U.S. patent application number 11/002535 was filed with the patent office on 2005-07-14 for system and method for monitoring quality control of chemical mechanical polishing pads.
This patent application is currently assigned to PsiloQuest. Invention is credited to Obeng, Yaw S..
Application Number | 20050153631 11/002535 |
Document ID | / |
Family ID | 34742284 |
Filed Date | 2005-07-14 |
United States Patent
Application |
20050153631 |
Kind Code |
A1 |
Obeng, Yaw S. |
July 14, 2005 |
System and method for monitoring quality control of chemical
mechanical polishing pads
Abstract
The present invention provides a method for predicting a
performance characteristic of a chemical mechanical polishing (CMP)
pad. The method comprises providing a CMP pad having a polishing
surface and measuring a frictional property of the polishing
surface. The method further includes estimating a performance
characteristic of the CMP pad based on the frictional property.
Other aspects of the present invention include a quality control
system for monitoring chemical mechanical polishing pad
performance.
Inventors: |
Obeng, Yaw S.; (Orlando,
FL) |
Correspondence
Address: |
HITT GAINES P.C.
P.O. BOX 832570
RICHARDSON
TX
75083
US
|
Assignee: |
PsiloQuest
Orlando
FL
|
Family ID: |
34742284 |
Appl. No.: |
11/002535 |
Filed: |
December 2, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60536136 |
Jan 13, 2004 |
|
|
|
Current U.S.
Class: |
451/5 ; 451/41;
451/56 |
Current CPC
Class: |
B24B 37/04 20130101;
B24B 49/16 20130101 |
Class at
Publication: |
451/005 ;
451/041; 451/056 |
International
Class: |
B24B 049/00 |
Claims
What is claimed is:
1. A method for predicting a performance characteristic of a
chemical mechanical polishing pad, comprising: providing a chemical
mechanical polishing (CMP) pad having a polishing surface;
measuring a frictional property of said polishing surface; and
estimating a performance characteristic of said CMP pad based on
said frictional property.
2. The method as recited in claim 1, wherein said frictional
property comprises a static coefficient of friction.
3. The method as recited in claim 1, wherein said frictional
property comprises a dynamic coefficient of friction.
4. The method as recited in claim 1, wherein said CMP pad comprises
a thermoplastic foam substrate comprising a blend of a crosslinked
ethylene vinyl acetate copolymer and a low-density polyethylene
copolymer, and said polishing surface comprises concave cells.
5. The method as recited in claim 1, wherein estimating said
performance characteristic comprises comparing said frictional
property to a database, wherein said database provides a functional
relationship between said frictional property and said performance
characteristic.
6. The method as recited in claim 1, wherein said performance
characteristic comprises a removal rate of a material from a
substrate.
7. The method as recited in claim 6, wherein said material
comprises a metal layer, a barrier layer, a dielectric films, or
combinations thereof.
8. The method as recited in claim 7, wherein said metal layer
comprises a refractory metal or a noble metal.
9. The method as recited in claim 1, wherein said performance
characteristic comprises a within substrate uniformity.
10. The method as recited in claim 1, wherein said frictional
property is measured using a detector comprising a tribometer and
said performance characteristic is estimated using a controller
comprising a computer.
11. A quality control system for monitoring chemical mechanical
polishing pad performance, comprising: a detector configured to
determine a frictional property of a surface of a chemical
mechanical polishing (CMP) pad; and a controller coupled to said
detector and configured to estimate a performance characteristic of
said CMP pad surface based on said frictional property.
12. The quality control system as recited in claim 11, wherein said
frictional property comprises a static coefficient of friction.
13. The quality control system as recited in claim 11, wherein said
frictional property comprises a dynamic coefficient of
friction.
14. The quality control system as recited in claim 11, wherein said
CMP pad comprises a thermoplastic foam substrate comprising a blend
of a crosslinked ethylene vinyl acetate copolymer and a low-density
polyethylene copolymer, and said polishing surface comprises
concave cells.
15. The quality control system as recited in claim 11, wherein said
controller adjusts one or more polishing parameter of a polishing
apparatus coupled to said controller, based on said estimated
performance characteristic.
16. The quality control system as recited in claim 15, wherein said
controller adjusts one or more polishing parameter for a subsequent
batch of wafers based on said estimated performance characteristic
for a previous batch of wafers.
17. The quality control system as recited in claim 15, wherein said
polishing parameter comprises a rotational speed of a platen of
said polishing apparatus.
18. The quality control system as recited in claim 15, wherein said
polishing parameter comprises a rotational speed of a carrier head
of said polishing apparatus.
19. The quality control system as recited in claim 15, wherein said
polishing parameter comprises a down-force imparted by a carrier
head against said CMP pad surface.
20. The quality control system as recited in claim 15, wherein said
polishing parameter comprises a duration of polishing.
21. The quality control system as recited in claim 11, wherein said
controller rejects a chemical mechanical polishing pad produced by
a manufacturing apparatus coupled to said controller based, on said
estimated performance characteristic.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/536,136 entitled, "SYSTEM AND METHOD FOR
MONITORING QUALITY CONTROL OF CHEMICAL MECHANICAL POLISHING PADS,"
filed on Feb. 5, 2004, and incorporated by reference as if
reproduced herein in its entirety.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention is directed to a method and a system
for estimating a chemical mechanical polishing pad's performance
characteristics based on the frictional properties of the polishing
pad.
BACKGROUND OF THE INVENTION
[0003] Chemical mechanical polishing (CMP) has been successfully
used for planarizing both metal and dielectric films. In one
plausible mechanism of planarizing, the polishing process is
thought to involve intimate contact between high points on a wafer
surface and a polishing pad material in the presence of slurry. In
this scenario, corroded materials, produced from reactions between
the slurry and wafer surface being polished, are removed by
shearing at the pad-wafer interface. The elastic properties of pad
material significantly influence the final planarity and polishing
rate. In turn, the elastic properties are a function of both the
intrinsic polymer and its foamed structure.
[0004] Despite considerable effort to produce polishing pads with
identical polishing characteristics, there are variations from pad
to pad. This, in turn, causes undesirable variations in the extent
of material removed, or in the planarity, of the wafer surfaces
being polished. It would be highly desirable to be able to predict
the performance characteristics of polishing pads a priori, that
is, before it is used for polishing or during polishing itself.
This goal has proven difficult to achieve, however.
[0005] Historically, polyurethane-based polishing pads have been
used for CMP because of their high strength, hardness, modulus and
high elongation at break. Because the performance characteristics
of polyurethane-based pads change as the pad decomposes, it has
proven difficult to predict the polishing characteristics of
polishing pad prior to, or during, their use. While
polyurethane-based pads can achieve both good uniformity and
efficient topography reduction, their ability to rapidly and
uniformly remove surface materials declines as a function of use.
The decline in the polishing performance of polyurethane-based pads
has been attributed to changes in the mechanical response of the
pad under conditions of critical shear. It is generally believed
that the loss in functionality of polyurethane-based CMP pads is
due to pad decomposition from the interaction between the pad and
the slurries used in the polishing. Additionally, decomposition
produces a surface modification in and of itself in the case of the
polyurethane pads which can be detrimental to uniform
polishing.
[0006] Traditional measures to maintain quality control of
polishing have been directed to intermittently testing individual
wafers after being polished. For instance, post-polishing
measurements can be used to determine if material removal rates and
surface uniformity remain within an acceptable range. If the
tolerance range is exceeded, then the polishing pad is either
reconditioned or replaced. Polyurethane pads generally require a
break-in period before polishing, in addition to the reconditioning
and retreatment after a period of use. Moreover, it is often also
necessary to keep traditional pads wet while the polishing
equipment is in idle mode. These characteristics undesirably reduce
the overall efficiency of CMP when using polyurethane or similar
conventional pads.
[0007] Accordingly, what is needed is a method and system of
estimating the performance characteristics of CMP polishing pads,
and a system of implementing the method so as to provide more
consistent polishing.
SUMMARY OF THE INVENTION
[0008] To address the above-discussed deficiencies of the prior
art, the present invention provides in one embodiment, a method for
predicting a performance characteristic of a CMP pad. The method
comprises providing a CMP pad having a polishing surface and
measuring a frictional property of the polishing surface. The
method further comprises estimating a performance characteristic of
the CMP pad based on the frictional property.
[0009] Another embodiment of the present invention is directed to a
quality control system for monitoring CMP pad performance. The
system comprises a detector configured to determine a frictional
property of a surface of a CMP pad. The system further comprises a
controller coupled to the detector, the controller configured to
estimate a performance characteristic of the CMP pad surface based
on the frictional property.
[0010] The foregoing has outlined preferred and alternative
features of the present invention so that those skilled in the art
may better understand the detailed description of the invention
that follows. Additional features of the invention will be
described hereinafter that form the subject of the claims of the
invention. Those skilled in the art should appreciate that they can
readily use the disclosed conception and specific embodiment as a
basis for designing or modifying other structures for carrying out
the same purposes of the present invention. Those skilled in the
art should also realize that such equivalent constructions do not
depart from the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] For a more complete understanding of the present invention,
reference is now made to the following descriptions taken in
conjunction with the accompanying drawings, in which:
[0012] FIG. 1 illustrates by flow diagram, an exemplary method for
predicting a performance characteristic of a chemical mechanical
polishing pad;
[0013] FIG. 2 presents an exemplary quality control system for
monitoring chemical mechanical polishing pad performance;
[0014] FIG. 3 presents exemplary data showing the change in
relative Blanket Tungsten Removal Rate (WRR) and the Mean Static
Coefficient of Friction (SCOF) obtained for thermoplastic foam
polishing pads as a function of coating time with TEOS; and
[0015] FIG. 4 presents exemplary data showing the relationship
between Blanket Tungsten Removal Rate (W-RR) and Mean Static
Coefficient of Friction (SCOF) and Dynamic Coefficient of Friction
(DCOF) for exemplary thermoplastic foam polishing pads.
DETAILED DESCRIPTION
[0016] The present invention benefits from discoveries made during
the course of characterizing the physical properties of novel
polishing pads. The pad's frictional properties were determined as
part of a battery of physical measurements to characterize the
polishing pads. It was accidentally discovered that the frictional
properties of the polishing pad's surface had a significant
correlation with the polishing properties of individual polishing
pads. This, in turn, led to the realization that surface frictional
properties can be generally used to predict the performance
characteristics of chemical mechanical polishing pads. The ability
to make such a priori predictions allows one to eliminate pads
whose predicted performance is outside of an acceptable tolerance,
or to modify polishing parameters to compensate for variations in
polishing performance.
[0017] The term performance characteristic as used herein refers to
any conventional quantitative measure of polishing performance,
including but not limited to: removal rate of material from a
substrate, within-substrate polishing uniformity (also commonly
referred to as within-wafer-non-uniformity, WIWNU), or the extent
or dishing, erosion, or defects on a polished substrate. The term
substrate as used herein refers to any material upon which a
microelectronic device can be formed, such as a semiconductor
device on a silicon wafer, and well as metal layers, barrier
layers, dielectric films, or combinations thereof, or other
material layers formed on the substrate's surface.
[0018] One aspect of the present invention, illustrated by the
exemplary flow diagram in FIG. 1, is a method 100 for predicting a
performance characteristic of a CMP pad. The method 100 comprises
in step 105, providing a CMP pad having a polishing surface. The
method 100 further comprises in step 110, measuring a frictional
property of the CMP pad's polishing surface. The method 100 also
comprises estimating, in step 115, a performance characteristic of
the CMP pad, based on the frictional property.
[0019] The measurement of the CMP pad's frictional properties can
be performed at any number of different times. In certain preferred
embodiments, the frictional property of the CMP pad's polishing
surface is measured in step 120 shortly after pad manufacture. In
some advantageous embodiments, the frictional property of the CMP
pad is measured in step 125, prior to use for CMP. In some case,
for example, the frictional property is measured in step 125 after
pad conditioning and just prior to CMP. In other advantageous
embodiments, the frictional property is measured in step 130,
during CMP of a substrate surface.
[0020] Any conventional measurement can be used to quantify the CMP
pad's frictional properties in step 110. In some preferred
embodiments, for instance, the frictional property measured in any
of steps 120, 125, 130 is a coefficient of friction (COF). The COF
can comprise a static COF, a dynamic COF or both, measured by any
number of conventional procedures well known to those of ordinary
skill in the art. Some preferred methods of measuring the static
COF and dynamic COF are presented in the Example section to follow.
In some cases, for example, the frictional property is measured
using a detector comprising a tribometer. In some preferred
embodiments, a static COF is measured in step 120 after pad
manufacture or in step 125 prior to polishing. In other preferred
embodiments, the dynamic COF is measured in step 125 or step 130,
before or during polishing, respectively.
[0021] In some preferred embodiments of the method 100, estimating
the performance characteristic in step 115 comprises comparing, in
step 135, the frictional property to a database. The database
provides a functional relationship between the frictional property
and the performance characteristic. The functional relationship is
then used to predict a performance characteristic, based on the
frictional property for a particular pad.
[0022] By way of example, the database can comprise the removal
rate of tungsten from a substrate surface for a plurality of CMP
pads having different COFs. Such a database can be empirically
determined in step 140 by producing a plurality of CMP pads having
surfaces with different COFs. The COF of the pad's surface can be
altered by changing one or more of: the composition of the material
comprising the polishing pad, the number or size of concave cells
on the thermoplastic foam polishing body of the pad, or the
composition of the polishing agent coating the interior surface of
the concave cells of the thermoplastic foam. For example, the
composition of the polishing agent can be altered by changing the
duration for which the interior surface of the concave cells is
coated with the polishing agent. In some instances, the longer the
coating time, the greater the COF of the pad surface.
[0023] Continuing with the determination of the database in step
140, a set of polishing pads having different frictional properties
, e.g., COFs, is used to polish tungsten-coated test substrate
wafers under standardized polishing conditions. The standardized
polishing conditions can comprise the polishing slurry composition,
slurry flow rate, the down force, table speed, backside pressure,
carrier speed of a rotational polishing platform coupled to the
polishing pad, or any other condition that effect the performance
characteristic of interest. After a period of polishing, the test
substrate wafers are then measured to determine the performance
characteristic, such as tungsten removal rate.
[0024] Conventional graphical or statistical procedures are then
used to elucidate the causal relationship between the frictional
property and the performance characteristic in step 145. For
instance, the relationship between the COF and a tungsten removal
rate can be represented graphically, such as illustrated in the
Example section below, or by one or more linear or nonlinear
equations that are fit to the database using linear or non-linear
regression analysis. Such graphs or equations can then be used to
predict the tungsten removal rate of an individual CMP pad based on
the COF for a particular pad, as per step 115.
[0025] Of course, the performance characteristic estimated in step
115 can comprise the rate of removal of any number of materials on
the substrate surface. Such materials include silicon wafers having
a metal layer comprising a refractory metal, such as tungsten,
nickel, or aluminum, or a noble metal, such as copper, gold,
platinum, iridium, ruthenium, cobalt, osmium or silver, and
combinations thereof. Such materials also include a dielectric
layer, such as silicon oxide or a barrier layer, such as tantalum,
metal silicides, such as nickel silicide, or polysilicon and
combinations thereof. Alternatively, the performance characteristic
can be some other indicator of polishing such as the WIWNU of a
substrate's surface after CMP using the pad, or other indicators
such as dishing, erosion, or defectivity.
[0026] In some preferred embodiments, the performance
characteristic is estimated in step 115 using a controller
comprising a computer system. The computer system can comprise a
memory unit capable of storing the database determined in step 140
and processing circuitry configured to determine the causal
relationship between the frictional property and the performance
characteristic from the database as per step 145, and compare the
measured frictional property of the instant pad to the database as
per step 135.
[0027] In some embodiments of the method 100, the predicted
performance characteristic is used to accept or eliminate CMP pads,
in step 150, whose predicted performance is outside of an
acceptable tolerance. For example, the controller, upon estimating
that a performance characteristic for a pad is outside of an
acceptable tolerance, would signal a pad manufacturing system in
step 150 to reject the pad for packaging and shipping to an
end-user.
[0028] In other embodiments, the predicted performance
characteristic is used to modify polishing parameters, in step 160,
to compensate for predicted deviations from a desired polishing
performance. For example, the controller, upon estimating that a
performance characteristic for a pad is outside of an acceptable
tolerance, may signal a polishing system to extend a polishing time
because the predicted removal rate is below an acceptable tolerance
range. As a further example, in some preferred embodiments the
controller adjusts one or more polishing parameter for a subsequent
batch of wafers based on said estimated performance characteristic
for a previous batch of wafers.
[0029] While the method 100 can be applied to estimate the
polishing parameters of any conventional CMP pad, the method is
particularly advantageous when the CMP pad provided in step 105
comprises a polishing body comprising a thermoplastic foam
substrate. While not limiting the scope of the present invention by
theory, it is believed that the static COF provides a measure of
the inherent physical properties of thermoplastic foam substrates.
The dynamic COF is believed to provide a measure of the
hydrodynamic properties of the CMP pads comprising such
thermoplastic foam substrates.
[0030] In particular, certain preferred embodiments of the
polishing pad provided in step 105 comprises a thermoplastic foam
substrate having a polishing surface comprising concave cells. In
other embodiments, a polishing agent coats an interior surface of
the concave cells of the polishing pad. Some advantageous polishing
pads are described in: U.S. patent application Ser. No. 10/000,101,
entitled, "THE SELECTIVE CHEMICAL-MECHANICAL POLISHING PROPERTIES
OF A CROSS LINKED POLYMER AND SPECIFIC APPLICATIONS THEREFOR," to
Yaw S. Obeng and Edward M. Yokely, filed Oct. 24, 2001; U.S. Pat.
No. 6,579,604, entitled "A METHOD OF ALTERING AND PRESERVING THE
SURFACE PROPERTIES OF A POLISHING PAD AND SPECIFIC APPLICATIONS
THEREFOR," to Yaw S. Obeng and Edward M. Yokely; its continuation
in part, U.S. Pat. No. 6,706,383, entitled "A POLISHING PAD SUPPORT
THAT IMPROVES POLISHING PERFORMANCE AND LONGEVITY" to Yaw S. Obeng
and Peter A. Thomas; its continuation application Ser. No.
10/641,866, filed Aug. 15, 2003; and its continuation-in-part U.S.
patent application Ser. No. 10/___,___, entitled, "A POLISHING PAD
WITH HIGH SELECTIVITY FOR BARRIER POLISHING," to Yaw S. Obeng,
filed Oct. 10, 2004, all of which are incorporated by reference
herein in their entirety.
[0031] In some preferred embodiments, for example, the
thermoplastic foam substrate provided in step 105 can comprise
cross-linked polyolefins, such as polyethylene, polypropylene, and
combinations thereof. In some cases, the thermoplastic foam
substrate comprises a closed-cell foam of crosslinked homopolymer
or copolymers. Examples of closed-cell foam crosslinked
homopolymers comprising polyethylene (PE) include: Volara.TM. and
Volextra.TM. from Voltek (Lawrence, Mass.); Aliplast.TM., from JMS
Plastics Supply, Inc. (Neptune, N.J.); or Senflex T-Cell.TM.
(Rogers Corp., Rogers, Conn.). Examples of closed-cell foams of
crosslinked copolymers comprising polyethylene and ethylene vinyl
acetate (EVA) include: Volara.TM. and Volextra.TM. (from Voltek
Corp.); Senflex EVATM (from Rogers Corp.); and J-foam.TM. (from JMS
Plastics JMS Plastics Supply, Inc.).
[0032] In other preferred embodiments, the closed-cell
thermoplastic foam substrate provided in step 105 comprises a blend
of crosslinked ethylene vinyl acetate copolymer and a low-density
polyethylene copolymer (preferably between about 0.1 and about 0.3
gm/cc). In yet other advantageous embodiments, the blend has a
ethylene vinyl acetate:polyethylene weight ratio between about 1:9
and about 9:1. In certain preferred embodiments, the blend
comprises ethylene vinyl acetate ranging from about 5 to about 45
wt %, preferably about 6 to about 25 wt % and more preferably about
12 to about 24 wt %. Such blends are thought to be conducive to the
desirable production of concave cells having a small size as
further discussed below. In still more preferred embodiments, the
blend has a ethylene vinyl acetate:polyethylene weight ratio
between about 0.6:9.4 and about 1.8:8.2. In even more preferred
embodiments, the blend has an ethylene vinyl acetate:polyethylene
weight ratio between about 0.6:9.4 and about 1.2:8.8.
[0033] In some instances, as further disclosed in the above-cited
U.S. Pat. No. 6,706,383, the thermoplastic foam substrate provided
in step 105 has cells formed throughout the substrate. In certain
preferred embodiments, the cells are substantially spherical. In
other preferred embodiments, the size of the cells are such that,
on skiving the substrate, the open concave cells at the surface of
the substrate have an average size between about 100 microns and
600 microns. The average size of the concave cells ranges from
about 100 to about 350 microns, preferably about 100 to about 250
microns and more preferably about 115 to about 200 microns. Cell
size may be determined using standard protocols, developed and
published by the American Society for Testing and Materials (West
Conshohocken, Pa.), for example, such as ASTM D3576, incorporated
herein by reference.
[0034] The polishing agent can comprise one or more ceramic
compounds or one or more organic polymers, resulting from the
grafting of the secondary reactants on the substrate's surface, as
disclosed in the above-cited U.S. Pat. No. 6,579,604. In some
preferred embodiments, the polishing agent comprises an inorganic
metal oxide that includes nitrides or carbides, as disclosed in
U.S. patent application Ser. No. 10/685,219 entitled, "A CORROSION
RETARDING POLISHING SLURRY FOR THE CHEMICAL MECHANICAL POLISHING OF
COPPER SURFACES" to Yaw S. Obeng, filed on Oct. 14, 2003, and
incorporated herein by reference in its entirety.
[0035] In some preferred embodiments, the ceramic polishing agent
can comprise an inorganic metal oxide resulting when an
oxygen-containing organometallic compound is used as the secondary
reactant to produce a grafted surface. For example, the secondary
plasma mixture may include a transition metal such as titanium,
manganese, or tantalum. However, any metal element capable of
forming a volatile organometallic compound, such as a metal ester
containing one or more oxygen atoms, and capable of being grafted
to the polymer surface is suitable. Silicon may also be employed as
the metal portion of the organometallic secondary plasma mixture.
In these embodiments, the organic portion of the organometallic
reagent may be an ester, acetate, or alkoxy fragment. In preferred
embodiments, the polishing agent is selected from a group of
ceramics consisting of Silicon Oxides and Titanium Oxides, such as
Silicon Dioxide and Titanium Dioxide; Tetraethoxy Silane (TEOS)
Polymer; and Titanium Alkoxide Polymer.
[0036] Another aspect of the present invention is a quality control
system for monitoring CMP pad performance. FIG. 2 presents an
exemplary quality control system 200 that applies the principles of
the present invention. The system 200 can be configured to
implement any of the embodiments of the method for predicting a
performance characteristic of a chemical mechanical polishing pad,
such as illustrated in FIG. 1 and described above.
[0037] The system 200 comprises a detector 210 configured to
determine a frictional property of a CMP pad 220. The term detector
210, as used herein, refers to any device capable of quantifying
the frictional properties of a polishing pad surface 225. In
certain preferred embodiments, for example, the detector 210
comprises a tribometer configured to measure static or dynamic COF,
or both.
[0038] The system 200 also comprises a controller 230 coupled to
the detector 210 and configured to estimate a performance
characteristic of the CMP pad 220 based on the frictional property
of the pad's surface 225. In some embodiments, the controller 230
comprises an input device 235 configured to receive a signal 240
from the detector 210, the signal 240 comprising information about
the pad's frictional property. The input device 235 is further
coupled to a computer system 250 of the controller 230.
[0039] The computer system 250 can comprise any conventional
processing devices well known to those skilled in the art, to
facilitate performing operations needed to estimate the pad's
performance characteristic. Preferred embodiments of the computer
system 250 comprise a central processing unit coupled via a bus to
a memory. The computer system 250 further comprises storage
circuitry 255 comprising various peripheral devices well known to
one skilled in the art for storing and providing data. Non-limiting
examples of storage circuitry 255 include floppy, hard, CD or
optical drives. The storage circuitry 255 can store a plurality of
files, including the above-described database relating the
frictional property to a performance characteristic, and a program
file comprising a conventional programming language.
[0040] The computer system 250 is programmed to estimate a
performance characteristic by applying the program file to the
database, provided by the storage circuitry 255, and the frictional
property, provide by the input device 235. For instance,
information in the program file and the database can be loaded into
the memory of the computer system, thereby programming the computer
processor to estimate the performance characteristic based on the
frictional property, in accordance with step 115 in FIG. 1.
[0041] The controller 230 can further comprise an output device 260
coupled to the computer system 240, thereby coupling the controller
230 to other components of the quality control system 200. In some
instances, for example, the output device 260 couples the
controller 230 to a pad manufacturing apparatus 270 of the quality
control system 200. In some preferred embodiments, the computer
system 240 is further programmed to send an alert signal 275, via
the output device 260, to the manufacturing apparatus 270. The
alert signal 275 instructs the manufacturing apparatus 270 to
accept or reject the polishing pad 220, depending on whether or not
the estimated performance characteristic is within or outside of a
predefined range.
[0042] In other embodiments, the output device 260 couples the
controller 230 to a polishing apparatus 280 of the quality control
system 200. In some preferred embodiments, the computer system 240
is further programmed to send a control signal 285, via the output
device 260, to the polishing apparatus 280. The control signal 285
instructs the polishing apparatus 280 to retain or modify any
number of polishing parameters depending on whether or not the
estimated performance characteristic is within or outside of a
predefined range. Non-limiting examples of polishing parameters
that can be modified include: a rotational speed of a platen of the
polishing apparatus 280 that holds the polishing pad 220; a
rotational speed of a carrier head of the polishing apparatus 280
that holds a substrate to be polished; a down force imparted by the
carrier head when positioned against the polishing platen; or a
duration of polishing time.
[0043] Having described the present invention, it is believed that
the same will become even more apparent by reference to the
following experiments. It will be appreciated that the experiments
are presented solely for the purpose of illustration and should not
be construed as limiting the invention. For example, although the
experiments described below may be carried out in a laboratory
setting, one skilled in the art could adjust specific numbers,
dimensions and quantities up to appropriate values for a full-scale
plant setting.
Experiments
[0044] Experiments were conducted to: 1) characterize the chemical
composition of thermoplastic foam substrates coated with polishing
agents as a function of coating time; 2) characterize the
mechanical properties of the foam substrate coated with polishing
agents; and 3) measure the polishing properties of the polishing
pads coated with the polishing agent.
[0045] A thermoplastic foam substrate was formed into circular
polishing pads of approximately 120 cm diameter of about 0.3 cm
thickness. The commercially obtained thermoplastic foam substrate
(J-foam from JMS Plastics, Neptune N.J.), designated as "J-60SE,"
comprised a blend of about 18% EVA, about 16 to about 20% talc, and
balance polyethylene and other additives, such as silicates,
present in the commercially provided substrate. The J-60 sheets
were skived with a commercial cutting blade (Model number D5100 K1,
from Fecken-Kirfel, Aachen, Germany). The sheets were then manually
cleaned with an aqueous/isopropyl alcohol solution.
[0046] The J-60SE substrate was then coated with a polishing agent
comprising Tetraethoxy Silane (TEOS), by placing the skived
substrate into a reaction chamber of a conventional commercial
Radio Frequency Glow Discharge (RFGD) plasma reactor having a
temperature controlled electrode configuration (Model PE-2;
Advanced Energy Systems, Medford, N.Y.). The plasma treatment of
the substrate was commenced by introducing the primary plasma
reactant, Argon, for 30 seconds within the reaction chamber
maintained at 350 mTorr. The electrode temperature was maintained
at 30.degree. C., and a RF operating power of 300 Watts was used.
Subsequently, the secondary reactant was introduced, for periods
ranging from about 0 to about 45 minutes at 0.10 SLM, and
comprising TEOS mixed with He or Ar gas. The amount of secondary
reactant in the gas stream was governed by the vapor back-pressure
(BP) of the secondary reactant monomer at the monomer reservoir
temperature (MRT; 50.+-.10.degree. C.).
[0047] In some experiments the polishing properties of the J60SE
polishing pads were examined by polishing wafers having an about
4000 Angstrom thick tungsten surface and an underlying about 250
Angstrom thick titanium nitride barrier layer. Tungsten polishing
properties were assessed using a commercial polisher (Product No.
EP0222 from Ebara Technologies, Sacramento, Calif.). Unless
otherwise noted, the removal rate of tungsten polishing was
assessed using a down force of about 25 kPa of substrate, table
speed of about 100 to about 250 rpm. A conventional slurry (Product
Number MSW2000, from Rodel, Newark Del.) adjusted to a pH of about
2 was used.
[0048] In other experiments, the static coefficient of friction
(SCOF) of the polishing pads was measured before polishing using a
hand-held tribometer (Heidon Tribogear .mu.s Type 94i, Kett US,
Villa Park, Calif.). The dynamic coefficient of friction (DCOF) was
measured using a CETR CP-4 bench top CMP tester (CETR, Inc.,
Campbell, Calif.), under polishing conditions substantial similar
to that described above. The DCOF was filtered using the wavelet
transform technique.
[0049] FIG. 3 illustrates the relationship between the Relative
Blanket Tungsten Removal Rate (W-RR) and the Static Coefficient of
Friction (SCOF) for exemplary thermoplastic foam substrates
subjected to different periods of coating times with TEOS. Both the
W-RR and COF increase with increased coating times up to 30
minutes, which in turn, corresponds to an increase the thickness of
polishing agent on the polishing surface of the pad.
[0050] FIG. 4 shows the relationship between Blanket Tungsten
Removal Rate (W-RR) and mean Static Coefficient of Friction (SCOF)
and mean Dynamic Coefficient of Friction (DCOF) for exemplary
thermoplastic foam polishing pads. There was a strong linear
correlation between W-RR and SCOF (r=0.81). A similar high
correlation was observed between SCOF and the removal rate of a
silicon dioxide layer (r=-0.92).
[0051] Although the present invention has been described in detail,
those skilled in the art should understand that they can make
various changes, substitutions and alterations herein without
departing from the scope of the invention.
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