U.S. patent application number 10/449028 was filed with the patent office on 2003-11-06 for method of manufacturing a semiconductor device and a process of a thin film transistor.
Invention is credited to Gosain, Dharam Pal, Nakagoe, Miyako, Usui, Setsuo, Westwater, Jonathan.
Application Number | 20030207507 10/449028 |
Document ID | / |
Family ID | 16709230 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030207507 |
Kind Code |
A1 |
Gosain, Dharam Pal ; et
al. |
November 6, 2003 |
Method of manufacturing a semiconductor device and a process of a
thin film transistor
Abstract
To enable radiating an optimum energy beam depending upon the
structure of a substrate (whether a metallic film is formed or not)
when an amorphous semiconductor film is crystallized and uniformly
crystallizing the overall film, first, a photoresist film and the
area of an N.sup.- doped amorphous silicon film on the photoresist
film are selectively removed by a lift-off method. Hereby, the
amorphous silicon film is thicker in an area except an area over a
metallic film (a gate electrode) than in the area over the metallic
film In this state, a laser beam is radiated. The N.sup.- doped
amorphous silicon film and an amorphous silicon film are melted by
radiating a laser beam and afterward, melted areas are crystallized
by cooling them to room temperature. As the amorphous silicon film
is thicker in the area except the area under which the metallic
film (the gate electrode) is formed than in the area under which
the metallic film is formed, the maximum temperature of the surface
of the film is equal and the overall film can be uniformly
crystallized.
Inventors: |
Gosain, Dharam Pal;
(Kanagawa, JP) ; Westwater, Jonathan; (Kanagawa,
JP) ; Nakagoe, Miyako; (Kanagawa, JP) ; Usui,
Setsuo; (Kanagawa, JP) |
Correspondence
Address: |
Jean C. Edwards
SONNENSCHEIN NATH & ROSENTHAL
P.O. Box 061080
Wacker Drive Station
Chicago
IL
60606-1080
US
|
Family ID: |
16709230 |
Appl. No.: |
10/449028 |
Filed: |
June 2, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10449028 |
Jun 2, 2003 |
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09507335 |
Feb 18, 2000 |
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09507335 |
Feb 18, 2000 |
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08902069 |
Jul 29, 1997 |
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6093586 |
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Current U.S.
Class: |
438/166 ;
257/E21.134; 257/E21.414 |
Current CPC
Class: |
H01L 29/66765 20130101;
Y10S 148/10 20130101; H01L 21/02532 20130101; H01L 21/02686
20130101; H01L 21/2026 20130101; H01L 21/02505 20130101; H01L
21/02491 20130101; H01L 21/02488 20130101; H01L 21/02422
20130101 |
Class at
Publication: |
438/166 |
International
Class: |
H01L 021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 1996 |
JP |
P08-217754 |
Claims
What is claimed is:
1. A method of manufacturing a semiconductor device, comprising: a
process for selectively forming a metallic film on a substrate; a
process for forming a semiconductor film over said substrate and
metallic film; and a process for crystallizing said semiconductor
film by radiating an energy beam on said semiconductor film in a
state in which said semiconductor film is thicker in an area over
said substrate than in an area over said metallic film.
2. A method of manufacturing a semiconductor device according to
claim 1, wherein: said semiconductor film is an amorphous
semiconductor film.
3. A method of manufacturing a semiconductor device according to
claim 1, wherein: said semiconductor film is a silicon film.
4. A method of manufacturing a semiconductor device according to
claim 1, wherein: said semiconductor film is an amorphous silicon
film.
5. A method of manufacturing a semiconductor device according to
claim 1, wherein: said energy beam is an excimer laser beam.
6. A method of manufacturing a semiconductor device according to
claim 1, wherein: the thickness of said semiconductor film in the
area over said substrate and that in the area over said metallic
film are selected in said process for polycrystallizing said
semiconductor film by radiating said energy beam so that the
maximum temperature in the respective areas of said semiconductor
film is substantially equal.
7. A method of manufacturing a semiconductor device according to
claim 1, wherein: a process for forming an insulating film on said
substrate and said metallic film is included before said process
for forming said semiconductor film and after said process for
forming said metallic film.
8. A method of manufacturing a semiconductor device according to
claim 7, wherein: the thickness of said insulating film, that in
the area over said substrate of said semiconductor film and that in
the area over said metallic film of said semiconductor film are
selected in said process for polycrystallizing said semiconductor
film by radiating said energy beam so that the maximum temperature
in the respective areas of said semiconductor film is substantially
equal.
9. A process of manufacturing a thin film transistor; comprising: a
process for forming a gate electrode on a part of a substrate
wherein said gate electrode is a metallic film; a process for
forming an insulating film on said substrate and said gate
electrode; a process for forming a first semiconductor film with a
uniform thickness on said insulating film; a process for forming a
lift-off film in an area corresponding to said gate electrode on
said first semiconductor film wherein said lift-off film is a
photoresist; a process for forming a second semiconductor film with
uniform thickness on said lift-off film and said first
semiconductor film wherein said thickness is determined based on a
material of said substrate; a process for removing said lift-off
film and said second semiconductor film on said lift-off film; a
process for uniformly crystallizing said first semiconductor film
and a residual area of said second semiconductor film by radiating
an energy beam with a set optimum value of energy required for
crystallization; and a process for forming source and drain
electrodes in a particular position on said first and second
semiconductor films.
10. A process of manufacturing a thin film transistor according to
claim 9, wherein: said lift-off film formed in an area
corresponding to said gate electrode by removing part of said
lift-off film over areas not corresponding to said gate electrode
and exposing a corresponding portion of said first semiconductor
film using said gate electrode as a mask.
11. A process of manufacturing a thin film transistor according to
claim 9, wherein: said second semiconductor film includes
impurities.
12. A process of a thin film transistor, comprising: a process for
forming a gate electrode in a part on a substrate; a process for
forming an insulating film on said substrate and said gate
electrode; a process for forming a lift-off film in an area
corresponding to said gate electrode on said insulating film; a
process for forming a first semiconductor film with uniform
thickness on said lift-off film and said insulating film; a process
for removing said lift-off film and said first semiconductor film
on said lift-off film; a process for forming a second semiconductor
film on the residual area of said first semiconductor film and said
insulating film; a process for crystallizing said first and second
semiconductor films by radiating an energy beam; and a process for
forming source and drain electrodes in a predetermined position on
said first and second semiconductor films.
13. A process of a thin film transistor according to claim 12,
wherein: said lift-off film is formed in an area corresponding to
said gate electrode by exposing from the side of said substrate
using said gate electrode as a mask.
14. A process of a thin film transistor according to claim 12,
wherein: said first semiconductor film includes impurities.
15. A method of manufacturing a semiconductor device, comprising: a
process for selectively forming a metallic film on a substrate; a
process for forming an insulating film on said substrate; a process
for forming a semiconductor film on said insulating film; and a
process for crystallizing said semiconductor film by radiating an
energy beam on said semiconductor film, wherein: the thickness of
said semiconductor film in an area over said metallic film and that
in an area in which said metallic film is not formed are selected
so that the maximum temperature in the respective areas when said
energy beam is radiated is substantially equal.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of manufacturing a
semiconductor device in which a film is formed by crystallizing a
semiconductor film by radiating an energy beam on the semiconductor
film such as amorphous silicon, particularly relates to a method of
manufacturing a semiconductor device provided with structure in
which the substrate material of a semiconductor film to be
crystallized is not even such as a thin film transistor (TFT) used
for a liquid crystal display (LCD) and others.
[0003] 2. Description of the Related Art
[0004] A TFT liquid crystal display uses a thin film transistor
(TFT) for a pixel provided with a switching function and this TFT
is formed on a glass substrate corresponding to each pixel of the
liquid crystal display. There are two types of TFTs of TFT
consisting of amorphous silicon films and TFT consisting of
polycrystalline silicon films, and high-performance TFT consisting
of polycrystalline silicon films of these can be produced on a
glass substrate at low temperature by irradiating an amorphous
silicon film with an energy beam, particularly an excimer laser
beam. The peripheral circuit of a liquid crystal display and a
pixel switching device can be produced on the same substrate by
using such TFT consisting of polycrystalline silicon films.
Recently, TFT provided with bottom gate structure attracts
attention of TFTs consisting of polycrystalline silicon films
because particularly, stable characteristics can be obtained.
[0005] This TFT provided with bottom gate structure is constituted
as shown in FIG. 9 for example. That is, a gate electrode 101
consisting of molybdenum tantalum (MoTa) is formed on a glass
substrate 100 and an oxide film (Ta.sub.2O.sub.5) 102 is formed on
this gate electrode 101. A gate insulating film consisting of a
silicon nitride (SiN.sub.x) film 103 and a silicon dioxide
(SiO.sub.2) film 104 is formed on the glass substrate 100 including
this oxide film 102 and further, a thin polycrystalline silicon
film 105 is formed on this silicon dioxide film 104. A source area
105a and a drain area 105b are respectively formed by doping N-type
impurities for example in this polycrystalline silicon film 105. A
silicon dioxide film (SiO.sub.2) 106 is selectively formed
corresponding to the channel area 105c of this polycrystalline
silicon film 105 on the polycrystalline silicon film 105. An
N.sup.+ doped polycrystalline silicon film 107 is formed on the
polycrystalline silicon film 105 and the silicon dioxide film 106
and further, a source electrode 108 and a drain electrode 109 are
respectively formed opposite to the source area 105a and the drain
area 105b on this N.sup.+ doped polycrystalline silicon film
107.
[0006] This TFT provided with bottom gate structure can be
manufactured by the following method: That is, after a molybdenum
tantalum (MoTa) film is formed on an overall glass substrate 100, a
gate electrode 101 is formed by patterning this molybdenum tantalum
film by etching so that the film is in a predetermined shape.
Afterward, an oxide film 102 is formed on the surface of the gate
electrode 101 by anodizing the gate electrode 101. Next, a silicon
nitride film 103, a silicon dioxide film 104 and an amorphous
silicon film are sequentially formed on the overall oxide film 102
by plasma enhanced chemical vapor deposition (PECVD).
[0007] Next, this amorphous silicon film is once fused by
irradiating this amorphous silicon film with a laser beam by an
excimer laser for example and afterward, crystallized by cooling
the film to room temperature. Hereby, the amorphous silicon film is
changed to a polycrystalline silicon film 105. Next, after a
silicon dioxide film 106 in the shape corresponding to a channel
area is selectively formed on the polycrystalline silicon film 105
of a part to be a channel area, an amorphous silicon film including
N-type impurities, for example phosphorus (P) and arsenic (As) is
formed and changed to an N.sup.+ doped polycrystalline silicon film
107 by irradiating the above amorphous silicon film with a laser
beam by an excimer laser again, and the impurities are electrically
activated.
[0008] Next, after an aluminum (Al) film is formed on the overall
film by a sputtering method using argon (Ar) as sputtering gas,
this aluminum film and the N.sup.+ doped polycrystalline silicon
film 107 are respectively patterned by etching so that they are in
a predetermined shape, and a source electrode 108 and a drain
electrode 109 are respectively formed on a source area 105a and a
drain area 105b. Next, dangling bond and others are inactivated by
exposing the above silicon dioxide film to hydrogen and
hydrogenating a channel area 105c by a hydrogen radical and atomic
hydrogen which both pass through the silicon dioxide film 106. TFT
provided with bottom gate structure shown in FIG. 9 can be obtained
by the above process.
OBJECT AND SUMMARY OF THE INVENTION
[0009] As described above, in the prior method, an energy beam is
radiated onto an amorphous silicon film in a process for
crystallizing it, however, at this time, the structure of a
substrate under the amorphous silicon film is not even. That is, a
metallic film (the gate electrode 101) is applied on the glass
substrate 100, the substrate under the amorphous silicon film
consists of metal and glass which are different in material and
heretofore, an energy beam is simultaneously radiated onto an
amorphous silicon film over the respective substrate and film. In
this case, the same energy beam as the following energy is also
radiated onto an amorphous silicon film over the glass substrate
100 based upon the optimum condition of the crystallizing energy of
the amorphous silicon film in a channel area over the metallic film
(the gate electrode 101).
[0010] However, even if the same amorphous silicon film is used,
the optimum value of energy required for crystallization is
different depending upon whether a substrate is made of metal or
glass because thermal conductivity is different. Therefore, more
energy beam is radiated onto the amorphous silicon film on the
glass substrate 100 by the prior method according to the optimum
condition of the amorphous silicon film on the metallic film (the
gate electrode 101) than the optimum condition and therefore, there
is a problem that partially a film is broken.
[0011] The present invention is made to solve such problems and the
object is to provide a method of manufacturing a semiconductor
device in which an optimum quantity of energy beams can be radiated
depending upon the structure of a substrate when an amorphous
semiconductor film is crystallized, an overall film can be
uniformly crystallized and a film is never broken.
[0012] A method of manufacturing a semiconductor device according
to the present invention comprises a process for selectively
forming a metallic film on a substrate, a process for forming an
amorphous semiconductor film on the substrate and the metallic film
so that an area on the substrate is thicker than an area on the
metallic film and a process for uniformly polycrystallizing the
semiconductor film by radiating an energy beam onto the
semiconductor film.
[0013] More concretely, a method of manufacturing a semiconductor
device according to the present invention comprises a process for
forming a metallic film as the gate electrode of a thin film
transistor on the surface of a substrate and forming an insulating
film on this metallic film and the substrate, a process for forming
a first amorphous semiconductor film the thickness of which is
uniform on the insulating film, a process for selectively forming a
lift-off film in an area on the first semiconductor film
corresponding to the metallic film, a process for forming a second
amorphous semiconductor film the thickness of which is uniform
including impurities on the lift-off film and the first
semiconductor film and a process for polycrystallizing the first
and second semiconductor films by radiating an energy beam after
the lift-off film and an area on the lift-off film of the second
semiconductor film are selectively removed and respectively forming
the source area and the drain area of the thin film transistor.
[0014] A method of manufacturing a semiconductor device according
to the present invention may be also constituted so that it
comprises a process for forming a metallic film as the gate
electrode of a thin film transistor on the surface of a substrate
and forming an insulating film on this metallic film and the
substrate, a process for selectively forming a lift-off film in an
area on the insulating film corresponding to the metallic film, a
process for forming a first amorphous semiconductor film the
thickness of which is uniform including impurities on the lift-off
film and the insulating film, a process for forming a second
amorphous semiconductor film the thickness of which is uniform on
the insulating film and the first semiconductor film after the
lift-off film and an area on the lift-off film of the first
semiconductor film are selectively removed and a process for
polycrystallizing the first and second semiconductor films by
radiating an energy beam after the second semiconductor film is
formed and respectively forming the source area and the drain area
of the thin film transistor.
[0015] According to a method of manufacturing a semiconductor
device according to the present invention, as the thickness of a
semiconductor film is different depending upon the state of a
substrate (whether a metallic film is formed or not) when an energy
beam is radiated to crystallize an amorphous semiconductor film,
the overall semiconductor film can be uniformly crystallized by
radiating beams with the same energy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIGS. 1 A to C are sectional views showing a method of
manufacturing a thin film transistor equivalent to a first
embodiment according to the present invention every process;
[0017] FIGS. 2A and 2B are sectional views showing a process next
to FIG. 1;
[0018] FIGS. 3A to-3D are sectional views showing a method of
manufacturing a thin film transistor equivalent to a second
embodiment according to the present invention every process;
[0019] FIGS. 4A and 4B explain the basic principle of the present
invention, FIG. 4A is a sectional view showing structure in which a
metallic film is formed under a silicon film and FIG. 4B is a
sectional view showing structure in which a metallic film is not
formed under a silicon film;
[0020] FIG. 5 shows parameters of each material used for simulation
for explaining the principle shown in FIGS. 4;
[0021] FIG. 6 is a drawing showing a characteristic for explaining
the change of the temperature of a silicon film when a laser beam
is radiated on the structure shown in FIG. 4A;
[0022] FIG. 7 is a drawing showing a characteristic for explaining
the change of the temperature of a silicon film when a laser beam
is radiated on the structure shown in FIG. 4B;
[0023] FIG. 8 is a drawing showing a characteristic showing the
thickness of a silicon film in the structure shown in FIG. 4B to
the thickness (30 nm) of an insulating film shown in FIG. 4A for
obtaining the maximum temperature of 2650 K in both structures
shown in FIGS. 4A and 4B; and
[0024] FIG. 9 is a sectional view for explaining the prior
structure of a thin film transistor and the manufacturing
method.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Referring to drawings, embodiments according to the present
invention will be described in detail below.
[0026] Prior to the concrete description of the embodiments, first,
the basic principle of the present invention will be described. As
described above, even if the same amorphous silicon film is used,
the optimum value of energy required for crystallization is
different depending upon whether a substrate is made by metal or
glass. According to the present invention, an overall semiconductor
film can be uniformly crystallized by radiating beams with the same
energy by changing the thickness of the amorphous silicon film
depending upon the structure of a substrate (whether a metallic
film is formed or not). The reasons will be described below.
[0027] FIGS. 4A and 4B show examples of substrates which are
different in the substrate structure of a silicon film. The
structure shown in FIG. 4A is formed by sequentially forming a
nickel (Ni) film 41 on a glass substrate 40, a silicon nitride
(SiN) film 42, an insulating film (SiO.sub.2) 43 and an amorphous
silicon film (a-Si) 44 on the nickel film. In the meantime, the
structure shown in FIG. 4B is formed by sequentially forming a
silicon nitride (SiN) film 42 on a glass substrate 40, an
insulating film (SiO.sub.2) 43 and an amorphous silicon film 44 and
is the same as the structure shown in FIG. 4A except that a
metallic film (the nickel film 41) is not formed under the
amorphous silicon film 44.
[0028] FIG. 6 shows the result of simulating the change of the
temperature of the surface of the amorphous silicon film 44 when an
excimer laser beam (energy: 360 mJ/cm.sup.2, pulse length: 30 ns,
wavelength: 308 nm) is radiated onto the amorphous silicon film 44
in the structure shown in FIG. 4A as an energy beam. In the
meantime, FIG. 7 shows the result of simulating the change of the
temperature of the surface of the amorphous silicon film 44 when
the same excimer laser beam is radiated onto the amorphous silicon
film 44 in the structure shown in FIG. 4B. FIG. 5 shows the
parameters of the material of each film.
[0029] As clear from the result of FIGS. 6 and 7, while an excimer
laser beam is radiated, the temperature of the amorphous silicon
film 44 rapidly rises to a melting point (the melting point of
a-Si) and when the temperature reaches the melting point, the
incline of rising is once gentle because of the latent heat of
melting and afterward, the temperature rapidly rises again. Even if
excimer laser beams with the same energy are radiated, the maximum
temperature is different depending upon the substrate structure of
the amorphous silicon film 44. That is, if a metallic film (the
nickel film 41) is formed below the amorphous silicon film 44 as
shown in FIG. 4A, the maximum temperature is approximately 2650
(K), while if a metallic film (the nickel film 41) is not formed
below the amorphous silicon film as shown in FIG. 4B, the maximum
temperature is approximately 2940 (K) and is greatly different
depending upon the structure of a substrate. The difference between
the maximum temperatures is increased as the insulating film 43 is
thinned. When the radiation of an excimer laser beam is finished
after the temperature reaches the maximum temperature, heat is
transmitted in the direction of the glass substrate 40 and the
temperature of the amorphous silicon film 44 gradually falls in
both structures shown in FIGS. 4 A and B. When the temperature
reaches temperature required for crystallizing silicon
(1410.degree. C.) , latent heat is generated by crystallization,
the temperature is held fixed for some time (crystallizing time)
and afterward, gradually falls again.
[0030] If an excimer laser beam is radiated onto the amorphous
silicon film 44 in the respective structures shown in FIGS. 4 A and
B, it is desirable so as to optimize a laser beam condition that
the maximum temperature which can be achieved by the same energy of
the surface of each amorphous silicon film 44 is the same. The
inventors of the present invention consider that if a silicon film
on a metallic film (the nickel film 41) is thickened in the
structure shown in FIG. 4B, the same temperature condition as in
the structure shown in FIG. 4A can be set and therefore, the
temperature of the surface of the silicon film can be equal
independent of the structure of a substrate (whether a metallic
film is formed or not), and obtain a drawing showing a
characteristic in FIG. 8 in experiments.
[0031] FIG. 8 shows the thickness of the silicon film 44 in the
structure shown in FIG. 4B to that of the silicon film 44 which is
30 nm shown in FIG. 4A for obtaining the maximum temperature of
2650 K in both structures shown in FIGS. 4 A and B. That is, FIG. 8
shows the result of simulating the thickness of the silicon film 44
in the structure shown in FIG. 4B in case that in the structure
shown in FIG. 4A, the thickness of the silicon film 44 on the
nickel (Ni) film 41 is set to 30 nm, the thickness of the nickel
film 41 is set to 100 nm, the thickness of the silicon nitride
(SiN) film 42 is set to 50 nm and the thickness of an insulating
film (SiO.sub.2) 43 is changed so that the temperature of the
surface of the silicon film in the structures shown in FIGS. 4 A
and B reaches 2650 K (the boiling point of silicon). This result
shows that when the thickness of the insulating film 43 in the
structure shown in FIG. 4A is reduced, the silicon film is required
to be thickened in the structure shown in FIG. 4B to obtain the
same maximum temperature. That is, the result shows that the
thickness of the silicon film in the structure shown in FIG. 4B has
only to be set according to the result shown in FIG. 8 so that the
maximum temperature of the surface of the silicon film 44 obtained
by radiating an energy beam in the structures shown in FIGS. 4 A
and B can be equal so as to optimize a laser beam condition.
[0032] The present invention utilizes such a result for uniformly
crystallizing an overall film at the same maximum temperature by
changing the thickness of a silicon film depending upon the
structure of a substrate (whether a metallic film is formed or not)
on the same substrate. An example in which the present invention is
applied to a method of manufacturing a thin film transistor will be
described below.
[0033] First Embodiment
[0034] FIGS. 1 A to C and FIGS. 2 A and B show a method of
manufacturing a thin film transistor equivalent to a first
embodiment of the present invention in the order of processes.
First, as shown in FIG. 1A, a gate electrode 11 consisting of a
nickel (Ni) film the thickness of which is 100 nm is formed on the
overall surface of a substrate, for example a glass substrate 10 by
sputtering using argon (Ar) as sputtering gas. Next, a laminated
insulting film 12 is formed by sequentially forming a silicon
nitride (SiN.sub.x) layer which is 50 nm thick and a silicon
dioxide (SiO.sub.2) layer which is 100 nm thick on the overall
surface similarly by sputtering using helium (He) as sputtering
gas, and next, an amorphous silicon film 13 which is 30 nm thick is
formed on the insulating film 12 by PECVD for example.
[0035] After the amorphous silicon film 13 is formed, a photoresist
is applied onto this amorphous silicon film 13 and exposure (back
exposure) 15 to this photoresist by gamma rays (wavelength: 436 nm)
for example is executed from the rear side of the glass substrate
10. At this time, a photoresist film 14 with the same width as the
gate electrode 12 as shown in FIG. 1B is formed by self-matching
with the gate electrode 12 functioning as a mask. Next, as shown in
FIG. 1C, an N.sup.+ doped amorphous silicon film 16 including
N-type impurities, for example phosphorus (P) is formed on the
insulating film 12 and the photoresist film 14 by PECVD for
example. The temperature of the substrate at this time shall be the
heat-resistant temperature (for example, 150.degree. C.) of the
photoresist or less. The thickness of the N.sup.+ doped amorphous
silicon film 16 is determined according to the result shown in FIG.
8 based upon the thickness of the SiO.sub.2 layer of the insulating
film 12. As the thickness of the SiO.sub.2 layer of the insulating
film 12 is set to 100 nm in this embodiment, the required thickness
of the amorphous silicon film in an area except the gate electrode
11 is 48 nm as shown in FIG. 8. Therefore, the thickness of the
N.sup.+ doped amorphous silicon film 16 is set to 18 nm obtained by
subtracting 30 nm (the thickness of the amorphous silicon film 13)
from 48 nm.
[0036] Afterward, as shown in FIG. 2A, the photoresist film 14 and
the area of the N.sup.+ doped amorphous silicon film 16 on the
photoresist film 14 (that is, an area corresponding to a channel
area) are selectively removed by a lift-off method. Hereby, the
amorphous silicon film is thicker in an area except an area over
metal (the gate electrode 11) than in the area over the metal. In
this state, next, a laser beam 17 is radiated from the surface of
the substrate. The N.sup.+ doped amorphous silicon film 16 and the
amorphous silicon film 13 are melted by radiating a laser beam 17
as described above and afterward, melted areas are crystallized by
cooling them to room temperature. At this time, the N-type
impurities in the N.sup.+ doped amorphous silicon film 16 are
diffused on the side of the amorphous silicon film 13 and an
N.sup.+ doped polycrystalline silicon film 18 provided with a
source area 18a and a drain area 18b is formed. As in this
embodiment, the amorphous silicon film is thicker in the area
except the area over the metallic film (the thickness of the
amorphous silicon film: 48 nm) than in the area over the metallic
film (the gate electrode 11) (thickness: 30 nm), the maximum
temperature of the surface of the film is substantially equal as
described above and the overall film can be uniformly
crystallized.
[0037] It is desirable for a laser beam 17 that a laser beam the
wavelength of which the N.sup.+ doped amorphous silicon film 18 can
absorb, particularly a pulse laser beam by an excimer laser is
used. In detail, a pulse laser beam (wavelength: 308 nm) by XeCl
excimer laser, a pulse laser beam (wavelength: 350 nm) by XeF
excimer laser and others are used.
[0038] Next, as shown in FIG. 2B, electrodes 19a and 19b consisting
of aluminum (Al) are respectively formed on the source area 18a and
the drain area 18b in the N.sup.+ doped polycrystalline silicon
film 18 by sputtering using argon (Ar) as sputtering gas. Next, the
channel area 18c in the N.sup.+ doped polycrystalline silicon film
18 is hydrogenated in hydrogen plasma to inactivate dangling bond
and others.
[0039] As described above, according to the method of manufacturing
a thin film transistor equivalent to this embodiment, as the
thickness of a silicon film is set to a different value depending
upon the structure of a substrate (whether a metallic film is
formed or not) when a laser beam 17 is radiated for
crystallization, the silicon film can be uniformly crystallized
over the overall substrate. Therefore, a film is never broken and a
process margin can be increased.
[0040] Second Embodiment
[0041] FIGS. 3A to 3D show a method of manufacturing a thin film
transistor equivalent to a second embodiment of the present
invention in the order of processes. In this embodiment, the order
in the first embodiment of forming an amorphous silicon film and a
doped amorphous silicon film is inverted.
[0042] That is, first as shown in FIG. 3A, a gate electrode 31
consisting of a nickel (Ni) film which is 100 nm thick is formed on
the overall surface of a substrate, for example a glass substrate
30 by sputtering using argon (Ar) as sputtering gas. Next, a
laminated insulating film 32 which is 100 nm thick is formed by
sequentially forming a silicon nitride (SiN.sub.x) film and a
silicon dioxide (SiO.sub.2) film on the overall substrate similarly
by sputtering using helium (He) as sputtering gas and next, a
photoresist is applied onto this insulating film 32 and exposure
(back exposure) 35 to this photoresist by gamma rays (wavelength:
436 nm) for example is executed from the rear side of the glass
substrate 30. At this time, a photoresist film 33 with the same
width as the gate electrode 31 is formed by self-matching with the
gate electrode 31 functioning as a mask. Next, an N.sup.+ doped
amorphous silicon film 34 including N-type impurities, for example
phosphorus (P) is formed on the insulating film 32 and the
photoresist film 33 by PECVD for example. The temperature of the
substrate at this time shall be the heat-resistant temperature (for
example, 150.degree. C.) of the photoresist or less. The thickness
of this N.sup.+ doped amorphous silicon film 34 is determined
according to a drawing showing a characteristic shown in FIG. 8
based upon the thickness of the insulating film 32 as in the first
embodiment. That is, as the thickness of the SiO.sub.2 layer of the
insulating film 32 is set to 100 nm in this embodiment, the
required thickness of the amorphous silicon film in an area except
the gate electrode 31 is 48 nm as shown in FIG. 8. Therefore, the
thickness of the N.sup.+ doped amorphous silicon film 34 is set to
18 nm obtained by subtracting 30 nm (the thickness of an amorphous
silicon film 36 to be formed continuously) from 48 nm.
[0043] Afterward, as shown in FIG. 3B, the photoresist film 33 and
the area of the N.sup.+ doped amorphous silicon film 34 on the
photoresist film 33 (that is, an area corresponding to a channel
area) are selectively removed by a lift-off method.
[0044] Next, as shown in FIG. 3C, an amorphous silicon film 36
which is 30 nm thick is formed on the N.sup.+ doped amorphous
silicon film 34 and the insulating film 32 by PECVD for example.
Hereby, the amorphous silicon film is thicker in an area (the
thickness of the amorphous silicon film: 48 nm) except an area over
metal (the gate electrode 31) than in the area (thickness: 30 nm)
over metal. In this state, next, a laser beam 37 is radiated on the
overall surface from the surface of the substrate. The N.sup.+
doped amorphous silicon film 34 and the amorphous silicon film 36
are melted by radiating a laser beam 17 as described above and
afterward, melted areas are crystallized by cooling them to room
temperature. At this time, the N-type impurities in the N.sup.+
doped amorphous silicon film 34 are diffused on the side of the
amorphous silicon film 36 and an N.sup.+ doped polycrystalline
silicon film 38 provided with a source area 38a and a drain area
38b is formed. As in this embodiment, the amorphous silicon film is
also thicker in the area (the thickness of the amorphous silicon
film: 48 nm) except the area over the metallic film than in the
area (thickness: 30 nm) over the metallic film (the gate electrode
31), the maximum temperature of the surface of the film is
substantially equal and the overall film can be uniformly
crystallized.
[0045] Next, as shown in FIG. 3D, electrodes 39a and 39b consisting
of aluminum (Al) are respectively formed on the source area 38a and
the drain area 38b in the N.sup.+ doped polycrystalline silicon
film 38 by sputtering using argon (Ar) as sputtering gas. Next, a
channel area 38c in the N.sup.+ doped polycrystalline silicon film
38 is hydrogenated in hydrogen plasma to inactivate dangling bond
and others.
[0046] As described above, according to the method of manufacturing
a thin film transistor equivalent to this embodiment, as the
thickness of a silicon film is set to a different value depending
upon the state of a substrate (whether a metallic film is formed or
not) when a laser beam 37 is radiated for crystallization, the
silicon film can be uniformly crystallized over the overall
substrate and a film can be prevented from being broken.
[0047] The embodiments according to the present invention are
described above, however, the present invention is not limited to
the above embodiments and may be variously transformed. For
example, in the above embodiments, a metallic film under a silicon
film is a nickel film, however, it may be also formed by the other
metallic film. In the above embodiments, a silicon film is used for
an amorphous semiconductor film, however, the other amorphous film
may be also used if only it can be crystallized by radiating an
energy beam. Further, in the above embodiments, the present
invention is applied to a method of manufacturing a thin film
transistor, however, it may be also applied to a process for
manufacturing the other semiconductor device. A method of forming
amorphous semiconductor films different in thickness depending upon
the structure of a substrate is not limited to the methods
described in the above embodiments and the other method may be also
used.
[0048] As described above, according to the methods of
manufacturing a semiconductor device according to the present
invention, as the thickness of a semiconductor film is set to a
different value depending upon the state of a substrate (whether a
metallic film is formed or not) when an energy beam is radiated to
crystallize the amorphous semiconductor film, the overall
semiconductor film can be uniformly crystallized by radiating beams
with the same energy. Therefore, there is effect that a film is
never broken and a process margin can be increased.
* * * * *