure ring
152
to the housing
102
, through the gimbal ring
220
. The damping material
230
is 0.06 inches thick. Pressure sensitive adhesive (not shown) adheres the damping material
230
to both the housing
102
and the flexure ring
152
.
The flexure ring
152
, which is a generally planar annular ring, is attached to the generally ring-shaped base
104
. The flexure ring
152
flexes in a direction perpendicular to the plane of the flexure ring
152
, thereby gimballing the base
104
to the gimbal rod
150
and the housing
102
. The gimbal mechanism also allows the base
104
to move up and down by allowing the gimbal rod
150
to move vertically within the bore
122
, while preventing any lateral motion of the base. The damping material
230
reduces or prevents the transmission of vibrational energy from the base
104
into the housing
102
through the gimbal mechanism
106
.
An outer clamp ring
164
, which is bolted onto the base
104
by a bolt
194
, clamps a rolling diaphragm
160
to the base
104
. Rolling diaphragm
160
may be a generally ring shaped sixty mil thick silicone sheet. An inner clamp ring
162
, which is bolted onto the housing
102
by bolts
240
, clamps the rolling diaphragm
160
onto the housing. Thus, the rolling diaphragm
160
seals the loading chamber
108
formed by the housing
102
, the gimbal rod
106
, the gimbal ring
220
, the damping material
230
, the flexure ring
152
, and the base
104
, leaving an opening
126
into the chamber
108
. The opening
126
is connected to a pump (not shown), which lowers or raises the base by pumping fluid, e.g., air, into or out of the chamber
108
, respectively. By controlling the pressure of the fluid pumped into the loading chamber
108
, the pump can press down the base towards the polishing surface with a desired loading force. The opening
126
is coupled to the pump by a coupling (also not shown), which allows the housing
102
to rotate, without interrupting the connection between the opening
126
and the pump.
The retaining ring
110
is a generally annular ring bolted onto the base
104
by bolts
194
(only one is shown in the cross-sectional view of FIG.
2
). During polishing, fluid is pumped into the loading chamber
108
, thereby generating pressure in the chamber
108
. The generated pressure exerts a downward force on the base
104
, which in turn exerts a downward force on the retaining ring
110
. The downward force presses the retaining ring
110
against the polishing pad
32
.
Substrate backing assembly
112
includes a flexure diaphragm
116
, which is clamped between the retaining ring
110
and the base
104
. The flexure diaphragm
116
is a generally planar annular ring, which is flexible and elastic in a direction perpendicular to the plane of the diaphragm
116
. The flexure diaphragm
116
may be formed from rubber, such as neoprene, an elastomeric-coated fabric, such as NYLON™ or NOMEX™, plastic, or a composite material, such as fiberglass. An inner edge of the flexure diaphragm
116
is clamped between an annular lower clamp
172
and an annular upper clamp
174
of a support structure
114
. A support plate
170
of the support structure
114
is attached to the lower clamp
172
. The flexure diaphragm allows some vertical motion of the support plate
170
relative to the base
104
. The support plate
170
is a generally disk-shaped rigid member with a plurality of apertures
176
through it (only one is labeled in FIG.
2
). The support plate
170
has a downwardly projecting lip
178
at its outer edge.
A flexible membrane
118
extends around the lip
178
of the support plate
170
and is clamped between the support plate
170
and the lower clamp
172
, to form a generally disk shaped lower surface
120
. The flexible membrane is formed from a flexible and elastic material, such as chloroprene or ethylene propylene rubber. Alternatively, the flexure diaphragm and the flexible membrane can be combined in a single-piece membrane. The sealed volume between the flexible membrane
118
, support structure
114
, flexure diaphragm
116
, base
104
, and flexure ring
152
defines a chamber
190
whose only opening
250
runs through the gimbal rod
150
. A pump (not shown) is connected to the opening
250
to control the pressure in the chamber
190
by pumping fluid, into the chamber through the opening
250
, thereby controlling the downward pressure of the membrane lower surface
120
on the substrate
10
.
An inner surface
188
of the retaining ring
110
in conjunction with the lower surface
120
of the flexible membrane
188
define a cavity
192
for receiving a substrate. The retaining ring keeps the substrate from slipping laterally out of the cavity
192
, while the lower surface
120
of the flexible membrane
188
pushes the substrate, contained within the cavity
192
, against the polishing pad
32
(FIG.
1
).
A second embodiment of the invention includes the damping material in the retaining ring itself. Referring to
FIG. 3A
, the annular retaining ring
110
includes four portions, which are stacked one on top of another. The upper portion
203
of the retaining ring
110
is an annular steel ring with a thickness of about 0.1 inches, which is in contact with the base
104
. The upper portion
203
is attached to a middle portion
184
through a damping material
200
, which is similar in thickness and is made from the same material as the damping material
230
of FIG.
2
. The damping material
200
reduces or prevents the transmission of vibration energy from the middle portion
184
to the upper portion
203
. Pressure sensitive adhesive
202
adheres the damping material
200
to the upper portion
203
, while pressure sensitive adhesive
201
adheres the damping material
200
to the middle portion
184
.
The middle portion
184
is a quarter-inch thick stainless steel ring, which is adhered to a lower portion
180
by a layer of epoxy adhesive
186
, specifically, Magnobond-6375™, available from Magnolia Plastics of Chamblee, Ga. The middle portion
184
adds rigidity to lower portion
180
, thereby reducing the deformation of the retaining ring during polishing. The lower portion
180
is an annular ring formed from polyphenylene sulfide (PPS), available from DSM Engineering Plastics of Evansville, Ind., under the trade name Techtrom™. The lower portion
180
is durable but gradually wears away with use. Other plastics, such as DELRIN™, available from Dupont of Wilmington, Del., polyethylene terephthalate (PET), polyetheretherketone (PEEK), or a composite material such as XYMAXX™, also available from Dupont, may be used instead. The lower portion
180
has a bottom surface
182
, which contacts the polishing pad
32
during polishing. The bottom surface has substantially radial grooves (not shown) for transporting slurry from the outside of the retaining ring to the surface of the substrate
10
.
The thickness T
L
of the lower portion
180
should be larger than the thickness T
S
of the substrate
10
. Specifically, the lower portion
180
should be thick enough that the substrate
10
does not contact the adhesive layer
186
. On the other hand, if the lower portion
180
is too thick, the bottom surface
182
of the retaining ring
110
may be subject to deformation due to the flexible nature of the lower portion
180
. The initial thickness of the lower portion is typically between 200 to 400 mils. The lower portion
180
is replaced when the remaining thickness of the retaining ring is about the same as the thickness of the substrate.
Referring to
FIG. 3B
, a third alternate embodiment has a damping material
211
located between the polishing pad
240
and the platen
210
to reduce or prevent the transmission of vibration energy from the polishing pad
240
to the platen
210
. The damping material
211
is similar in thickness and is made from the same material as the damping material
230
of
FIG. 2. A
pressure sensitive adhesive layer
213
adheres the damping material
211
to the polishing platen
210
.
The damping material
211
is attached to the polishing pad
240
through a protective layer
215
. The protective layer
215
is a 0.01-inch thick Teflon sheet that makes it easier to detach the polishing pad
240
from the damping material
211
. A layer of pressure sensitive adhesive
212
adheres the protective layer
215
to the damping material
213
, while a second layer of pressure sensitive adhesive (not shown) adheres the protective layer
215
to the polishing pad
240
.
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the damping material may be used with other kinds of polishing apparatus known to persons skilled in the art. For instance, the retaining ring in the apparatus need not contact the polishing pad, as described in the specification. One of the polishing pad and the retaining ring of the polishing system may not rotate at all. The damping material may be used in a polishing apparatus that uses a standard non-abrasive polishing pad provided with a slurry that contains abrasives, such as silicon dioxide particles, in a chemically reactive agent, such as deionized water or potassium hydroxide.
The vibration damping material may also be used in any pair of the locations described in the specification, or even in all of the locations described. Other materials with suitable damping properties may be used to damp vibrations, so long as they significantly reduce or prevent the transmission of vibrational energy from one end of the material to another. Any material that does not rebound to its original shape when deformed may be used as a damping material. Specifically, when subjected to a deformation, the damping material should rebound by less then ten percent of the deformation, although a rebound of less than six percent of the deformation is preferred. For instance, the damping material may be any isodamp C-1000 series isolation damping material, manufatured by E-A-R specialty composites, a visco-elastomer, a soft-plastic, or any other material that has better vibration damping properties than materials immediately adjacent to the damping material.
The thickness of the damping material may be varied to provide optimum results in operating conditions that have different loading, carrier head rotation speed, polishing pad rotation speed, damping material, and so on. A thicker damping material may be used to improve the vibration damping, although poor control of the relative motion of the substrate and the polishing pad may result from a damping material that is too thick. A thinner damping material may also be used, although if the damping material is too thin, it may not sufficiently reduce or prevent the transmission of vibrational energy.
The middle portion
184
and the upper portion
203
(
FIG. 3A
) of the retaining ring maybe manufactured from aluminum or any other material that provides a suitable amount of stiffness to the retaining ring. The thickness of the middle portion
184
and the upper portion
203
may be varied, although if the middle and upper portions are too thin, the retaining ring may deform and reduce the quality of polishing. Alternatively, the middle portion
184
and the lower portion
180
(Fig,
3
A) of the retaining ring
110
may be one integrated piece formed from the same kind of material, e.g., PPS or stainless steel. Other adhesive or attachment methods known to persons of skill may be used to affix the damping material.
Accordingly, other embodiments are within the scope of the following claims.
Claims
- 1. A carrier head for positioning a substrate on a polishing surface, comprising:a structure having a surface for contacting a substrate; a housing connectable to a drive shaft to rotate with the drive shaft about a rotation axis; and a gimbal mechanism located between the structure and the housing to prevent the structure from moving laterally while permitting the structure to gimbal relative to the housing, the gimbal mechanism having a top coupled to the housing, a bottom coupled to the structure, and a vibration damper separating the top from the bottom, the vibration damper including a vibration damping material that does not rebound to its original shape after being subjected to a deformation and that reduces the transmission of vibrational energy from the bottom to the top of the gimbal mechanism.
- 2. The carrier head of claim 1, wherein the vibration damper is mounted on at least one of the top and the bottom using a pressure sensitive adhesive.
- 3. The carrier head of claim 1, wherein the material rebounds by less than six percent of the deformation.
- 4. The carrier head of claim 1, wherein the gimbal mechanism includes a substantially planar flexure ring that flexes in a direction perpendicular to the plane of the flexure ring to gimbal the structure to the housing, the vibration damper being mounted on the flexure ring.
- 5. The carrier head of claim 4, wherein the vibration damper is adhered to the flexure ring using a pressure sensitive adhesive.
- 6. The carrier head of claim 1, wherein the housing defines a bushing, the top including:a gimbal rod extending into the bushing to couple the top to the housing, the bushing allowing the gimbal rod to move along the rotation axis while preventing the gimbal rod from moving out of the rotation axis; and a gimbal ring coupled to the gimbal rod, the vibration damper being mounted on the gimbal ring.
- 7. The carrier head of claim 6, wherein the vibration damper is adhered to the gimbal ring using a pressure sensitive adhesive.
- 8. A chemical mechanical polishing apparatus comprising:a polishing pad; and a carrier head for positioning a substrate on a polishing surface, the carrier head including a structure having a surface for contacting a substrate, a housing connectable to a drive shaft to rotate with the drive shaft about a rotation axis, and a gimbal mechanism between the structure and the housing to prevent the structure from moving laterally while permitting the structure to gimbal relative to the housing, the gimbal mechanism having a top coupled to the housing, a bottom coupled to the structure, and a vibration damper separating the top from the bottom, the vibration damper including a vibration damping material that does not rebound to its original shape after being subjected to a deformation and that reduces the transmission of vibrational energy from the bottom to the top of the gimbal mechanism.
- 9. A chemical mechanical polishing apparatus, comprising:a polishing station, including: a platen, and a substrate polishing pad mounted on the platen; and a carrier head to press a substrate on the polishing pad when the substrate is being polished; wherein at least one of the polishing station and the carrier head includes a vibration damping material in a load path between the platen or the carrier head respectively and the substrate that reduces the transmission of vibrational energy, the vibration damping material not rebounding to its original shape after being subjected to a deformation.
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