U.S. patent application number 10/109821 was filed with the patent office on 2002-11-21 for methods for break-in and conditioning a fixed abrasive polishing pad.
Invention is credited to Burke, Peter A., Golzarian, Reza, Koinkar, Vilas N., Luo, Qiuliang, Shen, James, VanHanehem, Matthew.
Application Number | 20020173235 10/109821 |
Document ID | / |
Family ID | 26870268 |
Filed Date | 2002-11-21 |
United States Patent
Application |
20020173235 |
Kind Code |
A1 |
Koinkar, Vilas N. ; et
al. |
November 21, 2002 |
Methods for break-in and conditioning a fixed abrasive polishing
pad
Abstract
The present invention relates to methods for break-in and
conditioning polishing pads containing a fixed abrasive matrix. The
polishing pads are useful for chemical-mechanical polishing (CMP).
The present invention also relates to a method of determining the
wear rate of a fixed abrasive polishing pad.
Inventors: |
Koinkar, Vilas N.;
(Wilmington, DE) ; Golzarian, Reza; (Santa Clara,
CA) ; VanHanehem, Matthew; (Bear, DE) ; Luo,
Qiuliang; (Newport Beach, CA) ; Shen, James;
(Portland, OR) ; Burke, Peter A.; (Avondale,
PA) |
Correspondence
Address: |
Rodel Holdings, Inc.
Suite 1300
1105 North Market Street
Wilmington
DE
19899
US
|
Family ID: |
26870268 |
Appl. No.: |
10/109821 |
Filed: |
March 29, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10109821 |
Mar 29, 2002 |
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09754424 |
Jan 4, 2001 |
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6419553 |
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60174482 |
Jan 4, 2000 |
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Current U.S.
Class: |
451/21 ;
451/56 |
Current CPC
Class: |
B24B 37/042 20130101;
B24B 53/017 20130101 |
Class at
Publication: |
451/21 ;
451/56 |
International
Class: |
B24B 001/00 |
Claims
What is claimed:
1. A method of conditioning a fixed abrasive polishing pad,
comprising: a. providing a fixed abrasive polishing pad; b.
providing a conditioning element, wherein the element, comprises:
an upper surface and a lower conditioning surface, comprising:
abrasive particles; c. contacting the polishing pad and
conditioning element; wherein one or both of the pad and
conditioning element are in motion relative to the other.
2. A method according to claim 1, wherein the abrasive particles
are diamond particles with a diameter of from 5 to 50 microns and
the density of the particles present on the conditioning surface is
from about 5 to 100 particles/mm.sup.2 of the surface.
3. A method according to claim 2, wherein the conditioning element
is a disk or a ring, the abrasive particles have a diameter of from
1 to 50 microns, and the density of the particles present on the
conditioning surface is from about 20 to 80 particles/mm.sup.2 of
the surface.
4. A method according to claim 3, wherein the conditioning element
is a disk, the abrasive particles have a diameter of about 35
microns, and the density of the particles present on the
conditioning surface is about 50 particles/mm.sup.2 of the
surface.
5. A method according to claim 1, wherein a down force is applied
to the conditioning element and the down force is about 0.5 to 6
lbs.
6. A method according to claim 5, wherein the down force is about 1
to 4 lbs.
7. A method according to claim 6, wherein the down force is about 2
lbs.
8. A method according to claim 1, wherein the conditioning is to
break-in the polishing pad and the conditioning element is swept
uni-directionally across the pad 1 to 50 times.
9. A method according to claim 8, wherein the conditioning element
is swept uni-directionally across the pad 1 to 10 times.
10. A method according to claim 8, wherein the conditioning element
is swept uni-directionally across the pad until surface temperature
of polishing pad during polishing is stable from run to run and
within preset temperature limits is achieved during the polishing
process.
11. A method according to claim 1, wherein the conditioning is to
recondition the polishing pad and the conditioning element is swept
uni-directionally across the pad 1 to 10 times.
12. A method according to claim 11, wherein the conditioning
element is swept uni-directionally across the pad 1 to 5 times.
13. A method according to claim 11, wherein the conditioning
element is swept uni-directionally across the pad until surface
temperature of polishing pad during polishing is stable from run to
run and within preset temperature limits is achieved during the
polishing process.
14. A method according to claim 1, wherein from 0.2 to 3.0 microns
of polishing pad are removed by the conditioning element.
15. A method according to claim 14, wherein from 1.5 to 3.0 microns
of polishing pad are removed by the conditioning element.
16. A method according to claim 1, wherein: the conditioning
element is a disk, the abrasive particles are diamond particles
with a diameter of about 35 microns, and the density of the
particles present on the conditioning surface is about 50
particles/mm.sup.2 of the surface; a down force is applied to the
conditioning element and the down force is about 2 lbs; the
conditioning is to recondition the polishing pad and the
conditioning element is swept uni-directionally across the pad 1 to
5 times; and, from 1.5 to 3.0 microns of the polishing pad are
removed by the conditioning element.
17. A method according to claim 1, wherein the fixed abrasive
polishing pad has a surface roughness of about 0.5 to 1.0 .mu.m
after contact with the conditioning element.
18. A method according to claim 1, wherein the fixed abrasive
polishing pad has a Peak-Valley distance of about 1 to 20 .mu.m
after contact with the conditioning element.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Division of application Ser. No.
09/754,424, filed Jan. 4, 2001, which claims the benefit of
Provisional Application No. 60/174,482, filed Jan. 4, 2000.
FIELD OF THE INVENTION
[0002] The present invention relates to methods for break-in and
conditioning polishing pads, specifically fixed abrasive polishing
pads. The polishing pads are useful for chemical-mechanical
polishing (CMP) of metal films and/or lines such as copper,
tungsten, aluminum, tantalum/tantalum nitride, titanium/titanium
nitride, platinum, and dielectric films and/or lines such as
silicon dioxide and polymer and semiconductor substrates.
[0003] The present invention also relates to a method of
determining the wear rate of a fixed abrasive polishing pad.
DESCRIPTION OF RELATED ART
[0004] Semiconductor wafers having integrated circuits fabricated
thereon must be polished to provide a very smooth and flat surface
which in some cases may vary from a given plane by as little as a
fraction of a micron. Such polishing is usually accomplished in a
chemical-mechanical polishing (CMP) operation utilizing a
chemically active slurry with abrasive particles that is buffed
against the wafer surface by a polishing pad. A conventional
polishing slurry contains appropriate chemistry and abrasive
particles that facilitate the removal of materials both
mechanically and chemically with a conventional pad.
[0005] Alternatively, a polishing pad containing a fixed abrasive
can be used. A fixed abrasive pad incorporates the abrasives into
the pad using a resin. Thus, the polishing solution accompanying
this pad does not require abrasive particles. In other words, a
solution comprised of appropriate chemistry in the absence of
abrasives can be used to remove the materials chemically while the
mechanical abrasion can be obtained from the relative motion of the
pad with abrasives to the wafer in the presence of pressure.
[0006] As with most polishing pads, fixed abrasive polishing pads
require break-in and conditioning to achieve consistent polishing
results. Break-in and conditioning are techniques that modify the
surface topography of the fixed abrasive pad to bring the pad
within an optimized CMP process window. Break-in is used to prepare
a fixed abrasive polishing pad for polishing. Conditioning is used
after a polishing pad has been used for polishing. During the
polishing process, the surface and polishing properties of
polishing pads can change. The topography of the polishing pad
surface can be worn down and the surface can become smooth as
polishing by-products such as removed wafer material become
embedded in the surface. The overall performance of the polishing
pad can, consequently, deteriorate and fall out of the optimized
process window. Conditioning is used to restore the polishing pad's
properties and thereby bring it back within the optimized process
window.
[0007] Break-in and conditioning are both techniques aimed at
affording a polishing pad with stable removal rates and better
uniformity. Conditioning generally involves making passes or sweeps
over the polishing surface of the pad with an abrasive material
that removes a thin layer of pad material and, if present,
polishing by-products. U.S. Pat. No. 5,486,131 describes an
abrasive conditioning technique that is suitable for use with a
conventional polyurethane polishing pad such as IC-1000 that is
available from Rodel, Inc., of Newark, Del.
[0008] A new generation of fixed abrasive polishing pads is
currently being developed. New generation fixed-abrasive polishing
pads have a planarizing surface with exposed abrasive particles.
The planarizing surface on some abrasive pads has a pattern of
topographical features. One type of fixed abrasive polishing pad is
described in U.S. Pat. No. 5,692,950. This polishing pad comprises
a three-dimensional, textured, fixed abrasive element; at least one
resilient element generally coextensive with the fixed abrasive
element; and at least one rigid element generally coextensive with
and interposed between the resilient element and the fixed abrasive
element. Generally, the fixed abrasive element is a fixed abrasive
article comprising a backing on which is disposed an abrasive
coating comprising a plurality of abrasive particles dispersed in a
binder in the form of a pre-determined pattern.
[0009] One method of conditioning polishing pads is to abrade them
with a conventional diamond-embedded abrasive disk. However, U.S.
Pat. No. 5,725,417 notes that, although conventional
diamond-embedded abrasive disks are well suited to condition
conventional polishing pads, they are not well suited to condition
the new generation fixed abrasive polishing pads. U.S. Pat. No.
5,725,417 indicates that when a fixed abrasive polishing pad is
conditioned with a diamond-embedded abrasive disk, the diamonds not
only remove waste material, but they also remove some of the
abrasive particles and damage the topographical features on the
polishing surface of the pad. Clearly such a result is not
desired.
[0010] In view of this, U.S. Pat. No. 5,725,417 describes a method
of conditioning a fixed abrasive polishing pad by diffusing a
conditioning fluid into the suspension medium of the polishing pad
in order to form a discrete stratum of material on the suspension
medium that is soluble in a wash fluid. The discrete stratum is
then removed by dissolving it in a wash fluid, thereby leaving a
new polishing surface on the suspension medium.
[0011] Since most manufacturers already use conventional
conditioning equipment, it would be useful to discover a method of
break-in and conditioning using this equipment. It is, therefore,
desirable to discover alternative methods of break-in and
conditioning fixed abrasive polishing pads that do not damage its
topographical features, use conventional equipment, and that are
simple, efficient, and effective.
SUMMARY OF THE INVENTION
[0012] The present invention provides a method of break-in and
conditioning a fixed abrasive polishing pad using a conditioning
element, wherein the element, comprises: an upper surface and a
lower conditioning surface, comprising: abrasive particles.
[0013] Also provided is a method of determining the wear rate of a
fixed abrasive polishing pad without using conventional abrasive
tests.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] The present invention provides a method of break-in and
conditioning fixed abrasive polishing pads using a conditioning
element, usually a conventional conditioning element. Break-in is
used to prepare the polishing pad prior to polishing. Breaking-in a
fixed abrasive polishing pad reduces the friction between the
polishing pad and substrate to be polished, increases the surface
roughness of the polishing pad, and removes any surface film that
may have formed during the manufacturing of the polishing pad.
Conditioning is used to regenerate the polishing pad after
polishing numerous wafers. Both types of conditioning have the same
general goal in mind, to provide a polishing pad that falls within
an optimized process window (i.e., a pad that provides stable
removal rates and uniform polishing).
[0015] The conditioning element comprises a flat device comprising
an upper surface that is attachable to conventional conditioning
equipment (e.g., a mechanical arm) and a lower surface that is a
conditioning surface. In order to effect conditioning, it is
necessary for relative movement between the conditioning element
and the polishing pad, or both. As a result one or both of the
element and pad should be in motion relative to one another.
Preferably, both the conditioning element and the polishing pad are
rotated. Preferably, both the conditioning element and the
polishing pad are rotated in the same direction. As one of ordinary
skill in the art recognizes, it is the mechanical arm or holder
that imparts movement (e.g., radial and/or rotational) to the
conditioning element.
[0016] Conditioning elements are usually considerably smaller in
diameter compared with the polishing pad they are conditioning. As
a result, the conditioning equipment holding the conditioning
element in contact with the polishing pad radially sweeps the
element from the center of the polishing pad to the edge and back
to the center. Such conditioning is hereinafter referred to as
bi-directional conditioning. In contrast, a preferred method of
conditioning is uni-directional conditioning. In uni-directional
conditioning, the element is radially swept from the center to the
edge of the polishing pad. If an additional sweep is desired, the
element is lifted off the pad, returned to the center, contacted
with the pad again, and then again swept to the edge of the pad. A
significant advantage of uni-directional conditioning is that the
particulate matter removed from the polishing pad is swept to the
edge and then off the pad.
[0017] The conditioning element used herein is an element
sufficient to break-in and/or condition a fixed abrasive polishing
pad. In other words, a conditioning element suitable for the
present invention is one that will modify a fixed abrasive
polishing pad to provide a pad that falls within an optimized
process window. The conditioning element is not limited with regard
to its shape, particle type or types, particle size, surface
topography, particle pattern, or modifications made to the element
surface or particles. For example, the conditioning element may
contain grooves in a circular, linear, or grid pattern. Also, the
particles may be present on the conditioning element in a circular,
linear, grid, or random pattern and there may be more than one type
of particle present.
[0018] The conditioning surface of the conditioning element
comprises abrasive particles. These particles are of a sufficient
hardness as to effect break-in and conditioning. Preferably, the
particles are diamond, silicon carbide, titanium nitride, titanium
carbide, alumina, alumina alloys, or alumina coated with a hard
material film, more preferably diamond. A preferred method of
adhering diamond particles to the conditioning surface is chemical
vapor deposition (CVD). How the particles are attached to the
surface of the conditioning element is, however, not to be limited.
For example, the particles may be applied to the surface of the
conditioning element (e.g., via CVD), may be a part of the surface
itself, or may even be embedded in the surface.
[0019] Preferably, the conditioning element is in the shape of a
disk. The diameter of the conditioning element is only limited to
that which is sufficient to provide break-in or conditioning.
Preferably the conditioning element is a disk having a diameter of
about 1 to 16 inches. More preferably, the disk has a diameter of
from 1, to 4 inches. Conditioner disks 22535, 22550, 23515, 23535
and 23550 manufactured by Dimonex, Inc., Allentown, Pa. were found
to be useful in the present invention. Diamond particles were used
as abrasive particles on these conditioner disks. Another preferred
conditioning element is a disk with its central portion removed
(i.e., a ring or donut shape). The width of the ring conditioning
element is preferably from 0.5 to 2 inches. The diameter of the
ring conditioning element is preferably about 1 to 16 inches.
[0020] Still another preferred conditioning element is a disk
wherein the abrasive particles are present only at the outer edge
of the disk. In other words, there is a ring of abrasive particles
present on the conditioning disk. Preferably, this ring of
conditioning particles has a width of about 0.5 to 2 inches. The
diameter of this type of disk conditioning element is preferably
about 1 to 16 inches.
[0021] Abrasive particle diameter can affect how much material the
conditioning element removes with each sweep. As a result, if is
preferable for the abrasive particles to have a diameter of from 1
to 50 microns. More preferably, the abrasive particles have a
diameter of from 25 to 45 microns. Even more preferably, the
abrasive particles have a diameter of about 35 microns.
[0022] Polishing pad conditioning is also dependent on the number
of abrasive particles present on the surface of the conditioning
element (i.e., the particle density). Accordingly, the abrasive
particles are disposed on the conditioning surface at a density of
from about 5 to 100 particles/mm.sup.2 of the element surface. More
preferably, the density is from about 40 to 60 particles/mm.sup.2.
Even more preferably, the density is about 50
particles/mm.sup.2.
[0023] As one of ordinary skill in the art recognizes, the
conditioning element is contacted with the polishing pad and some
force or down pressure is applied. The amount of force or down
pressure will affect the amount of conditioning that occurs.
Preferably, the down force applied to the conditioning element is
about 0.5 or 6 lbs. More preferably, the down force is about 1, 2,
or 3 lbs. Even more preferably, the down force is 2 lbs.
[0024] Another aspect of break-in and conditioning is the number of
sweeps performed. As one of ordinary skill in the art recognizes,
the more sweeps, the greater the conditioning or the amount of
polishing pad surface that is removed. Preferably, 1 to 50 sweeps
are performed for break-in. More preferably 1 to 10 sweeps are
performed for break-in. Even more preferably, 1 to 5 sweeps are
performed for break-in. Preferably, 1 to 50 sweeps are performed
for conditioning the polishing pad. More preferably 1 to 10 sweeps
are performed for conditioning. Even more preferably, 1 to 5 sweeps
are performed for conditioning.
[0025] Surface temperature of polishing pad during polishing is
used to monitor the pad break-in, conditioning and polishing
process stability. For polishing pad break-in and conditioning,
conditioning element is swept until the polishing pad surface
temperature stability is achieved for run-to-run process
performance. Any drift in surface temperature of polishing pad is
also used to determine an interval between pad conditioning. Pad
conditioning is performed when the temperature drift from preset
stable process limits.
[0026] An important aspect of break-in and conditioning is the
amount of fixed abrasive polishing pad material that is removed.
Preferably, from about 0.2 to 3.0 microns of polishing pad are
removed during break-in. More preferably, from about 1 to 3.0
microns are removed during break-in. Even more preferably, from
about 1.5 to 3.0 microns are removed during break-in. Preferably,
from about 0.2 to 3.0 microns of polishing pad are removed during
conditioning. More preferably, from about 1 to 3.0 microns are
removed during conditioning. Even more preferably, from about 1.5
to 3.0 microns are removed during conditioning.
[0027] A preferred fixed abrasive polishing pad to be used in the
present invention is a fixed abrasive polishing pad like that
described in U.S. Pat. No. 5,692,950, the contents of which are
incorporated herein by reference. This type of polishing pad can be
a continuous pad or a typical individual pad (e.g., circular). This
fixed abrasive polishing pad comprises a three-dimensional,
textured, fixed abrasive element, a resilient element, and a rigid
element interposed between the resilient element and the fixed
abrasive element. Generally, the fixed abrasive element is a fixed
abrasive article comprising a backing on which is disposed an
abrasive coating comprising a plurality of abrasive particles
dispersed in a binder in the form of a pre-determined pattern.
Typically this type of pad contains a pattern of raised areas
(e.g., posts or pyramids). It is this pattern that conventional
conditioning procedures typically damage. Preferably the raised
areas are posts that cover about 18% of the surface of the pad.
Preferably the posts are about 200 .mu.m in diameter and about 30
to 40 .mu.m in height. As a consequence of the manufacturing
process, there is usually about a 10 .mu.m depression between
posts.
[0028] It is another aspect of the present invention to modify the
surface topography of the raised areas (e.g., posts) in a
controlled manner. Typically, a fixed abrasive polishing pad has a
surface roughness of about 0.2 .mu.m after it is manufactured. It
is desirable to increase this roughness prior to polishing. Surface
roughness, as used herein, is intended to mean root mean square
deviation of the profile from the mean line. The mean line is the
height where the area above and below the mean line is equal.
Surface roughness increases after break-in and conditioning.
Preferably, the present invention, after break-in or conditioning,
yields a surface roughness of from about 0.2 to 1.5 .mu.m. More
preferably, the resulting surface roughness is from about 0.5 to
1.0 .mu.m.
[0029] Typically, a fixed abrasive polishing pad has a
Peak-to-Valley distance of about 2 .mu.m after it is manufactured.
It is desirable to increase this Peak-to-Valley distance prior to
polishing. Peak-Valley distance, as used herein, is the distance
between the highest and lowest points within the measured area.
Peak-to-Valley distances, like surface roughness, increase after
break-in and conditioning. Preferably, the present invention, after
break-in or conditioning, provides a Peak-to-Valley distance of
from about 1 to 20 .mu.m. More preferably, the resulting
Peak-to-Valley distance is from about 4 to 8 .mu.m.
[0030] With fixed abrasive polishing pads, conventional abrasive
tests are not reliable in determining the wear rate of pads from
different manufacturing lots. Specifically, conventional abrasive
tests are unable to reliably distinguish between different lots of
fixed abrasive polishing pads. The present invention solves this
problem by providing a method of determining the wear rate of a
fixed abrasive polishing pad. Knowing the wear rate of a specific
manufacturing lot of pads allows one to determine some or all of
the following items of interest: (1) how long the pads will last,
(2) how many conditioning sweeps will be necessary to break-in and
condition the pad, (3) when and how often the pads will need to be
conditioned, (4) how to control the fixed abrasive manufacturing
process, (5) the variations in hardness of fixed abrasive pads, (6)
the bonding strength between abrasive particles and resins used in
fixed abrasive pads, and (7) what the current manufacturing lot of
pads would be most suited to polish.
[0031] The present method of determining pad wear rates involves
measuring the height of the raised area (e.g., the posts) of a
polishing pad. An optical interferometer, non-contact optical
profilometer, or a stylus profiler can be used to measure these
heights. Once the average post height of a pad has been determined,
the pad is then subjected to one sweep of a conditioning element.
The average post height is then determined and a rate of post
material loss is calculated. Additional data can be obtained by
conducting additional sweeps and additional height measurements.
Preferably, 1, 2, 3, 4, or 5 sweeps are conducted. Preferably, the
conditioning sweep is conducted with an element having 25 to 35
micron diameter particles at a density of 50 particles/mm.sup.2
under 4 pounds of force.
[0032] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *