U.S. patent application number 09/766155 was filed with the patent office on 2001-11-15 for printing of polishing pads.
Invention is credited to Duong, Chau H., James, David B., Lack, Craig D..
Application Number | 20010041511 09/766155 |
Document ID | / |
Family ID | 26872640 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010041511 |
Kind Code |
A1 |
Lack, Craig D. ; et
al. |
November 15, 2001 |
Printing of polishing pads
Abstract
A polishing pad includes a flexible substrate and a polymeric
polishing layer that has a repeatable pattern of polymeric
asperities that are manufactured by printing, according to a
gravure printing process or a screen printing process.
Inventors: |
Lack, Craig D.; (Wilmington,
DE) ; Duong, Chau H.; (Newark, DE) ; James,
David B.; (Newark, DE) |
Correspondence
Address: |
Rodel Holdings, Inc.
1105 North Market Street Suite 1300
Wilmington
DE
19899
US
|
Family ID: |
26872640 |
Appl. No.: |
09/766155 |
Filed: |
January 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60176827 |
Jan 19, 2000 |
|
|
|
60178951 |
Feb 1, 2000 |
|
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Current U.S.
Class: |
451/41 |
Current CPC
Class: |
B24B 37/24 20130101;
B24D 11/001 20130101; B24D 18/009 20130101; B24D 3/28 20130101;
B24B 37/26 20130101 |
Class at
Publication: |
451/41 |
International
Class: |
B24B 001/00 |
Claims
What is claimed is:
1. A process for making polishing pads useful in the manufacture of
a semiconductor device or a precursor thereto, comprising applying
a hydrophilic polymeric polishing layer having a pattern of
polymeric asperities to a flexible base substrate using a printing
process.
2. The process of claim 1 in which the hydrophilic polymeric
polishing layer is a polymeric material having: i. a density
greater than 0.5 g/cm.sup.3; ii. a critical surface tension greater
than or equal to 34 miliNewtons per meter; iii. a tensile modulus
of 0.02 to 5 GigaPascals; iv. a ratio of tensile modulus at
30.degree. C. to tensile modulus at 60.degree. C. of 1.0 to 2.5; v.
a hardness of 25 to 80 Shore D; vi. a yield stress of 300-6000 psi;
vii. a tensile strength of 1000 to 15,000 psi; and viii. an
elongation to break less than or equal to 500%,
3. The process of claim 2 in which the hydrophilic polymeric
polishing layer is a polymeric material comprising at least one
moiety from the group consisting of: 1. a urethane; 2. a carbonate;
3. an amide; 4. an ester; 5. an ether; 6. an acrylate; 7. a
methacrylate; 8. an acrylic acid; 9. a methacrylic acid; 10. a
sulphone; 11. an acrylamide; 12. a halide; 13. an imide; 14. a
carboxyl; 15. a carbonyl; 16. an amino; 17. an aldehydric and 18. a
hydroxyl.
4. The process of claim 3 in which the printing process used is
gravure printing.
5. The process of claim 3 in which the printing process used is
screen printing.
6. The process of claim 1 wherein the hydrophilic polishing layer
further comprises a plurality of soft domains and a plurality of
hard domains, the hard domains and soft domains having an average
size of less than 100 microns.
7. A polishing pad for use in chemical mechanical polishing,
comprising: a polishing layer consisting essentially of a
hydrophilic polishing layer applied by a printing process selected
from the group of gravure printing and screen printing, said
polishing layer having: i. density greater than 0.5 g/cm.sup.3; ii.
a critical surface tension greater than or equal to 34 milliNewtons
per meter; iii. a tensile modulus of 0.02 to 5 GigaPascals; iv. a
ratio of tensile modulus at 30.degree. C. to tensile modulus at
60.degree. C. of 1.0 to 2.5; v. a hardness of 25 to 80 Shore D; vi.
a yield stress of 300-6000 psi; vii. a tensile strength of 1000 to
15,000 psi; and viii. an elongation to break less than or equal to
500%.
8. The polishing pad claim 7 in which the hydrophilic polymeric
polishing layer is a polymeric material comprising at least one
moiety from the group consisting of: 1. a urethane; 2. a carbonate;
3. an amide; 4. an ester; 5. an ether; 6. an acrylate; 7. a
methacrylate; 8. an acrylic acid; 9. a methacrylic acid; 10. a
sulphone; 11. an acrylamide; 12. a halide; 13. an imide; 14. a
carboxyl; 15. a carbonyl; 16. an amino; 17. an aldehydric and 18. a
hydroxyl.
9. A method of polishing a substrate of a semi-conductor device,
comprising: providing a polishing pad of claim 7 and interposing a
slurry of particles between the semiconductor device and the pad
and chemical mechanical polishing the surface of the semiconductor
device.
Description
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 60/176,827 filed on Jan. 19, 2000 and U.S.
Provisional Patent Application No. 60/178,951 filed on Feb. 1,
2000.
[0002] The present invention relates to polishing pads for
polishing dielectric/metal composites, semiconductors, integrated
circuits and metal substrates, especially copper and tungsten as
preferred substrates.
[0003] Polishing generally consists of the controlled wear of an
initially rough surface to produce a smooth specular finished
surface. This is accomplished by rubbing a polishing pad against
the surface of the article to be polished in a repetitive, regular
motion while a solution containing a suspension of fine particles,
typically a slurry, is present at the interface between the
polishing pad and the work piece. Commonly employed pads are made
by impregnating non-woven fibers such as polyester with a urethane
or are formed from filled cast polyurethanes. The polishing contact
area of these pads can be affected by texturing the surface of the
pads, grooving the pads, embossing or perforating the pads. s shown
in Cook et al, U.S. Pat. No. 5,489,233 issued Feb. 6, 1996, pads
having a macrotexture and microtexture can be formed. Such pads can
be produced by molding, pressing, embossing, casting, cutting,
sintering or by photolithographic means.
[0004] Typically, polishing pads are made in a batch process where
one pad is produced and then another which often results in
significant batch to batch variability. This variability in pads is
detrimental to semiconductor wafer manufacturing since it leads to
polishing process variability and ultimately yield losses. A pad
manufacturing process is needed that forms a pad having a uniform
surface, and in particular, a continuous process is needed that
forms a sheet having a uniform surface. From such a sheet, either
individual polishing pads can be cut or the sheet can be left
intact to form roll or belt type pads for next generation polishing
tools.
[0005] The invention relates to polishing pads and a process for
making polishing pads by printing.
[0006] Embodiments of the invention will now be described by way of
example with reference to the accompanying drawings, according to
which:
[0007] FIG. 1 is a perspective view of gravure printing that can be
used to form the polishing pads of this invention.
[0008] FIG. 2 is a perspective view of screen printing that can be
used to form the polishing pads of this invention.
[0009] The invention is directed to polishing pads and a process,
preferably a continuous process, for making these polishing pads;
wherein the pads have a flexible base substrate; and firmly adhered
to the base substrate a hydrophilic polymeric polishing layer
having a pattern of polymeric asperities formed by printing.
According to one embodiment, printing includes a process of gravure
printing. According to another embodiment, printing includes a
process of screen printing. An embodiment of a polishing pad
without abrasive particles is formed by the process of printing,
and perform polishing in combination with particulate containing
slurries. Another embodiment of a polishing pad includes abrasive
particles that may be incorporated into the pad by the process of
printing. The pad with abrasives perform polishing in which the pad
is used with a reactive polishing liquid that is without
abrasives.
[0010] The polishing pad made by the process of this invention has
a polishing layer of a hydrophilic polymer having a pattern of
polymeric asperities formed by gravure printing or screen printing.
The printing process forms a repeatable surface pattern of
polymeric asperities that have a controlled particle size, pattern,
geometry and height. Prior art methods for forming patterns on
polishing pads include molding, sintering, pressing, embossing,
casting or cutting. These methods are either not suitable for
manufacture of continuous pads or not repeatable with any great
accuracy. The use of a printing process, for example, a gravure or
screen printing process, provides an accurate repeatable surface
area pattern that is applied as a polishing layer of a polishing
pad. Gravure printing is best suited for the formation of a
polishing layer having a pattern of precise, low-profile polymeric
asperities. Screen printing is best suited for the formation of a
polishing layer having a pattern of higher aspect polymeric
asperities. These polymeric asperities are the numerous peaks of
polymeric material which may be of various heights and shapes that
forrn the polishing layer which are applied by the printing process
on the flexible substrate. The shapes, heights and area pattern of
the polymeric asperities are repeatably applied with minimized
variation, due to the fixed pattern on the surface of the gravure
printing roll or the fixed area pattern of a screen used in the
screen printing process.
[0011] FIG. 1 discloses a gravure printing apparatus and process
for manufacture of a polishing layer onto a flexible substrate on
which printing is performed. A rotogravure cylinder 1 is mounted on
a typical rotogravure printing machine. The cylinder 1 has an outer
peripheral surface 2 in which the pattern of the polishing layer is
etched. The fixed area pattern 3, is etched on the entire surface 2
of the cylinder 1. For simplicity, only a small portion of the
pattern is shown. In juxtaposed spaced relationship to cylinder 1
is impression roller 4 which is in intimate contact with cylinder 1
during the printing process. Cylinder 1 is partially immersed in a
tray 7 containing a polymeric material (polymer solution or
dispersion or a liquid low molecular weight polymer) 8 and is in
frictional engagement with a doctor blade 6, which wipes off the
excess polymeric solution or dispersion and returns this excess to
the tray 7.
[0012] A flexible base substrate sheet 5 that is to be printed
passes between the cylinder 1 and impression roller 4 and is
maintained in firm intimate contact with cylinder 1 by properly
adjusting roller 4. This printing process is advantageous since the
depth of the layer of polymeric material and the area pattern of
peaks and valleys are continuously applied and repeated with great
accuracy, due to the fixed dimensions of the etched pattern on the
cylinder 1. The intimate contact of the substrate sheet 5 and the
cylinder 1 is very important in order to assure the transfer of all
available polymeric material to the surface of the substrate being
printed. The impression roller 4 must maintain a constant force and
pressure on the cylinder 1 with the substrate 5 in order to assure
the desired result. Typically a force of about 150 psi (pounds per
square inch) is maintained but depending on the materials used a
force in the range of 50-300 psi can be used. After being printed
the polymeric material on the substrate sheet is cured, for
example, by being passed through a curing zone 13, FIG. 2, that is
a heating oven (typically, using temperatures of 75-150.degree. C.)
but radiation can be used such as UV radiation, to cure the
polymeric material printed onto the substrate. The resulting
substrate with the cured patterned coating then is wound up and can
be cut into individual polishing pads or provides a continuous
polishing belt form of polishing pad.
[0013] Further details of rotogravure printing and the construction
of cylinders used in rotogravure printing are known from Bardin,
U.S. Pat. No. 4,197,798, hereby incorporated by reference.
[0014] FIG. 2 discloses a screen printing apparatus and process
that can be used to form the polishing pads of this invention.
Screen printing is performed by dispensing the polymeric material,
with or without abrasive particles in suspension, through an open
screen. The fixed area pattern of the screen defines the repeatable
area pattern of the polymeric material that is dispensed through
the area pattern of the screen. A flexible base sheet substrate 9
is fed from a roll and is in juxtaposed position to a screen
template 10 being fed from a roll. A polymeric material (which can
be in the form of a solution or dispersion or a liquid low
molecular weight polymer) 11 is placed in contact with the template
10 and forced into and through the pattern of the template 10 by
doctor blade 12 and into contact with the substrate 9. The template
10, the polymeric material 11 on the substrate 9 are passed through
a curing zone 13 which may be an oven (typically, using
temperatures of 75-150.degree. C.) or for example UV radiation to
cure the polymeric material on the substrate. The template 10 is
simply removed after curing and wound up. The resulting substrate
with the cured patterned coating 14 then is wound up and can be cut
into individual polishing pads or into polishing belts.
[0015] Manufacturing of polishing pads by either gravure or screen
printing techniques enables a continuous polishing surface with a
single continuous region, or a region divided into discrete regions
of polishing surface to be defined separated by channels or gaps
therebetween. The shape of these discrete regions may be any
geometry (circular, square, triangular, polygonal, etc.) but
hexagons are preferred because of ease of achieving high-density,
regular packing. Typical dimensions of these regions are as
follows:
1 Feature Discrete Area Discrete Area Channel Dimension Diameter
(mm) Thickness (mm) Width (mm) Range 1-25 0.1-10 0.1-15 Preferred
Range 3-15 0.3-3 0.3-3 Most Preferred 5-10 0.5-2 0.5-2 Range
[0016] These discrete regions are advantageous for the following
reasons:
[0017] After a polishing pad is formed by screen printing, it is
necessary to remove moisture from the screened formulation. If
there is a continuous coating or layer, unacceptable cracking of
the coating or layer occurs. This is eliminated by forming discrete
regions.
[0018] The channels surrounding the discrete regions facilitate
slurry (or reactive liquid) transport across the pad surface and
the subsequent removal of polishing debris in the polishing
operation.
[0019] The flexible base substrates used in this invention can
comprise a single layer or multiple layers and can comprise of a
combination of layers that are bonded together. The substrate is
preferably a flexible web capable of being pulled from a roll or
easily wound into a roll. One preferred substrate is a
non-corrosive metal, such as aluminum or stainless steel. Other
preferred base substrates are plastics, such as engineering
plastics, for example a polyamide, polyimide, and/or polyester,
particularly "PET" poly(ethylene terephthalate).
[0020] The flexible base substrate of the present invention
preferably has a thickness of about 0.1-10 millimeters. In a
preferred embodiment, the support layer has a thickness of less
than 5 millimeters, more preferably less than 2 millimeters. yet
more preferably less than 1 millimeter.
[0021] The polishing layer of the polishing pad of this invention
comprises a hydrophilic polymeric material that optionally may be
filled with abrasive particles. The polishing layer preferably has:
(i) a density greater than 0.5 g/cm.sup.3; (ii). a critical surface
tension greater than or equal to 34 milliNewtons per meter; (iii) a
tensile modulus of 0.02 to 5.00 GigaPascals; (iv) a ratio of
tensile modulus at 30.degree. C. to tensile modulus at 60.degree.
C. of 1.0 to 2.5; (v) a hardness of 25 to 80 Shore D; (vi) a yield
stress of 300-6000 psi (2.1-41.4 MegaPascal); (vii) a tensile
strength of 1000 to 15,000 psi (7-105 MegaPascal); and (viii) an
elongation to break up to 500%. In a preferred embodiment, the
polishing layer farther comprises a plurality of soft domains and
hard domains.
[0022] Preferred hydrophilic polymeric materials used to provide a
polishing layer having a critical surface tension greater than or
equal to 34 milliNewtons per meter, more preferably greater than or
equal to 37 and most preferably greater than or equal to 40
milliNewtons per meter are shown below in comparison other
conventional polymers. Critical surface tension defines the
wettability of a solid surface by noting the lowest surface tension
a liquid can have and still exhibit a contact angle greater than
zero degrees on that solid. Thus, polymers with higher critical
surface tensions are more readily wet and are therefore more
hydrophilic.
2 Critical Surface Polymer Tension (mN/m) Polytetrafluoroethylene
19 Polydimethylsiloxane 24 Silicone Rubber 24 Polybutadiene 31
Polyethylene 31 Polystyrene 33 Polypropylene 34 Polyester 39-42
Polyacrylamide 35-40 Polyvinyl alcohol 37 Polymethyl methacrylate
39 Polyvinyl chloride 39 Polysulfone 41 Nylon 6 42 Polyurethane 45
Polycarbonate 45
[0023] In one preferred embodiment, the polishing layer of the pad
is derived from one of the following:
[0024] 1. an acrylated urethane;
[0025] 2. an acrylated epoxy;
[0026] 3. an ethylenically unsaturated organic compound having a
carboxyl, benzyl, or amide functionality;
[0027] 4. an aminoplast derivative having a pendant unsaturated
carbonyl group;
[0028] 5. an isocyanurate derivative having at least one pendant
acrylate group;
[0029] 6. a vinyl ether,
[0030] 7. a urethane
[0031] 8. a polyacrylamide
[0032] 9. an ethylene/ester copolymer or an acid derivative
thereof;
[0033] 10. a polyvinyl alcohol;
[0034] 11. a polymethyl methacrylate;
[0035] 12. a polysulfone;
[0036] 13. an polyamide;
[0037] 14. a polycarbonate;
[0038] 15. a polyvinyl chloride;
[0039] 16. an epoxy;
[0040] 17. a copolymer of the above; or
[0041] 18. a combination of any of the above.
[0042] In another preferred embodiment of this invention, the
polishing layer material comprises: (1) a plurality of rigid
domains which resists plastic flow during polishing; and (2) a
plurality of less rigid domains which are less resistant to plastic
flow during polishing. This combination of properties provides a
dual mechanism which has been found to be particularly advantageous
in the polishing of silicon dioxide and metal. The hard domains
tend to cause the protrusion to rigorously engage the polishing
interface, whereas the soft domains tend to enhance polishing
interaction between the protrusion and the substrate surface being
polished.
[0043] The rigid phase size in any dimension (height, width or
length) is preferably less than 100 microns, more preferably less
than 50 microns, yet more preferably less than 25 microns and most
preferably less than 10 microns. Similarly the non-rigid phase is
also preferably less than 100 microns, more preferably less than 50
microns, more preferably less than 25 microns and most preferably
less than 10 microns. Preferred dual phase materials include
polyurethane polymers having a soft segment (which provides the
non-rigid phase) and a hard segment (which provides the rigid
phase). The domains are produced during the forming of the
polishing layer by a phase separation, due to incompatibility
between the two (hard and soft) polymer segments.
[0044] Other polymers having hard and soft segments could also be
appropriate, including ethylene copolymers, copolyester, block
copolymers, polysulfones copolymers and acrylic copolymers. Hard
and soft domains within the pad material can also be created: (1)
by hard and soft segments along a polymer backbone; (2) by
crystalline regions and non-crystalline regions within the pad
material; (3) by alloying a hard polymer with a soft polymer; or
(4) by combining a polymer with an organic or inorganic filler.
Useful compositions include copolymers, polymer blends
interpenetrating polymer networks and the like.
[0045] In a another embodiment of this invention, thin polishing
layers less than 200 microns, more preferably less than 100 microns
and yet more preferably less than 50 microns and comprise a random
surface texture comprising pores and/or micro-voids of varying
sizes and dimensions can be formed.
[0046] The combination of a thin base layer and a thin polishing
layer can provide ultra high performance polishing, due to a more
precise and predictable polishing interaction when a rigid support
presses the thin polishing pad against (and the pad is moved in
relation to) a substrate to be polished. This polishing pad can be
manufactured to very tight tolerances and (together with the rigid
support) can provide predictable compressibility and planarization
length. "Planarization length" is intended to mean the span across
the surface of a polishing pad which lies substantially in a single
plane and remains in a single plane during polishing, such that as
tall peaks are polished, peaks of lesser height do not polish
unless or until the taller peak is diminished to the height of the
shorter peak.
[0047] The polishing pads formed according to this invention have a
polishing layer that is substantially free of macro-defects.
"Macro-defects" are intended to mean burrs or other protrusions
from the polishing surface of the pad which have a dimension
(either width, height or length) of greater than 25 microns.
Macro-defects should not be confused with "micro-asperities."
Micro-asperities are intended to mean burrs or other protrusions
from the polishing surface of the pad which have a dimension
(either width, height or length) of less than 10 microns. It has
been surprisingly discovered that micro-asperities are generally
advantageous in ultra precision polishing, particularly in the
manufacture of semi-conductor devices, and in a preferred
embodiment, the polishing layer provides a large number of
micro-asperities at the polishing interface.
[0048] To obtain adequate adhesion of the hydrophilic polymer
polishing layer to the flexible base substrate, the substrate may
require a primer or an adhesion promoter.
[0049] Conventional polishing compositions or slurries used with
the polishing pads of this invention to polish dielectric metal
composites, semiconductors or integrated circuits generally contain
finely divided abrasive particles in an aqueous slurry or
dispersion. The part or substrate that is to be polished is bathed
or rinsed in the composition while the polishing pad is pressed
against the substrate and the pad and substrate are moved relative
to each other. The abrasive particles are pressed against the
substrate under a load and the lateral motion of the pad causes the
abrasive particles to move across the surface of the substrate
resulting in wear and volumetric removal of the surface of the
substrate. The rate of removal is determined by the amount of
pressure applied, the velocity of the polishing pad and the
chemical activity of the abrasive particles.
[0050] Polishing rates can be increased by adding components to the
polishing composition which by themselves are corrosive to the
substrate. When used together with abrasive particles,
substantially higher polishing rates can be achieved. This process
is termed chemical-mechanical polishing (CMP) and is a preferred
technique used to polish semiconductors and semiconductor devices,
particularly integrated circuits. Additives can be introduced to
the polishing compositions to accelerate the dissolution of a metal
component of the substrate such as a dielectric/metal composite
structure, for example an integrated circuit. The purpose of this
is to preferentially remove the metal portion of the circuit so
that the resulting surface becomes coplanar with an insulating or
dielectric feature, typically composed of silicon dioxide. This
process is termed planarization. Oxidizing agents, such as hydrogen
peroxide, also can be added to the polishing compositions used for
CMP to convert a metal surface into an oxide that then is subject
to CMP.
[0051] Typical polishing compositions used for CMP of
semiconductors, integrated circuits wafers and the like are
disclosed in Brancaleoni et al, U.S. Pat. No. 5,264,010 issued Nov.
23, 1993; Cook et al, U.S. Pat. No. 5,382,272 issued Jan. 17, 1995;
Brancaleoni et al, U.S. Pat. No. 5,476,606 issued Dec. 19, 1995 and
Wang et al, U.S. Pat. No. 5,693,239 issued Dec. 2, 1997. While
these are excellent polishing compositions, it would be desirable
to have a composition that would remove an extremely thin layer
without scratching of the surface and can be used for polishing
substrates for semiconductor devices that require high
planarization.
[0052] These conventional polishing compositions typically are
slurries and the abrasive particles therein have a surface area of
about 40-430 m.sup.2/g, and mean aggregate size of less than 500 nm
and a force sufficient to repel and overcome van der Walls forces
between the particles. The surface area of the particles is
measured by the nitrogen adsorption method of S. Brunaure, P. H.
Emmet, and I. Teller, J. Am. Chemical Society, Vol. 60, page 309
(1938). The particles may comprise between 0.5% -55% by weight of
the slurry depending on the degree of abrasion required.
[0053] The abrasive particles can be primary particles having a
mean size range of 25-500 nm or a mixture of primary particles and
agglomerated smaller particles having a mean size range of 25-500
nm. In a preferred embodiment of the method of this invention, the
abrasive particles have a mean size ranging of 25 and 500 nm.
Typically useful abrasive particles are alumina, ceria, diamond,
silica, titania and the like. These particles and agglomerates can
be encapsulated and suspended satisfactorily so that, while
maintaining the hardness, the possibility of scratches to the
surface being polished is mininal.
[0054] It is preferred that the particles in the slurry not settle
and not be agglomerated. However, it is understood that depending
on the percentage of primary particles and agglomerated particles,
the particles in the slurry may settle and require redispersion by
mechanical means such as mixing.
[0055] Oxidizers can be added to these slurries in amounts of about
0.01-10.0% by weight, based on the weight of the slurry. A wide
variety of oxidizers can be used such as oxidizing metal salts,
oxidizing metal complexes, iron salts such as nitrates, sulfates,
potassium ferricyanide and the like, aluminum salts, sodium salts,
potassium salts, ammonium salts, quaternary ammonium salts,
phosphonium salts, peroxides, chlorates, perchlorates, iodates,
periodates, permanganates, persulfates and mixtures thereof. These
oxidizers also can be added to polishing compositions of this
invention wherein colloidal sulfur is the primary polishing
constituent and other abrasives are not present.
[0056] Organic additives can be used in the slurries in
concentrations of about 0.01-10% by weight, based on the weight of
the slurry. These additives function as an encapsulating,
suspending means for the particles, which are present, so that the
possibility of scratches is minimal in spite of the hardness of the
small particles. Alternatively, these additives may improve the
surface quality by adsorbing on the polished surface as well as
protecting the oxide surface and associated barrier layer during
polishing. These organic additives may also be incorporated to
improve the global wafer uniformity of the surface of the
semiconductor being polished. Preferred additives contain carboxy
or amino groups and are organic liquids such as polyvinyl
pyrrolidone, phthalates like ammonium hydrogen phthalate and
potassium phthalate and phosphates like acetodiphosphonic acid.
[0057] Typically, organic acids can be added. These acids are
defined as having functional groups having a dissociable proton.
These include, but are not limited to carboxylate, hydroxyl,
sulfonic and phosphonic groups. Carboxylate and hydroxyl groups are
preferred since these present the widest variety of effective
organic acids. Useful acids include citric acid, lactic acid, malic
acid and tartaric acid.
[0058] These organic additives also can be used in polishing
compositions in which colloidal silica is the primary polishing
constituent.
[0059] In order to further stabilize the slurry against settling,
flocculation and agglomeration a variety of additives such as
surfactants, polymeric stabilizers, or other surface active
dispersing agents may be used.
[0060] Physical, chemical and mechanical parameters all play a role
in polishing a surface. Polishing pressure is an external magnitude
with which the polishing can be controlled and optimized.
Relatively low polishing pressure yields an optimal result,
although it is not required, because the particles may be prevented
from being pressed through the encapsulating layer, created by the
organic additives, during polishing.
[0061] The following examples illustrate the invention. All numbers
and percentages are on a weight basis unless otherwise
specified.
EXAMPLES
Example 1
[0062] This example demonstrates the ability to achieve good
polishing performance with a pad made using a gravure printing
process.
[0063] Using the gravure printing process shown in FIG. 1, a sheet
of 2 millimeter thick polyethylene terephthalate (PET) film,
precoated with an adhesion promoting coating was printed with a
polishing pattern. An aqueous based latex urethane (W242 from
Witco) containing 2 weight % (40 vol. %) of polymeric microballons
(Expancel) was charged into tray 7. A rotogravure cylinder I etched
with a polishing pattern designed for a polishing pad was used to
apply the polishing layer. The roll pressure used on the impression
roll 4 was 150 psi. The polishing layer was cured to form a sheet
having a polishing layer having uniform pattern of polymeric
asperities. The sheet was die cut into 28 inch diameter pad. A
pressure sensitive adhesive was applied to the back of the pad and
attached to a polishing machine described below.
[0064] The pad was used to polish TEOS oxide films deposited on
silicon wafers. Polishing was performed on a Strasbaugh 6DS-SP
using a down-force of 9 psi, platen speed of 20 rpm and a carrier
speed of 15 rpm. The slurry was ILD1300 from Rodel, used at a flow
rate of 125 mil/min. No pad conditioning was done either during
polishing or between wafers. Wafers that were polished had
excellent planarization , good surface appearance and excellent
removal rate of material.
Example 2
[0065] This example demonstrates the ability to achieve good
polishing performance with a pad made by a screen printing process.
The abrasive is incorporated into the pad and the pad is used with
a particulate-free reactive liquid to polish tungsten.
[0066] Referring to the screen printing process shown in FIG. 2, a
sheet of 0-0.15 mm thick polyethylene terephthalate (PET) film 9
precoated with an adhesion promoting coating was used as a
substrate and was screen printed with a filled latex formulation
11. The filled latex formulation consisted of a mixture of an
aqueous based latex (Vinyl Acetate-Ethylene emulsion, A-460, from
Air Products) and an abrasive filler of 0.25 micron alumina. The
filler loading was 75% based on dry weight of total formulation and
total percent solids was 70%. A stainless steel stencil 10 was
placed in intimate contact with the PET film. The stencil had a 79%
open area, comprising hexagonal openings of 6 mm hole diameter
separated by 35 mil wide ribs. The filled latex formulation was
applied over the stencil using a doctor blade 12. This forced the
latex formulation material through the stencil onto the PET film.
The resulting layer which is the polishing layer, consists of
discrete hexagonal regions, and was cured at 60.degree. C. in an
oven to form a polishing layer of 1 mm uniform thickness and having
uniform distribution of asperities. A pressure sensitive adhesive
was subsequently applied to the back of the PET film and the
resultant polishing pad was used to polish a tungsten film as
described below.
[0067] A polishing pad was cut from the above prepared coated PET
film and attached to the polishing platen of a 12" Leco AP-300
polishing machine, using a down force of 7 psi, platen speed of 56
rpm and a carrier speed of 150 rpm. The pad was used in conjunction
with a particulate-free reactive liquid based on potassium iodate
as the oxidizing component (MSW2000B from Rodel Inc.), used at a
delivery rate of 20 ml/min. Pad concurrent conditioning was done
using a 3" 100-grit TBW diamond disc which rotated at 48 rpm. A
tungsten film was polished with the pad and a stable 7 grams/min.
removal rate of tungsten was achieved.
[0068] In this example, the screen printing process demonstrated
the following major advantages over pads made according to a
conventional process: (1) at high filler loading, 75% and above,
surface cracking on drying in a oven was eliminated and, (2) the
printing process automatically created channels for liquid
distribution across the pad surface. In conventional pad
manufacturing, the above are normally created in subsequent,
separate manufacturing steps.
[0069] Nothing from the above discussion is intended to be a
limitation of any kind with respect to the present invention. For
example, optionally, additional fillers such as polymeric
micro-balloons may be added to the latex formulation to control
rheology and/or polishing performance, polymer coated alumina
aggregates can be used as the abrasive and the stencil can be of
aluminum or plastic.
Example 3
[0070] Using the screen printing process described in Example 2, a
polishing pad was produced containing 72.5% by weight of abrasive
particle agglomerates, where the abrasive particle agglomerates
comprise alumina particles held together by a polymeric binder. The
resulting 24 inch diameter pad was used to polish tungsten wafers
using a Strasbaugh 6DS-SP machine, The reactive liquid was
MSW200BTM from Rodel Inc. and was delivered at a rate of 150
ml/min. Platen speed was 80 rpm, carrier speed was 83 rpm with a
down force of 7 psi. Pad concurrent conditioning was done using a
100-grit RESI disk at 7 psi. A tungsten removal rate of 1000 to
2000A was achieved.
Example 4
[0071] Another screen printed polishing pad, similar to the one
described in Example 3, was used to polish copper wafers using a
Westech 372U polisher. The reactive liquid used was an experimental
hydrogen peroxide based formulation (HR32-1) from Rodel Inc. at a
delivery rate of 150 ml/min. The pad was pre-conditioned using a
100-grit TBW diamond disk. Platen speed was 80 rpm and carrier
speed was 83 rpm with a 4 psi down force. A copper removal rate of
6000 to 7000A was achieved using post conditioning between
wafers.
Example 5
[0072] A screen printed polishing pad, similar to the one described
in example 2, was laminated to different sub-pads (SubaIV.TM. and
DPM100.TM., both from Rodel Inc.), and evaluated for copper
polishing using the Westech 372U polisher. The reactive liquid and
polishing conditions were the same as those used in Example 4. It
was found that the compressibility of the sub-pad significantly
affected the copper removal rate, such that the more compressible
the sub-pad the higher the copper removal rate. No sub-pad,
SubalV.TM., and DPM100.TM. gave removal rates of 3000 to 5000A,
8000 to 9000 A, and 12,000 to 14,000 A respectively. These removal
rates were achieved without post conditioning between wafers.
* * * * *