U.S. patent application number 11/786443 was filed with the patent office on 2007-11-01 for contoured cmp pad dresser and associated methods.
Invention is credited to Chien-Min Sung.
Application Number | 20070254566 11/786443 |
Document ID | / |
Family ID | 36142886 |
Filed Date | 2007-11-01 |
United States Patent
Application |
20070254566 |
Kind Code |
A1 |
Sung; Chien-Min |
November 1, 2007 |
Contoured CMP pad dresser and associated methods
Abstract
CMP pad dressers with increased pad dressing work loads on the
centrally located abrasive particles during dressing of a CMP pad,
and methods associated therewith are disclosed and described. The
increase in work load on centralized particles improves pad
dressing performance and also extends the service life of the pad
dresser.
Inventors: |
Sung; Chien-Min; (Tansui,
TW) |
Correspondence
Address: |
THORPE NORTH & WESTERN, LLP.
8180 SOUTH 700 EAST, SUITE 350
SANDY
UT
84070
US
|
Family ID: |
36142886 |
Appl. No.: |
11/786443 |
Filed: |
April 10, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10954956 |
Sep 29, 2004 |
7201645 |
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11786443 |
Apr 10, 2007 |
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10109531 |
Mar 27, 2002 |
6884155 |
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10954956 |
Sep 29, 2004 |
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09558582 |
Apr 26, 2000 |
6368198 |
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10109531 |
Mar 27, 2002 |
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09447620 |
Nov 22, 1999 |
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09558582 |
Apr 26, 2000 |
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Current U.S.
Class: |
451/443 |
Current CPC
Class: |
B24B 53/12 20130101;
B24D 7/02 20130101; B24B 53/017 20130101; B24D 18/00 20130101; B24D
3/06 20130101; B24D 2203/00 20130101 |
Class at
Publication: |
451/443 |
International
Class: |
B24B 21/18 20060101
B24B021/18 |
Claims
1. A method of increasing work load on centrally located
superabrasive particles in a CMP pad dresser during dressing of a
CMP pad with the dresser comprising: providing a brazing alloy
sheet; coating the brazing alloy sheet with an adhesive;
positioning the superabrasive particles in the adhesive on the
brazing alloy sheet in a pattern that reduces penetration of
peripherally located particles into the CMP pad and increases
penetration of centrally located particles into the CMP pad; and
brazing the particles to a substrate with the brazing alloy to form
the dresser.
2. The method of claim 1, wherein the superabrasive particles are
positioned on the brazing alloy using a template placed directly on
the sheet of brazing alloy.
3. The method of claim 1, wherein the superabrasive particles are
positioned on the brazing alloy using a transfer sheet having an
adhesive coated thereon and having received the superabrasive
particles in the pattern by use of a template.
Description
PRIORITY DATA
[0001] This patent application is a continuation of U.S. patent
application Ser. No. 10/954,956 filed on Sep. 29, 2004 which is a
continuation-in-part of U.S. patent application Ser. No. 10/109,531
filed Mar. 27, 2002, which is a continuation-in-part of U.S. patent
application Ser. No. 09/558,582 filed Apr. 26, 2000, which is a
continuation-in-part of U.S. patent application Ser. No. 09/447,620
filed Nov. 22, 1999, now abandoned, each of which is incorporated
herein by reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to a device and
methods for dressing or conditioning a chemical mechanical
polishing (CMP) pad. Accordingly, the present invention involves
the chemical and material science fields.
BACKGROUND OF THE INVENTION
[0003] Many industries are now using a chemical mechanical process
(CMP) for polishing certain work pieces. Particularly, the computer
manufacturing industry has begun to rely heavily on CMP processes
for polishing wafers of ceramics, silicon, glass, quartz, and
metals thereof. Such polishing processes generally entail applying
the wafer against a rotating pad made from a durable organic
substance such as polyurethane. To the pad, is added a chemical
slurry containing a chemical capable of breaking down the wafer
substance, and an amount of abrasive particles which act to
physically erode the wafer surface. The slurry is continually added
to the spinning CMP pad, and the dual chemical and mechanical
forces exerted on the wafer cause it to be polished in a desired
manner.
[0004] Of particular importance to the quality of polishing
achieved, is the distribution of the abrasive particles throughout
the pad. The top of the pad holds the particles, usually by a
mechanism such as fibers, or small pores, which provide a friction
force sufficient to prevent the particles from being thrown off of
the pad due to the centrifugal force exerted by the pad's spinning
motion. Therefore, it is important to keep the top of the pad as
flexible as possible, and to keep the fibers as erect as possible,
or to assure that there are an abundance of openings and pores
available to receive new abrasive particles.
[0005] A problem with maintaining the top of the pad is caused by
an accumulation of polishing debris coming from the work piece,
abrasive slurry, and dressing disk. This accumulation causes a
"glazing" or hardening of the top of the pad, and mats the fibers
down, thus making the pad less able to hold the abrasive particles
of the slurry, and significantly decreasing the pad's overall
polishing performance. Further, with many pads, the pores used to
hold the slurry, become clogged, and the overall asperity of the
pad's polishing surface becomes depressed and matted. Therefore,
attempts have been made to revive the top of the pad by "combing"
or "cutting" it with various devices. This process has come to be
known as "dressing" or "conditioning" the CMP pad. Many types of
devices and processes have been used for this purpose. One such
device is a disk with a plurality of super hard crystalline
particles, such as diamond particles attached to a surface, or
substrate thereof.
[0006] Unfortunately, such abrasive disks made by conventional
methods exhibit several problems. First, abrasive particles may
dislodge from the substrate of the disk and become caught in the
CMP pad fibers. This leads to scratching and ruin of the work piece
being polished. Second, the production methods of the past tend to
produce disks having abrasive particles that are clustered in
unevenly spaced groups on the surface of the substrate. The
resultant non-uniform spacing between particles causes some
portions of the CMP pad to be overdressed which creates wear marks,
while others are underdressed which creates glazing layers. Third,
the abrasive particles of these disks are not configured to
penetrate the pad to a uniform depth. This non-uniformity creates
additional uneven dressing of the CMP pad. Finally, depending on
the degree to which the CMP pad is flexible, it may tend to bulge
or bubble in front of the initial leading edge of the dresser due
to the downward force exerted by the dresser. Such bulging may
cause a depression of the pad to occur as it passes under the
remaining portion of the dresser, which may in turn, cause the
remaining abrasive particles, especially those that are centrally
located on the pad dresser to penetrate the pad less deeply or even
skip over the pad entirely. This uneven work load on the dresser
particles may cause the pad to be unevenly dressed, and may also
cause the dresser to wear unevenly and become worn out
prematurely.
[0007] Yet another disadvantage with modern CMP pad dressers is
reduced service life of the pad conditioner. The effectiveness and
efficiency of the service of a CMP pad conditioner is determined by
its number of working abrasive particles and the amount of work
that is experienced by each particle. As noted above, the service
life of a pad conditioner can be reduced by an uneven distribution
of work load on the superabrasive particles. When a flexible CMP
pad depresses under the pressure of a dresser excessive wear may
occur on the leading edge crystals of the pad conditioner as they
will bear the majority of the work load. Further, the centrally
located abrasive particles are prevented from receiving an equal
work load. This work load mismatch increases the wear rate on the
leading edge particles and can cause the dresser to become unusable
long before the exhaustion of the centrally located particles.
[0008] With respect to particle retention, two factors tend to
cause the abrasive particles to dislodge from the pad dresser disks
of the prior art. First, dislodging often occurs due to the
inferior method by which the abrasive particles have been attached.
Abrasive particles held to the substrate only by electroplated
nickel or other overlay materials are secured only by weak
mechanical forces and not by any form of chemical bonding. Hence,
these particles become easily dislodged upon exposure to strong
mechanical forces such as friction; Furthermore, particle
dislodging is facilitated by the chemical attack on the
electroplating material which is presented by the chemical
slurry.
[0009] In contrast, when the abrasive particles are brazed onto the
substrate, a chemical bond holds the particles more firmly.
However, the acids of the chemical slurry can quickly weaken the
braze-particle bonds and dislodge the abrasive particles. under the
friction of pad dressing. Therefore, to minimize the exposure of
the braze to the chemicals and extend the useful life of the pad
dresser, the polishing processes must be halted while dressing
occurs. The resultant sequence of alternating polishing and then
dressing wastes time, and is inefficient.
[0010] Warping of the pad dresser working surface during the
brazing process also often causes abrasive particles to dislodge.
During the brazing process the pad dresser must be exposed to very
high temperatures. Exposure to this extreme heat can cause the
working surface of the pad dresser to warp, thus compromising the
smoothness and planarity of the pad dresser's working surface. As a
result, the braze portion of the working surface will be rough,
having high and low spots. Such spots are undesirable, as they may
cause the braze to begin flaking off, and making micro-scratches on
the polished surface of the work piece. Further, such unevenness
may cause issues with further processing of the dresser, and
abrasive particle retention.
[0011] In view of the foregoing, a CMP pad dresser that is
constructed and configured to achieve optimal dressing results,
with maximized efficiency and lifespan continues to be sought.
SUMMARY OF THE INVENTION
[0012] Accordingly, in one aspect, the present invention provides
methods and CMP pad dresser configurations for increasing the work
load on centrally located superabrasive particles in a CMP pad
dresser during dressing of a CMP pad. In one such method, a CMP pad
dresser is provided which has a plurality of superabrasive
particles each coupled to a substrate member and held at specific
locations in accordance with a predetermined pattern. The
superabrasive particles can be configured in a pattern that reduces
the penetration of peripherally located particles into the CMP pad
and increases penetration of centrally located particles into the
CMP pad, thus optimizing the work load placed on the centrally
located superabrasive particles. Generally, the particles are of a
super hard substance such as diamond, or cubic boron nitride (cBN),
in either the single crystal or polycrystalline form.
[0013] In one embodiment of the present invention, the method for
increasing the work load on centrally located superabrasive
particles includes the utilization of a CMP pad dresser having a
substrate with superabrasive particles configured in a pattern that
provides a slope from the working ends of the peripherally located
particles upwardly to the working ends of the centrally located
particles. Further, the exact degree of slope employed can be
configured to control the work load experienced by the centrally
located particles. Such a slope can be created in various ways. For
example, in one aspect, a slope can be created by disposing
superabrasive particles on or in a substantially flat substrate,
where the superabrasive particles increase in height above a
working surface of the substrate from the peripherally located
particles to the centrally located particles. In some cases, the
preferred degree of slope can be determined as a measure of pad
velocity and pad flexibility.
[0014] In yet another embodiment of the present invention, a method
for increasing the work load on the centrally located particles may
include providing a CMP pad dresser having a plurality of
superabrasive particles coupled to a substrate in a pattern that
places the peripherally located superabrasive particles at a higher
density than the centrally located particles. It has been found
that particles clustered in a higher density are unable to
penetrate into the pad as deeply as those spaced farther apart from
one another. Therefore, by varying densities of particles on the
substrate work load can be transferred from one area to
another.
[0015] In still another embodiment of the present invention a
method of increasing the work load on centrally located particles
may be achieved by orienting the centrally located particles with
an attitude that causes higher particle penetration into the CMP
pad than penetration provided by an attitude of the peripherally
located particles. In one aspect, the attitude of the centrally
located particles can present an apex at the working end thereof,
and the attitude of the peripherally located particles can present
either a face or an edge at the working end thereof. In another
aspect, the attitude of the centrally located particles can present
an edge at the working end thereof, and the attitude of the
peripherally located particles can present a face at the working
end thereof. In yet another aspect, when the attitude of the
centrally located particles presents an apex at the working end
thereof, the attitude of the peripherally located particles can
present a face at the working end thereof, and the attitude of any
particles in between those peripherally and centrally located can
present an edge at the working end thereof.
[0016] In addition to the above-recited methods of use, the present
invention also includes methods for producing a CMP pad dresser
that displays an increased work load on the centrally located
superabrasive particles. Generally speaking, such a method includes
the steps of: 1) providing a substrate; and 2) attaching a
plurality of superabrasive particles on to the substrate in a
pattern that reduces the penetration of peripherally located
particles into the CMP pad and increases the penetration of the
centrally located particles into the CMP pad.
[0017] Using the methods described above, CMP pad dressers
exhibiting considerable advantages may be created. For example, the
working surface of the CMP pad dresser may be configured to
increase the contact of the CMP pad under a central portion of the
dresser, rather than overly contacting an outside or "leading edge"
thereof. Such increased central contact transfers a portion of the
work load from the peripheral area of the dresser to the central
area of the dresser, thus lengthening the service life of the
dresser and allowing the dresser to more effectively cut into and
groom the pad. CMP pad dressers that incorporate such
configurations are encompassed by the present invention, including
those with specific configurations made to support the methods
recited above.
[0018] The above-recited features and advantages of the present
invention will become apparent from a consideration of the
following detailed description presented in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a side view of a prior art CMP pad dresser
employing an electroplating method for fixing the abrasive
particles to the disk substrate in accordance with one embodiment
of the present invention.
[0020] FIG. 2 is a side view of a prior art CMP pad dresser made by
using a traditional brazing method for fixing the abrasive
particles to the disk substrate.
[0021] FIG. 3 is a side view of a CMP pad dresser made in
accordance with one embodiment of the present invention.
[0022] FIG. 4 is a side view of a sheet of brazing alloy with a
template for placing abrasive particles on the surface thereof in
accordance with one embodiment of the present invention.
[0023] FIG. 5 is a side view of a sheet of brazing alloy with a
template on its surface, and abrasive particles filling the
apertures of the template. A flat surface is shown for use in
pressing the abrasive particles into the sheet of brazing alloy in
accordance with one embodiment of the present invention.
[0024] FIG. 6 is a side view of a sheet of brazing alloy having
abrasive particles pressed into it in accordance with one
embodiment of the present invention.
[0025] FIG. 7 is a top view of the working surface of a CMP pad
dresser having abrasive particles coupled to the substrate such
that abrasive particles present substantially only along the
leading edge of the dresser, in accordance with one embodiment of
the present invention.
[0026] FIG. 8 is a top view of the working surface of a CMP pad
dresser having abrasive particles coupled to the substrate such
that more of the particles are at the leading edge than at the
center, in accordance with one embodiment of the present
invention.
[0027] FIG. 9 is a top view of the working surface of a CMP pad
dresser having abrasive particles coupled to the substrate such
that the particles are uniformly distributed throughout, in
accordance with one embodiment of the present invention.
[0028] FIG. 10 is a side view of a CMP pad dresser made in
accordance with one embodiment of the present invention.
[0029] FIG. 11 is a side view of a CMP pad dresser made in
accordance with one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Before the present CMP pad dresser and accompanying methods
of use and manufacture are disclosed and described, it is to be
understood that this invention is not limited to the particular
process steps and materials disclosed herein, but is extended to
equivalents thereof as would be recognized by those ordinarily
skilled in the relevant arts. It should also be understood that
terminology employed herein is used for the purpose of describing
particular embodiments only and is not intended to be limiting.
[0031] It must be noted that, as used in this specification and the
appended claims, the singular forms "a," and, "the" include plural
referents unless the context clearly dictates otherwise. Thus, for
example, reference to an "abrasive particle" or a "grit" includes
reference to one or more of such abrasive particles or grits.
[0032] Definitions
[0033] In describing and claiming the present invention, the
following terminology will be used in accordance with the
definitions set forth below.
[0034] As used herein, "abrasive particle," or "grit," or similar
phrases mean any super hard crystalline, or polycrystalline
substance, or mixture of substances and include but is not limited
to diamond, polycrystalline diamond (PCD), cubic boron nitride, and
polycrystalline cubic boron nitride (PCBN). Further, the terms
"abrasive particle," "grit," "diamond," "polycrystalline diamond
(PCD)," "cubic boron nitride," and "polycrystalline cubic boron
nitride, (PCBN)," may be used interchangeably.
[0035] As used herein, "substrate" means a portion of a CMP dresser
which supports abrasive particles, and to which abrasive particles
may be affixed. Substrates useful in the present invention may be
any shape, thickness, or material, that is capable of supporting
abrasive particles in a manner that is sufficient provide a tool
useful for its intended purpose. Substrates may be of a solid
material, a powdered material that becomes solid when processed, or
a flexible material. Examples of typical substrate materials
include without limitation, metals, metal alloys, ceramics, and
mixtures thereof. Further the substrate may include brazing alloy
material.
[0036] As used herein, "working surface" means the surface of a CMP
pad dresser that, during operation, faces toward, or comes in
contact with a CMP pad.
[0037] As used herein, "leading edge" means the edge of a CMP pad
dresser that is a frontal edge based on the direction that the CMP
pad is moving, or the direction that the pad is moving, or both.
Notably, in some aspects, the leading edge may be considered to
encompass not only the area specifically at the edge of a dresser,
but may also include portions of the dresser which extend slightly
inward from the actual edge. In one aspect, the leading edge may be
located along an outer edge of the CMP pad dresser. In another
aspect, the CMP pad dresser may be configured with a pattern of
abrasive particles that provides at least one effective leading
edge on a central or inner portion of the CMP pad dresser working
surface. In other words, a central or inner portion of the dresser
may be configured to provide a functional effect similar to that of
a leading edge on the outer edge of the dresser.
[0038] As used herein, "sharp portion" means any narrow portion to
which a crystal may come, including but not limited to comers,
ridges, edges, obelisks, and other protrusions.
[0039] As used herein, "centrally located particle" means any
particle of a dresser that under normal dressing circumstances
receives a reduced work load as compared to a peripherally located
particle. In some aspects, "central" or "centrally located" refers
to an area of a dresser that originates at a center point of the
dresser and extends outwardly towards the dresser's edge for up to
about 90% of the radius of the dresser. In some aspects, the area
may extend outwardly from about 20% to about 90% of the radius. In
other aspects, the area may extend out to about 50% of the radius.
In yet another aspect, the area may extend out to about 33% of the
radius of a dresser.
[0040] As used herein, "peripherally located" means any particle of
a dresser that under normal dressing circumstances that receives an
excess work load as compared to the centrally located particles. In
some aspects, "periphery" or "peripheral" or "peripherally located"
may refer to an area that originates at the leading edge or outer
rim of a dresser and extends inwardly towards the center for up to
about 90% of the radius of the dresser. In some aspects, the area
may extend inwardly from about 20% to 90% of the radius. In other
aspects, the area may extend in to about 50% of the radius. In yet
another aspect, the area may extend in to about 33% of the radius
of a dresser (i.e. 66% away from the center).
[0041] As used herein, "work load" means the amount of work or
force exerted on a particle in a dresser during use of the
dresser.
[0042] As used herein, "working end" refers to an end of a particle
which is oriented towards the CMP pad and during a dressing
operation makes contact with the pad. Most often the working end of
a particle will be distal from a substrate to which the particle is
attached.
[0043] As used herein, "amorphous braze" refers to a homogenous
braze composition having a non-crystalline structure. Such alloys
contain substantially no eutectic phases that melt incongruently
when heated. Although precise alloy composition is difficult to
ensure, the amorphous brazing alloy as used herein should exhibit a
substantially congruent melting behavior over a narrow temperature
range.
[0044] As used herein, "alloy" refers to a solid or liquid mixture
of a metal with a second material, said second material may be a
non-metal, such as carbon, a metal, or an alloy which enhances or
improves the properties of the metal.
[0045] As used herein, "metal brazing alloy," "brazing alloy,"
"braze alloy," "braze material," and "braze," may be used
interchangeably, and refer to a metal alloy which is capable of
chemically bonding to superabrasive particles, and to a matrix
support material, or substrate, so as to substantially bind the two
together. The particular braze alloy components and compositions
disclosed herein are not limited to the particular embodiment
disclosed in conjunction therewith, but may be used in any of the
embodiments of the present invention disclosed herein.
[0046] As used herein, the process of "brazing" is intended to
refer to the creation of chemical bonds between the carbon atoms of
the superabrasive particles and the braze material. Further,
"chemical bond" means a covalent bond, such as a carbide or boride
bond, rather than mechanical or weaker inter-atom attractive
forces. Thus, when "brazing" is used in connection with
superabrasive particles a true chemical bond is being formed.
However, when "brazing" is used in connection with metal to metal
bonding the term is used in the more traditional sense of a
metallurgical bond. Therefore, brazing of a superabrasive segment
to a tool body does not require the presence of a carbide
former.
[0047] As used herein, "superabrasive particles" and "superabrasive
grits" may be used interchangeably, and refer to particles of
either natural or synthetic diamond, super hard crystalline, or
polycrystalline substance, or mixture of substances and include but
are not limited to diamond, polycrystalline diamond (PCD), cubic
boron nitride (CBN), and polycrystalline cubic boron nitride
(PCBN). Further, the terms "abrasive particle," "grit," "diamond,"
"PCD," "CBN," and "PCBN," may be used interchangeably.
[0048] As used herein, in conjunction with the brazing process,
"directly" is intended to identify the formation of a chemical bond
between the superabrasive particles and the identified material
using a single brazing metal or alloy as the bonding medium.
[0049] As used herein, "asperity" refers to the roughness of a
surface as assessed by various characteristics of the surface
anatomy. Various measurements may be used as an indicator of
surface asperity, such as height of peaks or projections thereon,
and the depth of valleys or concavities depressing therein.
Further, measures of asperity include the number of peaks or
valleys within a given area of the surface (i.e. peak or valley
density), and the distance between such peaks or valleys.
[0050] As used herein, "ceramic" refers to a hard, often
crystalline, substantially heat and corrosion resistant material
which may be made by firing a non-metallic material, sometimes with
a metallic material. A number of oxide, nitride, and carbide
materials considered to be ceramic are well known in the art,
including without limitation, aluminum oxides, silicon oxides,
boron nitrides, silicon nitrides, and silicon carbides, tungsten
carbides, etc.
[0051] As used herein, "metallic" means any type of metal, metal
alloy, or mixture thereof, and specifically includes but is not
limited to steel, iron, and stainless steel.
[0052] As used herein, "grid" means a pattern of lines forming
multiple squares.
[0053] As used herein with respect to distances and sizes,
"uniform" refers to dimensions that differ by less than about 75
total micrometers.
[0054] As used herein, "Ra" refers to a measure of the roughness of
a surface as determined by the difference in height between a peak
and a neighboring valley. Further, "Rmax" is a measure of surface
roughness as determined by the difference in height between the
highest peak on the surface and the lowest valley on the
surface.
[0055] Concentrations, amounts, and other numerical data may be
expressed or presented herein in a range format. It is to be
understood that such a range format is used merely for convenience
and brevity and thus should be interpreted flexibly to include not
only the numerical values explicitly recited as the limits of the
range, but also to include all the individual numerical values or
sub-ranges encompassed within that range as if each numerical value
and sub-range is explicitly recited.
[0056] As an illustration, a numerical range of "about 1 micrometer
to about 5 micrometers" should be interpreted to include not only
the explicitly recited values of about 1 micrometer to about 5
micrometers, but also include individual values and sub-ranges
within the indicated range. Thus, included in this numerical range
are individual values such as 2, 3, and 4 and sub-ranges such as
from 1-3, from 2-4, and from 3-5, etc. This same principle applies
to ranges reciting only one numerical value. Furthermore, such an
interpretation should apply regardless of the breadth of the range
or the characteristics being described.
[0057] The Invention
[0058] Applicant has discovered devices and methods for improving
the efficiency and quality of conditioning or dressing a CMP pad.
By using the device to condition or dress a CMP pad, not only is
the pad life extended, but also the constancy at which the pad may
be used, and therefore, the speed at which the device accomplishes
its work is improved.
[0059] Referring now to FIG. 1, there is shown a prior art CMP pad
dresser 10, which has a plurality of abrasive particles 50
electroplated to a substrate 40. The electroplating material 60, is
generally nickel precipitated out of an acid solution.
[0060] CMP pad dressers 10 using only the electroplating material
60 to attach the abrasive particles 50 to a substrate have many
disadvantages that are apparent as shown in FIG. 1. First, the
electroplating material is incapable of forming chemical bonds with
the abrasive particles. Therefore, only weak mechanical forces hold
the abrasive particles onto the substrate 40. When the pad dresser
is rotated against a CMP pad, such mechanical forces are quickly
overcome by the friction force acting on the abrasive particles. As
a result the abrasive particles are easily loosened from the
electroplating material, leaving voids in the electroplating
material, such as spaces 70. Such voids are quickly filled with
residue polished off of the work piece, as well as chemicals and
abrasive particles from the slurry. These substances chemically
attack and further weaken the electroplating material.
[0061] Because the mechanical forces created by the electroplating
material 60 are the only means holding the abrasive particles 50
onto the substrate 40, exposure of the abrasive particles above the
electroplating material must be kept to a minimum. Nevertheless,
contact between electroplating material and the CMP pad is
inevitable. Such contact wears the electroplating material and
further facilitates the release of the abrasive particles.
Additionally, during manufacture, the electroplating material tends
to bubble up around the abrasive particles, in places such as
convex portion 80. These convex portions, in addition to the
already low exposure and tight spacing of the abrasive particles,
make significant penetration of the abrasive particles into the CMP
pad fibers difficult, if not impossible. Without such penetration,
the effectiveness of the dressing process is handicapped.
[0062] Referring now to FIG. 2, there is shown a prior art CMP
dresser pad 20 with a substrate 40, having abrasive particles 50,
brazed to the substrate, using a brazing material 90, and
conventional vacuum furnace brazing techniques. Brazing materials
90 generally comprise a metal alloy mixed with carbide formers.
Such carbide formers allow the abrasive particles to chemically
bond to the brazing material which in turn bonds with the
substrate. This bonding arrangement significantly increases the
overall strength of the CMP dresser, but is accompanied by some
undesirable side effects.
[0063] Brazing material 90 must be kept to a minimum in order to
avoid completely covering the abrasive particles 50. Therefore, the
abrasive particles are wrapped in only a thin coating of brazing
material. This problem is compounded by the fact that typical
brazing materials are mechanically very weak. This mechanical
weakness offsets the strength of the chemical bonds created between
the abrasive particles and the brazing material. In fact, when
dislodgment occurs, the chemical bonds between the abrasive
particles and the brazing material are strong enough that the
brazing material itself will often shear off along with detached
abrasive particles.
[0064] The brazing material 90 is also very susceptible to chemical
attack by the abrasive slurry. This contributes to the detachment
of abrasive particles 50, as it further weakens the brazing
material, which is already mechanically weak. Therefore, in order
to reduce exposure of the CMP pad dresser 20 to the chemical
slurry, polishing of the work piece must be paused, and the
chemical slurry allowed to leave the pad before the pad dresser is
applied. Such pauses in the polishing process greatly reduce the
constancy with which the pad may be used, increase the time
required to produce a finished product, and are therefore
inefficient.
[0065] Another drawback to coupling the abrasive particles 50 to a
substrate 40 by conventional brazing alone is that the surface
tension of the molten metal alloy tends to cause the abrasive
particles to "cluster" when applied to the substrate. Such
clustering is illustrated at 100, leaving unintended gaps 110. The
overall effect is a non-uniform distribution of abrasive particles,
which makes grooming inefficient. Further, the gaps cause uneven
conditioning of the pad, which ultimately wears out certain areas
of the CMP pad faster than others, with the overall result that the
work piece will receive an uneven polish because the worn out areas
polish less effectively than the properly conditioned areas.
[0066] The clustering of abrasive particles creates another
disadvantage by forming mounds in the brazing material 90. Mound
formation raises some abrasive particles to a height above the
substrate 40, which is greater than that of other abrasive
particles. Therefore, the highest protruding abrasive particles may
penetrate so deeply into the fibers of the CMP pad, that they will
prevent lesser protruding abrasive particles from contacting the
CMP pad or having a useful grooming effect.
[0067] In contrast to the CMP pad dressers of the prior art, the
present invention allows even dressing of the CMP pad. Referring
now to FIG. 3, there is shown a CMP pad dresser 30 made in
accordance with the principles of the present invention. The CMP
pad dresser has a plurality of abrasive particles 50 coupled to a
substrate 40 with a brazing material 90.
[0068] Abrasive particles 50 may be of a variety of super hard
materials. Examples of such materials include without limitation,
diamond, polycrystalline diamond (PCD), cubic boron nitride (CBN)
and polycrystalline cubic born nitride (PCBN).
[0069] Additionally shown in FIG. 3, is a layer of an overlay
material 120, which is applied after the final brazing process. As
recited above, the overlay provides a working surface that is
substantially smoother than the working surface of the brazing
alloy. Such smoothness and planarity provides a number of benefits,
including reduced incidence of micro-scratching from flaking braze,
and better bonding with the anti-corrosive layer when included. In
one aspect, the working surface of the overlay material may have an
Ra value of less than about 1 micrometer.
[0070] A number of suitable overlay materials may be used. However,
in one aspect, the overlay materials include, without limitation,
tin, nickel, tungsten, cobalt, chromium, and alloys thereof, such
as a zirconium nickel alloy. The overlay material may be applied by
a wide variety of methods. Examples of methods for applying the
overlay material include without limitation, electroplating and
physical vapor deposition (PVD). The layer of overlay material may
be of any thickness required to achieve a specific result, but in
one aspect of the invention the layer may have a thickness of from
about 0.1 to 50 micrometers thick. In another aspect, the thickness
of the overlay may be from about 0.1 to about 5 micrometers.
[0071] Further illustrated in FIG. 3, is an anti-corrosive layer
130. The optional anti-corrosive layer is formed over the surface
of the CMP pad dresser after the abrasive particles 50 have been
affixed to the substrate 40. In one aspect, the anti-corrosive
layer may be a super abrasive material such as diamond-like carbon
(DLC), or amorphous diamond. In one embodiment, the anti-corrosive
layer has an atomic carbon content of at least about 80%.
Additionally, while the anti-corrosive layer may have a variety of
thicknesses as required to achieve a specific result, generally the
thickness is in the range of 0.5 to 5 micrometers. In one aspect,
the anti-corrosive layer has a thickness less than 3 micrometers.
Such a thin anti-corrosive layer ensures that the working surface
of the CMP pad dresser is protected without reducing the ability of
the abrasive particles to dress the CMP pad. The anti-corrosive
layer is generally produced by use of a physical vapor deposition
(PVD) method. PVD methods such as the use of a cathodic arc with a
graphite cathode, which is generally known in the art.
[0072] One advantage provided by the anti-corrosive layer 130, is
that it effectively "seals" the working surface, and may also seal
any other desired surfaces of the CMP pad dresser 30 that may be
vulnerable to chemical attack. As a sealant, the anti-corrosive
layer protects the brazing material 90 from chemical attack by the
abrasive chemical slurry held within the CMP pad. This protection
allows CMP pad dresser to dress a CMP pad in situ, and eliminates
the production pauses used to prolong the useful life of prior art
CMP pad dressers. The continual and even dressing of the CMP pad
allows for greater production output, and prolongs the life and
efficiency of the CMP pad.
[0073] While the anti-corrosive layer 130 may be used in some
embodiments of the present invention, it is notable that the
overlay material 120 has significant anti-corrosive characteristics
in and of itself. As such, many of the production advantages may be
obtained to a substantial degree, only when the overlay material is
used, and without the use of the anti-corrosive layer.
[0074] One method of affixing abrasive particles 180 to a substrate
is shown in FIGS. 4-6. First, a template 140 having apertures 150
is placed upon a sheet of brazing alloy 190. In one aspect of the
present invention, the sheet may be a rolled sheet of continuous
amorphous brazing alloy. In another aspect, the sheet may be a
brazing alloy powder that is held together with a binder material.
In an additional aspect, the brazing alloy powder may include other
metallic powders, and such other powders may constitute a majority
of the material in the brazing sheet. In yet another aspect, the
sheet may be sufficient to act as a substrate. The use of the
template allows controlled placement of each abrasive particle at a
specific location by designing the template with apertures in a
desired pattern.
[0075] After the template 140 is place on the brazing alloy sheet
190, the apertures 150 are filled with abrasive particles 180. The
apertures have a predetermined size, so that only one abrasive
particle will fit in each. Any size of abrasive particle or grit is
acceptable, however in one aspect of the invention, the particle
sizes may be from about 100 to about 350 micrometers in
diameter.
[0076] In another aspect of the invention, the size of the
apertures in the template may be customized in order to obtain a
pattern of abrasive particles having a size within a uniform in
size range. In one embodiment, the apertures of the template are
sufficient to select only grits within a size range having a
variance no greater than 50 micrometers. This uniformity of grit
size contributes to the uniformity of CMP pad grooming, as the work
load of each abrasive particle is evenly distributed. In turn, the
even work load distribution reduces the stress on individual
abrasive particles, and extends the effective life of the CMP pad
dresser.
[0077] After the apertures of the template 150 are all filled with
grits 180, any excess abrasive particles are removed, and a flat
surface 160 is applied to abrasive particles. The flat surface 160
must be of an extremely strong, rigid material, so that it is
capable of pushing abrasive particles down into the brazing alloy
sheet 190. Such materials typically include, but are not limited to
steel, iron, alloys thereof, etc.
[0078] Abrasive particles 180 are shown to be embedded in brazing
alloy sheet 190 in FIG. 6. Because surface 160 was flat, the
abrasive particles will extend away from the substrate to a
predetermined, uniform height. This uniform height will be
determined by the thickness of template 140, and in a preferred
embodiment, each abrasive particle will extend to within 50
micrometers of this distance. As such, each abrasive particle
grooms to substantially the same depth on the CMP pad. However, it
is to be understood that in certain applications, grit height may
not be desired to be uniform. As such, those of ordinary skill in
the art will recognize that grit patterns of varied height may be
provided by so configuring the template, 140 and the surface 160 to
provide such a design. For example, in one aspect, the surface 160
may have a concave shape so as to press the peripherally located
particles further down than the centrally located particles. As can
be seen, such a concave shape will provide a slope for the abrasive
particles which begins at a low point with the working ends of the
peripherally particles and slopes up to a high point at the working
ends of the centrally located particles.
[0079] Abrasive particles 180 as shown in FIGS. 4-6 are rounded.
However, in FIG. 3, they are pointed. The scope of the present
invention encompasses abrasive particles of any shape, including
euhedral, octahedral, cubo-octaheral, or naturally shaped
particles. However, in one embodiment, the abrasive particles have
a predetermined shape with a sharp point or apex extending in a
direction away from the substrate 40.
[0080] In an alternative embodiment, rather than pressing the
abrasive particles 180 into the brazing alloy sheet 190, they may
be fixed in the templated position by disposing an adhesive on the
surface of the brazing alloy sheet. In this manner, the particles
remain fixed in place when the template is removed, and during heat
processing. In yet another embodiment of the invention, the
template 140 may be laid upon a transfer sheet (not shown) having a
thin adhesive film thereon. In this case, the particles become
adhered to the transfer sheet using the template procedure
specified above. The template is then removed, and the transfer
sheet is laid onto the brazing sheet 190 with abrasive particles
facing the sheet. Disposed upon the brazing sheet is the
afore-mentioned adhesive layer, which is more strongly adhesive
than the adhesive on the transfer sheet. Therefore, the abrasive
particles are transferred to the sheet of brazing alloy in the
pattern dictated by the template.
[0081] After the abrasive particles 180 are at least partially
embedded in, or adhered to, the brazing alloy sheet 190, the sheet
is affixed to the substrate 40 as shown in FIG. 3. Alternatively,
in some embodiments, the sheet of brazing alloy may be first
affixed to the substrate, and the abrasive particles subsequently
added thereto using the template procedure described herein. The
brazing alloy used may be any brazing material known in the art,
but in one aspect, may be a nickel alloy that has a chromium
content of at least 2% by weight. A brazing alloy of such a
composition will be nearly super hard in and of itself, and less
susceptible to chemical attack from the abrasive containing slurry.
Therefore, the anti-corrosive layer 130, and the overlay material
120 are optional.
[0082] Because the abrasive particles 50 are firmly held in, or on
the brazing alloy sheet 90, the surface tension of the liquid
brazing alloy is insufficient to cause particle clustering as shown
in FIG. 2. Additionally, braze thickening occurs to a much lesser
degree and few or no "mounds" are formed. Rather, the braze forms a
slightly concave surface between each abrasive particle, which
provides additional structural support. In one embodiment, the
thickness of the brazing alloy sheet 90 is predetermined to allow
at least about 10 to 90% of each abrasive particle to protrude
above the outer, or working, surface of brazing material 90. In
another aspect, when the overlay material 120 is used, the abrasive
particles may be selected or placed, so that at least about 10 to
about 90% of each abrasive particle protrudes above the outer, or
working, surface of the overlay material 120.
[0083] As a result of the methods for maintaining the abrasive
particles 50 in a fixed position during processing, even spaces may
be created between abrasive particles. Additionally, the abrasive
grits may extend to a uniform height or distance above the
substrate 40, which means when applied to a CMP pad, they will
protrude to a uniform depth within the pad fibers. The even spacing
and uniform protrusion causes the CMP to be dressed or groomed
evenly, which in turn increases the polishing efficiency of the CMP
pad and extends its useful life. In addition to the specific
methods of embedding, or adhering the abrasive particles to the
brazing alloy, those skilled in the art will recognize suitable
alternative procedures, such as fixing the abrasive particles to
the substrate, and then placing the braze thereon. In this case,
the particles may be positioned on the substrate using the template
method recited above, and held in place by a glue, or other
suitable binder. The braze material is then showered, or placed on
the substrate around the abrasive particles, and the overlay
material may be added.
[0084] Although the present invention encompasses a wide variety of
patterns for abrasive particle placement which may be created using
the method described above, one aspect of the present invention is
the recognition of specific predetermined patterns that more
adequately meet the particular needs and conditions for which CMP
pad dressers are used. In order to accomplish such patterns, each
grit is positioned and held at a specific location in accordance
with the design of the pattern. Such patterns are indeed useful for
achieving specific CMP pad dressing results, and may be varied in
order to achieve a specific grooming result as will be seen.
[0085] For example, the grooming results of many known pads could
be improved by placing grits in a certain configuration.
Particularly, as CMP pads are flexible, the downward pressure
exerted by the dresser causes the pad to rise or mound as it comes
in contact with the leading edge of the dresser that is moving in a
given direction. While the rising action may improve the dressing
of the pad at the leading edge of the dresser as it allows a fuller
contact with the abrasive particles, it may also cause a dipping
action in the portion of the pad that has already passed under the
leading edge of the dresser. Even if no dipping occurs, generally,
the dressing action of the remaining portion of the dresser behind
the leading edge is less effective than that of the leading edge
(i.e. the first row of abrasive particles encountered by the pad as
dictated by the directional movement of the dresser, or the
spinning CMP pad, or both), because the pad is not allowed to rise
again once underneath the dresser. As such, the majority of the
dressing burden is placed on the abrasive particles at the leading
edge of the dresser, and uneven particle wear occurs.
[0086] Penetration depth of each particle is primarily controlled
by two factors, separation distance from other particles and
protrusion height. Sparsely spaced particles will dress more
aggressively than densely populated ones. Therefore, in one aspect
of the present invention, the pattern of abrasive particles may be
configured to allow the CMP pad to rise while underneath the
dresser at an interior or central location (i.e. a location that
follows a leading edge), thus allowing them to be dressed by
abrasive particles following those of the leading edge. In effect,
such a configuration provides a multiplicity of leading edges along
the working surface of the dresser. In other words, the particles
on the periphery have a higher density than the density of the
centrally located particles. The density of the periphery particles
can be at least about 1.25, 2, or 5 times greater than the density
of the central particles. Further the density can be a gradient of
high at the periphery particles and low at the central particles.
In this manner, the various densities allow the CMP pad is to rise
while under a central portion of the pad dresser, and increase
dressing effectiveness. As will be seen, a variety of particle
configurations or patterns can provide the required spacing of
abrasive particles to achieve such actions and be used to achieve
specifically desired dressing results.
[0087] As illustrated by way of example in FIG. 7, in one aspect of
the invention, the abrasive particles may be arranged so as to have
abrasive particles located only along the leading edge 200 of the
pad dresser 30. Referring now to FIG. 8, in another aspect of the
invention, the abrasive particles may be arranged to be more highly
concentrated (i.e. have a higher density) along the leading edge
200 than in the center 210. By contrast, in a further aspect of the
invention, the abrasive particles may be arranged such that the
abrasive particles are more concentrated in the center than along
the leading edge (not illustrated). In still another aspect, the
particles may be arranged and distributed at a higher concentration
in the central portion of the pad dresser than the particles at the
periphery. Further, the particles located between the central and
peripheral portions are arranged to have a density that is between
the densities of the central portion and periphery portion.
Referring now to FIG. 9, in yet another aspect of the invention,
the abrasive particles may be arranged such that the they are
uniformly distributed with a space between each particle that is
sufficient to allow the afore-discussed pad rising. In one aspect,
the uniformly distributed particles may form a grid and be evenly
spaced at a distance of about 1.5 to about 10 times the size of
each individual grit. As will be recognized by those skilled in the
art, the abrasive particles may also be arranged in various
concentration gradients increasing or decreasing in concentration
from the leading edge toward the center of the CMP pad dresser (not
illustrated).
[0088] In another embodiment, the present invention provides a
method that increases the work load on centrally located
superabrasive particles in a CMP pad dresser during dressing of a
CMP pad with the dresser. The method configures superabrasive
particles to in a pattern that reduces penetration of peripherally
located particles into the CMP pad and increases penetration of
centrally located particles into the CMP pad dresser. In some
aspects, the superabrasive particles are each individually located
at specific positions on the CMP pad substrate in accordance with
the predetermined pattern. The work load on the centrally located
particles can be increased to within at least about 10% to about
30% of the work load of the peripherally located particles. The
work load can further be substantially equal with the work load of
the peripheral particles or all particles.
[0089] Increasing the work load on the centrally located particles
can be accomplished in several ways. For example, the superabrasive
particles can be configured in a pattern that provides an upward
slope from working ends of the peripheral particles to the working
ends of the central particles, as illustrated in FIG. 10. Another
alternative for increasing the work load is affixing the
superabrasive particles in a pattern which provides a density of
peripherally located particles higher than the density of centrally
located particles, as described above. Finally, the pattern can be
configured to provide centrally located particles with an attitude
that causes higher particle penetration into the CMP pad than the
penetration provided by the attitude of the peripherally located
particles, as illustrated in FIG. 11.
[0090] With reference to FIG. 10, the present invention provides a
CMP pad dresser which increases the work load on the centrally
located superabrasive particles by providing a substrate 300
coupled to superabrasive particles having an upward slope 305 from
the peripheral superabrasive particles 320 to the centrally located
particles 310. The upward slope can be created by increasing the
particle height from the particles located on the periphery to the
particles located centrally. As a result, the upward slope
transfers the work load from the peripheral particles to the
central particles by providing a fuller contact with the central
particles and the CMP pad. The increased contact improves the
dressing of the CMP pad and the total wear of the pad conditioner.
The slope is determined as a measure of pad velocity and pad
flexibility. Generally, the pad is a deformable medium which
depresses when it comes in contact with the leading edge particles.
Normally, the depression of the pad will intensify depending on the
flexibility of the pad and the rotational speed of the pad. In a
preferred embodiment of the present invention the slope is from
about 0.1% to 0.5%, preferably the slope is 0.2%.
[0091] As an alternative, the slope may be obtained by the altering
the configuration of the substrate. As shown in FIG. 10, the
substrate of the CMP pad dresser is substantially flat, however, in
some aspects, the substrate may be contoured to conform to the
depression of the rotating CMP pad. Such contour may provide the
desired slope for the working ends of the abrasive particles 310
and 320. In such a case, the height of the particles above the
working surface of the substrate will be substantially uniform. The
substrate is usually made of a metallic, ceramic, or flexible
material. In a one embodiment the substrate can be stainless steel.
In some aspects, the substrate can be a powdered material that
becomes a solid upon processing. In further aspects, the powder may
include a brazing alloy of a metal such as nickel in combination
with a carbide forming element, such as chromium in an amount of at
least about 2 wt %. In some aspects, the substrate Further, the
substrate can consist essentially of a brazing material.
[0092] FIG. 11 is an illustration of a CMP pad dresser which
increases the work load on centrally located particles of a CMP pad
dresser while dressing a CMP pad. Abrasive particles wear at
different rates depending on the attitude of the particle.
Generally, the attitude of an apex will provide more penetration
into the CMP pad and will groom more aggressively than the other
attitudes. A particle which has an attitude of a face provides the
least amount of penetration and is the least aggressive in dressing
the pad. A particle having an edge as an attitude provides
intermediate grooming and penetration characteristics. Referring to
FIG. 11, a substrate 400 receives a plurality of superabrasive
particles 410, 420, 430 in a predetermined pattern. The pattern is
configured to provide centrally located particles with an attitude
that causes higher particle penetration into the CMP pad than
penetration provided by an attitude of particles located at the
periphery of a pad dresser. The centrally located superabrasive
particles 410 are oriented in an attitude that provides an apex at
the working end 405 of the particles. These particles groom the pad
more aggressively and have a higher degree of penetration than the
attitude provided by the other particles. The peripheral particles
420 can be oriented in an attitude that provides either an edge or
a face 430 at the working end 405 thereof. Notably, as shown in the
embodiment of FIG. 11, when the centrally located particles are
oriented in an attitude that provides an apex at the working end
405 thereof, and the attitude of the periphery particles 430 is a
face at the working end 405 thereof, any particles 420 therebetween
can be oriented in an attitude that provides an edge at the working
end thereof. However, in other typical embodiments, any particles
located between those of the periphery and those of the center will
be the same as the either of the other types. In one additional
embodiment (not shown) the centrally located particles may be
oriented in an attitude that provides an edge at the working end
thereof and the peripherally located particles may be oriented in
an attitude that provides a face at the working end thereof.
[0093] In addition to the above recited methods and devices, the
present invention provides a method of producing a CMP pad dresser
as described herein. In one aspect, such a method includes the
steps of providing a substrate and attaching superabrasive
particles to the substrate in a pattern that reduces penetration of
peripherally located particles into the CMP pad and increases
penetration of centrally located particles into the CMP pad.
[0094] Numerous modifications and alternative arrangements may be
devised by those skilled in the art without departing from the
spirit and scope of the present invention and the appended claims
are intended to cover such modifications and arrangements. Thus,
while the present invention has been described above with
particularity and detail in connection with what is presently
deemed to be the most practical and preferred embodiments of the
invention, it will be apparent to those of ordinary skill in the
art that numerous modifications, including, but not limited to,
variations in size, materials, shape, form, function, manner of
operation, assembly, and use may be made without departing from the
principles and concepts set forth herein.
* * * * *