U.S. patent application number 10/342665 was filed with the patent office on 2003-06-12 for oscillating fixed abrasive cmp system and methods for implementing the same.
This patent application is currently assigned to LAM RESEARCH CORP.. Invention is credited to Owczarz, Alexsander A., Saldana, Miguel A..
Application Number | 20030109195 10/342665 |
Document ID | / |
Family ID | 24436828 |
Filed Date | 2003-06-12 |
United States Patent
Application |
20030109195 |
Kind Code |
A1 |
Saldana, Miguel A. ; et
al. |
June 12, 2003 |
Oscillating fixed abrasive CMP system and methods for implementing
the same
Abstract
A method for polishing a semiconductor wafer is provided. The
method includes providing a polishing pad strip connected between a
first point and a second point and applying a controlled tension to
the polishing pad strip. The method also includes oscillating the
polishing pad strip between the first point and the second point
while applying the controlled tension. Also included in the method
is applying the semiconductor wafer to the oscillating polishing
pad strip.
Inventors: |
Saldana, Miguel A.;
(Fremont, CA) ; Owczarz, Alexsander A.; (San Jose,
CA) |
Correspondence
Address: |
MARTINE & PENILLA, LLP
710 LAKEWAY DRIVE
SUITE 170
SUNNYVALE
CA
94085
US
|
Assignee: |
LAM RESEARCH CORP.
Fremont
CA
|
Family ID: |
24436828 |
Appl. No.: |
10/342665 |
Filed: |
January 14, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10342665 |
Jan 14, 2003 |
|
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|
09608513 |
Jun 30, 2000 |
|
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6520833 |
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Current U.S.
Class: |
451/5 |
Current CPC
Class: |
B24B 21/04 20130101;
B24B 37/04 20130101; B24B 21/004 20130101 |
Class at
Publication: |
451/5 |
International
Class: |
B24B 049/00 |
Claims
What is claimed is:
1. A method for polishing a semiconductor wafer, comprising:
providing a polishing pad strip connected between a first point and
a second point; applying a controlled tension to the polishing pad
strip; oscillating the polishing pad strip between the first point
and the second point while applying the controlled tension; and
applying the semiconductor wafer to the oscillating polishing pad
strip.
2. A method for polishing a semiconductor wafer as recited in claim
1, further comprising: applying a chemical solution to the
polishing pad strip before the applying of the semiconductor
wafer.
3. A method for polishing a semiconductor wafer as recited in claim
1, wherein the polishing pad strip is a fixed abrasive pad.
4. A method for polishing a semiconductor wafer as recited in claim
1, further comprising: monitoring a linear velocity of the
oscillating polishing pad strip; and controlling a setting of the
linear velocity.
5. A method for polishing a semiconductor wafer as recited in claim
1, further comprising: monitoring a tension of the polishing pad
strip; and controlling a setting of the tension.
6. A method for preparing a substrate, comprising: providing a
polishing pad strip connected between a first point and a second
point; applying a controlled tension to the polishing pad strip;
oscillating the polishing pad strip between the first point and the
second point while applying the controlled tension; applying the
substrate to the oscillating polishing pad strip; and continually
monitoring the controlled tension so as to enable adjustments while
applying the substrate to the polishing pad strip.
7. A method for preparing a substrate as recited in claim 6,
further comprising: applying a chemical solution to the polishing
pad strip before the applying of the substrate.
8. A method for preparing a substrate as recited in claim 6,
wherein the polishing pad strip is one of a fixed abrasive
polishing pad strip and a non-fixed abrasive polishing pad
strip.
9. A method for preparing a substrate as recited in claim 6,
further comprising: monitoring a linear velocity of the oscillating
polishing pad strip; and controlling a setting of the linear
velocity.
10. A method for preparing a substrate as recited in claim 6,
further comprising: monitoring a tension of the polishing pad
strip; and controlling a setting of the tension.
11. A method for preparing a substrate as recited in claim 6,
further comprising: providing a supply of the polishing pad strip
in a feed roll defined at the first point.
12. A method for preparing a substrate as recited in claim 11,
further comprising: collecting the supply of the polishing pad
strip in a take-up roll defined at the second point.
13. A method for preparing a substrate as recited in claim 12,
wherein the operation of applying controlled tension to the
polishing pad strip includes, pulling on the feed roll; and pulling
on the take-up roll.
14. A method for planarizing an active surface of a substrate,
comprising: providing a preparation strip connected between a first
point and a second point; applying a controlled tension to the
preparation strip; oscillating the preparation strip between the
first point and the second point while applying the controlled
tension; controlling a linear velocity of the oscillating; applying
the active surface of the substrate to the oscillating preparation
strip; and continually monitoring the controlled tension and the
linear velocity of the preparation strip so as to enable
adjustments while applying the active surface of the substrate to
the preparation strip.
15. A method for planarizing an active surface of a substrate as
recited in claim 14, further comprising: applying a chemical
solution to the preparation strip before the applying of the active
surface of the substrate.
16. A method for planarizing an active surface of a substrate as
recited in claim 6, wherein the preparation strip is one of a fixed
abrasive polishing pad strip and a non-fixed abrasive polishing pad
strip.
17. A method for planarizing an active surface of a substrate as
recited in claim 14, wherein the operation of controlling the liner
velocity of the oscillating includes, monitoring a linear velocity
of the oscillating preparation strip; and controlling a setting of
the linear velocity.
18. A method for planarizing an active surface of a substrate as
recited in claim 16, further comprising: providing a supply of the
preparation strip in a feed roll defined at the first point.
19. A method for planarizing an active surface of a substrate as
recited in claim 18, further comprising: collecting the supply of
the preparation strip in a take-up roll defined at the second
point.
20. A method for planarizing an active surface of a substrate as
recited in claim 18, wherein the operation of applying controlled
tension to the preparation strip includes, pulling on the feed
roll; and pulling on the take-up roll.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This Application is a divisional of application Ser. No.
09/608,513, filed Jun. 30, 2000, from which priority under 35
U.S.C. .sctn.120 is claimed. The disclosure of this Application is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to chemical
mechanical polishing (CMP) systems and techniques for improving the
performance and effectiveness of CMP operations. Specifically, the
present invention relates to CMP systems that use a fixed abrasive
polishing pad arranged in a web handling system.
[0004] 2. Description of the Related Art
[0005] In the fabrication of semiconductor devices, there is a need
to perform CMP operations, including polishing, buffing and wafer
cleaning. Typically, integrated circuit devices are in the form of
multi-level structures. At the substrate level, transistor devices
having diffusion regions are formed. In subsequent levels,
interconnect metallization lines are patterned and electrically
connected to the transistor devices to define the desired
functional device. As is well known, patterned conductive layers
are insulated from other conductive layers by dielectric materials,
such as silicon dioxide. As more metallization levels and
associated dielectric layers are formed, the need to planarize the
dielectric material increases. Without planarization, fabrication
of additional metallization layers becomes substantially more
difficult due to the higher variations in the surface topography.
In other applications, metallization line patterns are formed in
the dielectric material, and then metal CMP operations are
performed to remove excess metallization.
[0006] In the prior art, CMP systems typically implement belt,
orbital, or brush stations in which belts, pads, or brushes are
used to scrub, buff, and polish one or both sides of a wafer.
Slurry is used to facilitate and enhance the CMP operation. Slurry
is most usually introduced onto a moving preparation surface, e.g.,
belt, pad, brush, and the like, and distributed over the
preparation surface as well as the surface of the semiconductor
wafer being buffed, polished, or otherwise prepared by the CMP
process. The distribution is generally accomplished by a
combination of the movement of the preparation surface, the
movement of the semiconductor wafer and the friction created
between the semiconductor wafer and the preparation surface.
[0007] FIG. 1 illustrates an exemplary prior art CMP system 100.
The CMP system 100 in FIG. 1 is a belt-type system, so designated
because the preparation surface is an endless belt 108 mounted on
two drums 114 which drive the belt 108 in a rotational motion as
indicated by belt rotation directional arrows 116. A wafer 102 is
mounted on a carrier 104. The carrier 104 is rotated in direction
106. The rotating wafer 102 is then applied against the rotating
belt 108 with a force F to accomplish a CMP process. Some CMP
processes require significant force F to be applied. A platen 112
is provided to stabilize the belt 108 and to provide a solid
surface onto which to apply the wafer 102. Slurry 118 composing of
an aqueous solution such as NH.sub.4OH or DI water containing
dispersed abrasive particles is introduced upstream of the wafer
102. The process of scrubbing, buffing and polishing of the surface
of the wafer is achieved by using an endless polishing pad glued to
the belt 108. Typically, the polishing pad is composed of porous or
fibrous materials and lacks fixed abrasive particles.
[0008] After the polishing pad polishes a limited number of wafers,
the surface of the pad is conditioned and cleaned in order to
remove the attached abrasive materials of the slurry and the
particles removed from the wafer. Subsequent to cleaning and
conditioning, the polishing pad will have a significant amount of
particles that remain attached to the surface of the polishing pad
causing the polishing pad to lose its effectiveness. The polishing
pad also loses its effectiveness due to normal wear of the material
itself. As a result, the polishing pad must be replaced in its
entirety. The removal of the used polishing pad and its subsequent
replacement with a new polishing pad is very time consuming and
labor intensive. Additionally, the time needed to perform the
replacement necessarily requires that the polishing system be taken
off-line, which thus reduces throughput.
[0009] In view of the foregoing, a need therefore exists in the art
for a chemical mechanical polishing system that will enable
polishing surface layers of a wafer using a polishing pad that is
less expensive to maintain and is more effectively serviced after
its use degrades the effectiveness of the polishing.
SUMMARY OF THE INVENTION
[0010] Broadly speaking, the present invention fills these needs by
providing an apparatus and related methods for efficiently
polishing layer surfaces of a semiconductor wafer. Preferably, the
CMP system is designed to implement a polishing pad strip that is
less expensive to maintain and is more efficiently serviced after
it loses its effectiveness to polish. In preferred embodiments, the
polishing pad is a fixed abrasive polishing pad strip that is
connected between a feed roll and a take-up. It should be
appreciated that the present invention can be implemented in
numerous ways, including as a process, an apparatus, a system, a
device, or a method. Several inventive embodiments of the present
invention are described below.
[0011] In one embodiment, a method for polishing a semiconductor
wafer is provided. The method includes providing a polishing pad
strip connected between a first point and a second point and
applying a controlled tension to the polishing pad strip. The
method also includes oscillating the polishing pad strip between
the first point and the second point while applying the controlled
tension. Also included in the method is applying the semiconductor
wafer to the oscillating polishing pad strip.
[0012] In another embodiment, a method for preparing a substrate is
provided. The method includes providing a polishing pad strip
connected between a first point and a second point and applying a
controlled tension to the polishing pad strip. The method also
includes oscillating the polishing pad strip between the first
point and the second point while applying the controlled tension.
Also included in the method is applying the substrate to the
oscillating polishing pad strip. The method further includes
continually monitoring the controlled tension so as to enable
adjustments while applying the substrate to the polishing pad
strip.
[0013] In still a further embodiment, a method for planarizing an
active surface of a substrate is provided. The method includes
providing a preparation strip connected between a first point and a
second point and applying a controlled tension to the preparation
strip. Also included in the method is oscillating the preparation
strip between the first point and the second point while applying
the controlled tension. The method further includes controlling a
linear velocity of the oscillating and applying the active surface
of the substrate to the oscillating preparation strip. Also
included is continually monitoring the controlled tension and the
linear velocity of the preparation strip so as to enable
adjustments while applying the active surface of the substrate to
the preparation strip.
[0014] The advantages of the present invention are numerous. Most
notably, instead of a continuous belt polishing pad, a supply of
polishing pad strip is provided between a feed roll and a take-up
roll in a web handling arrangement. Thus, replacing used portions
of the polishing pad strip with fresh portions of the polishing pad
strip can be accomplished utilizing minimal effort and in
significantly less amount of time. Furthermore, the re-supplying of
the polishing pad strip can be achieved easily and expeditiously
thereby minimizing the length of time needed to take the polishing
system off-line thus having minimal effect on the throughput.
Accordingly, the apparatus and the methods of the present invention
provide for polishing surface layers of a wafer using a polishing
pad that is less expensive to maintain and is more effectively
serviced after its use degrades the effectiveness of the
polishing.
[0015] Other aspects and advantages of the invention will become
apparent from the following detailed description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The present invention will be readily understood by the
following detailed description in conjunction with the accompanying
drawings, and like reference numerals designate like structural
elements.
[0017] FIG. 1 illustrates an exemplary prior art CMP system.
[0018] FIG. 2A is a cross-sectional view of an oscillating CMP
system, in accordance with one embodiment of the present
invention.
[0019] FIG. 2B is a cross-sectional view of an oscillating CMP
system, illustrating the system's tension setting mechanism and
velocity control mechanism, in accordance with another embodiment
of the present invention.
[0020] FIG. 2C is a cross-sectional view of an oscillating CMP
system, illustrating the feed roll's design to hold an ample supply
of the polishing pad strip, in accordance with yet another
embodiment of the present invention.
[0021] FIG. 2D-1 is a plan-view of an abrasive polishing pad strip,
in accordance with yet another embodiment of the present
invention.
[0022] FIG. 2D-2 is a cross-sectional view of an abrasive polishing
pad strip, revealing the plurality of posts containing a plurality
of abrasive particles, in accordance with yet another embodiment of
the present invention.
[0023] FIG. 3A is a cross-sectional view of the CMP system in which
the tension actuators are positioned to the right and to the left
of the feed roll and the take-up roll, respectively, in accordance
with yet another embodiment of the present invention.
[0024] FIG. 3B is a cross-sectional view of the CMP system,
depicting the system's tension setting and velocity control
mechanisms, in accordance with yet another embodiment of the
invention.
[0025] FIG. 4A is a cross-sectional view of the CMP system in which
the tension actuators are connected to the idler rollers, in
accordance with yet another embodiment of the present
invention.
[0026] FIG. 4B is a cross-sectional view of the CMP system,
depicting the system's tension setting mechanism as well as
velocity control mechanism, in accordance with yet another
embodiment of the invention.
[0027] FIG. 5A is a cross-sectional view of the CMP system in which
the feed roll and take-up roll maintain and control both the
tension exerted on the polishing pad strip as well as the linear
velocity of the polishing pad strip, in accordance with yet another
embodiment of the invention.
[0028] FIG. 5B is a cross-sectional view of the CMP system,
depicting the system's tension and velocity control mechanism, in
accordance with yet another embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] An invention for a CMP system, which enables efficient
polishing of layer surfaces of a wafer is described. The CMP system
preferably implements a polishing pad that is less expensive to
maintain and is more efficiently serviced after it loses its
effectiveness to polish. In preferred embodiments, the polishing
pad is a fixed abrasive polishing pad. The fixed abrasive polishing
pad is preferably provided as a polishing pad strip that is
connected between a feed roll and a take-up. This configuration is
referred to herein as a web handling arrangement. In the following
description, numerous specific details are set forth in order to
provide a thorough understanding of the present invention. It will
be understood, however, to one skilled in the art, that the present
invention may be practiced without some or all of these specific
details. In other instances, well known process operations have not
been described in detail in order not to unnecessarily obscure the
present invention.
[0030] FIG. 2A is a cross-sectional view of an oscillating CMP
system 200, in accordance with one embodiment of the present
invention. The CMP system 200 in FIG. 2A includes a feed roll 212a
positioned at a first point 211a. The feed roll 212a is configured
to hold a roll of a polishing pad strip 202. A take-up roll 212b is
positioned at a second point 211b, and is placed, in this
embodiment, symmetrically across from the feed roll 212a and is
configured to receive the polishing pad strip 202. The direct
distance between the feed roll 212a and take-up roll 212b is
estimated to be about 20 inches. Of course, the distance between
the feed roll 212a and take-up roll 212b may vary depending on the
specific implementation. In this embodiment, each of the feed roll
212a and the take-up roll 212b is designed to contain an internal
motor. Preferably, the internal motor is a servo drive, such as a
direct drive servo. The internal motors are designed to allow the
feed roll 212a and take-up roll 212b to reciprocate. The
reciprocating motions of the feed roll 212a and take-up roll 212b
cause the polishing pad strip to oscillate at a linear velocity
ranging from about 140 feet per second to about 350 feet per
second. The actual linear velocity selected for a polishing
operation will also depend on the force at which a polishing head
holding a wafer is applied to the polishing pad strip and the
platen. The limits of the linear velocity and the force are
generally calibrated using the well known Preston's Equation.
According to Preston's Equation, Removal Rate=KpPV, where the
removal rate of material is a function of Downforce (P) and Linear
Velocity (V), with Kp being the Preston Coefficient, a constant
determined by the chemical composition of the slurry (or fixed
abrasive material and chemicals), the process temperature, and the
pad surface, among other variables.
[0031] In this embodiment, tension actuators 214a and 214b are
positioned directly below the feed roll 212a and take-up roll 212b,
respectively. The tension actuators 214a and 214b are configured to
controllably pull on the feed roll 212a and take-up roll 212b
thereby causing the feed roll 212a and take-up roll 212b to exert
tension on the polishing pad strip 202. It should be understood
that each of the tension actuators can be any type of linear
actuator. For instance, each tension actuator can be replaced with
cylinders, coils, screws or linear motors.
[0032] Positioned above the feed roll 212a is a load cell roller
208a defined by a roller that measures the tension exerted on the
polishing pad strip 202 on the side closest to intermediate point
207a (e.g., left side). The load cell roller 208b is also defined
by a roller that measures the tension exerted on the polishing pad
strip 202 on the side closest to the intermediate point 207b (e.g.,
right side). In this example, the load cell roller 208b is
positioned symmetrically across from the load cell roller 208a and
directly above the take-up roll 211b. Therefore, the polishing pad
strip 202 is located on top of the load cell rollers 208a and 208b,
and the load cell rollers 208a and 208b are configured to provide a
location where the polishing pad strip 202 is caused to change
angular orientation. For instance, the angular orientation may be
about 90 degrees so that only the horizontal components of the
forces applied on the load cell rollers 208a and 208b are measured.
An idler roller 210a defined by a roller fixed to a point is
positioned between feed roll 212a and load cell roller 208a. Across
from the idler roller 210a, is positioned an idler roller 210b. The
idler rollers 210a and 210b are designed to support the polishing
pad strip along a path that will ensure the 90-degree angle
described above. Thus, the idler rollers 210a and 210b are further
designed to allow the load cell rollers 208a and 208b to measure
only the horizontal components of the forces applied on the load
cell rollers 208a and 208b. The horizontal components of the
applied forces are equivalent to the tension exerted on the
polishing pad strip 202 on the left side and the right side of the
polishing head 204.
[0033] A polishing head 204 is designed to carry a wafer (not shown
in the figure) and rotates in a rotation direction 205. A platen
206 is positioned horizontally between load cell rollers 208a and
208b. Platen 206 is configured to stabilize the polishing pad strip
202 and to provide a solid surface onto which to apply the
polishing head 204. In some cases, it is possible to control the
surface between the platen 206 and the polishing pad strip 202 to
control the removal rate in different locations on the wafer. In
one embodiment, the polishing pad strip 202 is a fixed abrasive
polishing pad, which has a polishing layer containing abrasive
particles extended throughout the surface and the material
thickness. As the polishing head 204 applies the wafer (not shown
in the figure) against the polishing pad strip 202, the abrasive
particles of the polishing pad strip 202 become loose thereby
eliminating the necessity to use a slurry containing abrasive
materials. Although a slurry containing abrasive particles is not
required, a liquid solution (e.g., NH.sub.4OH or DI water) is
preferably used to facilitate the polishing process.
[0034] As depicted in the embodiment of FIG. 2B, a certain portion
of the supplied polishing pad strip 202 held in the feed roll 212a
is fed around the load cell rollers 208a and 208b to the take-up
roll 211b. After polishing a given number of wafers, the portion of
the polishing pad strip 202 which came into contact with the wafers
loses its effectiveness and must be replaced. The used portion of
the polishing pad strip 202 is replaced by an unused portion of the
polishing pad strip 202 by way of the feed roll 212a indexing the
polishing pad strip 202, utilizing a programmable amount (e.g.,
enough to place a fresh portion of the polishing pad strip 202 over
the platen 206). The indexing causes the used portions of the
polishing pad strip 202 to be pushed farther and farther away from
the polishing area. The used portions of the polishing pad strip
202 are collected by the take-up roll 212b and will ultimately be
discarded. Once the supply of the polishing pad strip 202 held in
feed roll 212a is completely consumed, it can easily be replaced
with a new roll of the polishing pad strip 202. The process of
re-supplying the feed roll 212a with the polishing pad strip 202 is
neither labor intensive nor time consuming. More importantly, the
CMP machine will be off-line, if necessary, less frequently and for
a significantly less amount of time thereby causing minimal effect
on the throughput of the machine.
[0035] Also clearly shown in FIG. 2B are the tension actuators 214a
and 214b which are configured to controllably pull on the feed roll
212a and take-up roll 212b causing the feed roll 212a and take-up
roll 212b to apply pressure to the polishing pad strip 202 at the
first intermediate point 207a and the second intermediate point
207b, respectively. Due to normal wear, the polishing pad strip 202
can stretch, thereby causing the amount of tension exerted on the
polishing pad strip 202 to reduce. This system is designed to
maintain a desired tension by way of changing the amount of force
the tension actuators 214a and 214b apply on the feed roll 212a and
take-up roll 212b, respectively.
[0036] This task is achieved by the load cell roller 208a sending a
tension feedback signal to an amplifier 222a, which is a part of a
first tension-velocity controller 220a. Subsequently, a tension
setting command, either supplied manually or automatically through
a computerized device, is fed to the amplifier 222a. Thereafter,
the amplifier 222a sends a tension output signal to a tension
control device 226a, which is also a part of the tension-velocity
controller 220a. Finally, the tension control device 226a sends a
tension (TN) signal to the tension actuator 214a.
[0037] In a like manner, an amplifier 222b, which is a part of a
tension-velocity controller 220b receives a tension feedback (FB)
signal from load cell roller 208b. Subsequently, a tension setting
command, either supplied manually or automatically through a
computerized device, is fed to the amplifier 222b. Thereafter, the
amplifier 222b sends a tension (TN) output signal to a tension
control device 226b, which is also a part of the tension-velocity
controller 220b. Finally, the tension control device 226b sends a
tension signal to the tension actuator 214a. Depending on the
tension signals received from the tension-velocity controllers 220a
and 220b, the tension actuators 214a and 214b may or may not exert
additional force on the feed roll 212a and take-up roll 212b so as
to achieve a desired tension (e.g., either higher or lower).
[0038] Once the desired tension is exerted on the polishing pad
strip 202, the internal motors located inside the feed roll 212a
and take-up roll 212b will cause the feed roll 212a and take-up
roll 212b to reciprocate, synchronously, thereby causing the
polishing pad strip 202 to oscillate at a linear velocity. In one
embodiment, to achieve optimum performance, the linear velocity of
the polishing pad strip 202 should be maintained within the range
of about 140 ft/sec and about 350 ft/sec. Thus, the linear velocity
of the polishing pad strip 202 should be measured frequently by the
feed roll 212a and take-up roll 212b. Besides measuring the
velocity of the polishing pad strip 202, the feed roll 212a and
take-up roll 212b control and change, if necessary, the velocity of
the polishing pad 202 so as to maintain a desired velocity.
[0039] As an example, the feed roll 212a initially sends out a
velocity feedback to a Proportional, Integral and Derivative (PID)
224a, which is a part of the tension-velocity controller 220a.
Then, a velocity setting command, either supplied manually or
automatically using a computerized device, is fed to the PID 224a.
Finally, the PID 224a sends out a velocity signal to the feed roll
212a.
[0040] Similarly, the take-up roll 212b sends out a velocity
feedback to a Proportional, Integral and Derivative (PID) 224b,
which is a part of the tension-velocity controller 220b. Then, a
velocity setting command, either supplied manually or by way of a
programmable machine, is fed to the PID 224b. Finally, the PID 224b
sends out a velocity signal to the take-up roll 212b. The velocity
signals received by the feed roll 212a and the take-up roll 212b
are the determinative factors as to whether the feed roll 212a and
take-up roll 212b must maintain or change the rate of
reciprocating. Although the tension-velocity controllers 220a and
220b have been illustrated using exemplary electronics, it should
be understood that the electronics and control signals can be
processed using any other suitable well known processing techniques
(e.g., software/hardware combinations). For instance, the PID
electronics can be substituted with other circuitry that can
process and control the signals as may be desired.
[0041] As clearly evident from the embodiment of FIG. 2C, the feed
roll 212a is designed to hold an ample supply of the polishing pad
strip 202. Utilizing minimal effort, the feed roll 212a can be
re-supplied with the fresh polishing pad strip 202 thereby having
minimum effect on the throughput of the CMP machine.
[0042] FIG. 2D-1 depicts one of many types of the polishing pad
strip 202, which has a fixed abrasive polishing layer. The
approximate thickness of this type of polishing pad strip 202
ranges from about 0.004 inch to about 0.010 inch. Embedded and
extended through out the surface of this type of polishing pad
strip 202 are several three-dimensional protrusions, which are
defined as posts 202'. The cross-sectional view of the polishing
pad strip 202, as shown in FIG. 2D-2, reveals that each post 202'
contains a plurality of abrasive particles having an approximate
size in the range from about 40 micrometer and about 200
micrometer.
[0043] Another embodiment of the present invention is shown in FIG.
3A wherein the tension actuator 314a is positioned to the right of
the feed roll 212a. In a like manner, the tension actuator 314b is
situated to the left of the take-up roll 212b. In this embodiment,
by respectively pulling on the feed roll 212a and take-up roll
212b, the tension actuators 314a and 314b will cause the feed roll
212a and take-up roll 212b to controllably exert tension on the
polishing pad strip 202.
[0044] For example, in the embodiment of FIG. 3B, the tension
actuators 314a and 314b control the amount of tension exerted on
the polishing pad strip 202. This is achieved by the load cell
roller 208a sending out a tension feedback to the tension/velocity
controller 220a, which in turn, after internally processing the
tension feedback, sends a tension signal to the tension actuator
314a. Similarly, the load cell roller 208b sends out a tension
feedback to the tension/velocity controller 220b. Once the
tension/velocity controller 220b processes the tension feedback,
internally, it sends a tension signal to the tension actuator 314b.
Depending on the tension signals received, if necessary, the
tension actuators 314a and 314b, may change the amount of force
each of them exerts on the feed roll 212a and take-up roll 212b so
as to achieve a desired tension.
[0045] Once the desired tension is set for the polishing pad strip
202, the synchronous reciprocation of the feed roll 212a and
take-up roll 212b start thereby causing the polishing pad strip 202
to oscillate at a linear velocity. In one embodiment, the linear
velocity of the polishing pad strip 202 may be measured frequently
or at set times. Depending upon the measurements, adjustments can
be made to the tension that is controlled by the feed roll 212a and
take-up roll 212b. The feed roll 212a and take-up roll 212b each
send out a velocity feedback to the tension/velocity controllers
220a and 220b, respectively. Then, after internally processing the
velocity feedbacks, the tension/velocity controllers 220a and 220b,
each sends out a velocity signal to the feed roll 212a and take-up
roll 212b. Depending on the velocity signals received, if
necessary, the feed roll 212a and take-up roll 212b may change the
rate of reciprocating, thus fixing a new linear velocity for the
polishing pad strip 202.
[0046] The embodiment of FIG. 4A depicts an oscillating CMP system
200b that is similar to the embodiment of FIG. 2A, with the
exception that the tension actuators 414a and 414b are positioned
outside the idler rollers 210a and 210b. In this embodiment, the
tension actuators are configured to pull on the idler rollers 210a
and 210b so as to cause the idler rollers 210a and 210b to exert
tension on the polishing pad strip 202.
[0047] In this case, there will be points in time when the vertical
portions of the polishing pad strip 202 will not be at a 90 degree
angle relative to the polishing region (e.g., where the platen 206
is located) of the polishing pad strip 202. Nevertheless, the
tension can be controllably adjusted to a correct desired level. It
should therefore be understood that it is not necessary to have the
vertical and horizontal portions of the polishing pad strip 202 at
a 90 degree angle at all times so long as the polishing pad strip
202 provides the desired optimum polishing condition at the
location where polishing is to be performed on the wafer
surfaces.
[0048] As shown in the embodiment of FIG. 4B, the load cell roller
208a sends out a tension feedback to the tension/velocity
controller 220a. After internally processing the tension feedback,
the tension/velocity controller 220a sends out a tension signal to
the tension actuator 414a. Similar signals are also exchanged
between the load cell roller 208b, tension/velocity controller 220b
and tension actuator 414b.
[0049] Once each of the tension actuators 414a and 414b
respectively receive a tension signal from 220a and 220b, depending
on the tension signals received, tension actuators may, if
necessary, change the force by which they exert tension on the
polishing pad strip 202. After achieving the desired tension, the
feed roll 212a and take-up roll 212b start reciprocating,
preferably synchronously, causing the polishing pad strip to
oscillate at a desired linear velocity. Similar to the embodiments
of FIGS. 2B and 3B, the feed roll 212a and take-up roll 212b
maintain and if necessary, change the velocity of the oscillation
of the polishing pad strip 202.
[0050] FIG. 5A depicts an oscillating CMP system 200c wherein the
feed roll 212a and take-up roll 212b maintain and control both the
tension exerted on the polishing pad strip 202 as well as the
linear velocity of the polishing pad 202. Accordingly, the tension
actuators have completely been eliminated from the CMP system
200c.
[0051] As illustrated in FIG. 5B, in a CMP system 200c', the load
cell roller 208a sends a tension feedback to an amplifier 322a that
is part of the tension-and-velocity controller 320a. Thereafter, a
tension setting command, supplied either manually or automatically
through a computerized device, is fed to the amplifier 322a. Then,
the amplifier 322a sends a tension output signal to a tension and
velocity control device 326a.
[0052] Thereafter, a velocity feedback is sent from feed roll 212a
to a PID 324a also positioned within the tension-and-velocity
controller 320a. In a subsequent operation, a velocity setting
command, supplied either manually or by way of a programmable
machine, is fed to the PID 324a. Then, the PID 324a sends a
velocity output signal to the tension and velocity control 326a.
After receiving the tension output signal and the velocity output
signal, the tension and velocity control 326a sends out a tension
and velocity signal to the feed roll 212a.
[0053] Similarly, a tension feedback and a velocity feedback are
respectively fed to an amplifier 322b and a PID 324b, which are
part of the tension-and-velocity controller 320b. Then, a tension
setting command is fed to the amplifier 322b, which in turn, sends
out a tension output signal to a tension and velocity control 326b,
which is also a part of the tension-and-velocity controller 320b.
Next, a velocity setting command is fed to the PID 324b, which
subsequently sends out a velocity command signal to the tension and
velocity control 326b. After receiving the tension output signal
and the velocity output signal, the tension and velocity control
326b sends out a tension and velocity signal to the take-up roll
212b.
[0054] Depending on the tension and velocity signals received by
the feed roll 212a and take-up roll 212b, the feed roll 212a and
take-up roll 212b may, if necessary, each rotate inwardly in the
direction (TA) so as to adjust the tension exerted on the polishing
pad strip 202 to a desired level. Once the tension applied to the
polishing pad strip 202 is set to a desired level, the feed roll
212a and take-up roll 212b start, preferably, a synchronous
reciprocation thereby causing the polishing pad to oscillate at a
linear velocity under the polishing head 204. Thus, in this
embodiment, similar to some of the embodiments, the feed roll 212a
and take-up roll 212b can change, if necessary, the velocity of the
polishing pad 202 so as to maintain a desired velocity for optimum
polishing performance.
[0055] Although the foregoing invention has been described in some
detail for purposes of clarity of understanding, it will be
apparent that certain changes and modifications may be practiced
within the scope of the appended claims. For example, embodiments
described herein have been primarily directed toward wafer
polishing, however, it should be understood that the polishing
operations are well suited for precision polishing of any type of
substrate. Accordingly, the present embodiments are to be
considered as illustrative and not restrictive, and the invention
is not to be limited to the details given herein, but may be
modified within the scope and equivalents of the appended
claims.
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