U.S. patent application number 12/100450 was filed with the patent office on 2008-10-16 for substrate processing method.
Invention is credited to Dai Fukushima, Atsushi SHIGETA, Hiroyuki Yano.
Application Number | 20080254719 12/100450 |
Document ID | / |
Family ID | 39854147 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080254719 |
Kind Code |
A1 |
SHIGETA; Atsushi ; et
al. |
October 16, 2008 |
SUBSTRATE PROCESSING METHOD
Abstract
In a substrate processing method of polishing a periphery of a
substrate, in a state where a first polishing surface to which
abrasive grains that include particles having a chemical effect on
an oxide-silicon-series or nitride-silicon-series film as a main
component have been fixed is brought into contact with the
periphery of a semiconductor substrate, polishing the periphery of
the substrate by sliding the substrate and the first polishing
surface. Moreover, in a state where a second polishing surface to
which abrasive grains mainly having a mechanical effect have been
fixed is brought into contact with the periphery of the substrate,
polishing the periphery of the substrate by sliding the substrate
and the second polishing surface.
Inventors: |
SHIGETA; Atsushi;
(Fujisawa-shi, JP) ; Fukushima; Dai;
(Kamakura-shi, JP) ; Yano; Hiroyuki;
(Yokohama-shi, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
39854147 |
Appl. No.: |
12/100450 |
Filed: |
April 10, 2008 |
Current U.S.
Class: |
451/44 |
Current CPC
Class: |
B24B 21/002 20130101;
B24B 9/065 20130101 |
Class at
Publication: |
451/44 |
International
Class: |
B24B 1/00 20060101
B24B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 11, 2007 |
JP |
2007-104068 |
Claims
1. A substrate processing method of polishing a periphery of a
substrate, comprising: in a state where a first polishing surface
to which abrasive grains that include particles having a chemical
effect on an oxide-silicon-series or nitride-silicon-series film as
a main component have been fixed is brought into contact with the
periphery of a semiconductor substrate, polishing the periphery of
the substrate by sliding the substrate and the first polishing
surface; and in a state where a second polishing surface to which
abrasive grains mainly having a mechanical effect have been fixed
is brought into contact with the periphery of the substrate,
polishing the periphery of the substrate by sliding the substrate
and the second polishing surface.
2. The substrate processing method according to claim 1, wherein
the abrasive grains fixed to the first polishing surface include
ceria as a main component and the abrasive grains fixed to the
second polishing surface include diamond or SiC as a main
component.
3. The substrate processing method according to claim 1, wherein
polishing with the first polishing surface and polishing with the
second polishing surface are performed in parallel by rotating the
substrate and, at the same time, bringing both the first polishing
surface and the second polishing surface into contact with the
periphery of the substrate.
4. The substrate processing method according to claim 1, wherein
polishing with the first polishing surface is followed by polishing
with the second polishing surface while rotating the substrate.
5. The substrate processing method according to claim 1, wherein
polishing with the first polishing surface and polishing with the
second polishing surface are alternately performed while rotating
the substrate.
6. The substrate processing method according to claim 1, wherein
the substrate is Si.
7. The substrate processing method according to claim 1, wherein
the periphery of the substrate is a bevel part where the cross
section has a curvature at an end of the substrate or a notch part
provided on a part of the periphery of the substrate.
8. The substrate processing method according to claim 1, wherein an
unnecessary film and needle-like projections at the periphery of
the substrate are removed by polishing with the first polishing
surface and by polishing with the second polishing surface.
9. The substrate processing method according to claim 8, wherein
the unnecessary film is SiO.sub.2, SiN, SiOC, or SiCN.
10. The substrate processing method according to claim 1, wherein
an oxide-silicon-series or nitride-silicon-series film and a
silicon-series film, a carbon film, a metal film, or metal silicide
film at the periphery of the substrate are removed by polishing
with the first polishing surface and by polishing with the second
polishing surface.
11. The substrate processing method according to claim 1, wherein
the first polishing surface is the surface of a first polishing
tape and the second polishing surface is the surface of a second
polishing tape and each of the polishing tapes is pressed by a
polishing head against the semiconductor substrate.
12. A substrate processing method of polishing a periphery of a
substrate, comprising: polishing the periphery of a semiconductor
substrate using a first polishing liquid that includes abrasive
grains having a chemical effect on an oxide-silicon-series or
nitride-silicon-series film as a main component; and polishing the
periphery of the semiconductor substrate using a second polishing
liquid that includes abrasive grains mainly having a mechanical
effect.
13. The substrate processing method according to claim 12, wherein
the polishing using the first and second polishing liquids is such
that a polishing surface is brought into contact with the periphery
of the substrate and, at the same time, each of the first and
second polishing liquids is supplied to the contact part between
the periphery of the substrate and the polishing surface.
14. The substrate processing method according to claim 12, wherein
the first polishing liquid includes abrasive grains having ceria as
a main component and the second polishing liquid includes abrasive
grains having diamond or SiC as a main component.
15. The substrate processing method according to claim 12, wherein
an unnecessary film and needle-like projections at the periphery of
the substrate are removed by polishing with the first polishing
liquid and by polishing with the second polishing liquid.
16. A substrate processing method of polishing a periphery of a
substrate, comprising: polishing the periphery of a semiconductor
substrate using fixed or free abrasive grains that include
particles having a chemical effect on an oxide-silicon-series or
nitride-silicon-series film as a main component; and polishing the
periphery of the semiconductor substrate using fixed or free
abrasive grains mainly having a mechanical effect.
17. The substrate processing method according to claim 16, wherein
the abrasive grains that include particles having a chemical effect
as a main component include ceria as a main component and the
abrasive grains mainly having a mechanical effect include diamond
or SiC as a main component.
18. The substrate processing method according to claim 17, wherein
an unnecessary film and needle-like projections at the periphery of
the substrate are removed by polishing with the abrasive grains
that include ceria as a main component and by polishing with the
abrasive grains that include diamond or SiC as a main
component.
19. The substrate processing method according to claim 16, wherein
the substrate is Si.
20. The substrate processing method according to claim 16, wherein
the periphery of the substrate is a bevel part where the cross
section has a curvature at an end of the substrate or a notch part
provided on a part of the periphery of the substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2007-104068,
filed Apr. 11, 2007, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a substrate processing method of
polishing the periphery of a semiconductor substrate, and more
particularly to a substrate processing method of removing
unnecessary films and uneven surfaces formed at the periphery of
the substrate.
[0004] 2. Description of the Related Art
[0005] With the recent miniaturization of wiring lines, the
concentration values of particles and impurities to be controlled
have been getting more severe. Moreover, it has been getting more
important to control not only the surface of the semiconductor
substrate but also its periphery (including notch parts and bevel
parts).
[0006] In the manufacturing processes of a semiconductor device,
insulating films, such as SiO.sub.2 films or SiN films, and
conducting films, such as polysilicon films, W films, or Cu films,
are repeatedly subjected to a film forming process, an exposure
process, and an etching process, thereby forming microscopic
interconnection lines. In the manufacturing processes, not only
insulating films and conducting films but also unnecessary films,
including insulating films and conducting films, and uneven
surfaces are formed at the periphery of the substrate. The
unnecessary films and uneven surfaces become the sources of
particles in the manufacturing processes and are coming up to the
surface as the factor that decreases the yield as a result of
miniaturization of interconnection lines.
[0007] For example, in the process of making a deep trench in a
trench capacitor, a resist pattern is formed on a stacked
insulating film obtained by forming an SiN film and an SiO.sub.2
film sequentially by CVD techniques. Then, with the resist pattern
as a mask, the SiO.sub.2 film, SiN film, and silicon substrate are
etched sequentially by RIE (Reactive Ion Etching) techniques,
thereby making a trench. In this case, the generation of plasma and
the supply of etching gas become unstable at the periphery of the
substrate, with the result that needle-like projections might be
formed. The needle-like projections are damaged during the
transportation of the substrate or in the course of processing and
contribute to the generation of particles. Since such particles
lead to a decrease in the yield of manufactured semiconductor
devices, it is necessary to remove the needle-like projections
formed at the periphery of the substrate.
[0008] One method of processing the periphery of the substrate is
the technique for sliding a substrate with a surface to be polished
and a polishing surface, while pressing the substrate against the
polishing surface, thereby polishing and removing the polished film
on the substrate. The polishing techniques include the free
abrasive grain method and the fixed abrasive grain method. In the
free abrasive grain method, the surface to be polished is polished,
while an abrading agent including abrasive particles is being
supplied to the contact surface between the polishing surface made
of nonwoven cloth and the surface to be polished. In the fixed
abrasive grain method, the surface to be polished is polished,
while purified water is being supplied to the contact surface
between the polishing surface to which abrasive grains are fixed
and the surface to be polished.
[0009] In polishing and removing the needle-like projections caused
during the formation of trenches by the fixed grain method, all of
the SiN film and needle-like projections on the silicon substrate
have been polished and removed using diamond abrasive grains #4000
(with a grain diameter of about 3 .mu.m) which have a high
polishing speed. Thereafter, final polishing has been done using
diamond abrasive grains #10000 (with a grain diameter of about 0.5
.mu.m). However, with this method, the polishing time has been
short, but scratches on the silicon substrate caused by diamond
abrasive grains #4000 have been large. Even after final polishing
with diamond abrasive grains #10000, scratches have remained (e.g.,
refer to Jpn. Pat. Appln. KOKAI Publication No. 2003-234314).
[0010] To cope with this problem, there has been a method of using
diamond abrasive grains #10000 even in polishing and removing the
SiN film. However, with this method, it takes an enormous amount of
time to polish and remove the SiN film, a high hardness film. As
another measure against this problem, there has been a method of
decreasing the size of diamond abrasive grains progressively in the
order of #4000, #8000, and #10000, thereby improving the finished
surface roughness. With this method, however, as many as three
kinds of polishing tape are used and therefore three polishing
heads are needed, which makes the apparatus larger. Moreover, since
the polishing amount of the silicon substrate becomes larger, if a
polishing process is carried out a plurality of times in the
manufacturing processes of semiconductor devices, the semiconductor
devices might depart from the original substrate shape standards
and therefore could not be put on the production line.
[0011] As described above, the plane roughness of the surface to be
polished has to be improved to suppress the occurrence of defects
in subsequent processes. The decrease of the size of abrasive
grains is effective in improving the plane roughness of the surface
to be polished. However, when a high hardness film, such as an SiN
film or an SiO.sub.2 film, is polished and removed, a decrease in
the abrasive grain size causes the polishing speed to reduce
significantly, which produces a side-effect that the productivity
might deteriorate.
[0012] To increase the polishing removal efficiency without
deteriorating the plane roughness of the surface to be polished,
the addition of the chemical during polishing has been proposed
(e.g., refer to Jpn. Pat. Appln. KOKAI Publication No.
2007-012943). In the proposal, to increase the removal efficiency
of the SiN film on a silicon substrate, polyethylenimine or
tetramethylammonium hydroxide has been added. However, with this
method, since the substrate surface is also exposed to the
chemical, a side-effect that the silicon substrate is etched
becomes a problem.
BRIEF SUMMARY OF THE INVENTION
[0013] According to an aspect of the invention, there is provided a
substrate processing method of polishing a periphery of a
substrate, comprising: in a state where a first polishing surface
to which abrasive grains that include particles having a chemical
effect on an oxide-silicon-series or nitride-silicon-series film as
a main component have been fixed is brought into contact with the
periphery of a semiconductor substrate, polishing the periphery of
the substrate by sliding the substrate and the first polishing
surface; and in a state where a second polishing surface to which
abrasive grains mainly having a mechanical effect have been fixed
is brought into contact with the periphery of the substrate,
polishing the periphery of the substrate by sliding the substrate
and the second polishing surface.
[0014] According to another aspect of the invention, there is
provided a substrate processing method of polishing the periphery
of a substrate, comprising: polishing the periphery of a
semiconductor substrate using a first polishing liquid that
includes abrasive grains having a chemical effect on an
oxide-silicon-series or nitride-silicon-series film as a main
component; and polishing the periphery of the semiconductor
substrate using a second polishing liquid that includes abrasive
grains mainly having a mechanical effect.
[0015] According to still another aspect of the invention, there is
provided a substrate processing method of polishing a periphery of
a substrate, comprising: polishing the periphery of a semiconductor
substrate using fixed or free abrasive grains that include
particles having a chemical effect on an oxide-silicon-series or
nitride-silicon-series film as a main component; and polishing the
periphery of the semiconductor substrate using fixed or free
abrasive grains mainly having a mechanical effect.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0016] FIGS. 1A and 1B are sectional views to help explain
substrate processing steps according to a first embodiment of the
invention;
[0017] FIG. 2 is a diagram schematically showing the configuration
of a fixed-abrasive-grain-type polishing apparatus applied to the
first embodiment;
[0018] FIGS. 3A and 3B are sectional views to help explain examples
of polishing tape used in the polishing apparatus of FIG. 2;
[0019] FIG. 4 is a diagram schematically showing the configuration
of another fixed-abrasive-grain-type polishing apparatus applied to
the first embodiment;
[0020] FIGS. 5A to 5C are sectional views to help explain substrate
processing steps according to a second embodiment of the
invention;
[0021] FIGS. 6A to 6D are sectional views to help explain substrate
processing steps according to a third embodiment of the invention;
and
[0022] FIG. 7 is a diagram schematically showing the configuration
of a free-abrasive-grain-type polishing apparatus according to a
modification of the embodiments.
DETAILED DESCRIPTION OF THE INVENTION
[0023] Hereinafter, referring to the accompanying drawings,
embodiments of the invention will be explained.
First Embodiment
[0024] FIGS. 1A and 1B are sectional views to help explain
substrate processing steps according to a first embodiment of the
invention. FIG. 1A shows the state of a substrate to be processed
before polishing. FIG. 1B shows the state of the substrate after
polishing. In FIGS. 1A and 1B, numeral 10 indicates a silicon
substrate, 11 an SiO.sub.2 film, and 12 an SiN film.
[0025] In the first embodiment, in the structure of FIG. 1A, a
first polishing surface to which abrasive grains that include ceria
(cerium oxide) having a chemical effect on SiO.sub.2 and SiN as a
main component have been fixed is brought into contact with the
periphery of the silicon substrate 10. In this state, the substrate
10 is rotated, thereby polishing the substrate periphery. Next, a
second polishing surface to which diamond abrasive grains that have
mainly a mechanical effect have been fixed is brought into contact
with the periphery of the silicon substrate 10. Then, in this
state, the substrate 10 is rotated, thereby polishing the substrate
periphery. As a result, not only are the SiO.sub.2 film 11 and SiN
film 12 removed at the periphery of the substrate 10, but also the
surface roughness of the substrate periphery becomes very
small.
[0026] Hereinafter, the first embodiment will be concretely
described.
[0027] FIG. 2 is a diagram schematically showing the configuration
of a fixed-abrasive-grain-type polishing apparatus applied to the
first embodiment.
[0028] A stage 21 on which a substrate to be processed 20 is placed
can be rotated by a motor 22. The substrate 20 is absorbed and
fixed to the stage 21 in such a manner that its center is aligned
with the center of the stage 21, with the result that a part of the
periphery of the substrate 20 makes contact with a polishing tape
23. A polishing head 24 connected to a cylinder (not shown) presses
the polishing tape 23 against the substrate. With the polishing
tape 23 being pressed against the periphery of the substrate 20 by
the polishing head 24, the motor 22 rotates the substrate 20,
thereby polishing the periphery of the substrate 20. Specifically,
a part of or all of the unnecessary film formed at the periphery of
the substrate 20 is polished and removed until the surface of the
substrate 10 has been exposed. During the polishing, purified water
is supplied from a nozzle 25 near the center of the substrate to
the substrate surface in such a manner that the water is supplied
to the polishing area of the substrate periphery.
[0029] Two types of polishing tape 23 are used as shown in FIGS. 3A
and 3B: one is a first polishing tape 23a to which abrasive grains
that include grains having a chemical effect as a main component
have been fixed and the other is a second polishing tape 23b to
which abrasive grains that mainly have a mechanical effect have
been fixed. As shown in FIG. 3A, the first polishing tape 23a is
such that ceria abrasive grains 33 (#10000: a grain diameter of
about 0.5 .mu.m) are fixed to a PET (polyethylene terephthalate)
film 31 with binder 32. The polishing tape 23a is 80 mm in width
and 50 .mu.m in thickness. As shown in FIG. 3B, the second
polishing tape 23b is such that diamond abrasive grains 34 (#10000:
a grain diameter of about 0.5 .mu.m) are fixed to a PET film 31
with the binder 32. The width and thickness of the polishing tape
23b are the same as those of the polishing tape 23a. These two
types of polishing tape 23 can be replaced with each other as
needed. Moreover, these polishing tapes 23 are so designed that the
part deteriorated as a result of polishing can be replaced with a
new polishing surface by rolling up the tape gradually during
polishing.
[0030] As shown in FIG. 1A, on the entire surface of the silicon
substrate 10, a 100-nm-thick SiO.sub.2 film 11 and a 100-nm-thick
SiN film 12 were formed sequentially by CVD techniques. The result
of applying a polishing method of the first embodiment to the
removal of the stacked insulating film formed at the periphery of
the substrate 10 will be explained below.
[0031] Using the polishing apparatus of FIG. 2, the first polishing
tape 23a to which ceria abrasive grains have been fixed shown in
FIG. 3A is set as the polishing tape 23. The substrate to be
processed 20 is absorbed and fixed to the stage 21, which is then
rotated at a predetermined speed. At the same time, the polishing
tape 23 is pressed against the substrate periphery, while the
polishing tape 23 is being transported at a predetermined speed,
thereby polishing the substrate periphery.
[0032] Although the polishing time was twice as long as that of the
conventional combination of diamond abrasive grains #4000 and
diamond abrasive grains #10000, the surface roughness after
polishing was 1/5 of that of the combination. Moreover, the
polishing time was 1/10 of that of the polishing removal using only
the same grain-diameter diamond abrasive grains #10000 and the
surface roughness after polishing was about 1/2 of that of the
polishing removal.
[0033] On the other hand, when the polishing capability for the
silicon substrate 10 is compared in terms of a change in the
substrate weight before and after polishing, it is as low as 1/150
of that of diamond abrasive grains #4000 and also as low as 1/5 of
that of diamond abrasive grains #10000. These mean that ceria
abrasive grains act chemically on the SiO.sub.2 film 11 or SiN film
12 effectively. Furthermore, there is no chemical action on Si,
which means that the polishing capability depends on the mechanical
strength of the abrasive grains themselves.
[0034] When the substrate periphery is polished, since the surface
to be polished has a curvature in the cross-sectional direction and
circumferential direction of the silicon substrate 10, polishing is
performed, while the contact surface of the polishing head 24 is
being moved so as to follow the curvature of the silicon substrate
10. At this time, to prevent polishing remains from occurring,
excessive polishing is needed. Ceria grains have the advantage of
having a high polishing capability for SiO.sub.2 and SiN and a low
polishing capability for Si. In the excessive polishing, this
advantage works effectively. That is, ceria abrasive grains are
very effective in polishing and removing the unnecessary film
(SiO.sub.2 film, SiN film) deposited on the periphery of the
silicon substrate 10.
[0035] As described above, although use of the first polishing tape
23a to which ceria abrasive grains have been fixed sufficiently
reduces the surface roughness after polishing as compared with use
of the conventional combination of diamond abrasive grains #4000
and diamond abrasive grains #10000, the polishing time gets longer
than that of the combination. To overcome this problem, the
polishing tape 23a to which ceria abrasive grains (#10000) have
been fixed and the polishing tape 23b to which diamond abrasive
grains (#10000) have been fixed are combined in the first
embodiment to shorten the polishing time, which will be explained
below.
[0036] First, the polishing removal of the stacked insulating film
was started with the polishing tape 23a to which ceria abrasive
grains had been fixed and continued until a part of the underlying
Si had been exposed. Then, polishing was performed with the
polishing tape 23b to which diamond abrasive grains whose polishing
capability for the silicon substrate is higher than that of ceria
abrasive grains had been fixed. As a result, the total polishing
time was reduced to about 1/2 of that when only ceria abrasive
grains were used. That is, the polishing time became the same as
that of the conventional combination of diamond abrasive grains
#4000 and diamond abrasive grains #10000. At this time, the surface
roughness after polishing was reduced to about 1/3 of that of the
conventional combination of diamond abrasive grains #4000 and
diamond abrasive grains #10000.
[0037] When the polishing step with the ceria abrasive grain
polishing tape 23a is switched to the polishing step with the
diamond abrasive grain polishing tape 23b or vice versa, the
switching between the polishing steps is performed efficiently by
using a change in the rotational load of the motor that holds and
rotates the substrate to be polished.
[0038] Furthermore, instead of polishing with the polishing tape
23b after the completion of polishing with the polishing tape 23a,
polishing with the polishing tape 23a was alternated with polishing
with the polishing tape 23b, which produced almost the same effect
as described above.
[0039] Moreover, as shown in FIG. 4, the polishing tape 23a to
which ceria abrasive grains had been fixed and the polishing tape
23b to which diamond abrasive grains had been fixed were brought
into contact with different places of the periphery of the
substrate 20 at the same time, thereby performing polishing with
ceria abrasive grains in parallel with polishing with diamond
abrasive grains. In this case, the polishing time was reduced to
about 1/3 of that when only ceria abrasive grains were used. That
is, the polishing time was reduced to 2/3 of that of the
conventional combination of diamond abrasive grains #4000 and
diamond abrasive grains #10000. The surface roughness after
polishing was reduced to about 1/3 of the conventional
combination.
[0040] This means that the removal efficiency of the stacked
insulating film was improved by the synergistic effect as a result
of the improvement of the polishing efficiency by polishing with
ceria abrasive grains whose polishing efficiency was high for the
high-hardness SiO.sub.2 film 11 and SiN film 12 and by silicon
polishing with diamond abrasive grains after a part of the
underlying silicon substrate had been exposed.
[0041] As described above, in the first embodiment, the silicon
substrate 10 on whose surface the unnecessary film including a high
hardness film, including the SiO.sub.2 film 11 and SiN film 12, has
been formed is polished using the polishing tape 23a to which ceria
abrasive grains have been fixed and the polishing tape 23b to which
diamond abrasive grains have been fixed. By doing this, not only
can the unnecessary film be removed at a high efficiency, but also
the polished surface accuracy can be increased. Accordingly, the
productivity can be increased and a decrease in the number of
defects enables the yield to be improved.
[0042] Specifically, a combination of polishing with abrasive
grains having a chemical effect and polishing with abrasive grains
having a mechanical effect makes it possible not only to remove the
unnecessary films, including oxide-silicon-series or
nitride-silicon-series high-hardness films, and uneven surfaces at
a high efficiency but also to increase the polished surface
accuracy.
[0043] Furthermore, in place of the stacked film of the SiO.sub.2
film 11 and SiN film, a 200-nm-thick SiO.sub.2 film was formed on
the silicon substrate 10 by CVD techniques. At this time, to remove
the film on the substrate periphery, the first embodiment was
applied using the polishing apparatus of FIG. 4. As a result, a
combination of ceria abrasive grains #10000 and diamond abrasive
grains #10000 reduced the polishing time to about 1/2 of that of
the conventional combination of diamond abrasive grains #4000 and
diamond abrasive grains #10000 and further reduced the surface
roughness to 1/3 of that of the conventional combination.
[0044] Similarly, a 200-nm-thick SiN film was formed on the silicon
substrate 10 by CVD techniques. At this time, to remove the film on
the substrate periphery, the first embodiment was applied using the
polishing apparatus of FIG. 4. As a result, a combination of ceria
abrasive grains #10000 and diamond abrasive grains #10000 reduced
the polishing time to about 3/4 of that of the conventional
combination of diamond abrasive grains #4000 and diamond abrasive
grains #10000 and further reduced the surface roughness to 1/3 of
that of the conventional combination.
Second Embodiment
[0045] FIGS. 5A to 5C are sectional views to help explain substrate
processing steps according to a second embodiment of the invention.
FIG. 5A shows a state where trenches are made. FIG. 5B shows a
state of a substrate to be processed before polishing. FIG. 5C
shows a state of the substrate after polishing. In FIGS. 5A to 5C,
numeral 10 indicates a silicon substrate, 11 an SiO.sub.2 film, 12
an SiN film, and 13 needle-like silicon projections.
[0046] As shown in FIG. 5A, on the surface of the silicon substrate
10, an SiN film 12 and an SiO.sub.2 film 11 are deposited
sequentially by LP-CVD techniques. These films are patterned,
thereby forming a hard mask composed of a stacked film of the SiN
film 12 and SiO.sub.2 film 11. Then, using the hard mask, the
silicon substrate 10 is etched by RIE techniques, thereby making
trenches. At this time, etching is disordered at the substrate
periphery, with the result that mask remains and needle-like Si
projections 13 are formed. Thereafter, the SiO.sub.2 film 11 is
peeled by wet etching.
[0047] FIG. 5B shows a state where the SiO.sub.2 film 11 has been
removed. At the periphery of the silicon substrate 10, an SiN film
12 and needle-like silicon projections 13 have been formed. A
polishing method of the second embodiment is applied to the removal
of the needle-like silicon projections 13 including the SiN film
formed during the formation of trenches and to the planarization of
the substrate.
[0048] In the second embodiment, too, a polishing method using a
combination of the polishing tape 23a to which ceria abrasive
grains #10000 had been fixed and the polishing tape 23b to which
diamond abrasive grains #10000 had been fixed was applied. Using
the polishing apparatus of FIG. 4, polishing was performed under
predetermined polishing conditions, thereby completing the process
as shown in a sectional view of the substrate in FIG. 5C.
[0049] Here, when an attempt was made to remove the SiN film 12 and
needle-like silicon projections 13 and planarize the substrate 10
only with the ceria-abrasive-grain polishing tape 23a, even making
the polishing time twice as long as that of the conventional
combination of diamond abrasive grains #4000 and diamond abrasive
grains #10000 failed to finish the removal of the silicon
needle-like projections 13. The reason for this is that the removal
of the SiN film 12 progressed, but the removal of the silicon
needle-like projections 13 and the planarization of the substrate
advance slowly.
[0050] On the other hand, use of a polishing method using a
combination of the ceria-abrasive-grain polishing tape 23a and the
diamond-abrasive-grain polishing tape 23b reduced the polishing
time to 2/3 of the conventional combination, eliminated flaws
caused by diamond abrasive grains #4000 observed in the
conventional art, and decreased the surface roughness to 1/3 of
that of the conventional combination. That is, when the removal of
the oxide-silicon-series or nitride-silicon-series unnecessary film
and the planarization of the substrate are needed, a combination of
the ceria-abrasive-grain polishing tape 23a and the
diamond-abrasive-grain polishing tape 23b produces a greater
effect.
[0051] As described above, a substrate to be processed where an SiN
film 12 and needle-like silicon projections 13 have been formed at
the surface of the silicon substrate 10 is polished using the
polishing tape 23a to which ceria abrasive grains have been fixed
and the polishing tape 23b to which diamond abrasive grains have
been fixed, which makes it possible to remove the unnecessary film
and needle-like projections 13 at the substrate periphery at a high
efficiency and further increase the polished surface accuracy.
Accordingly, the same effect as that of the first embodiment is
obtained.
Third Embodiment
[0052] FIGS. 6A to 6D are sectional views to help explain substrate
processing steps according to a third embodiment of the
invention.
[0053] In the third embodiment, the invention is applied to the
removal of metallic contaminants at the substrate periphery caused
in forming silicide for a metal film (e.g., Ni or Co).
[0054] First, as shown in FIG. 6A, after an SiN film 12 was
deposited on the silicon substrate 10, a resist film (not shown)
was applied to the SiN film 12. Thereafter, with the resist film as
a mask, openings were made to the silicon substrate 10 by
photolithography and etching techniques for the SiN film 12.
[0055] Next, as shown in FIG. 6B, metal (Co) was deposited by, for
example, sputtering techniques, thereby forming a metal film (Co
film) 61 on the substrate 10 in the exposed parts from the SiN film
12. Thereafter, the metal film was heat-treated, thereby causing
only the surface of the substrate Si exposed in the opening to
react with the metal to form a silicide film (CoSi film) 62. The
unreacted metal film 61 was removed by etching or the like. At this
time, if a resist film were not applied sufficiently to the
periphery of the silicon substrate 10, the substrate Si might be
exposed at the periphery when openings are made to the silicon
substrate 10. If a metal film is deposited on the Si substrate
exposed at the periphery and then is heat-treated, Si exposed at
the periphery reacts with the metal, producing a reactant of the
metal film and Si, such as a silicide film, which causes a problem:
metallic contaminants are emitted from the periphery of the silicon
substrate 10.
[0056] To prevent the emission of metallic contaminants, the metal
silicide film 62 and SiN film 12 at the periphery are to be removed
after a reactant, such as a silicide film, is formed. As seen from
FIG. 6C, the reason why the SiN film 12 at the substrate periphery
is removed is that the surrounding SiN film 12 is obstructive to
the polishing of the metal silicide film 62 at the substrate
periphery. That is, if the SiN film 12 remains around the metal
silicide film 62, the metal silicide film 62 cannot be polished
efficiently making use of the mechanical effect.
[0057] The result of applying the third embodiment to the removal
of metallic contaminants developed at the substrate periphery will
be explained. The method using the combination of the polishing
tape 23a to which ceria abrasive grains had been fixed and the
polishing tape 23b to which finishing diamond abrasive grains had
been fixed in the first embodiment was applied.
[0058] Using the polishing apparatus of FIG. 4, a substrate to be
processed is absorbed and fixed to the stage 21, which is rotated
at a predetermined speed. Then, the polishing tapes 23 (23a, 23b)
are pressed against the substrate periphery at a predetermined
pressure and polish the periphery, while the polishing tapes 23 are
being transported at a predetermined speed, thereby bringing the
substrate to completion as shown in a sectional view of the
substrate in FIG. 6D. In this case, polishing with the polishing
tape 23a having a chemical effect is performed in parallel with
polishing with the polishing tape 23b having a mechanical effect.
Accordingly, the SiN film around the metal silicide film to be
removed can be polished efficiently, which enables the metal
silicide film to be polished and removed reliably.
[0059] When polishing was done under the same conditions, the
polishing time was reduced to 2/3 of that of the conventional
combination of diamond rough abrasive grains (#4000) and finishing
abrasive grains (#10000). Moreover, flaws caused by rough diamond
abrasive grains observed in the conventional art were eliminated,
and the surface roughness was decreased to 1/3 of that of the
conventional combination. The reason why the surface roughness was
improved is that only finishing diamond abrasive grains were used
and rough diamond abrasive grains were not used. Furthermore, the
reason why the polishing time was reduced, regardless of using no
diamond abrasive grain is that use of the polishing tape 23a to
which ceria abrasive grains had been fixed enabled the SiN film
around the metal silicide film at the substrate periphery to be
removed efficiently by the chemical effect.
[0060] While in the third embodiment, a nitride film (Si nitride
film) has been used as a mask material in the third embodiment, an
oxide film (Si oxide film) may be used. Even when applied to a case
where an oxide film or a nitride film is formed after the formation
of silicide to temporarily suppress the metallic contamination of
other processes and then not only the silicide film but also the
oxide film and nitride film are removed, this produces the effects
of reducing the polishing time and improving the surface
roughness.
[0061] (Modification)
[0062] The invention is not limited to the above embodiments. While
in the embodiments, SiO.sub.2 and SiN have been used as the
unnecessary films at the substrate periphery, the invention is not
necessarily restricted to these and may be applied to, for example,
SiOC and SiCN. That is, the invention may be applied to
oxide-silicon-series and nitride-silicon-series unnecessary
films.
[0063] When not only an oxide-silicon-series film or a
nitride-silicon-series film but also the upper layer, lower layer,
or mixed layer of a material difficult to polish with a ceria
abrasive grain tape, such as a single-crystal silicon film, an
amorphous silicon film, a polysilicon film, or an another silicon
series film obtained by introducing impurities into those films, a
carbon film, or a metal film (tungsten, copper, aluminum,
ruthenium, titanium, tantalum, hafnium, and a compound including
those materials) are polished and removed, a combination of the
ceria abrasive grains with abrasive grains having a mechanically
polishing and removing capability, such as diamond abrasive grains,
is effective.
[0064] While in the embodiments, ceria particles have been used for
an oxide-silicon-series film or a nitride-silicon-series film as
abrasive grains having a chemical effect, silica particles may be
used instead of ceria particles. Moreover, SiC particles may be
used in place of diamond particles.
[0065] While in the embodiments, the fixed-abrasive-grain method
using polishing tapes has been used in polishing with abrasive
grains that include particles having a chemical effect as a main
component, a free-abrasive-grain method which performs polishing,
while supplying an abrading agent including abrasive particles to
the contact surface between the polishing surface and the polished
surface may be used instead. Moreover, in polishing by the
mechanical effect using diamond abrasive grains, not only the
fixed-abrasive-grain method but also free-abrasive-grain method may
be used.
[0066] Specifically, as shown in FIG. 7, a nonwoven cloth 72 fixed
to a polishing head 72 may be brought into contact with the
periphery of a substrate to be processed 20 absorbed and fixed to
the stage 21 and, at same time, a polishing liquid that includes
abrasive grains including ceria grains or the like as a main
component may be supplied from a nozzle 73 to the vicinity of the
periphery of the substrate 20, thereby causing the substrate
periphery to be polished at the part in contact with the nonwoven
cloth 72. In this case, too, a combination of polishing with ceria
abrasive grains and polishing with diamond abrasive grains produces
the same effects as the above embodiments. Here, what is supplied
from the nozzle 73 is a polishing liquid that includes abrasive
grains including grains having a chemical effect as a main
component, not the chemical reacting with the substrate Si.
Therefore, the disadvantage of the substrate surface being etched
or the like can be avoided.
[0067] Furthermore, while in the embodiments, the bevel part, a
part where the cross section has a curvature at the end of the
semiconductor substrate, has been polished, the invention may be
applied to the polishing of a notch part provided at a part of the
periphery of the substrate as an alignment mark or for recognizing
the crystal orientation on the wafer main surface. Moreover, the
semiconductor substrate is not necessarily limited to an Si
substrate. Another semiconductor material may be used instead.
[0068] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *