U.S. patent application number 10/772054 was filed with the patent office on 2005-08-04 for polyurethane polishing pad.
Invention is credited to Kulp, Mary Jo.
Application Number | 20050171224 10/772054 |
Document ID | / |
Family ID | 34808579 |
Filed Date | 2005-08-04 |
United States Patent
Application |
20050171224 |
Kind Code |
A1 |
Kulp, Mary Jo |
August 4, 2005 |
Polyurethane polishing pad
Abstract
The polishing pad is suitable for planarizing at least one of
semiconductor, optical and magnetic substrates. The polishing pad
includes a cast polyurethane polymeric material formed with an
isocyanate-terminated reaction product formed from a prepolymer
reaction of a prepolymer polyol and a polyfunctional isocyanate.
The isocyanate-terminated reaction product has 4.5 to 8.7 weight
percent NCO reaction group; and the isocyanate-terminated reaction
product is cured with a curative agent selected from the group
comprising curative polyamines, curative polyols, curative
alcoholamines and mixtures thereof. The polishing pad contains at
least 0.1 volume percent filler or porosity.
Inventors: |
Kulp, Mary Jo; (Newark,
DE) |
Correspondence
Address: |
Rohm and Haas Electronic Materials CMP Holdings,
Inc.
Suite 1300
1105 North Market Street
Wilmington
DE
19899
US
|
Family ID: |
34808579 |
Appl. No.: |
10/772054 |
Filed: |
February 3, 2004 |
Current U.S.
Class: |
521/155 |
Current CPC
Class: |
B24B 37/24 20130101;
C08G 18/10 20130101; C08G 18/4854 20130101; C08G 18/3812 20130101;
C08G 18/10 20130101 |
Class at
Publication: |
521/155 |
International
Class: |
C08G 018/00 |
Claims
1. A polishing pad suitable for planarizing at least one of
semiconductor, optical and magnetic substrates, the polishing pad
comprising a cast polyurethane polymeric material formed from a
prepolymer reaction of a prepolymer polyol and a polyfunctional
isocyanate to form an isocyanate-terminated reaction product, the
isocyanate-terminated reaction product having 4.5 to 8.7 weight
percent NCO reaction group, the isocyanate-terminated reaction
product being cured with a curative agent selected from the group
comprising curative polyamines, curative polyols, curative
alcoholamines and mixtures thereof; and the polishing pad
containing at least 0.1 volume percent filler or porosity.
2. The polishing pad of claim 1 wherein the prepolymer polyol is
selected from the group comprising polytetramethylene ether glycol,
polyester polyols, polypropylene ether glycols, polycaprolactone
polyols, copolymers thereof and mixtures thereof.
3. The polishing pad of claim 2 wherein the curative agent contains
curative amines that cure the isocyanate-terminated reaction
product and the isocyanate-terminated reaction product has an
NH.sub.2 to NCO stoichiometric ratio of 80 to 120 percent.
4. A polishing pad suitable for planarizing semiconductor
substrates, the polishing pad comprising a cast polyurethane
polymeric material formed from a prepolymer reaction of a
prepolymer polyol selected from the group comprising
polytetramethylene ether glycol, polyester polyols, polypropylene
ether glycols, copolymers thereof and mixtures therof and a
polyfunctional isocyanate to form an isocyanate-terminated reaction
product, the isocyanate-terminated reaction product having 4.5 to
8.7 weight percent NCO reaction group, the isocyanate-terminated
reaction product being cured with a curative agent with expandable
polymeric microspheres, the curative agent selected from the group
comprising curative polyamines, curative polyols, curative
alcoholamines and mixtures thereof; and the polishing pad
containing a porosity of at least 0.1 volume percent.
5. The polishing pad of claim 4 wherein the curative agent contains
curative amines that cure the isocyanate-terminated reaction
product and the isocyanate-terminated reaction product has an
NH.sub.2 to NCO stoichiometric ratio of 80 to 120 percent.
6. The polishing pad of claim 4 wherein the prepolymer polyol
contains polytetramethylene ether glycol, copolymer thereof or a
mixture thereof.
7. The polishing pad of claim 4 wherein the prepolymer polyol
contains polyester polyols, copolymer thereof or a mixture
thereof.
8. The polishing pad of claim 4 wherein the prepolymer polyol
contains polypropylene ether glycols, copolymer thereof or a
mixture thereof.
9. A method of forming a polishing pad suitable for planarizing
semiconductor substrates comprising casting polyurethane polymeric
material from a prepolymer reaction of a prepolymer polyol and a
polyfunctional isocyanate to form an isocyanate-terminated reaction
product, the isocyanate-terminated reaction product having 4.5 to
8.7 weight percent NCO reaction group, the isocyanate-terminated
reaction product being cured with a curative agent selected from
the group comprising curative polyamines, curative polyols,
curative alcoholamines and mixtures thereof, and the polishing pad
containing at least 0.1 volume percent filler or porosity.
10. The polishing pad of claim 1 wherein the polymeric material
includes expandable polymeric microspheres and including the step
of limiting the exotherm to a temperature below 120.degree. C.
Description
BACKGROUND
[0001] This specification relates to polishing pads useful for
polishing and planarizing substrates and particularly to polishing
pads having uniform polishing properties.
[0002] Polyurethane polishing pads are the primary pad-type for a
variety of demanding precision polishing applications. These
polyurethane polishing pads are effective for polishing silicon
wafers, patterned wafers, flat panel displays and magnetic storage
disks. In particular, polyurethane polishing pads provide the
mechanical integrity and chemical resistance for most polishing
operations used to fabricate integrated circuits. For example,
polyurethane polishing pads have high strength for resisting
tearing; abrasion resistance for avoiding wear problems during
polishing; and stability for resisting attack by strong acidic and
strong caustic polishing solutions.
[0003] The production of semiconductors typically involves several
chemical mechanical planarization (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 metallization levels.
These increasingly stringent device design requirements are driving
the adoption of copper metallization in conjunction with new
dielectric materials having lower dielectric constants. The
diminished physical properties, frequently associated with low k
and ultra-low k materials, in combination with the devices'
increased complexity have led to greater demands on CMP
consumables, such as polishing pads and polishing solutions.
[0004] In particular, low k and ultra-low k dielectrics tend to
have lower mechanical strength and poorer adhesion in comparison to
conventional dielectrics, rendering planarization more difficult.
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, dishing and
erosion specifications.
[0005] Casting polyurethane into cakes and cutting the cakes into
several thin polishing pads has proven to be an effective method
for manufacturing polishing pads with consistent reproducible
polishing properties. Vishwanathan et al., in PCT Pub. No. 01.91971
disclose a set of properties for improving polishing performance
including E' (elastic storage modulus) ratio at 30.degree. C. and
90.degree. C. and several other properties. Unfortunately,
polyurethane pads produced from the casting and skiving method can
have polishing variations arising from a polishing pad's casting
location. For example, pads cut from a bottom casting location and
a top casting can have different densities and porosities.
Furthermore, polishing pads can have center-to-edge variations in
density and porosity within a pad. These variations can adversely
affect polishing for the most demanding applications, such as low k
patterned wafers. Thus, there is a demand for a polyurethane
polishing pad with improved density and porosity uniformity.
STATEMENT OF INVENTION
[0006] The invention provides a polishing pad suitable for
planarizing at least one of semiconductor, optical and magnetic
substrates, the polishing pad comprising a cast polyurethane
polymeric material formed from a prepolymer reaction of a
prepolymer polyol and a polyfunctional isocyanate to form an
isocyanate-terminated reaction product, the isocyanate-terminated
reaction product having 4.5 to 8.7 weight percent NCO reaction
group, the isocyanate-terminated reaction product being cured with
a curative agent selected from the group comprising curative
polyamines, curative polyols, curative alcoholamines and mixtures
thereof; and the polishing pad containing at least 0.1 volume
percent filler or porosity.
[0007] In another aspect of the invention, the invention provides a
polishing pad suitable for planarizing semiconductor substrates,
the polishing pad comprising a cast polyurethane polymeric material
formed from a prepolymer reaction of a prepolymer polyol selected
from the group comprising polytetramethylene ether glycol,
polyester polyols, polypropylene ether glycols, copolymers thereof
and mixtures therof and a polyfunctional isocyanate to form an
isocyanate-terminated reaction product, the isocyanate-terminated
reaction product having 4.5 to 8.7 weight percent NCO reaction
group, the isocyanate-terminated reaction product being cured with
a curative agent with expandable polymeric microspheres, the
curative agent selected from the group comprising curative
polyamines, curative polyols, curative alcoholamines and mixtures
thereof; and the polishing pad containing a porosity of at least
0.1 volume percent.
[0008] In another aspect of the invention, the invention provides a
method of forming a polishing pad suitable for planarizing
semiconductor substrates comprising casting polyurethane polymeric
material from a prepolymer reaction of a prepolymer polyol and a
polyfunctional isocyanate to form an isocyanate-terminated reaction
product, the isocyanate-terminated reaction product having 4.5 to
8.7 weight percent NCO reaction group, the isocyanate-terminated
reaction product being cured with a curative agent selected from
the group comprising curative polyamines, curative polyols,
curative alcoholamines and mixtures thereof; and the polishing pad
containing at least 0.1 volume percent filler or porosity.
DETAILED DESCRIPTION
[0009] 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 alchol amines and mixtures
thereof to form a polishing pad. It has been discovered that
controlling the amount of NCO reaction group in the prepolymer
reaction product can improve porous pads' uniformity throughout a
polyurethane casting.
[0010] In particular, controlling the prepolymer's weight percent
NCO reaction group, appears to limit the exothermic chain extension
reaction. This limits the temperature increase within the cast
material and can improve the uniformity of density across pads and
through the "as cast" cakes. The lower pad uniformity of earlier
cast polyurethane polishing pads arises from the high weight
percent NCO of Adiprene L325 (Adiprene.RTM. is a urethane
prepolymer product of Crompton/Uniroyal Chemical) used to produce
IC.TM. pads from Rohm and Haas Electronic Materials CMP
Technologies. But because a large part of the available NCO in
Adiprene L325 is the less reactive aliphatic
4,4'-dicyclohexylmethane diisocyanate rather than all TDI, the
exotherm is not as large as it would be with an all aromatic
isocyanate system. Controlling the prepolymer reaction product's
weight percent NCO improves the temperature uniformity during the
manufacturing process by controlling the exothermic heat of
reaction. If the weight percent NCO is too high, then the polishing
pad can overheat in the middle and top portions, especially for
polishing pads skived from cast polyurethane cakes. If the weight
percent NCO is too low, then the polyurethane will have too long of
a gel time that can also lead to non-uniformity, such as, the
sinking of high-density particles or floating of low-density
particles and pores during an extended gelation process.
Controlling the prepolymer's weight percent NCO to between 4.5 and
8.7 weight percent provides cast polyurethane polishing pads with
uniform properties. Preferably, the prepolymer's weight percent NCO
is between 4.7 and 8.5.
[0011] The polymer is effective for forming porous and filled
polishing pads. For purposes of this specification, filler for
polishing pads include solid particles that dislodge or disolve
during polishing, and liquid-filled particles or spheres. For
purposes of this specification, porosity includes gas-filled
particles, gas-filled spheres and voids formed from other means,
such as mechanically frothing gas into a viscous system, injecting
gas into the polyurethane melt, introducing gas in situ using a
chemical reaction with gaseous product, or decreasing pressure to
cause disolved gas to form bubbles. The polishing pads contain a
porosity or filler concentration of at least 0.1 volume percent.
This porosity or filler contributes to the polishing pad's ability
to transfer polishing fluids during polishing. Preferably, the
polishing pad has a porosity or filler concentration of 0.2 to 70
volume percent. Most preferably, the polishing pad has a porosity
or filler concentration of 0.25 to 60 volume percent. Preferably
the pores or filler particles have a weight average diameter of 10
to 100 .mu.m. Most preferably, the pores or filler particles have
an weight average diameter of 15 to 90 .mu.m. The nominal range of
expanded hollow-polymeric microspheres' weight average diameters is
15 to 50 .mu.m.
[0012] Controlling the NCO concentration is particularly effective
for controlling the pore uniformity for pores formed directly or
indirectly with a filler gas. This is because gases tend to undergo
thermal expansion at a much greater rate and to a greater extent
than solids and liquids. For example, the method is particularly
effective for porosity formed by casting hollow microspheres,
either pre-expanded or expanded in situ; by using chemical foaming
agents; by mechanically frothing in gas; and by use of dissolved
gases, such as argon, carbon dioxide, helium nitrogen, and air, or
supercritical fluids, such as supercritical carbon dioxide or gases
formed in situ as a reaction product.
[0013] For polishing pads containing gaseous pores or
gaseous-filled microspheres, a polishing pad's non-uniformity
appears to be driven by 1) the temperature profile of the reacting
system; 2) the resulting pore expansion in areas where the
temperature increases above that of the expansion temperature of
the pore while the surrounding polymeric matrix remains
not-so-locked in place as to be able to respond; and 3) the
viscosity profile of the reacting or solidifying polymer matrix as
a result of reaction and various local heating and cooling effects.
In the case of a pore added through polymeric hollow microspheres,
their Tg is related to the threshhold temperature for response.
Polymeric microspheres above this temperature tend to grow and
deform in shape. When casting with hollow polymeric microspheres
and with the controlled weight percent NCO, the microspheres'
pre-casting volume and the microspheres' final volume preferably
remains within 8 percent of the average pre-casting volume
throughout the cast polyurethane material. Most preferably, the
microspheres' final volume remains within 7 percent of the
pre-casting volume throughout the cast polyurethane material.
[0014] Literature shows a volume decrease as a function of time for
pre-expanded Expancel microspheres maintained at elevated
temperatures. However, the further expansion of the expanded
microspheres contributes to increased non-uniformity of the
polishing pads. By controlling the thermal history in the casting
process by limiting weight percent NCO, polishing pads with more
uniform density throughout both individual pads and the cake are
produced. Pad formulations with more uniform density can provide
more consistent removal rates and topographical control than pad
formulations where this is uncontrolled, giving greater CMP process
control in actual use.
[0015] With Adiprene L325 prepolymers, peak exotherm temperatures
reach as high as 264.degree. F. (129.degree. C.). These
temperatures are well above the expansion onset temperature and
closely approach the temperatures of maximum expansion for Expancel
microsphere 551DU40--the unexpanded microspheres from which
551DE40d42 is produced--275-289.degree- . F. (135-143.degree. C.).
Typically, the density in the center of the cast cake is lower due
to greater heating and the resulting greater pore expansion.
Polishing pads' porosity variation also tends to increase with
increasing initial pore volume, increasing material temperatures
and increasing mass of cast material.
[0016] Because the pore can only expand if the surrounding polymer
is still sufficiently mobile that it can rearrange with a small
pressure, it is also important that the weight percent NCO of the
system and the ability of the polymer backbone to order is not too
low, or the pores or filler can slowly expand or segregate by
density, yielding a broader density distribution.
[0017] Preferably, the polymeric material is a polyurethane. For
purposes of this specification, "polyurethanes" are products
derived from difunctional or polyfunctional isocyanates, e.g.
polyetherureas, polyesterureas, polyisocyanurates, polyurethanes,
polyureas, polyurethaneureas, copolymers thereof and mixtures
thereof. An approach for controlling a pad's polishing properties
is to alter its chemical composition. In addition, the choice of
raw materials and manufacturing process affects the polymer
morphology and the final properties of the material used to make
polishing pads.
[0018] Preferably, urethane production involves the preparation of
an isocyanate-terminated urethane prepolymer from a polyfunctional
isocyanate and a prepolymer polyol. For purposes of this
specification, the term prepolymer polyol includes diols, polyols,
polyol-diols, copolymers thereof and mixtures thereof. Preferably,
the prepolymer polyol is selected from the group comprising
polytetramethylene ether glycol [PTMEG], polypropylene ether glycol
[PPG], ester-based polyols, such as ethylene or butylene adipates,
copolymers thereof and mixtures thereof. Example polyfunctional
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, 4,4'-dicyclohexylmethane
diisocyanate, isophorone diisocyanate and mixtures thereof. Example
prepolymer polyols include polyether polyols, such as,
poly(oxytetramethylene)glycol, poly(oxypropylene)glycol and
mixtures thereof, polycarbonate polyols, polyester polyols,
polycaprolactone polyols and mixtures thereof. Example polyols can
be mixed with low molecular weight polyols, including ethylene
glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol,
1,3-butanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, neopentyl
glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol,
diethylene glycol, dipropylene glycol and mixtures thereof.
[0019] Preferably the prepolymer polyol is selected from the group
comprising polytetramethylene ether glycol, polyester polyols,
polypropylene ether glycols, polycaprolactone polyols, copolymers
thereof and mixtures thereof. If the prepolymer polyol is PTMEG,
copolymer thereof or a mixture thereof, then the
isocyanate-terminated reaction product most preferably has a weight
percent NCO range of 5.8 to 8.7. Particular examples of PTMEG
family polyols are as follows: Terathane.RTM. 2900, 2000, 1800,
1400, 1000, 650 and 250 from DuPont; Polymeg.RTM. 2000, 1000, 1500,
650 from Lyondell; PolyTHF.RTM. 650, 1000, 1800, 2000 from BASF,
and lower molecular weight species such as 1,2-butanediol,
1,3-butanediol, and 1,4-butanediol. If the prepolymer polyol is a
PPG, copolymer thereof or a mixture thereof, then the
isocyanate-terminated reaction product most preferably has a weight
percent NCO range of 5 to 8. Particular examples of PPG polyols are
as follows: Arcol.RTM. PPG-425, 725, 1000, 1025, 2000, 2025, 3025
and 4000 from Bayer; Voranol.RTM. 220-028, 220-094, 220-110N,
220-260, 222-029, 222-056, 230-056 from Dow; Desmophen.RTM. 1110BD,
Acclaim.RTM. Polyol 4200 both from Bayer If the prepolymer polyol
is an ester, copolymer thereof or a mixture thereof, then the
isocyanate-terminated reaction product most preferably has a weight
percent NCO range of 4.5 to 7. Particular examples of ester polyols
are as follows: Millester 1, 11, 2, 23, 132, 231, 272, 4, 5, 510,
51, 7, 8, 9, 10, 16, 253, from Polyurethane Specialties Company,
Inc.; Desmophen.RTM. 1700, 1800, 2000, 2001KS, 2001K.sup.2, 2500,
2501, 2505, 2601, PE65B from Bayer; Rucoflex S-1021-70, S-1043-46,
S-1043-55 from Bayer.
[0020] Typically, the prepolymer reaction product is reacted or
cured with a curative polyol, polyamine, alcohol amine or mixture
thereof. 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 dip-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.
Optionally, it is possible to manufacture urethane polymers for
polishing pads with a single mixing step that avoids the use of
prepolymers.
[0021] 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-chloro- aniline [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 cross-linking 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, since 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.
[0022] The polyurethane polymeric material is preferably formed
from a prepolymer reaction product of toluene diisocyanate and
polytetramethylene ether glycol with
4,4'-methylene-bis-o-chloroaniline. Preferably, the prepolymer
reaction product has a 4.55 to 8.7 weight percent NCO. Examples of
suitable prepolymers within this NCO range include: Airthane.RTM.
prepolymers PET-70D, PHP-70D, PET-60D, PET-95A, PET-93A, PST-95A,
PPT-95A, Versathane.RTM. prepolymers STE-95A, STE-P95,
Versathane.RTM.-C prepolymers 1050, 1160, D-5QM, D-55, D-6
manufactured by Air Products and Chemicals, Inc. and Adiprene.RTM.
prepolymers LF600D, LF601D, LF700D, LF950A, LF952A, LF939A,
LFG963A, LF1930A, LF1950A, LF1600D, L167, L367 manufactured by
Uniroyal Chemical Products division of the Crompton Corporation. In
addition, blends of other prepolymers besides those listed above
could be used to reach to appropriate % NCO levels as a result of
blending. Many of the above-listed prepolymers, such as, LF600D,
LF601D, LF700D, and LFG963A are low-free isocyanate prepolymers
that have less than 0.1 weight percent free TDI monomer and have a
more consistent prepolymer molecular weight distribution than
conventional prepolymers, and so facilitate forming polishing pads
with excellent polishing characteristics. This improved prepolymer
molecular weight consistency and low free isocyanate monomer give
an initially lower viscosity prepolymer that tends to gel more
rapidly, facilitating viscosity control that can further improve
porosity distribution and polishing pad consistency. For most
prepolymers, the low free isocyanate monomer is preferably below
0.5 weight percent. Furthermore, "conventional" prepolymers that
typically have higher levels of reaction (i.e. more than one polyol
capped by a diisocyanate on each end) and higher levels of free
toluene diisocyanate prepolymer should produce similar results. In
addition, low molecular weight polyol additives, such as,
diethylene glycol, butanediol and tripropylene glycol facilitate
control of the prepolymer reaction product's weight percent
NCO.
[0023] In addition to controlling weight percent NCO, the curative
and prepolymer reaction product preferably has an OH or NH.sub.2 to
NCO stoichiometric ratio of 80 to 120 percent; and most preferably,
it has an OH or NH.sub.2 to NCO stoichiometric ratio of 80 to 110
percent.
[0024] If the polishing pad is a polyurethane material, then the
polishing pad preferably has a density of 0.5 to 1.25 g/cm.sup.3.
Most preferably, polyurethane polishing pads have a density of 0.6
to 1.15 g/cm.sup.3.
EXAMPLES
[0025] The following Table provides prepolymer and microsphere
formulations for casting polyurethane cakes. These formulations
contained various amounts of polymeric microspheres for producing
porosity with different prepolymer formulations. These formulations
tested toluene diiosocyanate [TDI] with polytetramethylene ether
glycol [PTMEG], polypropylene ether glycol [PPG] and ester
backbones from isocyanate-terminated prepolymers. As shown in
following Tables, formulations 1 to 9 represent formulations of the
invention and formulations A to E represent comparative examples.
In particular, comparative example A corresponds to the formulation
of Example 1 of U.S. Pat. No. 5,578,362; and comparative example B
corresponds to the formulation of the IC1000.TM. polyurethane
polishing pads sold by Rohm and Haas Electronic Materials CMP
Technologies. The amount of NCO contained in the
isocyanate-terminated prepolymers range from 5.3 to 9.11
percent.
1TABLE 1 Polishing Pad Ingredients Estimated Polyol Isocyanate NCO
Microsphere Microsphere Microsphere Density Formulation Backbone
ADIPRENE Wt. % EXPANCEL Wt. % (g/cc) A-1 PTMEG L325 9.11 551DE40d42
1.78 0.043 A-2 PTMEG L325 9.11 N/A 0.00 0.043 B-1 PTMEG L325 9.11
551DE40d42 1.58 0.043 B-2 PTMEG L325 9.11 551DE40d42 2.10 0.043 B-3
PTMEG L325 9.11 551DE40d42 1.56 0.043 B-4 PTMEG L325 9.11 N/A 0.00
0.043 B-5 PTMEG L325 9.11 551DE40d42 1.58 0.043 C-1 PTMEG LF751D
9.02 N/A 0.00 0.042 C-2 PTMEG LF751D 9.02 551DE40d42 0.89 0.042 C-3
PTMEG LF751D 9.02 551DE40d42 1.71 0.042 D PTMEG LF600D 7.12 N/A
0.00 0.042 1 PTMEG LF600D 7.12 551DE40d42 0.88 0.042 2 PTMEG LF600D
7.12 551DE40d42 1.75 0.042 E PTMEG LF700D 8.13 N/A 0.00 0.042 3
PTMEG LF700D 8.13 551DE40d42 0.87 0.042 4 PTMEG LF700D 8.13
551DE40d42 1.73 0.042 5 PTMEG LF600D 7.18 551DE40d42 1.25 0.043 6
PTMEG LF950A 5.99 551DE40d42 2.01 0.042 7-1 PTMEG LF950A 5.99
551DE20d60 1.76 0.060 7-2 PTMEG LF950A 5.99 551DE20d60 1.78 0.055 8
PPG LFG963A 5.75 551DE40d42 1.25 0.043 9-1 Ester LF1950A 5.4
551DE20d60 2.56 0.060 9-2 Ester LF1950A 5.3 551DE20d60 2.55 0.061
Adiprene .RTM. is a urethane prepolymer product of
Crompton/Uniroyal Chemical. L325 is a H.sub.12MDI/TDI - PTMEG
having an NCO of 8.95 to 9.25 wt %. LF600D is a TDI - PTMEG having
an NCO of 7.1 to 7.4 wt %. LF700D is a TDI - PTMEG having an NCO of
8.1 to 8.4 wt %. LF751D is a TDI - PTMEG having an NCO of 8.9 to
9.2 wt %. LF950A is a TDI - PTMEG having an NCO of 5.9 to 6.2 wt %.
LFG963A is a TDI-PPG having an NCO of 5.55 to 5.85 wt %. LF1950A is
a TDI-ester having an NCO of 5.24 to 5.54 wt %. Expancel .RTM.
551DE40d42 is a 30-50 .mu.m weight average diameter
hollow-polymeric microsphere manufactured by Akzo Nobel Expancel
.RTM. 551DE20d60 is a 15-25 .mu.m weight average diameter
hollow-polymeric microsphere manufactured by Akzo Nobel N/A = Not
Applicable
[0026] The microspheres represent hollow or gas-filled polymeric
spheres expanded from other Expancel.RTM. microspheres. Table 2
below provides the expansion onset and expansion maximum
temperatures for the microspheres before expansion.
2TABLE 2 Microsphere Expansion Temperatures Density Microsphere
Specification Expanded from Expansion Expansion Expansion Expansion
(Expanded) Range g/liter Microsphere Onset T, .degree. F. Onset T,
.degree. C. Max T, .degree. C. Max T, .degree. C. 551DE20d60 55 to
65 551DU20 199-210 93-98 264-279 129-137 551DE40d42 38 to 46
551DU40 199-210 93-98 275-289 135-143
[0027] The polymeric pad materials were prepared by mixing various
amounts of isocyanate-terminated-urethane prepolymers with
4,4'-methylene-bis-o-chloroaniline [MBCA] at the prepolymer
temperatures and MBCA temperatures provided in Table 3. At these
temperatures, the urethane/polyfunctional amine mixture had a gel
time on the order of 4 to 12 minutes after adding of hollow elastic
polymeric microspheres to the mixture. The 551DE40d42 microspheres
had a weight average diameter of 30 to 50 .mu.m, with a range of 5
to 200 .mu.m; and the 551DE20d60 microspheres had a weight average
diameter of 15 to 25 .mu.m, and were blended at approximately 3,600
rpm using a high shear mixer to evenly distribute the microspheres
in the mixture. The final mixture was transferred to a mold and
permitted to gel for about 15 minutes.
[0028] 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. (except comparative examples A-1 and A-2 where this
segment is changed to 5 h hours at 93.degree. C.) and two hours
with a set point reduced to 21.degree. C. 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.
3TABLE 3 Casting Conditions MBCA Time at Prepolymer Prepolymer flow
MBCA Expancel Pour Cake Main oven main Formu- flow rate,
temperature, rate, temperature, flow rate, time, Diameter, Cake
temperature, temperature, lation kg/min .degree. F./.degree. C.
g/min .degree. F./.degree. C. g/min minutes in./cm Height, "
.degree. F./.degree. C. hours A-1 3.00 122/50 770 240/116 68.3 3
26/66 2 200/93 5 A-2 3.00 122/50 770 240/116 0 3 26/66 1 200/93 5
B-1 4.15 123/51 1040 241/116 83.26 3 26/66 2 220/104 15.5 B-2 3.10
122/50 780 240/116 83.14 4 36/91 1 220/104 15.5 B-3 5.00 125/52
1250 240/116 99.3 4 34/36 2 220/104 15.5 B-4 4.15 123/51 1040
240/116 0 3 26/66 1.5 220/104 15.5 B-5 4.15 124/51 1040 241/116
83.56 3 26/66 2 220/104 15.5 C-1 4.61 127/53 1233 243/117 0 3 27/69
2 220/104 15.5 C-2 4.62 126/52 1238 244/118 52.5 4 36/91 1.5
220/104 15.5 C-3 4.61 128/53 1230 243/117 101.5 4 36/91 1.5 220/104
15.5 D 4.63 126/52 989 244/118 0 3 27/69 2 220/104 15.5 1 4.63
127/53 999 245/118 50 4 36/91 1.5 220/104 15.5 2 4.62 128/53 1001
243/117 100.1 4 36/91 1.5 220/104 15.5 E 4.62 127/53 1117 243/117 0
3 27/69 2 220/104 15.5 3 4.62 126/52 1117 242/117 50.2 4 36/91 1.5
220/104 15.5 4 4.61 125/52 1109 242/117 100.4 4 36/91 1.5 220/104
15.5 5 4.15 123/51 850 240/116 63.5 3 26/66 2 220/104 15.5 6 4.15
121/49 710 240/116 99.82 3 26/66 2 220/104 15.5 7-1 4.15 119/48 710
240/116 87.12 3 26/66 2 220/104 15.5 7-2 4.15 123/51 710 233/112
88.04 3 26/66 2 220/104 15.5 8 4.15 123/51 800 241/116 62.88 3
26/66 2 220/104 15.5 9-1 4.15 135/57 640 239115 126.02 3 26/66 2
220/104 15.5 9-2 4.15 140/60 640 237/114 125.15 4 34/36 1.25
220/104 15.5
[0029] The following Table compares calculated density with actual
top pad density for the prepolymer formulations containing
controlled amounts of NCO reaction groups. Predicted density and
actual top pad density begin to deviate more significantly for
comparative examples C-2 and C3 which use an all TDI, high % NCO
prepolymer and a large mold diameter--all factors tending to
increase product non-uniformity.
4TABLE 4 Density Variation Theor Theor Predicted Actual Top NCO
Microsphere Vol/g Theor Vol/g Vol/g Density Pad Density Formulation
Wt. % Wt. % Urethane Microsphere Mixture g/cc g/cc A-1 9.11 1.78
0.843 0.413 1.256 0.796 0.790 A-2 9.11 0.00 0.858 0.000 0.858 1.165
1.165 B-1 9.11 1.58 0.843 0.366 1.209 0.827 0.826 B-2 9.11 2.10
0.838 0.487 1.325 0.755 0.734 B-3 9.11 1.56 0.843 0.363 1.206 0.829
0.826 B-4 9.11 0.00 0.856 0.000 0.856 1.168 1.168 B-5 9.11 1.58
0.843 0.368 1.210 0.826 0.827 C-1 9.02 0 0.841 0.000 0.841 1.189
1.189 C-2 9.02 0.89 0.833 0.211 1.045 0.957 0.895 C-3 9.02 1.71
0.827 0.407 1.233 0.811 0.727 D 7.12 0 0.856 0.000 0.856 1.169
1.169 1 7.12 0.88 0.848 0.210 1.058 0.945 0.955 2 7.12 1.75 0.841
0.417 1.257 0.795 0.794 E 8.13 0 0.836 0.000 0.836 1.196 1.196 3
8.13 0.87 0.829 0.207 1.035 0.966 0.946 4 8.13 1.73 0.822 0.411
1.233 0.811 0.783 5 7.18 1.25 0.845 0.292 1.137 0.880 0.880 6 5.99
2.01 0.839 0.479 1.318 0.759 0.795 7-1 5.99 1.76 0.841 0.294 1.134
0.882 0.874 7-2 5.99 1.78 0.841 0.324 1.164 0.859 0.837 8 5.75 1.25
0.859 0.291 1.150 0.870 0.871 9-1 5.4 2.56 0.755 0.427 1.183 0.846
0.841 9-2 5.3 2.55 0.755 0.417 1.173 0.853 0.852 The formulation 8
calculation uses Uniroyal's Adiprene LFG963A S.G. of 1.15 for
unfilled material The formulation 9 calculation uses Uniroyal's
Adiprene LF1950A S.G. of 1.29 for unfilled material
[0030] Table 4 shows a general correlation between top pad density
and the predicted pad density.
[0031] Table 5 contains the maximum exotherm temperature obtained
for casting each polyurethane cake.
5TABLE 5 Maximum Exotherm Temperature NCO Exotherm Exotherm
Formulation Wt % max, .degree. F. max, .degree. C. B-1 9.11 257 125
B-5 9.11 258 126 5 7.18 235 113 6 5.99 215 102 7-2 5.99 209 98 8
5.75 163 73 9-1 5.4 230 110
[0032] The above Table illustrates that controlling the NCO to less
than 9.1 facilitates limiting the exotherm temperature to below
120.degree. C.
[0033] A series of density measurements taken from top, middle and
bottom pads compared through-cake uniformity of 80 mil (2 mm)
polishing pads. The average density represents the center, edge and
midpoint density for pads from the three cake locations. In
addition, the center, edge and midpoint densities represent the
average of four measurements.
6TABLE 6 Density Uniformity Avg Density through Cake Formu- NCO
Microspheres Exotherm Exotherm Cake Diameter, lation Wt. % Wt. %
max, .degree. F. max, .degree. C. g/cc St Dev in./cm A-1 9.11 1.78
ND ND 0.785 0.020 26/66 B-1 9.11 1.58 257 125 0.818 0.012 26/66 B-2
9.11 2.10 ND ND 0.741 0.030 36/91 5 7.18 1.25 235 113 0.877* 0.003
26/66 6 5.99 2.01 215 102 0.781 0.006 26/66 8 5.75 1.25 163 73
0.865 0.010 26/66 ND = Not Determined *Determined by measuring
entire pads through the cake.
[0034] These data indicate that an NCO range can improve the
density standard deviation for cast polishing pads.
[0035] Because the amount of pad material contacting the surface to
be polished is related to the density of the pad material,
polishing performance measures such as removal rates and
topographical control are expected to be greatly influenced by the
density of a particular formulation. As control of polishing
performance is driven to ever tighter requirements by smaller
linewidths and more fragile wafer materials, the importance of
improving the control of pad characteristics becomes increasingly
important. The porous-polyurethane polishing pads cast with a
prepolymer having a controlled amount of NCO show a smaller
standard deviation for density measurements both across a pad and
through a cake.
* * * * *