U.S. patent application number 12/403776 was filed with the patent office on 2009-07-16 for crystallization apparatus, optical member for use in crystallization apparatus, crystallization method, manufacturing method of thin film transistor, and manufacturing method of matrix circuit substrate of display.
Invention is credited to Masayuki Jyumonji, Yoshinobu Kimura, Masakiyo Matsumura, Mikihiko Nishitani, Yukio Taniguchi, Susumu Tsujikawa, Hirotaka Yamaguchi.
Application Number | 20090181483 12/403776 |
Document ID | / |
Family ID | 31183425 |
Filed Date | 2009-07-16 |
United States Patent
Application |
20090181483 |
Kind Code |
A1 |
Taniguchi; Yukio ; et
al. |
July 16, 2009 |
CRYSTALLIZATION APPARATUS, OPTICAL MEMBER FOR USE IN
CRYSTALLIZATION APPARATUS, CRYSTALLIZATION METHOD, MANUFACTURING
METHOD OF THIN FILM TRANSISTOR, AND MANUFACTURING METHOD OF MATRIX
CIRCUIT SUBSTRATE OF DISPLAY
Abstract
A crystallization method includes wavefront-dividing an incident
light beam into a plurality of light beams, condensing the
wavefront-divided light beams in a corresponding phase shift
portion of a phase shift mask or in the vicinity of the phase shift
portion to form a light beam having an light intensity distribution
of an inverse peak pattern in which a light intensity is minimum in
a point corresponding to the phase shift portion of the phase shift
mask, and irradiating a polycrystalline semiconductor film or an
amorphous semiconductor film with the light beam having the light
intensity distribution to produce a crystallized semiconductor
film.
Inventors: |
Taniguchi; Yukio;
(Yokohama-shi, JP) ; Matsumura; Masakiyo;
(Yokohama-shi, JP) ; Yamaguchi; Hirotaka;
(Yokohama-shi, JP) ; Nishitani; Mikihiko;
(Yokohama-shi, JP) ; Tsujikawa; Susumu;
(Yokohama-shi, JP) ; Kimura; Yoshinobu;
(Yokohama-shi, JP) ; Jyumonji; Masayuki;
(Yokohama-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
31183425 |
Appl. No.: |
12/403776 |
Filed: |
March 13, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11442331 |
May 30, 2006 |
7537660 |
|
|
12403776 |
|
|
|
|
10603821 |
Jun 26, 2003 |
7101436 |
|
|
11442331 |
|
|
|
|
Current U.S.
Class: |
438/33 ;
257/E21.328; 257/E21.412; 257/E21.599; 438/166; 438/795 |
Current CPC
Class: |
Y10T 117/1012 20150115;
Y10T 117/10 20150115; Y10T 117/1004 20150115; Y10T 117/1008
20150115; G03B 21/56 20130101 |
Class at
Publication: |
438/33 ; 438/795;
438/166; 257/E21.599; 257/E21.328; 257/E21.412 |
International
Class: |
H01L 21/336 20060101
H01L021/336; H01L 21/26 20060101 H01L021/26; H01L 21/78 20060101
H01L021/78 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2002 |
JP |
2002-188846 |
Claims
1. A crystallization method comprising: allowing an energy light
having a light intensity to melt a semiconductor layer to be
treated to be incident upon a mask having portions different in
transmittance from a light source; allowing the energy light from
the mask to be incident upon a wavefront dividing element which
divides the energy light into a plurality of energy light parts and
emitting a plurality of converged energy light parts; allowing the
plurality of converged energy light parts to be incident upon a
phase shift mask having a portion different in phase by 180 degrees
from the wavefront dividing element and emitting an energy light
having a concave light intensity distribution; and allowing the
energy light having the light intensity distribution to be incident
upon the semiconductor layer to be treated.
2. A crystallization method comprising: a step of allowing an
energy light having a light intensity to melt a semiconductor layer
to be treated to be incident upon a mask having portions different
in transmittance from a light source; a step of allowing the energy
light transmitted through the mask to be incident upon a wavefront
dividing element which divides the energy light into a plurality of
converged energy lights parts; and allowing the energy light parts
transmitted through the wavefront dividing element to be incident
upon the semiconductor layer to be treated.
3. A crystallization method comprising: allowing an energy light
transmitted through a phase shift mask to be incident upon a
non-crystalline semiconductor layer to crystallize the layer,
wherein the energy light incident upon the phase shift mask is a
light transmitted through a mask having a portion different in a
transmittance.
4. A crystallization method comprising: allowing an energy light
transmitted through a phase shift mask to be incident upon a
non-single-crystal semiconductor layer to crystallize the layer,
wherein an light intensity distribution of a light beam incident
upon the non-single-crystal semiconductor layer is a two-steps
inverse peak type light intensity distribution in which a further
linearly rising concave light intensity distribution is
superimposed upon an upper end of an inverse peak type light
intensity distribution waveform indicating an light intensity
distribution property of the phase shift mask.
5. A manufacturing method of a thin film transistor, comprising:
forming a polycrystalline semiconductor film or an amorphous
semiconductor film on one side of a substrate; wavefront-dividing
an incident light beam into a plurality of light beams; condensing
the wavefront-divided light beams in a corresponding phase shift
portion of a phase shift mask or in the vicinity of corresponding
portion to form a light beam having an light intensity distribution
of an inverse peak pattern in which a light intensity is minimum in
a point of the corresponding phase shift portion of the phase shift
mask; irradiating the polycrystalline semiconductor film or the
amorphous semiconductor film with the light beams having the light
intensity distribution to produce a crystallized semiconductor
film; successively forming a gate insulation film and a gate
electrode on the crystallized semiconductor film; forming a drain
and source between which a channel is positioned in the
crystallized semiconductor film; and forming a drain electrode and
source electrode electrically connected to on the drain and
source.
6. The manufacturing method of the thin film transistor according
to claim 5, wherein the generating of the crystallized
semiconductor film comprises: laterally growing and generating the
crystallized semiconductor film in a direction having a large light
intensity gradient from a crystal nucleus to form the source and
drain along the direction.
7. A manufacturing method of a matrix circuit substrate,
comprising: forming a polycrystalline semiconductor film or an
amorphous semiconductor film on one side of a transparent
substrate; wavefront-dividing an incident light beam into a
plurality of light beams; condensing the wavefront-divided light
beams in a corresponding phase shift portion of a phase shift mask
or in the vicinity of the portion to form a light beam having an
light intensity distribution including an inverse peak pattern in
which a light intensity is minimum in a point corresponding to the
phase shift portion of the phase shift mask; irradiating the
polycrystalline semiconductor film or the amorphous semiconductor
film with the light beam having the light intensity distribution to
produce a crystallized semiconductor film; separating the
crystallized semiconductor film into a large number of portions
positioned in a matrix shape; forming thin film transistors based
on the separated portions; and forming pixel electrodes on one side
of the transparent substrate so that each pixel electrode is
electrically connected to each thin film transistor to define a
pixel.
8. The manufacturing method according to claim 7, wherein the
generating of the crystallized semiconductor film comprises:
forming a light beam having an light intensity distribution
including a large number of inverse peak patterns apart from one
another; and irradiating the polycrystalline semiconductor film or
the amorphous semiconductor film with the light beam so that an
interval between the inverse peak patterns agrees with that between
the pixels.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional of U.S. patent application
Ser. No. 11/442,331, filed May 30, 2006, which is a Divisional of
U.S. patent application Ser. No. 10/603,821, filed Jun. 26, 2003,
and is based upon and claims the benefit of priority from the prior
Japanese Patent Application No. 2002-188846, filed Jun. 28, 2002.
The entire contents of these applications are incorporated herein
by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a crystallization apparatus
for irradiating an amorphous or polycrystalline semiconductor film
with a laser beam to produce a crystallized semiconductor film, an
optical member for use in the crystallization apparatus, a
crystallization method, a thin film transistor, and a display
apparatus. The present invention particularly relates to an
apparatus and method in which an amorphous or polycrystalline
semiconductor film is irradiated with a laser beam phase-modulated
using a phase shift mask to produce a crystallized semiconductor
film.
[0004] 2. Description of the Related Art
[0005] A material of a thin film transistor (TFT) for use in a
switching device for controlling a voltage to be applied to a
pixel, for example, of a liquid crystal display (LCD) has
heretofore roughly been classified into amorphous silicon, poly
silicon and single crystal silicon.
[0006] Amorphous silicon can obtain a high withstand property. Poly
silicon has an electron mobility higher than that of amorphous
silicon. Therefore, a transistor formed by poly silicon has
advantages that a switching speed is high, a response of a display
is high, and a design margin of another component is reduced as
compared with a transistor formed by amorphous silicon. In addition
to a main body of a display, peripheral circuits such as a driver
circuit and DAC can be incorporated in the display. In this case,
these peripheral circuits can be operated at a higher speed.
[0007] Poly silicon is constituted of an aggregate of crystal
grains, and has lower electron or hole mobility than single crystal
silicon. Moreover, in the thin film transistor (FET) formed using
the poly silicon, fluctuation of the number of crystal grain
boundaries existing in a channel portion is a problem. To solve the
problem, a crystallization method of producing poly silicon having
a larger grain diameter has been recently proposed in order to
enhance the mobility of electrons or holes and to reduce the
fluctuation of the number of crystal grain boundaries in the
channel portion of each FET.
[0008] As this type of crystallization method, a "phase control
excimer laser annealing (ELA)" has heretofore been known in which a
polycrystalline or amorphous semiconductor film is irradiated with
an excimer laser beam via a phase shift mask to produce a
crystallized semiconductor film. Details of the phase control ELA
are described in, for example, "Surface Science Vol. 21, No. 5, pp.
278 to 287, 2000" and Jpn. Pat. Appln. KOKAI Publication No.
2000-306859.
[0009] In the phase control ELA, an inverse peak type light
intensity distribution (light intensity distribution in which a
light intensity rapidly increases as a distance from a position
having a minimum light intensity increases) is generated by the
phase shift mask. The polycrystalline or amorphous semiconductor
film is irradiated with light beams which periodically have the
inverse peak type light intensity distribution. As a result, a
molten region is generated in accordance with the light intensity
distribution, and a crystal nucleus is formed in a portion which is
disposed opposite to a position having a minimum light intensity
and which is not molten or which first coagulates. When a crystal
grows from the crystal nucleus toward periphery in a lateral
direction (lateral growth), crystal grains having a large grain
diameter (mono-crystal) are generated.
[0010] For example, when a liquid crystal display is manufactured,
a ratio of a transistor forming region requiring the
above-described crystallization in each pixel region is usually
very small. In a conventional art, for example, the phase shift
mask including a plurality of two-dimensionally arranged phase
shift portions is uniformly irradiated with the laser beam.
Therefore, a large part of the laser beam supplied from an optical
illumination system does not contribute to the crystallization of
the transistor forming region, and a so-called light amount loss is
very large.
[0011] Moreover, as described above, in the conventional art, the
semiconductor film is irradiated with light beams which have the
inverse peak type light intensity distribution. In the light
intensity distribution, the crystal nucleus is formed in the
portion disposed opposite to the position in which the light
intensity is minimized. Therefore, it is possible to control the
forming position of the crystal nucleus. However, it is impossible
to control the light intensity distribution in an intermediate
portion between two inverse peak portions disposed opposite to each
other.
[0012] In actual, in the conventional art, in general, the light
intensity distribution in the intermediate portion involves
irregular surges (wave-shaped distribution in which increase and
decrease of the light intensity are repeated). In this case, in a
process of crystallization, the lateral growth started toward the
periphery from the crystal nucleus stops in a portion in which the
light intensity decreases in the intermediate portion, and there is
a problem that the growth of large crystals is inhibited. Moreover,
even if a substantially uniform light intensity distribution is
obtained in the intermediate portion, the lateral growth stops in
an arbitrary position in this uniform light intensity distribution,
and there is a problem that the growth of large crystals is
inhibited.
BRIEF SUMMARY OF THE INVENTION
[0013] An object of the present invention is to provide a
crystallization apparatus and method in which a large part of light
supplied from an optical illumination system can contribute to
crystallization of a desired region and in which light efficiency
is satisfactory.
[0014] Another object of the present invention is to provide a
crystallization apparatus and method in which sufficient lateral
growth from a crystal nucleus can be realized to produce a
crystallized semiconductor film having a large grain diameter.
[0015] Further object of the present invention is to provide a
manufacturing method of a thin film transistor having an effect
similar to the above-described effect, and a manufacturing method
of a matrix circuit substrate of a display.
[0016] To solve the problem, according to a first aspect of the
present invention, there is provided a crystallization apparatus
which comprises an optical illumination system to allow a light
beam having a homogeneous light intensity distribution to be
incident upon an amorphous semiconductor film or a polycrystalline
semiconductor film and which irradiates the amorphous semiconductor
film or the polycrystalline semiconductor film with the light beam
to crystallize the amorphous or polycrystalline semiconductor film.
The device comprises a wavefront dividing element which divides a
wavefront of the incident light beam into a so as plurality of
light beams, and a phase shift mask which gives a phase difference
between partially transmitted light beams and which converts the
light beams into a light beam having an inverse peak type light
intensity distribution and which comprises a phase shift portion to
determine a position where the inverse peak type light intensity
distribution is minimized. The wavefront dividing element is
positioned on a light path between the optical illumination system
and a non-crystallized semiconductor film. The phase shift mask is
positioned on the light path between the wavefront dividing element
and the non-crystallized semiconductor film. The wavefront dividing
element and phase shift mask are positioned so that a predetermined
region around the phase shift portion is irradiated with the light
beams having the divided wavefront.
[0017] The wavefront dividing element preferably comprises a
plurality of optical elements two-dimensionally arranged along two
directions crossing at right angles to each other, and each optical
element has a two-dimensional condensing function along two
directions crossing at right angles to each other. Instead, the
wavefront dividing element may comprise a plurality of optical
elements one-dimensionally arranged along a predetermined
direction, and each optical element has a one-dimensional
condensing function along the predetermined direction.
[0018] The optical illumination system preferably comprises an
light intensity distribution forming element which converts the
light beams having a homogeneous light intensity distribution into
light beams having an upward concave light intensity distribution.
The light intensity distribution forming element and phase shift
mask are positioned so that a position to minimize the upward
concave light intensity distribution may correspond to the phase
shift portion. The light beams which are converted by the light
intensity distribution forming element and phase shift mask and
with which a non-crystallized semiconductor film is irradiated have
an light intensity distribution including an inverse peak portion
inside an upward concave portion. The light intensity distribution
forming element may comprise a circular middle region having a
predetermined transmittance and an annular peripheral region which
is formed to surround the middle region and which has a higher
transmittance than the middle region. Instead, the light intensity
distribution forming element preferably comprises: an elongated
middle region which has a predetermined transmittance and which
extends along the predetermined direction; and peripheral regions
which are formed to hold the middle region between the regions and
which have a transmittance higher than that of the middle region.
Furthermore, the light intensity distribution forming element
preferably has a transmission filter which is disposed in an
emission pupil plane of the optical illumination system or in the
vicinity of the plane and which has a predetermined transmittance
distribution.
[0019] The polycrystalline or amorphous semiconductor film is
preferably disposed in parallel with or in the vicinity of the
phase shift mask. The apparatus further comprises an optical image
forming system which is disposed on a light path between the
polycrystalline or amorphous semiconductor film and the phase shift
mask disposed apart from the film. The polycrystalline or amorphous
semiconductor film may be disposed at a predetermined distance from
a plane optically conjugated with the phase shift mask along an
optical axis of the optical image forming system. Furthermore, in
the apparatus further comprising an optical image forming system
disposed on the light path between the polycrystalline or amorphous
semiconductor film and the phase shift mask, the polycrystalline or
amorphous semiconductor film is set in the vicinity of the plane
optically conjugated with the phase shift mask, and an image-side
numerical aperture of the optical image forming system may also be
set to a value required for generating the inverse peak type light
intensity distribution.
[0020] According to a second aspect of the present invention, there
is provided an optical member comprising: a wavefront dividing
portion which condenses light beams having a homogeneous incident
light intensity distribution so as to irradiate a predetermined
region only; and an optical converting portion which converts the
light beams into a light beam having an inverse peak type light
intensity distribution.
[0021] According to a third aspect of the present invention, there
is provided a crystallization method comprising: condensing light
beams so as to irradiate a predetermined region only; converting
the light beams into a light beam having an inverse peak type light
intensity distribution; and irradiating and crystallizing the
predetermined region of a non-crystallized semiconductor film
(amorphous or polycrystalline semiconductor film) with the
converted light beams.
[0022] According to the third aspect, the light beam having the
homogeneous light intensity distribution is converted to the light
beam having the upward concave light intensity distribution.
Alternatively, the light beam having an light intensity
distribution including an inverse peak portion inside an upward
concave portion are formed into an image in a position disposed
apart from an optically conjugated plane by a predetermined
distance along an optical axis, and a non-crystallized
semiconductor film is irradiated and crystallized with the light
beams formed into the image.
[0023] According to a fourth aspect, there is provided a
crystallization method comprising: condensing light beams having a
homogeneous light intensity distribution to irradiate a
predetermined region only; converting the condensed light beams
into a light beam having an inverse peak type light intensity
distribution; and irradiating and crystallizing the predetermined
region only of a non-crystallized semiconductor film with the
converted light beams.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0024] FIG. 1 is a diagram schematically showing a crystallization
apparatus according to a first embodiment of the present
invention;
[0025] FIGS. 2A and 2B are diagrams schematically showing a
transmission filter disposed in an emission pupil plane of an
optical illumination system or in the vicinity of the plane, and a
light intensity of a light beam transmitted through the filter;
[0026] FIG. 3A is a perspective view showing basic unit portions of
a phase shift mask and wavefront dividing element;
[0027] FIG. 3B is a side view showing a condensed state of an
incident light of a micro lens array 3;
[0028] FIG. 4 is a top plan view showing a structure or repetition
of the phase shift mask;
[0029] FIG. 5 is a diagram showing an light intensity distribution
of light beams transmitted through both the transmission filter and
micro lens array;
[0030] FIG. 6 is an explanatory view of a function of the phase
shift mask;
[0031] FIG. 7 is a diagram showing a transistor forming region
which is disposed in each pixel region and which needs to be
crystallized in a liquid crystal display;
[0032] FIG. 8A is a diagram showing the light intensity
distribution of a light beam transmitted through three members
including the transmission filter, micro lens array, and phase
shift mask;
[0033] FIG. 8B is a diagram showing light intensity distribution
patterns of the light beam passed through the transmission filter,
micro lens array, and phase shift mask;
[0034] FIG. 9 is a diagram three-dimensionally showing the light
intensity distribution shown in FIG. 8A;
[0035] FIG. 10 is a diagram schematically showing a crystallization
apparatus according to a second embodiment of the present
invention;
[0036] FIG. 11 is a diagram schematically showing the
crystallization apparatus according to a third embodiment of the
present invention;
[0037] FIG. 12 is a diagram showing a micro cylindrical lens array
according to a modification example of a wavefront dividing
element;
[0038] FIG. 13 is a diagram showing a modification example of the
transmission filter;
[0039] FIG. 14 is a diagram showing the transistor forming region
which is disposed in each pixel region and which needs to be
crystallized in the liquid crystal display;
[0040] FIG. 15 is a diagram showing an light intensity distribution
of the light beams transmitted through the transmission filter,
micro cylindrical lens array, and phase shift mask according to the
modification example;
[0041] FIG. 16 is a diagram showing a modification example of the
phase shift mask;
[0042] FIGS. 17A to 17K are explanatory views of a method of
integrally forming the micro lens array and phase shift mask;
[0043] FIGS. 18A to 18E are diagrams showing a process of using the
crystallization apparatus according to each embodiment to
manufacture an electronic device;
[0044] FIG. 19 is a view for illustrating a modification of FIG. 8B
in which the filter is omitted; and
[0045] FIG. 20 is a view for illustrating a modification of FIG. 8B
in which the phase shift mask is omitted.
DETAILED DESCRIPTION OF THE INVENTION
[0046] Embodiments of the present invention will be described with
reference to the accompanying drawings.
[0047] FIG. 1 is a diagram schematically showing a constitution of
a crystallization apparatus according to a first embodiment of the
present invention. As shown in FIG. 1, a crystallization apparatus
of a first embodiment comprises: an optical illumination system 2
for illuminating a semiconductor film of a substrate to be treated
4; a micro lens array 3 which is a wavefront dividing element
disposed on a light path between the substrate to be treated 4 and
optical illumination system 2; and a phase shifter, that is, phase
shift mask 1 disposed on the light path between the micro lens
array 3 and substrate to be treated 4.
[0048] A top surface of a semiconductor film of the substrate to be
treated 4 is disposed in parallel with and in the vicinity of
(e.g., several micrometers to several hundreds of micrometers) the
phase shift mask 1. The semiconductor film is constituted by a
non-single-crystal semiconductor film such as polycrystalline and
amorphous semiconductor films on a support substrate. The substrate
is obtained, for example, by forming an amorphous silicon film
directly on a glass plate for the liquid crystal display, or on
underlayer film such as an SiO.sub.2 film formed on the substrate
by a chemical vapor growth method. In the present embodiment, the
phase shift mask 1 is disposed opposite to the amorphous
semiconductor film. The substrate to be treated 4 is held in a
predetermined position on a substrate stage 5 by a vacuum chuck or
electrostatic chuck. For example, the substrate stage 5 is
constituted of an x-y-z-.theta. table. As a result, when the
substrate stage 5 is laterally moved, and while the optical
illumination system is fixed, the crystallization of the
semiconductor film of the substrate to be treated 4 can
successively be moved to perform a fixed crystallization step in a
broad range.
[0049] The optical illumination system 2 includes a KrF excimer
laser light source 2a for supplying a laser beam which has a
wavelength, for example, of 248 nm; a beam expander 2b for
expanding the laser beam from the light source 2a; first and second
fly eye lenses 2c, 2e; first and second optical condenser systems
2d, 2f; and a transmission filter 2g which is an light intensity
distribution forming element. Another appropriate light source such
as an XeCl excimer laser light source can also be used as the light
source 2a.
[0050] As schematically shown in FIG. 1, the light beam emitted
from the light source 2a is expanded by the beam expander 2b,
transformed into a parallel light beam, and incident upon the first
fly eye lens 2c. Since the light beam incident upon the first fly
eye lens 2c undergoes convergence functions by convex lenses of the
first fly eye lens 2c, a plurality of point light sources are
substantially formed in a focal plane on the back side of the first
fly eye lens 2c. The light beams from the plurality of point light
sources are picked up as an image by the first optical condenser
system 2d, and illuminate the incidence surface of the second fly
eye lens 2e disposed behind a focal point in a superimposing
manner.
[0051] Since the light beams incident upon the second fly eye lens
2e from the plurality of point light sources undergo the
convergence functions by the convex lenses of the second fly eye
lens 2e, point light sources more than those in the focal plane on
the back side of the first fly eye lens 2c are formed in the
back-side focal plane of the second fly eye lens 2e, that is, the
transmission filter 2g. The light beams from the plurality of point
light sources formed in the back-side focal plane of the second fly
eye lens 2e are further incident upon the second optical condenser
system 2f.
[0052] The first fly eye lens 2c and first optical condenser system
2d constitute a first homogenizer, and homogenize an incidence
angle on the phase shift mask 1. Similarly, the second fly eye lens
2e and second condenser optical system 2f constitute a second
homogenizer, and homogenize light intensities of laser beams
incident upon the phase shift mask 1. Therefore, the first and
second homogenizers change the light beam transmitted from the
light source 2a into light beam which has substantially homogeneous
light intensity distribution.
[0053] As shown in FIG. 2, the transmission filter 2g includes a
circular middle region 12a which has a transmittance, for example,
of 50% with respect to a wavelength of the light emitted from the
light source 2a, and an annular peripheral region 12b which is
formed so as to surround the middle region 12a and whose
transmittance is substantially 100%. Therefore, in an illumination
pupil plane or in the vicinity of the plane, the light intensity of
a part of the light beam transmitted through the middle region 12a
is relatively low, and the light intensity of a part of the light
beam transmitted through the peripheral region 12b is relatively
high. Therefore, the optical illumination system 2 emits the light
beam having an incidence angle light intensity distribution which
is homogeneous in an irradiated plane but which is low in a middle
rather in a periphery in a superimposing manner (FIG. 2).
[0054] The middle region 12a of the transmission filter 2g is
obtained by forming a chromium film (or a ZrSiO film) having a
thickness, for example, in accordance with transmittance on a
transparent substrate by a sputter process, and patterning the film
of the peripheral region to etch/remove the film. Chromium which is
a shield material reflects a part of light and absorbs a part of
light. Moreover, the middle region 12a may also be obtained by
forming a multilayered film designed so as to partially reflect the
light having a use wavelength emitted from the light source 2a on
the transparent substrate, and thereafter pattern the film. That
is, the middle region 12a is obtained by forming a reflective film
on the substrate transparent to the use wavelength, such as annular
quartz glass, and etching a portion of the reflective film of the
peripheral region 12b.
[0055] When the multilayered film is used as a reflective material,
there is an advantage that heat is not generated by absorption of
any unnecessary light. However, it needs to be considered that a
reflected light should not form a stray light to cause flare. Types
and thicknesses of the shield and reflective materials are
preferably adjusted so that a phase difference is not substantially
generated in the transmitted light in a boundary line between the
middle region 12a and peripheral region 12b. In the first
embodiment, an example of the middle region 12a which is formed in
a circular shape has been described, but other shapes such as
triangular and rectangular shapes may also be formed.
[0056] FIG. 3A is a perspective view schematically showing one of a
large number of basic unit portions constituting the phase shift
mask 1 in association with one of a large number of basic unit
portions consisting of a convergence/divergence device including
the micro lens array 3, that is, a wavefront dividing element. FIG.
3B is a side view showing the basic unit portions of the phase
shift mask and micro lens array, and is a diagram showing a
condensed state of an incident light of the micro lens array 3.
[0057] As shown in FIG. 3A, a micro lens element (optical element)
13 which is the basic unit portion of the micro lens array 3
includes a refractive surface 13a having a two-dimensional curved
surface shape such as a partially spherical shape which projects on
a phase shift mask 1 side. By this refractive surface 13a, the
micro lens element 13 of the micro lens array 3 has a
two-dimensional condensing function along x and y directions as
shown in FIG. 3B. That is, the light condensed from the optical
illumination system 2 by a large number of convex lenses is
incident upon each micro lens element 13. A state of each micro
lens element 13 which emits a large number of condensed beams (or
parts of the beam) is shown in FIG. 3B. As a result, an inverse
peak pattern can be obtained without being influenced by surges
described later in detail.
[0058] As shown in FIG. 3A, a basic unit portion 11 of the phase
shift mask 1 has substantially the same size in the x and y
directions as that of the micro lens element 13 of the micro lens
array 3, and is disposed in the x-direction, in parallel with the
micro lens element 13, and in the vicinity of the element in a
z-direction (light direction). The basic unit portion 11 of the
phase shift mask 1 includes four rectangular phase shift surfaces
including first to fourth regions 11a to 11d. The first and third
regions 11a and 11c, and the second and fourth regions 11b and 11d
are diagonally positioned, respectively. Two diagonally positioned
regions give a phase difference of .pi. between the transmitted
light beams. That is, the phase shift mask 1 has a staircase shape
stepped so that the first to fourth regions 11a to 11d successively
have a mutual difference of .pi./2. The regions 11a to 11d
including the steps may be formed by etching or depositing.
[0059] Concretely, for example, the phase shift mask 1 is formed by
etching quartz glass having a refractive index of 1.5 with respect
to the light beam which has a wavelength of 248 nm. In this case, a
step of 124 nm is given between the first and second regions 11a
and 11b (thickness difference between the first and second regions
of quartz glass). A step of 248 nm is given between the first and
third regions 11a and 11c (thickness difference between the first
and third regions of quartz glass). A step of 372 nm is given
between the first and fourth regions 11a and 11d (thickness
difference between the first and fourth regions of quartz glass). A
phase shift portion 11e is formed in the vicinity of intersections
of four phase shift lines which are boundary lines of the
respective regions 11a to 11d. In the phase shift lines of the
phase shift mask, the light passed through the second region 11b is
late in phase behind the light passed through the first region 11a.
Similarly, the lights passed through the third and fourth regions
11c and 11d also falls behind the light passed through the second
and third regions 11b and 11c by .pi./2 phase, respectively. As a
result, interference and diffraction occur in the light passed
through the regions 11a to 11d. In this manner, a portion disposed
opposite to the phase shift portion 11e in which the phase shift
lines intersect with each other indicates zero or nearly zero, and
therefore the light intensity distribution indicates an inverse
peak pattern.
[0060] The micro lens array 3 and phase shift mask 1 are positioned
so that a center of the refractive surface 13a is aligned with the
phase shift portion 11e on the optical axis. For example, as shown
in FIG. 4, the phase shift mask 1 is constituted by orderly
arranging a plurality of basic unit portions 11 in two dimensions,
that is, in a matrix shape of 2.times.2. In the same manner as the
phase shift mask 1, the micro lens array 3 is constituted by
orderly arranging a large number of micro lens elements 13
two-dimensionally (lengthwise and breadthwise and densely).
[0061] The basic unit portion 11 of the phase shift mask 1 shown in
FIG. 4 according to the first embodiment includes four regions, but
may include two regions which give a phase difference of .pi. to
the transmitted light beams. When the phase shift mask 1 includes
two regions in each unit portion 11, these regions are alternately
disposed in a stripe shape. The phase difference can be formed by
changing the thickness of the part or parts of a quartz glass
plate.
The thickness can be formed by etching.
[0062] The light beam which is emitted from the optical
illumination system 2 and which has a substantially homogeneous
light intensity distribution is transmitted through the micro lens
array 3 to irradiate the phase shift mask 1. The parts of the light
beam incident upon the respective micro lens elements 13 of the
micro lens array 3 pass through the refractive surface 13a, undergo
the condensing function, and are incident upon a focal position of
the micro lens element 13 or the phase shift portion 11e of the
phase shift mask 1 disposed in the vicinity of the focal position
in a spotted form. In this manner, the micro lens array 3
constitutes a wavefront dividing element which is disposed on a
light path between the optical illumination system 2 and phase
shift mask 1 and which wavefront-divides the light beam incident
from the optical illumination system 2 into a plurality of light
beams or light beam portions. The wavefront-divided light beams are
focused in the phase shift portion 11e disposed in the focal
position, or in the vicinity of the portion.
[0063] FIG. 5 is a diagram showing the light intensity distribution
of a laser light incident upon the phase shift mask 1 by both
functions of the transmission filter 2g and micro lens array 3. For
the light beam transmitted through the micro lens array 3 via the
transmission filter 2g which has the property shown in FIG. 2, an
obliquely outgoing part of the light beam is more intense than a
vertically outgoing part of the light beam. Therefore, as shown in
FIG. 5, the light beam has an upward concave light intensity
distribution of the laser beam on the phase shift mask 1, in which
the light intensity is minimum in each phase shift portion 11e
shown in FIG. 3B and increases as a distance from the phase shift
portion 11e increases. Concretely, in the upward concave light
intensity distribution of the laser beam, the light intensity is
lowest in a position disposed opposite to the center of the
refractive surface 13a of the micro lens array 3 shown in FIG. 3A,
and the light intensity of the laser beam is continuously highest
in an annular position around this point.
[0064] The upward concave light intensity distribution of the laser
beams has a similar profile both in the x and y-directions.
Moreover, a width of the upward concave light intensity
distribution of the laser beam is preferably set to be equal to a
pixel pitch of a liquid crystal display, when this technique is
applied to a manufacturing process of an image display circuit of
the liquid crystal display. The crystal grain diameter equal to the
pixel pitch is an area in which a thin film transistor circuit for
switching one pixel can be formed.
[0065] The light beam with which the phase shift mask 1 is
irradiated in a spot shape is phase-modulated and incident upon the
semiconductor film of the substrate to be treated 4 disposed in
parallel with and in the vicinity of the phase shift mask 1. FIG. 6
is an explanatory view of a function of the phase shift mask 1. A
basic function of the phase shift mask 1 having two elongated
regions in each unit will be described hereinafter in a case in
which the micro lens array 3 is not disposed on the light path
between the optical illumination system 2 and phase shift mask
1.
[0066] Since the phase difference between two adjacent elongated
regions is set to .pi./2 in the phase shift mask 1, the light
intensity decreases but does not turn to zero in positions
corresponding to the phase shift lines other than the
intersections. On the other hand, since an integral value of a
complex transmittance of a circular region around the intersection
of the phase shift lines is set to zero, the light intensity is
substantially zero in the position corresponding to the
intersection, that is, the phase shift portion 11e.
[0067] Therefore, for the light intensity distribution of the laser
beams transmitted through the respective basic unit portions 11 of
the phase shift mask 1, as shown in FIG. 6, on the semiconductor
film of the substrate to be treated 4, an inverse peak type light
intensity distribution pattern P is obtained. In the pattern, the
light intensity is substantially zero in the point corresponding to
each phase shift portion 11e of the phase shift mask 1, and the
light intensity continuously rapidly increases as the distance from
the phase shift portion 11e increases. Therefore, the light beam
passed through the phase shift mask 1 including a plurality of
phase shift portions 11e arranged in the matrix shape entirely
periodically has the inverse peak type light intensity
distribution. This periodical inverse peak type light intensity
distribution has substantially the same profile in the x and
y-directions. The width of the inverse peak type light intensity
distribution changes in proportion to 1/2 square of a distance
between the phase shift mask 1 and the semiconductor film of the
substrate to be treated 4 (i.e., a defocus amount).
[0068] As described above, when the semiconductor film is
irradiated with the light beams periodically having the inverse
peak type light intensity distribution only as shown in FIG. 6,
lateral growth started toward periphery from a crystal nucleus
stops in a swell portion of a waveform in an intermediate portion
between the inverse peak type patterns P disposed adjacent to each
other. In the first embodiment, to realize sufficient lateral
growth from the crystal nucleus, the transmission filter 2g is
disposed in an illumination pupil plane of the optical illumination
system 2, or in the vicinity of the plane.
[0069] FIG. 7 is a diagram schematically showing transistor forming
regions 60 which are disposed in pixel regions 61 and which need to
be crystallized in a liquid crystal display 59. Referring to FIG.
7, for example, when the liquid crystal display 59 is manufactured
as described above, the light beam from the phase shift mask 1 is
emitted also to the outside of spotted light beam region 62, and
therefore a light amount loss is very large. In the first
embodiment, the micro lens array 3 is disposed on the light path
between the optical illumination system 2 and phase shift mask 1 in
order to efficiently irradiate the transistor forming region 60
only with the light beam from the optical illumination system
2.
[0070] FIG. 8A is a diagram showing the light intensity
distribution obtained on the semiconductor film of the substrate to
be treated 4 by cooperative functions of the transmission filter
2g, micro lens array 3, and phase shift mask 1. As described above,
the transmission filter 2g, micro lens array 3, and phase shift
mask 1 have a function of forming the light beam having the light
intensity distribution in which the light intensity of the light
beams having the homogeneous light intensity distribution is
minimized in the center, and decreased, for example, by 50%.
The light intensity substantially linearly increases in a steep
gradient toward the periphery in the inverse peak type, and further
linearly increases in a little gentle gradient. As shown in FIG.
8B, the micro lens array 3 has a function of converting the
incident light beam into the spotted light beams with which the
predetermined region only is irradiated in the inverse peak pattern
P of FIG. 6. The phase shift mask 1 has a function of converting
the light beam having the homogeneous light intensity distribution
into the light having the inverse peak type light intensity
distribution shown in FIG. 6.
[0071] Since the crystallization apparatus according to the first
embodiment includes the phase shift mask 1, transmission filter 2g,
and micro lens array 3, the light beam reaching the substrate to be
treated 4 undergo the functions of these three members as shown in
FIG. 8B. Therefore, the light beam reaching the amorphous
semiconductor film of the substrate to be treated 4 is converted
into the spotted light beams which illuminate the predetermined
region only. As shown in FIG. 8A, a two-steps inverse peak type
light intensity distribution is obtained as represented by a
product with the concave light intensity distribution on the
inverse peak type light intensity distribution distributed in the
same period. In this two-steps inverse peak type light intensity
distribution, to follow the above-described inverse peak type light
intensity distribution, the light intensity is substantially zero
in the point corresponding to the phase shift portion 11e, and the
light intensity rapidly increases apart from this point to reach a
predetermined value. That is, a position of the two-steps inverse
peak type light intensity distribution in which the light intensity
is minimized is determined by the position of the phase shift
portion 11e.
[0072] In the first embodiment, the two-steps inverse peak type
light intensity distribution corresponds to the above-described
periodical upward concave light intensity distributions of the x
and y-directions. As shown in FIG. 9, in the light intensity
distribution between the inverse peak portions disposed adjacent to
each other, the light intensity substantially monotonously
increases along the x and y-directions. The waveform pattern of the
two-steps inverse peak type light intensity distribution shown in
FIG. 8A is a waveform pattern obtained by superimposing the
waveform pattern of the light intensity distribution of a linearly
rising concave portion shown in FIG. 5 upon the waveform pattern of
the light intensity distribution of the inverse peak portion shown
in FIG. 6. There are inflection points in which inclinations are
reduced in boundaries H between substantially linearly increasing
intensities.
[0073] When the semiconductor film of the substrate to be treated 4
is irradiated with the light beam having the two-steps inverse peak
type light intensity distribution, a crystal nucleus is formed in a
portion corresponding to the point indicating the minimum light
intensity, that is, substantially zero light intensity (point
corresponding to the phase shift portion 11e). This will be
described in detail. There is a phenomenon in which crystal growth
is started at a certain or more light intensity. This light
intensity is designed so as to be inside the inverse peak type
pattern. Then, the crystal nucleus can be defined inside the
inverse peak type light intensity distribution. That is, a
polycrystal is generated in a center portion of the inverse peak
portion, and thereafter the crystals outside the generated
polycrystal form nuclei and grow in a horizontal direction.
[0074] For irradiation with the laser beam which has the light
intensity distribution including the inverse peak pattern, lateral
growth is started from the crystal nucleus along the x and
y-directions including a large light intensity gradient (i.e.,
temperature gradient). In the two-steps inverse peak type light
intensity distribution, a portion in which the light intensity
decreases does not substantially exist in the intermediate portion.
Therefore, the lateral growth reaches its peak without stopping
halfway, and the growth of a larger crystal grain can be realized.
Especially in the first embodiment, the inflection point in which
the inclination is reduced exists between the inverse peak portion
and the upward concave portion. Therefore, the crystal nucleus can
be limited inside the inverse peak. Therefore, when the
semiconductor film of the substrate to be treated 4 is irradiated
with the light beam having the two-steps inverse peak type light
intensity distribution, the film is crystallized in a broad region
over the width from the center portion of the two-steps inverse
peak type light intensity distribution. When the width of the
two-steps inverse peak type light intensity distribution is set to
be equal to the pixel pitch of the liquid crystal display, the
single crystal can be generated with respect to each pixel. In
other words, the semiconductor film forming each pixel driving
circuit of a matrix circuit substrate of the liquid crystal display
or EL display can be mono-crystallized.
[0075] As described above, in the first embodiment, sufficient
lateral growth from the crystal nucleus is realized, and the
crystallized semiconductor film having a large grain size can be
produced. The crystal produced by the crystallization apparatus
according to the first embodiment has a large grain size, and has a
higher electron mobility especially in the directions (x and
y-directions) of the lateral growth. Therefore, when a source and
drain of the transistor are arranged in the direction of the
lateral growth, the transistor having a satisfactory property can
be manufactured.
[0076] In the first embodiment, the light incident upon the micro
lens array 3 is wavefront-divided by a large number of micro lens
elements 13, the light beam is condensed via the respective micro
lens elements 13, and the vicinity of the corresponding phase shift
portion 11e is irradiated in a spot shape. The part of light beam
transmitted in the vicinity of the phase shift portion 11e form the
spotted light beam region 62 to surround the transistor forming
region 60. Therefore, a large part of the light supplied from the
optical illumination system 2 can contribute to the crystallization
only of the desired transistor forming region 60, and the
crystallization satisfactory in light efficiency can be
realized.
[0077] In the first embodiment, as shown in FIG. 3B, the refractive
surface 13a of the micro lens element 13 of the micro lens array 3
is a partially spherical, but may also have another curved shape
having different curvatures in the x and y-directions. When the
curvature of the x-direction of the refractive surface 13a is
different from that of the y-direction, the spotted light beam
region has an elliptic shape. Long and short axes of the elliptic
shape correspond to the widths of the two-steps inverse peak type
light intensity distribution in the x and y-directions. Therefore,
when the spotted light beam region is formed in the elliptic shape,
the gradient of the light intensity in the inverse peak portion
differs with the x and y-directions. Therefore, when the curvature
of the refractive surface 13a is set to be arbitrary, a degree of
lateral growth can be changed along each direction.
[0078] In the first embodiment, assuming that a numerical aperture
of the optical illumination system 2 is NA1, a focal distance of
the micro lens array 3 (i.e., the focal distance of each micro lens
element 13) is f, the numerical aperture of the micro lens array 3
(i.e., the numerical aperture of each micro lens element 13) is
NA2, and the wavelength of an illuminative light is .lamda., the
micro lens array 3 preferably satisfies the following condition
equation (1).
R2=k.lamda./NA2<f.times.NA1 (1),
where the right side indicates a value corresponding to a size
(radius) of the spotted light beam region formed in the phase shift
portion 11e, and the left side indicates a value corresponding to a
resolution R2 of the micro lens array 3. A constant k indicates a
value substantially close to 1, depending on specifications of the
optical illumination system 2 for illuminating the phase shift mask
1, or definitions of the degree and resolutions of coherence of the
light beam supplied from the light source, and therefore the
constant is ignored here. When the condition equation (1) is
satisfied, the upward concave light intensity distribution of the
laser beams can clearly be formed as shown in FIG. 5. Therefore,
the two-steps inverse peak type light intensity distribution can
clearly be formed as shown in FIGS. 8A, 8B, and 9.
[0079] In the first embodiment, simulation concerning the condition
equation (1) is performed in accordance with usual design
conditions. In this simulation, the pitch (size) D of each micro
lens element 13 of the micro lens array 3 is set to 100 .mu.m, the
focal distance f is set to 500 .mu.m, and the numerical aperture
NA1 of the optical illumination system 2 is set to 0.02. In this
case, the numerical aperture of the micro lens array 3, that is,
the numerical aperture NA2 of each micro lens element 13 is
approximated by the following equation (a).
NA2.apprxeq.D/f=100/500=0.2 (a)
[0080] Therefore, the left and right sides of the condition
equation (1) are represented by the following equations (b) and
(c).
R2=.lamda./NA2.apprxeq.0.248/0.2.apprxeq.1.2 .mu.m (b)
f.times.NA1=500.times.0.02=10 .mu.m (c)
[0081] Therefore, the resolution R2 is 1.2 .mu.m, and sufficiently
small with respect to a radius of 10 .mu.m of the spotted light
beam region 62 which surrounds each transistor forming region 60.
It is therefore seen that the two-steps inverse peak type light
intensity distribution can clearly be formed as shown in FIGS. 8A,
8B, and 9.
[0082] FIG. 10 is a diagram schematically showing the constitution
of the crystallization apparatus according to a second embodiment
of the present invention.
The second embodiment includes a constitution similar to that of
the first embodiment, but is different from the first embodiment in
that the phase shift mask 1 is disposed apart from the substrate to
be treated 4 and an optical image forming system 6 is disposed on a
light path between the mask and substrate. The second embodiment
will be described hereinafter with respect to different respects
from the first embodiment. For the sake of clarification of the
drawing, in FIG. 10, the inner constitution of the optical
illumination system 2 is omitted, the same components as those of
FIGS. 1 to 9 are denoted with the same reference numerals, and
detailed description is redundant and is therefore omitted.
[0083] In the second embodiment, the substrate to be treated 4 is
distant from a plane optically conjugated with the phase shift mask
1 (image plane of the optical image forming system 6) along the
optical axis. In this case, the width of the inverse peak type
light intensity distribution of the laser beam formed into an image
on the semiconductor film of the substrate to be treated 4 by the
function of the phase shift mask 1 changes substantially in
proportion to 1/2 square of the distance between the image plane of
the optical image forming system 6 and the substrate to be treated
4 (i.e., a defocus amount), assuming that the resolution of the
optical image forming system 6 is sufficient. It is to be noted
that the optical image forming system 6 may be any of refractive,
reflective and refractive/reflective optical systems.
[0084] Also in the second embodiment, in the same manner as in the
first embodiment, the semiconductor film of the substrate to be
treated 4 is irradiated with the light beam which has the two-steps
inverse peak type light intensity distribution by the functions of
three members including the transmission filter 2g, micro lens
array 3, and phase shift mask 1. Therefore, the lateral growth from
the crystal nucleus reaches the peak without stopping halfway, and
the large-grain-size crystallized semiconductor film can be
produced.
Most of the light beam supplied from the optical illumination
system 2 by the cooperative function of the micro lens array 3 and
phase shift mask 1 can contribute to the crystallization of the
desired region, and the crystallization satisfactory in the light
efficiency can be realized.
[0085] Moreover, in the second embodiment, the optical image
forming system 6 is optically interposed between the phase shift
mask 1 and substrate to be treated 4, and a relatively large
interval is secured between the substrate to be treated 4 and
optical image forming system 6. Therefore, when the light beam is
incident upon the semiconductor film of the substrate to be treated
4, abraded portions generated from the semiconductor film are
prevented from adhering to the phase shift mask 1 or contaminating
the mask. Therefore, satisfactory crystallization can be realized
without being influenced by abrasion in the substrate to be treated
4.
[0086] Furthermore, in the second embodiment, since a relatively
large interval is secured between the substrate to be treated 4 and
optical image forming system 6, a detection light for detecting the
position is introduced onto the light path between the substrate to
be treated 4 and optical image forming system 6, and a positional
relation between the substrate to be treated 4 and optical image
forming system 6 is easily adjusted.
[0087] FIG. 11 is a diagram schematically showing the constitution
of the crystallization apparatus according to a third embodiment of
the present invention. The third embodiment includes the
constitution similar to that of the second embodiment, but is
different from the second embodiment in that a pattern forming
surface of the phase shift mask 1 and the substrate to be treated 4
are disposed so as to have an optically conjugated relation via an
optical image forming system 7. The third embodiment will be
described hereinafter with respect to the different respects from
the second embodiment. It is to be noted that for the sake of
clarification of the drawing, in FIG. 11, the inner constitution of
the optical illumination system 2 is omitted.
[0088] The optical image forming system 7 according to the third
embodiment includes an aperture diaphragm 7a. The aperture
diaphragm 7a is selected from a plurality of aperture diaphragms
different in the size of an aperture (light transmission portion).
These aperture diaphragms are constituted so that the diaphragms
can selectively be converted with respect to the light path.
Instead, the aperture diaphragm 7a may also be constituted such
that the size of the aperture continuously changes, for example by
moving the diaphragm. The size of the aperture of the aperture
diaphragm 7a (i.e., the image-side numerical aperture of the
optical image forming system 7) is set such that the light beam can
include the periodic two-steps inverse peak type light intensity
distribution on the semiconductor film of the substrate to be
treated 4. The width of the two-steps inverse peak type light
intensity distribution is preferably set to be equal to the pixel
pitch of a liquid crystal display.
[0089] By the function of the phase shift mask 1, the width of the
inverse peak type light intensity distribution formed on the
semiconductor film of the substrate to be treated 4 is of the same
degree as that of a resolution R3 of the optical image forming
system 7. The resolution R3 of the optical image forming system 7
is defined by R3=k.lamda./NA3, where k denotes the wavelength of a
light for use, and NA3 denotes the image-side numerical aperture of
the optical image forming system 7. Here, as described above, the
constant k indicates a value substantially close to 1. When the
image-side numerical aperture NA3 of the optical image forming
system 7 is reduced, and the resolution of the optical image
forming system 7 is lowered in this manner in the third embodiment,
the width of the inverse peak type light intensity distribution
increases.
[0090] That is, the inverse peak type pattern of the light
intensity distribution of the light beam converted in a phase shift
plane has an excessively small width on the phase shift plane.
However, when the resolution is appropriately lowered, a preferable
width is obtained. In the third embodiment, the image is formed on
the semiconductor film of the substrate to be treated 4 with a low
resolution by the optical image forming system 7 with respect to
the light intensity distribution on the phase shift plane.
Therefore, the inverse peak portion of the light intensity
distribution of the light beam with which the semiconductor film is
irradiated has a preferable width on the semiconductor film of the
substrate to be treated 4.
[0091] Also in the third embodiment, in the same manner as in the
first and second embodiments, the semiconductor film of the
substrate to be treated 4 is irradiated with the light beams which
have the two-steps inverse peak type light intensity distribution.
Therefore, the lateral growth from the crystal nucleus reaches the
peak without stopping halfway, and the large-grain-size
crystallized semiconductor film can be produced. The desired region
only can be irradiated with most of the light beams supplied from
the optical illumination system 2, and the crystallization
satisfactory in the light efficiency can be realized. Also in the
third embodiment, in the same manner as in the second embodiment,
the satisfactory crystallization can be realized without being
influenced by the abrasion in the semiconductor film of the
substrate to be treated 4. Furthermore, it is easy to adjust the
positional relation between the substrate to be treated 4 and
optical image forming system 7.
[0092] In the second and third embodiments, it is preferable to
satisfy the following condition equation (2) in addition to the
above condition equation (1). It is to be noted that in the
condition equation (2), NA3 denotes the image-side numerical
aperture of the optical image forming system (6, 7) as described
above.
.lamda./NA3<f.times.NA1 (2),
where the right side indicates the value corresponding to the size
(radius) of the spotted light beam region formed in the phase shift
portion 11e, and the left side indicates the value corresponding to
the resolution R3 of the optical image forming system (6, 7).
[0093] Next, modification examples of the wavefront dividing
element and transmission filter will be described with reference to
FIGS. 12 to 14. In the present modification example, the wavefront
dividing element is a micro cylindrical lens array 3' shown in FIG.
12. The micro cylindrical lens array 3' includes a plurality of
optical elements 13' which extend in a predetermined direction
(x-direction in the present example) and which are arranged in
parallel with one another one-dimensionally along a direction
crossing at right angles to the above direction (y-direction). Each
of the optical elements 13' includes a refractive surface 13'a
which has a one-dimensional condensing function in the
y-direction.
[0094] In the present example, for the micro cylindrical lens array
3', it is preferable to use a transmission filter 2h shown in FIG.
13, instead of the transmission filter 2g. The transmission filter
2h includes:
an elongated rectangular middle region 12c extending in the
x-direction and having a transmittance, for example, of 50%; and a
pair of semicircular peripheral regions 12d which are formed to
hold the middle region 12c and which substantially have a
transmittance of 100%. A longitudinal direction (x-direction) of
the middle region 12c of the transmission filter 2h is set to
optically correspond to that of each micro cylindrical lens element
13' of the micro cylindrical lens array 3'. The middle region 12c
is defined by a pair of substantially parallel chords, but is not
limited to this, and another shape may also be formed.
[0095] The light beam incident upon the micro cylindrical lens
array 3' is wavefront-divided by a large number of micro
cylindrical lens elements 13', and the light beams condensed via
the respective micro cylindrical lens elements 13' form slit-shaped
(linear) light beams in the respective corresponding phase shift
portions 11e. As shown in FIG. 14, the slit-shaped light beam form
slit-shaped light beam region 63 shown by dot lines, which surround
the plurality of transistor forming region 60 of transistor forming
region column direction in the semiconductor film of the substrate
to be treated 4.
[0096] Therefore, the light intensity distribution of the
slit-shaped light beam with which the semiconductor film of the
substrate to be treated 4 is irradiated has a two-steps inverse
peak type profile along the short-side direction of the slit as
shown in FIG. 8A, and has a uniform profile along the longitudinal
direction. That is, the light beam transmitted through the micro
cylindrical lens array 3' and transmission filter 2h to irradiate
the semiconductor film of the substrate to be treated 4 obtains the
light intensity distribution which is partially shown in FIG.
15.
[0097] When the semiconductor film of the substrate to be treated 4
is irradiated with the light beam having the two-steps inverse peak
type light intensity distribution as shown in FIG. 15, the crystal
nucleus is formed in a point in which the light intensity is
minimized, that is, in a point substantially of zero. Next, the
lateral growth is started along a direction having a light
intensity gradient from this crystal nucleus (lateral direction in
FIG. 13). In the two-steps inverse peak type light intensity
distribution shown in FIG. 15, the portion in which the light
intensity decreases does not substantially exist in the
intermediate portion. Therefore, the lateral growth reaches the
peak without stopping halfway from the crystal nucleus, and the
growth of a large grain can be realized.
[0098] In the above-described embodiments and modification
examples, the micro lens array 3 and micro cylindrical lens array
3' may have the refractive surface 13'a having a continuous curved
shape, or a stepped refractive surface. The constitution is not
limited to the continuous curved surface or the multiple-step
approximation, and the wavefront dividing element may also be
constituted as "quino form" folded back in a range of phase
differences of 0 to 2.pi.. Furthermore, a wavefront dividing
function can also be applied by a refractive index distribution of
an optical material without disposing the refractive surface in the
wavefront dividing element. For example, it is possible to use
conventional arts such as photo polymer whose refractive index is
modulated by the light intensity, and ion exchange of glass.
A hologram or diffractive optical device may also be used to apply
a function equivalent to that of the wavefront dividing
element.
[0099] Furthermore, in the above-described embodiments, the phase
shift mask 1 is constituted of four rectangular regions
corresponding to phases of 0, .pi./2, .pi., 3.pi./2, but the
present invention is not limited to this, and the phase shift mask
can variously be modified. For example, a phase shift mask may also
be used which includes an intersection (phase shift portion)
including three or more phase shift lines and in which the integral
value of the complex transmittance of the circular region around
the intersection is substantially zero. As shown in FIG. 16, a
phase shift mask 111 may also be used in which circular concave
portions corresponding to the phase shift portions, or convex
portions 111a have steps from a periphery and which is set so as to
have a phase difference of .pi. between the light beams transmitted
through the circular portions and the light beams transmitted
through a periphery 111b.
[0100] The light intensity distribution can also be calculated in a
stage of design, but it is preferable to observe and confirm the
light intensity distribution in an actual surface to be treated
(surface to be exposed). This observation is performed, for
example, by enlarging the surface to be treated by the optical
system and disposing image pickup devices such as CCD in the
surface to be treated to measure the light intensity distribution
of the light beams incident upon the image pickup device. When the
light for use is an ultraviolet ray, the optical system is
restricted, and therefore a fluorescent plate may be disposed in
the surface to be treated to convert the beam to a visible
light.
[0101] Moreover, in the above-described embodiments, the wavefront
dividing element (the micro lens array 3 or micro cylindrical lens
array 3') and the phase shift mask 1 may be formed as individual
optical members, but the present invention is not limited to this,
and the wavefront dividing element 3 and phase shift mask 1 may
also integrally be combined to form an integrated assembly. In this
case, the wavefront dividing element 3 and phase shift mask 1 do
not have to be positioned, respectively, when attached to the
apparatus, and the wavefront dividing element 3 and phase shift
mask 1 can be attached as one integrated optical member to the
apparatus with good accuracy.
[0102] The integrally formed wavefront dividing element 3 and phase
shift mask 1 preferably include an incident a plane on which the
light beam is incident upon the wavefront dividing element 3, a
boundary plane between the wavefront dividing element 3 and phase
shift mask 1, and the phase shift portion of the phase shift mask 1
in order from an incidence direction of the light beam. In this
manner, a constitution which does not include a layer structure of
glass is disposed on the side of the substrate to be treated 4
rather than the phase shift portion. Accordingly, in each
embodiment, the distance between the phase shift surface and the
substrate to be treated 4 is sufficiently reduced, and the
satisfactory crystallization can be performed.
[0103] Particularly, in the second and third embodiments which
require high resolution for exactly forming the inverse peak type
light intensity distribution, with the constitution which does not
include the layer structure of glass on the side of the substrate
to be treated 4 from the phase shift surface, generation of
unnecessary aberration can be avoided. After the phase shift
surface and wavefront dividing element are formed in one surface of
each of two substrates, the formed surfaces are disposed opposite
to each other at a predetermined distance, peripheral portions are
fixed to each other, and the substrates may also integrally be
formed in this manner.
[0104] Next, one example of a method of manufacturing the integral
assembly of the wavefront dividing element 3 and phase shift mask 1
will be described with respect to FIGS. 17A to 17K. FIGS. 17A to
17K are diagrams showing steps of the integral assembly of the
wavefront dividing element 3 and phase shift mask 1. For example,
one surface of a quartz substrate 40, having a refractive index of
1.50841, shown in FIG. 17A is entirely coated with a resist 41 as
shown in FIG. 17B. Next, electron beam drawing and developing are
performed to pattern the resist 41. Accordingly, a resist pattern
41a is formed on a predetermined position of the quartz substrate
40 as shown in FIG. 17C. Next, the resist pattern 41a is used as a
mask to perform dry etching, and an exposed surface portion of the
quartz substrate 40 is removed down to a predetermined depth.
Furthermore, the resist is removed from the quartz substrate 40 as
shown in FIG. 17D. Subsequently, the steps of applying and removing
the resist are repeated, while the portion and depth of the quartz
substrate 40 to be etched are successively shifted. Accordingly, a
refractive surface (e.g., depth of 0.124 .mu.m) 40a having a lens
shape is entirely formed in the surface of the quartz substrate
40.
[0105] Subsequently, a transparent film 42 having a thickness of 3
.mu.m formed of Si.sub.xN.sub.y (high refractive index material),
and for example, having a refractive index of about 2.3 is formed
on the lens-shaped refractive surface 40a of the quartz substrate
40 by a CVD process. Moreover, for example, by a chemical
mechanical polishing (CMP) technique, the surface of the
transparent film 42 is flatted shown in FIG. 17G. Next, a
transparent organic spin on glass (SOG) film (e.g., alkoxysilane
substituted with an alkyl group) 43, for example, having a
thickness of 40 .mu.m is formed in the flatted surface of the
transparent film 42 (FIG. 17H).
[0106] Furthermore, the whole surface of the organic SOG film 43 is
coated with a resist 44 (FIG. 17I), the electron beam drawing and
developing are performed with respect to the resist 44, and
accordingly a resist pattern 44a is formed (FIG. 17J).
Subsequently, the resist pattern 44a is used as the mask to perform
the dry etching with respect to the exposed surface portion of the
organic SOG film 43, a phase shift surface 45 having a depth, for
example, of 0.248 .mu.m is formed, and finally the resist is
removed (FIG. 17K). In this manner, the quartz substrate 40
constituting the wavefront dividing element 3 is formed integrally
with the transparent film 42 and organic SOG film 43 which
constitute the phase shift mask 1. The lens-shaped refractive
surface 40a constitutes an interface between the wavefront dividing
element 3 and phase shift mask 1.
[0107] FIGS. 18A to 18E show steps of using the crystallization
apparatus of each embodiment to manufacture an electronic device.
As shown in FIG. 18A, a chemical vapor phase growth process or
sputter process is used to successively form an underlayer film 21
(e.g., a stacked film of SiN having a film thickness of 50 nm and
SiO.sub.2 stacked film having a film thickness of 100 nm) and an
amorphous semiconductor film 22 (e.g., Si, Gc, SiGe, and the like
having a film thickness of about 50 nm to 200 nm) on a transparent
insulating substrate 20 (e.g., alkali glass, quartz glass, plastic,
polyimide, and the like). Accordingly, the substrate to be treated
4 is prepared.
[0108] The crystallization apparatus is used to irradiate a part or
whole of the surface of the formed amorphous semiconductor film 22
with laser beams 23 (e.g., KrF excimer laser beams or XeCl excimer
laser beams). For the crystallization apparatus according to each
embodiment of the present invention, the surface is irradiated with
the light beams which have the two-steps inverse peak type light
intensity distribution. Therefore, as shown in FIG. 18B, a
polycrystalline semiconductor film or single-crystal semiconductor
film 24 is produced which has crystals having large grain size as
compared with the polycrystalline semiconductor film produced using
the crystallization apparatus of the conventional art.
[0109] At this time, when the amorphous semiconductor film 22 has a
relatively broad surface, and a part only of the surface is
irradiated with one irradiation by the crystallization apparatus,
the crystallization of the whole surface of the amorphous
semiconductor film 22 is performed by relatively moving the
crystallization apparatus and the amorphous semiconductor film 22
with respect to each other in two directions crossing at right
angles to each other.
[0110] For example, the amorphous semiconductor film 22 is fixed,
the crystallization apparatus scans the surface of the amorphous
semiconductor film 22 in two directions crossing at right angles to
each other (x, y-directions), and a part of the surface of the
amorphous semiconductor film 22 is successively intermittently
irradiated and crystallized. Alternatively, the amorphous
semiconductor film 22 is laid on a stage which can move in two
directions crossing at right angles to each other, the stage is
moved with respect to the fixed crystallization apparatus, and the
surface of the amorphous semiconductor film may accordingly be
irradiated with the light beams. Alternatively, with respect to the
crystallization apparatus supported by an arm movable only in one
direction, the amorphous semiconductor film 22 is moved in the
direction crossing at right angles to the apparatus. In this
system, the crystallization apparatus and amorphous semiconductor
film 22 may be moved with respect to each other in two directions
crossing at right angles to each other to irradiate the surface of
the amorphous semiconductor film 22 with the light beams.
[0111] Next, as shown in FIG. 18C, a photolithography technique is
used to process the polycrystalline semiconductor film or the
single-crystal semiconductor film 24 into a semiconductor film 25
having an insular shape, and the chemical vapor phase growth
process or sputter process is used to form an SiO.sub.2 film having
a film thickness of 20 nm to 100 nm as a gate insulating film 26 on
the underlayer film 21 including the insular-shaped semiconductor
film 25. Furthermore, as shown in FIG. 18D, a gate electrode 27
(e.g., silicide, MoW, and the like) is formed on the gate
insulating film 26, and the gate electrode 27 is used as a mask to
implant impurity ions 28 (phosphor for an N-channel transistor,
boron for a P-channel transistor) into the semiconductor film 25.
Thereafter, an anneal treatment (e.g., at 450.degree. C. for one
hour) is performed in a nitrogen atmosphere to activate the
implanted impurities.
[0112] Next, as shown in FIG. 18E, an interlayer insulating film 29
is formed on the gate insulating film 26 contact holes are formed
through the interlayer insulating film 29 and gate insulating film
26.
A source electrode 33 and drain electrode 34 electrically connected
to a source 31 and drain 32 between which a channel 30 is
positioned are formed. At this time, the channel 30 is formed in
accordance with the position of the large grain size crystal of the
polycrystalline semiconductor film or the single-crystal
semiconductor film 24 produced in the steps shown in FIGS. 18A and
18B.
[0113] By the above-described steps, a polycrystalline transistor
or single-crystal semiconductor transistor can be formed. The
polycrystalline transistor or single-crystal transistor
manufactured in this manner can be applied to a driving circuit of
a matrix circuit substrate of displays such as a liquid crystal
display and electroluminescence (EL) display, or an integrated
circuit of a memory (SRAM or DRAM) or CPU.
[0114] When the matrix circuit substrate including the thin film
transistor is manufactured, the transparent substrate such as glass
is used as the substrate, and the polycrystalline or amorphous
semiconductor film is formed on the substrate. Next, the
crystallization technique is used to produce the semiconductor film
into the crystallized semiconductor film. Thereafter, as known in
this field, the crystallized semiconductor film is separated into a
large number of portions (insular-shaped regions) positioned in the
matrix shape, and the thin film transistor is formed in each
separated semiconductor portion by the manufacturing technique of
the thin film transistor. Thereafter, as well known, a pixel
electrode is formed on the substrate to be electrically connected
to each thin film transistor, and the pixel is defined to complete
the matrix circuit substrate.
[0115] Although the aforementioned embodiments use three
components, that is a transmission filter, wavefront dividing
element, and phase shift mask, the present invention is not limited
to the combination of three components as illustrated in FIG. 19
and FIG. 20.
In these figures, substantially same components as those shown in
FIG. 8B are denoted by the same reference numbers and their details
are omitted.
[0116] FIG. 19 shows a modification of the device shown in FIG. 8B,
in which the transmission filter is omitted, so that a light beam
emitted from a laser source may be directly incident on the
wavefront dividing element 3.
[0117] FIG. 20 shows a modification of the device shown in FIG. 8B,
in which the phase shift mask is omitted, so that a light beam from
the wavefront dividing element may be directly incident on the
semiconductor device.
[0118] As described above, according to the present invention, the
two-steps inverse peak type light intensity distribution is formed
on the semiconductor film of the substrate to be treated by the
cooperative function of the transmission filter, wavefront dividing
element, and/or phase shift mask. As a result, the sufficient
lateral growth from the crystal nucleus is realized, and a
crystallized semiconductor film having a large grain diameter can
be produced. Since there is an inside inverse peak, the crystal
nucleus can be limited to a narrow region, and a crystal growth
start point, that is, the crystal grain can two-dimensionally be
positioned with good accuracy.
[0119] Moreover, in the present invention, the light incident upon
the wavefront dividing element is wavefront-divided by a plurality
of optical elements, and the light beams condensed via the
respective optical elements form light beams to surround a desired
region in the corresponding phase shift portion and on the
semiconductor film of the substrate to be treated. As a result, a
large part of the light supplied from the optical illumination
system can contribute to the crystallization of the desired region,
and the crystallization can be realized with satisfactory light use
efficiency.
* * * * *