U.S. patent application number 10/635949 was filed with the patent office on 2005-02-10 for cmp slurry.
Invention is credited to Hegde, Sharath, Xu, Wen-Qing.
Application Number | 20050028450 10/635949 |
Document ID | / |
Family ID | 34116340 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050028450 |
Kind Code |
A1 |
Xu, Wen-Qing ; et
al. |
February 10, 2005 |
CMP slurry
Abstract
RNA, DNA and the building blocks forming these compounds provide
significant enhancement in the selectivity of a CMP slurry for
removing silicon dioxide in preference to silicon nitride during
chemical-mechanical polishing in the manufacture of semiconductor
wafers and chips by STI.
Inventors: |
Xu, Wen-Qing; (Northborough,
MA) ; Hegde, Sharath; (Potsdam, NY) |
Correspondence
Address: |
CALFEE HALTER & GRISWOLD, LLP
800 SUPERIOR AVENUE
SUITE 1400
CLEVELAND
OH
44114
US
|
Family ID: |
34116340 |
Appl. No.: |
10/635949 |
Filed: |
August 7, 2003 |
Current U.S.
Class: |
51/309 ; 216/89;
216/96; 216/99; 257/E21.244; 438/692; 438/693; 51/307; 51/308 |
Current CPC
Class: |
C09G 1/02 20130101; H01L
21/31053 20130101; C09K 3/1463 20130101 |
Class at
Publication: |
051/309 ;
051/307; 051/308; 438/692; 438/693; 216/089; 216/096; 216/099 |
International
Class: |
B24D 003/02 |
Claims
We claim:
1. A CMP slurry comprising a liquid, abrasive particles and a
selectivity enhancer comprising a nucleic acid related
compound.
2. The CMP slurry of claim 1, wherein the liquid is water and the
slurry contains at about 0.01 wt. % abrasive particles.
3. The slurry of claim 2, wherein the nucleic acid related compound
is RNA or DNA, a nitrogen-containing precursor of RNA or DNA, a
nitrogen-containing decomposition product of RNA or DNA, or mixture
of any of these compounds.
4. The slurry of claim 3, wherein the nucleic acid related compound
is RNA or DNA.
5. The slurry of claim 3, wherein the nucleic acid related compound
is a nucleotide.
6. The slurry of claim 5, wherein the nucleotide is adenosine
5'-phosphate, 2'-deoxyadenosine 5'-phosphate, guanosine
5'-phosphate, 2'-deoxyguanosine 5'-phosphate, cytidine
5'-phosphate, 2'-deoxycytidine 5'-phosphate, uridine 5'-phosphate,
2'-deoxythymidine 5'-phosphate, adenosine 5'-diphosphate,
2'-deoxyadenosine 5'-diphosphate, guanosine 5'-diphosphate
2'-deoxyguanosine 5'-diphosphate, cytidine 5'-diphosphate,
2'-deoxycytidine 5'-diphosphate, uridine 5'-diphosphate,
2'-deoxythymidine 5'-diphosphate, adenosine 5'-triphosphate,
2'-deoxyadenosine 5'-triphosphate, guanosine 5'-triphosphate,
2'-deoxyguanosine 5'-triphosphate, cytidine 5'-triphosphate,
2'-deoxycytidine 5'-triphosphate, uridine 5'-triphosphate,
2'-deoxythymidine 5'-triphosphate, or mixtures thereof.
7. The slurry of claim 3, wherein the nucleic acid compound is a
nucleoside.
8. The slurry of claim 7, wherein the nucleoside is adenosine,
2'-deoxyadenosine, guanosine, 2'-deoxyguanosine, cytidine,
2'-deoxycytidine, uridine, 2'-deoxythymidine or mixtures
thereof.
9. The slurry of claim 3, wherein the nucleic acid related compound
is adenine, guanine, cytosine, uracil, thymine or mixtures
thereof.
10. The slurry of claim 3, wherein the slurry contains a mixture of
a cationic surfactant, an anionic surfactant and a nonionic
surfactant.
11. The slurry of claim 10, wherein the cationic surfactant is an
alkyltrimethylammonium halide, an alkylbenzyldimethylammonium
halide, a pyridiniumalkyl halide, an alkylammonium ester, or
mixtures thereof, wherein the anionic surfactant is a polymer
containing carboxylic acid groups, an ammonium, sodium, potassium,
cesium, monoethanolamine, diethanolamine, or triethanolamine salt
of such a polymer, or mixtures thereof, and wherein the nonionic
surfactant is a water soluble polyvinyl alcohol, polyacrylamide,
polyvinylpyrrolidone, or mixtures thereof.
12. The slurry of claim 11, wherein the cationic surfactant is
hexadecyltrimethylammonium bromide, hexadecylbenzyldimethylammonium
bromide, dodecylbenzyldimethylammonium bromide, cetylpyridinium
chloride, dodecylammonium acetate, or mixtures thereof.
13. The slurry of claim 1, wherein the nucleic acid related
compound is a mixture of uridine and cytidine.
14. A chemical-mechanical polishing process for selectively
removing silicon dioxide from the surface of a workpiece containing
surface areas of silicon dioxide and surface areas of silicon
nitride in which the surface to be polished is contacted with a
polishing pad and a CMP slurry is applied to the interface between
the polishing pad the surface to be polished, wherein the CMP
slurry comprises a liquid, abrasive particles and a selectivity
enhancer for enhancing the removal of silicon dioxide in preference
to the removal of silicon nitride, the selectivity enhancer
comprising a nucleic acid related compound.
15. The process of claim 14, wherein the liquid comprises water and
the slurry contains at about 0.01 wt. % abrasive particles.
16. The process of claim 15, wherein the nucleic acid related
compound is RNA or DNA, a nitrogen-containing precursor of RNA or
DNA, a nitrogen-containing decomposition product of RNA or DNA, or
mixture of any of these compounds.
17. The process of claim 16, wherein the nucleic acid related
compound comprises RNA or DNA.
18. The process of claim 17, wherein the nucleic acid related
compound comprises a nucleotide.
19. The process of claim 16, wherein the nucleic acid related
compound comprises a nucleoside.
20. The process of claim 16, wherein the nucleic acid related
compound comprises adenine, guanine, cytosine, uracil, thymine or
mixtures thereof.
21. The process of claim 16, wherein the nucleic acid related
compound is a mixture of uridine and cytidine.
Description
FIELD
[0001] The present invention relates to chemical/mechanical
polishing ("CMP") slurries and to CMP process using such
slurries.
BACKGROUND
[0002] U.S. Pat. No. 6,491,843 B1 describes certain CMP slurries
having high selectivities for removing silicon dioxide in
preference to silicon nitride. These slurries are composed of
water, abrasive particles and a selectivity enhancer comprising an
organic compound having both a carboxylic acid functional group and
a second functional group selected from amines and halides. Amino
acids and especially proline, glycine, alanine, arginine and lysine
are preferred. See, also, U.S. Pat. No. 6,544,892 B2 and U.S.
6,468,910 B1.
SUMMARY OF THE INVENTION
[0003] It has now been found that CMP slurries in which the
selectivity enhancer is a nucleic acid related compound, e.g., RNA,
DNA, a nitrogen-containing precursor of RNA or DNA, a
nitrogen-containing decomposition product of RNA or DNA, or
mixtures of any of these compounds, also exhibit high selectivities
for removing silicon dioxide in preference to silicon nitride.
[0004] Thus, the present invention provides a novel CMP slurry for
use in chemical-mechanical polishing in the manufacture of a wafer
or chip, the slurry comprising water, abrasive particles and a
selectivity enhancer for causing the slurry to selectively remove
silicon dioxide in preference to silicon nitride, the selectivity
enhancer comprising a nucleic acid related compound, more
particularly RNA or DNA, a nitrogen-containing precursor of RNA or
DNA, a nitrogen-containing decomposition product of RNA or DNA, or
mixture of any of these compounds.
DETAILED DESCRIPTION
[0005] Chemical Mechanical Polishing
[0006] Chemical mechanical polishing is well known technology in
which the workpiece is rubbed with a polishing pad while a CMP
slurry is applied to the interface between the pad and the surface
being polished. The CMP slurry functions to chemically react with
the surface while the abrasive particles in the slurry mechanically
abrade the surface.
[0007] Chemical mechanical polishing is used extensively in the
manufacture of semiconductor chips and wafers by the shallow trench
isolation ("STI") technique. In STI, a pattern of shallow trenches
is made in the surface of a silicon or gallium arsenide wafer
carrying a silicon nitride barrier layer, the trenches normally
being space apart by distances as small as a few nanometers and as
large as several thousand microns, more typically about 0.065-5000
microns or even 0.09-3000 microns. A dielectric such as silicon
dioxide is then deposited by chemical vapor deposition, for
example, to completely fill the trenches in such a way that the
dielectric also forms a silicon dioxide overburden covering the
silicon nitride barrier layer. The process may over fill the
trenches. CMP is then used to remove the dielectric overburden
covering the silicon nitride barrier layer and remove any overfills
on the trenches, and ideally stop at the silicon nitride barrier
layer without dishing into the dielectric trenches, which produces
a completely planar surface. In subsequent steps, the silicon
nitride barrier layer is removed, polysilicon gate structures are
formed in the wafer surfaces between the dielectric-filled
trenches. For a complete description of STI and CMP, see: U.S. Pat.
No. 6,491,843 B1; U.S. Pat. No. 6,365,520; U.S. Pat. No. 5,738,800;
U.S. Pat. No. 6,548,373 B1; U.S. Pat. No. 5,759,917; U.S. Pat. No.
5,772,780; U.S. Pat. No. 6,043,155; U.S. Pat. No. 6,343,976; B1;
U.S. Pat. No. 6,544,892 B2; U.S. Pat. No. 6,468,910 B1; U.S. Pat.
6,303,506; U.S. 2003/0092271 A1; EP 0 846 740 A1; and EP 0 853 335
A2, the disclosures of which are incorporated herein by
reference.
[0008] CMP Slurries
[0009] The inventive CMP slurries are composed of water or other
slurry liquid, abrasive particles and at least one selectivity
enhancing nucleic acid related compound. Additional optional
organic and inorganic compounds may also be included.
[0010] Like most conventional CMP slurries, the inventive CMP
slurries use water as the slurry liquid. However, other liquids
which will accomplish the same purpose can also be used. Examples
are methanol, ethanol and the other alcohols, glycols, ketones and
aldehydes.
[0011] Any type of abrasive particles can be used in the inventive
CMP slurries. Examples include silica, alumina, ceria, copper
oxide, iron oxide, nickel oxide, manganese oxide, silicon carbide,
silicon nitride, tin oxide, titania, tungsten oxide, yttria,
zirconia, complex oxides such as zinc ferrite, magnesium ferrite,
aluminum silicate and barium carbonate, various metal carbides such
as titanium carbide, metal hydroxides such as aluminum hydroxide,
magnesium hydroxide, manganese hydroxide and cerium hydroxide, as
well as organic abrasives such as polystyrene, urea-formaldehyde
and latex particles. Mixtures of these abrasives can also be used.
Silica, alumina, titania, ceria and mixtures thereof are most often
used.
[0012] The particle size of the abrasive particles of the inventive
CMP slurries can vary widely, and essentially any conventional
particle size can be used. In this connection, care should be taken
to avoid particles which are too large, which may lead to
unacceptable scratching, as well as particles which are too small,
which may lead to unacceptably low polishing rates. In general,
this means that the mean particle size should be between about
0.001-10 microns, more typically between 0.005-5.0 microns, or even
0.01-2.0 microns, with particles larger than about 10 microns
preferably being avoided essentially completely for polishing
wafers for semiconductor manufacture. In addition, a bimodal
particle size distribution, i.e., a mixture of small and large
particles as described in U.S. Pat. No. 6,365,520 B1, can be
used.
[0013] The concentration of abrasive particles in the inventive CMP
slurries can also vary widely, and essentially any conventional
amount can also be used. Typically, this means the slurry will
contain about 0.01-50 wt. % particles, with 0.05-30 wt. % and even
0.1-10 wt. % being more typical.
[0014] In addition to the abrasive particles, the inventive CMP
slurries can contain a wide variety of optional ingredients. For
example, the inventive CMP slurries can contain anionic and
cationic surfactants such as shown, for example, in U.S. Pat. No.
5,738,800 and U.S. Pat. No. 6,303,506. In addition, the inventive
CMP slurries can contain organic compounds having a carboxylic acid
group and an electrophilic functional group such as an amine or
halide such as shown, for example, in U.S. Pat. No. 6,491,843 B1;
U.S. Pat. No. 6,544,892 B1 and U.S. Pat. No. 6,468,910 B1.
Similarly, the inventive CMP slurries can contain simple carboxylic
acids such as shown in U.S. Pat. No. 5,759,917, alone or in
combination with a water-soluble salt and soluble cerium compounds
as further shown in that patent, as well as organic particles
containing carboxyl and other anionic groups such as shown in U.S.
Pat. No. 6,559,056 B2. The inventive CMP slurries can also contain
acids, bases and other compounds for adjusting pH, such as the
tetramethyl ammonium hydroxide shown in EP 0 853 335 and the
polyelectrolytes shown in EP 0 846 740 A1 such as the
polyethylenimine and other organic and inorganic compounds
previously used in these slurries such as the H.sub.2O.sub.2 of
U.S. Pat. No. 6,043,155.
[0015] Nucleic Acid Compounds
[0016] In accordance with the present invention, the inventive CMP
slurries contain at least one nucleic acid related compound as a
selectivity enhancer. By "nucleic acid related compound" is meant
ribonucleic acid compounds ("RNA") and deoxyribonucleic acid
compounds ("DNA"), as well as the nucleotides, nucleosides and
heterocyclic amine bases which are the nitrogen-containing
precursors of or decomposition products of these RNA and DNA
compounds, and mixtures of these compounds. Nucleotides which are
not derived from or decomposition products of RNA and DNA are also
"nucleic acid related compounds" for the purposes of this
invention. Also included are synthetic analogs of such
compounds.
[0017] RNA and DNA molecules are polynucleotides, i.e., polymers
which are formed when the same or different nucleotides polymerize.
A nucleotide, in turn, is formed from a nucleoside, which is a unit
composed of one sugar combined with one heterocyclic amine base,
and a phosphate unit attached to the 5'-position of the sugar.
[0018] In the synthesis of RNA and DNA molecules in nature, a
single phosphate group attaches to the 5'-position of the sugar and
thereafter the heterocyclic amine base combines with or is built up
upon the sugar to form a monophosphate nucleotide. Then, an
additional phosphate group attaches to the existing phosphate group
to form a diphosphate nucleotide. Thereafter, a third phosphate
group attaches to the second phosphate group to form a triphosphate
nucleotide. Only the triphosphate nucleotides polymerize. In this
reaction, the second and third phosphate groups sever from the
first phosphate group, which in turn links to the C5' position of
the adjacent sugar.
[0019] Nucleosides can be obtained from the decomposition
(hydrolysis) of RNA and DNA. Nucleotides are found in nature and
can be obtained by isolation from organic matter. All RNA and DNA
molecules are formed from two specific sugars and five specific
heterocyclic amine bases. The sugars are ribose and deoxyribose.
The heterocyclic bases are adenine and guanine, which are
substituted purines, and cytosine, uracil and thymine, which are
substituted pyrimidines. Uracil is found only in RNA, while thymine
is found only in DNA. The other three are found in both RNA and
DNA. Synthetic analogs of these compounds are also known and are
useful in this invention. Thus,
[0020] Thus, there are a total of eight different nucleosides which
can be present in and which can be recovered from RNA and DNA,
namely adenosine, 2'-deoxyadenosine, guanosine, 2'-deoxyguanosine,
cytidine, 2'-deoxycytidine, uridine and 2'-deoxythymidine.
[0021] Similarly, there are a total of 24 different nucleotides
which form during the synthesis of RNA and DNA and can be recovered
from organic matter. The monophosphate nucleotides are adenosine
5'-phosphate, 2'-deoxyadenosine 5'-phosphate, guanosine
5'-phosphate, 2'-deoxyguanosine 5'-phosphate, cytidine
5'-phosphate, 2'-deoxycytidine 5'-phosphate, uridine 5'-phosphate
and 2'-deoxythymidine 5'-phosphate. The diphosphate nucleotides are
adenosine 5'-diphosphate, 2'-deoxyadenosine 5'-diphosphate,
guanosine 5'-diphosphate, 2'-deoxyguanosine 5'-diphosphate,
cytidine 5'-diphosphate, 2'-deoxycytidine 5'-diphosphate, uridine
5'-diphosphate and 2'-deoxythymidine 5'-diphosphate. The
triphosphate nucleotides are adenosine 5'-triphosphate,
2'-deoxyadenosine 5'-triphosphate, guanosine 5'-triphosphate,
2'-deoxyguanosine 5'-triphosphate, cytidine 5'-triphosphate,
2'-deoxycytidine 5'-triphosphate, uridine 5'-triphosphate and
2'-deoxythymidine 5'-triphosphate.
[0022] Synthetic analogs of such compounds are also useful in the
present invention. For example, 5-fluorocytidine and
5-fluorouridine are commercially-available and useful in the
present invention. In addition, the chloro, iodo, thio and mercapto
analogs of these compounds are also useful, as are the
corresponding 6-substituted compounds as well as the corresponding
substituted adenine, guanine and thymine compounds. Nucleotides
formed from these compounds are also useful.
[0023] For a further description of the chemistry of RNA and DNA,
see pages 1107-1149 of Organic Chemistry, 3.sup.rd Edition, by John
MaMurrry, Brooks/Cole Publishing Company, 1992. See, also,
Lehninger, Biochemistry, Second Edition, Worth Publishers, Inc.,
pp. 729-747, .COPYRGT. 1975. See, also, King et al., Chemistry of
Nucleic Acids, Version May 11, 2002, available on the web at
http://www.med.unibs.it/.about.marchesi/nucleic.h- tml. Note,
especially, the portion of this article on pages 7 and 8 relating
to synthetic nucleotides, which reads as follows:
Synthetic Nucleotide Analogs
[0024] "Many nucleotide analogues are chemically synthesized and
used for their therapeutic potential. The nucleotide analogues can
be utilized to inhibit specific enzymatic activities. A large
family of analogues are used as anti-tumor agents, for instance,
because they interfere with the synthesis of DNA and thereby
preferentially kill rapidly dividing cells such as tumor cells.
Some of the nucleotide analogues commonly used in chemotherapy are
6-mercaptopurine, 5-fluorouracil, 5-iodo-2'-deoxyuridine and
6-thioguanine. Each of these compounds disrupts the normal
replication process by interfering with the formation of correct
Watson-Crick base-pairing.
[0025] Nucleotide analogs also have been targeted for use as
antiviral agents. Several analogs are used to interfere with the
replication of HIV, such as AZT (azidothymidine) and ddI
(dideoxyinosine). Several purine analogs are used to treat gout.
The most common is allopurinol, which resembles hypoxanthine.
Allopurinol inhibits the activity of xanthine oxidase, an enzyme
involved in de novo purine biosynthesis. Additionally, several
nucleotide analogues are used after organ transplantation in order
to suppress the immune system and reduce the likelihood of
transplant rejection by the host."
[0026] In accordance with the present invention, it has been found
that these nucleic acid related compounds also cause CMP slurries
to exhibit a significant improvement in selectivity for removing
silicon dioxide in preference to silicon nitride during CMP
polishing in the manufacture of semiconductor wafers and chips.
Thus, the inventive CMP slurries contain at least one of the
nucleic acid related compound mentioned above, i.e., at least one
RNA or DNA compound and/or at least one of the nitrogen-containing
precursors forming these polymer compounds and/or the
nitrogen-containing decomposition products derived from these
compounds, i.e., the nucleotides, nucleosides and heterocyclic
amine bases mentioned above. These compounds can be used
individually or in admixtures.
[0027] The amount of nucleic acid compound that should be included
in the inventive CMP slurries can vary widely, and essentially any
amount can be used. In this connection, some RNA, DNA and the other
nucleic acid related compounds mentioned above are water soluble,
and some are water-soluble by adjusting the pH. So it is preferable
not to use more than a saturation amount since additional amounts
will precipitate out or agglomerate and provide essentially no
incremental benefit. Similarly, enough nucleic acid related
compound should be used to provide a noticeable enhancement in
selectivity during CMP polishing, i.e., selectivity for removing
silicon dioxide in preference to silicon nitride. Within these
parameters, however, essentially any amounts can be used.
Typically, this means that the amount of nucleic acid compound will
be about 0.01-50 wt. %, more typically about 0.1-20 wt. % or even
about 0.5 to 10 wt. %.
[0028] Mixed Surfactants
[0029] In a particular embodiment of the present invention, it has
been found that CMP slurries of the present invention, when
containing a mixture of anionic, cationic and non-ionic
surfactants, exhibit an enhanced ability to eliminate pits and
reduce surface roughness in the surfaces being polished.
[0030] In this connection, U.S. Pat. No. 6,303,506 B1 to Nojo et
al., the disclosure of which is incorporated herein by reference,
describes aqueous slurry-less compositions for CMP processing which
contains a cationic surfactant. The use of cationic surfactant is
said to reduce scratches and polishing defects during slurry-less
CMP processing of silicon wafer surfaces. Mixtures of cationic,
anion and nonionic surfactants can also be used. In accordance with
this aspect of the present invention, it has been found that
mixtures of cationic surfactants, nonionic surfactants, and anionic
surfactants will also enhance surface smoothness and prevent the
pits formation when used in the inventive CMP slurries.
[0031] In carrying out this aspect of the present invention, any
type of cationic, anionic and nonionic surfactants can be used. In
this regard, see WO 96/16154, the disclosure of which is
incorporated herein by reference, which describes a wide variety of
different cationic, anionic and nonionic surfactants, all of which
can be used in accordance with this aspect of the present
invention.
[0032] Preferred surfactants are those described in the above-noted
U.S. Pat. No. 6,303,506 B1. Thus, preferred cationic surfactants
are alkyltrimethylammonium halides and especially the C.sub.9-13
alkyltrimethylammonium halides, alkylbenzyldimethylammonium halides
and especially the C.sub.6-18 alkylbenzyldimethylammonium halides,
pyridiniumalkyl halides and especially the C.sub.6-.sub.18
pyridiniumalkyl halides and the alkylammonium esters, especially
the C.sub.6-18 alkylammonium esters. Particularly preferred are
hexadecyltrimethylammonium bromide, hexadecylbenzyldimethylammonium
bromide, dodecylbenzyldimethylammonium bromide, cetylpyridinium
chloride and dodecylammonium acetate.
[0033] Preferred anionic surfactants are polymers containing
carboxylic acid or salt groups such as polymers and copolymers of
acrylic acid and methacrylic acid and ammonium salts thereof as
well as analogous salts such as the sodium, potassium, cesium,
monoethanolamine, diethanolamine, and triethanolamine salts, soap,
and so forth. Also useful are the C.sub.12-18 alkyl sulfates, the
C.sub.9-13 alkyl benzenesulfonates, the C.sub.8-22 primary or
secondary alkanesulfonates, C.sub.8-24 olefinsulfonates, sulfonated
polycarboxylic acids, C.sub.8-24 alkylpolyglycolethersulfates, and
so forth.
[0034] Preferred nonionic surfactants are water soluble polymers
such as polyvinyl alcohol, polyacrylamide and polyvinylpyrrolidone,
preferably having a molecular weight of less than 20,000. Other
nonionic surfactants are the condensation products of ethylene
oxide and/or propylene oxide with alkyl phenols, primary and/or
secondary alcohols, and the polyhydroxy fatty acid amides.
[0035] The concentrations of these surfactants in the inventive CMP
slurries can vary widely, and essentially any amount can be used.
Typical concentrations run from 0.001-10 wt. %, 0.02-5 wt. %, or
even 0.05 to 3 wt. % in total. Also, it is desirable that the
concentration of the nonionic surfactant be greater than that of
the cationic surfactant while the concentration of the anionic
surfactant be greater than that of the nonionic surfactant.
Preferably, the concentration of the nonionic surfactant is 5-15
times greater than that of the cationic surfactant while the
concentration of the anionic surfactant is 5-15 greater than that
of the nonionic surfactant.
EXAMPLES
[0036] In order to more thoroughly describe the present invention,
the following working examples are provided.
Examples 1-4 and Comparative Examples A-D
[0037] In these examples, two types of blanket silicon wafers 6
inches (about 15 cm.) in diameter were used. One type was a silicon
dioxide blanket wafer formed by thermal oxidation with a SiO.sub.2
thickness of 10,000 .ANG. on silicon. Another type was a silicon
nitride blanket wafer with a silicon nitride layer of a thickness
of 2500 .ANG. over a SiO.sub.2 layer of 100 .ANG. thick. Both types
of silicon dioxide and silicon nitride blanket wafers were
subjected to CMP polishing for one minute using a Westech Model 372
polisher equipped with a Rodel's IC-1400 K-groove polishing pad.
Both platen rotation speed and carrier rotation speed were at 75
rpm. The pad was conditioned for 1 minutes for every polishing run.
A down pressure of 4 PSI was applied to the polishing head without
any back pressure. Polishing slurry was supplied to the polisher at
200 milliliters per minute. After polishing was done, each wafer
was cleaned with water and dried with ethanol (compressed air
drying). The polished wafer was then characterized with different
metrology tools including thickness measurements and surface
roughness measurements. The selectivity of each polishing slurry,
i.e., ratio of the removal rate of silicon dioxide (thermal oxide
blanket wafers) to the removal rate of silicon nitride (silicon
nitride blanket wafers) with that particular slurry, was also
calculated.
[0038] Each slurry of the present invention was composed of water,
an abrasive mixture comprising 0.5 wt. % 0.2 micron (200 nm) ceria
particles and 1.0 wt. % 0.015 micron (15 nm) ceria particles,
0.33-2.0 wt. % of an anionic surfactant comprising polyacrylic acid
("PA"), 0.05 wt. % of a nonionic surfactant comprising
polyacrylamide and 0.0033 wt. % of a cationic surfactant comprising
cetyl pryidinium chloride. Each slurry also contained 2.0 wt. % of
a nucleic acid related compound in accordance with the present
invention, unless otherwise indicated. Each slurry of the
comparative examples contained the same ingredients in the same
amounts, except that the nucleic acid selectivity enhancing
compounds of the present invention were replaced with 2.0 wt. % of
other selectivity enhancing organic compounds or nothing at
all.
[0039] Polishing was continued for 1 minute, after which the
thickness of either silicon dioxide or silicon nitride was measured
and the rate at which the SiO.sub.2 and silicon nitride were
removed were calculated. The results obtained are set forth in the
following Table 1:
1TABLE 1 Selectivities of Different CMP Slurries PA SiO.sub.2 conc
Selectivity Peak to RMS Surface Removal SiN Removal SiO.sub.2/SiN
Ex wt. % Enhancer Valley, Roughness, Rate, /min Rate, /min
Selectivity 1 0.5 ADP.sup.1 32 3.5 2750 .+-. 290 160 .+-. 30 17 2
0.5 uridine 40 5.0 3520 .+-. 460 80 .+-. 10 44 3 0.5 cytidine 33
3.9 2350 .+-. 240 50 .+-. 10 47 4 0.5 ADP.sup.2 38 3.9 2700 .+-.
350 245 .+-. 120 11 A 0.5 None 38 3.6 2740 .+-. 380 913 .+-. 50 3.0
B 0.5 proline 30 3.6 3010 .+-. 280 60 .+-. 40 50 C 2.0 proline 65
6.4 3460 .+-. 260 824 .+-. 190 4.2 D 0.33 proline 39 4.2 2920 .+-.
250 70 .+-. 40 42 2.0 wt. % adenosine 5'-phosphate 0.5 wt. %
adenosine 5'-phosphate
[0040] From Table 1, it can be seen that the CMP slurries of the
present invention provided significantly enhanced selectivities for
SiO.sub.2 removal in preference to SiN removal as compared with a
control composition containing no selectivity enhancer (Comparative
Example A). In addition, the level of selectivity enhancement
provided by the CMP slurries of the present invention, at least
when the selectivity enhancing compound used was a nucleoside,
specifically uridine or cytidine (Examples 2 and 3), was comparable
to that provided by the prior art amino acid proline (Comparative
Example B).
Example 5
[0041] In this example, the inventive CMP slurry was used in the
CMP processing of patterned wafers to demonstrate the planarization
capability and selectivity of the inventive slurry. STI patterned
wafers 8 inches in diameter were obtained from SKW Associates. The
wafers are characterized by areas of differing line widths and
relative line areas in order to allow characterization of the CMP
capability of the CMP slurry. The wafers are further characterized
as having 1400 .ANG. of silicon nitride as a barrier layer, with a
trench depth of 4000 .ANG. and a top layer of 7000 .ANG.. The
objective of CMP was to remove the top layer silicon dioxide
covering the silicon nitride barrier layer and the trenches without
appreciable loss of silicon nitride or dishing of silicon oxide in
the trench area.
[0042] The wafers were then polished by CMP processing using a
Westech Model 372M (472) polisher equipped with a Rodel's IC-1400
with K-groove polishing pad. Both platen rotation speed and carrier
rotation speed were at 75 rpm. The pad was conditioned for 1 minute
for every polishing run. A down pressure of 6 PSI down pressure was
applied to the polishing head with a 2 PSI back pressure. A CMP
slurry of the present invention was supplied to the polisher at 200
milliliters per minute, the slurry having the following
composition:
2 0.5 wt. % ceria (0.3 microns) 0.5 wt. % polyacrylic acid (anionic
surfactant) 0.05 wt % polyacrylamide (nonionic surfactant) 0.0033
wt. % cetylpyridinium chloride (cationic surfactant) 2 wt. %
cytidine (1%) + uridine (1%)
[0043] After polishing was done, each wafer was cleaned with water
and dried with ethanol (compressed air drying). The polished wafer
was then characterized with different metrology tools including
thickness measurements, surface roughness measurements, step height
measurements.
[0044] The following results were obtained:
[0045] The silicon dioxide overburden layer over the silicon
nitride barrier layer was removed across the wafer with little loss
of silicon nitride for feature densities of 30% to 100%. There was
still 50% retention of silicon nitride at 20% feature density. It
is expected that with optimization of the CMP process even better
results can be obtained.
[0046] Dishing was evaluated on 100 micron feature widths and found
to be less than 600 .ANG. across the wafer. This is considered good
for this application.
[0047] From this example, it can be seen that the inventive CMP
slurry is capable of allowing selective removal of the silicon
dioxide overburden while minimizing silicon nitride barrier layer
loss in actual structured wafers.
[0048] Although only a few embodiments of the present invention
have been described above, it should be appreciated that many
modifications can be made without departing from the spirit and
scope of the present invention. All such modifications are intended
to be included within the scope of the present invention, which is
to be limited only by the following claims:
* * * * *
References