U.S. patent application number 08/930916 was filed with the patent office on 2002-02-07 for cerium oxide abrasive for polishing insulating films formed on substrate and methods for using the same.
Invention is credited to HONMA, YOSHIO, KURATA, YASUSHI, MATSUZAWA, JUN, TANNO, KIYOHITO.
Application Number | 20020016060 08/930916 |
Document ID | / |
Family ID | 27581877 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020016060 |
Kind Code |
A1 |
MATSUZAWA, JUN ; et
al. |
February 7, 2002 |
CERIUM OXIDE ABRASIVE FOR POLISHING INSULATING FILMS FORMED ON
SUBSTRATE AND METHODS FOR USING THE SAME
Abstract
The invention relates to an abrasive containing a slurry of the
following cerium oxide grains as dispersed in water: (1) Cerium
oxide grains as obtained by adding hydrogen peroxide to an aqueous
dispersion of cerium carbonate. (2) Cerium oxide grains as obtained
by oxidizing a precipitate, which is formed through addition of
ammonium hydrogencarbonate to an aqueous solution of cerium
nitrate, with hydrogen peroxide. (3) Cerium oxide grains as
obtained by neutralizing or alkalifying an aqueous solution of
cerium ammonium nitrate.
Inventors: |
MATSUZAWA, JUN; (TSUKUBA,
JP) ; KURATA, YASUSHI; (TSUKUBA, JP) ; TANNO,
KIYOHITO; (TOKYO, JP) ; HONMA, YOSHIO; (TOKYO,
JP) |
Correspondence
Address: |
GRIFFIN & SZIPL, PC
SUITE PH-1
2300 NINTH STREET, SOUTH
ARLINGTON
VA
22204
US
|
Family ID: |
27581877 |
Appl. No.: |
08/930916 |
Filed: |
December 30, 1997 |
PCT Filed: |
February 7, 1997 |
PCT NO: |
PCT/JP97/00326 |
Current U.S.
Class: |
438/633 |
Current CPC
Class: |
H01L 2224/73215
20130101; C01F 17/235 20200101; C09K 3/1463 20130101; H01L
2924/12044 20130101; H01L 2924/181 20130101; C01P 2006/12 20130101;
H01L 2224/4826 20130101; H01L 2224/32245 20130101; H01L 2924/12044
20130101; H01L 2924/00 20130101; H01L 2924/181 20130101; H01L
2924/00012 20130101; H01L 2224/73215 20130101; H01L 2224/32245
20130101; H01L 2224/4826 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
438/633 |
International
Class: |
H01L 021/302 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 7, 1996 |
JP |
8-21563 |
Mar 29, 1996 |
JP |
8-77805 |
Mar 29, 1996 |
JP |
8-77806 |
Mar 29, 1996 |
JP |
8-77807 |
Mar 29, 1996 |
JP |
8-77808 |
Mar 29, 1996 |
JP |
8-77809 |
Mar 29, 1996 |
JP |
8-77810 |
Mar 29, 1996 |
JP |
8-77811 |
Mar 29, 1996 |
JP |
8-77812 |
Mar 29, 1996 |
JP |
8-77813 |
Apr 1, 1996 |
JP |
8-78734 |
Claims
What is claimed is:
1. A cerium oxide abrasive for polishing an insulating film formed
on predetermined substrates, which comprises a slurry of cerium
oxide grains as dispersed in water.
2. The cerium oxide abrasive as claimed in claim 1, in which said
cerium oxide grains are obtained by oxidizing a water-insoluble,
trivalent cerium compound as dispersed in water, with an oxidizing
agent.
3. The cerium oxide abrasive as claimed in claim 1, in which said
cerium oxide grains are obtained by oxidizing a water-insoluble
cerium compound as prepared from an aqueous solution of a
water-soluble, tri-valent cerium compound, with an oxidizing
agent.
4. The cerium oxide abrasive as claimed in claim 2 or 3, in which
said oxidizing agent is hydrogen peroxide.
5. The cerium oxide abrasive as claimed in claim 1, in which said
cerium oxide grains are obtained by neutralizing or alkalifying an
aqueous solution of a tri-valent cerium compound.
6. The cerium oxide abrasive as claimed in claim 1, in which said
cerium oxide grains have a specific surface area of not smaller
than 25 m.sup.2/g.
7. The cerium oxide abrasive as claimed in claim 1, in which said
cerium oxide grains have an apparent density as measured in a still
standing method of not larger than 1.30 g/ml.
8. The cerium oxide abrasive as claimed in claim 1, in which said
cerium oxide grains have an apparent density as measured in a
tapping method of not larger than 1.60 g/ml.
9. The cerium oxide abrasive as claimed in claim 1, in which the
powdery X-ray diffraction pattern of said cerium oxide grains gives
a main peak having a half-value width of not smaller than
0.4.degree..
10. The cerium oxide abrasive as claimed in claim 1, in which
primary grains of said cerium oxide grains having a primary grain
size of not larger than 10 nm, as observed through transmitting
electromicroscopy, are not smaller than 90% of the total number of
the grains.
11. The cerium oxide abrasive as claimed in claim 1, in which
primary grains of said cerium oxide grains having a primary grain
size of not larger than 10 nm are not smaller than 90% of the total
number of the grains and secondary grains as formed through
aggregation of said primary grains to have a secondary grain size
of not larger than 1 .mu.m are not smaller than 90% of the total
number of the gains.
12. The cerium oxide abrasive as claimed in claim 1, in which
secondary grains of said cerium oxide grains having a diameter of
not larger than 1 .mu.m are not smaller than 90% of the total
number of the grains and said secondary grains each give an outline
with no edges having an angle of smaller than 120.degree..
13. The cerium oxide abrasive as claimed in claim 1, in which
primary grains of said cerium oxide grains having an aspect ratio
of not larger than 2.0 are not smaller than 90% of the total number
of the grains.
14. The cerium oxide abrasive as claimed in any one of claims 1 to
13, in which said slurry contains a dispersant.
15. The cerium oxide abrasive as claimed in claim 14, in which said
dispersant is at least one selected from water-soluble organic
polymers, water-soluble anionic surfactants, water-soluble nonionic
surfactants, and water-soluble amines.
16. The cerium oxide abrasive as claimed in any one of claims 1 to
13, in which said slurry is an alkaline slurry.
17. The cerium oxide abrasive as claimed in claim 16, in which said
slurry has a pH of from 8 to 12.
18. The cerium oxide abrasive as claimed in any one of claims 1 to
17, in which said slurry comprises not larger than 10 parts by
weight of said cerium oxide grains as dispersed in 100 parts by
weight of an aqueous solvent.
19. A method for producing a cerium oxide abrasive, which comprises
a step of dispersing cerium oxide grains in water to prepare a
slurry.
20. A method for polishing substrates, which comprises a step of
forming an insulating film on a predetermined substrate and a step
of polishing said insulating film with a cerium oxide abrasive
described in any one of claims 1 to 18.
21. The method for polishing substrates as claimed in claim 20, in
which said predetermined substrate is a semiconductor
substrate.
22. The method for polishing substrates as claimed in any of claims
20 and 21, in which said insulating film comprises an insulating
layer containing a compound having an organic group.
23. The method for polishing substrates as claimed in claim 22, in
which said insulating layer containing said compound having said
organic group is formed by applying a coating liquid as prepared
through hydrolysis of an alkoxysilane and an alkylalkoxysilane in
the presence of water and a catalyst in an organic solvent, onto a
substrate, followed by curing it under heat.
24. The method for polishing substrates as claimed in claim 23, in
which a number of Si atoms derived from a siloxane bond and a
number of C atoms derived from an alkyl group have a relationship
as follows: (Number of C atoms)/[(Number of Si atoms)+(Number of C
atoms)].gtoreq.0.1 in said insulating layer containing a compound
having an organic group.
25. The method for polishing substrates as claimed in claim 20, in
which said insulating film comprises a silicon-free, organic
polymer resin layer.
26. A method for polishing substrates, which comprises a step of
forming two or more insulating layers of different in materials
from one another on a predetermined substrate, and a step of
selectively polishing at least one of said insulating layers with a
cerium oxide abrasive of any one of claims 1 to 18.
27. The method for polishing substrates as claimed in claim 26, in
which said insulating film comprises; an insulating film layer
containing a compound having an organic group, which is formed by
applying a coating liquid as prepared through hydrolysis of an
alkoxysilane and an alkylalkoxysilane in the presence of water and
a catalyst in an organic solvent, onto said substrate, followed by
curing it under heat; and an insulating SiO.sub.2 film layer; and
in which said insulating film layer containing said compound having
said organic group is selectively polished with said abrasive.
28. The method for polishing substrates as claimed in claim 26, in
which said polishing is implemented with said cerium oxide abrasive
having a ratio of a polishing speed for a first insulating film
layer to a polishing speed for a second insulating film layer not
smaller than 10.
29. The method for polishing substrates as claimed in claim 27, in
which said polishing is implemented with said cerium oxide abrasive
having a ratio of a polishing speed for the insulating film layer
containing an organic compound to a polishing speed for the
insulating SiO.sub.2 film layer is not smaller than 10.
30. The method for polishing substrates as claimed in any one of
claims 20 to 29, which further comprises a step of washing the
substrate, after the polishing of its Insulating film layer, with a
liquid comprising the following (a) and (b): (a) hydrogen peroxide,
and (b) at least one selected from nitric acid, sulfuric acid,
ammonium carbonate, ammonium carbamate and ammonium
hydrogencarbonate.
31. A method for producing semiconductor chips, which comprises a
step of forming an insulating film that comprises an insulating
layer containing a compound having an organic group, on a
predetermined semiconductor substrate, and a step of polishing said
insulating film layer containing said compound having said organic
group with a cerium oxide abrasive of any one of claims 1 to
18.
32. The method for producing semiconductor chips as claimed in
claim 31, in which said insulating film layer containing said
compound is formed by applying a coating liquid as prepared through
hydrolysis of an alkoxysilane and an alkylalkoxysilane in the
presence of water and a catalyst in an organic solvent, onto said
substrate, followed by curing it under heat.
33. The method for producing semiconductor chips as claimed in
claim 32, in which a number of Si atoms derived from a siloxane
bond and a number of C atoms derived from an alkyl group have a
relationship as follows: (Number of C atoms)/[(Number of Si
atoms)+(Number of C atoms)].gtoreq.0.1
34. A semiconductor chip as produced in the method of any one of
claims 31 to 33.
35. A method for producing semiconductor devices, which comprises
mounting semiconductor chips of claim 34 on a support substrate,
followed by encapsiating said semiconductor chips with a
sealant.
36. A semiconductor device as produced in the method of claim 35.
Description
TECHNICAL FIELD
[0001] The present invention relates to a cerium oxide abrasive, a
method for producing the cerium oxide abrasive, a method for
polishing substrates, a method for producing semiconductor chips, a
semiconductor chip, a method for producing semiconductor devices,
and a semiconductor device.
BACKGROUND ART
[0002] With the recent noticeable increase in the density and the
degree of integration of ultra-LSIs, which requires multi-layered
structures of aluminium wiring and fine wiring patterns, it is
desired to reduce the minimum line width of wiring patterns to be
processed. Therefore, for the interlayer insulating films to be in
those LSIs, required is a flattening technique of flattening their
surfaces with the films filling up in the distance between the
adjacent fine wiring lines with no empty space therebetween.
[0003] In general, such interlayer insulating films which needs to
be flattened are formed through vapor deposition such as plasma CVD
or ECR-CVD, or through coating such as SOG. Of those, SOG comprises
applying a coating liquid that is prepared by hydrolyzing an
alkoxysilane and an alkylalkoxysilane with water and a catalyst in
an organic solvent such as an alcohol, onto a substrate through
spin coating, followed by curing it through heat treatment, and the
thus-coated film is then flattened. For this, for example, mainly
employed is an organic SOG film which contains the organic
component (e.g., alkyl group) remaining therein in order to be
thick without being cracked. The organic SOG film is advantageous
in that its volume is shrunk little when it is cured, that it is
hydrophobic and that its dielectric constant is low. However, the
organic SOG film is not satisfactorily applicable to global
flattening of uneven surfaces caused by complicated sparse and
dense wiring, though being applicable to local flattening of a part
of such uneven surfaces.
[0004] As the material for forming the interlayer insulating films,
silicon-free, organic polymer resins with good insulation
performance and adhesiveness are being tried. For example, a
coating liquid as prepared by dissolving such a silicon-free,
organic polymer resin in an organic solvent such as an alcohol is
applied onto a substrate through spin coating, and thereafter
heated to form an insulating film on the substrate. This method
produces thick insulating films relatively with ease.
[0005] Multi-layered wiring structures are much used in ultra-LSIs
in order to make them have a higher density and a higher degree of
integration. In particular, current logic LSI devices have
four-layered or higher poly-layered structures, in which,
therefore, the difference in surface level is increasing. On the
other hand, the focal depth of resists to be used for patterning of
wiring in those devices is being reduced with the reduction in the
wiring width of the patterns, and such a high difference in surface
level in those fine patterns is problematic. In order to solve this
problem, it is desired to globally flatten the fine patterns. As
one method for this, it is expected to apply to the fine patterns a
chemical mechanical polishing (CMP) technique which has heretofore
been used for polishing Si wafers and which produces a synergistic
effect of the chemical polishing action and the mechanical
polishing action.
[0006] Of insulating films, those formed through CVD could be
relatively easily polished with an abrasive slurry comprising a
dispersion of colloidal silica, which has heretofore been used in
polishing Si wafers. However, CVD is problematic in that grooves
with a high aspect ratio to be between fine lines of wiring
patterns are poorly filled up through CVD, and it is said that CVD
is limitedly applicable to grooves having an aspect ratio of at
most 3 or so. In order to lower the dielectric constant of
insulating films, the introduction of fluorine into the films is
tried, for which, however, there are still outstanding problems in
that the fluorine once introduced into the films is often expelled
therefrom and that the hygroscopicity of the films increases.
[0007] On the other hand, organic SOG films formed through SOG are
advantageous in that even grooves with a high aspect ratio can be
well filled up with the films, and it is said that grooves having
an aspect ratio of 10 or larger could be filled up therewith. In
addition, those organic SOG films have a low dielectric constant of
3 or so in themselves, and the costs for producing the films are
lower than those for producing CVD films. However, when the organic
SOG films are polished with a colloidal silica-containing abrasive
such as that mentioned above, they are often scratched. If they are
polished with the abrasive under a mild condition in order to
protect them from being scratched, the polishing speed is greatly
lowered. In addition, even if polished under the same condition,
the polishing speed for the organic SOG films is significantly
lower than that for CVD films. Therefore, if the organic SOG films
are desired to be used in the art as they are, their costs shall be
too high, resulting in that their use in the art is impracticable.
Given that situation, it is desired to develop an abrasive capable
of polishing those organic SOG films at a high speed.
[0008] On the other hand, organic polymer resin films can form
thick films having a thickness of 10 .mu.m or larger in one-pass
coating, and it is considered that the films will be effectively
usable in global flattening of fine patterns. Those films have a
low dielectric constant of 3 or so in themselves, and their
dielectric constant may be reduced more if fluorine is introduced
thereinto. Acrylate polymer films can be formed with UV rays
without being heated. However, since the hardness of those organic
polymer resin films is much lower than that of CVD films and
organic SOG films, the organic polymer resin films are scratched if
polished with a colloidal silica-containing abrasive such as that
mentioned above. In order to protect the films from being
scratched, if the polishing condition is made mild to such a degree
that the films are not scratched, the films could not almost be
polished under such a mild condition. Therefore, it is desired to
develop an abrasive capable of polishing the organic polymer resin
films without scratching them.
DISCLOSURE OF THE INVENTION
[0009] The present invention is to provide a cerium oxide abrasive
favorably used for polishing insulating films such as organic SOG
films and organic polymer resin films which have a low dielectric
constant and can be globally flattened and with which even grooves
between fine wiring lines can be filled up; a method for producing
the cerium oxide abrasive; a method for polishing substrates using
the cerium oxide abrasive; a method for producing semiconductor
chips using the polishing method; a semiconductor chip; a method
for producing semiconductor devices; and a semiconductor
device.
[0010] Specifically, the invention provides a cerium oxide abrasive
for polishing an insulating film formed on a predetermined
substrate, which comprises a slurry of cerium oxide grains
dispersed in water. Desirably, this slurry comprises 100 parts by
weight of a water solvent and not larger than 10 parts by weight of
cerium oxide grains dispersed in the solvent. The invention also
provides a method for producing the cerium oxide abrasive, which
comprises a step of dispersing cerium oxide grains in water to
prepare a slurry.
[0011] The cerium oxide grains to be used herein are desirably at
least any of the following (1) to (11).
[0012] (1) Cerium oxide grains as obtained by oxidizing a
water-insoluble, tri-valent cerium compound as dispersed in water,
with an oxidizing agent.
[0013] (2) Cerium oxide grains as obtained by oxidizing a
water-insoluble cerium compound, which is obtained from an aqueous
solution of a water-soluble, tri-valent cerium compound, with an
oxidizing agent.
[0014] For those (1) and (2), the oxidizing agent is preferably
hydrogen peroxide.
[0015] (3) Cerium oxide grains as obtained by neutralizing or
alkalifying an aqueous solution of a tetra-valent cerium
compound.
[0016] (4) Cerium oxide grains having a specific surface area of
not smaller than 25 m.sup.2/g.
[0017] (5) Cerium oxide grains having an apparent density as
measured in a still standing method of not larger than 1.30
g/ml.
[0018] (6) Cerium oxide grains having an apparent density as
measured in a tapping method of not larger than 1.60 g/ml.
[0019] (7) Cerium oxide grains of which the powdery X-ray
diffraction pattern gives a main peak having a half-value width of
not smaller than 0.4.
[0020] (8) Cerium oxide grains of which the primary grains having a
primary grain size of not larger than 10 nm, as observed through
transmitting electromicroscopy, are not smaller than 90% of the
total number of the grains.
[0021] (9) Cerium oxide grains of which the primary grains having a
primary grain size of not larger than 10 nm are not smaller than
90% of the total number of the grains and the secondary grains as
formed through aggregation of the primary grains to have a
secondary grain size of not larger than 1 .mu.m are not smaller
than 90% of the total number of the grains.
[0022] (10) Cerium oxide grains of which the secondary grains
having a diameter of not larger than 1 .mu.m are not smaller than
90% of the total number of the grains and in which the secondary
grains each give an outline with no edges having an angle of
smaller than 120.degree..
[0023] (11) Cerium oxide grains of which the primary grains having
an aspect ratio of not larger than 2.0 are not smaller than 90% of
the total number of the grains.
[0024] Preferably, the slurry contains a dispersant. The dispersant
may be at least one selected from, for example, water-soluble
organic polymers, water-soluble anionic surfactants, water-soluble
nonionic surfactants and water-soluble amines. Preferably, the
slurry is alkaline, especially preferably having a pH of from 8 to
12.
[0025] The present invention further provides a method for
polishing substrates, which comprises a step of forming an
insulating film on a predetermined substrate followed by polishing
the insulating film with the cerium oxide abrasive mentioned above.
This polishing method is especially suitable for polishing
insulating layers of semiconductor substrates. The invention still
further provides a method for producing semiconductor chips, which
comprises a step of forming an insulating film that comprises an
insulating layer containing a compound having an organic group on a
semiconductor substrate, followed by polishing the insulating layer
containing a compound having an organic group with the cerium oxide
abrasive mentioned above, and provides the semiconductor chips as
produced by the method. The invention still further provides a
method for producing semiconductor devices, which comprises a step
of mounting the semiconductor chips on a support substrate followed
by encupslating the semiconductor chips with a sealant, and
provides the semiconductor devices as produced by the method.
[0026] The insulating film may be either a single-layered one or a
multi-layered one comprising two or more insulating layers. In the
latter multi-layered insulating film, at least one of those plural
insulating layers shall be selectively polished with the cerium
oxide abrasive mentioned above.
[0027] Preferably, the multi-layered insulating film composed of
such a plurality of insulating layers comprises an insulating layer
containing a organic compound having an organic group. The
insulating layer containing a compound having an organic group may
be formed, for example, by applying a coating liquid, which is
obtained by hydrolyzing an alkoxysilane and an aikylaikoxysilane in
the presence of water and a catalyst in an organic solvent, onto a
substrate, followed by curing it under heat. It is desirable that
the insulating film comprises this insulating layer as formed
through thermal curing of the hydrolysate, and an insulating layer
comprising SiO.sub.2. The cerium oxide abrasive of the invention
can selectively polish the insulating layer comprising a compound
having an organic group.
[0028] It is preferable that the number of the Si atoms derived
from a siloxane bond and the number of the C atoms derived from an
alkyl group have the relationship as follows:
(Number of C atoms)/[(Number of Si atoms)+(Number of C
atoms)].gtoreq.0.1
[0029] in this insulating layer comprising a compound having an
organic group.
[0030] A silicon-free, organic polymer resin layer may be used as
the layer in the multi-layered insulating film.
[0031] The present invention provides a method for polishing a
substrate in which the insulating film is polished with the cerium
oxide abrasive, and the ratio of the polishing speed for the first
insulating layer to that for the second insulating layer is not
smaller than 10 when the substrate has thereon a multi-layered
insulating film comprising two or more insulating layers. In this,
the first insulating layer and the second insulating layer are, for
example, the insulating layer comprising a compound having an
organic group and the SiO.sub.2 insulating layer, respectively.
[0032] Preferably, the substrate-polishing method of the invention
comprises an additional step of washing the substrate, of which the
insulating layer has been polished, with a liquid comprising at
least one selected from a mixture of hydrogen peroxide and nitric
acid, and sulfuric acid, ammonium carbonate, ammonium carbamate and
ammonium hydrogencarbonate.
[0033] In general, cerium oxide is obtained by baking a cerium
compound (e.g., hydroxide, carbonate, sulfate, oxalate, etc.),
which is separated and purified from typical rare earth minerals
such as bastnaesite and mosanite. Where organic SOG films are
polished with the cerium oxide abrasive, if cerium oxide of the
abrasive has a too high degree of crystallinity, the polishing
speed with the abrasive is often lowered. Therefore, the cerium
oxide grains for use in the invention shall be prepared without too
much increasing their crystallinity. In addition, since the
abrasive is used for polishing semiconductor chips, it is desirable
that the alkali metal content and the halogen content of the
abrasive are controlled to be not larger than 1 ppm in order to
prevent any undesirable introduction of impurities into the
polished chips.
[0034] To prepare the cerium oxide grains in the invention,
preferably employed are the following methods:
[0035] (1) A method starting from a water-insoluble, tri-valent
cerium compound, in which the compound is dispersed in water and an
oxidizing agent is dropwise added thereto thereby oxidizing the
compound, while it is solid, to obtain tetra-valent cerium oxide
grains. (2) A method starting from a water-soluble, tri-valent
cerium compound, in which ammonium hydrogencarbonate or the like is
added to an aqueous solution comprising the cerium compound to give
a water-insoluble cerium compound (as a precipitate) and an
oxidizing agent is then dropwise added thereto thereby oxidizing
the resulting water-insoluble cerium compound, while it is solid,
to obtain tetra-valent cerium oxide grains. (3) A method starting
from a tetra-valent cerium salt, in which aqueous ammonia is added
to an aqueous solution of the cerium salt thereby neutralizing or
alkalifying the solution to give tetra-valent cerium oxide
grains.
[0036] The water-insoluble, tri-valent cerium compound to be used
herein is not specifically defined, including, for example,
water-insoluble cerium salts such as cerium carbonate, cerium
hydroxide, cerium oxalate and cerium acetate or the like. The
water-insoluble, tri-valent cerium compound may be dispersed in
water by any means, for example, using ordinary stirrers, or using
homogenizers, ultrasonic dispersing machines or ball mills. Since
it is preferable to finely disperse the grains of the compound for
facilitating the subsequent oxidization of the grains, the
dispersion is desirably effected using ball mills. The
concentration of the water-insoluble, trl-valent cerium compound is
not specifically defined, but is preferably from 1 to 30% by weight
in view:, of the easiness in handling the resulting dispersion. By
adding an oxidizing agent to the dispersion of the water-insoluble,
tri-valent cerium compound, the cerium compound can be oxidized,
while it is solid, to give tetra-valent cerium oxide grains. The
oxidizing agent to be used herein includes, for example, nitrates
such as potassium nitrate; permanganates such as potassium
permanganate; chromates such as potassium chromate; and hydrogen
peroxide, halogens, and ozone. Of those, preferred is hydrogen
peroxide in order to prevent the oxidation from being accompanied
by the introduction of impurities into the oxidized grains. The
amount of the oxidizing agent to be added must be not smaller than
one mol, relative to one mol of the water-insoluble, tri-valent
cerium compound, in order to complete the oxidation, the amount is
preferably from 1 to 10 mols. The processing temperature for the
oxidation is not specifically defined. When a sell-decomposing
oxidizing agent, such as hydrogen peroxide, is used, it is
desirable to start the oxidation at a temperature not lower than
40.degree. C., and to heat at 80.degree. C. or higher in order to
decompose the excess oxidizing agent after the addition of the
entire amount of the oxidizing agent to the reaction system. To
recover the grains as obtained after the oxidation, employable is
any ordinary means such as decantation, filtration or
centrifugation or the like. Preferred is centrifugation as being
able to efficiently separate the oxidized grains within a short
period of time. However, if the reaction system is acidic, the
grains precipitate too slowly and the system is therefore difficult
to centrifuge through solid-liquid separation using ordinary
centrifugers. Therefore, it is preferable to make the system have a
pH of not smaller than 8 by adding thereto any non-metallic
alkaline substance such as ammonia, prior to its centrifugation. In
order to reduce the impurity content of the isolated grains, it is
effective to repeatedly wash the precipitate. The thus-recovered
precipitate of cerium oxide grains may be directly used herein as
it is, but, if desired, it may be dried by a dryer or the like to
remove water therefrom. The drying temperature is not specifically
defined. However, if dried at 420.degree. C. or higher, the cerium
oxide grains shall have an extremely increased degree of
crystallinity. Therefore, it is desired to dry the precipitate at a
temperature as low as possible to be not higher than 420.degree.
C.
[0037] The water-soluble, tri-valent cerium compound is not
specifically defined, including, for example, water-soluble cerium
salts such as cerium nitrate, cerium sulfate and cerium chloride or
the like. The concentration of the compound in its aqueous solution
is not also specifically defined. However, in view of the easiness
in handling the resulting suspension comprising a precipitate of
the water-insoluble cerium compound formed, the concentration is
preferably from 1 to 30% by weight. When an aqueous solution of
ammonium hydrogencarbonate or the like is added to the aqueous
solution of the compound, the solution gives a white precipitate
(of a water-insoluble cerium compound). The concentration of
ammonium hydrogencarbonate to be added must be not smaller than 1.5
mols, relative to one mol of the water-soluble, tri-valent cerium
compound. In order to complete the reaction, the concentration is
preferably from 1.5 to 30 mols. By adding an oxidizing agent to the
resulting dispersion of the precipitate (of a water-insoluble
cerium compound) as formed from the water-soluble, tri-valent
cerium compound, the precipitate can be oxidized, while it is
solid, to give tetra-valent cerium oxide grains. The oxidizing
agent to be used for this may be the same as that for the oxidation
the water-insoluble, tri-valent cerium compound mentioned above.
Preferred is hydrogen peroxide in order to prevent the oxidation
from being accompanied by the introduction of impurities into the
oxidized grains. The amount of the oxidizing agent to be added must
be not smaller than one mol, relative to one mol of the
water-soluble, tri-valent cerium compound. In order to complete the
oxidation, the amount is preferably from 1 to 10 mols. The
processing temperature for the oxidation is not specifically
defined. When a self-decomposing oxidizing agent, such as hydrogen
peroxide, is used, it is desirable to start the oxidation at a
temperature not lower than 40.degree. C., and to heat at 80.degree.
C. or higher in order to decompose the excess oxidizing agent after
the addition of the entire amount of the oxidizing agent to the
reaction system. To recover the grains as obtained after the
oxidation, employable is any ordinary means such as decantation,
filtration or centrifugation or the like. Preferred is
centrifugation as being able to efficiently separate the oxidized
grains within a short period of time. However, if the reaction
system is acidic, the grains precipitate too slowly and the system
is therefore difficult to centrifuge through solid-liquid
separation using ordinary centrifugers. Therefore, it is preferable
to make the system have a pH of not smaller than 8 by adding
thereto any non-metallic alkaline substance such as ammonia, prior
to its centrifugation. In order to reduce the impurity content of
the isolated grains, it is effective to repeatedly wash the
precipitate. The thus-recovered precipitate of cerium oxide grains
may be directly used herein as it is, but, if desired, it may be
dried by a dryer or the like to remove water therefrom. The drying
temperature is not specifically defined. However, if dried at
420.degree. C. or higher, the cerium oxide grains shall have an
extremely increased degree of crystallinity. Therefore, it is
desired to dry the precipitate at a temperature as low as possible
to be not higher than 420.degree. C.
[0038] The tetra-valent cerium compound is not specifically
defined, Including, for example, cerium salts such as cerium
sulfate, cerium ammonium sulfate, and cerium ammonium nitrate or
the like. The concentration of the compound in its aqueous solution
is not also specifically defined. However, in view of the easiness
in handling the resulting suspension comprising a precipitate (of
cerium oxide grains formed), the concentration is preferably from 1
to 30% by weight. The aqueous solution of the cerium compound is
acidic, but can be neutralized or alkalifed by adding aqueous
ammonia or the like thereto to give a white precipitate (of cerium
oxide grains). The amount of aqueous ammonia to be added must be
such that the suspension which is originally acidic is neutralized
with the aqueous ammonia added thereto, and is preferably such that
the suspension is finally alkalifled. For the latter, a little
excess amount of aqueous ammonia may be added to the suspension. To
recover the thus-precipitated grains, employable is any ordinary
means such as decantation, filtration or centrifugation or the
like. Preferred is centrifugation as being able to efficiently
separate the oxidized grains within a short period of time. In
order to reduce the impurity content of the isolated grains, it is
effective to repeatedly wash the precipitate. The thus-recovered
precipitate of cerium oxide grains may be directly used herein as
it is, but, if desired, it may be dried by a dryer or the like to
remove water therefrom. The drying temperature is not specifically
defined. However, if dried at 420.degree. C. or higher, the cerium
oxide grains shall have an extremely increased degree of
crystalilnity. Therefore, it is desired to dry the precipitate at a
temperature as low as possible to be not higher than 420.degree.
C.
[0039] In the present invention, used are cerium oxide grains
having the following physical properties.
[0040] Specifically, the cerium oxide grains for use in the
invention have a specific surface area of not smaller than 25
m.sup.2/g but preferably not larger than 1,000 m.sup.2/g, more
preferably not smaller than 50 m.sup.2/g but not larger than 500
m.sup.2/g. If a slurry comprising cerium oxide grains with a
specific surface area of smaller than 25 m.sup.2/g as dispersed in
water is used, the primary grain size of the grains is too large,
and if an abrasive comprising the slurry is used for polishing
objects, the surfaces of the objects are often scratched. If, on
the other hand, cerium oxide grains with a specific surface area of
larger than 1,000 m.sup.2/g are used, the polishing speed with the
abrasive comprising the grains is extremely low, resulting in that
the abrasive could hardly exhibit its polishing effect. To measure
the specific surface area of those grains, employable is any of
nitrogen absorption method, nitrogen desorption method and mercury
penetration method or the like, and the measuring method is not
specifically defined. However, as being simple, nitrogen absorption
method is preferred.
[0041] In the invention, the cerium oxide grains to be used have an
apparent density as measured in a still standing method of
preferably from 0.80 g/ml to 1.30 g/ml inclusive, more preferably
from 0.90 g/ml to 1.20 g/ml inclusive. If a slurry comprising
cerium oxide grains with an apparent density of larger than 1.30
g/ml as dispersed in water is used, the primary grain size of the
grains is too large, and if an abrasive comprising the slurry is
used for polishing objects, the surfaces of the objects are often
scratched. If, on the other hand, cerium oxide grains with an
apparent density of smaller than 0.80 g/ml are used, the polishing
speed with the abrasive comprising the grains is extremely low,
resulting in that the abrasive could hardly exhibit its polishing
effect.
[0042] To measure the apparent density of those grains, known are
static methods and dynamic methods, and any of which may be
employable herein with no limitation. However, as being simple,
preferred is the still standing method stipulated in JIS
K-5101.
[0043] In the invention, the cerium oxide grains to be used have an
apparent density as measured in a tapping method of preferably from
1.00 g/ml to 1.60 g/ml inclusive, more preferably from 1.05 g/ml to
1.55, g/ml inclusive. If a slurry comprising cerium oxide grains
with an apparent density of larger than 1.6 g/ml as dispersed in
water is used, the primary grain size of the grains is too large,
and if an abrasive comprising the slurry is used for polishing
objects, the surfaces of the objects are often scratched. If, on
the other hand, cerium oxide grains with an apparent density of
smaller than 1.00 g/ml are used, the polishing speed with the
abrasive comprising the grains is extremely low, resulting in that
the abrasive could hardly exhibit its polishing effect.
[0044] To measure the apparent density of those grains, known are
static methods and dynamic methods, and any of which may be
employable herein with no limitation. However, as being simple,
preferred is the tapping method stipulated in JIS K-5101.
[0045] In the invention, the powdery X-ray diffraction pattern of
the cerium oxide grains to be used gives a main peak having a
half-value width of preferably from 0.4.degree. to 5.0.degree.
inclusive, more preferably from 0.5.degree. to 2.0.degree.
inclusive. Within the defined range, the abrasive comprising the
cerium oxide grains exhibits a 10-fold or higher polishing speed in
polishing organic SOG films and organic polymer resin films than in
CVD films (of S102), and is favorable for selectively polishing the
former films. If a slurry comprising cerium oxide grains, of which
the powdery X-ray diffraction pattern gives a main peak having a
half-value width of smaller than 0.4.degree., as dispersed in water
is used, the crystallinity of the grains is too high, and if an
abrasive comprising the slurry is used for polishing objects, the
surfaces of the objects are often scratched. In addition, since the
polishing speed with the abrasive for polishing CVD films is
elevated to be almost comparable to that for polishing organic SOG
films and organic polymer resin films, the abrasive could not
selectively polish only the latter films. If, on the other hand,
cerium oxide grains, of which the powdery X-ray diffraction pattern
gives a half-value width of larger than 5.0.degree., are used, the
polishing speed with the abrasive comprising the grains is
extremely low, resulting in that the abrasive could hardly exhibit
its polishing effect.
[0046] The cerium oxide grains for use in the invention are such
that the primary grains having a primary grain size of not larger
than 10 nm are not smaller than 90% of the total number of the
grains and that the secondary grains as formed through aggregation
of the primary grains to have a secondary grain size of not larger
than 1 .mu.m are not smaller than 90% of the total number of the
grains. The measurement of the grain size of the grains is not
specifically limitted. As being simple, however, employed is
transmitting electromicroscopic observation for the primary grain
size, and scanning electromicroscopic observation or grain size
distribution measurement for the secondary grain size. The cerium
oxide grains failing within the defined range produce good
polishing speed even when their concentration in the slurry
comprising them is low, so that the costs for producing the slurry
comprising them can be reduced. In addition, since the slurry
having such a low concentration of the grains has a low viscosity,
it can be easily fed into polishing devices with preventing the
pipes, through which the slurry is fed into the devices, from being
clogged with the grains. Moreover, since the slurry as dropped down
onto a polishing pad can easily disperse thereon, the wafers on the
pad can be uniformly polished. However, if a slurry comprising
cerium oxide grains, of which the secondary grains as formed
through aggregation of large primary grains with a primary grain
size of larger than 10 nm have a secondary grain size of larger
than 1 .mu.m, as dispersed in water is used, and if an abrasive
comprising the slurry is used for polishing objects, the surfaces
of the objects are often scratched.
[0047] The cerium oxide grains for use in the invention are such
that the primary grains having a primary grain size of not larger
than 10 nm are not smaller than 90% of the total number of the
grains and that the secondary grains as formed through aggregation
of the primary grains to have a secondary grain size of not larger
than 1 .mu.m are not smaller than 90% of the same. The measurement
of the grain size of the grains is not specifically limitted. As
being simple, however, employed is transmitting electromicroscopic
observation for the primary grain size, and scanning
electromicroscopic observation or grain size distribution
measurement for the secondary grain size. The cerium oxide grains
failing within the defined range produce good polishing speed, even
when their concentration in the slurry comprising them is low, so
that the costs for producing the slurry comprising them can be
reduced. In addition, since the slurry having such a low
concentration of the grains has a low viscosity, it can be easily
fed into polishing devices with preventing the pipes, through which
the slurry is fed into the devices, from being clogged with the
grains. Moreover, since the slurry as dropped down onto a polishing
pad can easily disperse thereon, the wafers on the pad can be
uniformly polished. However, if a slurry comprising cerium oxide
grains, of which the secondary grains as formed through aggregation
of large primary grains with a primary grain size of larger than 10
nm have a secondary grain size of larger than 1 .mu.m, as dispersed
in water is used, and if an abrasive comprising the slurry is used
for polishing objects, the surfaces of the objects are often
scratched. If so, in addition, the concentration of the grains in
the slurry for the abrasive must be increased in order to attain
the same polishing speed as above, which is often problematic in
that the costs for producing the slurry are high and that the
viscosity of the slurry is increased.
[0048] The cerium oxide grains for use in the present invention are
such that the secondary grains having a diameter of not larger than
1 .mu.m are not smaller than 90% of the total number of the grains
and that the secondary grains each give an outline with no edges
having an angle of smaller than 120.degree.. The measurement of the
size of the grains is not specifically limitted. As being simple,
however, preferred is scanning electromicroscopic observation or
grain size distribution measurement. The cerium oxide grains
falling within the defined range produce good polishing speed even
when their concentration in the slurry comprising them is low, so
that the costs for producing the slurry comprising them can be
reduced. In addition, since the slurry having such a low
concentration of the grains has a low viscosity, it can be easily
fed into polishing devices with preventing the pipes, through which
the slurry is fed into the devices, from being clogged with the
grains. Moreover, since the slurry as dropped down onto a polishing
pad can easily disperse thereon, the wafers on the pad can be
uniformly polished. However, if a slurry comprising cerium oxide
grains, of which the secondary grains have a secondary grain size
of larger than 1 .mu.m, is used for polishing objects, the surfaces
of the objects are scratched. If so, in addition, the concentration
of the grains in the slurry must be increased in order to attain
the same polishing speed as above, which is often problematic in
that the costs for producing the slurry are high and that the
viscosity of the slurry is increased. Even though the secondary
grains have a secondary grain size of not larger than 1 .mu.m, they
will still often scratch the surfaces of the objects polished
therewith if their outline has edges having an angle of smaller
than 120.degree..
[0049] The cerium oxide grains for use in the invention are such
that the primary grains having an aspect ratio of not larger than
2.0 are not smaller than 90% of the total number of the grains. If
a slurry comprising cerium oxide grains, of which the primary
grains have an aspect ratio of larger than 2.0, is used for
polishing objects, the surfaces of the objects are often scratched.
To determine the aspect ratio, preferably employed is a simple
method of measuring the minor diameter and the major diameter of
each grain through transmitting electromicroscopic observation,
followed by obtaining the ratio of the two.
[0050] To produce the cerium oxide grains having the physical
properties mentioned above, for example, preferably employed is any
of the following methods, which are mentioned hereinabove. However,
those methods are not specifically limitative.
[0051] (1) A method starting from a water-insoluble, tri-valent
cerium compound, in which the compound is dispersed in water and an
oxidizing agent is dropwise added thereto thereby oxidizing the
compound, while it is solid, to obtain tetra-valent cerium oxide
grains.
[0052] (2) A method starting from a water-soluble, tri-valent
cerium compound, in which ammonium hydrogencarbonate or the like is
added to an aqueous solution comprising the cerium compound to give
a water-insoluble cerium compound (as a precipitate) and an
oxidizing agent is then dropwise added thereto thereby oxidizing
the resulting water-insoluble cerium compound, while it is solid,
to obtain tetra-valent cerium oxide grains.
[0053] (3) A method starting from a tetra-valent cerium compound,
in which aqueous ammonia is added to an aqueous solution of the
cerium salt thereby neutralizing or alkalifying the solution to
give tetra-valent cerium oxide grains.
[0054] More preferably, the cerium oxide grains for use in the
invention are provided with two or more of the following
characteristics which have been referred to hereinabove.
[0055] (1) Their specific surface area is not smaller than 25
m.sup.2/g.
[0056] (2) Their apparent density as measured in a still standing
method is not larger than 1.3 g/ml.
[0057] (3) Their apparent density as measured in a tapping method
is not larger than 1.6 g/ml.
[0058] (4) Their powdery X-ray diffraction pattern gives a main
peak having a half-value width of not smaller than 0.4.degree..
[0059] (5) The primary grains that are found to have a primary
grain size of not larger than 20 nm are not smaller than 90% of the
total number of the grains.
[0060] (6) The primary grains having a primary grain size of not
larger than 20 nm are not smaller than 90% of the total number of
the grains, and the secondary grains as formed through aggregation
of the primary grains to have a secondary grain size of not larger
than 1 .mu.m are not smaller than 90% of the total number of
grains.
[0061] (7) The secondary grains having a diameter of not larger
than 1 .mu.m are not smaller than 90% of the total number of the
grains, and the secondary grains each give an outline with no edges
having an angle of smaller than 120.degree..
[0062] (8) The primary grains having an aspect ratio of not larger
than 2.0 are not smaller than 90% of the total number of the
grains.
[0063] The cerium oxide slurry of the invention is obtained by
dispersing a composition comprising water, the cerium oxide grains
and preferably a dispersant. In the slurry, the concentration of
the cerium oxide grains is not specifically defined, but is
preferably between 1 and 30% by weight from the viewpoint of the
easiness in handling the resulting suspension. Preferably, the
cerium oxide grains are dispersed in an aqueous solvent in an
amount of not larger than 10 parts by weight relative to 100 parts
by weight of the aqueous solvent to give the intended slurry.
[0064] The dispersant is preferably a non-metallic one, and
includes, for example, water-soluble organic polymers, such as
acrylic acid polymers and their ammonium salts, methacrylic acid
polymers and their ammonium salts, and polyvinyl alcohol;
water-soluble anionic surfactants such as ammonium lauryl sulfate,
and polyoxyethylene lauryl ether ammonium sulfate; water-soluble
nonionic surfactants such as polyoxyethylene lauryl ether, and
polyethylene glycol monostearate; and water-soluble amines such as
monoethanolamine, and diethanolamine. The amount of the dispersant
to be in the slurry is preferably from 0.1 parts by weight to 100
parts by weight, relative to 100 parts by weight of the cerium
oxide grains, in view of the dispersibility of the grains and of
the ability of the dispersant to prevent the grains from
precipitating in the slurry. More preferably, in order to more
highly disperse the grains in the slurry, the dispersant is put
into the dispersing machine along with the grains prior to starting
the dispersion of the grains in the machine. To disperse the cerium
oxide grains in water, employable is any of ordinary dispersion
method using general stirring machines, and that using homoger,
ultrasonic dispersion machines and ball mill or the like. In order
to disperse the cerium oxide grains to be fine grains of not larger
than 1 .mu.m in size in water, preferably employed are wet
dispersing machines such as ball mills, shaking ball mills,
planetary ball mills, and medium-stirring mills or the like. The
slurry is preferably alkaline. If the alkali degree of the slurry
is desired to be increased, a non-metallic alkaline substance, such
as aqueous ammonia, may be added to the slurry during or after
dispersing it. Preferably, the slurry has a pH of from 8 to 12.
[0065] The slurry of the invention may contain, in addition to the
cerium oxide grains for example, any other oxides and salts of rare
earth metals. Those additives, if any in the slurry, could improve
the characteristics of the slurry, such as its dispersibility,
chemical reactivity, slidability and selectivity. Preferably, the
amount of the additives is not larger than 50% by weight of the
total solid content of the slurry.
[0066] The insulating layer comprising a compound having an organic
group, which is polished with the cerium oxide abrasive of the
invention, can be formed by applying a coating liquid, which is
prepared by hydrolyzing an alkoxysilane and an alkylalkoxysilane in
the presence of water and a catalyst in an organic solvent such as
an alcohol, onto a substrate through spin coating, followed by
curing it under heat.
[0067] The alkoxysilane includes, for example, monomers such as
tetramethoxysilane, tetraethoxysilane and tetrapropoxysilane, and
their oligomers. These can be used herein either singly or as
combined. The alkylaikoxysilane includes, for example,
methyltrimethoxysilane, phenyltrimethoxysilane,
dimethyidimethoxysilane, diphenyidimethoxysilane,
amlnopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane,
3-methacryloxypropyltrimethoxysilane, and vinyltrimethoxysilane.
These can be used herein either singly or as combined. Apart from
these, also employable herein are alkoxysilanes and
alkylalkoxysilanes with fluorine as bonded to Si, such as
fluorotrimethoxysilane and fluoromethyidimethoxysilane;
alkylalkoxysilanes of which at least a part of the alkyl moiety is
fluorinated, such as trifluoromethyltrimethoxysila- ne, and
trifluoromethylmethyidimethoxysilane; and alkoxysilanes and
alkylalkoxysilanes with fluorine as bonded to Si. These can be used
herein either singly or as combined. Preferably, the ratio of the
amount of alkoxysilane to the amount of alkylalkoxysilane is to
satisfy the following condition:
(number of C atoms)/(number of Si atoms+number of C
atoms).gtoreq.0.1
[0068] in which the number of Si atoms and that of C atoms are
derived from the siloxane bonds and the alkyl groups, respectively,
in the insulating layer as formed from the coating liquid. If the
ratio is smaller than 0.1, the film of the insulating layer formed
is cracked, resulting in the defect such as a loss of film or
lowering of the insulating performance.
[0069] The organic solvent includes, for example, monoalcohols such
as methyl alcohol, and ethyl alcohol or the like; their ethers and
asters; polyalcohols such as glycerin, and ethylene glycol or the
like; their ethers and asters; and ketones such as acetone, and
methyl ethyl ketone or the like. These can be used herein either
singly or as combined. The catalyst may be any acid or alkali for
hydrolysis, including, for example, inorganic acids such as
hydrochloric acid, nitric acid, and phosphoric acid; organic acids
such as acetic acid, and maleic acid or the like; their anhydrides
and derivatives; and alkalis such as sodium hydroxide, ammonia, and
methylamine or the like.
[0070] The amount of water to be in the hydrolyzing system is
preferably smaller than 75% relative to 100% of the alkoxy group in
the alkoxysilane and alkylalkoxysilane. If it is not smaller than
75% the alkoxysilane and alkylalkoxysilane are hydrolyzed too
greatly, whereby the coating liquid formed is gelled or becomes
cloudy. The amount of the catalyst to be added to the hydrolyzing
system is preferably from 0.1 parts by weight to 5 parts by weight,
relative to 100 parts by weight of the alkoxysilane and
alkylalkoxysilane. If it is smaller than 0.1 parts by weight, the
alkoxysilane and alkylalkoxysilane are hydrolyzed insufficiently so
that the coating liquid could not form a film. On the other hand,
however, if it is larger than 5 parts by weight, the alkoxysilane
and alkylalkoxysilane are hydrolyzed too greatly, whereby the
coating liquid formed is gelled. The amount of the alkoxysilane and
alkylalkoxysilane is preferably between 1 part by weight and 40
parts by weight relative to 100 parts by weight of the organic
solvent used. If the amount of the alkoxysilane and
alkylalkoxysilane is smaller than 1 part by weight, the coating
liquid could not form a film, if, on the other hand, it is larger
than 40 parts by weight, the coating liquid could hardly form a
uniform film. The reaction temperature at which the hydrolysate is
processed to have an increased molecular weight is not specifically
defined, but is preferably not higher than the boiling point of the
organic solvent used. In order to suitably control the molecular
weight of the thus-processed hydrolysate, the reaction temperature
is preferably between 5.degree. C. and 70.degree. C. The reaction
time for the hydrolysis is not also specifically defined. The
hydrolysis may be stopped after the molecular weight of the
hydrolysate formed has reached the predetermined one. The
measurement of the molecular weight of the hydrolysate is not
specifically defined. However, as being simple, preferably employed
is liquid chromatography for the measurement.
[0071] The insulating layer-forming material comprising those four
components may be prepared as follows: First, a predetermined
amount of an alkoxysilane and a predetermined amount of an
alkylalkoxysilane are dispersed in an organic solvent, to which are
added water and a catalyst and stirred for a while, and thereafter
these are reacted at room temperature or under heat to give a
hydrolysate having an increased molecular weight.
[0072] The insulating layer-forming material as prepared in the
manner mentioned above is applied onto a predetermined
semiconductor substrate, such as a semiconductor substrate in the
step that circuit elements and wiring patterns are formed on (e.g.,
a semiconductor substrate on which predetermined circuit elements
such as IC circuits are formed and then aluminium wiring patterns
are formed thereon), or a semiconductor substrate in the step that
circuit elements are formed, or the like, then dried to remove the
organic solvent, and thereafter cured under heat at 100.degree. C.
or higher to form an insulating layer on the substrate. In FIG. 1,
11 is an Si wafer having thereon a predetermined circuit element
such as an IC element; 12 is an aluminium wiring pattern; 13 is a
CVD-SiO.sub.2 film (TEOS film); and 14 is an insulating layer
containing a compound having an organic group. Preferably, the
insulating layer is thicker than the wirings. For example, the
thickness of the insulating layer is not smaller than 1.2 times
that of the wirings.
[0073] The semiconductor substrate is not specifically defined,
Including, for example, Si wafer and GaAs wafer or the like. The
coating method is not also specifically defined. For example, the
coating liquid may be applied onto the substrate through spin
coating, spraying, or dip coating. The drying temperature is not
also specifically defined, but is preferably between 100.degree. C.
and 300.degree. C. in order to promote the vaporization of the
organic solvent. The thermal curing temperature is not also
specifically defined, and may be 300.degree. C. or higher. However,
depending on the substrate to be used, the uppermost temperature
for the curing is limited. For example, for the substrate having
thereon an aluminium wiring, it is preferable that the insulating
layer is formed through curing at a temperature not higher than
500.degree. C. The thermal curing time is not also specifically
defined. When the physical properties of the cured film have been
mostly equilibrated, the heating is stopped. To determine the
condition of the cured film for which the heating is stopped, there
is no specific limitation. For example, preferred is a simple
method of measuring the surface hardness and the thickness of the
cured film formed or the like. The atmosphere for the thermal
curing is not also specifically defined. Preferably, however, an
inert gas such as nitrogen or argon is introduced into the curing
system in order to minimize the removal of the alkyl group from the
alkylalkoxysilane being heated.
[0074] The insulating layer thus formed on the predetermined
semiconductor substrate, such as a semiconductor substrate at a
stage where substrate circuit component element and wiring patterns
are formed on it, or a semiconductor substrate at a stage where
wiring patterns are formed on it, are polished with the cerium
oxide slurry of the invention, whereby the uneven surface of the
insulating layer is flattened and, after all, the entire surface of
the resulting semiconductor device is flattened, as in FIG. 2.
[0075] As the polishing device, herein employable is any ordinary
one which comprises a holder to hold a semiconductor substrate to
be polished, and a surface plate with a pad of abrasive cloth
attached thereto (the surface plate is provided with a motor or the
like of which the number of revolution is variable). As the pad,
ordinary nonwoven cloth, expanded polyurethane, porous fluorine
resin etc. may be used and there is no special limitations.
Preferably, the pad is worked to have grooves capable of keeping
therein the slurry of the invention. The polishing condition is not
specifically defined, but the surface plate is preferably rotated
at a low rotating speed of not larger than 100 rpm in order that
the semiconductor substrate being polished is not detached from the
device. The pressure to be applied to the semiconductor substrate
being polished is preferably not larger than 1 kg/cm.sup.2 in order
that the polished surface of semiconductor substrate is not
scratched. During the polishing operation, the slurry is
continuously fed to the pad using a pump or the like. The amount of
the slurry to be fed is not specifically defined, but it is
desirable that the surface of the pad is always covered with the
slurry. For this, especially preferably, the amount of the slurry
to be fed to the unit area of the surface plate is, for example,
not smaller than 25 ml/min for a 18-inch surface plate. If the
amount is smaller than 25 ml/min in that case, the substrate could
not be polished to a sufficient degree of polishing speed. If so,
in addition, the slurry is insufficiently dispersed so that the
substrate could not be polished uniformly. Moreover, if so, the
substrate is too greatly influenced by mechanical polishing with
the pad, resulting in that the CVD film on the substrate will be
greatly polished, so that the selectivity of the slurry abrasive of
the invention, which is represented by the ratio of the polishing
speed for the organic SOG film to that for the CVD film, is
lowered, and therefore the intended selective polishing with the
slurry abrasive could not be attained.
[0076] After having been thus polished, the semiconductor substrate
is well washed with running water. Next, in order to remove the
cerium oxide grains still adhering onto the surface of the
substrate, the substrate is dipped in a liquid comprising (a)
hydrogen peroxide, and (b) at least one selected from nitric acid,
sulfuric acid, ammonium carbonate, ammonium carbamate and ammonium
hydrogencarbonate, and thereafter again washed with water, and then
dried, A mixture of two or more different liquids each comprising
(a) and (b) may be used, if desired,
[0077] The dipping time is not specifically defined, and the
dipping treatment may be finished after the bubbles to be formed as
a result of the dissolution of the remaining cerium oxide grains
are no more formed, The dipping temperature is not also
specifically defined. However, when aqueous hydrogen peroxide or
the like that has self-decomposability is used, the dipping therein
is effected preferably at a temperature not higher than 40.degree.
C. After the final washing with water, it is desirable that water
drops adhering onto the semiconductor substrate are removed, using
a spin drier or the like, and thereafter the substrate is
dried.
[0078] Over the thus-flattened insulating layer, a second aluminium
wiring layer is formed, and an additional insulating layer is
formed in the space with no wirings and on the wirings to thereby
entirely cover the surface of the wirings, in the same manner as
previously. Then, the insulating layer thus formed is polished with
the cerium oxide slurry of the invention in the same manner as
previously to flatten the uneven surface of the insulating layer,
thereby after all flattening the entire surface of the resulting
semiconductor substrate. This step is repeated predetermined times
to finally obtain the intended semiconductor chips.
[0079] Using the cerium oxide abrasive of the invention,
silicone-free, organic polymer resin layers formed on substrates,
for example, on semiconductor substrates can be polished.
[0080] The silicon-free, organic polymer resins include, for
example, thermosetting resins such as phenolic resins, epoxy
resins, unsaturated polyesters, polyesters, polyimides, and
polyamidimides; and thermoplastic resins such as polyamides,
polyurethanes, polyethylenes, ethylene-vinyl acetate copolymers,
polypropylenes, polystyrenes, ABS resins, AS resins, polymethyl
methacrylates, polyvinyl chlorides, polyvinyl formalins,
polytetrafluoroethylenes, and polytrifluorochloroethylenes. Of
those, preferred are fluorine resins such as
polytetrafluoroethylenes and polytrifluorochloroethylenes, since
the substrates having thereon the films of those resins may have a
lowered dielectric constant. Also preferred are polyamidimide
resins and polyimide resins, since the films of those resins have
good heat resistance. However, the resins for the films to be
polished with the abrasive of the invention are not specifically
defined.
[0081] The insulating layer-forming material comprising such a
silicon-free, organic polymer resin may be prepared as follows:
Where the material comprising a thermosetting resin is prepared,
monomers and/or low-molecular-weight polymers for the resin are
dissolved in an organic solvent such as an alcohol or the like
mentioned above to form a coating liquid for the intended
insulating layer. In order to enhance the curability of the layer
to be formed, any ordinary curing agent, curing promoter and
catalyst may be added to the coating liquid. Where the material
comprising a thermoplastic resin is prepared, the resin is
dissolved in an organic solvent such as an alcohol or the like
mentioned above to form a coating liquid for the intended
insulating layer. Preferably, 10 parts by weight of the organic
polymer resin is combined with from 0 to 900 parts by weight of the
organic solvent. If the amount of the organic solvent is over 900
parts by weight, the coating liquid could hardly form the intended
insulating layer film.
[0082] Using the cerium oxide abrasive of the invention, at least
one of two or more kinds of insulating layers different in material
from one another formed on a substrate, for example, on a
semiconductor substrate can be selectively polished.
[0083] Preferably, those two or more kind of insulating layers
comprise an insulating layer as formed by applying a coating
liquid, which is formed by hydrolyzing an alkoxysilane and an
alkylalkoxysilane in the presence of water and a catalyst in an
organic solvent, onto a substrate followed by curing it under heat;
and an insulating SiO.sub.2 layer. With the cerium oxide abrasive
of the invention, only the former insulating layer can be
selectively polished.
[0084] The substrate on which such two or more kind of insulating
layers different in material from one another are formed includes,
for example, wiring boards having an insulating SiO.sub.2 film or
the like formed thereon; optical glass articles such as photomasks,
lenses and prisms or the like; optical integrated circuits,
photo-switching elements and optical wave guides composed of glass
and crystalline materials; edges of optical fibers; optical single
crystals such as scintillators or the like; solid laser single
crystals; LED sapphire substrates for blue lasers; semiconductive
single crystals of SiC, GaP, GaAs or the like; glass substrates for
magnetic discs; and magnetic heads.
[0085] Where at least one of two or more kind of insulating layers
different in material from one another formed on a substrates such
as semiconductor substrates or the like is selectively polished
with the cerium oxide abrasive of the invention, it is desirable
that the ratio of the polishing speed with the abrasive for the
first insulating layer (for example, an insulating layer containing
a compound having an organic group) to that therewith for the
second insulating layer (for example, an insulating SiO.sub.2
layer) is not smaller than 10. With the ratio within the defined
range, the selective polishing of only the first insulating layer
with the abrasive can be favorably attained.
[0086] FIG. 3 shows one embodiment of the semiconductor device of
the invention, which has, on a support substrate, a semiconductor
chip as produced by polishing its insulating film with the abrasive
of the invention, and in which the semiconductor chip is
encupslated with a sealant. The semiconductor device is not limited
to only the lead-on-chip (LOC) type one, as in FIG. 3, but may be
any other ordinary one including, for example, chip-on-lead (COL)
type ones and even those with chips as mounted on a die pad. As the
sealant, ordinary epoxy resin may be used. In FIG. 3, 1 is a
bonding material; 2 is a semiconductor chip as produced by
polishing its insulating film with the abrasive of the invention; 3
is a lead frame; 4 is a wire; and 5 is a sealant.
[0087] Using the abrasive of the invention, insulating films such
as organic SOG films, organic polymer resin films or the like can
be polished at a high speed without scratching the polished
surfaces.
[0088] Where a substrate having therein a plurality of layers is
polished according to the polishing method of the invention, the
difference in surface level is almost completely removed throughout
the entire surface of the polished substrate. Therefore, the
polishing method of the invention is satisfactorily applied to any
and every substrate having fine wirings thereon, by which,
therefore, multi-layered wirings can be realized for high-density
and large-scale integration circuits. In addition, since insulating
films of organic SOG films or organic polymer resin films can be
used, capability of filling the space between fine wiring lines and
lowering of dielectric constant can be achieved at the same
time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0089] FIG. 1 is a cross-sectional view showing a semiconductor
substrate, of which the Si wafer having thereon a circuit element,
an aluminium wiring and a CVD-SiO.sub.2 film is coated with an
insulating layer containing a compound having an organic group.
[0090] FIG. 2 is a cross-sectional view of the semiconductor
substrate, in which the insulating layer has been polished.
[0091] FIG. 3 is a cross-sectional view showing a semiconductor
device which has a semiconductor chip as produced by polishing its
insulating film with the abrasive of the invention mounted on a
support substrate.
BEST MODES OF CARRYING OUT THE INVENTION
[0092] Now, various examples of the invention are mentioned
below.
EXAMPLE 1
[0093] Formation of Cerium Oxide Grains, 1-1:
[0094] 50 g of cerium carbonate was added to 450 g of delonized
water, and dispersed therein with a planetary ball mill at 2800 rpm
for 15 minutes to obtain a white, cerium carbonate slurry. With
stirring the slurry, 29.2 g of aqueous hydrogen peroxide (about
35%) was dropwise added thereto, reacted for 1 hour with further
stirring, and thereafter heated up to 90.degree. C. In a water
bath. After having been still stirred for 1 hour at 90.degree. C.,
this was cooled to room temperature, separated solid from liquid by
a centrifuger, and then dried in a drier at 120.degree. C. for 24
hours to obtain 30 g of a white powder. From its X-ray diffraction
pattern, this white powder was identified as cerium oxide.
[0095] Formation of Cerium Oxide Grains, 1-2:
[0096] Fifty grams of cerium nitrate was added to 500 g of
deionized water, and well mixed. Then, with stirring the resulting
mixture, an aqueous solution as prepared by dissolving 75 g of
ammonium hydrogencarbonate in 400 g of distilled water was dropwise
added thereto, and reacted as they were for 1 hour at room
temperature to give a white precipitate. This white precipitate was
separated through centrifugation at 3000 rpm for 10 minutes for
solid-liquid separation by a centrifuger. This was again put into
500 g of deionized water and well dispersed therein. Then, 60.9 g
of aqueous hydrogen peroxide (about 35%) was dropwise added to the
resulting dispersion and reacted for 1 hour with still stirring it.
Next, this was heated up to 90.degree. C. in a water bath. After
having been still stirred for 1 hour at 90.degree. C., this was
cooled to room temperature, separated the solid from separation by
a centrifuger, and then dried in a drier at 120.degree. C. for 24
hours to obtain 20 g of a white powder. From its X-ray diffraction
pattern, this white powder was identified as cerium oxide.
[0097] Formation of Cerium Oxide Grains, 1-3:
[0098] Fifty grams of cerium ammonium nitrate was added to 500 g of
deionized water, and well mixed. With stirring the resulting
mixture, an aqueous solution as prepared by dissolving 27 g of
aqueous ammonia in 500 g of distilled water was dropwise added
thereto (pH 10), and reacted as they were for 1 hour at room
temperature to give a white precipitate.
[0099] This white precipitate was separated through centrifugation
at 3000 rpm for 10 minutes for solid-liquid separation, and then
dried in a drier at 120.degree. C. for 24 hours to obtain 15 g of a
white powder. From its X-ray diffraction pattern, this white powder
was identified as cerium oxide.
[0100] Formation of Cerium Oxide Slurries:
[0101] Ten grams of each of those three cerium oxide powders was
dispersed in 100 g of deionized water, to which was added 1 g of
ammonium polyacrylate, and dispersed with a planetary ball mill
(P-5 Model, manufactured by Flitche) at 2800 rpm for 30 minutes.
Thus were obtained three milky white cerium oxide slurries. Using a
Coulter counter (N-4 Model, manufactured by Nikka-ki), the grain
size distribution of each slurry was measured. It was found that
the mean grain size of the grains in each slurry was small to be
176 nm, and that each slurry was a mono-dispersed one having a
relatively narrow grain size distribution.
[0102] Formation of Insulating Layer:
[0103] A 4-inch Si wafer having thereon an IC circuit and an
aluminium wiring in that order was set in a spin coater, onto which
was applied 5 ml of a coating liquid that had been prepared by
hydrolyzing tetramethoxysilane (4 mols) and methyltrimethoxysilane
(1 mol) with water and nitric acid in isopropyl alcohol. Then, this
was rotated at 2,500 rpm for 30 seconds, and dried on a hot plate
at 250.degree. C. for 1 minute. This wafer was set in a heating
furnace and baked therein at 450.degree. C. for 30 minutes to
thereby form an insulating layer thereon.
[0104] Polishing of Insulating Layer:
[0105] The Si wafer having the insulating layer formed thereon was
set on a holder provided with a suction pad, via which the Si wafer
was held by the holder, and the holder was set on a surface plate
having an abrasive pad of a porous fluorine resin attached thereto
(the surface plate was provided with a motor or the like of which
the number of revolution is variable), with the side of the Si
wafer being facedown. A weight of 5 kg was put on the holder. In
that condition, the surface plate was rotated at 50 rpm for 4
minutes, while each of the three cerium oxide slurries prepared
above was dropped thereonto, whereby the insulating film existing
on the Si wafer was polished. After having been thus polished, the
Si wafer was released from the holder, then well washed with
running water, and thereafter put into a beaker filled with nitric
acid. This beaker was set in an ultrasonic washer, in which the Si
wafer was washed for 10 minutes. After having confirmed that the
bubbling resulting from the dissolution of cerium oxide stopped,
the Si wafer was taken out of the beaker, water drops existing on
its surface were removed with a spin drier, and thereafter the Si
wafer thus processed was dried in a drier at 120.degree. C. for 10
minutes. Using an automatic ellipsometer, the change in the film
thickness of the Si wafer before and after polishing it was
determined, which verified that about 4,000 .ANG. of the insulating
layer of the Si wafer was cut off through the polishing, resulting
in that the thickness of the thus-polished insulating layer was
almost completely unified throughout the entire surface of the Si
wafer. The thus-polished Si wafer was cut, and its cross section
was observed with SEM, which verified that the insulating layer
well covered the Si wafer with no defects such as empty pores even
in the grooves between the wiring lines having a width of 0.1 .mu.m
and a depth of 1.0 .mu.m. This process was repeated 6 times in all
to form a 6-layered wiring pattern on the Si wafer, of which the
cross section was observed with SEM, The SEM observation verified
that there was almost no difference in surface level in each layer
throughout the entire surface of the Si wafer substrate and that
the wiring patterns formed were all good and accurate.
COMPARATIVE EXAMPLE 1
[0106] In the same manner as in Example 1, an insulating film layer
was formed on a semiconductor substrate. Without using the cerium
oxide slurry herein, tried was the formation of multi-layered
wiring on the substrate. However, in the samples prepared herein to
have wirings of 3 or more layers, the difference in surface level
was so great that the adjacent upper and lower layers could not
ensure the insulating performance therebetween. It was found that
multi-layered wirings of 3 or more layers could not be formed in
this Comparative Example 1.
[0107] On the other hand, the insulating film layer formed herein
was polished with a colloidal silica slurry with aqueous ammonia
(SS-225, trade name of Cabot). In this, however, only about 400
.ANG. of the layer was polished at 50 rpm for 10 minutes. Thus, it
was found that the performance of the colloidal silica slurry
abrasive was very poor for flattening the entire surface of SI
wafers.
EXAMPLE 2
[0108] Formation of Cerium Oxide Grains, 2-1:
[0109] Fifty frams of cerium carbonate was added to 450 g of
deionized water, and dispersed therein with a planetary ball mill
at 2800 rpm for 15 minutes to obtain a white, cerium carbonate
slurry. With stirring the slurry, 29.2 g of aqueous hydrogen
peroxide (about 35%) was dropwise added thereto, reacted for 1 hour
with further stirring, and thereafter heated up to 90.degree. C. in
a water bath. After having been still stirred for 1 hour at
90.degree. C., this was cooled to room temperature, centrifuged for
solidliquid separation, and then dried in a drier at 120.degree. C.
for 24 hours to obtain 30 g of a white powder. From its X-ray
diffraction pattern, this white powder was identified as cerium
oxide. Its specific surface area was measured through nitrogen
adsorption to be 111 m.sup.2/g.
[0110] Formation of Cerium Oxide Grains, 2-2:
[0111] Fifty grams of cerium nitrate was added to 500 g of
deionized water, and well mixed. Then, with stirring the resulting
mixture, an aqueous solution as prepared by dissolving 75 g of
ammonium hydrogencarbonate in 400 g of distilled water was dropwise
added thereto, and reacted as they were for 1 hour at room
temperature to give a white precipitate. This white precipitate was
separated through centrifugation at 3000 rpm for 10 minutes for
solid-liquid separation by a centrifuger. This was again put into
500 g of deionized water and well dispersed therein. Then, 60.9 g
of aqueous hydrogen peroxide (about 35%) was dropwise added to the
resulting dispersion and reacted for 1 hour with still stirring it.
Next, this was heated up to 90.degree. C. in a water bath. After
having been still stirred for 1 hour at 90.degree. C., this was
cooled to room temperature, separated for the solid from liquid by
a centrifuger, and then dried in a drier at 120.degree. C. for 24
hours to obtain 20 g of a white powder. From its X-ray diffraction
pattern, this white powder was identified as cerium oxide. Its
specific surface area was measured through nitrogen adsorption to
be 112 m.sup.2/g.
[0112] Formation of Cerium Oxide Grains, 2-3:
[0113] Fifty grams of cerium ammonium nitrate was added to 500 g of
deionized water, and well mixed. With stirring the resulting
mixture, an aqueous solution as prepared by dissolving 27 g of
aqueous ammonia in 500 g of distilled water was dropwise added
thereto, and reacted as they were for 1 hour at room temperature to
give a white precipitate. This white precipitate was separated
through centrifugation at 3000 rpm for 10 minutes for solid-liquid
separation by a centrifuger, and then dried in a drier at
120.degree. C. for 24 hours to obtain 15 g of a white powder. From
its X-ray diffraction pattern, this white powder was identified as
cerium oxide. Its specific surface area was measured through
nitrogen adsorption to be 130 m.sup.2/g.
[0114] Formation of Cerium Oxide Slurries:
[0115] Ten grams of each of those three cerium oxide powders was
dispersed in 100 g of deionized water, to which was added 1 g of
ammonium polyacrylate, and dispersed with a planetary ball mill
(P-5 Model, manufactured by Flitche) at 2800 rpm for 30 minutes.
Thus were obtained three milky white cerium oxide slurries. Using a
Coulter counter (N-4 Model, manufactured by Nikka-ki), the grain
size distribution of each slurry was measured. It was found that
the mean grain size of the grains in each slurry was small to be
176 nm, and that each slurry was a mono-dispersed one having a
relatively narrow grain size distribution.
[0116] Formation of Insulating Layer:
[0117] A 4-inch Si wafer having thereon an IC circuit and an
aluminium wiring in that order was processed in the same manner as
in Example 1 to form an insulating layer thereon.
[0118] Polishing of Insulating Layer:
[0119] Using any of the cerium oxide slurries prepared above, the
insulating layer formed on the Si wafer was polished in the same
manner as in Example 1. Using an automatic ellipsometer, the change
in the film thickness of the Si wafer before and after polishing it
was determined, which verified that about 4,000 .ANG. of the
insulating layer of the Si wafer was cut off through the polishing,
resulting in that the thickness of the thus-polished insulating
layer was almost completely unified throughout the entire surface
of the SI wafer. The thus-polished Si wafer was cut, and its cross
section was observed with SEM, which verified that the insulating
layer well covered the Si wafer with no defects such as empty pores
even in the grooves between the wiring lines having a width of 0.1
pm and a depth of 1.0 .mu.m. This process was repeated 6 times in
all to form a 6-layered wiring on the Si wafer, of which the cross
section was observed with SEM. The SEM observation verified that
there was almost no difference in surface level in each layer
throughout the entire surface of the Si wafer substrate and that
the wiring patterns formed were all good and accurate.
COMPARATIVE EXAMPLE 2
[0120] In the same manner as in Example 2, an insulating film layer
was formed on a semiconductor substrate. Without using the cerium
oxide slurry herein, tried was the formation of multi-layered
wirings on the substrate. However, in the samples prepared herein
to have wirings of 3 or more layers, the difference in surface
level was so great that the adjacent upper and lower layers could
not ensure the insulating performance therebetween. It was found
that multi-layered wirings of 3 or more layers could not be formed
in this Comparative Example 2.
[0121] On the other hand, polishing of the insulating film layer
same as mentioned above was tried with a slurry prepared in the
same manner as mentioned above using a commercially-available
cerium oxide grains having a specific surface area of 4 m.sup.2/g.
As a result, about 4,100 .ANG. of the insulating layer was cut off,
which was almost the same as that cut off in Example 2, but the
surface of the insulating layer polished herein was much scratched.
Then, the weight to the holder, which had been 5 kg, was reduced to
1 kg. Using the weight of 1 kg, the polished surface of the
insulating layer was not scratched. In this condition, however,
only about 1000 .ANG. of the layer was cut off even after having
been polished at 50 rpm for 10 minutes. Thus, it was found that the
performance of this slurry was very poor for flattening the entire
surface of Si wafers.
EXAMPLE 3
[0122] Formation of Cerium Oxide Grains, 3-1:
[0123] Fifty grams of cerium carbonate was added to 450 g of
deionized water, and dispersed therein with a planetary ball mill
at 2800 rpm for 15 minutes to obtain a white, cerium carbonate
slurry. With stirring the slurry, 29.2 g of aqueous hydrogen
peroxide (about 35%) was dropwise added thereto, reacted for 1 hour
with further stirring, and thereafter heated up to 90.degree. C. in
a water bath. After having been still stirred for 1 hour at
90.degree. C., this was cooled to room temperature, separated the
solid from liquid by a centrifuger, and then dried in a drier at
120.degree. C. for 24 hours to obtain 30 g of a white powder. From
its X-ray diffraction pattern, this white powder was identified as
cerium oxide. Its apparent density as measured in a still standing
method was 1,07 g/ml.
[0124] Formation of Cerium Oxide Grains, 3-2:
[0125] Fifty grams of cerium nitrate was added to 500 g of
deionized water, and well mixed. Then, with stirring the resulting
mixture, an aqueous solution as prepared by dissolving 75 g of
ammonium hydrogencarbonate in 400 g of distilled water was dropwise
added thereto, and reacted as they were for 1 hour at room
temperature to give a white precipitate. This white precipitate was
separated through centrifugation at 3000 rpm for 10 minutes for
solid-liquid separation by a centrifuger. This was again put into
500 g of deionized water and well dispersed therein. Then, 60.9 g
of aqueous hydrogen peroxide (about 35%) was dropwise added to the
resulting dispersion and reacted for 1 hour with still stirring it.
Next, this was heated up to 90.degree. C. in a water bath. After
having been still stirred for 1 hour at 90.degree. C., this was
cooled to room temperature, separated the solid from liquid by a
centrifuger, and then dried in a drier at 120.degree. C. for 24
hours to obtain 20 g of a white powder. From its X-ray diffraction
pattern, this white powder was identified as cerium oxide. Its
apparent density as measured in a still standing method was 1.11
g/ml.
[0126] Formation of Cerium Oxide Grains, 3-3:
[0127] Fifty grams of cerium ammonium nitrate was added to 500 g of
deionized water, and well mixed. With stirring the resulting
mixture, an aqueous solution as prepared by dissolving 27 g of
aqueous ammonia in 500 g of distilled water was dropwise added
thereto, and reacted as they were for 1 hour at room temperature to
give a white precipitate. This white precipitate was separated
through centrifugation at 3000 rpm for 10 minutes for solid-liquid
separation by a centrifuger, and then dried in a drier at
120.degree. C. for 24 hours to obtain 15 g of a white powder. From
its X-ray diffraction pattern, this white powder was identified as
cerium oxide. Its apparent density as measured in a still standing
method was 1.08 g/ml.
[0128] Formation of Cerium Oxide Slurries:
[0129] Ten grams of each of those three cerium oxide powders was
dispersed in 100 g of deionized water, to which was added 1 g of
ammonium polyacrylate, and dispersed with a planetary ball mill
(P-5 Model, manufactured by FLITCHE) at 2800 rpm for 30 minutes.
Thus were obtained three milky white cerium oxide slurries. Using a
Coulter counter (N-4 Model, manufactured by Nikka-ki), the grain
size distribution of each slurry was measured. It was found that
the mean grain size of the grains in each slurry was small to be
176 nm, and that each slurry was a mono-dispersed one having a
relatively narrow grain size distribution.
[0130] Formation of Insulating Layer:
[0131] A 4-inch Si wafer having thereon an IC circuit and an
aluminium wiring in that order was processed in the same manner as
in Example 1 to form an insulating layer thereon.
[0132] Polishing of Insulating Layer:
[0133] Using any of the cerium oxide slurries prepared above, the
insulating layer formed on the Si wafer was polished in the same
manner as in Example 1. Using an automatic ellilpsometer, the
change in the film thickness of the SI wafer before and after
polishing it was determined, which verified that about 4,000 A of
the insulating layer of the Si wafer was cut off through the
polishing, resulting in that the thickness of the thus-polished
insulating layer was almost completely unified throughout the
entire surface of the Si wafer. The thus-polished Si wafer was cut,
and its cross section was observed with SEM, which verified that
the insulating layer well covered the Si wafer with no defects such
as empty pores even in the grooves between the wiring lines having
a width of 0.1 .mu.m and a depth of 1.0 .mu.m. This process was
repeated 6 times in all to form a 6-layered wiring on the Si wafer,
of which the cross section was observed with SEM. The SEM
observation verified that there was almost no difference in surface
level in each layer throughout the entire surface of the Si wafer
substrate and that the wiring patterns formed were all good and
accurate.
COMPARATIVE EXAMPLE 3
[0134] In the same manner as in Example 3, an insulating film layer
was formed on a semiconductor substrate. Without using the cerium
oxide slurry herein, tried was the formation of multi-layered
wirings on the substrate. However, in the samples prepared herein
to have wirings of 3 or more layers, the difference in surface
level was so great that the adjacent upper and lower layers could
not ensure the insulating performance therebetween. It was found
that multi-layered wirings of 3 or more layers could not be formed
in this Comparative Example 3.
[0135] On the other hand, polishing of the insulating film layer
same as mentioned above was tried with a slurry prepared in the
same manner as mentioned above using a commercially-available
cerium oxide grains having an apparent density as measured in a
still standing method of 1.33 g/ml. As a result, about 4,100 .ANG.
of the insulating layer was cut off, which was almost the same as
that cut off in Example 3, but the surface of the insulating layer
polished herein was much scratched. Then, the weight to the holder,
which had been 5 kg, was reduced to 1 kg. Using the weight of 1 kg,
the polished surface of the insulating layer was not scratched, in
this condition, however, only about 1000 .ANG. of the layer was cut
off even after having been polished at 50 rpm for 10 minutes. Thus,
it was found that the performance of this slurry was very poor for
flattening the entire surface of Si wafers.
EXAMPLE 4
[0136] Formation of Cerium Oxide Grains, 4-1:
[0137] Fifty grams of cerium carbonate was added to 450 g of
deionized water, and dispersed therein with a planetary ball mill
at 2800 rpm for 15 minutes to obtain a white, cerium carbonate
slurry. With stirring the slurry, 29.2 g of aqueous hydrogen
peroxide (about 35%) was dropwise added thereto, reacted for 1 hour
with further stirring, and thereafter heated up to 90.degree. C. in
a water bath. After having been still stirred for 1 hour at
90.degree. C., this was cooled to room temperature, separated the
solid from liquid by a centrifuger, and then dried in a drier at
120.degree. C. for 24 hours to obtain 30 g of a white powder. From
its X-ray diffraction pattern, this white powder was identified as
cerium oxide. Its apparent density as measured in a tapping method
was 1.43 g/mi.
[0138] Formation of Cerium Oxide Grains, 4-2:
[0139] Fifty grams of cerium nitrate was added to 500 g of
deionized water, and well mixed. Then, with stirring the resulting
mixture, an aqueous solution as prepared by dissolving 75 g of
ammonium hydrogencarbonate in 400 g of distilled water was dropwise
added thereto, and reacted as they were for 1 hour at room
temperature to give a white precipitate. This white precipitate was
separated through centrifugation at 3000 rpm for 10 minutes for
solid-liquid separation by a centrifuger. This was again put into
500 g of deionized water and well dispersed therein. Then, 60.9 g
of aqueous hydrogen peroxide (about 35%) was dropwise added to the
resulting dispersion and reacted for 1 hour with still stirring it.
Next, this was heated up to 90.degree. C. in a water bath. After
having been still stirred for 1 hour at 90.degree. C., this was
cooled to room temperature separated the solid from liquid by a
centrifuger, and then dried in a drier at 120.degree. C. for 24
hours to obtain 20 g of a white powder. From its X-ray diffraction
pattern, this white powder was identified as cerium oxide. Its
apparent density as measured in a tapping method was 1.52 g/ml.
[0140] Formation of Cerium Oxide Grains, 4-3:
[0141] Fifty grams of cerium ammonium nitrate was added to 500 g of
deionized water, and well mixed. With stirring the resulting
mixture, an aqueous solution as prepared by dissolving 27 g of
aqueous ammonia in 500 g of distilled water was dropwise added
thereto, and reacted as they were for 1 hour at room temperature to
give a white precipitate. This white precipitate was separated
through centrifugation at 3000 rpm for 10 minutes for solid-liquid
separation by a centrifuger, and then dried in a drier at
120.degree. C. for 24 hours to obtain 15 g of a white powder. From
its X-ray diffraction pattern, this white powder was identified as
cerium oxide, its apparent density as measured in a tapping method
was 1.49 g/ml.
[0142] Formation of Cerium Oxide Slurries:
[0143] Ten grams of each of those three cerium oxide powders was
dispersed in 100 g of deionized water, to which was added 1 g of
ammonium polyacrylate, and dispersed with a planetary ball mill
(P-5 Model, manufactured by Flitche) at 2800 rpm for 30 minutes.
Thus were obtained three milky white cerium oxide slurries. Using a
Coulter counter (N-4 Model, manufactured by Nikka-ki), the grain
size distribution of each slurry was measured. It was found that
the mean grain size of the grains in each slurry was small to be
176 nm, and that each slurry was a mono-dispersed one having a
relatively narrow grain size distribution.
[0144] Formation of Insulating Layer:
[0145] A 4-inch Si wafer having thereon an IC circuit and an
aluminium wiring pattern in that order was processed in the same
manner as in Example 1 to form an insulating layer thereon.
[0146] Polishing of Insulating Layer:
[0147] Using any of the cerium oxide slurries prepared above, the
insulating layer formed on the Si wafer was polished in the same
manner as in Example 1. Using an automatic ellipsometer, the change
in the film thickness of the Si wafer before and after polishing it
was determined, which verified that about 4,000 .ANG. of the
insulating layer of the Si wafer was cut off through the polishing,
resulting in that the thickness of the thus-polished insulating
layer was almost completely unified throughout the entire surface
of the Si wafer. The thus-polished Si wafer was cut, and its cross
section was observed with SEM, which verified that the insulating
layer well covered the Si wafer with no defects such as empty pores
even in the grooves between the wiring lines having a width of 0.1
.mu.m and a depth of 1.0 .mu.m. This process was repeated 6 times
in all to form a 6-layered wiring on the Si wafer, of which the
cross section was observed with SEM. The SEM observation verified
that there was almost no difference in surface level in each layer
throughout the entire surface of the Si wafer substrate and that
the wiring patterns formed were all good and accurate.
COMPARATIVE EXAMPLE 4
[0148] In the same manner as in Example 4, an insulating film layer
was formed on a semiconductor substrate. Without using the cerium
oxide slurry herein, tried was the formation of multi-layered
wirings on the substrate. However, in the samples prepared herein
to have wirings of 3 or more layers, the difference in surface
level was so great that the adjacent upper and lower layers could
not ensure the insulating performance therebetween. It was found
that multi-layered wirings of 3 or more layers could not be formed
in this Comparative Example 4.
[0149] On the other hand, polishing of the insulating film layer
same as mentioned above was tried with a slurry prepared in the
same manner as mentioned above using a commercially-available
cerium oxide grains having an apparent density as measured in a
tapping method of 1.67 g/ml. As a result, about 4,100 .ANG. of the
insulating layer was cut off, which was almost the same as that cut
off in Example 4, but the surface of the insulating layer polished
herein was much scratched. Then, the weight to the holder, which
had been 5 kg, was reduced to 1 kg. Using the weight of 1 kg, the
polished surface of the insulating layer was not scratched. In this
condition, however, only about 1000 .ANG. of the layer was cut off
even after having been polished at 50 rpm for 10 minutes, Thus, it
was found that the performance of this slurry was very poor for
flattening the entire surface of Si wafers.
EXAMPLE 5
[0150] Formation of Cerium Oxide Grains, 5-1:
[0151] Fifty grams of cerium carbonate was added to 450 g of
deionized water, and dispersed therein with a planetary ball mill
at 2800 rpm for 15 minutes to obtain a white, cerium carbonate
slurry. With stirring the slurry, 29.2 g of aqueous hydrogen
peroxide (about 35%) was dropwise added thereto, reacted for 1 hour
with further stirring, and thereafter heated up to 90.degree. C. In
a water bath. After having been still stirred for 1 hour at
90.degree. C., this was cooled to room temperature, separated the
solid from liquid by centrifuger, and then dried in a drier at
120.degree. C. for 24 hours to obtain 30 g of a white powder. From
its X-ray diffraction pattern, this white powder was identified as
cerium oxide. The half-value width of the main peak appearing in
the powdery X-ray diffraction pattern of this powder was measured
to be 1.38.degree..
[0152] Formation of Cerium Oxide Grains, 5-2:
[0153] Fifty grams of cerium nitrate was added to 500 g of
deionized water, and well mixed. Then, with stirring the resulting
mixture, an aqueous solution as prepared by dissolving 75 g of
ammonium hydrogencarbonate in 400 g of distilled water was dropwise
added thereto, and reacted as they were for 1 hour at room
temperature to give a white precipitate. This white precipitate was
separated through centrifugation at 3000 rpm for 10 minutes for
solid-liquid separation by a centrifuger. This was again put into
500 g of deionized water and well dispersed therein. Then, 60.9 g
of aqueous hydrogen peroxide (about 35%) was dropwise added to the
resulting dispersion and reacted for 1 hour with still stirring it.
Next, this was heated up to 90.degree. C. In a water bath. After
having been still stirred for 1 hour at 90.degree. C., this was
cooled to room temperature, centrifuged for solid-liquid
separation, and then dried in a drier at 120.degree. C. for 24
hours to obtain 20 g of a white powder. From its X-ray diffraction
pattern, this white powder was identified as cerium oxide. The
half-value width of the main peak appearing in the powdery X-ray
diffraction pattern of this powder was measured to be
1.30.degree..
[0154] Formation of Cerium Oxide Grains, 5-3:
[0155] Fifty grams of cerium ammonium nitrate was added to 500 g of
deionized water, and well mixed. With stirring the resulting
mixture, an aqueous solution as prepared by dissolving 27 g of
aqueous ammonia in 500 g of distilled water was dropwise added
thereto, and reacted as they were for 1 hour at room temperature to
give a white precipitate. This white precipitate was separated
through centrifugation at 3000 rpm for 10 minutes for solid-liquid
separation by a centrifuger, and then dried in a drier at
120.degree. C. for 24 hours to obtain 15 g of a white powder. From
its X-ray diffraction pattern, this white powder was identified as
cerium oxide.
[0156] The half-value width of the main peak appearing in the
powdery X-ray diffraction pattern of this powder was measured to be
1.44.degree..
[0157] Formation of Cerium Oxide Slurries:
[0158] Ten grams of each of those three cerium oxide powders was
dispersed in 100 g of deionized water, to which was added 1 g of
ammonium polyacrylate, and dispersed with a planetary ball mill
(P-5 Model, manufactured by Flitche) at 2800 rpm for 30 minutes.
Thus were obtained three milky white cerium oxide slurries. Using a
Coulter counter (N-4 Model, manufactured by Nikka-ki), the grain
size distribution of each slurry was measured. It was found that
the mean grain size of the grains in each slurry was small to be
176 nm, and that each slurry was a mono-dispersed one having a
relatively narrow grain size distribution.
[0159] Formation of Insulating Layer:
[0160] A 4-inch Si wafer having thereon an IC circuit and an
aluminium wiring pattern in that order was processed in the same
manner as in Example 1 to form an insulating layer thereon.
[0161] Polishing of Insulating Layer:
[0162] Using any of the cerium oxide slurries prepared above, the
insulating layer formed on the Si wafer was polished in the same
manner as in Example 1. Using an automatic ellipsometer, the change
in the film thickness of the Si wafer before and after polishing it
was determined, which verified that about 4,000 .ANG. of the
insulating layer of the Si wafer was cut off through the polishing,
resulting in that the thickness of the thus-polished insulating
layer was almost completely unified throughout the entire surface
of the Si wafer. The thus-polished SI wafer was cut, and its cross
section was observed with SEM, which verified that the insulating
layer well covered the Si wafer with no defects such as empty pores
even in the grooves between the wiring lines having a width of 0.1
PM and a depth of 1.0 .mu.m. This process was repeated 6 times in
all to form a 6-layered wiring on the Si wafer, of which the cross
section was observed with SEM. The SEM observation verified that
there was almost no difference in surface level in each layer
throughout the entire surface of the Si wafer substrate and that
the wiring patterns formed were all good and accurate.
[0163] Under the same condition, the CVD film (of SiO.sub.2) formed
on the Si wafer was polished, resulting in that only about 200
.ANG. of the film was cut off. In this, the ratio of the polishing
speed for the organic SOG film to that for the CVD film was about
20, from which it was confirmed that only the SOG film was well
selectively polished with the abrasive used herein.
COMPARATIVE EXAMPLE 5
[0164] In the same manner as in Example 5, an insulating film layer
was formed on a semiconductor substrate. Without using the cerium
oxide slurry herein, tried was the formation of multi-layered
wirings on the substrate. However, in the samples prepared heroin
to have wirings of 3 or more layers, the difference in surface
level was so great that the adjacent upper and lower layers could
not ensure the insulating performance therebetween. It was found
that multi-layered wirings of 3 or more layers could not be formed
in this Comparative Example 5.
[0165] On the other hand, polishing of the insulating film layer
same as mentioned above was tried with a slurry prepared in the
same manner as mentioned above using a commercially-available
cerium oxide grains, of which the powdery X-ray diffraction pattern
gave a main peak having a half-value width of 0.25.degree.. As a
result, about 4,100 .ANG. of the organic SOG film layer was cut
off, which was almost the same as that cut off in Example 5, but,
about 4000 .ANG. of the CVD film formed on the substrate was also
cut off. Thus, using this slurry, it was found impossible to
selectively polish only the organic SOG film. In addition, both the
organic SOG film and the CVD film as polished were much scratched.
Then, the weight to the holder, which had been 5 kg, was reduced to
1 kg. Using the weight of 1 kg, the polished surfaces of the layers
were not scratched. In this condition, however, only about 1000
.ANG. of the layers was cut off even after having been polished at
50 rpm for 10 minutes. Thus, it was found that the performance of
this slurry was very poor for flattening the entire surface of Si
wafers.
EXAMPLE 6
[0166] Formation of Cerium Oxide Grains, 6-1:
[0167] 50 g of cerium carbonate was added to 450 g of deionized
water, and dispersed therein with a planetary ball mill at 2800 rpm
for 15 minutes to obtain a white, cerium carbonate slurry. With
stirring the slurry, 29.2 g of aqueous hydrogen peroxide (about
35%) was dropwise added thereto, reacted for 1 hour with further
stirring, and thereafter heated up to 90.degree. C. in a water
bath. After having been still stirred for 1 hour at 90.degree. C.,
this was cooled to room temperature, centrifuged for solid-liquid
separation, and then dried in a drier at 120.degree. C. for 24
hours to obtain 30 g of a white powder. From its X-ray diffraction
pattern, this white powder was identified as cerium oxide. The size
of the primary grain in the powder was measured through
transmitting electromicroscopic observation to be from about 5 to
about 10 nm.
[0168] Formation of Cerium Oxide Grains, 6-2:
[0169] Fifty grams of cerium nitrate was added to 500 g of
deionized water, and well mixed. Then, with stirring the resulting
mixture, an aqueous solution as prepared by dissolving 75 g of
ammonium hydrogencarbonate in 400 g of distilled water was dropwise
added thereto, and reacted as they were for 1 hour at room
temperature to give a white precipitate. This white precipitate was
separated through centrifugation at 3000 rpm for 10 minutes for
solid-liquid separation by a centrifuger. This was again put into
500 g of deionized water and well dispersed therein. Then, 60.9 g
of aqueous hydrogen peroxide (about 35%) was dropwise added to the
resulting dispersion and reacted for 1 hour with still stirring it.
Next, this was heated up to 90.degree. C. in a water bath. After
having been still stirred for 1 hour at 90.degree. C., this was
cooled to room temperature, separated the solid from liquid by a
centrifuger, and then dried in a drier at 120.degree. C. for 24
hours to obtain 20 g of a white powder. From its X-ray diffraction
pattern, this, white powder was identified as cerium oxide. The
size of the primary grain in the powder was measured through
transmitting electromicroscopic observation to be from about 2 to
about 5 nm.
[0170] Formation of Cerium Oxide Grains, 6-3:
[0171] Fifty grams of cerium ammonium nitrate was added to 500 g of
deionized water, and well mixed. With stirring the resulting
mixture, an aqueous solution as prepared by dissolving 27 g of
aqueous ammonia in 500 g of distilled water was dropwise added
thereto, and reacted as they were for 1 hour at room temperature to
give a white precipitate. This white precipitate was separated
through centrifugation at 3000 rpm for 10 minutes for solid-liquid
separation by a centrifuger, and then dried in a drier at
120.degree. C. for 24 hours to obtain 15 g of a white powder. From
its X-ray diffraction pattern, this white powder was identified as
cerium oxide. The size of the primary grain in the powder was
measured through transmitting electromicroscopic observation to be
from about 5 to about 10 nm.
[0172] Formation of Cerium Oxide Slurries:
[0173] Ten grams of each of those three cerium oxide powders was
dispersed in 100 g of deionized water, to which was added 1 g of
ammonium polyacrylate, and dispersed with a planetary ball mill
(P-5 Model, manufactured by Flitche) at 2800 rpm for 30 minutes.
Thus were obtained three milky white cerium oxide slurries. Using a
Coulter counter (N-4 Model, manufactured by Nlkka-ki), the grain
size distribution of each slurry was measured. It was found that
the mean grain size of the grains in each slurry was small to be
176 nm, and that each slurry was a mono-dispersed one having a
relatively narrow grain size distribution.
[0174] Formation of Insulating Layer:
[0175] A 4-inch Si wafer having thereon an IC circuit and an
aluminium wiring pattern in that order was processed in the same
manner as in Example 1 to form an insulating layer thereon.
[0176] Polishing of Insulating Layer:
[0177] Using any of the cerium oxide slurries prepared above, the
insulating layer formed on the Si wafer was polished in the same
manner as in Example 1. Using an automatic ellipsometer, the change
in the film thickness of the Si wafer before and after polishing it
was determined, which verified that about 4,000 .ANG. of the
insulating layer of the Si wafer was cut off through the polishing,
resulting in that the thickness of the thus-polished insulating
layer was almost completely unified throughout the entire surface
of the Si wafer. The thus-polished Si wafer was cut, and its cross
section was observed with SEM, which verified that the insulating
layer well covered the Si wafer with no defects such as empty pores
even in the grooves between the wiring lines having a width of 0.1
.mu.m and a depth of 1.0 pm. This process was repeated 6 times in
all to form a 6-layered wiring on the Si wafer, of which the cross
section was observed with SEM. The SEM observation verified that
there was almost no difference in surface level in each layer
throughout the entire surface of the SI wafer substrate and that
the wiring patterns formed were all good and accurate.
COMPARATIVE EXAMPLE 6
[0178] In the same manner as in Example 6, an insulating film layer
was formed on a semiconductor substrate. Without using the cerium
oxide slurry herein, tried was the formation of multi-layered
wirings on the substrate. However, in the samples prepared herein
to have wirings of 3 or more layers, the difference in surface
level was so great that the adjacent upper and lower layers could
not ensure the insulating performance therebetween. It was found
that multi-layered wirings of 3 or more layers could not be formed
in this Comparative Example 6.
[0179] On the other hand, polishing of the insulating film layer
same as mentioned above was tried with a slurry prepared in the
same manner as mentioned above using a commercially-available
cerium oxide grains, of which the primary grains were found to have
a primary grain size of about 50 nm through transmitting
electromicroscopic observation. As a result, only about 2,000 .ANG.
of the insulating layer was cut off through the polishing and, in
addition, the polished surface of the layer was much scratched.
Then, the weight to the holder, which had been 5 kg, was reduced to
1 kg. Using the weight of 1 kg, the polished surface of the layer
was not scratched. In this condition, however, only about 500 .ANG.
of the layer was cut off even after having been polished at 50 rpm
for 10 minutes. Thus, it was found that the performance of this
slurry was very poor for flattening the entire surface of Si
wafers.
EXAMPLE 7
[0180] Formation of Cerium Oxide Grains, 7-1:
[0181] Fifty grams of cerium carbonate was added to 450 g of
deionized water, and dispersed therein with a planetary ball mill
at 2800 rpm for 15 minutes to obtain a white, cerium carbonate
slurry. With stirring the slurry, 29.2 g of aqueous hydrogen
peroxide (about 35%) was dropwise added thereto, reacted for 1 hour
with further stirring, and thereafter heated up to 90.degree. C. in
a water bath. After having been still stirred for 1 hour at
90.degree. C., this was cooled to room temperature, centrifuged for
solid-liquid separation, and then dried in a drier at 120.degree.
C. for 24 hours to obtain 30 g of a white powder. From its X-ray
diffraction pattern, this white powder was identified as cerium
oxide. The primary grain size in the powder was measured through
transmitting electromicroscopic observation to be from about 5 to
about 10 nm. Through scanning electromicroscopic observation, the
secondary grain size in it was measured to be about 0.2 .mu.m.
[0182] Formation of Cerium Oxide Grains, 7-2:
[0183] Fifty frams of cerium nitrate was added to 500 g of
deionized water, and well mixed. Then, with stirring the resulting
mixture, an aqueous solution as prepared by dissolving 75 g of
ammonium hydrogencarbonate in 400 g of distilled water was dropwise
added thereto, and reacted as they were for 1 hour at room
temperature to give a white precipitate. This white precipitate was
separated through centrifugation at 3000 rpm for 10 minutes for
solid-liquid separation by a centrifuger. This was again put into
500 g of deionized water and well dispersed therein. Then, 60.9 g
of aqueous hydrogen peroxide (about 35%) was dropwise added to the
resulting dispersion and reacted for 1 hour with still stirring it.
Next, this was heated up to 90.degree. C. in a water bath. After
having been still stirred for 1 hour at 90.degree. C., this was
cooled to room temperature, separated the solid from liquid by a
centrifuger, and then dried in a drier at 120.degree. C. for 24
hours to obtain 20 g of a white powder. From its X-ray diffraction
pattern, this white powder was identified as cerium oxide. The size
of the primary grain in the powder was measured through
transmitting electromicroscopic observation to be from about 2 to
about 5 nm. Through scanning electromicroscopic observation, the
size of the secondary grain in it was measured to be from about 0.2
to about 0.3 pm.
[0184] Formation of Cerium Oxide Grains, 7-3:
[0185] Fifty grams of cerium ammonium nitrate was added to 500 g of
deionized water, and well mixed. With stirring the resulting
mixture, an aqueous solution as prepared by dissolving 27 g of
aqueous ammonia in 500 g of distilled water was dropwise added
thereto, and reacted as they were for 1 hour at room temperature to
give a white precipitate. This white precipitate was separated
through centrifugation at 3000 rpm for 10 minutes for solid-liquid
separation by a centrifuger, and then dried in a drier at
120.degree. C. for 24 hours to obtain 15 g of a white powder. From
its X-ray diffraction pattern, this white powder was identified as
cerium oxide. The size of the primary grain in the powder was
measured through transmitting electromicroscopic observation to be
from about 5 to about 10 nm. Through scanning electromicroscopic
observation, the size of the secondary grain in it was measured to
be from about 0.2 .mu.m.
[0186] Formation of Cerium Oxide Slurries:
[0187] Ten grams of each of those three cerium oxide powders was
dispersed in 100 g of deionized water, to which was added 1 g of
ammonium polyacrylate, and dispersed with a planetary ball mill
(P-5 Model, manufactured by Flitche) at 2800 rpm for 30 minutes.
Thus were obtained three milky white cerium oxide slurries. Using a
Coulter counter (N-4 Model, manufactured by Nikka-ki), the grain
size distribution of each slurry was measured, it was found that
the mean grain size of the grains in each slurry was small to be
176 nm, and that each slurry was a mono-dispersed one having a
relatively narrow grain size distribution.
[0188] Formation of Insulating Layer:
[0189] A 4-inch Si wafer having thereon an IC circuit and an
aluminium wiring pattern in that order was processed in the same
manner as in Example 1 to form an insulating layer thereon.
[0190] Polishing of Insulating Layer:
[0191] Using any of the cerium oxide slurries prepared above, the
insulating layer formed on the Si wafer was polished in the same
manner as in Example 1. Using an automatic ellipsometer, the change
in the film thickness of the Si wafer before and after polishing it
was determined, which verified that about 4,000 .ANG. of the
insulating layer of the Si wafer was cut off through the polishing,
resulting in that the thickness of the thus-polished insulating
layer was almost completely unified throughout the entire surface
of the Si wafer. The thus-polished Si wafer was cut, and its cross
section was observed with SEM, which verified that the insulating
layer well covered the Si wafer with no defects such as empty pores
even in the grooves between the wiring lines having a width of 0.1
.mu.m and a depth of 1.0 pm. This process was repeated 6 times in
all to form a 6-layered wiring pattern on the Si wafer, of which
the cross section was observed with SEM. The SEM observation
verified that there was almost no difference in surface level in
each layer throughout the entire surface of the Si wafer substrate
and that the wiring patterns formed were all good and accurate.
COMPARATIVE EXAMPLE 7
[0192] In the same manner as in Example 7, an insulating film layer
was formed on a semiconductor substrate. Without using the cerium
oxide slurry herein, tried was the formation of multi-layered
wirings on the substrate. However, in the samples prepared herein
to have wirings of 3 or more layers, the difference in surface
level was so great that the adjacent upper and lower layers could
not ensure the insulating performance therebetween. It was found
that multi-layered wirings of 3 or more layers could not be formed
in this Comparative Example 7.
[0193] On the other hand, polishing of the insulating film layer
same as mentioned above was tried with a slurry prepared in the
same manner as mentioned above using a commercially-available
cerium oxide grains, of which the primary grains and the secondary
grains were found to have a primary grain size of about 50 nm and a
secondary grain size of about 5.0 .mu.m, respectively, through
transmitting electromicroscopic observation and scanning
electromicroscopic observation. As a result, only about 2,000 .ANG.
of the insulating layer was cut off through the polishing and, in
addition, the polished surface of the layer was much scratched.
Then, the weight to the holder, which had been 5 kg, was reduced to
1 kg, Using the weight of 1 kg, the polished surface of the layer
was not is scratched. In this condition, however, only about 500 A
of the layer was cut off even after having been polished at 50 rpm
for 10 minutes. Thus, it was found that the performance of this
slurry was very poor for flattening the entire surface of Si
wafers.
EXAMPLE 8
[0194] Formation of Cerium Oxide Grains, 8-1:
[0195] Fifty grams of cerium carbonate was added to 450 g of
deionized water, and dispersed therein with a planetary ball mill
at 2800 rpm for 15 minutes to obtain a white, cerium carbonate
slurry. With stirring the slurry, 29.2 g of aqueous hydrogen
peroxide (about 35%) was dropwise added thereto, reacted for 1 hour
with further stirring, and thereafter heated up to 90.degree. C. in
a water bath. After having been still stirred for 1 hour at
90.degree. C., this was cooled to room temperature, centrifuged for
solid-liquid separation, and then dried in a drier at 120.degree.
C. for 24 hours to obtain 30 g of a white powder. From its X-ray
diffraction pattern, this white powder was identified as cerium
oxide. The size of the secondary grain in the powder was measured
through scanning electromicroscopic observation to be about 0.2
.mu.m. In addition, it was found that the outline of each of those
secondary grains had almost no sharp corners and was gently
roundish.
[0196] Formation of Cerium Oxide Grains, 8-2.
[0197] Fifty grams of cerium nitrate was added to 500 g of
deionized water, and well mixed. Then, with stirring the resulting
mixture, an aqueous solution as prepared by dissolving 75 g of
ammonium hydrogencarbonate in 400 g of distilled water was dropwise
added thereto, and reacted as they were for 1 hour at room
temperature to give a white precipitate. This white precipitate was
separated through centrifugation at 3000 rpm for 10 minutes for
solid-liquid separation by a centrifuger. This was again put into
500 g of deionized water and well dispersed therein. Then, 60.9 g
of aqueous hydrogen peroxide (about 35%) was dropwise added to the
resulting dispersion and reacted for 1 hour with still stirring it.
Next, this was heated up to 90.degree. C. In a water bath. After
having been still stirred for 1 hour at 90.degree. C., this was
cooled to room temperature, separated the solid from liquid by a
centrifuger, and then dried in a drier at 120.degree. C. for 24
hours to obtain 20 g of a white powder. From its X-ray diffraction
pattern, this white powder was identified as cerium oxide. The size
of the secondary grain in the powder was measured through scanning
electromicroscopic observation to be from about 0.2 to about 0.3
.mu.m. In addition, it was found that the outline of each of those
secondary grains had almost no sharp corners and was gently
roundish.
[0198] Formation of Cerium Oxide Grains, 8-3:
[0199] Fifty grams of cerium ammonium nitrate was added to 500 g of
deionized water, and well mixed. With stirring the resulting
mixture, an aqueous solution as prepared by dissolving 27 g of
aqueous ammonia in 500 g of distilled water was dropwise added
thereto, and reacted as they were for 1 hour at room temperature to
give a white precipitate. This white precipitate was separated
through centrifugation at 3000 rpm for 10 minutes for solid-liquid
separation by a centrifuger, and then dried in a drier at
120.degree. C. for 24 hours to obtain 15 g of a white powder. From
its X-ray diffraction pattern, this white powder was identified as
cerium oxide. The size of the secondary grain in the powder was
measured through scanning electromicroscopic observation to be
about 0.2 .mu.m. In addition, it was found that the outline of each
of those secondary grains had almost no sharp corners and was
gently roundish.
[0200] Formation of Cerium Oxide Slurries:
[0201] Ten grams of each of those three cerium oxide powders was
dispersed in 100 g of deionized water, to which was added 1 g of
ammonium polyacrylate, and dispersed with a planetary ball mill
(P-5 Model, manufactured by Flitche) at 2800 rpm for 30 minutes.
Thus were obtained three milky white cerium oxide slurries. Using a
Coulter counter (N-4 Model, manufactured by Nikka-ki), the grain
size distribution of each slurry was measured. It was found that
the mean grain size of the grains in each slurry was small to be
176 nm, and that each slurry was a mono-dispersed one having a
relatively narrow grain size distribution.
[0202] Formation of Insulating Layer:
[0203] A 4-inch SI wafer having thereon an IC circuit and an
aluminium wiring pattern in that order was processed in the same
manner as in Example 1 to form an insulating layer thereon.
[0204] Polishing of Insulating Layer:
[0205] Using any of the cerium oxide slurries prepared above, the
insulating layer formed on the Si wafer was polished in the same
manner as in Example 1. Using an automatic ellipsometer, the change
in the film thickness of the Si wafer before and after polishing it
was determined, which verified that about 4,000 .ANG. of the
insulating layer of the Si wafer was cut off through the polishing,
resulting in that the thickness of the thus-polished insulating
layer was almost completely unified throughout the entire surface
of the Si wafer. The thus-polished Si wafer was cut, and its cross
section was observed with SEM, which verified that the insulating
layer well covered the Si wafer with no defects such as empty pores
even in the grooves between the wiring lines having a width of 0.1
.mu.m and a depth of 1.0 .mu.m. This process was repeated 6 times
in all to form a 6-layered wiring on the Si wafer, of which the
cross section was observed with SEM. The SEM observation verified
that there was almost no difference in surface level in each layer
throughout the entire surface of the Si wafer substrate and that
the wiring patterns formed were all good and accurate.
COMPARATIVE EXAMPLE 8
[0206] In the same manner as in Example 8, an insulating film layer
was formed on a semiconductor substrate. Without using the cerium
oxide slurry herein, tried was the formation of multi-layered
wirings on the substrate. However, in the samples prepared herein
to have wirings of 3 or more layers, the difference in surface
level was so great that the adjacent upper and lower layers could
not ensure the insulating performance therebetween. It was found
that multi-layered wirings of 3 or more layers could not be formed
in this Comparative Example 8.
[0207] On the other hand, polishing of the insulating film layer
same as mentioned above was tried with a slurry prepared in the
same manner as mentioned above using a commercially-available
cerium oxide grains, of which the secondary grains were found to
have a secondary grain size of about 1.0 .mu.m through scanning
electromicroscopic observation and in which the outline of each
secondary grains was found to have edges having an angle falling
between 60.degree. and 120.degree.. As a result, only about 2,100
.ANG. of the insulating layer was cut off through the polishing
and, in addition, the polished surface of the layer was much
scratched. Then, the weight to the holder, which had been 5 kg, was
reduced to 1 kg, Using the weight of 1 kg, the polished surface of
the layer was not scratched. In this condition, however, only about
500 .ANG. of the layer was cut off even after having been polished
at 50 rpm for 10 minutes. Thus, it was found that the performance
of this slurry was very poor for flattening the entire surface of
SI wafers.
EXAMPLE 9
[0208] Formation of Cerium Oxide Grains, 9-1:
[0209] Fifty grams of cerium carbonate was added to 450 g of
deionized water, and dispersed therein with a planetary ball mill
at 2800 rpm for 15 minutes to obtain a white, cerium carbonate
slurry. With stirring the slurry, 29.2 g of aqueous hydrogen
peroxide (about 35%) was dropwise added thereto, reacted for 1 hour
with further stirring, and thereafter heated up to 90.degree. C. in
a water bath. After having been still stirred for 1 hour at
90.degree. C., this was cooled to room temperature, centrifuged for
solid-liquid separation, and then dried in a drier at 120.degree.
C. for 24 hours to obtain 30 g of a white powder. From its X-ray
diffraction pattern, this white powder was identified as cerium
oxide. The aspect ratio of the primary grains in the powder was
measured through transmitting electromicroscopy to be 1.1.
[0210] Formation of Cerium Oxide Grains, 9-2:
[0211] Fifty grams of cerium nitrate was added to 500 g of
deionized water, and well mixed. Then, with stirring the resulting
mixture, an aqueous solution as prepared by dissolving 75 g of
ammonium hydrogencarbonate in 400 g of distilled water was dropwise
added thereto, and reacted as they were for 1 hour at room
temperature to give a white precipitate. This white precipitate was
separated through centrifugation at 3000 rpm for 10 minutes for
solid-liquid separation by a centrifuger. This was again put into
500 g of deionized water and well dispersed therein. Then, 60.9 g
of aqueous hydrogen peroxide (about 35%) was dropwise added to the
resulting dispersion and reacted for 1 hour with still stirring it.
Next, this was heated up to 90.degree. C. in a water bath. After
having been still stirred for 1 hour at 90.degree. C., this was
cooled to room temperature, separated the solid from liquid by a
centrifuger, and then dried in a drier at 120.degree. C. for 24
hours to obtain 20 g of a white powder. From its X-ray diffraction
pattern, this white powder was identified as cerium oxide. The
aspect ratio of the primary grains in the powder was measured
through transmitting electromicroscopy to be 1.4.
[0212] Formation of Cerium Oxide Grains, 9-3:
[0213] Fifty grams of cerium ammonium nitrate was added to 500 g of
deionized water, and well mixed. With stirring the resulting
mixture, an aqueous solution as prepared by dissolving 27 g of
aqueous ammonia in 500 g of distilled water was dropwise added
thereto, and reacted as they were for 1 hour at room temperature to
give a white precipitate. This white precipitate was separated
through centrifugation at 3000 rpm for 10 minutes for solid-liquid
separation by a centrifuger, and then dried in a drier at
120.degree. C. for 24 hours to obtain 15 g of a white powder. From
its X-ray diffraction pattern, this white powder was identified as
cerium oxide.
[0214] The aspect ratio of the primary grains in the powder was
measured through transmitting electromicroscopy to be 1.2.
[0215] Formation of Cerium Oxide Slurries:
[0216] Ten grams of each of those three cerium oxide powders was
dispersed in 100 g of deionized water, to which was added 1 g of
ammonium polyacrylate, and dispersed with a planetary ball mill
(P-5 Model, manufactured by Flitche) at 2800 rpm for 30 minutes.
Thus were obtained three milky white cerium oxide slurries. Using a
Coulter counter (N-4 Model, manufactured by Nikka-ki), the grain
size distribution of each slurry was measured. It was found that
the mean grain size of the grains in each slurry was small to be
176 nm, and that each slurry was a mono-dispersed one having a
relatively narrow grain size distribution.
[0217] Formation of Insulating Layer:
[0218] A 4-inch Si wafer having thereon an IC circuit and an
aluminium wiring pattern in that order was processed in the same
manner as in Example 1 to form an insulating layer thereon.
[0219] Polishing of Insulating Layer:
[0220] Using any of the cerium oxide slurries prepared above, the
insulating layer formed on the Si wafer was polished in the same
manner as in Example 1. Using an automatic ellipsometer, the change
in the film thickness of the Si wafer before and after polishing it
was determined, which verified that about 4,000 .ANG. of the
insulating layer of the Si wafer was cut off through the polishing,
resulting in that the thickness of the thus-polished insulating
layer was almost completely unified throughout the entire surface
of the Si wafer. The thus-polished Si wafer was cut, and its cross
section was observed with SEM, which verified that the insulating
layer well covered the Si wafer with no defects such as empty pores
even in the grooves between the wiring lines having a width of 0.1
.mu.m and a depth of 1.0 .mu.m. This process was repeated 6 times
in all to form a 6-layered wiring on the Si wafer, of which the
cross section was observed with SEM. The SEM observation verified
that there was almost no difference in surface level in each layer
throughout the entire surface of the Si wafer substrate and that
the wiring patterns formed were all good and accurate.
COMPARATIVE EXAMPLE 9
[0221] In the same manner as in Example 9, an insulating film layer
was formed on a semiconductor substrate. Without using the cerium
oxide slurry herein, tried was the formation of multi-layered
wirings on the substrate. However, in the samples prepared herein
to have wirings of 3 or more layers, the difference in surface
level was so great that the adjacent upper and lower layers could
not ensure the insulating performance therebetween. It was found
that multi-layered wirings of 3 or more layers could not be formed
in this Comparative Example 9.
[0222] On the other hand, polishing of the insulating film layer
same as mentioned above was tried with a slurry prepared in the
same manner as mentioned above, but using a commercially-available
cerium oxide grains, of which the primary grains were found to have
an aspect ratio of 3.0 through transmitting electromicroscopic
observation. As a result, about 4,000 .ANG. of the insulating layer
was cut off, which was almost the same as that cut off in Example
9, but the surface of the insulating layer polished herein was much
scratched. Then, the weight to the holder, which had been 5 kg, was
reduced to 1 kg. Using the weight of 1 kg, the polished surface of
the layer was not scratched. In this condition, however, only about
500 .ANG. of the layer was cut off even after having been polished
at 50 rpm for 10 minutes. Thus, it was found that the performance
of this slurry was very poor for flattening the entire surface of
Si wafers.
EXAMPLE 10
[0223] Formation of Cerium Oxide Grains, 10-1:
[0224] Fifty grams of cerium carbonate was added to 450 g of
deionized water, and dispersed therein with a planetary ball mill
at 2800 rpm for 15 minutes to obtain a white, cerium carbonate
slurry. With stirring the slurry, 29.2 g of aqueous hydrogen
peroxide (about 35%) was dropwise added thereto, reacted for 1 hour
with further stirring, and thereafter heated up to 90.degree. C. In
a water bath. After having been still stirred for 1 hour at
90.degree. C., this was cooled to room temperature, separated the
solid from liquid by a centrifuger, and then dried in a drier at
120.degree. C. for 24 hours to obtain 30 g of a white powder. From
its X-ray diffraction pattern, this white powder was identified as
cerium oxide. Its specific surface area as measured through
nitrogen adsorption was 111 m.sup.2/g; Its apparent density as
measured in a still standing method was 1.07 g/ml; Its apparent
density as measured in a tapping method was 1.43 g/ml; its powdery
X-ray diffraction pattern gave a main peak, of which the half-value
width was 1.38 the size of the primary grain in the powder was
measured through transmitting electromicroscopy to be from about 5
to about 10 nm; the secondary grain size of the secondary grains
constituting the powder was measured through scanning
electromicroscopy to be about 0.2 .mu.m; and the outline of each of
those secondary grains had almost no sharp corners and was gently
roundish.
[0225] Formation of Cerium Oxide Grains, 10-2:
[0226] Fifty grams of cerium nitrate was added to 500 g of
deionized water, and well mixed. Then, with stirring the resulting
mixture, an aqueous solution as prepared by dissolving 75 g of
ammonium hydrogencarbonate in 400 g of distilled water was dropwise
added thereto, and reacted as they were for 1 hour at room
temperature to give a white precipitate. This white precipitate was
separated through centrifugation at 3000 rpm for 10 minutes for
solid-liquid separation by a centrifuger. This was again put into
500 g of deionized water and well dispersed therein. Then, 60.9 g
of aqueous hydrogen peroxide (about 35%) was dropwise added to the
resulting dispersion and reacted for 1 hour with still stirring it.
Next, this was heated up to 90.degree. C. in a water bath. After
having been still stirred for 1 hour at 90.degree. C., this was
cooled to room temperature, separated the solid from liquid by a
centrifuger, and then dried in a drier at 120.degree. C. for 24
hours to obtain 20 g of a white powder. From its X-ray diffraction
pattern, this white powder was identified as cerium oxide. Its
specific surface area as measured through nitrogen adsorption was
112 m.sup.2/g; Its apparent density as measured in a still standing
method was 1.11 g/ml; its apparent density as measured in a tapping
method was 1.52 g/ml; its powdery X-ray diffraction pattern gave a
main peak, of which the half-value width was 1.30.degree.; the size
of the primary grain in the powder was measured through
transmitting electromicroscopy to be from about 2 to about 5 nm;
the secondary grain size of the secondary grains constituting the
powder was measured through scanning electromicroscopy to be from
about 0.2 to about 0.3 .mu.m; and the outline of each of those
secondary grains had s almost no sharp corners and was gently
roundish.
[0227] Formation of Cerium Oxide Grains, 10-3:
[0228] Fifty grams of cerium ammonium nitrate was added to 500 g of
deionized water, and well mixed. With stirring the resulting
mixture, an aqueous solution as prepared by dissolving 27 g of
aqueous ammonia in 500 g of distilled water was dropwise added
thereto, and reacted as they were for 1 hour at room temperature to
give a white precipitate. This white precipitate was separated
through centrifugation at 3000 rpm for 1.0 minutes for solid-liquid
separation by a centrifuger, and then dried in a drier at
120.degree. C. for 24 hours to obtain 15 g of a white powder. From
its X-ray diffraction pattern, this white powder was identified as
cerium oxide. Its specific surface area as measured through
nitrogen adsorption was 130 m.sup.2/g; its apparent density as
measured in a still standing method was 1.08 g/ml; Its apparent
density as measured in a tapping method was 1.49 g/ml; its powdery
X-ray diffraction pattern gave a main peak, of which the half-value
width was 1.44.degree.; the size of the primary grain in the powder
was measured through transmitting electromicroscopy to be from
about 5 to about 10 nm; the size of the secondary grain in the
powder was measured through scanning electromicroscopy to be about
0.2 .mu.m; and the outline of each of those secondary grains had
almost no sharp corners and was gently roundish.
[0229] Formation of Cerium Oxide Slurries:
[0230] Two and a half grams of each of those three cerium oxide
powders was dispersed in 100 g of deionized water, to which was
added 1 g of ammonium polyacrylate, and dispersed with a planetary
ball mill (P-5 Model, manufactured by Flitche) at 2800 rpm for 30
minutes. Thus were obtained three milky white cerium oxide
slurries. Using a Coulter counter (N-4 Model, manufactured by
Nlkka-ki), the grain size distribution of each slurry was measured.
It was found that the mean grain size of the grains in each slurry
was small to be 176 nm, and that each slurry was a mono-dispersed
one having a relatively narrow grain size distribution.
[0231] Formation of Insulating Layer:
[0232] A 4-inch Si wafer having thereon an IC circuit and an
aluminium wiring pattern in that order was processed in the same
manner as in Example 1 to form an insulating layer thereon.
[0233] Polishing of Insulating Layer:
[0234] Using any of the cerium oxide slurries prepared above, the
insulating layer formed on the Si wafer was polished in the same
manner as in Example 1. Using an automatic ellipsometer, the change
in the film thickness of the Si wafer before and after polishing it
was determined, which verified that about 4,000 .ANG. of the
insulating layer of the Si wafer was cut off through the polishing,
resulting in that the thickness of the thus-polished insulating
layer was almost completely unified throughout the entire surface
of the Si wafer. The thus-polished Si wafer was cut, and its cross
section was observed with SEM, which verified that the insulating
layer well covered the Si wafer with no defects such as empty pores
even in the grooves between the wiring lines having a width of 0.1
.mu.m and a depth of 1.0 .mu.m. This process was repeated 6 times
in all to form a 6-layered wiring on the Si wafer, of which the
cross section was observed with SEM. The SEM observation verified
that there was almost no difference in surface level in each layer
throughout the entire surface of the Si wafer substrate and that
the wiring patterns formed were all good and accurate.
[0235] Under the same condition, the CVD film (of SiO.sub.2) formed
on the Si wafer was polished, resulting in that only about 200
.ANG. of the film was cut off. In this, the ratio of the polishing
speed for the CVD film to that for the organic SOG film was about
1/20, from which it was confirmed that only the SOG film was well
selectively polished with the abrasive used herein.
COMPARATIVE EXAMPLE 10
[0236] In the same manner as in Example 10, an insulating film
layer was formed on a semiconductor substrate. Without using the
cerium oxide slurry herein, tried was the formation of
multi-layered wirings on the substrate. However, in the samples
prepared herein to have wirings of 3 or more layers, the difference
in surface level was so great that the adjacent upper and lower
layers could not ensure the insulating performance therebetween. It
was found that multi-layered wirings of 3 or more layers could not
be formed in this Comparative Example 9.
[0237] On the other hand, the insulating film layer formed herein
was polished with a colloidal silica slurry with aqueous ammonia
(SS-225, trade name of Cabot). In this, however, only about 400
.ANG. of the layer was polished at 50 rpm for 10 minutes. Thus, it
was found that the performance of the colloidal silica slurry
abrasive was very poor for flattening the entire surface of Si
wafers. Under the same condition, the CVD film formed on the
substrate was polished, resulting in that about 400 .ANG. of the
film was cut off. In this, therefore, the ratio of the polishing
speed for the CVD film to that for the organic SOG film was 1,
which indicates that the colloidal silica slurry cannot be used in
selectively polishing only the organic SOG film.
* * * * *