U.S. patent application number 11/407196 was filed with the patent office on 2006-08-24 for cmp abrasive, liquid additive for cmp abrasive and method for polishing substrate.
This patent application is currently assigned to HITACHI CHEMICAL CO., LTD.. Invention is credited to Toshihiko Akahori, Toranosuke Ashizawa, Keizo Hirai, Yasushi Kurata, Miho Kurihara, Masato Yoshida.
Application Number | 20060186372 11/407196 |
Document ID | / |
Family ID | 18491604 |
Filed Date | 2006-08-24 |
United States Patent
Application |
20060186372 |
Kind Code |
A1 |
Akahori; Toshihiko ; et
al. |
August 24, 2006 |
CMP abrasive, liquid additive for CMP abrasive and method for
polishing substrate
Abstract
A CMP abrasive comprising a cerium oxide slurry containing
cerium oxide particles, a dispersant and water, and a liquid
additive containing a dispersant and water; and a liquid additive
for the CMP abrasive. A method for polishing a substrate which
comprises holding a substrate having, formed thereon, a film to be
polished against a polishing pad of a polishing platen, followed by
pressing, and moving the substrate and the polishing platen while
supplying the above CMP abrasive in between the film to be polished
and the polishing pad to thereby polish the film to be polished.
The CMP abrasive and the method for polishing can be used for
polishing a surface to be polished such as a silicone oxide film or
a silicon nitride film without contaminating the surface to be
polished with an alkali metal such as sodium ions and with no
flaws, and the CMP abrasive is excellent in storage stability.
Inventors: |
Akahori; Toshihiko;
(Shimodate-shi, JP) ; Ashizawa; Toranosuke;
(Hitachi-shi, JP) ; Hirai; Keizo; (Hitachi-shi,
JP) ; Kurihara; Miho; (Hitachi-shi, JP) ;
Yoshida; Masato; (Tsukuba-shi, JP) ; Kurata;
Yasushi; (Tsukuba-shi, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW
SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
HITACHI CHEMICAL CO., LTD.
Shinjuku-ku
JP
|
Family ID: |
18491604 |
Appl. No.: |
11/407196 |
Filed: |
April 20, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11177352 |
Jul 11, 2005 |
|
|
|
11407196 |
Apr 20, 2006 |
|
|
|
10990427 |
Nov 18, 2004 |
|
|
|
11177352 |
Jul 11, 2005 |
|
|
|
10759163 |
Jan 20, 2004 |
|
|
|
10990427 |
Nov 18, 2004 |
|
|
|
09856491 |
Jun 19, 2001 |
6783434 |
|
|
PCT/JP99/07209 |
Dec 22, 1999 |
|
|
|
10759163 |
Jan 20, 2004 |
|
|
|
Current U.S.
Class: |
252/79.1 ;
257/E21.244 |
Current CPC
Class: |
B24D 3/34 20130101; C09K
3/1463 20130101; H01L 21/31053 20130101; B24B 37/04 20130101; C09G
1/02 20130101 |
Class at
Publication: |
252/079.1 |
International
Class: |
C09K 13/00 20060101
C09K013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 25, 1998 |
JP |
10-368355 |
Claims
1-7. (canceled)
8. A liquid additive for CMP abrasive, comprising a dispersant and
water, wherein the liquid additive for CMP abrasive is to be used
in a method for polishing a substrate comprising holding a
substrate having, formed thereon, a film to be polished against a
polishing pad of a polishing platen, followed by pressing, and
moving the substrate and the polishing platen while supplying a CMP
abrasive in between the film to be polished and the polishing pad
to thereby polish the film to be polished; and wherein the CMP
abrasive is prepared by separately preparing, a cerium oxide slurry
containing cerium oxide particles, a dispersant and water, and the
liquid additive for CMP abrasive containing the dispersant and
water, and mixing, at the time of the polishing, the cerium oxide
slurry and the liquid additive for CMP abrasive.
9. The liquid additive for CMP abrasive of claim 8, wherein the
dispersant is a polymer dispersant selected from the group
consisting of a polymer containing ammonium acrylate as a
copolymerized ingredient, a polyammonium-acrylate and a
polyamine-acrylate.
10. The liquid additive for CMP abrasive of claim 9, wherein the
polymer dispersant has a weight average molecular weight of 100 to
50,000.
11. The liquid additive for CMP abrasive of claim 9, wherein the
polymer dispersant has a molecular weight distribution (weight
average molecular weight/number average molecular weight) of 1.005
to 1.300.
12. The liquid additive for CMP abrasive of claim 9, wherein the
polymer dispersant contains 10 mol % or less of free ammonia or a
free amine, which does not form a salt.
13. The liquid additive for CMP abrasive of claim 8, which contains
1 to 10% by weight of the dispersant.
14. The liquid additive for CMP abrasive of claim 13, wherein the
dispersant is a polyammonium-acrylate or a polyamine-acrylate.
15. The liquid additive for CMP abrasive of claim 14, wherein each
of the polyammonium-acrylate and the polyamine-acrylate has a
weight average molecular weight of 1,000 to 100,000.
16. The liquid additive for CMP abrasive of claim 15, wherein each
of the polyammonium-acrylate and the polyamine-acrylate has a
molecular weight distribution (weight average molecular
weight/number average molecular weight) of 1.005 to 1.300.
17. The liquid additive for CMP abrasive of claim 14, wherein each
of the polyammonium-acrylate and the polyamine-acrylate contains 10
mol % or less of free ammonia or a free amine, which does not form
a salt.
18. The liquid additive for CMP abrasive of claim 8, which is pH 4
to 8.
19. The liquid additive for CMP abrasive of claim 8, which has a
viscosity of 1.20 to 2.50 mPas.
Description
[0001] This application is a divisional of application Ser. No.
11/177,352, filed Jul. 11, 2005 which is a continuation of
application Ser. No. 10/990,427, filed Nov. 18, 2004, which is a
continuation of application Ser. No. 10/759,163, filed Jan. 20,
2004 (now abandoned), which is a Divisional of application Ser. No.
09/856,491 filed Jun. 19, 2001 (now U.S. Pat. No. 6,783,434), which
is a national stage application filed under 35 U.S.C. .sctn. 371 of
International Application No. PCT/JP99/07209, filed Dec. 22, 1999,
the entire disclosures of which are hereby incorporated by
reference.
TECHNICAL FIELD
[0002] The invention relates to a CMP abrasive usable in the
production of semiconductor elements, a liquid additive for CMP
abrasive and a method for polishing substrates. Particularly, it
relates to a CMP abrasive usable in the step of planarizing the
surface of a substrate, typically the steps of planarizing an
interlayer insulating film and forming shallow-trench separation,
to a liquid additive for the CMP abrasive and to a method for
polishing substrates by using the CMP abrasive.
BACKGROUND ART
[0003] In present ultra large scale integrated circuits, packaging
density is increasing, and various fine processing techniques have
been studied and developed. Design rules have already reached the
order of sub half micron. CMP (Chemical Mechanical Polishing) is
one of the techniques developed to satisfy such a strict
requirement for fineness. This technique is essential for the
production of semiconductor devices, typically for planarizing
interlayer insulating films and for shallow-trench separation,
because it can completely planarize layers to be exposed, reducing
the burden on exposure techniques and stabilizing the production
yield.
[0004] Colloidal silica abrasives have been investigated as common
CMP abrasives to be used in the production of semiconductor devices
to planarize inorganic insulating films, such as silicon oxide
insulating film, formed by plasma-CVD (Chemical Vapor Deposition),
low pressure-CVD or the like. Colloidal silica abrasives may be
produced by using silica particles, which are typically formed from
tetrachlorosilane through thermal decomposition, and adjusting pH.
Such abrasives, however, cannot polish inorganic insulating films
fast enough, and need higher polishing rate for their practical
use.
[0005] In integrated circuits with design rules of 0.5 .mu.m or
more, devices were separated by LOCOS (Localized Oxidation of
Silicon). As the processing measurements have become finer,
shallow-trench separation has become used in response to the
requirement for a technique giving narrower separation gap between
devices. For shallow-trench separation, the surplus parts of a
silicon oxide film formed on a substrate are removed by CMP, and a
stopper film reducing the polishing rate is provided under the
silicon oxide film to stop polishing. The stopper film is typically
made of silicon nitride, and the rates of polishing the silicon
oxide film and the stopper film are preferably in a large ratio.
Where conventional colloidal silica abrasives are used, the ratio
between the rate of polishing the silicon oxide film and the rate
of polishing the stopper film is as small as the order of 3, and
such abrasives cannot satisfy the requirements of practical
shallow-trench separation.
[0006] On the other hand, cerium oxide abrasives have been used for
polishing photo masks or the surface of glass, such as lenses.
Having lower hardness as compared to silica particles and alumina
particles, cerium oxide particles hardly make flaws on the polished
surface and are suitable for finish mirror polishing. However, the
cerium oxide abrasives for polishing glass surfaces cannot be used
as abrasives for polishing semiconductors, because they contain a
dispersant containing sodium salts.
DISCLOSURE OF INVENTION
[0007] An object of the invention is to provide a CMP abrasive,
which can speedily polish a surface to be polished, such as a
silicon oxide insulating film, without making flaws.
[0008] Another object of the invention is to provide a CMP
abrasive, which can speedily polish a surface to be polished, such
as a silicon oxide insulating film, without contaminating the
surface to be polished with alkali metals, such as sodium ions, nor
making flaws.
[0009] Another object of the invention is to provide a CMP
abrasive, which is more advantageous in that it can increase the
ratio of the rate of polishing a silicon oxide insulating film to
the rate of polishing a silicon nitride insulating film.
[0010] Another object of the invention is to provide a CMP
abrasive, which can speedily polish a surface to be polished, such
as a silicon oxide insulating film, without contaminating the
surface to be polished with alkali metals, such as sodium ions nor
making flaws and contains a cerium oxide slurry improved in storage
stability.
[0011] Another object of the invention is to provide a CMP
abrasive, which can speedily polish a surface to be polished, such
as a silicon oxide insulating film, without contaminating the
surface to be polished with alkali metals, such as sodium ions, nor
making flaws, and can increase the ratio of the rate of polishing a
silicon oxide insulating film to the rate of polishing a silicon
nitride insulating film to 50 or more.
[0012] Another object of the invention is to provide a liquid
additive, which is to be used to give a CMP abrasive improved in
storage stability.
[0013] Another object of the invention is to provide a liquid
additive for CMP abrasive to be used to improve the flatness of the
polished surface of a substrate.
[0014] Another object of the invention is to provide a method for
polishing a substrate, which can polish a surface of the substrate
without making flaws on its polished surface.
[0015] Another object of the invention is to provide a method for
polishing a substrate, which can speedily polish a surface to be
polished, such as a silicon oxide insulating film, without making
flaws, and can increase the ratio of the rate of polishing a
silicon oxide insulating film to the rate of polishing a silicon
nitride insulating film to 50 or more.
[0016] Accordingly, the invention relates to:
[0017] (1) a CMP abrasive comprising a cerium oxide slurry
containing cerium oxide particles, a dispersant and water; and
[0018] a liquid additive containing a dispersant and water;
[0019] (2) the CMP abrasive of (1), wherein each of the dispersants
contained in the cerium oxide slurry and the liquid additive
respectively is a polymer dispersant, which is a polymer containing
ammonium acrylate as a copolymerized ingredient;
[0020] (3) the CMP abrasive of (1), wherein each of the dispersants
contained in the cerium oxide slurry and the liquid additive
respectively is a polymer dispersant, which is a
polyammonium-acrylate or a polyamine-acrylate;
[0021] (4) the CMP abrasive of (2) or (3), wherein the polymer
dispersants have a weight average molecular weight of 100 to
50,000;
[0022] (5) the CMP abrasive of (1), wherein the cerium oxide slurry
contains 0.01 to 2.0 parts by weight of the dispersant relative to
100 parts by weight of the cerium oxide particles and contains 0.3
to 40% by weight of the cerium oxide particles based on the cerium
oxide slurry;
[0023] (6) the CMP abrasive of any one of (1) to (5), wherein the
cerium oxide slurry is pH 6 to 10;
[0024] (7) the CMP abrasive of any one of (1) to (6), which is 50
or more in ratio of rate of polishing a silicon oxide film to rate
of polishing a silicon nitride film;
[0025] (8) a liquid additive for CMP abrasive comprising a
dispersant and water;
[0026] (9) the liquid additive for CMP abrasive of (8), which
contains 1 to 10% by weight of the dispersant;
[0027] (10) the liquid additive for CMP abrasive of (9), wherein
the dispersant is a polyammonium-acrylate or a
polyamine-acrylate;
[0028] (11) the liquid additive for CMP abrasive of (10), wherein
the polyammonium-acrylate or the polyamine-acrylate has a weight
average molecular weight of 1,000 to 100,000;
[0029] (12) the liquid additive for CMP abrasive of (11), wherein
the polyammonium-acrylate or the polyamine-acrylate has a molecular
weight distribution (weight average molecular weight/number average
molecular weight) of 1.005 to 1.300;
[0030] (13) the liquid additive for CMP abrasive of (10), wherein
the polyammonium-acrylate or the polyamine-acrylate contains 10 mol
% or less of free ammonia or a free amine, which does not form a
salt;
[0031] (14) the liquid additive for CMP abrasive of (10), which is
pH 4 to 8;
[0032] (15) the liquid additive for CMP abrasive of (10), which has
a viscosity of 1.20 to 2.50 mPas;
[0033] (16) a method for polishing a substrate, comprising holding
a substrate having, formed thereon, a film to be polished against a
polishing pad of a polishing platen, followed by pressing, and
moving the substrate and the polishing platen while supplying the
CMP abrasive of any one of (1) to (7) in between the film to be
polished and the polishing pad to thereby polish the film to be
polished; and
[0034] (17) the method of (16), wherein the substrate to be
polished has at least a silicon oxide film or a silicon nitride
film formed thereon.
BEST MODE FOR CARRYING OUT THE INVENTION
[0035] Cerium oxide may be produced by the oxidation of a cerium
compound, such as carbonate, nitrate, sulfate or oxalate of cerium.
Conventional cerium oxide abrasives for polishing silicon oxide
films formed by TEOS-CVD or the like contain monocrystalline cerium
oxide particles with large primary particle sizes, and tend to make
polishing flaws. Therefore, the cerium oxide particles to be used
in the invention are not limited in the method of production, but
are preferably polycrystals that are aggregates of monocrystals of
5 nm to 300 nm. For polishing semiconductor chips, the cerium oxide
particles preferably contain as little as 10 ppm or less of alkali
metals and halogens.
[0036] The methods usable in the invention to produce the cerium
oxide particles include burning or oxidation using hydrogen
peroxide or the like. Preferred burning temperatures range from 350
to 900.degree. C. The raw material suitable for the method is
cerium carbonate.
[0037] The above method gives aggregates of cerium oxide particles,
which are then preferably pulverized mechanically. Examples of
preferred pulverizing methods include dry grinding using a jet
mill, and wet grinding using a planetary bead mill.
[0038] The cerium oxide slurry to be used in the invention is
obtainable, for example, by dispersing a composition comprising the
cerium oxide particles having the above characteristics, a
dispersant for dispersing the cerium oxide particles in water and
water. The content of the cerium oxide particles is not limited but
is preferably 0.3 to 40% by weight, more preferably 0.5 to 20% by
weight to handle the dispersion easily. In the CMP abrasive
obtainable by mixing the cerium oxide slurry and a liquid additive,
the content of the cerium oxide particles is preferably 0.01 to 10%
by weight, more preferably 0.1 to 5% by weight.
[0039] The dispersant to be used in the invention comprises one or
two compounds selected from polymer dispersants, water-soluble
anionic surfactants, water-soluble nonionic surfactants,
water-soluble cationic surfactants and water-soluble amphoteric
surfactants. For polishing semiconductor chips, the dispersant
preferably contains as little as 10 ppm or less of alkali metals,
such as sodium ions and potassium ions, halogens and sulfur.
[0040] Examples of polymer dispersants include polymers of
unsaturated carboxylic acids, such as acrylic acid, methacrylic
acid or maleic acid, or ammonium salts or amine salts of the
polymers; copolymers of an unsaturated carboxylic acid, such as
acrylic acid, methacrylic acid or maleic acid, with a
copolymerizable monomer, for example, an alkyl acrylate, such as
methyl acrylate or ethyl acrylate, a hydroxyalkyl acrylate, such as
hydroxyethyl acrylate, an alkyl methacrylate, such as methyl
methacrylate or ethyl methacrylate, a hydroxyalkyl methacrylate,
such as hydroxyethyl methacrylate, vinyl acetate or vinyl alcohol,
and ammonium salts or amine salts of the copolymers. The
unsaturated carboxylic acid moieties in the polymers or copolymers
may be converted into ammonium salts either before or after
polymerization. The polymers and copolymers preferably contain 1 to
100 mol %, more preferably 10 to 100 mol % of unsaturated
carboxylic acid moieties.
[0041] Preferred dispersants are polymers containing ammonium
acrylate as a copolymerized ingredient, polyammonium-acrylates and
polyamine-acrylates. Polyammonium-acrylates and polyamine-acrylates
preferably have weight average molecular weights of 1,000 to
100,000, more preferably 3,000 to 60,000, further preferably 10,000
to 40,000. If the weight average molecular weight is less than
1,000, cerium oxide particles may aggregate, and if more than
100,000, polishing rate ratio may be reduced. The
polyammonium-acrylates and polyamine-acrylates preferably have
molecular weight distributions (weight average molecular
weight/number average molecular weight) of 1.005 to 1.300, more
preferably 1.100 to 1.250, further preferably 1.150 to 1.200. If
the molecular weight distribution is less than 1.005, the cerium
oxide particles may aggregate, and if more than 1.300, the
polishing rate ratio may be reduced. Herein, the weight average
molecular weight and number average molecular weight are measured
through gel permeation chromatography, based on the calibration
curve of a standard, polystyrene.
[0042] The polyammonium-acrylates and polyamine-acrylates are
obtainable through neutralization of a mixture comprising a
polyacrylic acid and an equimolar amount of ammonia or an amine
relative to carboxyl groups, and, in view of high flatness,
preferably contain as little as 10 mol % or less of free ammonia or
amine forming no salts (that is, at least 90 mol % of the carboxyl
groups of polyacrylic acid are preferably neutralized). The amount
of the free ammonia or amine forming no salts can be determined by
adding an organic solvent to precipitate the polymer, filtering the
polymer and quantitatively determining the amount of ammonia or
amine in the filtrate.
[0043] Examples of water-soluble anionic surfactants include
triethanolamine lauryl sulfate, ammonium lauryl sulfate and
triethanolamine polyoxyethylene alkyl ether sulfates.
[0044] Examples of water-soluble nonionic surfactants include
polyoxyethylene lauryl ether, polyoxyethylene cetyl ether,
polyoxyethylene stearyl ether, polyoxyethylene oleyl ether,
polyoxyethylene higher alcohol ethers, polyoxyethylene octyl phenyl
ether, polyoxyethylene nonyl phenyl ether, polyoxyalkylene alkyl
ethers, polyoxyethylene derivatives, polyoxyethylenesorbitan
monolaurate, polyoxyethylenesolbitan monoparmitate,
polyoxyethylenesolbitan monostearate, plyoxyethylenesolbitan
tristearate, polyoxyethylenesolbitan monooleate,
polyoxyethylenesolbitan trioleate, polyoxyethylenesolbitol
tetraoleate, polyethylene glycol monolaurate, polyethylene glycol
monostearate, polyethylene glycol distearate, polyethylene glycol
monooleate, polyoxyethylene alkyl amines, polyoxyethylene hardened
castor oil and alkylalkanolamides. Examples of water-soluble
cationic surfactants include coconutamine acetate and stearylamine
acetate.
[0045] Examples of water-soluble amphoteric surfactants include
laurylbetaine, stearylbetaine, lauryldimethylamine oxide and
2-alkyl-N-carboxymethyl-N-hydroxyethylimidazoliniumbetaine.
[0046] In view of the dispersibility of particles in the cerium
oxide slurry, the prevention of their sedimentation and the
relationship between polishing flaws and the amount of the
dispersants added, the amount of the dispersant added in the cerium
oxide slurry is preferably 0.01 to 2.0 parts by weight relative to
100 parts by weight of cerium oxide particles.
[0047] Among the dispersants described above, the polymer
dispersants preferably have weight average molecular weights of 100
to 100,000, more preferably 100 to 50,000, further preferably 1,000
to 10,000, as measured through gel permeation chromatography based
on the calibration curve of the standard, polystyrene. If the
molecular weight of the dispersant is too low, silicon oxide films
or silicon nitride films may not be polished speedily enough, and
if it is too high, the cerium oxide slurry may be too viscous and
lose storage stability.
[0048] The pH of the cerium oxide slurry is preferably 6 to 10. If
the pH is too low, a liquid mixture of the cerium oxide slurry and
a liquid additive may lose storage stability and make polishing
flaws on polished silicon oxide or silicon nitride films, and if
the pH is too high, a liquid mixture of the cerium oxide slurry and
a liquid additive may also lose storage stability and make
polishing flaws on polished silicon oxide or silicon nitride films.
The pH may be adjusted by adding an aqueous ammonia and
stirring.
[0049] The cerium oxide particles can be dispersed in water by
using a common stirrer or others, such as a homogenizer, an
ultrasonic disperser or a wet ball mill.
[0050] The cerium oxide particles in the slurry thus produced
preferably have an average particle size of 0.01 to 1.0 .mu.m. This
is because cerium oxide particles with a too small average particle
size have a considerably low polishing rate, and that with a too
large average particle size tends to make flaws on the polished
film.
[0051] The liquid additive for CMP abrasive of the invention
comprises a dispersant and water. The dispersant is for dispersing
the cerium oxide particles contained in the above-described cerium
oxide slurry in water. In view of the polishing rate ratio and the
high flatness of the polished surface, the dispersants suitable for
the cerium oxide slurry are also suitable for the liquid additive.
The dispersants used in the cerium oxide slurry and the liquid
additive may be identical with or different from each other. The
concentration of the dispersant in the liquid additive is
preferably 1 to 10% by weight. If it is less than 1% by weight, the
polished surface may be less flat, and if more than 10% by weight,
the cerium oxide particles may aggregate.
[0052] The CMP abrasive of the invention is used so that the cerium
oxide slurry and the liquid additive prepared apart from each other
are mixed at the time of polishing. If the cerium oxide slurry and
the liquid additive are stored in a form of a mixture, the cerium
oxide particles will aggregate, thereby making polishing flaws and
causing a change in polishing rate. Therefore, the liquid additive
and the cerium oxide slurry are supplied on a polishing platen
separately and mixed thereon, or mixed immediately before polishing
and then supplied onto a polishing platen. The mixing ratio between
the cerium oxide slurry and the liquid additive is not particularly
limited so far as the desired concentrations are finally given.
[0053] In view of the dispersibility of particles in the slurry,
the prevention of their sedimentation and the relationship between
polishing flaws and the amount of the dispersant added, the amount
of the dispersant in the liquid additive relative to the cerium
oxide is preferably 0.001 to 2000 parts by weight, more preferably
0.01 to 1000 parts by weight, further preferably 0.01 to 500 parts
by weight, relative to 100 parts by weight of the cerium oxide
particles in the cerium oxide slurry.
[0054] The specific gravity of the liquid additive is preferably
1.005 to 1.050, more preferably 1.007 to 1.040, further preferably
1.010 to 1.030. If the specific gravity is less than 1.005, the
polished surface may be less flat, and if more than 1.050, the
cerium oxide particles may aggregate. The pH of the liquid additive
is preferably 4 to 8, more preferably 5 to 7, further preferably 6
to 7. If the pH is less than 4, the polishing rate may be reduced,
and if more than 8, the polished surface may be less flat. The
adjustment of pH may be performed by adding an acid or an alkali,
such as acetic acid or aqueous ammonia, to the liquid additive. The
viscosity of the liquid additive at 25.degree. C. is preferably
1.20 to 2.50 mPas, more preferably 1.30 to 2.30 mPas, further
preferably 1.40 to 2.20 mPas. If the viscosity is less than 1.20
mPas, the cerium oxide particles may aggregate, and if more than
2.50 mPas, the polished surface may be less flat.
[0055] In the CMP abrasive of the invention, the cerium oxide
slurry and the liquid additive may be used as they are, or
non-polymeric additives, such as N,N-diethylethanolamine,
N,N-dimethylethanolamine or aminoethylethanolamine, may be added to
the cerium oxide slurry or the liquid additive for CMP. The amounts
of such additives are such that their total concentration in the
resulting CMP abrasive is preferably 0.001 to 20% by weight, more
preferably 0.01 to 10% by weight.
[0056] The inorganic insulating film for which the CMP abrasive of
the invention is used may be formed, for example, by low pressure
CVD or plasma CVD. To form a silicon oxide film by low pressure
CVD, monosilane: SiH.sub.4 is used as an Si-source, and oxygen:
O.sub.2 as an oxygen-source, and SiH.sub.4--O.sub.2 oxidation is
carried out at a low temperature of 400.degree. C. or lower. After
CVD, heat treatment at a temperature not higher than 1000.degree.
C. may optionally be carried out. Where phosphorus: P is doped to
planarize the surface by high temperature reflow, an
SiH.sub.4--O.sub.2--PH.sub.3 reaction gas is preferably used.
Plasma CVD is advantageous in that chemical reactions requiring
high temperatures under normal, thermal equilibrium can undergo at
lower temperatures. The methods for generating plasma include two
types of capacitive coupling and inductive coupling. Examples of
reaction gases include an SiH.sub.4--N.sub.2O gas comprising
SiH.sub.4 as an Si-source and N.sub.2O as an oxygen-source; and a
TEOS-O.sub.2 gas containing tetraethoxysilane (TEOS) as an
Si-source (TEOS-plasma CVD). The preferred temperature of the
substrate ranges from 250 to 400.degree. C., and preferred reaction
pressure ranges from 67 to 400 Pa. As described above, the silicon
oxide film to be used in the invention may be doped with other
elements, such as phosphorus or boron.
[0057] To form a silicon nitride film by low pressure CVD,
dichlorosilane: SiH.sub.2Cl.sub.2 is used as an Si-source, and
ammonia: NH.sub.3 as a nitrogen-source, and the
SiH.sub.2Cl.sub.2--NH.sub.3 oxidation is carried out at a high
temperature of 900.degree. C. An example of the reaction gas for
plasma CVD is an SiH.sub.4--NH.sub.3 gas comprising SiH.sub.4 as an
Si-source and NH.sub.3 as a nitrogen-source. The preferred
temperature of the substrate ranges from 300 to 400.degree. C.
[0058] The substrate to be used may be a semiconductor substrate
bearing circuit devices and wiring patterns formed thereon, or a
semiconductor substrate which bears circuit devices formed thereon
and is further coated with a silicon oxide film layer or a silicon
nitride film layer. Polishing a silicon oxide film layer or a
silicon nitride film layer formed on such a semiconductor substrate
by using the CMP abrasive smoothes out the unevenness on the
surface of the silicon oxide film layer, to planarize whole the
surface of the semiconductor substrate. It is also applicable for
shallow-trench separation. Shallow-trench separation needs a ratio
of the rate of polishing a silicon oxide film to the rate of
polishing a silicon nitride film (silicon oxide film-polishing
rate/silicon nitride film-polishing rate) of 10 or more. If the
ratio is too small, the difference between the silicon oxide
film-polishing rate and the silicon nitride film-polishing rate
will be too small to stop polishing at a position predetermined for
shallow-trench separation. If the ratio is 50 or more, polishing
can be stopped easily by the further reduced polishing rate of
silicon nitride film, and the CMP abrasive with such a ratio is
more suitable for shallow-trench separation.
[0059] The polishing apparatus to be used may be a common one,
which has a holder for holding a semiconductor substrate and a
platen (equipped with a motor or the like capable of changing
rotational speed) applied with a polishing pad. The material of the
polishing pad may be any one, such as a non-woven fabric, a
polyurethane foam or a porous fluorine resin. The polishing pad is
preferably grooved to collect the CMP abrasive in the grooves. The
polishing conditions are not limited, but the rotational speed of
the platen is preferably as low as 200 rpm or less to prevent the
semiconductor substrate from being emitted. The pressure applied to
the semiconductor substrate is preferably 1 kg/cm.sup.2 or less not
to make polishing flaws. For shallow-trench separation, polishing
should make few flaws. During polishing, the slurry is continuously
supplied to the polishing pad by some means, such as a pump. Not
limitative but preferred amount of the slurry supplied is such that
the surface of the polishing pad is always coated with the
slurry.
[0060] After polishing, the semiconductor substrate is preferably
washed well in running water and then dried after blowing away the
water droplets from the semiconductor substrate by a spin drier or
the like. Thus a planarized shallow-trench structure is formed.
Subsequently, aluminum wiring is formed on the silicon oxide
insulating film layer, and a silicon oxide insulating film is again
formed between and on the wiring by the same method as described
above and polished by using the CMP abrasive to smooth out the
unevenness on the insulating film surface, thereby planarizing
whole the surface of the semiconductor substrate. The process is
repeated to produce a semiconductor with desired layers.
[0061] The CMP abrasive of the invention can polish not only the
silicon oxide film formed on a semiconductor substrate but also an
inorganic insulating film formed on a wiring board bearing a
predetermined wiring, such as a silicon oxide film, glass or
silicon nitride; optical glass, such as photo masks, lenses and
prisms; inorganic conductor films, such as ITO; optical integrated
circuits, optical switching devices and optical guides, which are
made of glass and crystalline materials; the end faces of optical
fibers; optical monocrystals, such as scintillators; solid-state
laser monocrystals; sapphire substrates for blue laser LED;
semiconductor monocrystals, such as SiC, GaP and GAS; glass
substrates for magnetic discs; and magnetic heads.
[0062] Hereinafter, the invention will be described in more detail
referring to Examples and Comparative Examples, which however do
not limit the scope of the invention.
Preparation 1 (Preparation of Cerium Oxide Particles)
[0063] 2 kg of cerium carbonate hydrate was placed in a platinum
vessel and burned in the air at 700.degree. C. for 2 hours, to give
about 1 kg of yellowish white powder. The powder was identified to
be cerium oxide by X-ray diffractiometry. The cerium oxide powder
was mixed with deionized water to 10% by weight concentration, and
pulverized with a horizontal wet ultrafine dispersing-pulverizer at
1400 rpm for 120 minutes. The resulting liquid abrasive was heated
to 110.degree. C. for 3 hours to give dry cerium oxide particles.
The cerium oxide particles were polycrystals comprising 10 to
60-nm-particle size primary particles as observed by a transmission
electron microscope, and had a specific surface area of 39.5
m.sup.2/g as measured by the BET method.
Preparation 2 (Preparation of Cerium Oxide Particles)
[0064] 2 kg of cerium carbonate hydrate was placed in an platinum
vessel and burned in the air at 700.degree. C. for 2 hours, to give
about 1 kg of yellowish white powder. The powder was identified to
be cerium oxide by X-ray diffractiometry.
[0065] 1 kg of the cerium oxide powder was dry-ground with a jet
mill. The cerium oxide particles were polycrystals comprising 10 nm
to 60-nm-particle size primary particles as observed by a
transmission electron microscope, and had a specific surface area
of 41.2 m.sup.2/g as measured by the BET method.
Preparation 3 (Preparation of Cerium Oxide Slurry)
[0066] 125 g of the cerium oxide particles prepared in Preparation
1, 3 g of a 40-wt % aqueous solution of an ammonium salt of a
polyacrylic acid copolymer, which was a 3:1--copolymerization
product of acrylic acid and methyl acrylate and had an weight
average molecular weight of 10,000, and 2372 g of deionized water
were mixed, and ultrasonically dispersed with stirring. The
dispersing was conducted for 10 minutes with an ultrasonic
frequency of 40 kHz. The resulting slurry was filtered through a
0.8-.mu.m filter, and deionized water was added thereto to give a
2-wt % cerium oxide slurry (A-1). The pH of the cerium oxide slurry
(A-1) was 8.5. The cerium oxide slurry (A-1) contained particles
with an average particle size of as small as 0.20 .mu.m as
determined from their particle size distribution measured with a
laser diffraction size distribution measuring apparatus. 95.0% of
the particles were 1.0 .mu.m or less.
Preparation 4 (Preparation of Cerium Oxide Slurry)
[0067] A cerium oxide slurry (A-2) was prepared in the same manner
as in Preparation 3, except the cerium oxide particles prepared in
Preparation 1 were replaced by the cerium oxide particles prepared
in Preparation 2. The pH of the cerium oxide slurry (A-2) was 8.7.
The cerium oxide slurry (A-2) contained particles with an average
particle size of as small as 0.21 .mu.m as determined from their
particle size distribution. 95.0% of the particles were 1.0 .mu.m
or less.
Preparation 5 (Preparation of Cerium Oxide Particles)
[0068] 2 kg of cerium carbonate hydrate was placed in a platinum
vessel and burned in the air at 900.degree. C. for 2 hours, to give
about 1 kg of yellowish white powder. The powder was identified to
be cerium oxide by X-ray diffractiometry. 1 kg of the cerium oxide
powder was dry-ground with a jet mill. The cerium oxide particles
were monocrystals of 80 to 150 nm in particle size as observed by a
transmission electron microscope, and had a specific surface area
of 18.5 m.sup.2/g as measured by the BET method.
Preparation 6 (Preparation of Cerium Oxide Slurry)
[0069] A cerium oxide slurry (B-1) was prepared in the same manner
as in Preparation 3, except the cerium oxide particles prepared in
Preparation 1 were replaced by the cerium oxide particles prepared
in Preparation 5. The pH of the cerium oxide slurry (B-1) was 8.4.
The cerium oxide slurry (B-1) contained particles with an average
particle size of as small as 0.35 .mu.m as determined from their
particle size distribution. 85.5% of the particles were 1.0 .mu.m
or less.
EXAMPLES 1-10 AND COMPARATIVE EXAMPLES 1 AND 2
[0070] Cerium oxide slurries and liquid additives were prepared to
prepare the CMP abrasives as shown in Table 1, and mixtures of a
cerium oxide slurry and a liquid additive were used for polishing
an insulating film in the manner described below. The results are
listed in Table 1.
[0071] The liquid additive used in each of Examples 1-5, 7 and 9
was prepared by dissolving in deionized water a predetermined
amount of the same dispersant as that used in the cerium oxide
slurry of Example 1.
[0072] The dispersant used in Examples 6, 8 and 10 was a
polyammonium-acrylate having a weight average molecular weight of
10,000, a number average molecular weight of 8,333, a molecular
weight distribution of 1.2 and a content of free ammonium of 4.3
mol %. The liquid additive used in Example 6 had a viscosity of
1.46 mPas and a specific gravity of 1.010.
[0073] In Comparative Example 2, the same cerium oxide slurry and
liquid additive as those used in Example 1 were previously mixed,
and the mixture was used for polishing an insulating film one day
after.
(Polishing of Insulating Film)
[0074] A 125-mm-diameter silicon wafer with a silicon oxide film
formed thereon by TEOS-plasma CVD was fixed to a holder to which an
attraction pad for fixing substrates was bonded, and was then set,
with the surface of the insulating film directed downwardly, on a
platen to which a polishing pad made of a porous urethane resin was
bonded. A weight was then placed on it to produce a load of 300
g/cm.sup.2. The insulating film was polished by rotating the platen
at 40 rpm for 2 minutes while feeding a cerium oxide slurry (solid
content: 2% by weight) and a liquid additive separately both at a
rate of 25 ml/min and dropping them as one liquid onto the platen
by controlling nozzles so that they joined together just above the
platen. After polishing, the wafer was removed from the holder,
washed with running water well, and then with an ultrasonic cleaner
for 20 minutes. After washing, water droplets were removed by a
spin drier, and the wafer was dried for 10 minutes in a 120.degree.
C. drier. The change in the film thickness before and after
polishing was measured with a photo-interferent film thickness
measuring apparatus to determine the polishing rate.
[0075] In place of the silicon oxide film formed by TEOS-plasma
CVD, a silicon nitride film produced by low pressure CVD was
polished in the same manner under the same conditions, and the
change in the film thickness before and after polishing was
measured, to determine the polishing rate. The results of the
measurements of film thickness show that the silicon oxide film
produced by TEOS-plasma CVD and the silicon nitride film produced
by low pressure CVD were made uniform in thickness all over the
wafers. No flaws were observed on the surfaces of the insulating
films by visual observation under a mercury-vapor lamp, but the
surfaces were further observed precisely with an apparatus for
examining the appearance of wafers (trade name: OLYMPUS Al-2000,
produced by Olympus Optical Co., Ltd.).
[0076] Similarly, a silicon oxide film having 20-.mu.m-square
5,000-.ANG.-high projections at 100-.mu.m distances was polished,
and the degree of dishing was measured at intermediate points
between the polished projections to evaluate the flatness.
TABLE-US-00001 TABLE 1-1 Example 1 Example 2 Example 3 Example 4
Example 5 Example 6 Cerium Name (A-1) (A-1) (A-1) (A-2) (A-2) (A-1)
oxide Primary 10-60 10-60 10-60 10-60 10-60 10-60 slurry particle
size Polycrystal Polycrystal Polycrystal Polycrystal Polycrystal
Polycrystal (500 g) (nm) pH 8.5 8.5 8.5 8.7 8.7 8.5 Liquid
Dispersant Acrylic acid/ Acrylic acid/ Acrylic acid/ Acrylic acid/
Acrylic acid/ Acrylic acid/ additive methyl methyl methyl methyl
methyl methyl (500 g) acrylate = 3/1 acrylate = 3/1 acrylate = 3/1
acrylate = 3/1 acrylate = 3/1 acrylate = 10/0 Weight 10,000 10,000
10,000 10,000 10,000 10,000 average molecular weight Conc. (wt %) 1
2 6 2 2 3 pH 7.3 7.5 7.7 7.5 7.5 6.8 Plasma-CVD-TEOS-silicon 2,000
2,000 1,500 2,000 2,000 1,800 oxide film polishing rate (.ANG./min)
Low pressure-CVD- 40 20 20 20 20 20 silicon nitride film polishing
rate (.ANG./min) Polishing rate ratio 50 100 75 100 100 90 (silicon
oxide film/ silicon nitride film) Flaws on polished oxide 0.05 0.05
0.05 0.05 0.05 0.05 film (number/cm.sup.2) Degree of dishing
(.ANG.) 150 120 100 130 130 80
[0077] TABLE-US-00002 TABLE 1-2 Comparative Comparative Example 7
Example 8 Example 9 Example 10 example 1 example 2 Cerium Name
(B-1) (A-1) (A-1) (A-1) (A-1) (A-1) oxide Primary 80-150 10-60
10-60 10-60 10-60 10-60 slurry particle size Monocrystal
Polycrystal Polycrystal Polycrystal Polycrystal Polycrystal (500 g)
(nm) pH 8.4 8.5 8.5 8.5 8.5 8.5 Liquid Dispersant Acrylic acid/
Acrylic acid/ Acrylic acid/ Acrylic acid/ Deionized Acrylic acid/
additive methyl methyl methyl methyl water only methyl (500 g)
acrylate = 3/1 acrylate = 10/0 acrylate = 3/1 acrylate = 10/0
acrylate = 3/1 Weight 10,000 10,000 10,000 10,000 -- 10, 000
average molecular weight Conc. (wt %) 2 4 9 6 -- 1 pH 7.5 6.5 7.9
6.0 7 7.3 Plasma-CVD-TEOS-silicon 2,000 1,500 1,400 1,200 2,000
1,000 oxide film polishing rate (.ANG./min) Low pressure-CVD- 40 20
20 20 400 50 silicon nitride film polishing rate (.ANG./min)
Polishing rate ratio 50 75 70 60 5 20 (silicon oxide film/ silicon
nitride film) Flaws on polished oxide 0.10 0.05 0.04 0.05 0.50 0.45
film (number/cm.sup.2) Degree of dishing (.ANG.) 140 70 130 60 850
170
[0078] As apparent from Table 1, the CMP abrasive and method for
polishing substrates according to the invention can polish a
surface to be polished, such as a silicon oxide film or a silicon
nitride film, without contaminating the surface to be polished with
alkali metals, such as sodium ions, nor making flaws, and further
can increase ratio of (silicon oxide film polishing rate)/(silicon
nitride film polishing rate) to 50 or more.
INDUSTRIAL APPLICABILITY
[0079] The CMP abrasive of the invention is suitable for polishing
methods used in the production of semiconductor elements,
particularly for polishing substrates for shallow-trench separation
because it can speedily polish a surface to be polished, such as a
silicon oxide film, without making flaws.
[0080] The CMP abrasive of the invention is as well advantageous in
that it does not contaminate the surface to be polished with alkali
metals, such as sodium ions, and can increase the ratio of (silicon
oxide film polishing rate)/(silicon nitride film polishing
rate).
[0081] The CMP abrasive of the invention is suitable for polishing
methods used in the production of semiconductor elements because it
can improve the storage stability of cerium oxide slurries.
[0082] The method for polishing substrates of the invention is
suitably applicable in the production of semiconductor elements
because it excels in polishing speedily a surface to be polished,
such as silicon oxide film, without making flaws.
* * * * *