U.S. patent application number 11/446936 was filed with the patent office on 2007-12-06 for compositions for chemical mechanical polishing silica and silicon nitride having improved endpoint detection.
Invention is credited to Brian L. Mueller.
Application Number | 20070281483 11/446936 |
Document ID | / |
Family ID | 38650726 |
Filed Date | 2007-12-06 |
United States Patent
Application |
20070281483 |
Kind Code |
A1 |
Mueller; Brian L. |
December 6, 2007 |
COMPOSITIONS FOR CHEMICAL MECHANICAL POLISHING SILICA AND SILICON
NITRIDE HAVING IMPROVED ENDPOINT DETECTION
Abstract
The present invention provides a method of manufacturing a
composition for polishing silica and silicon nitride on a
semiconductor substrate. The method comprises ion-exchanging
carboxylic acid polymer to reduce ammonia and combining by weight
percent 0.01 to 5 of the ion-exchanged carboxylic acid polymer with
0.001 to 1 quaternary ammonium compound, 0.001 to 1 phthalic acid
and salts thereof, 0.01 to 5 abrasive, and balance water.
Inventors: |
Mueller; Brian L.;
(Middletown, DE) |
Correspondence
Address: |
ROHM AND HAAS ELECTRONIC MATERIALS;CMP HOLDINGS, INC.
451 BELLEVUE ROAD
NEWARK
DE
19713
US
|
Family ID: |
38650726 |
Appl. No.: |
11/446936 |
Filed: |
June 5, 2006 |
Current U.S.
Class: |
438/692 ;
257/E21.244; 438/693 |
Current CPC
Class: |
H01L 21/31053 20130101;
C09G 1/02 20130101 |
Class at
Publication: |
438/692 ;
438/693 |
International
Class: |
H01L 21/461 20060101
H01L021/461 |
Claims
1. (canceled)
2. The method of claim 11 wherein the quaternary ammonium compound
is selected from tetramethyl ammonium hydroxide, tetraethyl
ammonium hydroxide, tetrapropyl ammonium hydroxide, tetraisopropyl
ammonium hydroxide, tetracyclopropyl ammonium hydroxide, tetrabutyl
ammonium hydroxide, tetraisobutyl ammonium hydroxide,
tetratertbutyl ammonium hydroxide, tetrasecbutyl ammonium
hydroxide, tetracyclobutyl ammonium hydroxide, tetrapentyl ammonium
hydroxide, tetracyclopentyl ammonium hydroxide, tetrahexyl ammonium
hydroxide, tetracyclohexyl ammonium hydroxide, and mixtures
thereof.
3. The method of claim 11 wherein the phthalic acid or phthalic
acid salt is potassium hydrogen phthalate.
4. The method of claim 11 wherein the abrasive is ceria.
5. The method of claim 4 wherein the ceria has an average particle
size of between 50-200 nm.
6. The method of claim 4 wherein the ceria has an average particle
size of between 80-150 nm.
7. The method of claim 11 wherein the slurry has a pH of 4 to
7.
8. (canceled)
9. The method of claim 15 wherein the ceria abrasive has an average
particle size of between 50-200 nm.
10. The method of claim 15 wherein the slurry has a pH of 4 to
7.
11. A method of manufacturing a composition for polishing silica
and silicon nitride on a semiconductor substrate comprising:
providing a carboxylic acid polymer in aqueous solution; contacting
the aqueous solution with an ion exchange resin to remove soluble
cations and ammonia from the aqueous solution providing an
ion-exchanged carboxylic acid polymer in aqueous solution; adding
(i) an abrasive, (ii) a quaternary ammonium compound and (iii)
phthalic acid or a phthalic acid salt to the ion-exchanged
carboxylic acid polymer in aqueous solution to provide a slurry
having 0.01 to 5 wt % of the ion-exchagned carboxylic acid polymer,
0.001 to 1 wt % of the quaternary ammonium compound, 0.001 to 1 wt
% of the phthalic acid or phthalic acid salt and 0.01 to 5 wt %
abrasive.
12. The method of claim 11, wherein the ion-exchanged carboxylic
acid polymer in aqueous solution has a cation concentration of 10
ppb to 2 ppm.
13. The method of claim 11, wherein the ion-exchanged carboxylic
acid polymer in aqueous solution has a cation concentration of 50
ppb to 1 ppm.
14. The method of claim 11, wherein the ion-exchanged carboxylic
acid polymer is aqueous solution has a cation concentration of 100
ppb to 200 ppb.
15. A method of chemical mechanical polishing silica and silicon
nitride on a semiconductor substrate comprising: providing a
polishing pad; providing a slurry, wherein the slurry is obtained
by: providing a carboxylic acid polymer in aqueous solution;
contacting the aqueous solution with an ion exchange resin to
remove soluble cations and ammonia from the aqueous solution
providing an ion-exchanged carboxylic acid polymer in aqueous
solution; adding (i) an abrasive, (ii) a quaternary ammonium
compound and (iii) phthalic acid or a phthalic acid salt to the
ion-exchanged carboxylic acid polymer in aqueous solution to
provide a slurry having 0.01 to 5 wt % of the ion-exchagned
carboxylic acid polymer, 0.001 to 1 wt % of the quaternary ammonium
compound, 0.001 to 1 wt % of the phthalic acid or phthalic acid
salt and 0.01 to 5 wt % abrasive; polishing the semiconductor
substrate utilizing the polishing pad and the slurry.
16. The method of claim 15, further comprising: chemically
detecting a polishing endpoint and stopping polishing, wherein
chemically detecting comprises monitoring the level of ammonia in
the slurry.
Description
BACKGROUND OF THE INVENTION
[0001] In the semiconductor industry, critical steps in the
production of integrated circuits are the selective formation and
removal of films on an underlying substrate. The films are made
from a variety of substances, and can be conductive or
non-conductive. Conductive films are typically used for wiring or
wiring connections. Non-conductive or dielectric films are used in
several areas, for example, as interlevel dielectrics between
layers of metallization, or as isolations between adjacent circuit
elements.
[0002] Typical processing steps involve: (1) depositing a film, (2)
patterning areas of the film using lithography and etching, (3)
depositing a film that fills the etched areas, and (4) planarizing
the structure by etching or chemical-mechanical polishing (CMP).
Films are formed on a substrate by a variety of well-known methods,
for example, physical vapor deposition (PVD) by sputtering or
evaporation, chemical vapor deposition (CVD), plasma enhanced
chemical vapor deposition (PECVD). Films are removed by any of
several well-known methods, including, chemical-mechanical
polishing, dry etching such as reactive ion etching (RIE), wet
etching, electrochemical etching, vapor etching, and spray
etching.
[0003] It is extremely important with removal of films to stop the
process when the correct thickness has been removed. In other
words, during the removal of films, it is important to know when
the endpoint has been reached. In CMP, a film is selectively
removed from a semiconductor wafer by rotating the wafer against a
polishing pad (or rotating the pad against the wafer, or both) with
a controlled amount of pressure in the presence of a chemically
reactive slurry. Overpolishing of a film results in yield loss, and
underpolishing requires costly rework. Accordingly, various methods
have been employed to detect when the desired endpoint for removal
has been reached, and the polishing should be stopped.
[0004] The prior art methods for CMP endpoint detection suitable
for all types of films involve the following types of measurement:
(1) simple timing, (2) friction or motor current, (3) capacitive,
(4) optical, (5) acoustical, (6) conductive and (7) chemical. In
particular, chemical endpoint detection (e.g., Li et al., U.S. Pat.
No. 6,021,679) has been popular due to its ability to provide
real-time and continuous analysis of the slurry during polishing, a
direct signal endpoint as soon as the nitride layer is polished and
a fast response time, typically less than one second, in addition
to other benefits.
[0005] It has been discovered that when chemically-mechanically
polishing a substrate with a target film of oxide (SiO.sub.2) over
a stopping film of nitride (Si.sub.3N.sub.4) with a slurry
containing potassium hydroxide (KOH), a chemical reaction occurs
when the oxide/nitride interface is reached, resulting in the
production of ammonia (NH.sub.3). When polishing oxide, the
following reaction occurs:
SiO.sub.2+2KOH+H.sub.2O.fwdarw.K.sub.2SiO.sub.3+2H.sub.2O When
polishing nitride, the following reaction occurs:
Si.sub.3N.sub.4+6KOH+3H.sub.2O.fwdarw.3K.sub.2SiO.sub.3+4NH.sub.3
[0006] The ammonia produced is dissolved in the slurry and it
exists primarily in the form of NH.sub.3 rather than
NH.sub.4.sup.+. Thus, the presence of ammonia in the slurry
indicates that the underlying nitride film has been reached and
polished, and the endpoint for removal of the oxide film can be
determined by monitoring the level of ammonia in the slurry. Once
the endpoint is reached, the polishing is stopped.
[0007] Typically, in order to detect and monitor ammonia in a
gaseous form, slurry from a polishing apparatus is pumped through
an ammonia extraction unit. The ammonia-containing gas stream can
be analyzed and monitored for endpoint detection for removal of the
target film. Gas phase chemical analysis, such as standard mass
spectroscopy can be highly sensitive and have a fast response time,
that would be desirable for endpoint detection. Unfortunately, with
slurry sampling, there may be substantial interference from any
residual ammonia created from the slurry composition itself, making
accurate endpoint detection extremely difficult.
[0008] Hence, what is needed is a composition and method for
chemical-mechanical polishing of silica and silicon nitride for
shallow trench isolation processes having improved end-point
detection capability.
STATEMENT OF THE INVENTION
[0009] In a first aspect, the present invention provides a method
of manufacturing a composition for polishing silica and silicon
nitride on a semiconductor substrate comprising: ion-exchanging
carboxylic acid polymer to reduce ammonia; and combining by weight
percent 0.01 to 5 of the ion-exchanged carboxylic acid polymer with
0.001 to 1 quaternary ammonium compound, 0.001 to 1 phthalic acid
and salts thereof, 0.01 to 5 abrasive, and balance water.
[0010] In a second aspect, the present invention provides a method
of chemical mechanical polishing silica and silicon nitride on a
semiconductor substrate comprising: providing a polishing pad and a
ceria-abrasive containing slurry; ion-exchanging a solution of
carboxylic acid polymer to be utilized in the slurry to reduce
ammonia in the solution to between 10 ppb to 2 ppm; and polishing
the substrate utilizing the polishing pad and the slurry containing
the ammonia-reduced solution of carboxylic acid polymer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1A illustrates the averages of post polishing results
from center, middle and edge dies for retaining degree of wafer
scale uniformity;
[0012] FIG. 1B illustrates the averages of post polishing results
from center, middle and edge dies for retaining degree of wafer
scale uniformity;
[0013] FIG. 2 illustrates results obtained utilizing various
end-point detection techniques;
[0014] FIG. 3A illustrates planarization efficiencies obtained
utilizing various end-point detection techniques;
[0015] FIG. 3B illustrates planarization efficiencies obtained
utilizing various end-point detection techniques.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The composition and method provide improved end-point
detection signals for use in chemical end-point detection systems.
In particular, the composition and method of the present invention
is ammonia-reduced, thereby improving the accuracy of the chemical
end-point detection system. The invention advantageously utilizes
an ion-exchange resin to reduce the ammonia content of the
composition to reduce the interference from any slurry-originated
ammonia contamination. In particular, the carboxylic acid polymer
is ion-exchanged to reduce the ammonia content in the ceria-based
slurry. In addition, the composition provides unexpected
selectivity for removing silica relative to silicon nitride. The
composition advantageously relies upon a chelating agent or a
selectivity enhancer to selectively polish silica relative to
silicon nitride for shallow trench isolation processes. In
particular, the composition comprises a quaternary ammonium
compound to selectively polish silica relative to silicon nitride,
at the pH of the application.
[0017] The quaternary ammonium compounds of the present invention
include the following structure: ##STR1## where R.sub.1, R.sub.2,
R.sub.3 and R.sub.4 are an organic compound that has a carbon chain
length of 1 to 15 carbon atoms. More preferably, R.sub.1, R.sub.2,
R.sub.3 and R.sub.4 have a carbon chain length of 1 to 10. Most
preferably, R.sub.1, R.sub.2, R.sub.3 and R.sub.4 have a carbon
chain length of 1 to 5 carbon atoms. The organic compound of
R.sub.1, R.sub.2, R.sub.3 and R.sub.4 may be a substituted or
unsubstituted aryl, alkyl, aralkyl, or alkaryl group. Example
anions include, nitrate, sulfate, halides (such as, bromide,
chloride, fluoride and iodide), citrate, phosphate, oxalate,
malate, gluconate, hydroxide, acetate, borate, lactate,
thiocyanate, cyanate, sulfonate, silicate, per-halides (such as,
perbromate, perchlorate and periodate), chromate, and mixtures
comprising at least one of the foregoing anions.
[0018] Preferred quaternary ammonium compounds include, tetramethyl
ammonium hydroxide, tetraethyl ammonium hydroxide, tetrapropyl
ammonium hydroxide, tetraisopropyl ammonium hydroxide,
tetracyclopropyl ammonium hydroxide, tetrabutyl ammonium hydroxide,
tetraisobutyl ammonium hydroxide, tetratertbutyl ammonium
hydroxide, tetrasecbutyl ammonium hydroxide, tetracyclobutyl
ammonium hydroxide, tetrapentyl ammonium hydroxide,
tetracyclopentyl ammonium hydroxide, tetrahexyl ammonium hydroxide,
tetracyclohexyl ammonium hydroxide, and mixtures thereof. Most
preferred quaternary ammonium compounds is tetramethyl ammonium
hydroxide.
[0019] The composition advantageously contains 0.001 to 1 weight
percent quaternary ammonium compound to selectively remove the
silica relative to the silicon nitride. Advantageously, the
composition contains 0.01 to 0.5 weight percent quaternary ammonium
compound.
[0020] In addition to the quaternary ammonium compound, the
composition advantageously contains 0.001 to 1 weight percent
complexing agent. Advantageously, the composition contains 0.01 to
0.5 weight percent complexing agent. Example complexing agents
include carbonyl compounds (e.g., acetylacetonates and the like),
simple carboxylates (e.g., acetates, aryl carboxylates, and the
like), carboxylates containing one or more hydroxyl groups (e.g.,
glycolates, lactates, gluconates, gallic acid and salts thereof,
and the like), di-, tri-, and poly-carboxylates (e.g., oxalates,
phthalates, citrates, succinates, tartrates, malates, edetates
(e.g., disodium EDTA), mixtures thereof, and the like),
carboxylates containing one or more sulfonic and/or phosphonic
groups. Also, other suitable complexing agents include, for
example, di-, tri-, or poly-alcohols (e.g., ethylene glycol,
pyrocatechol, pyrogallol, tannic acid, and the like) and
phosphate-containing compounds (e.g., phosphonium salts and
phosphonic acids). Preferably, the complexing agent is phthalic
acid and salts thereof. Preferred phthalate salts include, ammonium
hydrogen phthalate and potassium hydrogen phthalate, and mixtures
thereof.
[0021] Advantageously, the novel polishing composition contains
about 0.01 to 5 weight percent of a carboxylic acid polymer.
Preferably, the composition contains about 0.05 to 3 weight percent
of a carboxylic acid polymer. Also, the polymer preferably has a
number average molecular weight of about 20,000 to 1,500,000. In
addition, blends of higher and lower number average molecular
weight carboxylic acid polymers can be used. These carboxylic acid
polymers generally are in solution but may be in an aqueous
dispersion. The number average molecular weight of the
aforementioned polymers are determined by GPC (gel permeation
chromatography).
[0022] The carboxylic acid polymers are formed from unsaturated
monocarboxylic acids and unsaturated dicarboxylic acids. Typical
unsaturated monocarboxylic acid monomers contain 3 to 6 carbon
atoms and include acrylic acid, oligomeric acrylic acid,
methacrylic acid, crotonic acid and vinyl acetic acid. Typical
unsaturated dicarboxylic acids contain 4 to 8 carbon atoms and
include the anhydrides thereof and are, for example, maleic acid,
maleic anhydride, fumaric acid, glutaric acid, itaconic acid,
itaconic anhydride, and cyclohexene dicarboxylic acid. In addition,
water soluble salts of the aforementioned acids also can be
used.
[0023] In addition, carboxylic acid containing copolymers and
terpolymers can be used in which the carboxylic acid component
comprises 5-75% by weight of the polymer. Typical of such polymer
are polymers of (meth)acrylic acid and acrylamide or
methacrylamide; polymers of (meth)acrylic acid and styrene and
other vinyl aromatic monomers; polymers of alkyl(meth)acrylates
(esters of acrylic or methacrylic acid) and a mono or dicarboxylic
acid, such as, acrylic or methacrylic acid or itaconic acid;
polymers of substituted vinyl aromatic monomers having
substituents, such as, halogen, i.e., chlorine, fluorine, bromine,
nitro, cyano, alkoxy, haloalkyl, carboxy, amino, amino alkyl and a
unsaturated mono or dicarboxylic acid and an alkyl(meth)acrylate;
polymers of monethylenically unsaturated monomers containing a
nitrogen ring, such as, vinyl pyridine, alkyl vinyl pyridine, vinyl
butyrolactam, vinyl caprolactam, and an unsaturated mono or
dicarboxylic acid; polymers of olefins, such as, propylene,
isobutylene, or long chain alkyl olefins having 10 to 20 carbon
atoms and an unsaturated mono or dicarboxylic acid; polymers of
vinyl alcohol esters, such as, vinyl acetate and vinyl stearate or
vinyl halides, such as, vinyl fluoride, vinyl chloride, vinylidene
fluoride or vinyl nitriles, such as, acrylonitrile and
methacrylonitrile and an unsaturated mono or dicarboxylic acid;
polymers of alkyl(meth)acrylates having 1-24 carbon atoms in the
alkyl group and an unsaturated monocarboxylic acid, such as,
acrylic acid or methacrylic acid. These are only a few examples of
the variety of polymers that can be used in the novel polishing
composition of this invention. Also, it is possible to use polymers
that are biodegradeable, photodegradeable or degradeable by other
means. An example of such a composition that is biodegradeable is a
polyacrylic acid polymer containing segments of poly(acrylate
comethyl 2-cyanoacrylate).
[0024] Advantageously, the carboxylic acid polymer of the present
invention is ion-exchanged to reduce the ammonia content that may
interfere with an ammonia-detecting, end-point detection system. In
particular, the ion-exchange resin of the present invention has
anionic groups incorporated therein. These anionic groups render
the cationic ion exchange resin capable of adsorbing soluble
cations, such as, metal ions (e.g., Na.sup.+, K.sup.+, Ca.sup.+2,
Fe.sup.+3 . . . etc.) and ammonia from an aqueous solution. Resins
of the present invention are capable of reducing the cation
concentrations to between 10 ppb to 2 ppm. More preferably, resins
of the present invention are capable of reducing the cation
concentrations to between 50 ppb to 1 ppm. Most preferably, resins
of the present invention are capable of reducing the cation
concentrations to less than 100 ppb to 200 ppb. These ion exchange
resins are typically regenerated using strong acids to desorb the
adsorbed ions and replace them with hydronium ions. Preferred ion
exchange resins include, Amberlite.RTM. ion exchange resins from
the Rohm and Haas Company, of Philadelphia, Pa. A preferred ion
exchange resin is Amberlite.RTM. IRN-77.
[0025] The cation exchange resins of the present invention may have
the physical form of gel beads, e.g. spherical gel beads, or
macroporous beads, including macroreticular beads or comminuted
resin particles that are gel or macroporous resin. Such comminuted
particles may be derived from bulk-polymerized or
suspension-polymerized polymers using known comminution
techniques.
[0026] Preferred ion exchange resin particles are those prepared by
functionalizing crosslinked, suspension-polymerized copolymer beads
that are well known in the art as precursors for ion exchange
resins. Gel copolymer beads bear their functional groups in an
outer shell of uniform depth. Because the functionalization
processes used to prepare these beads penetrate the copolymer at a
uniform rate, the thickness of the functionalized layers tend to be
uniform for all beads regardless of bead size, provided only that
the smallest beads are not completely functionalized, i.e., not
completely sulfonated. As a result, the diffusion paths are highly
uniform, regardless of the uniformity of bead size.
[0027] Monomers suitable for preparing crosslinked copolymer
include monovinyl aromatic monomers, for example, styrene,
vinyltoluene, vinyl naphthalene, ethyl vinyl benzene, vinyl
chlorobenzene, chloromethylstyrene and the like, which may comprise
from about 50 to about 99.5 mole percent, preferably 80 to about 99
mole percent, of the monomers from that the copolymer is made, and
polyvinyl monomers having at least two active vinyl groups
polymerizable with the monovinyl monomer, which may comprise from
about 0.5 to about 50 mole percent, preferably from 1 to about 20
mole percent, of the monomers from that the copolymer is made.
Examples of suitable polyvinyl monomers include divinylbenzene,
trimethylolpropane trimethacrylate, ethylene glycol dimethacrylate,
divinyltoluene, trivinylbenzene, divinylchlorobenzene, diallyl
phthalate, divinylpyridine, divinylnaphthalene, ethylene glycol
diacrylate, neopentyl glycol dimethacrylate, diethylene glycol
divinyl ether, bis-phenol-A-dimethacrylate, pentaerythritol tetra-
and trimethacrylates, divinyl xylene, divinylethylbenzene, divinyl
sulfone, divinyl ketone, divinyl sulfide, allyl acrylate,diallyl
maleate, diallyl fumarate, diallyl succinate, diallyl carbonate,
diallyl malonate, diallyl oxylate, diallyl adipate, diallyl
sebacate, diallyl tartrate, diallyl silicate, diallyl
tricarballylate, triallyl aconitate, triallyl citrate, triallyl
phosphate, N,N'-methylene-diacrylamide,
N,N'-methylene-dimethacrylamide, N,N'-ethylenediacrylamide,
trivinyl naphthalene, polyvinylanthracenes and the polyallyl and
polyvinyl ethers of glycol, glycerol, pentaerythritol, resorcinol,
and the monothio and dithio derivatives of glycols. The monomer
mixture may also contain up to about 5 mole percent of other vinyl
monomers that do not affect the basic nature of the resulting resin
matrix, for example, acrylonitrile, butadiene, methacrylic acid and
others known in the art. In one embodiment of the invention, the
copolymer particles are acrylic ester copolymer particles.
[0028] One desirable form of functionalization is sulfonation, and
the present invention is capable of providing partially sulfonated
resins that are significantly better able to withstand the stress
of the loading and regeneration cycle in aqueous ion exchange
applications than resins formed by sulfonating conventional
copolymers, either in the solvent-swollen or non-swollen state.
[0029] Advantageously, the polishing composition contains 0.01 to 5
weight percent abrasive to facilitate silica removal. Within this
range, it is desirable to have the abrasive present in an amount of
greater than or equal to 0.1 weight percent. Also, desirable within
this range is an amount of less than or equal to 3 weight
percent.
[0030] The abrasive has an average particle size between 50 to 200
nanometers (nm). For purposes of this specification, particle size
refers to the average particle size of the abrasive. More
preferably, it is desirable to use an abrasive having an average
particle size between 80 to 150 nm. Decreasing the size of the
abrasive to less than or equal to 80 nm, tends to improve the
planarization of the polishing composition, but, it also tends to
decrease the removal rate.
[0031] Example abrasives include inorganic oxides, inorganic
hydroxides, metal borides, metal carbides, metal nitrides, polymer
particles and mixtures comprising at least one of the foregoing.
Suitable inorganic oxides include, for example, silica (SiO.sub.2),
alumina (Al.sub.2O.sub.3), zirconia (ZrO.sub.2), ceria (CeO.sub.2),
manganese oxide (MnO.sub.2), or combinations comprising at least
one of the foregoing oxides. Modified forms of these inorganic
oxides, such as, polymer-coated inorganic oxide particles and
inorganic coated particles may also be utilized if desired.
Suitable metal carbides, boride and nitrides include, for example,
silicon carbide, silicon nitride, silicon carbonitride (SiCN),
boron carbide, tungsten carbide, zirconium carbide, aluminum
boride, tantalum carbide, titanium carbide, or combinations
comprising at least one of the foregoing metal carbides, boride and
nitrides. Diamond may also be utilized as an abrasive if desired.
Alternative abrasives also include polymeric particles and coated
polymeric particles. The preferred abrasive is ceria.
[0032] The compounds provide efficacy over a broad pH range in
solutions containing a balance of water. This solution's useful pH
range extends from at least 4 to 7. In addition, the solution
advantageously relies upon a balance of deionized water to limit
incidental impurities. The pH of the polishing fluid of this
invention is preferably from 4.5 to 6.8, more preferably a pH of 5
to 6.5. The acids used to adjust the pH of the composition of this
invention are, for example, nitric acid, sulfuric acid,
hydrochloric acid, phosphoric acid and the like. Exemplary bases
used to adjust the pH of the composition of this invention are, for
example, potassium hydroxide.
[0033] Accordingly, the present invention provides a composition
and method having improved end-point detection signals for use in
chemical end-point detection systems. In particular, the
composition and method of the present invention is ammonia-reduced,
thereby improving the accuracy of the chemical end-point detection
system. The invention advantageously utilizes an ion-exchange resin
to reduce the ammonia content of the composition to reduce the
interference from any slurry-originated ammonia contamination. a
composition useful for polishing silica and silicon nitride on a
semiconductor wafer for shallow trench isolation processes. In
particular, the carboxylic acid polymer is ion-exchanged to reduce
the ammonia content in the ceria-based slurry. In addition, the
composition advantageously comprises quaternary ammonium compounds
for improved selectivity. In particular, the present invention
provides an aqueous composition useful for polishing silica and
silicon nitride on a semiconductor wafer comprising quaternary
ammonium compound, phthalic acid and salts thereof, carboxylic acid
polymer, abrasive and balance water. The composition exhibits
particularly improved selectivity at a pH range of 4 to 7. Note,
although the present embodiment concerns reduction of the ammonia
content from the carboxylic acid polymer, the invention is not so
limited. In other words, any constituent or component of the
slurry, for example, the quaternary ammonium compound may be
ion-exchanged to reduce any ammonia content, as necessary.
EXAMPLE 1
[0034] All example solutions contained, by weight percent, 1.8
ceria, 0.18 polyacrylic acid, and 0.21 potassium hydrogen
phthalate. In addition, the examples of the invention contained
0.12 weight percent, of a quaternary ammonium compound, in
particular, tetramethyl ammonium hydroxide. The slurry was prepared
by combining an abrasive package with a chemical package. The
abrasive package was made by dissolving the polyacrylic acid
concentrate in deionized water using a blade mixer and adding the
ceria concentrate into the polyacrylic acid solution.
Advantageously, the polyacrylic acid polymer was ion-exchanged with
Amberlite IRN-77 ion exchange resin. The ion exchange resin was
purchased in cylinders from Siemens Water Technologies, of
Warrendale, Pa. The solution of carboxylic acid polymer is diluted
to 5 percent to reduce the viscosity of the solution. The solution
is pumped through the cylinders packed with the cationic ion
exchange resin. The resin passes through the resin bed and comes
out at a pH less than 3 and essentially free of all cationic
species such as metal ions or ammonia. Then, the ceria-polyacrylic
acid-water mixture was titrated using nitric acid. The mixture was
then fed into a high shear Kady Mill. The chemical package was
prepared by dissolving all remaining chemicals into deionized
water, in proper amounts, mixing with a blade mixer and titrating
to the final pH as desired using nitric acid. The final slurry is
prepared by mixing the abrasive package with the chemical package
and titrating to the desired pH.
[0035] The patterned wafers were STI-MIT-864.TM. masks from
Praesagus, Inc. with HDP and LPCVD-SiN films. The MIT-864 mask
design had 20 mm by 20 mm die consisting of 4 mm by 4 mm features.
The features in the mask had 100 .mu.m pitches with densities
ranging from 10% to 100% each, and 50% densities with pitches
ranging from 1 to 1000 .mu.m. Here, 50% density is defined as the
spaces in an array of repeated structures wherein the space
width/(space width+line width).times.100%=50%. For example, if the
space width+line width=1000 microns, the 50% space has a width of
500 microns. IC1010.TM. polishing pads were used for all tests. An
Applied Materials Mirra.RTM. 200mm polishing machine using an
IC1010.TM. polyurethane polishing pad (Rohm and Haas Electronic
Materials CMP Inc., of Newark, Del.) under downforce conditions of
2.7 psi and a polishing solution flow rate of 85 cc/min, a platen
speed of 123 RPM and a carrier speed of 44 RPM planarized the
samples. The polishing solutions had a pH of 6.1 adjusted with
nitric acid. All solutions contained a balance of deionized water.
Oxide and nitride film thicknesses were measured using an
Opti-probe.RTM. 2600 metrology tool from Therma-Wave, Inc.
[0036] As illustrated in FIG. 1A, 1B, the averages of post
polishing results from center, middle and edge dies for retaining
degree of wafer scale uniformify information is shown. As shown in
FIG. 1A, the average trench within-die range was 300-400 .ANG.. As
shown in FIG. 1B, the nitride thickness within-die range was 150
.ANG.. Total trench oxide loss reflects the combination of dishing
and erosion.
EXAMPLE 2
[0037] This experiment compared results of chemical end-point data
with that of frictional and optical data for analyzing endpoint
robustness. The chemical end-point detection system was an Eco
Systems M17 N-EPD by Eco Physics. All other parameters were the
same as those of Example 1.
[0038] As illustrated in FIG. 2, the chemical endpoint was the most
straightforward to interpret ("on/off"), allowing high
manufacturability. The chemical endpoint was determinable 10-15
seconds ahead of frictional or optical endpoints. The chemical
endpoint allowed enhanced overpolish window confidence and process
robustness.
EXAMPLE 3
[0039] This experiment compared results of chemical end-point data
with that of frictional and optical data for analyzing
planarization efficiency. The chemical end-point detection system
was the same as in Example 2. All other parameters were the same as
those of Example 1.
[0040] As illustrated in FIG. 3A, 3B, the optimized process
utilizing chemical end-point significantly improved planarization
efficiency. The chemical end-point system improved oxide clearing
confidence and shorter over-polish requirement.
[0041] Accordingly, the present invention provides a composition
and method having improved end-point detection signals for use in
chemical end-point detection systems. In particular, the
composition and method of the present invention is ammonia-reduced,
thereby improving the accuracy of the chemical end-point detection
system. The invention advantageously utilizes an ion-exchange resin
to reduce the ammonia content of the composition to reduce the
interference from any slurry-originated ammonia contamination. a
composition useful for polishing silica and silicon nitride on a
semiconductor wafer for shallow trench isolation processes.
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