U.S. patent application number 13/129351 was filed with the patent office on 2013-05-16 for pad conditioning force modeling to achieve constant removal rate.
This patent application is currently assigned to APPLIED MATERIALS, INC. The applicant listed for this patent is Shou-Sung Chang, Sang J. Cho, Christopher D. Cocca, Slvakumar Dhandapani, Jason G. Fung, Charles C. Garretson, Gregory E. Menk, Stan D. Tsai. Invention is credited to Shou-Sung Chang, Sang J. Cho, Christopher D. Cocca, Slvakumar Dhandapani, Jason G. Fung, Charles C. Garretson, Gregory E. Menk, Stan D. Tsai.
Application Number | 20130122783 13/129351 |
Document ID | / |
Family ID | 44904300 |
Filed Date | 2013-05-16 |
United States Patent
Application |
20130122783 |
Kind Code |
A1 |
Menk; Gregory E. ; et
al. |
May 16, 2013 |
PAD CONDITIONING FORCE MODELING TO ACHIEVE CONSTANT REMOVAL
RATE
Abstract
A method and apparatus for conditioning a polishing pad in a CMP
system is provided. In one embodiment, a method for conditioning a
polishing pad includes applying a down force to the conditioning
disk that urges the conditioning disk against the polishing pad,
measuring a torque required to sweep the conditioning disk across
the polishing pad, determining a change in down force by comparing
the measured torque to a model force profile (MFP), and adjusting
the down force that the conditioning disk applies against the
polishing pad in response to the determined change.
Inventors: |
Menk; Gregory E.;
(Pleasanton, CA) ; Tsai; Stan D.; (Fremont,
CA) ; Cho; Sang J.; (San Jose, CA) ;
Dhandapani; Slvakumar; (San Jose, CA) ; Cocca;
Christopher D.; (Fremont, CA) ; Fung; Jason G.;
(Sunnyvale, CA) ; Chang; Shou-Sung; (Mt. View,
CA) ; Garretson; Charles C.; (Sunnyvale, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Menk; Gregory E.
Tsai; Stan D.
Cho; Sang J.
Dhandapani; Slvakumar
Cocca; Christopher D.
Fung; Jason G.
Chang; Shou-Sung
Garretson; Charles C. |
Pleasanton
Fremont
San Jose
San Jose
Fremont
Sunnyvale
Mt. View
Sunnyvale |
CA
CA
CA
CA
CA
CA
CA
CA |
US
US
US
US
US
US
US
US |
|
|
Assignee: |
APPLIED MATERIALS, INC
Santa Clara
CA
|
Family ID: |
44904300 |
Appl. No.: |
13/129351 |
Filed: |
April 13, 2011 |
PCT Filed: |
April 13, 2011 |
PCT NO: |
PCT/US2011/032319 |
371 Date: |
November 2, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61330300 |
Apr 30, 2010 |
|
|
|
Current U.S.
Class: |
451/11 ;
451/443 |
Current CPC
Class: |
B24B 37/042 20130101;
B24B 53/017 20130101 |
Class at
Publication: |
451/11 ;
451/443 |
International
Class: |
B24B 53/017 20060101
B24B053/017 |
Claims
1. A method for conditioning a polishing pad, comprising: applying
a down force to a conditioning disk that urges the conditioning
disk against the polishing pad; measuring a torque required to
sweep the conditioning disk across the polishing pad; determining a
change in down force by comparing the measured torque to a model
force profile (MFP); and adjusting the down force that the
conditioning disk applies against the polishing pad in response to
the determined change.
2. The method of claim 1, wherein the MFP comprises an estimated
relationship between the down force, the torque, and a rate of
removal of material from a substrate by the polishing pad.
3. The method of claim 1, wherein the determining comprises:
determining the change in down force necessary to maintain a rate
of material removal from a substrate by the polishing pad.
4. The method of claim 1, wherein the determining comprises:
determining a decrease in down force necessary to achieve a target
torque of the MFP.
5. The method of claim 1, wherein the determining comprises:
determining an increase in down force necessary to maintain a
constant removal rate of the polishing pad in response to the
measured torque being less than the MFP.
6. The method of claim 1, wherein the adjusting the down force
comprises modifying a conditioning recipe for the polishing
pad.
7. The method of claim 1, wherein the adjusting the down force
comprises adjusting the down force in-situ during conditioning of
the polishing pad.
8. A method for conditioning a polishing pad, comprising: applying
a down force to urge a conditioning disk against the polishing pad;
measuring a frictional force generated by the conditioning disk
contacting the polishing pad; comparing the measured frictional
force to a model force profile (MFP) to determine a change in down
force; and adjusting the applied down force in response to the
comparison between the measured frictional force and the MFP.
9. The method of claim 8, wherein the MFP further comprises: an
estimated relationship between the down force, the frictional
force, and a rate of removal of material from a substrate by the
polishing pad.
10. The method of claim 9, wherein the frictional force comprises a
rotational torque required to rotate at least one of a conditioning
head, a platen, or a polishing head.
11. An apparatus for conditioning a polishing pad with a
conditioning disk, comprising: a platen adapted to support the
polishing pad; a conditioning head adapted to retain the
conditioning disk; a down force actuator operable to move the
conditioning head in a manner that the conditioning head applies a
down force against the polishing pad with; an arm coupled to the
conditioning head to support the conditioning head above the
platen; and a sweep actuator coupled to the arm and operable to
sweep the conditioning head across the platen; and a sweep torque
sensor operable to measure a torque required to sweep the
conditioning head across the platen when the conditioning disk is
in contact with the polishing pad.
12. The apparatus of claim 11, further comprising: a controller
coupled to the down force actuator and operable to instruct the
down force actuator to apply the down force at a value selected in
response to a model force profile (MFP)
13. The apparatus of claim 12, wherein the controller is operable
to provide a closed loop control of down force applied by the down
force actuator based on the torque measured by the sweep torque
sensor to maintain a substantially constant removal rate of
material from a substrate by the polishing pad.
14. The apparatus of claim 11, further comprising: a pad thickness
sensor coupled to the conditioning head.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] Embodiments of the present invention generally relate a
method for conditioning a polishing surface in an electrochemical
mechanical processing system.
[0003] 2. Description of the Related Art
[0004] During the manufacture of semiconductor devices, layers and
structures are deposited and formed on a semiconductor substrate by
various processes. Chemical mechanical polishing (CMP) is a widely
used process by which a polishing pad in combination with a
polishing solution removes excess material in a manner that
planarizes the substrate or maintains flatness for receipt of a
subsequent layer. Over time, the effectiveness of the polishing pad
diminishes as pressure, friction, and heat combine with particulate
matter from processing slurries, materials removed from the
substrate (or from the pad itself), and the like, to form a hard,
relatively smooth surface on the pad. This effect is typically
called "glazing." In order to improve the effectiveness of the
polishing pad after glazing has occurred, the polishing pad may be
periodically conditioned. Pad conditioning generally involves
scouring the polishing pad with an abrasive conditioning disk to
remove any accumulated polishing by-products on the pad surface
and/or to refresh the surface of the polishing pad. The
conditioning of the polishing pad surface may be performed prior to
polishing with a new polishing pad, during the polishing process to
maintain and/or enhance surface roughness and removal rate of the
polishing pad surface, or post-processing to prepare the polishing
pad surface for a new substrate to be polished.
[0005] It is generally known that the effectiveness of the
conditioning disk declines over time due to disk and pad wear. As a
result, the effectiveness of the polishing pad drifts over time,
producing non-uniform results from substrate to substrate. Thus,
there is a need for an improved method for conditioning a polishing
pad to improve polishing pad performance over the life of the
conditioning disk.
SUMMARY OF THE INVENTION
[0006] Embodiments of the invention provide methods for
conditioning a polishing pad. In one embodiment, a method for
conditioning a polishing pad includes applying a down force to the
conditioning disk that urges the conditioning disk against the
polishing pad, measuring a torque required to sweep the
conditioning disk across the polishing pad, determining a change in
down force by comparing the measured torque to a model force
profile (MFP), and adjusting the down force that the conditioning
disk applies against the polishing pad in response to the
determined change.
[0007] In another embodiment, a method for conditioning a polishing
pad includes applying a down force to urge a conditioning disk
against a polishing pad, measuring a frictional force generated by
the conditioning disk contacting the polishing pad, comparing the
measured frictional force to a model force profile (MFP) to
determine a change in down force, and adjusting the applied down
force in response to the comparison between the measured frictional
force and the MFP.
[0008] In yet another embodiment, an apparatus conditioning a
polishing pad with a conditioning disk includes a platen adapted to
support the polishing pad, a conditioning head adapted to retain
the conditioning disk, a down force actuator operable to move the
conditioning head in a manner that conditioning head applies a down
force against the polishing pad, an arm coupled to the conditioning
head to support the conditioning head above the platen, a sweep
actuator coupled to the arm and operable to sweep the conditioning
head across the platen, a sweep torque sensor operable to measure a
torque required to sweep the conditioning head across the platen
when the conditioning disk is in contact with polishing pad.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] So that the manner in which the above recited features of
the present invention are attained and can be understood in detail,
a more particular description of the invention, briefly summarized
above, may be had by reference to the embodiments thereof which are
illustrated in the appended drawings.
[0010] FIG. 1 is a sectional view of an exemplary CMP system which
may be used to practice embodiments of the invention.
[0011] FIG. 2 is a top view of the CMP system of FIG. 1.
[0012] FIG. 3 is a flow diagram of one embodiment of a method of
pad conditioning.
[0013] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is contemplated that elements
and features of one embodiment may be beneficially incorporated in
other embodiments without further recitation.
[0014] It is to be noted, however, that the appended drawings
illustrate only exemplary embodiments of this invention and are
therefore not to be considered limiting of its scope, for the
invention may admit to other equally effective embodiments.
DETAILED DESCRIPTION
[0015] Embodiments of the invention are directed towards the
performance of a CMP polishing pad. Embodiments of the disclosure
provide a method and apparatus for controlling a CMP polisher based
on a relationship between conditioning arm sweep torque and
friction between the polishing pad and conditioning disk.
Embodiments include a method for adjusting a down-force (down
force) applied by a conditioning disk to a polishing pad based on a
difference between a measured force and a modeled force profile to
improve processing results. It is contemplated that aspects of the
present disclosure that enable use of conditioner sweep torque to
monitor polisher performance may be applied in real time and/or
when the polishing pad is being conditioned while a substrate is
being polished (i.e., in-situ conditioning), when the polishing pad
is conditioned in-between substrate polishing (i.e., ex-situ
conditioning), or any combination thereof.
[0016] FIG. 1 is a sectional view of one embodiment of an exemplary
CMP system according to certain aspects of the present disclosure.
As shown in FIG. 1, the CMP system comprises a polisher 100 having
a machine base 130, a polishing fluid delivery arm 190, a polishing
pad 104 disposed on a platen 102, a polishing head 106, a
conditioner assembly 122, and a controller 152. The machine base
130 supports the platen 102, the polishing fluid delivery arm 190
and the conditioner assembly 122. The platen 102 supports polishing
head 106.
[0017] The polishing head 106 retains and rotatably contacts a
substrate 118 to the polishing pad 104 during processing. The
polishing head 106 may include a retaining ring 116 which prevents
the substrate 118 from moving out from under the polishing head 106
during polishing. The polishing head 106 may be rotated by a motor
120, thereby rotating the substrate 118 against the polishing pad
104 about a central axis D of the polishing head 106. A sensor 148
may be utilized to obtain a metric of force required to rotate the
substrate 118 against the polishing pad 104.
[0018] The platen 102 is utilized to rotate the polishing pad 104
during processing such that the polishing pad 104 planarizes (or
"polishes") the surface of the substrate 118 disposed on the pad
104. The polishing pad 104 is a consumable product having a
polishing surface and may be secured to the platen 102. The platen
102 and the polishing pad 104 is rotated by a motor 112 coupled to
the platen 102 by a shaft 114. The motor 112 is utilized to move
the polishing pad 104 relative to the substrate 118 retained in the
polishing head 106. In the embodiment depicted in FIG. 1, the motor
112 rotates the platen 102 in the X-Z plane about a central axis A
normal to the platen 102. A sensor 150 may be utilized to obtain a
metric indicative of the force required to rotate the platen 102
and polishing pad 104 relative to the substrate 118 and/or
conditioner assembly 122.
[0019] The polishing fluid delivery arm 190 provides a polishing
fluid to the surface of the polishing pad 104 during polishing. The
polishing fluid may comprise an abrasive-containing polishing
slurry or may comprise an abrasive-free liquid, which may be
reactive.
[0020] The conditioner assembly 122 generally includes a
conditioning head 108, a shaft 126, and an arm 128. The shaft 126
and arm 128 support the conditioning head 108 above the platen 102.
The conditioning head 108 retains a conditioning disk 124 which is
selectively placed in contact with the polishing pad 104 to
condition the surface of the polishing pad 104.
[0021] The shaft 126 is disposed through the machine base 130 of
polisher 100. The shaft 126 may rotate about an axis B normal to
the machine base 130, the rotation facilitated by bearings 132
between the machine base 130 and the shaft 126, such that the arm
128 rotates the conditioning head 108. In one embodiment, a sweep
actuator 144 coupled to the shaft 126 may rotate the shaft 126 to
urge the arm 128 to sweep the conditioning head 108 across the
polishing pad 104.
[0022] The conditioner assembly 122 further includes a sweep torque
sensor 146 to detect sweep torque required to move the conditioning
disk 124 across the surface of the polishing pad 104. In one
embodiment, the sweep torque sensor 146 may be a torque or other
force sensor coupled to the sweep actuator 144. In other
embodiments, the sweep torque sensor 146 may be an electrical
current sensor or pressure sensor coupled to the sweep actuator
144. An electrical current sensor may detect changes in the current
drawn by the sweep actuator 144 as the frictional forces between
the conditioning disk 124 and the polishing pad 104 change. A
pressure sensor may interface with the sweep actuator 144 to detect
changes in the pressure utilized to actuate the sweep actuator 144
as the frictional forces between the conditioning disk 124 and the
polishing pad 104 change. In another embodiment, the sweep actuator
144 may be a direct drive motor configured to provide clean torque
feedback for measurement and control of the pad conditioner sweep
torque. In still other embodiments, the sweep torque sensor 146 may
be any other sensor suitable for providing a metric indicative of
the force required to move the conditioning disk 124 across the
surface of the polishing pad 104.
[0023] The conditioning head 108 rotates the conditioning disk 124
about an axis C disposed normally through the conditioning disk
124. The conditioning disk 124 is fabricated from a material
suitable for conditioning the material of the polishing pad 104.
The conditioning disk 124 may be a brush, polymer or abrasive
surface. In one embodiment, the conditioning disk 124 has a surface
containing abrasive particles such as diamonds or other relatively
hard substance.
[0024] In one embodiment, a motor 134 is utilized to rotate the
conditioning disk 124 relative to the polishing pad 104. In one
embodiment, the motor 134 is disposed in a housing 136 at a distal
end of the arm 128.
[0025] A sensor 138 may detect a torque or rotational force
required to rotate the conditioning disk 124 about the axis C when
the conditioning disk 124 is in contact with the polishing pad 104.
In one embodiment, the sensor 138 may be disposed within the
housing 136. In one embodiment, the sensor 138 may be an electrical
current sensor coupled to the motor 134. The electrical current
sensor may detect changes in the current drawn by the motor 134 as
the frictional forces between the conditioning disk 124 and the
polishing pad 104 change. In another embodiment, the sensor 138 may
be a torque sensor, deflection sensor, or strain gauge, and may be
positioned in the drive train between the motors and the
conditioning head to measure forces on the drive train caused by
friction on the conditioning head.
[0026] A down force actuator 140 is utilized to urge the
conditioning disk 124 against the polishing pad 104. The down force
actuator 140 is configured to selectably set the force applied by
the conditioning disk 124 on the polishing pad 104. In one
embodiment, the down force actuator 140 may be disposed between the
arm 128 and the shaft 126, or in other suitable locations.
[0027] A down force sensor 142 is utilized to detect a metric
indicative of the down force of the conditioning disk 124 applied
against the polishing pad 104. In one embodiment, the down force
sensor 142 may be positioned in-line of the down force actuator
140, or may be placed in other suitable locations.
[0028] In one embodiment, the polisher 100 may optionally include a
pad thickness sensor (not shown) coupled to the conditioning head
108. The pad thickness sensor may be adapted to detect the
thickness of a polishing pad disposed on the platen 102. The pad
thickness sensor may be utilized to determine an end of life of a
polishing pad 104 disposed on the platen 102. In one embodiment,
the pad thickness sensor may be utilized to further provide an
additional feedback signal to the controller 152 to control the
conditioning down force.
[0029] In general, the controller 152 is used to control one or
more components and processes performed in the polisher 100. In one
embodiment, the controller 152 may use sensory data as a feedback
signal to control the rate of material removed from the substrate
118 during processing. The controller 152 may be coupled at various
points to the polisher 100 in order to transmit and receive signals
from various components. For example, the controller 152 may
transmit control signals to motors 112, 120, 134, sweep actuator
144, and down force actuator 140 and receive signals corresponding
to forces detected by sensors 138, 142, 146, 148, 150.
[0030] The controller 152 is generally designed to facilitate the
control and automation of the polisher 100 and typically includes a
central processing unit (CPU) 154, memory 156, and support circuits
(or I/O) 158. The CPU 154 may be one of any form of computer
processors that are used in industrial settings for controlling
various system functions, substrate movement, chamber processes,
process timing and support hardware (e.g., sensors, robots, motors,
timing devices, etc.), and monitor the processes (e.g., chemical
concentrations, processing variables, chamber process time, I/O
signals, etc.). The memory 156 is connected to the CPU 154, and may
be one or more of a readily available memory, such as random access
memory (RAM), read only memory (ROM), floppy disk, hard disk, or
any other form of digital storage, local or remote. Software
instructions and data can be coded and stored within the memory for
instructing the CPU 154. The support circuits 158 are also
connected to the CPU 154 for supporting the processor in a
conventional manner. The support circuits 158 may include cache,
power supplies, clock circuits, input/output circuitry, subsystems,
and the like. A program, or computer instructions, readable by the
controller 152 determines which tasks are performable on a
substrate. Preferably, the program is software readable by the
controller 152 that includes code to perform tasks relating to
monitoring, execution and control of the movement, support, and/or
positioning of a substrate in the polisher 100. In one embodiment,
the controller 152 is used to control robotic devices to control
the strategic movement, scheduling and running of the polisher 100
to make the processes repeatable, resolve queue timing issues and
prevent over- or under-processing of the substrates.
[0031] In operation, as illustrated in FIG. 2, a polishing fluid
202 is provided to the surface of the polishing pad 104 by the
polishing fluid delivery arm 190. The polishing head 106 urges the
substrate 118 against the polishing pad 104. Contact with the
surface of the rotating polishing pad 104 in the presence of the
polishing fluid 202 planarizes the surface of the substrate 118. In
one embodiment, the polishing pad 104 may be operated to planarize
the substrate to remove material from the surface of the substrate
at a pre-determined rate, sometimes referred to as a removal rate,
according to aspects described below.
[0032] Before, during and/or after planarizing the substrate 118,
the polishing pad 104 may be conditioned. During conditioning, the
conditioning head 108 urges the conditioning disk 124 against the
polishing pad 104 with a pre-defined down force. The conditioning
disk 124 rotates relative to the surface of the polishing pad 104
while sweeping back and forth across the polishing pad 104. Contact
between the conditioning disk and polishing pad provides the
surface of the polishing pad with texture suitable for maintaining
a removal rate of the substrate. The interaction of the
conditioning disk 124 with the polishing pad 104 generates
frictional forces which may be detected as described below.
According to one embodiment, the removal rate of the polishing pad
and frictional forces exerted on the conditioning disk may be
directly related to the conditioning down force. As such, removal
rate may be estimated based on the frictional forces observed for a
particular down force.
[0033] FIG. 3 is a flow diagram of a method 300 that may be
performed using the polisher 100 in accordance with aspects of the
present disclosure. It is contemplated that the method 300 that may
be performed using other suitable CMP systems and apparatuses.
[0034] At 302, the conditioning disk 124 is urged against the
polishing pad 104 using a down force. The down force of the
conditioning disk 124 against the polishing pad 104 may be measured
to provide feed-back to the force actuator 140. In one embodiment,
the down force is measured using a metric provided by the down
force sensor 142. The measured down force may take into account the
weight of the conditioning head 108.
[0035] At 304, a force required to move the conditioning disk 124
relative to the polishing pad 104 is measured. The force required
to move the conditioning disk 124 relative to the polishing pad 104
is defined herein as either a force or a torque. In one embodiment,
the force or torque required to sweep the conditioning disk across
the polishing pad is measured utilizing a metric providing by the
sweep torque sensor. The sweep torque may vary over time as a
result of the change in resistive frictional forces between the
conditioning disk and the polishing pad as one or both of the
conditioning disk and the polishing pad wear, and/or process
conditions change. If the conditioning process is not changed over
time, the measured sweep torque may decrease over the lifetime of a
conditioning disk as the conditioning disk wears and its effective
cut rate gradually reduces. As such, according to aspects described
below, by using the sweep torque as a feedback signal, the down
force may be adjusted to compensate for the worn conditioning disk,
thereby improving the conditioning process to maintain a constant
removal rate. In another embodiment, a frictional force between the
conditioning disk 124 and the polishing pad 104 generates a
resistive force that may be detected by monitoring changes in the
forces required to rotate at least one of the conditioning disk 124
and/or the polishing pad 104. In another embodiment, a frictional
force between the substrate 118 and the polishing pad 104 generates
a resistive force that may be measured by one or more of the
sensors 138, 142, 146, 148 and 150 described above. It is
understood that, in one embodiment, any of the above-described
frictional forces may be used as a feedback signal to maintain a
constant removal rate.
[0036] At 306, the force measured at 304 may be compared to a model
force profile (MFP) to determine a change in down force required to
maintain a uniform removal. In the case that torque is the force
measured at 306, the MFP is a model torque profile (MTP). For the
sake of brevity, reference to MFP here is intended MTP when
applicable. In one embodiment, the controller may compare the
measured force or torque to a model force profile to determine a
change in down force. In one embodiment, a new down force suitable
to maintain a constant removal rate of material from the substrate
may be calculated based on the MFP. In one embodiment, the new down
force may be utilized during processing of the substrate as a close
loop control routine. In another embodiment, the new down force
value may be utilized for the next substrate to be processed as a
feed back control routine. The MFP permits calculation of the new
down force, given an amount of measured force and a desired rate of
removal. In most applications, it has been determined that the MFP
involved with maintaining a constant removal rate is non-linear,
and thus, the change in torque is not linearly proportional to a
change in the down force. It is contemplated that for certain
process conditions, the change in torque may be linearly
proportional to a change in the down force.
[0037] According to one embodiment, a new down force may be
determined to improve polishing pad lifetimes. Polishing pad wear
may be lessened by determining a reduced initial down force that is
nonetheless suitable to achieve a specified sweep torque target.
Excessive polishing pad wear due to over-conditioning may be
avoided by utilizing reduced initial down force values when the
conditioning disk is new, and the down force may be increased to
maintain polishing performance as the surface of the conditioning
disk wears.
[0038] At 308, the down force may be adjusted in response to the
difference between the measured force and the MFP. In one
embodiment, the down force may be adjusted in response to the
difference between the measured torque and a MFP. In one
embodiment, a control signal may be transmitted to a down force
actuator to increase the down force exerted on the conditioning
disk. In another embodiment, a control signal may be transmitted to
the down force actuator to decrease the down force to reduce
excessive wear on the polishing pad and conditioning disk. It is
contemplated that a down force upper limit may be predefined to
limit the amount of the down force applied by the down force
actuator.
[0039] The new down force may be adjusted while a substrate is
currently undergoing processing, as a closed loop control routine,
or may be adjusted for the next substrate to be processed, as a
feedback control routine.
[0040] The MFP may be generated through empirical evidence, prior
experimentation and testing, modeling, calculating, or may be
provided as a reference curve with the specification of the
conditioning disk. Generally, it has been determined that the
relationships between removal rate, sweep torque, and down force
may evolve as a conditioning disk ages. As the surface of the
conditioning disk experiences greater wear, the removal rate
consequently decreases for a fixed conditioning down force.
Accordingly, higher down force values would be used to provide the
same level of disruption or regeneration of the polishing pad
surface, and to maintain a constant removal rate, the conditioning
down force may be increased periodically.
[0041] According to certain aspects, it has also been determined
that the relationship between sweep torque and conditioning down
force may follow a similar trend with continued use of a
conditioning disk. For a fixed conditioning down force, the
frictional forces between the conditioning disk and polishing pad
decreases as the abrasive surface of the conditioning disk wears,
leading to a reduced torque experienced by a sweep actuator. The
reduction in sweep torque may indicate a decrease in pad
conditioning effectiveness due to wear of the abrasive surface.
Similarly, it has been determined that the relationship between
removal rate and conditioning sweep torque also evolves over the
life of the conditioning disk. A worn conditioning disk may less
effectively condition a polishing pad which results in a reduced
removal rate over time.
[0042] According to certain aspects, a MFP may be developed using
analysis of two different data sets. A first data set may be
derived using a design of experiments performed using conditioning
disks at different stages of wear. The root mean square (RMS) of
sweep torque may be measured for every down force condition, along
with a blanket substrate removal rate. A second dataset may be a
marathon run of blanket substrates where the down force was changed
in a step-wise fashion, using a manual CLC. In one embodiment, a
down force applied may begin at 3 lb down force and may increase to
11 lb down force over the course of processing 2,500 substrates.
The RMS of sweep torque may be measured on every substrate while
the blanket RR may be measured less frequently. These two data sets
may be combined and a least squares estimation technique or any
other suitable data fitting technique may be used to estimate a
model force profile between the RMS sweep torque (T), down force
(DF), and blanket RR. In one embodiment, the structure of the model
may be as follows:
Log.sub.e(T)=b*Log.sub.e(RR)+a*Log.sub.e(DF) (1)
where a and b are constants obtained from a least squares
estimation. In one specific example, the values b and a calculated
for an oxide CMP system utilizing a low down force conditioning arm
manufactured by Applied Material, are 0.228 and 0.3, respectively.
The constants b and a may be selected for specific pad materials,
polishing fluids, substrate material being polished, among other
criteria.
[0043] The Equation 1 may also be rewritten as:
Log e ( T ) - Log e ( DF ) a = Log e ( RR ) b Log e ( T DF a ) =
Log e ( RR ) b ( 2 ) ##EQU00001##
[0044] For a constant RR=k, the equation may be reduced as
follows:
Log e ( T DF a ) = Log e k ( 3 ) ( T DF a ) = k 1 , or ( 4 ) T = k
1 * DF a ( 5 ) ##EQU00002##
[0045] Equation 5 illustrates a model force profile for a target
sweep torque as a function of down force to achieve a constant
removal rate.
[0046] Thus, a methodology has been provided to maintain constant
removal rates over the life of a conditioning disk. Embodiments of
the invention advantageously compensate for loss of conditioning
effectiveness to maintain a desired process performance. The
methodology may be utilized in-situ as a running process, or as a
feedback routine to substantially eliminate process drift.
Additionally, embodiments of the invention advantageously extend
the useful lifetime of polishing pads by determining a reduced down
force still sufficient to achieve a specified sweep torque target.
Consequently, embodiments of the invention advantageously reduce
excessive polishing pad wear due to over-conditioning, for example,
when the conditioning disk is new and freshly abrasive. According
to certain embodiments, the pad lifetime may be improved by 20% to
60% over conventional approaches. Likewise, it is understood that
embodiments of the invention advantageously increase the useful
lifetime of conditioning disks.
[0047] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow. For
example, while the foregoing is directed to embodiments of the
present invention focused on a sweep torque of a conditioning disk,
it is contemplated that torques measured throughout a CMP system,
such as at other motors or actuators, may be used to determine a
model force profile for controlling the polisher.
* * * * *