U.S. patent application number 10/774492 was filed with the patent office on 2004-08-12 for semiconductor film and method of forming the same, and semiconductor device and display apparatus using the semiconductor film.
This patent application is currently assigned to Sharp Kabushiki Kaisha. Invention is credited to Mizuki, Toshio, Nakamura, Yoshinobu.
Application Number | 20040155246 10/774492 |
Document ID | / |
Family ID | 26625509 |
Filed Date | 2004-08-12 |
United States Patent
Application |
20040155246 |
Kind Code |
A1 |
Mizuki, Toshio ; et
al. |
August 12, 2004 |
Semiconductor film and method of forming the same, and
semiconductor device and display apparatus using the semiconductor
film
Abstract
A semiconductor film comprising a polycrystalline semiconductor
film provided on a substrate having an insulating surface. Nearly
all crystal orientation angle differences between adjacent crystal
grains constituting the polycrystalline semiconductor film are
present in the ranges of less than 10.degree. or
58.degree.-62.degree..
Inventors: |
Mizuki, Toshio; (Nara-shi,
JP) ; Nakamura, Yoshinobu; (Daito-shi, JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
1100 N GLEBE ROAD
8TH FLOOR
ARLINGTON
VA
22201-4714
US
|
Assignee: |
Sharp Kabushiki Kaisha
Osaka
JP
|
Family ID: |
26625509 |
Appl. No.: |
10/774492 |
Filed: |
February 10, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10774492 |
Feb 10, 2004 |
|
|
|
10294760 |
Nov 15, 2002 |
|
|
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Current U.S.
Class: |
257/66 ; 257/627;
257/E21.133; 257/E21.134; 257/E21.413; 257/E29.293 |
Current CPC
Class: |
H01L 29/66757 20130101;
H01L 21/02595 20130101; H01L 21/0262 20130101; H01L 21/02609
20130101; H01L 29/78675 20130101; H01L 21/2022 20130101; H01L
21/2026 20130101; H01L 21/02422 20130101; H01L 21/02686 20130101;
H01L 21/02672 20130101; H01L 21/02532 20130101 |
Class at
Publication: |
257/066 ;
257/627 |
International
Class: |
H01L 029/76 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 11, 2002 |
JP |
2002-005403 |
Sep 17, 2002 |
JP |
2002-270726 |
Claims
What is claimed is:
1. A semiconductor film, comprising: a polycrystalline
semiconductor film provided on a substrate having an insulating
surface, wherein nearly all crystal orientation angle differences
between adjacent crystal grains constituting the polycrystalline
semiconductor film are present in the ranges of less than
10.degree. or 58.degree.-62.degree..
2. A semiconductor film according to claim 1, wherein the
proportion of the crystal orientation angle difference between
adjacent crystal grains of 1.degree.-10.degree. or
58.degree.-62.degree. is 0.5-1.
3. A semiconductor film according to claim 1, wherein the
polycrystalline semiconductor film is made of silicon.
4. A method of forming a semiconductor film, comprising the steps
of: forming an amorphous semiconductor film on a substrate having
an insulating surface; introducing a catalytic substance for
accelerating crystallization into a surface of the amorphous
semiconductor film; applying first energy to the amorphous
semiconductor film to crystallize the amorphous semiconductor film
into a crystalline semiconductor film; and applying second energy
to the crystalline semiconductor film so that nearly all crystal
orientation angle differences between adjacent crystal grains are
present in the ranges of less than 10.degree. or
58.degree.-62.degree., wherein the crystallinity of the crystalline
semiconductor film is increased to be turned into a polycrystalline
semiconductor film.
5. A method according to claim 4, wherein the first energy is heat
energy and the second energy is strong light.
6. A method according to claim 5, wherein the energy density of the
strong light is such that after irradiation of the strong light,
the proportion of the crystal orientation angle difference between
adjacent crystal grains of less than 10.degree. or
58.degree.-62.degree. is highest.
7. A method according to claim 4, wherein the semiconductor film is
made of silicon.
8. A method according to claim 4, wherein the catalytic substance
is a metal selected from the group consisting of Fe, Co, Ni, Cu,
Ge, Pd, and Au, a compound containing at least one of these metals,
or a combination of at least one of these metals and a compound
containing at least one of these metals.
9. A method according to claim 4, wherein the concentration of the
catalytic substance at a surface of the amorphous semiconductor
film is greater than or equal to 1.times.10.sup.11 atoms/cm.sup.2
and smaller than or equal to 1.times.10.sup.16 atoms/cm.sup.2.
10. A method according to claim 5, wherein the strong light is
excimer laser light.
11. A semiconductor device, comprising a semiconductor film
according to claim 1.
12. A display apparatus, comprising a semiconductor device
according to claim 11.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of forming a
polycrystalline semiconductor film, and a semiconductor device and
a display apparatus fabricated using the method. More particularly,
the present invention relates to a method of forming a
polycrystalline semiconductor film, which has a small amount of
crystal defects, on a non-single crystal insulating film or a
non-single crystal insulating substrate. The polycrystalline
semiconductor film is produced by applying heat energy and light
energy (strong irradiation) to an amorphous semiconductor film. And
the present invention relates to a semiconductor device, such as a
liquid crystal driver, a semiconductor memory, a semiconductor
logic circuit, and the like, comprising a polycrystalline
semiconductor film formed by the method. And the present invention
relates to a display apparatus comprising the semiconductor
device.
[0003] 2. Description of the Related Art
[0004] Conventionally, there has been a known method of
crystallizing an amorphous semiconductor film provided on a
non-single crystal insulating film or substrate by applying
energy.
[0005] An example of such a method is disclosed in TECHNICAL REPORT
OF IEICE (the Institute of Electronics, Information and
Communication Engineers), Vol. 100, No. 2, ED2000-14 (April, 2000)
pp. 27-32 (hereinafter referred to as conventional example 1).
Specifically, PE-CVD (Plasma Enhanced Chemical Vapor Deposition) is
used to form an amorphous silicon film having a thickness of 45-50
nm on a glass substrate, and thereafter, the amorphous silicon film
is irradiated with excimer laser light, so that the film is
crystallized into a polycrystalline silicon film having a grain
size of 700 nm. In conventional example 1, when a polycrystalline
silicon film obtained by this method was used to fabricate a thin
film transistor (TFT), the mobility was improved up to 320
cm.sup.2/V.multidot.sec.
[0006] A crystallization method is disclosed in Japanese Laid-Open
Publication No. 2000-150382 (hereinafter referred to as
conventional example 2). Specifically, a catalytic substance is
introduced into a surface of an amorphous silicon film, the
resultant amorphous silicon film is crystallized by thermal
treatment, followed by irradiation with laser light, whereby a
crystalline silicon film having improved crystallinity can be
obtained.
[0007] FIG. 7 is a schematic diagram for explaining the
crystallization method described in conventional example 2.
[0008] In the method of conventional example 2, an amorphous
silicon film 2 having a thickness of 100 nm is formed on a glass
substrate 1 using PE-CVD, and thereafter, a silicon oxide film 3
having a thickness of about 2 nm is formed on the amorphous silicon
film 2 in order to improve wettability.
[0009] Thereafter, a solution containing nickel, which is a
catalytic substance for accelerating crystallization, is applied
onto the silicon oxide film 3, followed by spinning and drying, so
that a solution film 4 is formed on the silicon oxide film 3.
[0010] Thereafter, in this situation, annealing is performed at
550.degree. C. for 4 hours to crystallize the amorphous silicon
film 2.
[0011] Thereafter, the crystallized silicon film 2 is irradiated
with KrF excimer laser light having a wavelength of 248 nm and an
energy density of 200-350 mJ/cm.sup.2 to improve the
crystallinity.
[0012] In such a crystallization method of conventional example 2,
since crystallization is accelerated by a catalytic substance, a
crystalline silicon film can be obtained at low temperature in a
short time.
[0013] However, the method of conventional example 1 has the
following drawback. The irradiation of an amorphous silicon film
with laser light is not optimized, so that crystal grains having a
small diameter of several micrometers are obtained, potentially
leading to a polycrystalline silicon film containing a number of
grain boundaries. The grain boundary acts as a recombination center
which provides a trap level for carriers. Therefore, when a TFT is
fabricated using a polycrystal containing a number of grain
boundaries, the mobility of the TFT is reduced.
[0014] The method of conventional example 1 also has the following
drawback. Since it is not easy to irradiate the entire surface of a
large-area substrate uniformly with sufficiently stable laser
light, it is difficult to form a silicon film having uniform
crystallinity.
[0015] The method of conventional example 2 has the following
drawback. In the method, the silicon film 2 crystallized with the
introduced catalytic substance is irradiated with laser light so as
to improve the crystallinity. The optimum conditions for the laser
light irradiation are not disclosed. A number of crystal defects
may occur in a silicon film formed by the method.
[0016] If such a semiconductor film having a number of crystal
defects is used to fabricate a semiconductor device (transistor),
such as a liquid crystal driver, a semiconductor memory, a
semiconductor logic circuit, and the like, problems arise, such as
the mobility of carriers is small, the threshold voltage is high,
and the like. Moreover, dispersions in carrier mobility and
threshold voltage are large between a number of semiconductor
devices (transistors) fabricated in a liquid crystal driver, or the
like.
SUMMARY OF THE INVENTION
[0017] According to an aspect of the present invention, a
semiconductor film is provided, which comprises a polycrystalline
semiconductor film provided on a substrate having an insulating
surface. Nearly all crystal orientation angle differences between
adjacent crystal grains constituting the polycrystalline
semiconductor film are present in the ranges of less than
10.degree. or 58.degree.-62.degree..
[0018] In one embodiment of this invention, the proportion of the
crystal orientation angle differences between adjacent crystal
grains of 1.degree.-10.degree. or 58.degree.-62.degree. is
0.5-1.
[0019] In one embodiment of this invention, the polycrystalline
semiconductor film is made of silicon.
[0020] According to another aspect of the present invention, a
method of forming a semiconductor film is provided, which comprises
the steps of: forming an amorphous semiconductor film on a
substrate having an insulating surface; introducing a catalytic
substance for accelerating crystallization into a surface of the
amorphous semiconductor film; applying first energy to the
amorphous semiconductor film to crystallize the amorphous
semiconductor film into a crystalline semiconductor film; and
applying second energy to the crystalline semiconductor film so
that nearly all crystal orientation angle differences between
adjacent crystal grains are present in the ranges of less than
10.degree. or 58.degree.-62.degree.. The crystallinity of the
crystalline semiconductor film is increased to be turned into a
polycrystalline semiconductor film.
[0021] In one embodiment of this invention, the first energy is
heat energy and the second energy is strong light.
[0022] In one embodiment of this invention, the energy density of
the strong light is such that after irradiation of the strong
light, the proportion of the crystal orientation angle difference
between adjacent crystal grains of less than 10.degree. or
58.degree.-62.degree. is highest.
[0023] In one embodiment of this invention, the semiconductor film
is made of silicon.
[0024] In one embodiment of this invention, the catalytic substance
is a metal selected from the group consisting of Fe, Co, Ni, Cu,
Ge, Pd, and Au, a compound containing at least one of these metals,
or a combination of at least one of these metals and a compound
containing at least one of these metals.
[0025] In one embodiment of this invention, the concentration of
the catalytic substance at a surface of the amorphous semiconductor
film is greater than or equal to 1.times.10.sup.11 atoms/cm.sup.2
and smaller than or equal to 1.times.10.sup.16 atoms/cm.sup.2.
[0026] In one embodiment of this invention, the strong light is
excimer laser light.
[0027] According to another aspect of the present invention, a
semiconductor device is provided, which comprises the
above-described semiconductor film.
[0028] According to another aspect of the present invention, a
display apparatus is provided, which comprises the above-described
semiconductor device.
[0029] Thus, the invention described herein makes possible the
advantages of providing a method of forming a semiconductor film
having a reduced number of crystal defects and good crystallinity,
and a semiconductor device and a display apparatus fabricated by
the method.
[0030] These and other advantages of the present invention will
become apparent to those skilled in the art upon reading and
understanding the following detailed description with reference to
the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a cross-sectional view for explaining a method of
forming a crystalline semiconductor film according to Example 1 of
the present invention.
[0032] FIGS. 2A and 2B are cross-sectional views for explaining a
method of forming a crystalline semiconductor film according to
Example 2 of the present invention.
[0033] FIG. 3 is a cross-sectional view for explaining a method of
forming a crystalline semiconductor film according to Example 3 of
the present invention.
[0034] FIG. 4 is a cross-sectional view for explaining a method of
forming a semiconductor device according to Example 4 of the
present invention.
[0035] FIGS. 5A and 5B are cross-sectional views for explaining a
method of fabricating a display apparatus comprising the
semiconductor device according to Example 4.
[0036] FIG. 6 is a graph showing the misorientation length in a
crystalline silicon film after thermal treatment with respect to
crystal orientation.
[0037] FIG. 7 is a schematic diagram for explaining a
crystallization method described in conventional example 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] The inventors have focused their attention to an appropriate
condition for irradiation with excimer laser when an amorphous
silicon film is crystallized by introducing a crystallization
accelerating catalytic substance thereinto and heating, and the
film is irradiated with excimer laser in order to improve the
crystallinity. The inventors experimentally revealed that when a
crystalline silicon film, of which crystallization has been
performed by introduction of a catalytic substance and subsequent
thermal treatment, is irradiated with excimer laser under the
appropriate condition, nearly all differences in crystal
orientation between adjacent crystal grains are present in the
ranges of less than 10.degree. or 58.degree.-62.degree., i.e., good
crystallinity with a reduced number of crystal defects.
[0039] Such an experiment will be described in detail below.
[0040] An amorphous silicon film having a thickness of 50 nm was
formed on a glass substrate using PE-CVD, where the film growth
temperature was 300.degree. C. and SiH.sub.4 gas was used.
[0041] Thereafter, a nickel thin film was formed on the amorphous
silicon film by sputtering, where the nickel atomic concentration
at a surface of the thin film was
1.times.10.sup.13-5.times.10.sup.13/cm.sup.2.
[0042] Thereafter, the resultant amorphous silicon film was heated
in an electric furnace at 550.degree. C. for 4 hours. This thermal
treatment allowed the introduced nickel to react with silicon in
the amorphous silicon film, whereby nickel silicide was randomly
formed on the entire surface of the amorphous silicon film.
Further, the nickel silicide acts as a crystal nucleus,
accelerating crystallization of the amorphous silicon film. The
nickel silicide was moved laterally, crystallizing the amorphous
silicon. A crystalline silicon film was formed at sites through
which the nickel silicide had passed.
[0043] Subsequently, in order to improve the crystallinity of the
crystalline silicon film crystallized with the nickel silicide, the
film was irradiated with a XeCl excimer laser to form a
polycrystalline silicon film (for the sake of clearance, a silicon
film after thermal treatment is herein referred to as a crystalline
silicon film, and a silicon film after excimer laser irradiation is
herein referred to as a polycrystalline silicon film).
[0044] The energy density of the excimer laser, which was directed
onto a crystalline silicon film after thermal treatment in order to
improve the crystallinity, was variously changed in the range of
280 mJ/cm.sup.2-380 mJ/cm.sup.2 so as to investigate an appropriate
condition for the energy density of the excimer laser.
[0045] The crystal orientation of a crystalline silicon film
obtained by thermal treatment and a polycrystalline silicon film
obtained by excimer laser irradiation can be measured by an EBSP
(Electron Backscatter Diffraction Pattern) method. In the EBSP
method, an electron beam is directed onto a sample whose crystal
orientation is to be measured. With an electron back-scatter
(Kikuchi) diffraction pattern representing the electron beam
scattered by the sample, the crystal orientation is measured with
an angle precision of .+-.1.degree. or less.
[0046] In accordance with the EBSP method, a silicon film having an
area of 4 .mu.m.times.12 .mu.m was scanned with an electron beam at
a measurement pitch of 0.05 .mu.m, and the angle difference in
crystal orientation (i.e., misorientation) between adjacent
measurement points was measured.
[0047] FIG. 6 is a graph showing the number of misorientations
which occurred in a crystalline silicon film after thermal
treatment with respect to crystal orientation, which is converted
to length.
[0048] Referring to FIG. 6, the misorientation length is
distributed from 1.degree., which is the lower limit of measurement
precision, to about 65.degree.. The misorientation length is
greater in the ranges of 1.degree.-10.degree. and
58.degree.-62.degree..
[0049] The reason that the misorientation length is greater in the
range of 1.degree.-10.degree. is believed as follows.
[0050] When the amorphous silicon film containing the introduced
nickel was subjected to thermal treatment, nickel reacted with
silicon, whereby nickel silicide was randomly formed on the entire
surface of the amorphous silicon film. The thus-formed nickel
silicide acted as a crystal nucleus for crystallization of the
amorphous silicon film. The crystallization proceeded from the
crystal nucleus laterally with respect to the substrate.
[0051] In the crystallization wherein the nickel silicide acted as
a crystal nucleus, crystals were grown in the amorphous silicon
film by extending in the form of needles or columns. The crystal
orientation gradually changed in the course of the crystal growth
so as to relax stress. For this reason, there were many small angle
misorientations, and the misorientation length is greater in the
range of 1.degree.-10.degree..
[0052] The reason that the misorientation length is greater in the
range of 58.degree.-62.degree. is believed as follows.
[0053] The crystalline silicon film, which was obtained by
subjecting the amorphous silicon film containing the introduced
nickel to thermal treatment, was irradiated with an excimer laser
in order to improve the crystallinity.
[0054] When the energy density of the excimer laser is high, a
portion of the crystalline silicon film is locally melted. When the
melted crystal is recrystallized, small crystal grains are formed.
These small crystal grains are responsible for misorientation in
the range of 58.degree.-62.degree.. Note that the crystalline
structure causing misorientation in the range of
58.degree.-62.degree. was investigated, and as a result, it was
found that the structure is a twin structure. This twin structure
is constructed with a crystal having a crystal orientation rotated
by 58.degree.-62.degree. with respect to <111> orientation as
a rotation axis and a crystal having a crystal orientation before
rotation. The boundary between the two crystals has substantially
no recombination center.
[0055] The results of measurement of the misorientation length of a
polycrystalline silicon film are shown in Table 1 below, where the
energy density of the excimer laser which was directed onto a
crystalline silicon film after thermal treatment was changed in the
range of 280 mJ/cm.sup.2-380 mJ/cm.sup.2. Table 1 shows
misorientation length for three regions of misorientation angle,
i.e., 1.degree.-10.degree., 58.degree.-62.degree. and
1.degree.-62.degree..
[0056] Column (d) in Table 1 shows the mobility of an N-channel TFT
which was fabricated using a polycrystalline silicon film obtained
by irradiation by an excimer laser having each range of energy
density.
1TABLE 1 (a) Laser (b) (c) (d) energy Misorientation Misorientation
length Mobility density length (.mu.m) proportion (cm.sup.2/V
.multidot. (mJ/cm.sup.2) 1.degree.-10.degree. 58.degree.-62.degree.
1.degree.-65.degree. 1.degree.-10.degree. 58.degree.-62.degree.
1.degree.-10.degree., 58.degree.-62.degree. sec) 380 200 160 1500
0.13 0.11 0.24 -- 370 160 170 1300 0.12 0.13 0.25 -- 360 210 180
800 0.26 0.23 0.49 180 350 220 220 750 0.29 0.29 0.59 200 340 220
180 790 0.28 0.23 0.51 210 330 390 180 800 0.49 0.23 0.71 220 320
380 20 500 0.76 0.04 0.8 235 310 390 20 570 0.68 0.04 0.72 225 300
500 20 700 0.71 0.03 0.74 220 280 550 20 750 0.73 0.03 0.76 195 0
600 20 800 0.75 0.03 0.78 60
[0057] Referring to Table 1, when the energy density of the excimer
laser was in the range of 280 mJ/cm.sup.2-320 mJ/cm.sup.2, most
misorientations were present in the range of 1.degree.-10.degree..
It is believed that when a low misorientation angle was small, the
number of lattice defects was small and the mobility was high. As
the energy density of the excimer laser was increased from 280
mJ/cm.sup.2-320 mJ/cm.sup.2, the misorientation length decreased
and the crystallinity was improved. Further, the mobility tends to
be increased with increase in the crystallinity.
[0058] When the energy density was increased from 320
mJ/cm.sup.2-330 mJ/cm.sup.2, the number of misorientations in the
range of 58.degree.-62.degree. was rapidly increased. It is
considered to be that when an excimer laser having an energy
density of 330 mJ/cm.sup.2 was applied, the crystalline silicon
film was locally melted completely from the surface to the
substrate interface, and recrystallization was initiated.
[0059] When the energy density of the excimer laser was in the
range of 330 mJ/cm.sup.2-360 mJ/cm.sup.2, most misorientations were
present in the ranges of 1.degree.-10.degree. or
58.degree.-62.degree.. In either crystal structure, the number of
recombination centers is small, and the electric characteristics
are not lowered, thereby obtaining a high mobility.
[0060] When a polycrystalline silicon film was irradiated with an
eximer laser having an energy density of 320 mJ/cm.sup.2 slightly
lower than the lowest energy density at which a crystalline silicon
film is locally melted completely from the surface to the substrate
interface (in the case of Table 1), the misorientation length was
small and the quality is considered to be highest. The mobility
also had the highest value.
[0061] When the energy density exceeded 370 mJ/cm.sup.2, the
misorientation length was substantially the same in the
misorientation angle ranges of 1.degree.-10.degree. and
58.degree.-62.degree., whereas the misorientation length was great
in the misorientation angle range of 1.degree.-62.degree.. The
reason is believed to be that after the crystalline silicon was
completely melted, the crystalline silicon was precipitated as a
very small crystal. In this case, there were a number of
misorientations having a misorientation angle other than
1.degree.-10.degree. and 58.degree.-62.degree., so that a number of
recombination centers existed. Therefore, it was considered that
the recombination centers acted as a carrier trap level, leading to
a reduction in the mobility of a TFT.
[0062] According to Table 1, the optimum energy density of excimer
laser for a TFT having a mobility of 200 cm.sup.2/V.multidot.sec,
is in the range of 300 mJ/cm.sup.2-350 mJ/cm.sup.2. When
crystallization of a polycrystalline silicon film was performed by
irradiation of an excimer laser under this condition, most
misorientations were present in the angle ranges of
1.degree.-10.degree. or 58.degree.-62.degree..
[0063] The proportion (P) of the crystal orientation difference
between adjacent crystal grains is represented by expression (1)
below and the proportion is shown in Table 1 above.
[0064] When the energy density of the excimer laser was in the
range of 300 mJ/cm.sup.2-350 mJ/cm.sup.2, the proportion of the
crystal orientation difference between adjacent crystal grains of
1.degree.-10.degree. or 58.degree.-62.degree. was at least 0.5.
Therefore, the appropriate proportion was 0.5-1.
[0065] The highest mobility was obtained when the proportion of the
crystal orientation difference between adjacent crystal grains of
1.degree.-10.degree. or 58.degree.-62.degree. was greatest. 1 P =
misori . ( 1 .degree. - 10 .degree. ) + misori . ( 58 .degree. - 62
.degree. ) misori . ( 1 .degree. - 65 .degree. ) ( 1 )
[0066] where P represents the proportion of the crystal orientation
difference between adjacent crystal grains of 1.degree.-10.degree.
or 58.degree.-62.degree., misori.(1.degree.-10.degree.) represents
the misorientation length of misorientation 1.degree.-10.degree.,
misori. (58.degree.-62.degree.) represents the misorientation
length of misorientation 58.degree.-62.degree., and misori.
(10-65.degree.) represents the misorientation length of
misorientation 1.degree.-65.degree..
[0067] Hereinafter, a method of forming a polycrystalline
semiconductor film according to the present invention will be
described by way of specific examples with reference to the
accompanying drawings. The present invention is not limited to
Examples 1 to 4 below.
EXAMPLE 1
[0068] FIG. 1 is a cross-sectional view for explaining a method of
forming a crystalline semiconductor film according to Example 1 of
the present invention.
[0069] An amorphous silicon film 12 having a thickness of 50 nm was
formed on the entire surface of a glass substrate 11 using PE-CVD.
SiH.sub.4 gas was used as a material gas for forming a film, and a
substrate temperature was 300.degree. C.
[0070] Thereafter, a nickel thin film 13 was formed on the entire
surface of the amorphous silicon film 12 by depositing nickel (Ni)
using a sputtering method. In Example 1, the atomic concentration
of nickel in the nickel thin film 13 was
1.times.10.sup.13/cm.sup.2.
[0071] Thereafter, thermal treatment was performed using an
electric furnace. Conditions for the thermal treatment were
550.degree. C. and 4 hours, for example. The thermal treatment
allowed nickel in the nickel thin film 13 to react with silicon in
the amorphous silicon film 12, whereby nickel silicide was formed.
The nickel silicide acted as a crystal nucleus, thereby allowing
crystallization.
[0072] Thereafter, the silicon film 12 crystallized by heating was
irradiated with a XeCl excimer laser, thereby improving the
crystallinity. In this case, the energy density of the excimer
laser was set to be in the range of 300-350 mJ/cm.sup.2.
[0073] With the above-described steps, a polycrystalline silicon
film was formed such that nearly all crystal orientation angle
differences between adjacent crystal grains were present in the
ranges of less than 10.degree. or 58.degree.-62.degree..
EXAMPLE 2
[0074] FIGS. 2A and 2B are cross-sectional views for explaining a
method of forming a crystalline semiconductor film according to
Example 2 of the present invention.
[0075] As shown in FIG. 2A, an amorphous silicon film 12 having a
thickness of 50 nm was formed on the entire surface of a glass
substrate 11 using PE-CVD with SiH.sub.4 gas.
[0076] Thereafter, a SiO.sub.2 film 14 having a thickness of 100 nm
was formed on the entire amorphous silicon film 12. Thereafter, a
predetermined portion of the SiO.sub.2 film 14 was removed by a RIE
method, and the portion was used as a catalytic substance
introducing region 15. The catalytic substance introducing region
15 was in the shape of a line having a width of 10 .mu.m, for
example.
[0077] Thereafter, as shown in FIG. 2B, a nickel thin film 13 was
formed on the SiO.sub.2 film 14 by a sputtering method. In Example
2, the atomic concentration of nickel in the nickel thin film 13
was 5.times.10.sup.13/cm.sup.2.
[0078] Thereafter, thermal treatment was performed using an
electric furnace. Conditions for the thermal treatment were
550.degree. C. and 4 hours. The thermal treatment allowed nickel in
the catalytic substance introducing region 15 to react with silicon
in the amorphous silicon film 12, whereby nickel silicide was
formed. The nickel silicide acted as a crystal nucleus, thereby
allowing crystallization. The nickel silicide moved laterally with
respect to the substrate surface, allowing the silicon in the
amorphous silicon film 12 to be crystallized. A crystalline
silicone film was formed in the wake of the moving nickel
silicide.
[0079] Thereafter, the SiO.sub.2 film 14 was removed from the
silicon film 12 which was turned into crystalline silicon by
heating.
[0080] Thereafter, the silicon film 12 was irradiated with XeCl
excimer laser, thereby improving the crystallinity. In this case,
the energy density of the excimer laser was set to be in the range
of 300-350 mJ/cm.sup.2.
[0081] With the above-described steps, a polycrystalline silicon
film was formed such that nearly all crystal orientation angle
differences between adjacent crystal grains were present in the
ranges of less than 10.degree. or 58.degree.-62.degree..
EXAMPLE 3
[0082] FIG. 3 is a cross-sectional view for explaining a method of
forming a crystalline semiconductor film according to Example 3 of
the present invention.
[0083] An amorphous silicon film 12 having a thickness of 50 nm was
formed on the entire surface of a glass substrate 11 using PE-CVD.
SiH.sub.4 gas was used as material gas for forming a film, and a
substrate temperature was 300.degree. C.
[0084] Thereafter, a nickel thin film 13 was formed on the entire
surface of the amorphous silicon film 12 by depositing nickel (Ni)
using a sputtering method. In Example 3, the atomic concentration
of nickel in the nickel thin film 13 was
1.times.10.sup.13/cm.sup.2.
[0085] Thereafter, thermal treatment was performed using an
electric furnace. Conditions for the thermal treatment were
550.degree. C. and 4 hours, for example. The thermal treatment
allowed nickel in the nickel thin film 13 to react with silicon in
the amorphous silicon film 12, whereby nickel silicide was formed.
The nickel silicide acted as a crystal nucleus, thereby allowing
crystallization.
[0086] Thereafter, high-temperature thermal treatment
(900-1000.degree. C.) was performed, thereby improving the
crystallinity thereof. The high-temperature thermal treatment was
intended to apply heat energy to the amorphous silicon film 12
instead of laser energy in order to improve the crystallinity
thereof. Si was not melted by the high-temperature thermal
treatment. The resultant misorientation distribution was
substantially the same as that of a polycrystalline silicon
irradiated with excimer laser having a laser energy density of 300
mJ/cm.sup.2-320 mJ/cm.sup.2.
[0087] With the above-described steps, a polycrystalline silicon
film was formed such that nearly all crystal orientation angle
differences between adjacent crystal grains were present in the
ranges of less than 10.degree. or 58.degree.-62.degree..
EXAMPLE 4
[0088] FIG. 4 is a cross-sectional view for explaining a method of
fabricating a semiconductor device according to Example 4 of the
present invention.
[0089] In Example 4, the crystalline silicon film described in any
of Examples 1 to 3 was used to form a semiconductor device, such as
a thin film transistor or the like. The semiconductor device
fabricated in Example 4 can be used in a liquid crystal driver, a
semiconductor memory, a semiconductor logic circuit, or the
like.
[0090] The method of Example 4 will be specifically described below
with reference to FIG. 4.
[0091] A polycrystalline silicon film was formed on a glass
substrate 21 using the method of fabricating a crystalline
semiconductor film described in any of Examples 1 to 3. Thereafter,
the polycrystalline silicon film was patterned into a predetermined
shape by a RIE method using CF.sub.4 gas and O.sub.2 gas so as to
form an island-shaped polycrystalline silicon film 22. Thereafter,
the entire substrate surface with the polycrystalline silicon film
22 was subjected to plasma CVD using TEOS (tetraethoxysilane) gas
and O.sub.3 gas, thereby forming a gate SiO.sub.2 film 23.
[0092] Thereafter, a WSi.sub.2 layer was formed on the glass
substrate 21, on which the gate SiO.sub.2 film 23 had been formed,
by a sputtering method. Thereafter, a substantially middle portion
of the crystalline silicon film 22 was etched by a RIE method using
CF.sub.4 gas and O.sub.2 gas so as to obtain a pattern such that
the WSi.sub.2 layer remained only on the substantially middle
portion. As a result, a WSi.sub.2 polycrystalline gate electrode 24
was formed.
[0093] Thereafter, an impurity was introduced into the crystalline
silicon film 22 in order to form the source and drain regions of a
thin film transistor by an ion doping method. In Example 4, the
above-described WSi.sub.2 polycrystalline gate electrode 24 served
as a mask when introducing the impurity. Thus, the impurity was
introduced into the crystalline silicon film 22 other than the
portion on which the WSi.sub.2 polycrystalline gate electrode 24
was provided. When an n-type transistor is formed, an introduced
impurity is phosphorous (P). When a p-type transistor is formed, an
introduced impurity is boron (B).
[0094] Thereafter, an SiO.sub.2 film 25 was formed on the entire
surface of the glass substrate 21 by a plasma CVD method using TEOS
gas and O.sub.3 gas. Thereafter, a contact hole 26 was formed on
portions of the crystalline silicon film 22, which were to be
source and drain regions, by a RIE method using CF.sub.4 gas and
CHF.sub.3 gas.
[0095] Thereafter, Al was deposited on the entire substrate surface
by a sputtering method. Thereafter, an Al conductor 27, which is
electrically connected via the contact hole 26 provided in the
SiO.sub.2 film 25 to the crystalline silicon film 22 by a RIE
method using BCl.sub.3 gas and Cl.sub.2 gas.
[0096] Thereafter, a SiN protection film 28 was formed on the
entire substrate surface by a plasma CVD using SiH.sub.4 gas,
NH.sub.3 gas or N.sub.2 gas. Thereafter, a portion of the SiN
protection film 28 was etched using CF.sub.4 gas and CHF.sub.3 gas
so as to form a through hole 29 which is electrically connected to
the Al conductor 27. Thus, a semiconductor device including a
semiconductor transistor, a resistor, a capacitor and the like was
completed.
EXAMPLE 5
[0097] FIGS. 5A and 5B are cross-sectional views for explaining a
method of fabricating a display apparatus comprising the
semiconductor device according to Example 4.
[0098] In Example 5, a method of fabricating a display apparatus,
such as a liquid crystal display apparatus, or the like, comprising
a semiconductor device fabricated by a method similar to that in
Example 4, will be described.
[0099] Hereinafter, Example 5 will be described with reference to
FIGS. 5A and 5B.
[0100] According to the method of Example 4, a semiconductor device
was fabricated on an insulating substrate 21, such as a glass
substrate. Note that in Examples 4 and 5, like reference characters
refer to like parts, and each part of the semiconductor device
provided on the insulating substrate 21 is not described in
detail.
[0101] Thereafter, an ITO film was formed on the entire substrate
surface on which a SiN protection film 28 had been provided.
Thereafter, the resultant structure was subjected to patterning by
etching using HCl gas and FeCl.sub.3 gas so as to form a pixel
electrode 30 which was electrically connected via a through hole 29
provided in a SiN protection film 28 to an Al conductor 27 of the
semiconductor device.
[0102] Thereafter, a SiN film 31 was formed on the entire substrate
surface by a plasma CVD method using SiH.sub.4 gas and NH.sub.3 gas
or N.sub.2 gas. Further, a polyimide film 32 was formed on the SiN
film 31 by an offset printing method. The polyimide film 32 was
subjected to rubbing treatment so as to act as an alignment
film.
[0103] On the other hand, as shown in FIG. 5B, a film with R (red),
G (green) and B (blue) photosensitive resin films was transcribed
to another glass substrate 41 by thermo compression bonding. The
resultant structure was subjected to patterning by
photolithography. Further, a black matrix portion, which blocks
light, was formed between each of the R, G and B photosensitive
regions. Thus, a color filter 42 was fabricated.
[0104] An ITO film (counter electrode 43) was formed on the entire
surface of the color filter 42 by a sputtering method. A polyimide
film 44 was formed on the counter electrode 43 by an offset
printing method, followed by rubbing treatment.
[0105] The glass substrate 41 with the color filter 42 and the like
(FIG. 5B) and the glass substrate 21 with the semiconductor device
and the like (FIG. 5A) are attached to each other with a sealing
resin, where the rubbed sides of the substrates 41 and 21 face each
other. In this case, spherical silica particles were distributed
between the glass substrates 41 and 21 so that the glass substrates
41 and 21 are uniformly spaced. Liquid crystal (display medium) was
injected into the space between the glass substrates 41 and 21, and
thereafter, a polarizer was attached to an outer side of each of
the glass substrates 41 and 21. A driver IC and the like were
mounted on the periphery of the glass substrates 41 and 21. Thus, a
liquid crystal display was completed.
[0106] Next, the scope of the present invention will be
described.
[0107] In Examples 1 to 3, the substrate constituting the
semiconductor film was a glass substrate or a quartz substrate. A
Si wafer with a SiO.sub.2 film and a SiN film, or the like can be
used as the substrate.
[0108] In Examples 1 to 3, a silicon film was fabricated as a
specific example of a semiconductor film fabricated by the method
of the present invention. The method of fabricating a crystalline
semiconductor film according to the present invention is not
limited to a silicon film, but can be applied to a SiGe film and
the like.
[0109] In Examples 1 to 3, an amorphous silicon film was formed by
a PE-CVD method using SiH.sub.4 gas. Other methods, such as a
low-pressure CVD using Si.sub.2H.sub.6 gas, a sputtering method,
and the like, can be used.
[0110] In Examples 1 to 3, the thickness of the semiconductor film
was 50 nm. The method of forming a semiconductor film according to
the present invention can be applied to formation of a
semiconductor film having a thickness of 50-150 nm.
[0111] In Examples 1 to 3, nickel as a catalytic substance was
introduced by a deposition method using sputtering. Other methods,
such as a vacuum deposition method, a plating method, an ion doping
method, a CVD method, a spin coating method, and the like, can be
used. When the spin coating method is used to introduce a catalytic
substance, a solution containing the catalytic substance desirably
contains a solvent selected from the group consisting of water,
methanol, ethanol, n-propanol, and acetone. When nickel is used as
a catalytic substance, nickel acetate may be dissolved in the
above-described solvent and the resultant solvent may be applied
onto an insulating substrate or an amorphous silicon film.
[0112] In Examples 1 to 3, nickel was used as a catalytic substance
for accelerating crystallization. A metal selected from the group
consisting of Fe, Co, Ni, Cu, Ge, Pd, and Au, a compound containing
at least one of these metals, or a combination of at least one of
these metals and a compound containing at least one of these
metals, can be used.
[0113] Examples of a laser used for irradiating a semiconductor
film include an excimer laser having a wavelength region
corresponding to ultraviolet light, and a YAG laser having a
wavelength region corresponding to visible.multidot.ultraviolet
light. These lasers are selected depending on the type and
thickness of a semiconductor film. For example, since the
absorbance coefficient of silicon with respect to ultraviolet light
is high, an excimer laser having a wavelength region corresponding
to ultraviolet light is suitable for melting a thin silicon film.
Since the absorbance coefficient of silicon with respect to visible
ultraviolet light is low, a YAG laser having a wavelength region
corresponding to visible.multidot.ultraviolet light is suitable for
melting a thick silicon film. In Examples 1 to 3, since the silicon
film was a thin film having a thickness of 50 nm, an excimer laser
was suitable.
[0114] As described above, a semiconductor film of the present
invention is formed by the following steps of: forming an amorphous
semiconductor film on a substrate having an insulating surface;
introducing a catalytic substance for accelerating crystallization
into a surface of the amorphous semiconductor film; applying first
energy to the amorphous semiconductor film to crystallize; and
applying second energy to the crystalline semiconductor film so
that nearly all crystal orientation angle differences between
adjacent crystal grains are present in the ranges of less than
10.degree. or 58.degree.-62.degree. wherein the crystallinity of
the crystalline semiconductor film is increased to be turned into a
polycrystalline semiconductor film. As a result, a polycrystalline
semiconductor film having a small number of defects is formed while
nearly all crystal orientation angle differences between adjacent
crystal grains are present in the ranges of less than 10.degree. or
58.degree.-62.degree.. Such a semiconductor film having the
improved crystallinity can be used for a semiconductor device, such
as a TFT, thereby making it possible to provide a semiconductor
device having higher performance.
[0115] Various other modifications will be apparent to and can be
readily made by those skilled in the art without departing from the
scope and spirit of this invention. Accordingly, it is not intended
that the scope of the claims appended hereto be limited to the
description as set forth herein, but rather that the claims be
broadly construed.
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