U.S. patent application number 12/221581 was filed with the patent office on 2010-02-11 for chemical mechanical polishing pad.
Invention is credited to T. Tood Crkvenac, Mary Jo Kulp.
Application Number | 20100035529 12/221581 |
Document ID | / |
Family ID | 41203879 |
Filed Date | 2010-02-11 |
United States Patent
Application |
20100035529 |
Kind Code |
A1 |
Kulp; Mary Jo ; et
al. |
February 11, 2010 |
Chemical mechanical polishing pad
Abstract
The polishing pad is for polishing patterned semiconductor
substrates. The pad includes a polymeric matrix and hollow
polymeric particles within the polymeric matrix. The polymeric
matrix is a polyurethane reaction product of a curative agent and
an isocyanate-terminated polytetramethylene ether glycol at an
NH.sub.2 to NCO stoichiometric ratio of 80 to 97 percent. The
isocyanate-terminated polytetramethylene ether glycol has an
unreacted NCO range of 8.75 to 9.05 weight percent. The hollow
polymeric particles having an average diameter of 2 to 50 .mu.m and
a wt %.sub.b and density.sub.b of constituents forming the
polishing pad as follows: wt % a * density b density a = wt % b
##EQU00001## where density.sub.a equals an average density of 60
g/l, where density.sub.b is an average density of 5 g/l to 500 g/l,
where wt %.sub.a is 3.25 to 4.25 wt %. The polishing pad has a
porosity of 30 to 60 percent by volume; and a closed cell structure
within the polymeric matrix forms a continuous network surrounding
the closed cell structure.
Inventors: |
Kulp; Mary Jo; (Newark,
DE) ; Crkvenac; T. Tood; (Hockessin, DE) |
Correspondence
Address: |
ROHM AND HAAS ELECTRONIC MATERIALS;CMP HOLDINGS, INC.
451 BELLEVUE ROAD
NEWARK
DE
19713
US
|
Family ID: |
41203879 |
Appl. No.: |
12/221581 |
Filed: |
August 5, 2008 |
Current U.S.
Class: |
451/540 |
Current CPC
Class: |
B24D 3/32 20130101; B24B
37/24 20130101 |
Class at
Publication: |
451/540 |
International
Class: |
B24B 7/00 20060101
B24B007/00 |
Claims
1. A polishing pad suitable for polishing patterned semiconductor
substrates containing at least one of copper, dielectric, barrier
and tungsten, the polishing pad comprising a polymeric matrix and
hollow polymeric particles within the polymeric matrix, the
polymeric matrix being a polyurethane reaction product of a
curative agent and an isocyanate-terminated polytetramethylene
ether glycol at an NH.sub.2 to NCO stoichiometric ratio of 80 to 97
percent, the isocyanate-terminated polytetramethylene ether glycol
having an unreacted NCO range of 8.75 to 9.05 weight percent, the
curative agent containing curative amines that cure the
isocyanate-terminated polytetramethylene ether glycol to form the
polymeric matrix; and the hollow polymeric particles having an
average diameter of 2 to 50 .mu.m and a wt %.sub.b and
density.sub.b of constituents forming the polishing pad as follows:
wt % a * density b density a = wt % b ##EQU00005## where
density.sub.a equals an average density of 60 g/l, where
density.sub.b is an average density of 5 g/l to 500 g/l, where wt
%.sub.a is 3.25 to 4.25 wt %, the polishing pad having a porosity
of 30 to 60 percent by volume and a closed cell structure within
the polymeric matrix forming a continuous network surrounding the
closed cell structure.
2. The polishing pad of claim 1 wherein the continuous network
forms a roughened surface upon conditioning with an abrasive; and
the roughened surface is capable of trapping fumed silica particles
during polishing.
3. The polishing pad of claim 1 wherein the polishing pad has a
Shore D hardness of 44 to 54.
4. The polishing pad of claim 1 wherein the polishing pad has a
porosity of 35 to 55 volume percent.
5. The polishing pad of claim 1 wherein the hollow polymeric
particles have an average diameter of 10 to 30 .mu.m.
6. A polishing pad suitable for polishing patterned semiconductor
substrates containing at least one of copper, dielectric, barrier
and tungsten, the polishing pad comprising a polymeric matrix and
hollow polymeric particles within the polymeric matrix, the
polymeric matrix being a polyurethane reaction product of a
curative agent and an isocyanate-terminated polytetramethylene
ether glycol at an NH.sub.2 to NCO stoichiometric ratio of 80 to 90
percent, the isocyanate-terminated polytetramethylene ether glycol
having an unreacted NCO range of 8.75 to 9.05 weight percent, the
curative agent containing curative amines that cure the
isocyanate-terminated polytetramethylene ether glycol to form the
polymeric matrix; and the hollow polymeric particles having an
average diameter of 2 to 50 .mu.m and a wt %.sub.b and
density.sub.b of constituents forming the polishing pad as follows:
wt % a * density b density a = wt % b ##EQU00006## where
density.sub.a equals an average density of 60 g/l, where
density.sub.b is an average density of 10 g/l to 300 g/l, where wt
%.sub.a is 3.25 to 3.6 wt %, the polishing pad having a porosity of
35 to 55 percent by volume and a closed cell structure within the
polymeric matrix forming a continuous network surrounding the
closed cell structure.
7. The polishing pad of claim 6 wherein the continuous network
forms a roughened surface upon conditioning with an abrasive; and
the roughened surface is capable of trapping fumed silica particles
during polishing.
8. The polishing pad of claim 6 wherein the polishing pad has a
Shore D hardness of 44 to 54.
9. The polishing pad of claim 6 wherein the polishing pad has a
porosity of 35 to 50 volume percent.
10. The polishing pad of claim 6 wherein the hollow polymeric
particles have an average diameter of 10 to 30 .mu.m.
Description
BACKGROUND
[0001] This specification relates to polishing pads useful for
polishing or planarizing semiconductor substrates. The production
of semiconductors typically involves several chemical mechanical
polishing (CMP) processes. In each CMP process, a polishing pad in
combination with a polishing solution, such as an
abrasive-containing polishing slurry or an abrasive-free reactive
liquid, removes excess material in a manner that planarizes or
maintains flatness for receipt of a subsequent layer. The stacking
of these layers combines in a manner that forms an integrated
circuit. The fabrication of these semiconductor devices continues
to become more complex due to requirements for devices with higher
operating speeds, lower leakage currents and reduced power
consumption. In terms of device architecture, this translates to
finer feature geometries and increased numbers of metallization
levels. These increasingly stringent device design requirements are
driving the adoption of smaller and smaller line spacing with a
corresponding increase in pattern density. The devices' smaller
scale and increased complexity have led to greater demands on CMP
consumables, such as polishing pads and polishing solutions. In
addition, as integrated circuits' feature sizes decrease,
CMP-induced defectivity, such as, scratching becomes a greater
issue. Furthermore, integrated circuits' decreasing film thickness
requires improvements in defectivity while simultaneously providing
acceptable topography to a wafer substrate; these topography
requirements demand increasingly stringent planarity, line dishing
and small feature array erosion polishing specifications.
[0002] Historically, cast polyurethane polishing pads have provided
the mechanical integrity and chemical resistance for most polishing
operations used to fabricate integrated circuits. For example,
polyurethane polishing pads have sufficient tensile strength and
elongation for resisting tearing; abrasion resistance for avoiding
wear problems during polishing; and stability for resisting attack
by strong acidic and strong caustic polishing solutions.
Unfortunately, the hard cast polyurethane polishing pads that tend
to improve planarization, also tend to increase defects.
[0003] M. J. Kulp, in U.S. Pat. No. 7,169,030, discloses a family
of polyurethane polishing pads having high tensile modulus. These
polishing pads provide excellent planarization and defectivity for
several combinations of polishing pads and polishing slurries. For
example, these polishing pads can provide excellent polishing
performance for ceria-containing polishing slurries, for polishing
silicon oxide/silicon nitride applications, such as direct shallow
trench isolation (STI) polishing applications. For purposes of this
specification, silicon oxide refers to silicon oxide, silicon oxide
compounds and doped silicon oxide formulations useful for forming
dielectrics in semiconductor devices; and silicon nitride refers to
silicon nitrides, silicon nitride compounds and doped silicon
nitride formulations useful for semiconductor applications.
Unfortunately, these pads do not have universal applicability for
improving polishing performance with all polishing slurries for the
multiple substrate layers contained in today's and future
semiconductor wafers. Furthermore, as the cost of semiconductor
devices decreases, there remains a need for further and further
increases in polishing performance.
[0004] Increasing a polishing pad's removal rate can increase
throughput to decrease a semiconductor fabrication plant's
equipment footprint and expenditure. Because of this demand for
increasing performance, there remains a desire for a polishing pad
to remove substrate layers with increased performance. For example,
oxide dielectric removal rates are important for removing
dielectrics during inter-layer dielectric ("ILD") or inter-metallic
dielectric ("IMD") polishing. Specific types of dielectric oxides
in use include the following: BPSG, TEOS formed from the
decomposition of tetraethyloxysilicates, HDP ("high-density
plasma") and SACVD ("sub-atmospheric chemical vapor deposition").
There is an ongoing need for polishing pads that have increased
removal rate in combination with acceptable defectivity performance
and wafer uniformity. In particular, there is a desire for
polishing pads suitable for ILD polishing with an accelerated oxide
removal rate in combination with acceptable planarization and
defectivity polishing performance.
STATEMENT OF INVENTION
[0005] The invention provides a polishing pad suitable for
polishing patterned semiconductor substrates containing at least
one of copper, dielectric, barrier and tungsten, the polishing pad
comprising a polymeric matrix and hollow polymeric particles within
the polymeric matrix, the polymeric matrix being a polyurethane
reaction product of a curative agent and an isocyanate-terminated
polytetramethylene ether glycol at an NH.sub.2 to NCO
stoichiometric ratio of 80 to 97 percent, the isocyanate-terminated
polytetramethylene ether glycol having an unreacted NCO range of
8.75 to 9.05 weight percent, the curative agent containing curative
amines that cure the isocyanate-terminated polytetramethylene ether
glycol to form the polymeric matrix; and the hollow polymeric
particles having an average diameter of 2 to 50 .mu.m and a wt
%.sub.b and density.sub.b of constituents forming the polishing pad
as follows:
wt % a * density b density a = wt % b ##EQU00002##
where density.sub.a equals an average density of 60 g/l, where
density.sub.b is an average density of 5 g/l to 500 g/l, where wt
%.sub.a is 3.25 to 4.25 wt %, the polishing pad having a porosity
of 30 to 60 percent by volume and a closed cell structure within
the polymeric matrix forming a continuous network surrounding the
closed cell structure.
[0006] Another embodiment of the invention provides a polishing pad
suitable for polishing patterned semiconductor substrates
containing at least one of copper, dielectric, barrier and
tungsten, the polishing pad comprising a polymeric matrix and
hollow polymeric particles within the polymeric matrix, the
polymeric matrix being a polyurethane reaction product of a
curative agent and an isocyanate-terminated polytetramethylene
ether glycol at an NH.sub.2 to NCO stoichiometric ratio of 80 to 90
percent, the isocyanate-terminated polytetramethylene ether glycol
having an unreacted NCO range of 8.75 to 9.05 weight percent, the
curative agent containing curative amines that cure the
isocyanate-terminated polytetramethylene ether glycol to form the
polymeric matrix; and the hollow polymeric particles having an
average diameter of 2 to 50 .mu.m and a wt %.sub.b and
density.sub.b of constituents forming the polishing pad as
follows:
wt % a * density b density a = wt % b ##EQU00003##
where density.sub.a equals an average density of 60 g/l, where
density.sub.b is an average density of 10 g/l to 300 g/l, where wt
%.sub.a is 3.25 to 3.6 wt %, the polishing pad having a porosity of
35 to 55 percent by volume and a closed cell structure within the
polymeric matrix forming a continuous network surrounding the
closed cell structure.
DESCRIPTION OF THE DRAWING
[0007] FIG. 1 is a 250.times. magnification post-polishing scanning
electron photomicrograph of the polishing surface of a pad of the
invention.
[0008] FIG. 2 is a 500.times. magnification post-polishing scanning
electron photomicrograph of the polishing surface of a pad of the
invention.
[0009] FIG. 3 is a 500.times.EDS image of the polishing pad of
FIGS. 1 and 2, in the same region as FIG. 2, illustrating a high
concentration of silicon after polishing with a silica-containing
polishing slurry.
DETAILED DESCRIPTION
[0010] The invention provides a polishing pad suitable for
planarizing at least one of semiconductor, optical and magnetic
substrates, the polishing pad comprising a polymeric matrix. The
polishing pads are particularly suitable for polishing and
planarizing ILD dielectric materials as in inter-layer dielectric
(ILD) applications, but could also be used for polishing metals
such as copper or tungsten. The pad provides increased removal rate
over current pads--especially in the first 30 seconds of polishing.
The accelerated response of the pad during the early part of
polishing makes possible increased wafer throughput by shortening
needed polishing time to remove a specified amount of material from
a wafer surface.
[0011] The removal rate for ILD polishing with fumed silica at 30
seconds can be greater than 3750 .ANG./minute. Furthermore, the
invention may provide at least a 10% higher removal rate than the
removal rate at 30 seconds given by IC 1010.TM. polyurethane
polishing pads in the same polishing test. (IC1010 is a trademark
of Rohm and Haas Company or its affiliates.) Advantageously, the
removal rate for the polishing pads of the invention at thirty
seconds for polishing TEOS sheet wafers with a silica-containing
abrasive is equal to or greater than the removal rate for IC1000
polishing pads for polishing TEOS sheet wafers with a
silica-containing abrasive at both thirty and sixty seconds.
IC1000.TM. may increase TEOS removal rate with polishing time
because it comprises aliphatic isocyanate that tends to impart
thermoplastic character to parts made from the ingredients. (IC1000
is a trademark of Rohm and Haas Company or its affiliates.) The
thermoplastic character of IC1000 polishing pads appears to
facilitate an increase in contact between the polishing pad and the
wafer along with an increase in removal rate until some maximum in
removal rate occurs. Increasing pad to wafer contact area to ever
higher levels appears to decrease removal rate as the localized
asperity to wafer contact pressure decreases. Similarly,
formulations not comprising aliphatic isocyanate will have more
thermoplastic character as the degree of cross-linking or molecular
weight decreases; and they may show more of an increase in removal
rate with a wafer's polishing time. The pad of the invention,
however, has sufficient levels of porosity to maximize pad to wafer
contact very early in the polishing process; and the relatively
high level of cross-linking appears to provide the pad sufficient
localized stiffness to facilitate the polishing process.
[0012] Although removal rate can increase with abrasive content, an
improvement over IC1010 polishing pad's removal rate independent of
abrasive level represents an important advance in polishing
performance. For example, this facilitates increasing removal rate
with low defectivity and may decrease slurry costs. In addition to
removal rate, wafer-scale nonuniformity also represents an
important polishing performance consideration. Typically, because
polished wafer uniformity is important for getting the maximum
number of well-polished dies, the wafer-scale nonuniformity should
be less than 6%.
[0013] For purposes of this specification, "polyurethanes" are
products derived from difunctional or polyfunctional isocyanates,
e.g. polyetherureas, polyisocyanurates, polyurethanes, polyureas,
polyurethaneureas, copolymers thereof and mixtures thereof. Cast
polyurethane polishing pads are suitable for planarizing
semiconductor, optical and magnetic substrates. The pads'
particular polishing properties arise in part from a prepolymer
reaction product of a prepolymer polyol and a polyfunctional
isocyanate. The prepolymer product is cured with a curative agent
selected from the group comprising curative polyamines, curative
polyols, curative alcohol amines and mixtures thereof to form a
polishing pad. It has been discovered that controlling the ratio of
the curative agent to the unreacted NCO in the prepolymer reaction
product can improve porous pads' defectivity performance during
polishing.
[0014] The urethane production involves the preparation of an
isocyanate-terminated urethane prepolymer from a polyfunctional
aromatic isocyanate and a prepolymer polyol. The prepolymer polyol
is polytetramethylene ether glycol [PTMEG]. Example polyfunctional
aromatic isocyanates include 2,4-toluene diisocyanate, 2,6-toluene
diisocyanate, 4,4'-diphenylmethane diisocyanate,
naphthalene-1,5-diisocyanate, tolidine diisocyanate, para-phenylene
diisocyanate, xylylene diisocyanate and mixtures thereof. The
polyfunctional aromatic isocyanate contains less than 20 weight
percent aliphatic isocyanates, such as 4,4'-dicyclohexylmethane
diisocyanate, isophorone diisocyanate and cyclohexanediisocyanate.
Preferably, the polyfunctional aromatic isocyanate contains less
than 15 weight percent aliphatic isocyanates and more preferably,
less than 12 weight percent aliphatic isocyanate.
[0015] Typically, the prepolymer reaction product is reacted or
cured with a curative amine such as a polyamine or
polyamine-containing mixture. For example, it is possible to mix
the polyamine with an alcohol amine or a monoamine. For purposes of
this specification, polyamines include diamines and other
multifunctional amines. Example curative polyamines include
aromatic diamines or polyamines, such as,
4,4'-methylene-bis-o-chloroaniline [MBCA],
4,4'-methylene-bis-(3-chloro-2,6-diethylaniline) [MCDEA];
dimethylthiotoluenediamine; trimethyleneglycol di-p-aminobenzoate;
polytetramethyleneoxide di-p-aminobenzoate; polytetramethyleneoxide
mono-p-aminobenzoate; polypropyleneoxide di-p-aminobenzoate;
polypropyleneoxide mono-p-aminobenzoate;
1,2-bis(2-aminophenylthio)ethane; 4,4'-methylene-bis-aniline;
diethyltoluenediamine; 5-tert-butyl-2,4- and
3-tert-butyl-2,6-toluenediamine; 5-tert-amyl-2,4- and
3-tert-amyl-2,6-toluenediamine and chlorotoluenediamine. A MBCA
addition represents the preferred curative amine. Optionally, it is
possible to manufacture urethane polymers for polishing pads with a
single mixing step that avoids the use of prepolymers.
[0016] The components of the polymer used to make the polishing pad
are preferably chosen so that the resulting pad morphology is
stable and easily reproducible. For example, when mixing
4,4'-methylene-bis-o-chloroaniline [MBCA] with diisocyanate to form
polyurethane polymers, it is often advantageous to control levels
of monoamine, diamine and triamine. Controlling the proportion of
mono-, di- and triamines contributes to maintaining the chemical
ratio and resulting polymer molecular weight within a consistent
range. In addition, it is often important to control additives such
as anti-oxidizing agents, and impurities such as water for
consistent manufacturing. For example, because water reacts with
isocyanate to form gaseous carbon dioxide, controlling the water
concentration can affect the concentration of carbon dioxide
bubbles that form pores in the polymeric matrix. Isocyanate
reaction with adventitious water also reduces the available
isocyanate for reacting with chain extender, so changes the
stoichiometry along with level of crosslinking (if there is an
excess of isocyanate groups) and resulting polymer molecular
weight.
[0017] The polyurethane polymeric material is preferably formed
from a prepolymer reaction product of toluene diisocyanate with
polytetramethylene ether glycol and an aromatic diamine. Most
preferably the aromatic diamine is
4,4'-methylene-bis-o-chloroaniline or
4,4'-methylene-bis-(3-chloro-2,6-diethylaniline). Preferably the
range of unreacted prepolymer % NCO is 8.75-9.05. A particular
example of a suitable prepolymer within this unreacted NCO range is
Adiprene.RTM. prepolymer LF750D manufactured by Chemtura. In
addition, LF750D represents a low-free isocyanate prepolymer that
has less than 0.1 weight percent each of free 2,4 and 2,6 TDI
monomers and has a more consistent prepolymer molecular weight
distribution than conventional prepolymers. This "low-free"
prepolymer with improved prepolymer molecular weight consistency
and low free isocyanate monomer facilitates a more regular polymer
structure, and contributes to improved polishing pad consistency.
In addition to controlling weight percent unreacted NCO, the
curative and prepolymer reaction product typically has an OH or
NH.sub.2 to unreacted NCO stoichiometric ratio of 80 to 97 percent,
preferably 80 to 90 percent; and most preferably, it has an OH or
NH.sub.2 to unreacted NCO stoichiometric ratio of 83 to 87 percent.
It is possible to achieve this stoichiometry either directly, by
providing the stoichiometric levels of the raw materials, or
indirectly by reacting some of the NCO with water, either purposely
or by exposure to adventitious moisture.
[0018] If the polishing pad is a polyurethane material, then the
finished polishing pad preferably has a density of 0.4 to 0.8
g/cm.sup.3. Most preferably, the finished polyurethane polishing
pads have a density of 0.5 to 0.75 g/cm.sup.3. A hollow polymeric
particle loading density (before casting) of 3.25 to 4.25 weight
percent and preferably 3.25 to 3.6 weight percent of the nominal 20
.mu.m pores or hollow polymeric particles based on the total pad
formulation can produce the desired density with excellent
polishing results. In particular, the hollow polymeric particles
provide a random pore distribution throughout the polymer matrix.
In particular, the polishing pad has a closed cell structure with
the polymeric matrix forming a continuous network surrounding the
closed cell structure. Despite this high porosity, the polishing
pad typically has a Shore D hardness of 44 to 54. For purposes of
the specification, the Shore D test includes conditioning pad
samples by placing them in 50 percent relative humidity for five
days at 25.degree. C. before testing and using methodology outlined
in ASTM D2240 to improve the repeatability of the hardness
tests.
[0019] The hollow polymeric particles have a weight average
diameter of 2 to 50 .mu.m. For purposes of the specification,
weight average diameter represents the diameter of the hollow
polymeric particle before casting; and the particles may have a
spherical or non-spherical shape. Most preferably, the hollow
polymeric particles have a spherical shape. Preferably, the hollow
polymeric particles have a weight average diameter of 2 to 40
.mu.m. Most preferably, the hollow polymeric particles have a
weight average diameter of 10 to 30 .mu.m; these hollow polymeric
particles typically have an average density of 60 grams per liter.
For purposes of this specification, average density of the hollow
polymeric particles represents the close-packed-non-crushed density
of the hollow particles within a one liter volume. Hollow particles
with an average diameter of 35 to 50 .mu.m typically have lower
density averaging 42 grams per liter because there are fewer pores
and less wall material. Hollow particles of different sizes and
types can be added at equivalent pore volumes by taking the mass of
the hollow polymeric particles of one size and dividing by their
density to determine the volume of pores. This volume can then be
multiplied by the density of the other pore to determine the mass
of the hollow polymeric particles of that size and type to give
equivalent pore volume For example, a formulation with 3 wt % of 20
.mu.m hollow polymeric particles with a density of 60 grams per
liter would be equivalent to 2.1 wt % of 42 .mu.m hollow polymeric
particles with a density of 40 grams per liter as shown by the
equation that follows.
wt % a * density b density a = wt % b ##EQU00004##
In forming polishing pads of the invention, density.sub.a equals an
average density of 60 g/l, density.sub.b is an average density of 5
g/l to 500 g/l and wt %.sub.a is 3.25 to 4.25 wt %. Preferably,
density.sub.b is an average density of 10 g/l to 150 g/l and wt
%.sub.a is 3.25 to 3.6 wt %.
[0020] The nominal range of expanded hollow-polymeric particles'
weight average diameters is 15 to 90 .mu.m. Furthermore, a
combination of high porosity with small pore size can have
particular benefits in reducing defectivity. If the porosity level
becomes too high, however, the polishing pad loses mechanical
integrity and strength. For example, adding hollow polymeric
particles of 2 to 50 .mu.m weight average diameter constituting 30
to 60 volume percent of the polishing layer facilitates a reduction
in defectivity. Furthermore, maintaining porosity between 35 and 55
volume percent or specifically, 35 and 50 volume percent can
facilitate increased removal rates. For purposes of this
specification, volume percent porosity represents the volume
percent of pores determined as follows: 1) subtracting the measured
density of the formulation from the nominal density of the polymer
without porosity to determine the mass of polymer "missing" from
the a cm.sup.3 of formulation; then 2) dividing the mass of
"missing" polymer by the nominal density of the polymer without
porosity to determine the volume of polymer missing from a cm.sup.3
of formulation and multiplying by 100 to convert it to a porosity
volume percentage. Alternatively, the volume percent of pores in a
formulation or volume percent porosity can be determined as
follows: 1) subtracting the mass of hollow polymeric particles in
100 g formulation from 100 g to determine the mass of polymer
matrix in 100 g of formulation; 2) dividing the mass of polymer
matrix by the nominal density of the polymer to determine the
volume of polymer in 100 g of formulation; 3) dividing the mass of
hollow polymeric particles in 100 g of formulation by the nominal
hollow polymeric particle density to determine the volume of hollow
polymeric particles in 100 g of formulation; 4) adding the volume
of polymer in 100 g of formulation to the volume of hollow
particles or pores in 100 g of formulation, to determine the volume
of 100 g of formulation; then 5) dividing the volume of hollow
particles or pores in 100 g of formulation by the total volume of
100 g of formulation and multiplying by 100 to give the volume
percent of pores or porosity in the formulation. The two methods
will produce similar values for volume percent porosity or pores,
although the second method will show lower values of volume percent
pores or porosity than the first method where parameters during
processing, such as the reaction exotherm, can cause hollow
polymeric particles or microspheres to expand beyond their nominal
"expanded volume." Because a decrease in pore size tends to
increase polishing rate for a specific pore or porosity level, it
is important to control the exotherm during casting to prevent
further expansion of the pre-expanded hollow polymeric particles or
microspheres. For example, casting into a room temperature mold,
limiting cake height, reducing prepolymer temperature, reducing
curative amine temperature, reducing the NCO and limiting the free
TDI monomer all contribute to reducing the exotherm produced by the
reacting isocyanate.
[0021] As with most conventional porous polishing pads, polishing
pad conditioning, such as diamond disk conditioning, serves to
increase removal rate and improve wafer-scale nonuniformity.
Although conditioning can function in a periodic manner, such as
for 30 seconds after each wafer or in a continuous manner,
continuous conditioning provides the advantage of establishing
steady-state polishing conditions for improved control of removal
rate. The conditioning typically increases the polishing pad
removal rate and prevents the decay in removal rate typically
associated with the wear of a polishing pad's surface. In
particular, the abrasive conditioning forms a roughened surface
that can trap fumed silica particles during polishing. FIGS. 1 to 3
illustrate that silica particles can accumulate in the roughened
surface adjacent the polishing pad's pores. This accumulation of
silica particles into the polishing pad appears to increase the
polishing pad's efficiency by contributing to a high removal rate.
In addition to conditioning, grooves and perforations can provide
further benefit to the distribution of slurry, polishing
uniformity, debris removal and substrate removal rate.
Example
[0022] The polymeric pad materials were prepared by mixing various
amounts of isocyanates as urethane prepolymers with
4,4'-methylene-bis-o-chloroaniline [MBCA] at 49.degree. C. for the
prepolymer and 115.degree. C. for MBCA for examples of the
invention (Comparative Examples included 43 to 63.degree. C. for
the prepolymer). In particular, a certain toluene diisocyanate
[TDI] with polytetramethylene ether glycol [PTMEG] prepolymer
provided polishing pads with different properties. The
urethane/polyfunctional amine mixture was mixed with the hollow
polymeric microspheres (EXPANCEL.RTM. 551DE20d60 or 551DE40d42
manufactured by AkzoNobel) either before or after mixing the
prepolymer with the chain extender. The hollow polymeric
microspheres were either mixed with the prepolymer at 60 rpm before
adding the polyfunctional amine, then mixing the mixture at 4500
rpm or were added to the urethane/polyfunctional amine mixture in a
mixhead at 3600 rpm. The microspheres had a weight average diameter
of 15 to 50 .mu.m, with a range of 5 to 200 .mu.m. The final
mixture was transferred to a mold and permitted to gel for about 15
minutes.
[0023] The mold was then placed in a curing oven and cured with a
cycle as follows: thirty minutes ramped from ambient temperature to
a set point of 104.degree. C., fifteen and one half hours at
104.degree. C. and two hours with a set point reduced to 21.degree.
C. Comparative Examples F to K used a shorter cure cycle of
100.degree. C. for about eight hours. The molded article was then
"skived" into thin sheets and macro-channels or grooves were
machined into the surface at room temperature--skiving at higher
temperatures may improve surface roughness and sheet thickness
uniformity. As shown in the Tables, samples 1 to 2 represent
polishing pads of the invention and samples A to Z represent
comparative examples.
TABLE-US-00001 TABLE 1 Hollow Nominal Polymeric Sphere NCO
Stoichiometry Spheres Diameter Formulation Formulation (wt %)
Prepolymer (%) (wt %) (um) 1 MJK1859C 8.75-9.05 LF750D 85 3.36 20 2
MJK1859C 8.75-9.05 LF750D 85 3.36 20 A S58 8.75-9.05 LF750D 85 2.25
40 B T58 8.75-9.05 LF750D 85 3.21 20 C S52 8.75-9.05 LF750D 105
0.75 40 D S53 8.75-9.05 LF750D 85 0.75 40 E T53 8.75-9.05 LF750D 85
1.07 20 F MJK3101A 11.4-11.8 Royalcast 85 3.01 20 2505 G MJK3101C
11.4-11.8 Royalcast 85 3.01 20 2505 H MJK3101B 11.4-11.8 Royalcast
95 2.93 20 2505 I MJK3101D 11.4-11.8 Royalcast 95 2.93 20 2505 J
MJK1864A 11.4-11.8 Royalcast 105 2.86 20 2505 K MJK1864J 11.4-11.8
Royalcast 105 2.86 20 2505 L MJK3122B 8.75-9.05 LF750D 85.00 3.87
20 M MJK3122F 8.75-9.05 LF750D 90.00 3.83 20 N MJK3122E 8.75-9.05
LF750D 95.00 3.79 20 O MJK3122D 8.75-9.05 LF750D 100.00 3.74 20 P
MJK3122A 8.45-8.75 LF750D 105.00 3.70 20 Q MJK3122C 8.45-8.75
LF750D 110.00 3.66 20 R VP3000 7.1-7.4 LF600D 85 1.8 40 S MJK1803C
8.75-9.05 LF750D 90.00 2.94 20 T MJK1803E 8.75-9.05 LF750D 90.00
2.94 20 U MJK1803A 8.75-9.05 LF750D 115.00 2.94 20 V MJK1803F
8.75-9.05 LF750D 115.00 2.94 20 W MJK1803D 8.75-9.05 LF750D 90.00
2.20 20 X MJK1803H 8.75-9.05 LF750D 90.00 2.20 20 Y MJK1803B
8.75-9.05 LF750D 115.00 2.20 20 Z MJK1803G 8.75-9.05 115.00 2.20 20
Adiprene LF600D, LF750D and Royalcast 2505 correspond to blends of
toluene diiosocyanate and PTMEG products manufactured by Chemtura.
LF600D and LF750D are low-free isocyanate prepolymers while
Royalcast 2505 has high levels of free isocyanate monomer.
[0024] Example polishing pads were tested on a Mirra.RTM. polisher
from Applied Materials, Inc. using a platen rotation rate of 93
rpm, a wafer carrier head rotation rate of 87 rpm and a downforce
of 5 psi to polish TEOS sheet wafers. The polishing slurry was
ILD3225 used as a 1:1 mixture with DI water and supplied at the
polishing pad surface a rate of 150 ml/min. A Diagrid.RTM.
AD3BG150855 conditioning disk was used to diamond-condition the
polishing pad using an in situ conditioning process. TEOS sheet
wafers were polished for 30 seconds or for 60 seconds and each test
with example pads also included wafers polished with the IC1010 pad
as a baseline. The greatest importance was placed on the 30 second
polish rates relative to IC1010 because they would have the
greatest effect on reducing polishing times over the standard
polishing pad. The polishing results are below in Table 2.
TABLE-US-00002 TABLE 2 Hollow Nominal Polymeric Sphere RR at RR, RR
at RR, Spheres Diameter 30 sec 30 sec 60 sec 60 sec Formulation
Formulation (wt %) (um) (.ANG./min) norm (.ANG./min) norm NU, %
Target >3750 .gtoreq.1.10 .gtoreq.4100 .gtoreq.1.08 <6.0 1
MJK1859C 3.36 20 3778 1.18 4183 1.15 2.5 2 MJK1859C 3.36 20 3949
1.10 4235 1.08 5.7 A S58 2.25 40 3802 1.08 4263 1.10 3.0 B T58 3.21
20 4043 1.15 4414 1.17 2.8 C S52 0.75 40 3786 1.07 4070 1.04 5.5 D
S53 0.75 40 3582 1.02 4043 1.01 3.4 E T53 1.07 20 3736 1.06 4175
1.05 3.1 F MJK3101A 3.01 20 3303 0.94 3755 0.95 4.2 G MJK3101C 3.01
20 3123 0.89 3600 0.91 4.6 H MJK3101B 2.93 20 3162 0.90 3652 0.92
4.6 I MJK3101D 2.93 20 3087 0.88 3587 0.91 4.5 J MJK1864A 2.86 20
3180 0.91 3611 0.91 4.3 K MJK1864J 2.86 20 3114 0.89 3583 0.91 5.4
L MJK3122B 3.87 20 3886 1.09 4219 1.07 6.0 M MJK3122F 3.83 20 3788
1.06 4050 1.03 6.0 N MJK3122E 3.79 20 3747 1.05 4079 1.04 11.4 O
MJK3122D 3.74 20 3715 1.04 4015 1.02 7.8 P MJK3122A 3.70 20 3683
1.03 3915 1.00 7.1 Q MJK3122C 3.66 20 3450 0.97 3647 0.93 8.4 R
VP3000 1.8 40 3330 0.80 2.3 S MJK1803C 2.94 20 3893 1.06 4219 1.03
3.2 T MJK1803E 2.94 20 4025 1.11 4251 1.05 7.6 U MJK1803A 2.94 20
3803 1.03 4025 0.98 4.8 V MJK1803F 2.94 20 3673 1.01 3856 0.95 8.2
W MJK1803D 2.20 20 3688 1.00 4029 0.98 3.8 X MJK1803H 2.20 20 3692
1.01 3976 0.98 5.5 Y MJK1803B 2.20 20 3783 1.03 4053 0.99 4.6 Z
MJK1803G 2.20 20 3654 1.00 3859 0.95 7.6
[0025] These data indicate that a loading of 3.36 weight percent
hollow polymeric microspheres provided an unexpected increase in
removal rate. In particular, Samples 1 and 2 had excellent removal
rate at thirty seconds and sixty seconds. The Sample 1 and 2
removal rates at thirty seconds indicate that the polishing pad has
high removal rate during an earlier part of a shortened polishing
process that supports higher throughput polishing. The comparative
examples with 3.01 (2.94 for same prepolymer) or of 3.66 weight
percent and above resulted in a lower removal rate at thirty
seconds and a lower overall removal rate. In addition, FIGS. 1 to 3
illustrate that the polishing pad's surface appears to trap
fumed-silica in an advantageous location for polishing. This
affinity to fumed silica appears to contribute to the increased
polishing performance.
TABLE-US-00003 TABLE 3 Calculated # spheres in Calculated # Hollow
Nominal cm.sup.3 spheres in cm.sup.3 Difference Polymeric Sphere
formulation formulation in Spheres Diameter based on based on pad
Calculated # Formulation Formulation (wt %) (.mu.m) formulation
density of Spheres Preferred >3.1 20 >9.25E+07 1 MJK1859C
3.36 20 9.79E+07 9.50E+07 2.89E+06 2 MJK1859C 3.36 20 9.79E+07
9.34E+07 4.42E+06 A S58 2.25 40 1.18E+07 1.27E+07 -8.73E+05 B T58
3.21 20 9.52E+07 1.05E+08 -9.55E+06 C S52 0.75 40 5.30E+06 5.95E+06
-6.53E+05 D S53 0.75 40 5.30E+06 5.80E+06 -4.99E+05 E T53 1.07 20
4.25E+07 4.33E+07 -8.60E+05 F MJK3101A 3.01 20 9.21E+07 1.10E+08
-1.80E+07 G MJK3101C 3.01 20 9.21E+07 9.56E+07 -3.46E+06 H MJK3101B
2.93 20 9.04E+07 1.10E+08 -2.00E+07 I MJK3101D 2.93 20 9.04E+07
9.55E+07 -5.01E+06 J MJK1864A 2.86 20 8.90E+07 9.56E+07 -6.53E+06 K
MJK1864J 2.86 20 8.90E+07 9.98E+07 -1.07E+07 L MJK3122B 3.87 20
1.07E+08 1.14E+08 -7.20E+06 M MJK3122F 3.83 20 1.06E+08 1.30E+08
-2.40E+07 N MJK3122E 3.79 20 1.05E+08 1.18E+08 -1.32E+07 O MJK3122D
3.74 20 1.04E+08 1.17E+08 -1.26E+07 P MJK3122A 3.70 20 1.04E+08
1.20E+08 -1.63E+07 Q MJK3122C 3.66 20 1.03E+08 1.22E+08 -1.92E+07 R
VP3000 1.8 40 1.00E+07 2.98E+07 -1.98E+07 S MJK1803C 2.94 20
9.01E+07 9.21E+07 -2.02E+06 T MJK1803E 2.94 20 9.01E+07 1.06E+08
-1.60E+07 U MJK1803A 2.94 20 9.01E+07 1.07E+08 -1.68E+07 V MJK1803F
2.94 20 9.01E+07 1.17E+08 -2.70E+07 W MJK1803D 2.20 20 7.41E+07
6.82E+07 5.91E+06 X MJK1803H 2.20 20 7.41E+07 9.73E+07 -2.32E+07 Y
MJK1803B 2.20 20 7.41E+07 8.71E+07 -1.31E+07 Z MJK1803G 2.20 20
7.41E+07 9.45E+07 -2.04E+07
[0026] Table 3 illustrates that the hollow polymeric microspheres
achieve a loading level in excess of one million microspheres per
cubic centimeter of pad formulation.
[0027] Table 4 below shows prepolymer % NCO and compares mechanical
strength properties of MBCA-cured elastomers, without filler or
porosity, made from the prepolymers used in the example
formulations as tested using methodology in ASTM D412. The tensile
properties shown are defined in ASTM D1566-08A. In addition, Table
4 shows the nominal density of the prepolymer cured with MBCA as
reported by the prepolymer manufacturer.
TABLE-US-00004 TABLE 4 Tensile Tensile Tensile strength Stress at
Stress at Nominal unfilled cured 100% 200% Polymer Prepolymer with
MBCA, Elongation, Elongation, Density Prepolymer NCO (wt %) psi
(MPa) psi (MPa) psi (MPa) (g/cm.sup.3) Adiprene 7.1-7.4 6700 (46.2)
3600 (24.8) 4800 (33.1) 1.16 LF600D Adiprene 8.75-9.05 7100 (48.9)
5300 (36.5) 5900 (40.7) 1.20 LF750D Royalcast 2505 11.4-11.8 9200
(63) -- -- 1.21
[0028] Table 4 illustrates that in addition to filler
concentration, the polishing pad's mechanical properties also
appear to impact polishing performance. Specifically, the polymer
of Comparative Example R with LF600D appears to have inadequate
stiffness, as best indicated by its 100% modulus, for high removal
rates for fumed silica polishing; and Comparative Examples F to K
made with Royalcast.RTM. 2505 quasi-prepolymer, which appears to be
excessively stiff for high removal rates in fumed silica polishing.
Polyurethane materials cast from Royalcast 2505 were so brittle
that they broke prior to elongation at 100%.
[0029] In summary, the polishing pad is effective for polishing
copper, dielectric, barrier and tungsten wafers. In particular, the
polishing pad is useful for ILD polishing and in particular, ILD
polishing applications with fumed silica. The polishing pad has a
rapid ramp to efficient polishing that provides a high removal rate
at thirty seconds. The removal rate of polishing pads of the
invention at both thirty and sixty seconds can exceed the removal
rate of IC1000 polishing pads at thirty seconds and at sixty
seconds. This rapid polishing response of the pads of the invention
facilitates high wafer throughput in comparison to conventional
porous polishing pads.
* * * * *