U.S. patent application number 12/243426 was filed with the patent office on 2009-02-12 for crystallization apparatus, crystallization method, device, optical modulation element, and display apparatus.
This patent application is currently assigned to Advanced LCD Technologies Dev. Ctr. Co., Ltd.. Invention is credited to Masayuki Jyumonji, Hiroyuki Ogawa, Yukio Taniguchi.
Application Number | 20090038536 12/243426 |
Document ID | / |
Family ID | 35052867 |
Filed Date | 2009-02-12 |
United States Patent
Application |
20090038536 |
Kind Code |
A1 |
Taniguchi; Yukio ; et
al. |
February 12, 2009 |
CRYSTALLIZATION APPARATUS, CRYSTALLIZATION METHOD, DEVICE, OPTICAL
MODULATION ELEMENT, AND DISPLAY APPARATUS
Abstract
A first optical modulation element irradiates a
non-single-crystal substance with a light beam which is to have a
first light intensity distribution on the non-single crystal
substance by modulating an intensity of an incident first light
beam, thereby melting the substance. A second optical modulation
element irradiates the substance with a light beam which is to have
a second light intensity distribution on the substance by
modulating an intensity of an incident second light beam, thereby
melting the substance. An illumination system causes the light beam
having the second light intensity distribution to enter the molten
part of the substance in a period that the substance is partially
molten by irradiation of the light beam having the first light
intensity distribution.
Inventors: |
Taniguchi; Yukio;
(Yokohama-shi, JP) ; Jyumonji; Masayuki;
(Yokohama-shi, JP) ; Ogawa; Hiroyuki;
(Yokohama-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Advanced LCD Technologies Dev. Ctr.
Co., Ltd.
Yokohama-shi
JP
|
Family ID: |
35052867 |
Appl. No.: |
12/243426 |
Filed: |
October 1, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11087619 |
Mar 24, 2005 |
7445674 |
|
|
12243426 |
|
|
|
|
Current U.S.
Class: |
117/7 |
Current CPC
Class: |
Y10T 117/1012 20150115;
Y10T 117/1016 20150115; Y10T 117/1004 20150115; Y10T 117/1008
20150115; C30B 13/24 20130101 |
Class at
Publication: |
117/7 |
International
Class: |
C30B 1/02 20060101
C30B001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2004 |
JP |
2004-103373 |
Claims
1. A crystallization method which generates a crystallized
substance by irradiating a non-single-crystal substance with a
light beam having a predetermined light intensity distribution,
comprising: a first irradiation step of irradiating the
non-single-crystal substance with a first light beam having a first
light intensity distribution; and a second irradiation step of
irradiating a molten part of the non-single-crystal substance with
a second light beam having a second light intensity distribution
substantially different from the first light intensity distribution
within a time in which the non-single-crystal substance is molten
by the first irradiation step.
2. The method according to claim 1, wherein the non-single-crystal
semiconductor is irradiated with the first light beam subjected to
phase modulation through the first optical modulation element in
the first irradiation step, and the non-single-crystal
semiconductor is irradiated with the second light beam subjected to
phase modulation through the second optical modulation element
having different characteristics from those of the first optical
modulation element in the second irradiation step.
3. The method according to claim 1, wherein the first light beam is
caused to enter a common optical modulation element including the
first and second optical modulation elements, and the
non-single-crystal semiconductor is irradiated with the first light
beam subjected to phase modulation through the common optical
modulation element in the first irradiation step, and the second
light beam has characteristics different from those of the first
light beam and is caused to enter the common optical modulation
element and the non-single-crystal semiconductor is irradiated with
the second light beam subjected to phase modulation through the
common optical element in the second irradiation step.
4. The method according to claim 1, wherein the first light
intensity distribution has a plurality of V-shaped intensity
patterns, and the second light intensity distribution has a
plurality of patterns each having a central peak shape.
5. A crystallization method which generates a crystallized
substance by irradiating a non-single-crystal substance with a
light beam having a predetermined light intensity distribution,
comprising: irradiating firstly the non-single-crystal substance
with a first light beam which is to have on the non-single-crystal
substance a light intensity distribution having at least two
V-shaped unit intensity distributions which are adjacent to define
a chevron unit light intensity distribution therebetween; and
irradiating secondly a high-temperature region formed to the
non-single-crystal substance in accordance with an apex of the
chevron unit light intensity distribution with a light beam having
a second light intensity distribution after an elapse of a
predetermined time from start of the first irradiation step in
order to compensate flattening of a temperature gradient with time
in the high-temperature region of the non-single-crystal
substance.
6. The method according to claim 5, wherein the non-single-crystal
semiconductor is irradiated with the first light beam subjected to
phase modulation through the first optical modulation element in
the firstly irradiating, and the non-single-crystal semiconductor
is irradiated with the second light beam subjected to phase
modulation through the second optical modulation element having
different characteristics from those of the first optical
modulation element in the secondly irradiating.
7. The method according to claim 5, wherein the first light beam is
caused to enter a common optical modulation element including the
first and second optical modulation elements, and the
non-single-crystal semiconductor is irradiated with the first light
beam subjected to phase modulation through the common optical
modulation element in the firstly irradiating, and the second light
beam has characteristics different from those of the first light
beam and is caused to enter the common optical modulation element
and the non-single-crystal semiconductor is irradiated with the
second light beam subjected to phase modulation through the common
optical element in the secondly irradiating.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional of and claims the benefit
of priority under 35 U.S.C. .sctn. 120 from the U.S. Ser. No.
11/087,619, filed Mar. 24, 2005 and claims the benefit of priority
from prior Japanese Patent Application No. 2004-103373, filed Mar.
31, 2004, the entire contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a crystallization
apparatus, a crystallization method, a device and an optical
modulation element, and more particularly to a technique which
generates a crystallized semiconductor film by irradiating a
non-single-crystal substance such as a non-single-crystal
semiconductor film with a laser light having a predetermined light
intensity distribution.
[0004] 2. Description of the Related Art
[0005] A thin film transistor (TFT) used for a switching element or
the like which selects a display pixel in, e.g., a liquid crystal
display (LCD) has been conventionally formed by using amorphous
silicon or polysilicon.
[0006] Polysilicon has a higher mobility of electrons or holes than
that of amorphous silicon. Therefore, when a transistor is formed
by using polysilicon, a switching speed and hence a display
response speed become higher than those in case of forming the same
by using amorphous silicon. Further, a peripheral LSI can comprise
a thin film transistor. Furthermore, there is an advantage of
reducing a design margin of any other component. Moreover, when
peripheral circuits such as a driver circuit or a DAC are
incorporated in a display, these peripheral circuits can be
operated at a higher speed.
[0007] Since polysilicon comprises an aggregation of crystal
grains, when, e.g., a TFT transistor is formed in this polysilicon,
crystal grain boundaries present in a channel region, this crystal
grain boundary serves as a barrier, and a mobility of electrons or
holes is reduced as compared with that of single-crystal silicon.
Additionally, each of many thin film transistors formed by using
polysilicon has a different number of crystal grain boundaries
formed in a channel region, and this difference becomes
irregularities, resulting in a problem of unevenness in display in
case of a liquid crystal display. Thus, there has been recently
proposed a crystallization method which generates crystallized
silicon having a crystal grain with a large particle size enabling
at least one channel region to be formed in order to improve the
mobility of electrons or holes and reduce irregularities in number
of crystal grain boundaries in a channel portion.
[0008] As this type of crystallization method, there has been
conventionally known a "phase control ELA (Excimer Laser Annealing)
method" which generates a crystallized semiconductor film by
irradiating a phase shifter approximated in parallel with a
polycrystal semiconductor film or a non-single-crystal
semiconductor film with an excimer laser light. The detail of the
phase control ELA method is disclosed in, e.g., Journal of The
Surface Science Society of Japan, Vol. 21, No. 5, pp. 278-287,
2000.
[0009] In the phase control ELA method, a light intensity
distribution having an inverse peak pattern (a pattern in which a
light intensity is minimum at the center and the light intensity is
suddenly increased toward the periphery (lateral sides)) in which a
light intensity at a point corresponding to a phase shift portion
of a phase shifter is lower than that in the periphery is
generated, and a non-single-crystal semiconductor film (a
polycrystal semiconductor film or an amorphous semiconductor film)
is irradiated with a light having this light intensity distribution
with an inverse peak shape. As a result, a temperature gradient is
generated in a fusion area in accordance with a light intensity
distribution in an irradiation target area, a crystal nucleus is
formed at a part which is solidified first or a part which is not
molten in accordance with a point where the light intensity is
minimum, and a crystal grows from the crystal nucleus in a lateral
direction toward the periphery (which will be referred to as a
"lateral growth" or a "growth in the lateral direction"
hereinafter), thereby generating a single-crystal grain with a
large particle size.
[0010] Further, "Growth of Large Si Grains at Room Temperature by
Phase-Modulated Excimer-Laser Annealing Method" by H. Ogawa et al.,
IDW'03 Proceedings of the 10th International Display Workshops, p.
323 releases a crystallization method which generates a crystal
grain by irradiating a non-single-crystal semiconductor film with a
light having a V-shaped light intensity distribution which can be
obtained through a phase shifter and an image formation optical
system. Furthermore, this known reference discloses that it is
desirable for an intensity distribution of a light with which the
non-single-crystal semiconductor film is irradiated to vary in a
V-shape in an intensity range of 0.5 to 1.0 when the maximum value
of the intensity is standardized as 1.0.
[0011] In the crystallization method disclosed in this known
reference, a pulse oscillation type laser light source like an
excimer laser light source is used, and each typical pulse light
emission time thereof is 20 to 30 nsec (nanoseconds). This time is
set in order to obtain a large light intensity required to melt a
semiconductor by concentrating an light emission energy on a part
of the semiconductor like silicon in a very short time. As a
result, a semiconductor can be irradiated with the same light
intensity distribution (V-shaped) for each pulse light emission
time.
[0012] Disadvantages caused due to irradiating a semiconductor with
the same V-shaped light intensity distribution in the prior art
disclosed in the last known reference will now be described
hereinafter with reference to FIGS. 18A to 18D (FIGS. 18C and 18D
are views showing calculation results concerning a change in
temperature distribution in an a-Si (noncrystalline silicon or
amorphous silicon) layer obtained when the a-Si layer is irradiated
with a light beam having a V-shaped light intensity distribution
over a fixed time in accordance with the prior art). On the
occasion of calculating this temperature distribution, a
calculation method described in "A New Nucleation-Site-Control
Excimer-Laser-Crystallization Method" by Mitsuru Nakata et al.,
Jpn. J. Apple. Phys. Vol. 40 (2001) Pt. 1, No. 5A, 3049 p is
adopted, and this cited reference is incorporated herein as a
reference. Moreover, on the occasion of calculating a temperature
distribution, an influence of latent heat which is
absorbed/generated when a-Si is molten/solidified is ignored. As
calculation conditions, there is assumed a layer structure
comprising an SiO.sub.2 layer having a thickness of 200 nm, an a-Si
layer having a thickness of 200 nm, and an SiO.sub.2 layer having
an infinite thickness in the order from a light incidence side. It
is assumed that a maximum light intensity is 1.0.times.10.sup.11
W/cm.sup.2 in a unit light intensity distribution having a V-shape
shown in FIG. 18A (which indicates one mountain-shape unit
intensity portion in a light intensity distribution comprising a
plurality of V-shaped unit light intensity distributions which are
continuously formed in the drawing), and each pulse light emission
time is 20 nsec as shown in FIG. 18B. Additionally, it is assumed
that a-Si has a thermal conductivity of 24 W/mK, specific heat of
861 J/KKg and a density of 2340 Kg/m.sup.3. Further, it is assumed
that SiO.sub.2 has a heat conductivity of 1.5 W/mK, specific heat
of 1000 J/KKg and a density of 2300 Kg/m.sup.3.
[0013] Referring to FIG. 18C showing a change in temperature
distribution during pulse light emission, it can be understood that
the temperature distribution keeps the V-shape (which indicates a
chevron part in the continuously formed V-shaped light intensity
distribution in the drawing) and achieves an increase in
temperature with an elapse of time in 20 nsec during which a light
beam having a V-shaped light intensity distribution is applied.
However, referring to FIG. 18D showing a change in temperature
distribution after pulse light emission, it can be recognized that
a temperature is gradually reduced with an elapse of time after end
of pulse light emission and a temperature gradient in a
high-temperature region (a peak portion) in the V-shaped
temperature distribution is flattened with a time. A factor of this
phenomenon is thermal diffusion in an in-plane direction in the
a-Si layer.
[0014] FIG. 19 is a view schematically showing an advancing state
of crystallization of a-Si involved by a change in temperature
distribution depicted in FIG. 18C. In crystallization of Si
involved by a change in temperature distribution depicted in FIG.
18C, as shown in FIG. 19, after an entire light reception region of
a-Si is once molten and incidence of a laser light is interrupted,
partial crystallization occurs at a part where a temperature is
lowest, i.e., a bottom part of the V-shaped temperature
distribution (and hence a light intensity distribution).
Thereafter, a crystal grows in the lateral direction with this
crystallized part serving as a nucleus due to heat of a temperature
gradient in the V-shaped temperature distribution. However, when
the crystal growth is in the final stage and a high-temperature
region (in the vicinity of a peak) of the V-shaped temperature
distribution (and hence the light intensity distribution) is
reached, the temperature gradient in the high-temperature region is
in a flat state (a state in which the temperature distribution is
rounded) due to an advance of thermal diffusion.
[0015] Therefore, the primarily desired crystal growth is
terminated before reaching the high-temperature region, an
undesired crystal nucleus is generated in the high-temperature
region in the V-shaped temperature distribution, and this
high-temperature region is polycrystallized. As a result, the
influence of thermal diffusion in the final stage of the crystal
growth disables realization of the sufficient crystal growth from
the crystal nucleus and hence generation of a crystallized
semiconductor having a crystal grain with a large particle size. In
this case, the "crystal grain with a large particle size" means a
crystal grain having a size with which a channel region of one TFT
can be completely formed in the crystal grain. Further, in this
case, a margin of a positioning accuracy is narrowed, for
example.
[0016] Although the influence of latent heat is not considered in
the above-described calculation, a temperature increases in the
vicinity of a solid-liquid interface due to latent heat generated
during solidification. This phenomenon is introduced in "formation
of an Si thin film with a huge crystal grain using an excimer
laser" by Masakiyo Matsumura, Journal of The Surface Science
Society of Japan, Vol. 21, No. 5, pp. 278, 2000. Analogizing from a
result introduced in this reference, it can be conjectured that a
temperature distribution is affected by latent heat and is as shown
in FIG. 20 when a temperature gradient in a high-temperature region
is flattened in FIG. 19. In this case, it can be considered that
flattening of the temperature gradient due to the influence of
emission of latent heat further widely occurs and the crystal
growth from the crystal nucleus from which crystallization has
first started becomes shorter (a crystal grain which is short in
the lateral direction is obtained).
BRIEF SUMMARY OF THE INVENTION
[0017] It is an object of the present invention to provide a
crystallization apparatus, a crystallization method, a device, an
optical modulation element and a display apparatus which can
realize the sufficient crystal growth from a crystal nucleus and
thereby generate a crystallized substance with a large particle
size while suppressing an influence of thermal diffusion or
emission of latent heat in the final stage of the crystal
growth.
[0018] A first aspect of the present invention provides a
crystallization apparatus comprising:
[0019] a first optical modulation element which irradiates a
non-single-crystal substance with a light beam which is to have a
first light intensity distribution on the non-single crystal
substance by modulating an intensity of an incident first light
beam, thereby melting the non-single-crystal substance;
[0020] a second optical modulation element which irradiates the
non-single-crystal substance with a light beam which is to have a
second light intensity distribution substantially different from
the first light intensity distribution on the non-single-crystal
substance by modulating an intensity of an incident second light
beam, thereby melting the non-single-crystal substance; and
[0021] an illumination system which causes the light beam having
the second light intensity distribution to enter the molten part of
the non-single-crystal substance in a period that the
non-single-crystal substance is partially molten by irradiation of
the light beam having the first light intensity distribution.
[0022] A second aspect of the present invention provides a
crystallization apparatus comprising:
[0023] a first optical modulation element which irradiates a
non-single-crystal substance with a first light beam which is to
have on the non-single-crystal substance a light intensity
distribution having at least two V-shaped unit intensity
distributions which are adjacent to define a chevron unit light
intensity distribution therebetween by modulating an intensity of
the incident first light beam, thereby melting the
non-single-crystal substance;
[0024] a second optical modulation element which irradiates the
non-single-crystal substance with a second light beam which is to
have a second light intensity distribution on the
non-single-crystal substance by modulating an intensity of the
incident second light beam, thereby melting the non-single-crystal
substance; and
[0025] an illumination system which irradiates a part of the
non-single-crystal molten by the first light beam with the second
light beam after an elapse of a predetermined time from start of
irradiation of the first light beam.
[0026] In the first and second aspects, the illumination system can
have a light source which supplies an illumination light beam, a
beam splitter which divides a light beam supplied from the light
source, a first optical system which leads one light beam from the
beam splitter to the first optical modulation element, and a second
optical system which has a longer optical path length than the
first optical system and leads the other light beam from the beam
splitter to the second optical modulation element.
[0027] Further, in these aspects, preferably, the first optical
modulation element and the second optical modulation element are a
common optical modulation element, and the illumination system
causes the first light beam having a first angular distribution to
enter the common optical modulation element and then causes the
second light beam having a second angular distribution
substantially different from the first angular distribution to
enter the common optical modulation element. In this case, the
illumination system preferably has a light source which supplies an
illumination light beam, a beam splitter which divides a light beam
supplied from the light source, a first shaping optical system
which shapes one light beam from the beam splitter and leads this
light beam to a predetermined position, a second shaping optical
system which has a longer optical path length than the first
shaping optical system, shapes the other light beam from the beam
splitter and leads this light beam to the predetermined position,
an optical path combining element which is arranged at the
predetermined position and combines an optical path of the light
beam transmitted through the first shaping optical system and an
optical path of the light beam transmitted through the second
shaping optical system, and a common illumination optical system
arranged between the optical path combining element and the common
optical modulation element.
[0028] Furthermore, in these aspects, preferably, the first optical
modulation element and the second optical modulation element are a
common optical modulation element, and the illumination system
causes the first light beam having a first polarization state to
enter the common optical modulation element and then causes the
second light beam having a second polarization state substantially
different from the first polarization state to enter the common
optical modulation element. In this case, the illumination system
preferably has a light source which supplies an illumination light
beam, a polarizing beam splitter which divides a light beam
supplied from the light source, a first optical system which leads
a light beam of S polarization reflected by the beam splitter to a
predetermined position, a second optical system which has a longer
optical path length than the first optical system and leads a light
beam of P polarization transmitted through the beam splitter to the
predetermined position, an optical path combining element which is
arranged at the predetermined position and combines an optical path
of the light beam of S polarization transmitted through the first
optical system with an optical path of the light beam of P
polarization transmitted through the second optical system, and a
common illumination optical system arranged between the optical
path combining element and the optical modulation element.
Furthermore, in this case, it is preferable for the common optical
modulation element to include a pattern area in which a
transmission factor for the first light beam having the first
polarization state is substantially different from a transmission
factor for the second light beam having the second polarization
state.
[0029] Moreover, in these aspects, preferably, there is further
provided a common image formation optical system arranged between
the first and second optical modulation elements and the
non-single-crystal semiconductor.
[0030] A third aspect of the present invention provides a
crystallization method which generates a crystallized substance by
irradiating a non-single-crystal substance with a light beam having
a predetermined light intensity distribution, comprising:
[0031] a first irradiation step of irradiating the
non-single-crystal substance with a first light beam having a first
light intensity distribution; and
[0032] a second irradiation step of irradiating a molten part of
the non-single-crystal substance with a light beam having a second
light intensity distribution substantially different from the first
light intensity distribution within a time in which the
non-single-crystal substance is molten by the first irradiation
step.
[0033] A fourth aspect of the present invention provides a
crystallization method which generates a crystallized substance by
irradiating a non-single-crystal substance with a light beam having
a predetermined light intensity distribution, comprising:
[0034] irradiating firstly the non-single-crystal substance with a
first light beam which is to have on the non-single-crystal
substance a light intensity distribution having at least two
V-shaped unit intensity distributions which are adjacent to define
a chevron unit light intensity distribution therebetween; and
[0035] irradiating secondly a high-temperature region formed to the
non-single-crystal substance in accordance with an apex of the
chevron unit light intensity distribution with a light beam having
a second light intensity distribution after an elapse of a
predetermined time from start of the first irradiation step in
order to compensate flattening of a temperature gradient with time
in the high-temperature region of the non-single-crystal
substance.
[0036] In the third and fourth aspects, preferably, the
non-single-crystal semiconductor is irradiated with a light beam
subjected to phase modulation through the first optical modulation
element in the first irradiation step, and the non-single-crystal
semiconductor is irradiated with a light beam subjected to phase
modulation through the second optical modulation element having
different characteristics from those of the first optical
modulation element. Alternatively, it is preferable that the first
light beam is caused to enter the common optical modulation element
and the non-single-crystal semiconductor is irradiated with the
light beam subjected to phase modulation through the common optical
modulation element in the first irradiation step, and that the
second light beam having characteristics different from those of
the first light beam is caused to enter the common optical
modulation element and the non-single-crystal semiconductor is
irradiated with the light beam subjected to phase modulation
through the common optical element.
[0037] According to a fifth aspect of the present invention, there
is provided a device manufactured by using the crystallization
apparatus of the first or second aspect or the crystallization
method of the third or fourth aspect.
[0038] According to a sixth aspect of the present invention, there
is provided an optical modulation element including a pattern area
in which a trans-mission factor differs depending on a polarization
state of an incident light beam, and a phase modulation area.
[0039] According to a seventh aspect of the present invention,
there is provided a crystallization apparatus comprising:
[0040] an optical modulation element which forms on a
non-single-crystal substance a first light beam having a first
light intensity distribution obtained by modulating a phase of the
incident first light beam; and
[0041] an illumination system which causes a second light beam
having a second light intensity distribution having the same peak
position as a peak position of the first light intensity
distribution to enter a portion of the non-single-crystal substance
irradiated with the light beam having the first light intensity
distribution within a period in which the non-single-crystal
substance irradiated with the first light beam through the optical
modulation element is partially fused.
[0042] In the seventh aspect, a minimum value to a maximum value of
the light beam having the first light intensity distribution may
have a light intensity which is not less than a fusing point of the
non-single-crystal substance, and a light beam of at least a
maximum value portion in the light beam having the second light
intensity distribution may form on the non-single-crystal substance
a light intensity which is not less than the fusing point of the
non-single-crystal substance.
[0043] A channel area may be formed by using the crystallization
apparatus and/or the crystallization method as described above.
[0044] It should be noted that the in the present specification,
term "non-single-crystal" is used to mean non-single-crystal in
molten state, too, for descriptive purpose.
[0045] With the technique according to the above-described aspects,
it is possible to compensate flattening of a temperature gradient
with time in, e.g., a high-temperature region of a V-shaped
temperature distribution against an influence of thermal diffusion
or emission of latent heat, and assuredly maintain a necessary
temperature gradient in the high-temperature region even in the
final stage of crystal growth. As a result, the sufficient crystal
growth from a crystal nucleus can be realized and a crystal grain
with a large particle size can be generated while suppressing the
influence of thermal diffusion or emission of latent heat in the
final stage of the crystal growth.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0046] FIG. 1 is a view schematically showing a structure of a
crystallization apparatus according to a first embodiment of the
present invention;
[0047] FIG. 2 is a view schematically showing internal structures
of a first illumination optical system and a second illumination
optical system depicted in FIG. 1;
[0048] FIGS. 3A and 3B are views schematically showing a phase
pattern of a first optical modulation element in the first
embodiment and a light intensity distribution formed on a processed
substrate by using the first optical modulation element,
respectively;
[0049] FIGS. 4A and 4B are views schematically showing a phase
pattern of a second optical modulation element in the first
embodiment and a light intensity distribution formed on the
processed substrate by using the second optical modulation element,
respectively;
[0050] FIGS. 5A and 5B are views schematically showing pulse light
emission characteristics of a light source in the first embodiment
and a temporal relationship between a first pulse light which
enters the first optical modulation element and a second pulse
light which enters the second optical modulation element,
respectively;
[0051] FIG. 6 is a view schematically showing how crystallization
advances in the first embodiment;
[0052] FIG. 7 is a view schematically showing a structure of a
crystallization apparatus according to a second embodiment of the
present invention;
[0053] FIGS. 8A and 8B are views schematically showing internal
structures of a first illumination optical system and a second
illumination optical system depicted in FIG. 7, respectively;
[0054] FIGS. 9A and 9B are views schematically showing a positional
relationship between a common optical modulation element and a
processed substrate in the second embodiment and a phase pattern of
the common optical modulation element, respectively;
[0055] FIG. 10 is a view schematically showing a light intensity
distribution formed on the processed substrate when a first pulse
light is caused to enter the common optical modulation element in
the second embodiment;
[0056] FIG. 11 is a view schematically showing a light intensity
distribution formed on the processed substrate when a second pulse
light is caused to enter the common optical modulation element in
the second embodiment;
[0057] FIG. 12 is a view schematically showing a structure of a
crystallization apparatus according to a third embodiment of the
present invention;
[0058] FIGS. 13A, 13B and 13C are views schematically showing a
phase pattern of a common optical modulation element in the third
embodiment, an electroconductive film pattern, and the common
optical modulation element, respectively;
[0059] FIG. 14 is a view schematically showing a light intensity
distribution formed on a processed substrate when a first pulse
light is caused to enter the common optical modulation element in
the third embodiment;
[0060] FIG. 15 is a view schematically showing a light intensity
distribution formed on the processed substrate when a second pulse
light is caused to enter the common optical modulation element in
the third embodiment;
[0061] FIGS. 16A and 16B are views schematically showing different
modifications of a time relationship between the first pulse light
and the second pulse light, respectively;
[0062] FIGS. 17A to 17E are process cross-sectional views showing
processes for manufacturing an electronic device by using a
crystallization apparatus according to this embodiment;
[0063] FIGS. 18A to 18D are views illustrating a calculation result
concerning a change in temperature distribution obtained when a-Si
is irradiated with a light beam having a V-shaped light intensity
distribution over a fixed time in accordance with a prior art;
[0064] FIG. 19 is a view schematically showing a state of advance
of crystallization of a-Si involved by a change in temperature
distribution depicted in FIG. 18D; and
[0065] FIG. 20 is a view schematically illustrating an
inconvenience of a prior art when affected by latent heat.
DETAILED DESCRIPTION OF THE INVENTION
[0066] Embodiments according to the present invention will now be
described hereinafter with reference to the accompanying
drawings.
[0067] FIG. 1 is a view schematically showing a structure of a
crystallization apparatus according to a first embodiment of the
present invention. FIG. 2 is a view schematically showing internal
structures of a first illumination optical system and a second
illumination optical system.
[0068] Referring to FIG. 1, the crystallization apparatus according
to the first embodiment comprises a first optical modulation
element 1 and a second optical modulation element 2 each of which
modulates a phase of an incident light beam, an illumination system
3, an image formation optical system 4, and a substrate stage 6 on
which a processed substrate 5 is mounted.
[0069] The detailed structures and effects of the first optical
modulation element 1 and the second optical modulation element 2
will be described later. The illumination system 3 includes a KrF
excimer laser light source 31 which supplies a pulse laser light
having a wavelength of, e.g., 248 nm as a light source which
outputs an energy light which melts a non-single-crystal
semiconductor of the processed substrate 5. As the light source 31,
it is also possible to use any other appropriate light source such
as an XeCl excimer laser light source or a YAG laser light source
which has a performance of emitting an energy light ray which melts
a crystallization processing target or a non-single-crystal
semiconductor. A laser light emitted from the light source 32
enters a beam splitter 32 by which the laser light is divided into
two portions.
[0070] One part of the laser light reflected by the beam splitter
32 (a first laser light) is led to the first optical modulation
element 1 through a first illumination optical system 33. The other
part of the laser light transmitted through the beam splitter 32 (a
second laser light) is led to the second optical modulation element
2 through a delay optical system 34 which includes, e.g., a
plurality of reflection members and has a relatively long optical
path, a pair of mirrors 35 and 36, and a second illumination
optical system 37 having the same configuration as the first
illumination optical system 33. Therefore, an optical path length
from the beam splitter 32 to the second optical modulation element
2 is set to be longer than an optical path length from the beam
splitter 32 to the first optical modulation element 1 by a
predetermined distance. This predetermined distance is a distance
corresponding to a timing with which irradiation is performed
through the second optical modulation element 2 in a period that
the non-single-crystal semiconductor of the processed substrate 5
irradiated through the first optical modulation element 1 is
partially molten. Partial fusion of the non-single-crystal
semiconductor means a period in which at least a maximum value of a
light intensity distribution is molten in a temperature drop
process of the non-single-crystal semiconductor irradiated through
the first optical modulation element 1 in a pulse-like manner.
[0071] The light beam which has been emitted from the light source
31 and entered the first illumination optical system 33 (or the
second illumination optical system 37) is expanded through a beam
expander 3a and then enters a first fly-eye lens 3b as shown in
FIG. 2. In this manner, a plurality of small light sources are
formed on a rear focal surface of the first fly-eye lens 3b, and
light fluxes from the plurality of small light sources illuminate
an incidence surface of a second fly-eye lens 3d in an overlapping
manner. As a result, more small light sources than those on the
rear focal surface of the first fly-eye lens 3b are formed on a
rear focal surface of the second fly-eye lens 3d.
[0072] Light fluxes from the plurality of small light sources
formed on the rear focal surface of the second fly-eye lens 3d
illuminate the first optical modulation element 1 (or the second
optical modulation element 2) through a second condenser optical
system 3e in an overlapping manner. Here, the first fly-eye lens 3b
and the first condenser optical system 3c constitute a first
homogenizer. The first homogenizer homogenizes the laser light
supplied from the light source 31 in relation to an incidence angle
on the first optical modulation element 1 (or the second optical
modulation element 2).
[0073] The second fly-eye lens 3d and the second condenser optical
system 3e constitute a second homogenizer. The second homogenizer
homogenizes the laser light having the incidence angle homogenized
by the first homogenizer in relation to a light intensity at each
in-plane position on the first optical modulation element 1 (or the
second optical modulation element 2). In this manner, the
illumination system 3 illuminates each of the first optical
modulation element 1 and the second optical modulation element 2
with the laser light having the substantially homogeneous light
intensity distribution. In the above explanation, it can be
understood that the illumination system 3 causes a first pulse
light having a predetermined light emission time to enter the first
optical modulation element 1, and then causes a second pulse light
having the same light emission time as the first pulse light to
enter the second optical modulation element 2 after a predetermined
time (corresponding to the predetermined distance) from start of
incidence of the first pulse light to the first optical modulation
element 1. The predetermined distance is a distance corresponding
to a timing with which irradiation is performed through the second
optical modulation element 2 in a period that the
non-single-crystal semiconductor of the processed substrate 5
irradiated through the first optical modulation element 1 is
partially molten.
[0074] The first laser light subjected to phase modulation by the
first optical modulation element 1 is transmitted through the beam
splitter 7 and then enters the processed substrate 5 through the
image formation optical system 4. On the other hand, the second
laser light subjected to phase modulation by the second optical
modulation element 2 is reflected by the beam splitter 7 and then
enters the processed substrate 5 through the image formation
optical system 4. Here, in the image formation optical system 4,
pattern surfaces of the first optical modulation element 1 and the
second optical modulation element 2 and the processed substrate 5
(which is precisely an upper surface of the non-single-crystal
semiconductor layer) are arranged in an optically conjugate
relationship. In other words, the processed substrate 5 is set to a
surface (an image surface of the image formation optical system 4)
which is optically conjugate with the pattern surfaces of the first
optical modulation element 1 and the second optical modulation
element 2).
[0075] The image formation optical system 4 includes an aperture
diaphragm assembly 4c between a front positive lens assembly 4a and
a rear positive lens assembly 4b. The aperture diaphragm assembly
4c comprises a plurality of aperture diaphragms having aperture
portions (light transmission portions) of different sizes. In
practice, one selected diaphragm is used. Thus, the plurality of
aperture diaphragms 4c may be replaceable with respect to an
optical path. Alternatively, as the aperture diaphragm 4c, it is
possible to use an iris diaphragm which can continuously change a
size of an aperture portion. In any case, a size of an aperture
portion of the aperture diaphragm 4c (and hence an image side
numerical aperture NA of the image formation optical system 4) is
set so that a necessary light intensity distribution can be
generated on the semiconductor layer of the processed substrate 5
as will be described later. This image formation optical system 4
may be a refraction type optical system, a reflection type optical
system, or a refraction/reflection type optical system.
[0076] The processed substrate 5 is crystallized in a process where
an image of the first laser light subjected to phase modulation by
the first optical modulation element 1 is formed and fusion and
solidification are carried out. The processed substrate 5 is
obtained, for example, by sequentially forming an underlying film,
an amorphous silicon film (a semiconductor layer) and a cap film
on, e.g., a liquid crystal display glass sheet substrate by
chemical vapor deposition (CVD). The underlying insulating film is
formed of an insulating material, e.g., SiO.sub.2, and avoids
mixing of a foreign particle such as Na in the glass substrate into
the amorphous silicon film which occurs when the amorphous silicon
film is directly brought into contact with the glass substrate, and
prevents a melting temperature of the amorphous silicon film from
being directly transmitted to the glass substrate. The amorphous
silicon film is a semiconductor film to be crystallized, and this
is a non-single-crystal film, an amorphous semiconductor film or a
polycrystal semiconductor.
[0077] The non-single-crystal film is not restricted to the
semiconductor film, and it may be a film formed of a
non-single-crystal material such as a non-single-crystal metal. An
insulating film, e.g., an SiO.sub.2 film is preferably formed as
the cap film on the amorphous silicon film. The cap film is heated
by a part of a light beam which enters the amorphous silicon film,
and stores a temperature when heated. Although a temperature in a
high-temperature portion is relatively rapidly reduced on an
irradiation target surface of the amorphous silicon film when
incidence of a light beam is interrupted if no cap film is
provided, the thermal storage effect alleviates this temperature
drop gradient and facilitates the lateral crystal growth with a
large particle size. The processed substrate 5 is positioned and
held at a predetermined position on the substrate stage 6 by a
vacuum chuck or an electrostatic chuck.
[0078] FIG. 3A is a view schematically showing a phase pattern of
the first optical modulation element 1 in the first embodiment, and
FIG. 3B is a view schematically showing a light intensity
distribution of the first laser light formed on the processed
substrate by using the first optical modulation element. As shown
in FIG. 3A, the first optical modulation element 1 in the first
embodiment has a reference phase area (indicated by a blank portion
in the figure) 1a having a reference phase value of 0 degree, and
each rectangular (square in this embodiment) modulation phase area
(indicated by a shaded portion in the drawing) 1b having a
modulation phase value of 90 degrees in a cycle in the lateral
direction (a direction parallel to a cross section A). Here, the
modulation phase areas 1b are arranged in a matrix form in the
vertical and horizontal directions in accordance with a pitch of
1.0 .mu.m (a reduced value on the image surface of the image
formation optical system 4, and a dimension concerning the optical
modulation element is indicated by an image surface reduced value
and so forth).
[0079] Further, an area share ratio (a duty) 1c of the modulation
phase area 1b with respect to a unit cell (an area surrounded by a
dotted line) of 1.0 .mu.m.times.1.0 .mu.m including one phase area
varies between 0% and 50% in the lateral direction (along the cross
section A). Specifically, an area share ratio of the modulation
phase area 1b on the both sides of a repeated unit area 1d of the
phase pattern is 50% (a maximum area share ratio), whilst an area
share ratio of the modulation phase area 1b at the center of the
repeated unit area 1d is 0% (a minimum area share ratio), and the
area share ratio of the modulation phase area 1b between these
ratios varies in the order of 28%, 18%, 11% and 5%. The unit cell
1c of 1.0 .mu.m.times.1.0 .mu.m has a dimension which is not more
than a point spread function range of the image formation optical
system 4.
[0080] When the first optical modulation element 1 according to the
first embodiment is used, as shown in FIG. 3B, a mountain-shape
unit light intensity distribution (a light intensity distribution
between minimum peak value portions of adjacent V-shaped unit light
intensities) is formed on the surface of the processed substrate 5
set at the image surface position of the image formation optical
system 4 in accordance with the unit area 1d. That is, there is
formed a mountain-shape unit light intensity distribution in which
a light intensity is minimum in accordance with a position of the
cross section A where the area share ratio of the modulation phase
area 1b is 50% and the light intensity is maximum in accordance
with a position of the cross section A where the area share ratio
of the modulation phase area 1b is 0%. Actually, the first optical
modulation element 1 has a plurality of phase patterns shown in
FIG. 3A aligned in the lateral direction. As a result, the
plurality of chevron (i.e., V-shaped) unit light intensity
distributions shown in FIG. 3B are formed in the lateral direction
on the irradiation target surface, and the light intensity
distribution on the irradiation surface is therefore defined as a
plurality of V-shaped light intensity distributions. FIG. 3B shows
one chevron or mountain-shape light intensity distribution
corresponding to the repeated unit area 1d of the phase pattern in
the plurality of V-shaped light intensity distributions
continuously formed along the direction of the cross section A.
[0081] FIGS. 4A and 4B are views schematically showing a phase
pattern of the second optical modulation element 2 in the first
embodiment and a light intensity distribution formed on the
processed substrate 5 by using the second optical modulation
element 2, respectively. As shown in FIG. 4A, the second optical
modulation element 2 according to the first embodiment has a
reference phase area (indicated by a blank portion in the figure)
2a having a reference phase value of 0 degree and each rectangular
(square in this embodiment) modulation phase area (indicated by a
shaded portion in the figure) 2b having a modulation phase value of
180 degrees. Here, the modulation phase areas 2b are arranged in
the vertical and horizontal directions in accordance with a pitch
of 1.0 .mu.m (an image surface reduced value).
[0082] An area share ratio (a duty) of the modulation phase area 2b
with respect to a unit cell (a square area surrounded by a dotted
line) 2c of 1.0 .mu.m.times.1.0 .mu.m including one phase area
varies between 0% and 50% along the horizontal direction (along the
cross section A) in the drawing. Specifically, an area share ratio
of the modulation phase area 2b on the both sides of a repeated
unit area 2d of the phase pattern is 50%, whilst an area share
ratio of the modulation phase area 2b at the center of the repeated
unit area 2d is 0%, and an area share ratio of the modulation phase
area 2b between these ratios varies in the order of 50%, 50%, 28%
and 11%. The unit cell 2c of 1.0 .mu.m.times.1.0 .mu.m also has a
dimension which is not more than a point spread function range of
the image formation optical system 4.
[0083] When the second optical modulation element 2 according to
the first embodiment is used, as shown in FIG. 4B, a unit light
intensity distribution having a peak shape is formed on the surface
(the irradiation target surface) of the processed substrate 5 set
at the image surface position of the image formation optical system
4 in accordance with the repeated unit area 2d of the phase
pattern. This unit light intensity distribution has a central peak
shape in which a light intensity is maximum in accordance with a
position of the cross section A where the area share ratio of the
modulation phase area 2b is 0% and the light intensity is
substantially zero in accordance with a position of the cross
section A where the area share ratio of the modulation phase area
2b is 50%.
[0084] Comparing the light intensity distributions shown in FIGS.
3B and 4B, it can be understood that a gradient of the light
intensity distribution having the central peak share formed by
using the second optical modulation element 2 is larger than a
gradient of the chevron light intensity distribution in the V-shape
formed by using the first optical modulation element 1. The light
intensity distributions shown in these drawings are calculated on
the assumption that a wavelength .lamda. of a light is 248 nm, an
image side numeral aperture NA of the image formation optical
system 4 is 0.13, and a value a (a coherence factor) of the image
formation optical system 4 is 0.5. The calculation of a light
intensity distribution according to the third embodiment presumes
the same conditions.
[0085] FIGS. 5A and 5B are views schematically showing pulse light
emission characteristics of the light source in the first
embodiment, and a temporal relationship between the first pulse
light which enters the first optical modulation element and the
second pulse light which enters the second optical modulation
elements. In the first embodiment, as shown in FIG. 5A, a light
emission period of a pulse light from the light source 31 is set to
20 nsec. Furthermore, an optical path length difference between an
optical path length of the first laser light from the first beam
splitter 32 to the first optical modulation element 1 and an
optical path length of the second laser light from the beam
splitter 32 to the second optical modulation element 2 is set to
correspond to a delay time 40 nsec (a distance from the second beam
splitter 7 to the first optical modulation element 1 is set to be
equal to a distance from the second beam splitter 7 to the second
optical modulation element 2). The optical path length difference
corresponding to the delay time 40 nsec=40.times.10.sup.-9 sec can
be calculated by the following Expression (1). As to setting of the
delay time, a period until a period in which a molten part (this
part is referred to as a maximum value molten portion and it is an
area corresponding to an apex of a chevron light intensity
distribution) remains without crystallization on the irradiation
target surface which is molten and crystallized by the light
intensity distribution formed by utilizing at least the first
optical modulation element 1 is appropriately selected.
( Optical path length difference ) = ( Light speed ) .times. (
Delay time ) = ( 3.0 .times. 10 8 m / sec ) .times. ( 40 .times. 10
- 9 sec ) = 12 m ( 1 ) ##EQU00001##
[0086] In this manner, an internal structure of the delay optical
system 34 comprising a plurality of reflection members is
determined in such a manner that the optical path length difference
between the optical path length from the beam splitter 32 to the
first optical modulation element 1 and the optical path length from
the beam splitter 32 to the second optical modulation element 2
becomes approximately 12 m (although a distance between the beam
splitter 32 and the first optical modulation element 1 is
apparently different from a distance between the beam splitter 32
and the second optical modulation element 2 (excluding a distance
of the delay optical system 34) in FIG. 1, these distances are set
to be equal to each other). It is desirable to reduce a size of the
delay optical system 34 by providing relatively many bent optical
paths.
[0087] Thus, in the first embodiment, as shown in FIG. 5B, the
first pulse light having a light emission time 20 nsec enters the
first optical modulation element 1, and the second pulse light
having the same light emission time 20 nsec as the first pulse
light then enters the second optical modulation element 2 after an
elapse of 40 nsec from start of incidence of the first pulse light
to the first optical modulation element 1. In order to facilitate
understanding, it is assumed that the pulse light emission
characteristics of the light source and the temporal relationship
between the first pulse light and the second pulse light satisfy
the conditions shown in FIG. 5B in other embodiments like the first
embodiment.
[0088] FIG. 6 is a view schematically showing a state of advance of
crystallization in the first embodiment. In the first embodiment,
as shown in FIG. 6, the surface of the processed substrate 5 is
irradiated with the V-shaped light intensity distribution (the
first light intensity distribution) by causing the first pulse
light to enter the first optical modulation element 1, thereby
forming a V-shaped temperature distribution corresponding to the
V-shaped light intensity distribution on the surface of the
processed substrate 5. Moreover, before a temperature gradient in a
high-temperature region (a peak portion) in the V-shaped
temperature distribution is reduced to a temperature which is not
more than a melting point due to a drop of a temperature, a maximum
temperature portion and the vicinity thereof in the chevron light
intensity distribution obtained by the first pulse light is
irradiated with a light pattern having a temperature which is not
less than the melting point. That is, the second pulse light is
caused to enter the second optical modulation element 2 and the
surface of the processed substrate 5 is irradiated with the light
intensity distribution having the central peak shape (the second
light intensity distribution) within a time that the
non-single-crystal semiconductor on the processed substrate 5 is
partially molten.
[0089] As a result, flattening of a temperature gradient with a
time can be compensated (corrected) in the high-temperature region
in the V-shaped temperature distribution against an influence of
thermal diffusion or emission of latent heat by adding a
temperature distribution corresponding to the second light
intensity distribution having the central peak shape, and a
necessary temperature gradient in the high-temperature region can
be assuredly maintained even in the final stage of the crystal
growth. FIG. 6 shows this state. That is, the first light intensity
distribution formed on the non-single-crystal semiconductor through
the first optical modulation element 1 is shown in (a). (b) shows a
temperature distribution of the non-single-crystal semiconductor 5
before light irradiation, in which an entire surface shows an
ordinary temperature and the semiconductor is in a solid state.
[0090] Then, when a pulse-like light beam (the first laser light)
having the light intensity distribution shown in (a) enters the
non-single-crystal semiconductor layer 5, a temperature
distribution which is not less than a melting point and shown in
(c) is formed on the irradiation target surface of this
semiconductor layer 5. That is, the irradiation target surface
having a temperature which is not less than the melting point is
molten while maintaining the temperature distribution (a liquid
state). When the pulse-like light beam irradiation time is
terminated, a temperature drop state begins. In the temperature
drop process, as shown in (d), when a partial melting point is
passed, the crystal growth starts from a crystal nucleus existing
in the minimum value portion in the light intensity distribution.
This state is shown in (e). Additionally, when the temperature drop
advances as shown in (f), the crystal growth proceeds in the
horizontal direction, and a state shown in (g) is obtained. In a
state where this partially molten area partially remains, the
non-single-crystal semiconductor 5 is coaxially irradiated with a
light beam of a light intensity distribution shown in (h) having
the second light intensity distribution. That is, a molten portion
in the irradiation target portion of the non-single-crystal
semiconductor 5 corresponding to the maximum value of the first
light intensity distribution is irradiated with a light beam (the
second laser beam) which has a maximum value equal to or above the
melting point of the second light intensity distribution and is
shown in FIG. 6(h). In other words, the non-single-crystal
semiconductor 5 is irradiated with a light beam which is shown in
(f) and demonstrates a high temperature equal to or above the
melting point in the liquid state portion shown in (g). As a
result, the crystal growth further advances in the horizontal
direction even at a crest portion of the chevron light intensity
distribution as shown in (i).
[0091] In the first embodiment, therefore, since a necessary
temperature gradient in the high-temperature region of the V-shaped
temperature distribution is assuredly maintained even in the final
stage of the crystal growth, the lateral growth of a sufficiently
long crystal is realized without termination of the crystal growth
before reaching the high-temperature region and without
crystallization in the high-temperature region. That is, in the
first embodiment, an influence of thermal diffusion or emission of
latent heat can be suppressed in the final stage of the crystal
growth, and the sufficient crystal growth from a crystal nucleus
can be realized, thereby generating a crystallized semiconductor
with a large particle size. As a result, a margin of, e.g., a
positioning accuracy can be widened.
[0092] In the first embodiment, a light beam from one light source
31 is divided into two light beams by the beam splitter 32.
However, the present invention is not restricted thereto, and it is
possible to adopt a structure in which a light from a first light
source is led to the first optical modulation element 1 and a light
from a second light source is led to the second optical modulation
element 2, and timings of pulse light emission from the two light
sources may be shifted.
[0093] In the first embodiment, the common image formation optical
system 4 is provided between the first optical modulation element 1
and the second optical modulation element 2 and the processed
substrate 5. However, the present invention is not restricted
thereto, a first image formation optical system which leads a light
from the first optical modulation element to the processed
substrate 5 and a second image formation optical system which leads
a light from the second optical modulation element 2 to the
processed substrate 5 may be separately provided. In this case, an
optical path combining element which combines two optical paths
must be arranged between the first and second image formation
optical systems and the processed substrate 5.
[0094] FIG. 7 is a view schematically showing a structure of a
crystallization apparatus according to a second embodiment of the
present invention. FIGS. 8A and 8B are views schematically showing
internal structures of a first illumination optical system and a
second illumination optical system depicted in FIG. 7. Referring to
FIG. 7, the crystallization apparatus according to the second
embodiment is an apparatus which complies with a proximity
(defocus) method (a method which applies a Fresnel diffraction
pattern generated in proximity exposure) using no image formation
optical system, and comprises an illumination system 3A, a
substrate stage 6 on which a processed substrate 5 is mounted, and
an optical modulation element 10 which is arranged between these
members and common to a first pulse light (a first laser light) and
a second pulse light (a second laser light). In FIG. 7, like
reference numerals denote elements having the same functions as
those of the constituent elements in FIG. 1.
[0095] In the illumination system 3A, a laser light emitted from a
light source 31 enters a beam splitter 32. A light (a first laser
light) reflected by the beam splitter 32 enters an optical path
combining element 42 such as a beam splitter through a first
shaping optical system 41. On the other hand, a light (a second
laser light) transmitted through the beam splitter 32 enters the
optical path combining element 42 through a delay optical system
34, a pair of mirrors 35 and 36 and a second shaping optical system
43. The first laser light transmitted through the optical path
combining element 42 passes through the common illumination optical
system 44 and then illuminates a common optical modulation element
10 as a first pulse light. Likewise, the second laser light
reflected by the optical path combining element 42 passes through
the common illumination optical system 44 and then illuminates the
common optical modulation element 10 as a second pulse light.
[0096] In the second embodiment, the first shaping optical system
41 which magnifies a diameter of the first laser light with a first
magnifying power and the common illumination optical system 44
constitute a first illumination optical system which causes the
first pulse light having a first angular distribution (an angular
width) to enter the common optical modulation element 10. Further,
the second shaping optical system 43 which magnifies a diameter of
the second laser light with a second magnifying power smaller than
the first magnifying power and the common illumination optical
system 44 constitute a second illumination optical system which
causes the second pulse light having a second angular distribution
(an angular width) different from the first angular distribution to
enter the common optical modulation element 10. As shown in FIG.
8A, the first shaping optical system 41 has a negative lens group
3f and a positive lens group 3g in the order from the light source.
Likewise, the second shaping optical system 43 has a negative lens
group 3h and a positive lens group 3i in the order from the light
source as shown in FIG. 8B.
[0097] As shown in FIGS. 8A and 8B, the common illumination optical
system 44 has a fly-eye lens 3j and a condenser optical system 3k
in the order from the light source. Here, the common illumination
optical system 44 is constituted in such a manner that a rear focal
surface of the fly-eye lens 3j substantially matches with a front
focal surface of the condenser optical system 3k. A light beam (the
first laser light) whose diameter has been magnified by the first
shaping optical system 41 performs Koehler illumination with
respect to the common modulation element 10 as a first pulse light
having a maximum incidence angle .theta.1 with a homogenized
illumination distribution through the common illumination optical
system 44. Likewise, a light beam (the second laser light) whose
diameter has been magnified by the second shaping optical system 43
performs Koehler illumination with respect to the common optical
modulation element 10 as a second pulse light having a maximum
incidence angle .theta.2 with a homogenized illumination
distribution through the common illumination optical system 44. In
this case, since a magnifying power of the first shaping optical
system 41 is set larger than a magnifying power of the second
shaping optical system 43, a light beam which enters the fly-eye
lens 3j through the first shaping optical system 41 has a larger
than cross section than that of a light beam which enters the
fly-eye lens 3j through the second shaping optical system 43.
[0098] As a result, the maximum incidence angle .theta.1 of the
first pulse light which enters the common optical modulation
element 10 through the first shaping optical system 41 becomes
larger than the maximum incidence angle .theta.2 of the second
pulse light which enters the common optical modulation element 10
through the second shaping optical system 43. That is because the
maximum incidence angle of the light which enters the common
optical modulation element 10 depends on a cross-sectional size of
a light beam at an exist surface of the fly-eye lens 3j which
determines an exit pupil of the common illumination optical system
44. In the following simulation, it is assumed that the maximum
incidence angle .theta.1 of the first pulse light is 2.1 degrees
and the maximum incidence angle .theta.2 of the second pulse light
is 1.0 degree.
[0099] FIGS. 9A and 9B are views schematically showing a positional
relationship between the common optical modulation element and the
processed substrate in the second embodiment, and a part of a phase
pattern of the common optical modulation element, respectively.
FIG. 10 is a view schematically showing a light intensity
distribution formed on the processed substrate when the first pulse
light is caused to enter the common optical modulation element in
the second embodiment. FIG. 11 is a view schematically showing a
light intensity distribution formed on the processed substrate when
the second pulse light is caused to enter the common optical
modulation element in the second embodiment. The common optical
modulation element 10 is arranged in proximity to the processed
substrate with a gap of 155 .mu.m from the surface of the processed
substrate 5 as shown in FIG. 9A.
[0100] Furthermore, as shown in FIG. 9B, the common optical
modulation element 10 is a so-called line type phase shifter, and
comprises two rectangular areas 10a and 10b which are alternately
repeated in one direction or the lateral direction. In this
example, each of the two areas 10a and 10b has a widthwise
dimension of, e.g., 10 .mu.m, and a phase difference of 180 degrees
is provided between the two areas 10a and 10b. In the common
optical modulation element 10, a linear boundary 10c between the
two areas 10a and 10b having a phase difference of 180 degrees
constitutes a phase shift line.
[0101] When the first pulse light having the maximum incidence
angle .theta.1=2.1 degrees enters the common optical modulation
element 10, as shown in FIG. 10B, a substantially chevron light
intensity distribution (a first light intensity distribution) which
is similar to the light intensity distribution shown in FIG. 3B and
corresponds to an intensity distribution between minimum intensity
portions of adjacent V-shaped unit intensity distributions is
formed on the surface of the processed substrate 5 arranged in
proximity to the optical modulation element 10. FIG. 10B shows a
unit light intensity distribution formed by the respective areas
10a and 10b, and a light intensity distribution consisting of a
plurality of unit light intensity distributions in which the unit
light intensity distributions are coupled in the lateral direction
can be actually obtained on the processed substrate 5. As can be
understood from this drawing, there is formed a substantially
chevron light intensity distribution in which a light intensity is
minimum in accordance with the phase shift line 10c and the light
intensity is maximum in accordance with a central area (a central
area of the area 10b) of the two phase shift lines 10c.
[0102] On the other hand, when the second pulse light having the
maximum incidence angle .theta.2=1.0 degree enters the common
optical modulation element 10, as shown in FIG. 11, a light
intensity distribution (a second light intensity distribution)
having a substantially central peak shape which is similar to the
light intensity distribution depicted in FIG. 4B is formed on the
surface of the processed substrate 5. That is, there is formed a
light intensity distribution having a substantially central peak
shape in which a light intensity is substantially zero in
accordance with the phase shift line 10c and the light intensity is
maximum in accordance with an intermediate position of the two
phase shift lines 10c. The light intensity distributions shown in
FIGS. 10 and 11 are calculated on the assumption that a wavelength
.lamda. of a light is 248 nm.
[0103] In this manner, flattening of a temperature gradient with
time in a high-temperature region in the V-shaped temperature
distribution can be compensated against an influence of thermal
diffusion or emission of latent heat by adding a temperature
distribution corresponding to the second light intensity
distribution having a substantially central peak shape in the
second embodiment like the first embodiment. As a result, in the
second embodiment, likewise, an influence of thermal diffusion or
emission of latent heat in the final stage of the crystal growth
can be suppressed, and the sufficient crystal growth from a crystal
nucleus can be realized, thereby generating a crystallized
semiconductor of a crystal grain having a large particle size.
[0104] In the second embodiment, a light beam from one light source
31 is divided into two light beams by a beam splitter 32. However,
the present invention is not restricted thereto and, for example,
in a structure in which a light from a first light source is led to
the common optical modulation element 10 through the first shaping
optical system 41 and the common illumination optical system 44 and
a light from a second light source is led to the common optical
modulation element 10 through a delay optical system 34, the second
shaping optical system 43 and the common illumination optical
system 44, timings of pulse light emission from the two light
sources may be shifted from each other.
[0105] Moreover, in the second embodiment, the common optical
modulation element 10 and the processed substrate 5 are arranged in
proximity to each other. However, the present invention is not
restricted thereto, and it is possible to adopt a structure in
which the same image formation optical system as the first
embodiment is provided between the common optical modulation
element 10 and the processed substrate 5, for example.
[0106] FIG. 12 is a view schematically showing a structure of a
crystallization apparatus according to a third embodiment of the
present invention. Referring to this drawing, the crystallization
apparatus comprises an illumination system 3B, a substrate stage 6
on which a processed substrate 5 is mounted, and a common optical
modulation element 11 and an image formation optical system 4 which
are sequentially arranged between the illumination system 3B and
the processed substrate 5 and common to a first pulse light (a
first laser light) and a second pulse light (a second laser light).
In FIG. 12, like reference numerals denote elements having the same
functions as those of the constituent elements depicted in FIG.
1.
[0107] In this illumination system 3B, a laser light exiting from a
light source 31 enters a polarizing beam splitter 51. This
polarizing beam splitter 51 reflects a light component of S
polarization and transmits a light component of P polarization
therethrough. A light component or a light beam (the first laser
light) of S polarization reflected by the polarized beam splitter
51 enters an optical path combining element 53 such as a polarizing
beam splitter through a mirror 52, and is reflected by this optical
path combining element 53. On the other hand, a light component or
a light beam (the second laser light) of P polarization transmitted
through the polarizing beam splitter 51 enters the optical path
combining element 53 through the delay optical system 34 and a
mirror 35. The first laser light reflected by the optical path
combining element 53 is transmitted through a common illumination
optical system 54 having, e.g., an internal structure shown in FIG.
2, and then illuminates the common optical modulation element 11 as
the first pulse light in the S polarization state. The second laser
light transmitted through the optical path combining element 53 is
transmitted through the common illumination optical system 54, and
then illuminates the common optical modulation element 11 as the
second pulse light in the P polarization state. In this example,
the S polarization is defined as that an electric field vector of a
light is vertical to the page space and the P polarization is
defined as that an electric field vector of a light is parallel to
the page space, and so forth.
[0108] FIGS. 13A and 13B are views schematically showing a phase
pattern of the common optical modulation element in the third
embodiment, and a part of an electroconductive pattern,
respectively. FIG. 14 is a view schematically showing a unit light
intensity distribution formed on the processed substrate when the
first pulse light is caused to enter the common optical modulation
element in the third embodiment. Further, FIG. 15 is a view
schematically showing a unit light intensity distribution formed on
the processed substrate when the second pulse light is caused to
enter the common optical modulation element in the third
embodiment. The common optical modulation element 11 in the third
embodiment has the phase pattern depicted in FIG. 13A, and a
pattern comprising an electroconductive film pattern shown in FIG.
13B.
[0109] The phase pattern of the common optical modulation element
11 basically has the same structure as the phase pattern of the
first optical modulation element according to the first embodiment
shown in FIG. 3A. That is, the phase pattern of the common optical
modulation element 11 has a reference phase area (indicated by a
blank portion in the drawing) 11a having a reference phase value of
0 degree, and each rectangular modulation phase area (indicated by
a shaded portion in the drawing) 11b having a modulation phase
value of 90 degrees. Here, the modulation phase areas 11b are
arranged in the vertical and horizontal directions in accordance
with a pitch of 1.0 .mu.m (an image surface reduced value of the
image formation optical system 4).
[0110] An area share ratio (a duty) of the modulation phase area
11b with respect to a unit cell 11c of 1.0 .mu.m.times.1.0 .mu.m
varies between 0% and 50% along the horizontal direction in the
drawing (along a cross section A). Specifically, an area share
ratio of the modulation phase area 11b on the both sides of a
repeated unit area 11d of the phase pattern is 50%, whilst an area
share ratio of the modulation phase area 11b at the center of the
repeated unit area 11d is 0%, and an area share ratio of the
modulation phase area 11b between these ratios varies in the order
of 28%, 18%, 11% and 5%.
[0111] On the other hand, an electroconductive film pattern of the
common optical modulation element 11 has two types of pattern areas
11e and 11f which are alternately repeated along the direction of
the cross section A of the phase pattern. In a first area 11e,
square dot patterns 11g formed of chrome having a thickness of 0.05
.mu.m and a size of 0.3 .mu.m.times.0.3 .mu.m (an image surface
reduced value of the image formation optical system 4) are formed
in the vertical and horizontal directions or in a matrix shape in
accordance with a pitch of 0.5 .mu.m (an image surface reduced
value of the image formation optical system 4). In a second area
11f, a line-and-space pattern having a pitch direction is formed in
the direction of the cross section A of the phase pattern or in the
lateral direction.
[0112] In this example, the line-and-space pattern of the second
area 11f comprises a strip-like line portion 11h consisting of
chrome having a thickness of 0.05 .mu.m and a widthwise dimension
of 0.05 .mu.m (an image surface reduced value of the image
formation optical system 4), and a light-permeable space portion
11i having a widthwise dimension of 0.05 .mu.m (an image surface
reduced value of the image formation optical system 4). The first
area 11e of the electroconductive film pattern is formed to
correspond to a central position of the repeated unit area 11d of
the phase pattern. The second area 11f of the electroconductive
film pattern is formed to have substantially the same widthwise
dimension as that of the first area 11e of the electroconductive
film pattern along the direction of the cross section A of the
phase pattern.
[0113] The common optical modulation element 11 is positioned in
such a manner that a direction of an oscillation surface (a
direction of an electric field) of the first pulse light which
enters in the S polarization state matches with the direction of
the cross section A of the phase pattern.
[0114] When manufacturing the common optical modulation element 11,
it is desirable to form the phase pattern and the electroconductive
film pattern on the same surface of one substrate. One example of
this formation is shown in FIG. 13C. In this common optical
modulation element 11, an electroconductive film is formed on one
surface of a transparent substrate, and this film is selectively
etched, thereby forming electroconductive film patterns 11f and
11e. A film consisting of a transparent material is formed on these
patterns, and this film is selectively etched, thereby forming a
phase pattern comprising a reference phase area 11a and a
modulation phase area 11b. The optical modulation element 11 may be
also constituted by forming a phase pattern on one surface of one
transparent substrate, forming an electroconductive film pattern on
one surface of the other transparent substrate and attaching the
both substrates on their surfaces on one side.
[0115] In the common optical modulation element 11 according to the
third embodiment, the line-and-space pattern (11h and 11i) has a
pitch smaller than a wavelength of a light (248 nm=0.248 .mu.m).
Further-more, chrome constituting the line portion 11h of the
line-and-space pattern (11h and 11i) is a conductor. Therefore, a
light of P polarization having an oscillation surface along a
direction orthogonal to a pitch direction of the line-and-space
pattern (11h and 11i) is reflected without being substantially
transmitted through the second area 11f of the electroconductive
film pattern.
[0116] On the other hand, in the first area 11e of the
electroconductive film pattern having a chrome dot pattern formed
thereto, a transmission factor of a light is fixed without being
dependent on the polarization state. As described above, in the
first area 11e of the electroconductive film pattern, both a
transmission factor with respect to the first pulse light in the S
polarization state and a transmission factor with respect to the
second pulse light in the P polarization state are 40%. However, in
the second area 11f of the electroconductive film pattern, a
transmission factor with respect to the first pulse light in the S
polarization state is 40%, but a transmission factor with respect
to the second pulse light in the P polarization state is as very
small as 2%. That is, the second area 11f of the electroconductive
film pattern is a pattern area in which a transmission factor
varies depending on the polarization state of an incident light
beam.
[0117] Therefore, when the first pulse light in the S polarization
state enters the common optical modulation element 11, as shown in
FIG. 14, a chevron (the both sides have a V shape) light intensity
distribution (the first light intensity distribution) similar to
the light intensity distribution depicted in FIG. 3B is formed on
the surface of the processed substrate 5 set at the image surface
position of the image formation optical system 4. That is, there is
formed a V-shaped light intensity distribution in which a light
intensity is minimum in accordance with a position of the cross
section A where an area share ratio of the modulation phase area
11b is 50% and the light intensity is maximum in accordance with a
position of the cross section A where an area share ratio of the
modulation phase area 11b is 0%. It is to be noted that FIG. 14
shows a chevron light intensity distribution corresponding to the
repeated unit area 11d of the phase pattern in a plurality of
V-shaped light intensity distributions continuously formed along
the direction of the cross section A.
[0118] On the other hand, when the second pulse light in the P
polarization state enters the common optical modulation element 11,
as described above, although a light is excellently transmitted
through the first area 11e of the electroconductive film pattern, a
light is rarely transmitted through the second area 11f of the
electroconductive film pattern. As a result, as shown in FIG. 15, a
light intensity distribution having a substantially peak shape (the
second light intensity distribution) which substantially
corresponds to the central portion alone of the chevron light
intensity distribution depicted in FIG. 14 is formed on the surface
of the processed substrate 5.
[0119] As described above, in the third embodiment, flattening of a
temperature gradient with time in a high-temperature region of a
V-shaped temperature distribution (an apex of a chevron temperature
distribution) can be compensated against an influence of thermal
diffusion or emission of latent heat by adding a temperature
distribution corresponding to the second light intensity
distribution having the substantially central peak shape like the
first and second embodiments. As a result, in the third embodiment,
likewise, an influence of thermal diffusion or emission of latent
heat in the final stage of the crystal growth can be suppressed,
and the sufficient crystal growth from a crystal nucleus can be
realized, thereby generating a crystallized semiconductor of a
crystal grain with a large particle size.
[0120] In each of the foregoing embodiments, as shown in FIG. 5B, a
time interval of 20 nsec is assured between irradiation of the
first pulse light with respect to the optical modulation elements
1, 10 and 11 and irradiation of the second pulse light with respect
to the optical modulation elements 2, 10 and 11. However,
irradiation timings of the both pulse lights are not restricted
thereto, and irradiation of the first pulse light with respect to
the optical modulation elements 1, 10 and 11 and irradiation of the
second pulse light with respect to the optical modulation elements
2, 10 and 11 may be temporally substantially continuous as shown in
FIG. 16A, for example. Moreover, as shown in FIG. 16B, irradiation
of the first pulse light and irradiation of the second pulse light
may temporally partially overlap. In the foregoing embodiments, the
first embodiment is an example in which a light beam having
different distributions, i.e., the light intensity distribution of
the first irradiation and the light intensity distribution of the
second irradiation is emitted. The second and third embodiments are
examples in which a light beam having the same light intensity
distribution is emitted.
[0121] FIGS. 17A to 17E are process cross-sectional views showing
processes for manufacturing an electronic device in an area
crystallized by utilizing the crystallization apparatus according
to this embodiment. As shown in FIG. 17A, there is prepared a
processed substrate 5 obtained by forming an underlying film 81
(e.g., a laminated film of SiN having a film thickness of 50 nm and
SiO.sub.2 having a film thickness of 100 nm), an amorphous
semiconductor film 82 (e.g., Si, Ge or SiGe having a film thickness
of approximately 50 nm to 200 nm) and a non-illustrated cap film
82a (e.g., an SiO.sub.2 film having a film thickness of 30 nm to
300 nm) on a transparent insulating substrate 80 (e.g., alkali
glass, quartz glass, plastic or polyimide) by using a chemical
vapor deposition method, a sputtering method or the like. Then, a
laser light 83 (e.g., a KrF excimer laser light or an XeCl excimer
laser light) is applied to a predetermined area of the surface of
the amorphous semiconductor film 82.
[0122] In this manner, as shown in FIG. 17B, a polycrystal
semiconductor film or a single-crystallized semiconductor film 84
having a crystal with a large particle size is generated.
Subsequently, after the cap film 82a is removed by etching, as
shown in FIG. 17C, the polycrystal semiconductor film or the
single-crystallized semiconductor film 84 is processed into an
island-shaped semiconductor film 85 which becomes an area in which,
e.g., a thin film transistor is formed by utilizing a
photolithography technique, and an SiO.sub.2 film having a film
thickness of 20 nm to 100 nm is formed on the surface as a gate
insulating film 86 by using the chemical vapor deposition method,
the sputtering method or the like. Additionally, as shown in FIG.
17D, a gate electrode 87 (e.g., silicide or MoW) is formed on the
gate insulating film, and an impurity ion 88 (phosphor in case of
an N channel transistor, and boron in case of a P channel
transistor) is implanted with the gate electrode 87 being used as a
mask. Thereafter, annealing processing (e.g., one hour at
450.degree. C.) is performed in a nitrogen atmosphere so that the
impurity is activated, and a source area 91 and a drain area 92 are
formed to the island-shaped semiconductor film 85. Then, as shown
in FIG. 17E, an interlayer insulating film 89 is formed, contact
holes are formed, and a source electrode 93 and a drain electrode
94 which are connected with a source 91 and a drain 92 coupled
through a channel 90 are formed.
[0123] In the above-described processes, the channel 90 is formed
in accordance with a position of a crystal with a large particle
size of the polycrystal semiconductor film or the
single-crystallized semiconductor film 84 generated in the
processes shown in FIGS. 17A and 17B. With the above-described
processes, a thin film transistor (TFT) can be formed to a
polycrystal transistor or a single-crystallized semiconductor. The
thus manufactured polycrystal transistor or single-crystallized
transistor can be applied to a drive circuit for a liquid crystal
display unit (display) or an EL (electroluminescence) display, an
integrated circuit for a memory (an SPAM or a DRAM) or a CPU.
[0124] In the foregoing embodiments, although the phase modulation
element is used as the first optical modulation element, the
present invention is not restricted thereto as long as the phase
modulation element is an optical element capable of performing
modulation to, e.g., transmit, reflect, refract and/or diffract an
incident light in such a manner that V-shaped light intensity
distributions aligned with a chevron unit light intensity
distribution defined therebetween are formed on an irradiation
target surface. Likewise, the second optical modulation element is
not restricted to the phase modulation element as long as it can
perform optical modulation with respect to an incident light in
such a manner that a light intensity distribution having an
intensity peak value corresponding to an apex of the chevron unit
light intensity distribution is provided on an irradiation target
surface.
* * * * *