U.S. patent application number 11/276157 was filed with the patent office on 2006-06-08 for cerium oxide abrasive and method of polishing substrates.
This patent application is currently assigned to HITACHI CHEMICAL CO., LTD.. Invention is credited to Toranosuke Ashizawa, Yasushi Kurata, Jun Matsuzawa, Yuuto Ootuki, Kiyohito Tanno, Hiroki Terazaki, Masato Yoshida.
Application Number | 20060118524 11/276157 |
Document ID | / |
Family ID | 27583174 |
Filed Date | 2006-06-08 |
United States Patent
Application |
20060118524 |
Kind Code |
A1 |
Yoshida; Masato ; et
al. |
June 8, 2006 |
CERIUM OXIDE ABRASIVE AND METHOD OF POLISHING SUBSTRATES
Abstract
A cerium oxide abrasive slurry having, dispersed in a medium,
cerium oxide particles whose primary particles have a median
diameter of from 30 nm to 250 nm, a maximum particle diameter of
600 nm or smaller, and a specific surface area of from 7 to 45
m..sup.2/g, and slurry particles have a median diameter of from 150
nm to 600 nm. The cerium oxide particles have structural parameter
Y, representing an isotropic microstrain obtained by an X-ray
Rietveld method (with RIETAN-94), of from 0.01 to 0.70, and
structural parameter X, representing a primary particle diameter
obtained by an X-ray Rietveld method (with RIETAN-94), of from 0.08
to 0.3. The cerium oxide abrasive slurry is made by a method of
obtaining particles by firing at a temperature of from 600.degree.
C. to 900.degree. C. and then pulverizing, then dispersing the
resulting cerium oxide particles in a medium.
Inventors: |
Yoshida; Masato;
(Ibaraki-ken, JP) ; Ashizawa; Toranosuke;
(Ibaraki-ken, JP) ; Terazaki; Hiroki;
(Ibaraki-ken, JP) ; Kurata; Yasushi; (Ibaraki-ken,
JP) ; Matsuzawa; Jun; (Ibraki-ken, JP) ;
Tanno; Kiyohito; (Ibaraki-ken, JP) ; Ootuki;
Yuuto; (Ibaraki-ken, JP) |
Correspondence
Address: |
GRIFFIN & SZIPL, PC
SUITE PH-1
2300 NINTH STREET, SOUTH
ARLINGTON
VA
22204
US
|
Assignee: |
HITACHI CHEMICAL CO., LTD.
Tokyo
JP
|
Family ID: |
27583174 |
Appl. No.: |
11/276157 |
Filed: |
February 16, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10960941 |
Oct 12, 2004 |
|
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|
11276157 |
Feb 16, 2006 |
|
|
|
09782241 |
Feb 13, 2001 |
6863700 |
|
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11276157 |
Feb 16, 2006 |
|
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09269650 |
Aug 10, 1999 |
6221118 |
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PCT/JP97/03490 |
Sep 30, 1997 |
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11276157 |
Feb 16, 2006 |
|
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Current U.S.
Class: |
216/88 ; 216/89;
252/79.1; 257/E21.244; 423/263; 51/309 |
Current CPC
Class: |
H01L 21/02024 20130101;
H01L 21/02065 20130101; C01P 2004/62 20130101; C09K 3/1409
20130101; H01L 21/31053 20130101; C01P 2004/61 20130101; C01F
17/235 20200101; C01P 2006/12 20130101; C09G 1/02 20130101; C09K
3/1463 20130101 |
Class at
Publication: |
216/088 ;
051/309; 423/263; 216/089; 252/079.1 |
International
Class: |
C01F 17/00 20060101
C01F017/00; B24D 3/02 20060101 B24D003/02; C09K 13/00 20060101
C09K013/00; B44C 1/22 20060101 B44C001/22; C23F 1/00 20060101
C23F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 1996 |
JP |
08258766 |
Sep 30, 1996 |
JP |
08258767 |
Sep 30, 1996 |
JP |
08258768 |
Sep 30, 1996 |
JP |
08258770 |
Sep 30, 1996 |
JP |
08258774 |
Sep 30, 1996 |
JP |
08258775 |
Sep 30, 1996 |
JP |
08258776 |
Sep 30, 1996 |
JP |
08258781 |
Sep 30, 1996 |
JP |
08259138 |
Jan 28, 1997 |
JP |
09014371 |
Apr 30, 1997 |
JP |
09112396 |
Aug 1, 1997 |
JP |
09207866 |
Claims
1-16. (canceled)
17. A cerium oxide abrasive comprising a slurry formed by
dispersing cerium oxide particles in water containing ammonium
polyacrylate salt.
18. A cerium oxide abrasive according to claim 17, wherein said
cerium oxide particles comprise cerium oxide obtained by firing
cerium carbonate.
19. A cerium oxide abrasive according to claim 17, wherein said
ammonium polyacrylate salt has a weight-average molecular weight of
from 5,000 to 20,000.
20. A cerium oxide abrasive according to claim 18, wherein said
ammonium polyacrylate salt has a weight-average molecular weight of
from 5,000 to 20,000.
21. A method of polishing substrates comprising the steps of:
providing a given substrate; and polishing the substrate with the
cerium oxide abrasive according to claim 17.
22. A method of polishing substrates comprising the steps of:
providing a given substrate; and polishing the substrate with the
cerium oxide abrasive according to claim 18.
23. A method of polishing substrates comprising the steps of:
providing a given substrate; and polishing the substrate with the
cerium oxide abrasive according to claim 19.
24. A method of polishing substrates comprising the steps of:
providing a given substrate; and polishing the substrate with the
cerium oxide abrasive according to claim 20.
25. A method of polishing substrates according to claim 21, wherein
said given substrate is a semiconductor chip on which a silica film
has been formed.
26. A method of polishing substrates according to claim 22, wherein
said given substrate is a semiconductor chip on which a silica film
has been formed.
27. A method of polishing substrates according to claim 23, wherein
said given substrate is a semiconductor chip on which a silica film
has been formed.
28. A method of polishing substrates according to claim 24, wherein
said given substrate is a semiconductor chip on which a silica film
has been formed.
Description
TECHNICAL FIELD
[0001] This invention relates to a cerium oxide abrasive and a
method of polishing substrates.
BACKGROUND ART
[0002] In semiconductor device fabrication processes, colloidal
silica type abrasives have commonly been studied as chemomechanical
abrasives for smoothing inorganic insulating film layers such as
SiO.sub.2 insulating films formed by a process such as
plasma-assisted CVD (chemical vapor deposition) or low-pressure
CVD. Colloidal silica type abrasives are produced by growing silica
particles into grains by, e.g., thermal decomposition of silicon
tetrachloride, followed by pH-adjustment with an alkali solution
containing non alkali metal, such as aqueous ammonia. Such
abrasives, however, have a technical problem of a low polishing
rate which prevents them being put into practical use, because the
inorganic insulating films can not be polished at a sufficiently
high polishing rate.
[0003] Meanwhile, cerium oxide abrasives are used in glass-surface
polishing for photomasks. The cerium oxide abrasives are useful for
finish mirror polishing because they have a hardness lower than
silica particles and alumina particles and hence the polishing
surface is very difficult to scratch. Also, cerium oxide has a
chemically active nature and is known as a strong oxidizing agent.
Making the most of this advantage, it is useful to apply the cerium
oxide in chemomechanical abrasives for insulating films. However,
if the cerium oxide abrasives used in glass-surface polishing for
photomasks are used in the polishing of inorganic insulating films
as they are, they have so large a primary particle diameter that
the insulating film surface may come to have polish scratches which
are visually perceivable.
DISCLOSURE OF THE INVENTION
[0004] The present invention provides a cerium oxide abrasive that
can polish the surfaces of objects such as SiO.sub.2 insulating
films without causing scratches and at a high rate, and also
provides a method of polishing substrates.
[0005] The cerium oxide abrasive of the present invention comprises
a slurry comprising cerium oxide particles whose primary particles
have a median diameter of from 30 nm to 250 nm and slurry particles
have a median diameter of from 150 nm to 600 nm; the cerium oxide
particles being dispersed in a medium.
[0006] The cerium oxide abrasive of the present invention may also
comprise a slurry made up of cerium oxide particles whose primary
particles have a median diameter of from 100 nm to 250 nm and
slurry particles have a median diameter of from 150 nm to 350 nm;
the cerium oxide particles being dispersed in a medium.
[0007] In the above cerium oxide particles, the primary particles
may preferably have a maximum diameter of 600 nm or smaller and a
primary-particle diameter of from 10 nm to 600 nm.
[0008] The cerium oxide abrasive of the present invention may still
further comprise a slurry made up of cerium oxide particles whose
primary particles have a median diameter of from 30 nm to 70 nm and
slurry particles have a median diameter of from 250 nm to 600 nm;
the cerium oxide particles being dispersed in a medium.
[0009] The above cerium oxide particles may preferably have a
primary-particle diameter of from 10 nm to 100 nm.
[0010] In the cerium oxide abrasive of the present invention, the
cerium oxide particles may preferably have a maximum particle
diameter of 3,000 nm or smaller.
[0011] Water may be used as the medium, and at least one dispersant
selected from a water-soluble organic high polymer, a water-soluble
anionic surface-active agent, a water-soluble nonionic
surface-active agent and a water-soluble amine may be used, of
which ammonium polyacrylate is preferred.
[0012] As the cerium oxide particles, cerium oxide obtained by
firing cerium carbonate may preferably be used.
[0013] The cerium oxide abrasive of the present invention can
polish a given substrate for semiconductor chips or the like, on
which silica films have been formed.
BEST MODES FOR PRACTICING THE INVENTION
[0014] The cerium oxide is commonly obtained by firing a cerium
compound such as cerium carbonate, cerium sulfate or cerium
oxalate. SiO.sub.2 insulating films formed by TEOS-CVD, for
example, can be polished at a higher rate as abrasives have a
larger primary-particle diameter and a lower crystal strain, i.e.,
have better crystallinity, but tend to be prone to polish
scratches. Accordingly, the cerium oxide particles used in the
present invention are produced without making their crystallinity
so high. Also, since the abrasive may be used to polish
semiconductor chips, its content of alkali metals and halogens may
preferably be controlled to be 1 ppm or less.
[0015] The abrasive of the present invention has a high purity, and
does not contain more than 1 ppm of Na, K, Si, Mg, Ca, Zr, Ti, Ni,
Cr and Fe each and more than 10 ppm of Al.
[0016] In the present invention, firing may be employed as a
process for producing the cerium oxide particles. In particular,
low-temperature firing is preferred, which can make the
crystallinity as low as possible in order to produce particles that
do not cause polish scratches. Since the cerium compounds have an
oxidation temperature of 300.degree. C., they may preferably be
fired at a temperature of from 600.degree. C. to 900.degree. C.
[0017] The cerium carbonate may preferably be fired at a
temperature of from 600.degree. C. to 900.degree. C. for 5 to 300
minutes in an oxidative atmosphere of oxygen gas or the like.
[0018] The cerium oxide obtained by firing may be pulverized by
dry-process pulverization such as jet milling or by wet-process
pulverization such as bead milling. The jet milling is described
in, e.g., KAGAKU KOGYO RONBUNSHU (Chemical Industry Papers), Vol.
6, No. 5 (1980), pages 527-532. Cerium oxide obtained by firing was
pulverized by dry-process pulverization such as jet milling,
whereupon a pulverization residue was seen to occur.
[0019] The slurry of cerium oxide in the present invention is
obtained by dispersion-treating an aqueous solution containing
cerium oxide particles produced in the manner described above or a
composition comprising cerium oxide particles collected from this
aqueous solution, water and optionally a dispersant. Here, the
cerium oxide particles may preferably be used in a concentration
ranging, but not particularly limited to, from 0.1 to 10% by weight
in view of readiness to handle suspensions. As the dispersing
agent, it may include, as those containing no metal ions,
water-soluble organic high polymers such as acrylic polymers and
ammonium salts thereof, methacrylic polymers and ammonium salts
thereof, and polyvinyl alcohol, water-soluble anionic
surface-active agents such as ammonium lauryl sulfate and ammonium
polyoxyethylene lauryl ether sulfate, water-soluble nonionic
surface-active agents such as polyoxyethylene lauryl ether and
polyethylene glycol monostearate, and water-soluble amines such as
monoethanolamine and diethanolamine.
[0020] Ammonium polyacrylate, in particular, ammonium polyacrylate
having weight-average molecular weight of from 5,000 to 20,000 is
preferred. Any of these dispersing agents may preferably be added
in an amount ranging from 0.01 part by weight to 5 parts by weight
based on 100 parts by weight of the cerium oxide particles in view
of the dispersibility and anti-sedimentation properties of
particles in the slurry. In order to improve its dispersion effect,
the dispersing agent may preferably be put in a dispersion machine
simultaneously with the particles at the time of dispersion
treatment.
[0021] These cerium oxide particles may be dispersed in water by
dispersion treatment using a conventional agitator, and besides by
using a homogenizer, an ultrasonic dispersion machine or a ball
mill. Particularly for dispersing the cerium oxide particles as
fine particles of 1 .mu.m or smaller, it is preferable to use
wet-process dispersion machines such as a ball mill, a vibration
ball mill, a satellite ball mill and a media agitating mill. In a
case where the slurry should be made more highly alkaline, an
alkaline substance containing no metal ions, such as aqueous
ammonia, may be added during the dispersion treatment or after the
treatment.
[0022] The cerium oxide abrasive of the present invention may be
used as it is in the form of the above slurry. It may also be used
as an abrasive to which an additive such as
N,N-diethylethanolamine, N,N-dimethylethanolamine or
aminoethylethanolamine has been added.
[0023] Primary particles constituting the cerium oxide particles
dispersed in the slurry of the present invention have a median
diameter of from 30 to 250 nm and their particles have a median
diameter of from 150 to 600 nm.
[0024] If the primary particles have a median diameter smaller than
30 nm or the particles standing dispersed have a median diameter
smaller than 150 nm, the surfaces of objects to be polished such as
SiO.sub.2 insulating films can not be polished at a high rate. If
the primary particles have a median diameter larger than 250 nm or
the particles have a median diameter larger than 600 nm, scratches
may occur on the surfaces of objects to be polished such as
SiO.sub.2 insulating films.
[0025] Cerium oxide particles whose primary particles have a median
diameter of from 100 nm to 250 nm and particles having a median
diameter of from 150 nm to 350 nm are preferred. If their
respective median diameters are smaller than the above lower-limit
values, a low polishing rate may result and, if they are larger
than the above upper-limit values, scratches tend to occur.
[0026] In the above cerium oxide particles, the primary particles
may preferably have a maximum diameter not larger than 600 nm, and
may preferably have a primary-particle diameter of from 10 to 600
nm. The primary particles having a particle diameter larger than
the upper-limit value 600 nm may result in occurrence of scratches
and those having a particle diameter smaller than 10 nm may result
in a low polishing rate.
[0027] Cerium oxide particles whose primary particles have a median
diameter of from 30 nm to 70 nm and particles having a median
diameter of from 250 nm to 600 nm are also preferred. If their
respective median diameters are smaller than the above lower-limit
values, a low polishing rate may result and, if they are larger
than the above upper-limit values, scratches tend to occur.
[0028] In the above cerium oxide particles, the primary particles
may preferably have a diameter of from 10 to 100 nm. If the primary
particles have a particle diameter smaller than 10 nm, a low
polishing rate may result. If they have a particle diameter larger
than the upper-limit value 100 nm, scratches tend to occur.
[0029] In the cerium oxide abrasive of the present invention, the
cerium oxide particles may preferably have a maximum diameter not
larger than 3,000 nm. If the cerium oxide particles have a maximum
diameter larger than 3,000 nm, scratches tend to occur.
[0030] The cerium oxide particles obtained by pulverizing fired
cerium oxide by dry-process pulverization such as jet milling
contains a pulverization residue. Such pulverization residue
particles differ from agglomerates of primary particles having
re-agglomerated, and are presumed to be broken by stress at the
time of polishing to generate active surfaces, which are considered
to contribute to the polishing of the surfaces of objects to be
polished, such as SiO.sub.2 insulating films, at a high rate
without causing scratches.
[0031] The slurry of the present invention may contain
pulverization residue particles having a particle diameter of 3,000
nm or smaller.
[0032] In the present invention, the primary-particle diameter is
measured by observing the particles on a scanning electron
microscope (e.g., Model S-900, manufactured by Hitachi, Ltd.). The
particle diameter of the cerium oxide particles as slurry particles
is measured by laser diffraction (using, e.g., MASTER SIZER
MICROPLUS, manufactured by Malvern Instruments Ltd.; refractive
index:1.9285; light source: He--Ne laser; absorption: 0).
[0033] The primary particles constituting the cerium oxide
particles dispersed in the slurry of the present invention may
preferably have an aspect ratio of from 1 to 2 and a median value
of 1.3. The aspect ratio is measured by observing the particles on
a scanning electron microscope (e.g., Model S-900, manufactured by
Hitachi Ltd.).
[0034] As the cerium oxide particles to be dispersed in the slurry
of the present invention, cerium oxide particles whose structural
parameter Y which represents an isotropic microstrain in analysis
by the powder X-ray Rietvelt method (RIETAN-94) has a value of from
0.01 to 0.70 may be used. The use of cerium oxide particles having
such a crystal strain makes it possible to carry out polishing
without scratching the surfaces of objects and also at a high
rate.
[0035] The cerium oxide particles dispersed in the slurry of the
present invention may preferably have a specific surface area of
from 7 to 45 m.sup.2/g. Those having a specific surface area
smaller than 7 m.sup.2/g tend to make scratches on the surfaces of
polish objects, and those having a specific surface area larger
than 45 m.sup.2/g tend to result in a low polishing rate. The
specific surface area of the cerium oxide particles of the slurry
is identical with the specific surface area of cerium oxide
particles to be dispersed.
[0036] The cerium oxide particles in the slurry of the present
invention may preferably have a zeta potential of from -100 mV to
-10 mV. This brings about an improvement in dispersibility of the
cerium oxide particles and makes it possible to carry out polishing
without scratching the surfaces of polish objects and also at a
high rate.
[0037] The cerium oxide particles dispersed in the slurry of the
present invention may have an average particle diameter of from 200
nm to 400 nm and a particle size distribution half width of 300 nm
or smaller.
[0038] The slurry of the present invention may preferably have a pH
of from 7 to 10, and more preferably from 8 to 9.
[0039] After the slurry has been prepared, it may be put in a
container of polyethylene or the like and left at 5 to 55.degree.
C. for 7 days or more, and more preferably 30 days or more, so that
the slurry may cause less scratches.
[0040] The slurry of the present invention has such good dispersion
and such a low rate of sedimentation that its rate of change in
concentration after 2-hour leaving is less than 10% at every height
and every position of a column of 10 cm in diameter and 1 m in
height.
[0041] The inorganic insulating films on which the cerium oxide
abrasive of the present invention is used may be formed by a
process including low-pressure CVD and plasma-assisted CVD. The
formation of SiO.sub.2 insulating films by low-pressure CVD makes
use of monosilane SiH.sub.4 as an Si source and oxygen O.sub.2 as
an oxygen source. Oxidation reaction of this SiH.sub.4--O.sub.2
system may be carried out at a low temperature of about 400.degree.
C. or below. When phosphorus (P) is doped in order to make the
surface smooth by high-temperature reflowing, it is preferable to
use a reaction gas of SiH.sub.4--O.sub.2--PH.sub.3 system. The
plasma-assisted CVD has an advantage that any chemical reaction
which requires a high temperature under normal heat equilibrium can
be carried out at a low temperature. Plasma may be generated by a
process including two types of coupling, namely capacitive coupling
and inductive coupling. Reaction gas may include gases of
SiH.sub.4--N.sub.2O system making use of SiH.sub.4 as an Si source
and N.sub.2O as an oxygen source and gases of TEOS--O.sub.2 system
making use of tetraethoxysilane (TEOS) as an Si source (i.e., TEOS
plasma-assisted CVD method). Substrate temperature may preferably
be within the range of from 250.degree. C. to 400.degree. C., and
reaction pressure from 67 Pa to 400 Pa. Thus, the SiO.sub.2
insulating films in the present invention may be doped with an
element such as phosphorus or boron.
[0042] As the given substrate, substrates may be used which are
obtained by forming SiO.sub.2 insulating films on semiconductor
substrates, i.e., semiconductor substrates such as a semiconductor
substrate at the stage where circuit elements and wiring patterns
have been formed thereon or a substrate at the stage where circuit
elements have been formed thereon. The SiO.sub.2 insulating film
formed on such a semiconductor substrate is polished with the
cerium oxide abrasive described above, whereby any unevenness on
the SiO.sub.2 insulating film surface can be removed to provide a
smooth surface over the whole area of the semiconductor substrate.
Here, as a polishing apparatus, commonly available polishing
apparatus may be used, having i) a holder for holding a
semiconductor substrate and ii) a platen (provided with a motor
whose number of revolution is variable) on which a polishing cloth
(a pad) is stuck. As the polishing cloth, commonly available
nonwoven fabric, foamed polyurethane or porous fluorine resin may
be used, and there are no particular limitations. The polishing
cloth may also preferably be processed to provide grooves where the
slurry may gather. There are no particular limitations on polishing
conditions, and preferably the platen may be rotated at a small
number of revolution of 100 rpm or below so that the semiconductor
substrate may not run out. Pressure applied to the semiconductor
substrate may preferably be 1 kg/cm.sup.2 or below so that the
substrate does not get scratched as a result of polishing. In the
course of polishing, the slurry is fed continuously to the
polishing cloth by means of a pump or the like. There are no
particular limitations on the feed rate of this slurry. It is
preferable for the surface of the polishing cloth to always be
covered with the slurry.
[0043] Semiconductor substrates on which the polishing has been
completed may preferably be well rinsed in running water and
thereafter water drops adhering to the surfaces of semiconductor
substrates are brushed off by means of a spin dryer or the like,
followed by drying. On the SiO.sub.2 insulating film having been
thus smoothed, second-layer aluminum wiring is formed. An SiO.sub.2
insulating film is again formed between the wiring and on the
wiring, followed by polishing with the cerium oxide abrasive
described above, whereby any unevenness on the insulating film
surface is removed to provide a smooth surface over the whole area
of the semiconductor substrate. This process may be repeated a
given number of times so that a semiconductor having the desired
number of layers can be produced.
[0044] The cerium oxide abrasive of the present invention may be
used to polish not only the SiO.sub.2 insulating films formed on
semiconductor substrates, but also SiO.sub.2 insulating films
formed on wiring boards having given wiring, glass, inorganic
insulating films such as silicon nitride film, optical glass such
as photomasks, lenses and prisms, inorganic conductive films such
as ITO (indium tin oxide) film, optical integrated circuits,
optical switching devices or optical waveguides which are
constituted of glass and a crystalline material, optical fiber end
faces, optical single crystals such as scintillators, solid-state
laser single crystals, blue-laser LED (light-emitting diode)
sapphire substrates, semiconductor single crystals such as SiC, GaP
and GaAs, magnetic disk glass substrates, magnetic heads and so
forth.
[0045] Thus, in the present invention, what is referred to as the
given substrate includes semiconductor substrates on which
SiO.sub.2 insulating films have been formed, wiring boards on which
SiO.sub.2 insulating films have been formed, glass, inorganic
insulating films such as silicon nitride film, optical glasses such
as photomasks, lenses and prisms, inorganic conductive films such
as ITO film, optical integrated circuits, optical switching devices
or optical waveguides which are constituted of glass and a
crystalline material, optical fiber end faces, optical single
crystals such as scintillators, solid-state laser single crystals,
blue-laser LED sapphire substrates, semiconductor single crystals
such as SiC, GaP and GaAs, magnetic disk glass substrates, and
magnetic heads.
[0046] The slurry prepared by dispersing the cerium oxide particles
in the medium reacts chemically with part of an insulating film
layer provided on the given substrate to form a reactive layer, and
the reactive layer is removed mechanically with the cerium oxide
particles, thus making it possible to polish the insulating film
layer at a high rate and also without causing any polish
scratches.
[0047] Cerium oxide abrasives are used in glass-surface polishing
for photomasks. The cerium oxide abrasives are useful for finish
mirror polishing because they have a lower hardness than silica
particles and alumina particles and hence the polishing surface is
unlikely to be scratched. Also, cerium oxide has a chemically
active nature and is known as a strong oxidizing agent. Making the
most of this advantage, it is useful for the cerium oxide to be
applied in chemomechanical abrasives for insulating films. However,
if the cerium oxide abrasives used in glass-surface polishing for
photomasks are used in the polishing of insulating films as they
are, the particles have such high crystallinity that the insulating
film surface may be subject to polish scratches which are visually
perceivable.
[0048] Factors that determine the crystallinity include crystallite
size and crystal strain. When the crystallite size is as large as 1
.mu.m or more, polish scratches tend to occur. Also, even when the
crystallite size is small, polish scratches may occur if particles
having no crystal strain are used. However, some cerium oxide
particles have too low a crystallinity to cause any polish
scratches, but are not able to effect high-rate polishing. Thus,
cerium oxide particles which make it possible to prevent polish
scratches and to effect high-rate polishing have a range of proper
particle size and a proper degree of strain. Factors that determine
the polishing rate include not only the crystallinity of particles
stated above but also the active chemical nature inherent in cerium
oxide.
[0049] Even with use of silica particles having a higher particle
hardness than the cerium oxide particles, silica slurries have a
much lower polishing rate than the cerium oxide slurry. This
indicates that the cerium oxide slurry has a stronger chemical
factor in the chemomechanical polishing. The surface of SiO.sub.2
insulating film stands charged negatively in a solution having a
hydrogen ion concentration of pH 3 or more. When polished with a
slurry making use of cerium oxide particles standing charged
positively, an inert film composed chiefly of cerium oxide is
formed. This inert film can not be removed by washing with water,
and is removed using a strongly acidic solution such as nitric
acid. Simultaneously with the removal of the inert film by the use
of an acid, the insulating layer is removed to an extent of 1,000
nm or more. The insulating film thus removed is a reactive layer
formed when the inert film is formed. The inert film is also formed
when the cerium oxide particles stand charged negatively. The
degree of adhesion of the inert film to the insulating film depends
on how far the particles are charged. For example, an inert film
formed when the absolute negative value where the particles stand
charged is great can be removed by washing with water or brush
cleaning. That is, the degree of formation of the inert layer and
reactive layer depends on the state of charging of particles. This
phenomenon of formation of the inert film is not seen in silica
slurries, and is a phenomenon inherent in the cerium oxide slurry.
This phenomenon is one of the factors that determine the high-rate
polishing. The cerium oxide particles scrape off these inert film
and reactive layer. This phenomenon is the mechanical factor in the
chemomechanical polishing. If particles have a low crystallinity,
the reactive layer can not be removed, resulting in a low polishing
rate. On the other hand, particles having a high crystallinity can
remove the reactive layer with ease, and can quickly scrape off the
reactive layer formed immediately after removal. Thus, the
formation of reactive layers and the polishing with particles take
place one after another, so that the polishing can be carried out
at a high rate.
[0050] As a method for examining the state of charging of particles
in the slurry, the zeta potential measurement is available. To
describe its specific principle, the cerium oxide slurry is put in
a measuring cell like the one provided with platinum electrodes on
both sides, and a voltage is applied to the both electrodes. Cerium
oxide particles having come to have charges upon application of the
voltage move toward the electrode side having a polarity reverse to
that of the charges. The mobility thereof is determined, and the
zeta potential of particles can be determined from a known
expression of the relationship between mobility and zeta potential.
To form the inert film and reactive layer, the cerium oxide slurry
may preferably have a zeta potential of -100 mV or above. However,
when particles are charged positively or, even though charged
negatively, have an absolute value smaller than 10 mV, the inert
film is formed so strongly that the polishing with optimum
particles that do not cause polish scratches is impossible.
Accordingly, the slurry may preferably have a zeta potential of
from -100 mV to -10 mV.
[0051] Using the cerium oxide abrasive comprising the slurry
prepared by dispersing the cerium oxide particles in the medium, an
inert film that may prevent the polishing proceeding thereon may be
formed only on the surface of one certain type of film and the
other film may be polished selectively, whereby layers formed of
two or more types of different films on the substrate can be
polished.
[0052] The inert film that may prevent the polishing proceeding
thereon may be formed only on the surface of one certain type of
film among the layers formed of two or more types of different
films on the substrate, and the film area where such an inert film
has been formed, may serve as a stopper so that the other film may
be polished selectively, whereby the layers formed as described
above can be made smooth.
[0053] This polishing method utilizes the properties that the
polishing barely proceeds on the surfaces of a certain interlayer
insulating film and a certain interlayer smoothing film because an
inert film comprised of abrasive particles or a reaction product of
a polishing liquid composition with a film composition is formed on
such surfaces. The inert film refers to a surface layer that may
make the polishing rate lower than the film to be polished
originally. When such a certain interlayer insulating film and
interlayer smoothing film on which the inert film may be formed are
used to form patterns of semiconductor chips, another interlayer
film on which the polishing proceeds may be formed as its upper
layer, whereby a global smoothness can be achieved using the lower
layer film as a stopper.
[0054] Those comprised of such two or more types of different films
formed on a substrate may include those in which the substrate is a
semiconductor substrate and the layers formed thereon are an
organic SOG (spin-on glass) film and an SiO.sub.2 film formed by
chemical vapor deposition or thermal oxidation, where the film on
which the inert film is formed is the SiO.sub.2 film and the film
to be polished selectively is the organic SOG film.
[0055] The organic SOG film is a film formed by coating a coating
solution obtained by, e.g., hydrolyzing an alkoxysilane and an
alkylalkoxysilane in an organic solvent such as alcohol with
addition of water and a catalyst, on a substrate by spin coating or
the like, followed by heating to cause the coating to cure.
[0056] In such an insulating film, preferred is an insulating film
in which the number of Si atoms originating from siloxane bonds and
the number of C atoms originating from alkyl groups in the
insulating film have the relationship of: Number of C atoms/(number
of Si atoms+number of C atoms).gtoreq.0.1.
[0057] On the organic SOG insulating film layer having been
smoothed, a CVD-SiO.sub.2 film and second-layer aluminum wiring are
formed, and lower layer CVD-SiO.sub.2 film and organic SOG
insulating film are formed between the wiring and on the wiring,
followed by polishing using the above cerium oxide slurry to
thereby remove unevenness of the insulating film layer surface to
provide a smooth face over the whole area of the semiconductor
substrate. This process may be repeated a given number of times so
that a semiconductor having the desired number of layers can be
produced. In the process where the films formed of two or more
types of films are polished to form the intended structure by
utilizing this polishing method, the smoothing that utilizes the
selective polishing can make the process simple and highly
precise.
EXAMPLE 1
[0058] (Production 1 of Cerium Oxide Particles)
[0059] 2 kg of cerium carbonate hydrate was placed in a container
made of platinum, followed by firing at 800.degree. C. for 2 hours
in air to obtain about 1 kg of a yellowish white powder. Phase
identification of this powder was made by X-ray diffraction to
confirm that it was cerium oxide. The fired powder had particle
diameters of 30 to 100 .mu.m. The particle surfaces of the fired
powder were observed on a scanning electron microscope, where grain
boundaries of cerium oxide were seen. Diameters of cerium oxide
primary particles surrounded by the grain boundaries were measured
to find that the median diameter and maximum diameter in their
particle size distribution were 190 nm and 500 nm, respectively.
Precision measurement by X-ray diffraction was made on the fired
powder, and the results obtained were analyzed by the Rietvelt
method (RIETAN-94) to find that the value of structural parameter X
which represents primary-particle diameter was 0.080 and the value
of structural parameter Y which represents an isotropic microstrain
was 0.223. Using a jet mill, 1 kg of the cerium oxide powder was
dry-process pulverized. The pulverized particles obtained were
observed on a scanning electron microscope to find that large
pulverization residue particles of from 1 .mu.m to 3 .mu.m diameter
and pulverization residue particles of from 0.5 .mu.m to 1 .mu.m
diameter were present in a mixed state in addition to small
particles having the same size as primary-particle diameter. The
pulverization residue particles were not agglomerates of primary
particles. Precision measurement by X-ray diffraction was made on
the pulverized particles, and the results obtained were analyzed by
the Rietvelt method (RIETAN-94) to find that the value of
structural parameter X which represents primary-particle diameter
was 0.085 and the value of structural parameter Y which represents
an isotropic microstrain was 0.264. As the result, there was almost
no variation in primary-particle diameter caused by pulverization
and also strains were introduced into particles as a result of
pulverization. Measurement of specific surface area by the BET
method also revealed that it was 10 m.sup.2/g.
[0060] (Production 2 of Cerium Oxide Particles)
[0061] 2 kg of cerium carbonate hydrate was placed in a container
made of platinum, followed by firing at 750.degree. C. for 2 hours
in air to obtain about 1 kg of a yellowish white powder. Phase
identification of this powder was made by X-ray diffraction to
confirm that it was cerium oxide. The fired powder had particle
diameters of 30 to 100 .mu.m. The particle surfaces of the fired
powder were observed on a scanning electron microscope, where grain
boundaries of cerium oxide were seen. Diameters of cerium oxide
primary particles surrounded by the grain boundaries were measured
to find that the median diameter and maximum diameter in their
particle size distribution were 141 nm and 400 nm, respectively.
Precision measurement by X-ray diffraction was made on the fired
powder, and the results obtained were analyzed by the Rietvelt
method (RIETAN-94) to find that the value of structural parameter X
which represents primary-particle diameter was 0.101 and the value
of structural parameter Y which represents an isotropic microstrain
was 0.223. Using a jet mill, 1 kg of the cerium oxide powder was
dry-process pulverized. The pulverized particles obtained were
observed on a scanning electron microscope to find that large
pulverization residue particles of from 1 .mu.m to 3 .mu.m diameter
and pulverization residue particles of from 0.5 .mu.m to 1 .mu.m
diameter were present in a mixed state in addition to small
particles having the same size as primary-particle diameter. The
pulverization residue particles were not agglomerates of primary
particles. Precision measurement by X-ray diffraction was made on
the pulverized particles, and the results obtained were analyzed by
the Rietvelt method (RIETAN-94) to find that the value of
structural parameter X which represents primary-particle diameter
was 0.104 and the value of structural parameter Y which represents
an isotropic microstrain was 0.315. As the result, there was almost
no variation in primary-particle diameter caused by pulverization
and also strains were introduced into particles as a result of
pulverization. Measurement of specific surface area by the BET
method also revealed that it was 16 m.sup.2/g.
[0062] (Production of Cerium Oxide Slurry)
[0063] 1 kg of the cerium oxide particles obtained in the above
production 1 or 2, 23 g of an aqueous ammonium polyacrylate
solution (40% by weight) and 8,977 g of deionized water were mixed,
and the mixture formed was subjected to ultrasonic dispersion for
10 minutes with stirring. The slurries thus obtained were filtered
with a 1 .mu.m filter, followed by further addition of deionized
water to obtain a 3% by weight abrasive. The slurries had a pH of
8.3.
[0064] Particle size distribution of slurry particles was examined
by laser diffraction (measured with a measuring apparatus: MASTER
SIZER MICROPLUS, manufactured by Malvern Instruments Ltd.;
refractive index: 1.9285; light source: He--Ne laser; absorption:
0) to find that the median diameter was 200 nm for each slurry.
With regard to maximum particle diameter, particles of 780 nm or
larger were in a content of 0% by volume.
[0065] To examine dispersibility of the slurries and charges of the
slurry particles, the zeta potentials of the slurries were
measured. Each cerium oxide slurry was placed in a measuring cell
provided with platinum electrodes on both sides, and a voltage of
10 V was applied to both electrodes. Slurry particles having come
to have charges upon application of the voltage move toward the
electrode side having a polarity reverse to that of the charges.
The zeta potential of particles can be determined by determining
their mobility. As a result of the measurement of zeta potential,
it was confirmed that the particles in each slurry were charged
negatively, and showed a large absolute value of -50 mV or -63 mV,
respectively, having a good dispersibility.
[0066] (Polishing of Insulating Film Layer)
[0067] Silicon wafers on which SiO.sub.2 insulating films produced
by TEOS plasma-assisted CVD were formed were each set on a holder
provided with a suction pad stuck thereon for attaching the
substrate to be held, and the holder was placed, with its
insulating film side down, on a platen on which a polishing pad
made of porous urethane resin was stuck. A weight was further
placed thereon so as to provide a processing load of 300
g/cm.sup.2.
[0068] The platen was rotated at 30 rpm for 2 minutes to polish the
insulating film while dropwise adding the above cerium oxide slurry
(solid content: 3% by weight) onto the platen at a rate of 50
ml/minute. After the polishing was completed, the wafer was
detached from the holder and then well rinsed in running water,
followed by further cleaning for 20 minutes by an ultrasonic
cleaner. After the cleaning was completed, the wafer was set on a
spin dryer to remove drops of water, followed by drying for 10
minutes by a 120.degree. C. dryer.
[0069] Changes in layer thickness before and after the polishing
were measured with a light-interference type layer thickness
measuring device. As a result, it was found that as a result of
this polishing the insulating films were abraded by 600 nm and 580
nm (polishing rate: 300 nm/minute, 290 nm/minute), respectively,
and each wafer was in a uniform thickness over its whole area. The
surfaces of the insulating films were also observed using an
optical microscope, where no evident scratches were seen.
EXAMPLE 2
[0070] (Production of Cerium Oxide Particles)
[0071] 2 kg of cerium carbonate hydrate was placed in a container
made of platinum, followed by firing at 700.degree. C. for 2 hours
in air to obtain about 1 kg of a yellowish white powder. Phase
identification of this powder was made by X-ray diffraction to
confirm that it was cerium oxide. The fired powder had particle
diameters of 30 to 100 .mu.m. The particle surfaces of the fired
powder were observed on a scanning electron microscope, where grain
boundaries of cerium oxide were seen. Diameters of cerium oxide
primary particles surrounded by the grain boundaries were measured
to find that the median diameter and maximum diameter in their
particle size distribution were 50 nm and 100 nm, respectively.
Precision measurement by X-ray diffraction was made on the fired
powder, and the results obtained were analyzed by the Rietvelt
method (RIETAN-94) to find that the value of structural parameter X
which represents primary-particle diameter was 0.300 and the value
of structural parameter Y which represents an isotropic microstrain
was 0.350.
[0072] Using a jet mill, 1 kg of the cerium oxide powder was
dry-process pulverized. The pulverized particles obtained were
observed on a scanning electron microscope to find that large
pulverization residue particles of from 2 .mu.m to 4 .mu.m diameter
and pulverization residue particles of from 0.5 .mu.m to 1.2 .mu.m
diameter were present in a mixed state in addition to small
particles having the same size as primary-particle diameter. The
pulverization residue particles were not agglomerates of primary
particles. Precision measurement by X-ray diffraction was made on
the pulverized particles, and the results obtained were analyzed by
the Rietvelt method (RIETAN-94) to find that the value of
structural parameter X which represents primary-particle diameter
was 0.302 and the value of structural parameter Y which represents
an isotropic microstrain was 0.412. As the result, there was almost
no variation in primary-particle diameter to be caused by
pulverization and also strains were introduced into particles as a
result of pulverization. Measurement of specific surface area by
the BET method also revealed that it was 40 m.sup.2/g.
[0073] (Production of Cerium Oxide Slurry)
[0074] 1 kg of the cerium oxide particles produced in the above, 23
g of an aqueous ammonium polyacrylate solution (40% by weight) and
8,977 g of deionized water were mixed, and the mixture formed was
subjected to ultrasonic dispersion for 10 minutes with stirring.
The slurry thus obtained was filtered with a 2 .mu.m filter,
followed by further addition of deionized water to obtain a 3% by
weight abrasive. The slurry had a pH of 8.0. Particle size
distribution of slurry particles was examined by laser diffraction
(measuring apparatus: MICROPLUS, manufactured by Master Sizer;
refractive index: 1.9285) to find that the median diameter was 510
nm. With regard to maximum particle diameter, particles of 1,430 nm
or larger were in a content of 0%.
[0075] To examine dispersibility of the slurry and charges of the
slurry particles, the zeta potential of the slurry was measured.
The cerium oxide slurry was put in a measuring cell provided with
platinum electrodes on both sides, and a voltage of 10 V was
applied to both electrodes. Slurry particles having come to have
charges upon application of the voltage move toward the electrode
side having a polarity reverse to that of the charges. The zeta
potential of particles can be determined by determining their
mobility. As a result of the measurement of zeta potential, it was
confirmed that the particles were charged negatively, and showed a
large absolute value of -64 mV, having a good dispersibility.
[0076] (Polishing of Insulating Film Layer)
[0077] A silicon wafer on which an SiO.sub.2 insulating film
produced by TEOS plasma-assisted CVD was formed was set on a holder
provided with a suction pad stuck thereon for attaching the
substrate to be held, and the holder was placed, with its
insulating film side down, on a platen on which a polishing pad
made of porous urethane resin was stuck. A weight was further
placed thereon so as to provide a processing load of 300
g/cm.sup.2.
[0078] The platen was rotated at 30 rpm for 2 minutes to polish the
insulating film while dropwise adding the above cerium oxide slurry
(solid content: 3% by weight) onto the platen at a rate of 35
ml/minute. After the polishing was completed, the wafer was
detached from the holder and then well rinsed in running water,
followed by further cleaning for 20 minutes using an ultrasonic
cleaner. After the cleaning was completed, the wafer was set on a
spin dryer to remove drops of water, followed by drying for 10
minutes using a 120.degree. C. dryer. Changes in layer thickness
before and after the polishing were measured with a
light-interference type layer thickness measuring device. As the
result, it was found that as a result of this polishing the
insulating film was abraded by 740 nm (polishing rate: 370
nm/minute) and the wafer was in a uniform thickness over its whole
area. The surface of the insulating film was also observed using an
optical microscope, where no evident scratches were seen.
EXAMPLE 3
[0079] (Production of Cerium Oxide Particles)
[0080] 2 kg of cerium carbonate hydrate was placed in a container
made of platinum, followed by firing at 800.degree. C. for 2 hours
in air to obtain about 1 kg of a yellowish white powder. Phase
identification of this powder was made by X-ray diffraction to
confirm that it was cerium oxide. The fired powder had particle
diameters of 30 to 100 .mu.m. The particle surfaces of the fired
powder were observed on a scanning electron microscope, where grain
boundaries of cerium oxide were seen. Diameters of cerium oxide
primary particles surrounded by the grain boundaries were measured
to find that the median diameter and maximum diameter in their
particle size distribution were 190 nm and 500 nm, respectively.
Precision measurement by X-ray diffraction was made on the fired
powder, and the results obtained were analyzed by the Rietvelt
method (RIETAN-94) to find that the value of structural parameter X
which represents primary-particle diameter was 0.080 and the value
of structural parameter Y which represents an isotropic microstrain
was 0.223.
[0081] Using a bead mill, 1 kg of the cerium oxide powder was
wet-process pulverized. A fluid containing the pulverized particles
obtained was dried, and the dried particles were ball-mill
pulverized. The resultant pulverized particles were observed on a
scanning electron microscope to find that they had been pulverized
to particles having the same size as primary-particle diameter and
no large pulverization residue particles were seen. Precision
measurement by X-ray diffraction was made on the pulverized
particles, and the results obtained were analyzed by the Rietvelt
method (RIETAN-94) to find that the value of structural parameter X
which represents primary-particle diameter was 0.085 and the value
of structural parameter Y which represents an isotropic microstrain
was 0.300. As a result, there was almost no variation in
primary-particle diameter caused by pulverization and also strains
were introduced into particles as a result of pulverization.
Measurement of specific surface area by the BET method also
revealed that it was 10 m.sup.2/g.
[0082] (Production of Cerium Oxide Slurry)
[0083] 1 kg of the cerium oxide particles produced in the above, 23
g of an aqueous ammonium polyacrylate solution (40% by weight) and
8,977 g of deionized water were mixed, and the mixture formed was
subjected to ultrasonic dispersion for 10 minutes with stirring.
The slurry thus obtained was filtered with a 1 .mu.m filter,
followed by further addition of deionized water to obtain a 3% by
weight abrasive. The slurry had a pH of 8.3. Particle size
distribution of slurry particles was examined by laser diffraction
(measuring apparatus: MICROPLUS, manufactured by Master Sizer;
refractive index: 1.9285) to find that the median diameter was 290
nm. With regard to maximum particle diameter, particles of 780 nm
or larger were in a content of 0%.
[0084] To examine dispersibility of the slurry and charges of the
slurry particles, the zeta potential of the slurry was measured.
The cerium oxide slurry was put in a measuring cell provided with
platinum electrodes on both sides, and a voltage of 10 V was
applied to both electrodes. Slurry particles having come to have
charges upon application of the voltage move toward the electrode
side having a polarity reverse to that of the charges. The zeta
potential of particles can be determined by determining their
mobility. As a result of the measurement of zeta potential, it was
confirmed that the particles were charged negatively, and showed a
large absolute value of -50 mV, having a good dispersibility.
[0085] (Polishing of Insulating Film Layer)
[0086] A silicon wafer on which an SiO.sub.2 insulating film
produced by TEOS plasma-assisted CVD was formed was set on a holder
provided with a suction pad stuck thereon for attaching the
substrate to be held, and the holder was placed, with its
insulating film side down, on a platen on which a polishing pad
made of porous urethane resin was stuck. A weight was further
placed thereon so as to provide a processing load of 300
g/cm.sup.2. The platen was rotated at 30 rpm for 2 minutes to
polish the insulating film while dropwise adding the above cerium
oxide slurry (solid content: 3% by weight) onto the platen at a
rate of 35 ml/minute.
[0087] After the polishing was completed, the wafer was detached
from the holder and then well rinsed in running water, followed by
further cleaning for 20 minutes using an ultrasonic cleaner. After
the cleaning was completed, the wafer was set on a spin dryer to
remove drops of water, followed by drying for 10 minutes using a
120.degree. C. dryer. Changes in layer thickness before and after
the polishing were measured with a light-interference type layer
thickness measuring device. As a result, it was found that as a
result of this polishing the insulating film was abraded by 560 nm
(polishing rate: 280 nm/minute) and the wafer was in a uniform
thickness over its whole area. The surface of the insulating film
was also observed using an optical microscope, where no evident
scratches were seen.
EXAMPLE 4
[0088] (Production of Cerium Oxide Particles)
[0089] 2 kg of cerium carbonate hydrate was placed in a container
made of platinum, followed by firing at 700.degree. C. for 2 hours
in air to obtain about 1 kg of a yellowish white powder. Phase
identification of this powder was made by X-ray diffraction to
confirm that it was cerium oxide. The fired powder had particle
diameters of 30 to 100 .mu.m. The particle surfaces of the fired
powder were observed on a scanning electron microscope, where grain
boundaries of cerium oxide were seen. Diameters of cerium oxide
primary particles surrounded by the grain boundaries were measured
to find that the median diameter and maximum diameter in their
particle size distribution were 50 nm and 100 nm, respectively.
Precision measurement by X-ray diffraction was made on the fired
powder, and the results obtained were analyzed by the Rietvelt
method (RIETAN-94) to find that the value of structural parameter X
which represents primary-particle diameter was 0.300 and the value
of structural parameter Y which represents an isotropic microstrain
was 0.350.
[0090] Using a bead mill, 1 kg of the cerium oxide powder was
wet-process pulverized. A fluid containing the pulverized particles
obtained was dried, and the dried particles were ball-mill
pulverized. The resultant pulverized particles were observed on a
scanning electron microscope to find that they had been pulverized
to particles having the same size as primary-particle diameter and
no large pulverization residue particles were seen. Precision
measurement by X-ray diffraction was made on the pulverized
particles, and the results obtained were analyzed by the Rietvelt
method (RIETAN-94) to find that the value of structural parameter X
which represents primary-particle diameter was 0.302 and the value
of structural parameter Y which represents an isotropic microstrain
was 0.450. As a result, there was almost no variation in
primary-particle diameter caused by pulverization and also strains
were introduced into particles as a result of pulverization.
Measurement of specific surface area by the BET method also
revealed that it was 40 m.sup.2/g.
[0091] (Production of Cerium Oxide Slurry)
[0092] 1 kg of the cerium oxide particles produced in the above, 23
g of an aqueous ammonium polyacrylate solution (40% by weight) and
8,977 g of deionized water were mixed, and the mixture formed was
subjected to ultrasonic dispersion for 10 minutes with stirring.
The slurry thus obtained was filtered with a 1 .mu.m filter,
followed by further addition of deionized water to obtain a 3% by
weight abrasive. The slurry had a pH of 8.5. Particle size
distribution of slurry particles was examined by laser diffraction
(measuring apparatus: MICROPLUS, manufactured by Master Sizer;
refractive index: 1.9285) to find that the median diameter was 290
nm. With regard to maximum particle diameter, particles of 780 nm
or larger were in a content of 0%.
[0093] To examine dispersibility of the slurry and charges of the
slurry particles, the zeta potential of the slurry was measured.
The cerium oxide slurry was put in a measuring cell provided with
platinum electrodes on both sides, and a voltage of 10 V was
applied to both electrodes. Slurry particles having come to have
charges upon application of the voltage move toward the electrode
side having a polarity reverse to that of the charges. The zeta
potential of particles can be determined by determining their
mobility. As a result of the measurement of zeta potential, it was
confirmed that the particles were charged negatively, and showed a
large absolute value of -65 mV, having a good dispersibility.
[0094] (Polishing of Insulating Film Layer)
[0095] A silicon wafer on which an SiO.sub.2 insulating film
produced by TEOS plasma-assisted CVD was formed was set on a holder
provided with a suction pad stuck thereon for attaching the
substrate to be held, and the holder was placed, with its
insulating film side down, on a platen on which a polishing pad
made of porous urethane resin was stuck. A weight was further
placed thereon so as to provide a processing load of 300
g/cm.sup.2. The platen was rotated at 30 rpm for 2 minutes to
polish the insulating film while dropwise adding the above cerium
oxide slurry (solid content: 3% by weight) onto the platen at a
rate of 35 ml/minute.
[0096] After the polishing was completed, the wafer was detached
from the holder and then well rinsed in running water, followed by
further cleaning for 20 minutes using an ultrasonic cleaner. After
the cleaning was completed, the wafer was set on a spin dryer to
remove drops of water, followed by drying for 10 minutes using a
120.degree. C. dryer. Changes in layer thickness before and after
the polishing were measured with a light-interference type layer
thickness measuring device. As the result, it was found that as a
result of this polishing the insulating film was abraded by 400 nm
(polishing rate: 200 nm/minute) and the wafer was in a uniform
thickness over its whole area. The surface of the insulating film
was also observed using an optical microscope, where no evident
scratches were seen.
COMPARATIVE EXAMPLE
[0097] A silicon wafer on which an SiO.sub.2 insulating film
produced by TEOS plasma-assisted CVD was formed in the same manner
as in Examples, was polished using a commercially available silica
slurry (SS225, available from Cabot Corp.). This commercially
available silica slurry is one having a pH of 10.3 and containing
12.5% by weight of SiO.sub.2 particles. The polishing was carried
out under the same conditions as in Examples. As a result,
scratches caused by polishing were not seen, and the insulating
film layer was polished uniformly, but was abraded only by 150 nm
as a result of polishing for 2 minutes (polishing rate: 75
nm/minute).
POSSIBILITY OF INDUSTRIAL APPLICATION
[0098] As described above, the abrasive according to the present
invention can polish the surfaces of polish objects such as
SiO.sub.2 insulating films at a high rate without causing
scratches, and is especially suited for use in the polishing of
given substrates such as semiconductor chips.
* * * * *