U.S. patent application number 16/672331 was filed with the patent office on 2020-02-27 for laser annealing method, laser annealing apparatus, and thin film transistor substrate.
The applicant listed for this patent is V TECHNOLOGY CO., LTD.. Invention is credited to Michinobu MIZUMURA.
Application Number | 20200066518 16/672331 |
Document ID | / |
Family ID | 59686360 |
Filed Date | 2020-02-27 |
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United States Patent
Application |
20200066518 |
Kind Code |
A1 |
MIZUMURA; Michinobu |
February 27, 2020 |
LASER ANNEALING METHOD, LASER ANNEALING APPARATUS, AND THIN FILM
TRANSISTOR SUBSTRATE
Abstract
A laser annealing method is for irradiating an amorphous silicon
film formed on a substrate 6 with laser beams and crystallizing the
amorphous silicon film, wherein a plurality of first and second TFT
formation portions 23, 24 on the substrate 6 are irradiated with
laser beams at differing irradiation doses so as to crystallize the
amorphous silicon film in the first TFT formation portions 23 into
a polysilicon film having a crystalline state and crystallize the
amorphous silicon film in the second TFT formation portions 24 into
a polysilicon film having another crystalline state that is
different from that of the polysilicon film in the first TFT
formation portions 23.
Inventors: |
MIZUMURA; Michinobu;
(Yokohama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
V TECHNOLOGY CO., LTD. |
Yokohama-shi |
|
JP |
|
|
Family ID: |
59686360 |
Appl. No.: |
16/672331 |
Filed: |
November 1, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16109640 |
Aug 22, 2018 |
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16672331 |
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PCT/JP2016/088857 |
Dec 27, 2016 |
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16109640 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 29/04 20130101;
H01L 21/02381 20130101; H01L 21/02433 20130101; H01L 21/02532
20130101; B23K 26/352 20151001; H01L 27/1288 20130101; H01L 21/324
20130101; H01L 21/02691 20130101; H01L 21/02675 20130101; H01L
27/1285 20130101; H01L 29/78675 20130101; H01L 21/02678
20130101 |
International
Class: |
H01L 21/02 20060101
H01L021/02; H01L 29/786 20060101 H01L029/786; H01L 29/04 20060101
H01L029/04; H01L 21/324 20060101 H01L021/324; H01L 27/12 20060101
H01L027/12 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2016 |
JP |
2016-032469 |
Claims
1. A thin film transistor substrate on which a plurality of driver
thin film transistors for driving pixels and a plurality of
selector thin film transistors for activating the driver thin film
transistors to select pixels are provided, wherein a polysilicon
semiconductor layer in each of the driver thin film transistors has
a crystalline state different from that of a polysilicon
semiconductor layer in each of the selector thin film
transistors.
2. The thin film transistor substrate according to claim 1, wherein
a crystal grain size or electron mobility of the polysilicon
semiconductor layer of each of the driver thin film transistors is
greater than a crystal grain size or electron mobility of the
polysilicon semiconductor layer of each of the selector thin film
transistors.
3. The thin film transistor substrate according to claim 1, wherein
the differing crystalline states of the polysilicon semiconductor
layers of the driver thin film transistors and the selector thin
film transistors are achieved by, while scanning an
annealing-target substrate, irradiating driver thin film transistor
formation portions and selector thin film transistor formation
portions with laser beams through a plurality of mask patterns
formed in a light shielding mask so as to be arranged in a matrix
with columns extending in a scanning direction of the
annealing-target substrate and rows extending in a direction
orthogonal to the scanning direction at differing irradiation
doses.
4. The thin film transistor substrate according to claim 3, wherein
the differing irradiation doses of the laser beams on the driver
and selector thin film transistor formation portions are obtained
by adjusting an amount of light transmitted through mask patterns,
among the plurality of mask patterns, corresponding to the selector
thin film transistor formation portions to be smaller than an
amount of light transmitted through mask patterns, among the
plurality of mask patterns, corresponding to the driver thin film
transistor formation portions.
5. The thin film transistor substrate according to claim 3, wherein
the differing irradiation doses of the laser beams on the driver
and selector thin film transistor formation portions are obtained
by adjusting a number of mask patterns, among the plurality of mask
patterns, that are lined up in the scanning direction of the
annealing-target substrate so as to correspond to the selector thin
film transistor formation portions to be smaller than a number of a
mask patterns, among the plurality of mask patterns, that are lined
up in the scanning direction so as to correspond to the driver thin
film transistor formation portions.
Description
[0001] This application is a divisional application of application
Ser. No. 16/109,640, filed on Aug. 22, 2018, which is a
continuation application of International Application No.
PCT/JP2016/088857, filed on Dec. 27, 2016, the entirety of each of
which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention relates to a laser annealing method
for irradiating an amorphous silicon film with laser beams and
crystallizing the amorphous silicon film, and specifically relates
to a laser annealing method, a laser annealing apparatus, and a
thin film transistor substrate which allow for manufacturing a
plurality of thin film transistors with different electronic
properties in a single laser annealing step.
Description of Related Art
[0003] In a conventional laser annealing method, an amorphous
silicon film formed on the entire surface of a substrate is
uniformly irradiated with a line beam produced using a cylindrical
lens while the substrate is scanned in the direction orthogonal to
the longitudinal axis of the line beam, so that the amorphous
silicon film is uniformly crystallized (for example, refer to JP
2013-191743 A).
[0004] With such a conventional laser annealing method, which
uniformly crystallizes the amorphous silicon film over the entire
surface of the substrate, the resultant polysilicon semiconductor
layers in all thin film transistor formation portions have the same
crystalline state as each other. Consequently, all the thin film
transistors formed with this conventional laser annealing method
have the same electronic properties.
[0005] Here, in thin film transistor substrates for, for example,
organic EL applications, electronic properties required for driver
thin film transistors that control currents for driving pixels are
inherently different from those required for selector thin film
transistors that control the gate voltages of the driver thin film
transistors to select pixels. However, when such a thin film
transistor substrate is manufactured by using the conventional
laser annealing method, the driver thin film transistors and the
selector thin film transistors must have the same electronic
properties for the above reason.
[0006] Therefore, conventionally, to make all the thin film
transistors capable of supplying a large current sufficient to
satisfy the electronic properties required for driver thin film
transistors, laser annealing has been performed so as to
sufficiently promote crystal growth and increase the mobility of
electrons by increasing the irradiation doses (energy) of the laser
beams. However, this increases the off-state leakage current in
each selector thin film transistor, thereby making it difficult to
maintain the gate voltage of each driver thin film transistor at a
constant level.
SUMMARY OF THE INVENTION
[0007] In order to deal with at least some of these problems, an
object of the invention is to provide a laser annealing method, a
laser annealing apparatus, and a thin film transistor substrate,
which allow for manufacturing a plurality of thin film transistors
with different electronic properties in a single laser annealing
step.
[0008] In order to achieve this object, according to a first aspect
of the invention, provided is a laser annealing method for
irradiating an amorphous silicon film formed on a substrate with
laser beams and crystallizing the amorphous silicon film, wherein a
plurality of thin film transistor formation portions on the
substrate are irradiated with laser beams at differing irradiation
doses so as to crystallize the amorphous silicon film in the
plurality of thin film transistor formation portions into
polysilicon films having different crystalline states.
[0009] According to a second aspect of the invention, provided is a
laser annealing method for irradiating an amorphous silicon film
formed on a substrate with laser beams and crystallizing the
amorphous silicon film, wherein, while the substrate is scanned,
first and second thin film transistor formation portions on the
substrate are irradiated with laser beams at differing irradiation
doses so as to crystallize the amorphous silicon film in the first
thin film transistor formation portions into a polysilicon film
having a crystalline state and crystallize the amorphous silicon
film in the second thin film transistor formation portions into a
polysilicon film having another crystalline state that is different
from that of the polysilicon film in the first thin film transistor
formation portions.
[0010] According to a third aspect of the invention, provided is a
laser annealing apparatus for using in the laser annealing method
according to the second aspect of the invention, for irradiating an
amorphous silicon film formed on a substrate with laser beams and
crystallizing the amorphous silicon film, the apparatus comprising:
a scanning means for scanning the substrate; a light shielding mask
which is disposed facing a scanning surface of the scanning means
and provided with a plurality of mask patterns corresponding to
first and second thin film transistor formation portions on the
substrate; and a projecting optical system which is provided on a
scanning means side of the light shielding mask and forms images of
the plurality of mask patterns on the substrate, wherein the light
shielding mask has a plurality of mask patterns arranged either in
a row extending in a direction orthogonal to a scanning direction
of the substrate or in a matrix with columns extending in the
scanning direction of the substrate and rows extending in the
direction orthogonal to the scanning direction, and a light
transmission amount of mask patterns, among the plurality of mask
patterns, corresponding to the second thin film transistor
formation portions is adjusted to be smaller than a light
transmission amount of mask patterns, among the plurality of mask
patterns, corresponding to the first thin film transistor formation
portions, so that the first and second thin film formation portions
are irradiated with laser beams at differing irradiation doses so
as to crystallize the amorphous silicon film in the first thin film
transistor formation portions into a polysilicon film having a
crystalline state and crystallize the amorphous silicon film in the
second thin film transistor formation portions into a polysilicon
film having another crystalline state that is different from that
of the polysilicon film in the first thin film transistor formation
portions.
[0011] According to a fourth aspect of the invention, provided is
laser annealing apparatus for using in the laser annealing method
according to the second aspect of the invention, for irradiating an
amorphous silicon film formed on a substrate with laser beams and
crystallizing the amorphous silicon film, the apparatus comprising:
a scanning means for scanning the substrate; a light shielding mask
which is disposed facing a scanning surface of the scanning means
and provided with a plurality of mask patterns corresponding to
first and second thin film transistor formation portions on the
substrate; and a projecting optical system which is provided on a
scanning means side of the light shielding mask and forms images of
the plurality of mask patterns on the substrate, wherein the light
shielding mask has a plurality of mask patterns arranged in a
matrix with columns extending in a scanning direction of the
substrate and rows extending in a direction orthogonal to the
scanning direction, and a number of mask patterns, among the
plurality of mask patterns, that are lined up in the scanning
direction of the substrate so as to correspond to the second thin
film transistor formation portions is adjusted to be smaller than a
number of mask patterns, among the plurality of mask patterns, that
are lined up in the scanning direction so as to correspond to the
first thin film transistor formation portions, so that the first
and second thin film formation portions are irradiated with laser
beams at differing irradiation doses so as to crystallize the
amorphous silicon film in the first thin film transistor formation
portions into a polysilicon film having a crystalline state and
crystallize the amorphous silicon film in the second thin film
transistor formation portions into a polysilicon film having
another crystalline state that is different from that of the
polysilicon film in the first thin film transistor formation
portions.
[0012] According to a fifth aspect of the invention, provided is a
thin film transistor substrate manufactured by using the laser
annealing method according to the second aspect of the invention,
on which a plurality of driver thin film transistors for driving
pixels and a plurality of selector thin film transistors for
activating the driver thin film transistors to select pixels are
provided, wherein a polysilicon semiconductor layer in each of the
driver thin film transistors has a crystalline state different from
that of a polysilicon semiconductor layer in each of the selector
thin film transistors.
[0013] According to the present invention, by irradiating a
plurality of thin film transistor formation portions on a substrate
with laser beams at differing irradiation doses, it is possible to
crystallize the amorphous silicon film in thin film transistor
formation portions into polysilicon films having different
crystalline states. Thus, the present invention allows for
manufacturing a plurality of thin film transistors with different
electronic properties in a single laser annealing step.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic configuration diagram showing a first
embodiment of a laser annealing apparatus according to the present
invention.
[0015] FIGS. 2A to 2C are diagrams showing a configuration example
of a microlens array used in the first embodiment: FIG. 2A is a
plan view; and FIG. 2B is a cross-sectional view taken along line
A-A in FIG. 2A; and FIG. 2C is a cross-sectional view taken along
line B-B in FIG. 2A.
[0016] FIG. 3 is a circuit diagram showing a configuration example
of a thin film transistor for organic EL applications.
[0017] FIG. 4 is a plan view showing a configuration example of an
annealing-target substrate on which a plurality of thin film
transistor formation portions are arranged.
[0018] FIG. 5 is a block diagram showing a schematic configuration
of a controller of the laser annealing apparatus according to the
present invention.
[0019] FIG. 6 is a diagram for illustrating the first round of
annealing by a laser annealing method according to the present
invention.
[0020] FIG. 7 is a diagram for illustrating the second round of
annealing by the laser annealing method according to the present
invention.
[0021] FIG. 8 is a diagram for illustrating the third round of
annealing by the laser annealing method according to the present
invention.
[0022] FIG. 9 is a plan view of a substrate having thin film
transistors for organic EL applications manufactured by the laser
annealing method according to the present invention.
[0023] FIGS. 10A and 10B are diagrams showing the electronic
properties of the thin film transistors for organic EL applications
manufactured by the laser annealing method according to the present
invention: FIG. 10A shows the properties of the driver thin film
transistors; and FIG. 10B shows the properties of the selector thin
film transistors.
[0024] FIGS. 11A and 11B are diagrams showing a modified example of
the microlens array used in the first embodiment: FIG. 11A is a
plan view; and FIG. 11B is a cross-sectional view taken along line
A-A in FIG. 11A.
[0025] FIG. 12 is an enlarged front view of substantial portions
for illustrating a second embodiment of a laser annealing apparatus
according to the present invention.
[0026] FIGS. 13A and 13B are diagrams showing a configuration
example of a light shielding mask used in the second embodiment:
FIG. 13A is a plan view; and FIG. 11B is a cross-sectional view
taken along line A-A in FIG. 13A.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0027] Embodiments of the present invention will be described in
detail with reference to the accompanying drawings. FIG. 1 is a
schematic configuration diagram showing a first embodiment of a
laser annealing apparatus according to the present invention. FIGS.
2A to 2C are diagrams showing a configuration example of a
microlens array used in the first embodiment. FIG. 2A is a plan
view. FIG. 2B is a cross-sectional view taken along line A-A in
FIG. 2A. FIG. 2C is a cross-sectional view taken along line B-B in
FIG. 2A. This laser annealing apparatus crystallizes an amorphous
silicon film formed on a substrate by irradiating the film with
laser beams, and comprises a scanning means 1, a laser illumination
optical system 2, an imaging means 3, an alignment means 4, and a
controller 5.
[0028] The scanning means 1 scans, in the direction indicated by
the arrow in FIG. 1, an annealing-target substrate (simply referred
to as "substrate" below) 6 having an amorphous silicon film formed
on its surface on which a plurality of thin film transistor
formation portions are arranged in a matrix by holding, for
example, the edges of the substrate 6 with the substrate 6 floating
slightly above the scanning surface. The scanning means 1 has a
plurality of flotation units 7 arranged in a row and thus can
uniformly impart a floating ability to the substrate 6.
[0029] The description herein assumes that the substrate 6 is
formed into a substrate having thin film transistors for organic EL
applications. In the thin film transistor substrate for organic EL
applications, thin film transistors (hereafter, referred to as
"TFTs") for organic EL applications as shown in FIG. 3 are formed
at the intersections of data lines 8 and select lines 9 provided
longitudinally and laterally as shown in FIG. 3.
[0030] More specifically, the TFT positioned on the right side in
FIG. 3 is a driver TFT 10 that controls the drive current of an
organic EL pixel. The driver TFT 10 includes a drain 11 connected
to a power supply line 12 and a source 13 connected to the anode of
the organic EL 14. The TFT positioned on the left side in FIG. 3 is
a selector TFT 15 that controls the gate voltage of the driver TFT
10. The selector TFT 15 includes a gate 16 connected to a select
line 9, a drain 17 connected to a data line 8, and a source 18
connected to a gate 19 of the driver TFT 10. In addition, a storage
capacitor 20 is provided between the gate 19 and the source 13 of
the driver TFT 10. The cathode of the organic EL 14 is grounded.
Note that the drains and sources of the TFTs may be arranged in the
opposite way.
[0031] As shown in FIG. 4, the data lines 8, the select lines 9,
and the power supply lines 12 are provided on the substrate 6 so as
to be insulated from each other. Also, the gate electrodes 21 of
the driver TFTs 10 and the gate electrodes 22 of the selector TFTs
15 are previously provided on the substrate 6. On the gate
electrodes 21, 22, an amorphous silicon film is formed with an
insulating film (not shown) made of Sift or the like interposed
therebetween. In this case, the region on the gate electrode 21 of
each driver TFT 10 serves as a first TFT formation portion 23, and
the region on the gate electrode 22 of each selector TFT 15 serves
as a second TFT formation portion 24. In the present embodiment,
the substrate 6 is scanned in the direction (indicated by the arrow
in FIG. 4) orthogonal to the direction in which the first and
second TFT formation portions 23, 24 are arranged alternately, that
is, scanned in the direction parallel with the data lines 8.
[0032] A laser illumination optical system 2 is provided above the
scanning means 1. This laser illumination optical system 2
irradiates the first and second TFT formation portions 23, 24 on
the substrate 6 with pulse laser beams L at different irradiation
doses so as to crystallize the amorphous silicon film in the first
TFT formation portions 23 into a polysilicon film having a
crystalline state and crystallize the amorphous silicon film in the
second TFT formation portions 24 into a polysilicon film having
another crystalline state that is different from that of the
polysilicon film in the first TFT formation portions 23. The laser
illumination optical system 2 comprises, in order from upstream to
downstream in the direction of laser travel, a laser source 25, a
coupling optical system 26, and a microlens array 27.
[0033] Here, the laser source 25 emits, for example, a pulse laser
beam L at a predetermined frequency, such as a YAG laser with a
wavelength of 355 nm or an excimer laser with a wavelength of 308
nm.
[0034] The coupling optical system 26 expands the luminous flux
diameter of the pulse laser beam L emitted from the laser source
25, and then converts the pulse laser beam L into parallel beams
having uniform luminance distribution, thereby irradiating the
microlens array 27 (described later) with the parallel beams. The
coupling optical system 26 comprises a beam expander, a photo
integrator, a collimator lens, and the like which are not
shown.
[0035] The microlens array 27 is disposed facing the scanning
surface of the scanning means 1. As shown in FIG. 2B, the microlens
array 27 includes a transparent substrate 28 such as a quartz
substrate, a light shielding mask 30, and a plurality of
microlenses (projecting optical system) 31. The light shielding
mask 30 is provided on the light incidence side of the transparent
substrate 28, and has a plurality of mask patterns 29 so as to
correspond to the first and second TFT formation portions 23, 24 on
the substrate 6. The microlenses 31 are provided on the light
exiting side of the transparent substrate 28 so as to correspond to
the mask patterns 29, and each project a reduced-size image of the
corresponding mask pattern 29 onto the substrate 6.
[0036] Specifically, as shown in FIG. 2A, the microlens array 27
has the plurality of mask patterns 29 and the plurality of
microlenses 31, which are arranged in a matrix with columns
extending in the scanning direction of the substrate 6 (the
direction indicated by the arrow in FIG. 2A) and rows extending in
the direction orthogonal to the scanning direction. Furthermore, as
shown in FIG. 2A, the number of mask patterns 29 and microlenses 31
lined up in the scanning direction of the substrate 6 (hereafter,
referred to as "substrate transport direction") so as to correspond
to the second TFT formation portions 24 is adjusted to be smaller
than the number of mask patterns 29 and microlenses 31 lined up in
this transport direction so as to correspond to the first TFT
formation portions 23.
[0037] With the above configuration, simply by multiply irradiating
each of the first and second TFT formation portions 23, 24 with the
pulse laser beams L through a plurality of microlenses 31 that are
lined up in the substrate transport direction, the first and second
TFT formation portions 23, 24 can be irradiated with different
irradiation doses (energies) of the pulse laser beams L. Thus, upon
completion of such annealing, the amorphous silicon film in the
first and second TFT formation portions 23, 24 can be crystallized
into polysilicon films having different crystalline states.
[0038] In the present embodiment, the laser annealing of the first
TFT formation portions 23 is completed with multiple irradiation,
in particular, three shots of irradiation of the pulse laser beams
L, and the laser annealing of the second TFT formation portions 24
is completed with a single shot of such laser irradiation, but the
numbers of shots of irradiation of the pulse laser beams L are not
limited to these. Furthermore, although the number of microlenses
31 for the second TFT formation portions 24 does not have to be
adjusted in accordance with the adjusted number of the second TFT
formation portions 24, the number of microlenses 31 is adjusted to
match the adjusted number of mask patterns 29 in this
embodiment.
[0039] The imaging means 3 is provided upstream, in the substrate
scanning direction, of the positions irradiated with the pulse
laser beams L by the laser illumination optical system 2. This
imaging means 3, which is disposed between adjacent two of the
plurality of flotation units 7 in the scanning means 1, is a line
camera comprising a linear light receiving part whose longitudinal
axis is oriented in the direction orthogonal to the substrate
scanning direction, and captures an image of the data lines 8 and
select lines 9 previously formed on the substrate 6. The imaging
means 3 is capable of capturing an image of the data lines 8 and
select lines 9 on the surface of the substrate 6 through the rear
surface of the substrate 6. Furthermore, the imaging means 3 is
configured to move in fine increments in the direction orthogonal
to the substrate scanning direction integrally in synchronization
with the alignment movement of the laser illumination optical
system 2 or the microlens array 27 in this direction caused by the
alignment means 4 (described later).
[0040] The alignment means 4 is provided so as to be able to move
the laser illumination optical system 2 or the microlens array 27
in fine increments in the direction orthogonal to the substrate
scanning direction. This alignment means 4 is provided for aligning
the positions of the mask patterns 29 of the microlens array 27
with the positions of the first and second TFT formation portions
23, 24 on the substrate 6. Under the control of a controller 5
(described later), the alignment means 4 moves the laser
illumination optical system 2 or microlens array 27 in fine
increments in the direction orthogonal to the scanning direction of
the substrate 6 so as to correct lateral misalignment of the
substrate 6 in this direction. The following description assumes a
case in which the alignment means 4 moves the microlens array 27 in
fine increments.
[0041] The controller 5 is provided which is electrically connected
to the scanning means 1, the laser illumination optical system 2,
the imaging means 3, and the alignment means 4. The controller 5
controls the scanning means 1 so as to scan the substrate 6, in a
state of floating a predetermined distance above the flotation
units 7, at a constant speed in the direction indicated by the
arrow in FIG. 1. Also, the controller 5 controls the light emission
timing by driving the laser source 25 to emit laser beams each time
first and second TFT formation portion 23 or 24 reach focal
positions of the pulse laser beams L that are established by a
microlens 31 of the microlens array 27, and controls the driving of
the alignment means 4 so as to correct lateral misalignment of the
substrate 6 by calculating the amount of lateral misalignment based
on the image data received from the imaging means 3. As shown in
FIG. 5, the controller 5 comprises a scanning means drive
controller 32, a laser source drive controller 33, an image
processing part 34, an alignment means drive controller 35, a
memory 36, an operation part 37, and a controller 38.
[0042] Here, the scanning means drive controller 32 controls the
start and stop of air blowing from the flotation units 7, and also
controls the start and stop as well as the scanning direction and
scanning speed of the substrate 6 by the scanning means 1.
[0043] The laser source drive controller 33 controls the emission
of the pulse laser beams L by the laser source 25 based on a light
emission instruction received from the operation part 37 (described
later).
[0044] The image processing part 34 processes the image data
received from the imaging means 3, and detects the positions of the
data lines 8 based on luminance variation in the direction
orthogonal to the scanning direction of the substrate 6, and
detects a select line 9, based on luminance variation in the
scanning direction of the substrate 6. Then, the image processing
part 34 outputs, to the operation part 37 (described later),
position information of a previously specified data line 8
indicating, for example, the position of the right edge of the data
line 8, and detection information of the select line 9,
specifically, detection information of, for example, its edge
located downstream in the scanning direction of the substrate
6.
[0045] The alignment means drive controller 35 controls the driving
of the alignment means 4 so as to reduce the amount of lateral
misalignment of the substrate 6 calculated by the operation part 37
to zero.
[0046] The memory 36 stores information such as the scanning speed
of the scanning means 1, a target travel distance that the
substrate 6 is to travel in a period from the time the imaging
means 3 first detects a select line 9 to the time the driving of
the laser source 25 starts, position information indicating a
reference position predefined for the light receiving part of the
imaging means 3, and the array pitch W of the first and second TFT
formation portions 23, 24 in the scanning direction. The memory 36
can also temporarily store the calculation results of the operation
part 37.
[0047] The operation part 37 calculates the travel distance of the
substrate 6 based on the scanning speed and time of the scanning
means 1. The operation part 37 compares the calculated travel
distance with the target travel distance of the substrate 6
retrieved from the memory 36 as well as with the array pitch W of
the first and second TFT formation portions 23, 24 in the scanning
direction, and outputs a light emission instruction of the pulse
laser beams L to the laser source drive controller 33. Also, based
on the position information of the data line 8 received from the
image processing part 34 and the position information indicating
the reference position predefined for the imaging means 3 and
retrieved from the memory 36, the operation part 37 calculates the
distance between the data line 8 and the reference position. The
operation part 37 compares this calculated distance with a
reference distance between the data line 8 and the reference
position stored in the memory 36, thereby calculating the
difference between these distances. Then, the operation part 37
outputs the difference to the alignment means drive controller 35.
Here, the travel distance of the substrate 6 may be detected by a
position sensor provided in the scanning means 1, or may be
calculated by counting the number of pulses of a pulse motor in the
movement mechanism that moves the substrate 6.
[0048] The controller 38 controls the entire apparatus in an
integrated manner, and is for example a control PC (Personal
Computer).
[0049] Next, the operation of the first embodiment of the laser
annealing apparatus configured in this manner and the laser
annealing method are described. First, the substrate 6 is placed on
the scanning surface of the scanning means 1 with the surface on
which the amorphous silicon film is formed facing up, and the edges
of the substrate 6 are held by the movement mechanism.
Specifically, the substrate 6 is disposed such that the data lines
8 are parallel with the substrate scanning direction.
[0050] Next, when the switch to start annealing is thrown, air is
blown from the flotation units 7 of the scanning means 1 and causes
the substrate 6 to float, and scanning of the substrate 6 by the
movement mechanism begins in the direction indicated by the arrow
in FIG. 1.
[0051] Then, an image of the data lines 8 and the select lines 9
formed on the front surface of the substrate 6 is captured from the
rear surface side by the imaging means 3 through the substrate 6.
The image data captured by the imaging means 3 is processed by the
image processing part 34. Specifically, the image processing part
34 detects the select line 9 that is located furthest downstream in
the substrate scanning direction based on the luminance variation
in the substrate scanning direction, specifically, detects, for
example, the edge, located downstream in the substrate scanning
direction, of this select line 9, and outputs the resultant
detection information to the operation part 37.
[0052] Triggered by the receipt of the detection information of the
select line 9 from the image processing part 34, the operation part
37 calculates the travel distance of the substrate 6. The operation
part 37 compares the thus-calculated travel distance of the
substrate 6 with the target travel distance of the substrate 6
retrieved from the memory 36. When these distance values match, the
operation part 37 outputs, to the laser source drive controller 33,
an instruction to emit a pulse laser beam L. As shown in FIG. 6,
this moment coincides with when the first and second TFT formation
portions 23, 24 positioned furthest downstream in the substrate
scanning direction arrive at the focal positions of the pulse laser
beams L established by the microlenses 31 of the microlens array 27
(collectively referred to as "first microlens row 31A" below) that
are positioned furthest upstream in the substrate scanning
direction.
[0053] Upon receiving the instruction from the operation part 37 to
emit a pulse laser beam L, the laser source drive controller 33
drives the laser source 25 to emit a pulse laser beam L at a
predetermined frequency. Then, the coupling optical system 26
expands the luminous flux diameter of the pulse laser beam L
emitted from the laser source 25, and then converts the pulse laser
beam L into parallel beams having uniform luminance distribution,
so that the resultant pulse laser beams L illuminate the microlens
array 27. After that, the pulse laser beams L pass through the mask
patterns 29 formed in the light shielding mask 30 of the microlens
array 27, and are then each focused on the substrate 6 by the
corresponding microlens 31.
[0054] Through this process, as shown in FIG. 6, the first round of
annealing with the pulse laser beams L is performed on the
amorphous silicon film in the first and second TFT formation
portions 23, 24 positioned furthest downstream in the substrate
scanning direction. As a result, the amorphous silicon film in
these first and second TFT formation portions 23, 24 is
crystallized into a polysilicon film.
[0055] Meanwhile, the operation part 37 continues to calculate the
travel distance of the substrate 6. When the travel distance of the
substrate 6 matches the array pitch W of the first and second TFT
formation portions 23, 24 in the substrate scanning direction, the
operation part 37 outputs, to the laser source drive controller 33,
another instruction to emit a pulse laser beam L.
[0056] In response, the laser source drive controller 33 drives the
laser source 25 to emit a pulse laser beam L in a similar manner as
described above, so that the resultant pulse laser beams L
illuminate the microlens array 27.
[0057] After that, the pulse laser beams L pass through the mask
patterns 29 of the microlens array 27, and are then each focused on
the substrate 6 by the corresponding microlens 31. At that time,
the substrate 6 has moved further by a distance equivalent to the
array pitch W of the first and second TFT formation portions 23, 24
in the substrate scanning direction. Accordingly, as shown in FIG.
7, the first and second TFT formation portions 23, 24 positioned
furthest downstream in the substrate scanning direction arrive at
the focal positions of the pulse laser beams L established by the
microlenses 31 of the microlens array 27 (collectively referred to
as "second microlens row 31B" below) that are positioned adjacently
downstream of the first microlens row 31A.
[0058] Furthermore, as shown in FIG. 7, the first and second TFT
formation portions 23, 24 positioned adjacently upstream of the
first and second TFT formation portions 23, 24 that are positioned
furthest downstream in the substrate scanning direction arrive at
the focal positions of the pulse laser beams L established by the
first microlens row 31A of the microlens array 27.
[0059] Accordingly, among the pulse laser beams L having passed
through the microlens array 27, the pulse laser beams L having
passed through the second microlens row 31B are focused on the
first TFT formation portions 23 positioned furthest downstream in
the substrate scanning direction, thereby subjecting these first
TFT formation portions 23 to the second round of annealing. As a
result, the irradiation dose (energy) of the pulse laser beam L in
each of these first TFT formation portions 23 increases and
promotes crystal growth in these portions.
[0060] The third microlens row 31B contains no mask patterns 29 or
microlenses 31 at positions corresponding to the second TFT
formation portions 24. Thus, the second TFT formation portions 24
positioned furthest downstream in the substrate scanning direction
are not irradiated with pulse laser beams L. Accordingly, these
second TFT formation portions 24 are maintained in the state of
having undergone only the first round of annealing, without further
crystal growth toward a polysilicon film.
[0061] Among the pulse laser beams L having passed through the
microlens array 27, the pulse laser beams L having passed through
the first microlens row 31A are focused on the first and second TFT
formation portions 23, 24 positioned adjacently upstream of the
first and second TFT formation portions 23, 24 that are positioned
furthest downstream in the substrate scanning direction, thereby
subjecting these first and second TFT formation portions 23, 24 to
the first round of annealing. As a result, the amorphous silicon
film in these portions is crystallized into a polysilicon film.
[0062] Meanwhile, the operation part 37 continues to calculate the
travel distance of the substrate 6. When the travel distance of the
substrate 6 matches the array pitch W of the first and second TFT
formation portions 23, 24 in the substrate scanning direction, the
operation part 37 outputs, to the laser source drive controller 33,
another instruction to emit a pulse laser beam L.
[0063] In response, the laser source drive controller 33 drives the
laser source 25 to emit a pulse laser beam L, so that the resultant
pulse laser beams L illuminate the microlens array 27.
[0064] After that, the pulse laser beams L pass through the mask
patterns 29 on the microlens array 27, and are then each focused on
the substrate 6 by the corresponding microlens 31. At that time,
the substrate 6 has moved still further by a distance equivalent to
the array pitch W of the first and second TFT formation portions
23, 24 in the substrate scanning direction. Accordingly, as shown
in FIG. 8, the first and second TFT formation portions 23, 24
positioned furthest downstream in the substrate scanning direction
arrive at the focal positions of the pulse laser beams L
established by the microlenses 31 of the microlens array 27
(collectively referred to as "third microlens row 31C" below) that
are positioned one row away downstream from the first microlens row
31A.
[0065] Furthermore, as shown in FIG. 8, the first and second TFT
formation portions 23, 24 positioned adjacently upstream of the
first and second TFT formation portions 23, 24 that are positioned
furthest downstream in the substrate scanning direction arrive at
the focal positions of the pulse laser beams L established by the
second microlens row 31B of the microlens array 27.
[0066] In addition, as shown in FIG. 8, the first and second TFT
formation portions 23, 24 positioned one row away upstream from the
first and second TFT formation portions 23, 24 that are positioned
furthest downstream in the substrate scanning direction arrive at
the focal positions of the pulse laser beams L established by the
first microlens row 31A of the microlens array 27.
[0067] Accordingly, among the pulse laser beams L having passed
through the microlens array 27, the pulse laser beams L having
passed through the third microlens row 31C are focused on the first
TFT formation portions 23 positioned furthest downstream in the
substrate scanning direction, thereby subjecting these first TFT
formation portions 23 to the third round of annealing. As a result,
the irradiation dose (energy) in each of these first TFT formation
portions 23 further increases, and promotes further crystal growth
in these portions.
[0068] As shown in FIG. 8, the third microlens row 31C contains no
mask patterns 29 or microlenses 31 at positions corresponding to
the second TFT formation portions 24. Thus, the second TFT
formation portions 24 positioned furthest downstream in the
substrate scanning direction are not irradiated with the pulse
laser beams L. Accordingly, these second TFT formation portions 24
are maintained in the state of having undergone only the first
round of annealing, without further crystal growth toward a
polysilicon film.
[0069] Among the pulse laser beams L having passed through the
microlens array 27, the pulse laser beams L having passed through
the second microlens row 31B are focused on the first TFT formation
portions 23 positioned adjacently upstream of the first TFT
formation portions 23 that are positioned furthest downstream in
the substrate scanning direction, thereby subjecting these first
TFT formation portions 23 to the second round of annealing. As a
result, the irradiation dose (energy) of the pulse laser beam L in
each of these first TFT formation portions 23 increases and
promotes crystal growth in these portions.
[0070] The second microlens row 31B contains no mask patterns 29 or
microlenses 31 at positions corresponding to the second TFT
formation portions 24. Thus, the second TFT formation portions 24
positioned adjacently upstream of the second TFT formation portions
24 that are positioned furthest downstream in the substrate
scanning direction are not irradiated with the pulse laser beams L.
Accordingly, these second TFT formation portions 24 are maintained
in the state of having undergone only the first round of annealing,
without further crystal growth toward a polysilicon film.
[0071] Among the pulse laser beams L having passed through the
microlens array 27, the pulse laser beams L having passed through
the first microlens row 31A are focused on the first and second TFT
formation portions 23, 24 positioned one row away upstream from the
first and second TFT formation portions 23, 24 that are positioned
furthest downstream in the substrate scanning direction, thereby
subjecting the former first and second TFT formation portions 23,
24 to the first round of annealing. As a result, the amorphous
silicon film in these portions is crystallized into a polysilicon
film.
[0072] After that, in the same manner as above, annealing with
multiple irradiation, in particular, three shots of irradiation of
the pulse laser beams L is also performed in the other first TFT
formation portions 23, and annealing with a single shot of
irradiation of the pulse laser beams L is also performed in the
other second TFT formation portions 24. As a result, the
irradiation dose of the pulse laser beam L (cumulative energy of
the pulse laser beam L) in each first TFT formation portion 23
differs from that of each second TFT formation portion 24. This
makes it possible to crystallize the amorphous silicon film in the
first and second TFT formation portions 23, 24 into polysilicon
films having different crystalline states.
[0073] Subsequently, unnecessary portions of the amorphous silicon
film and polysilicon film are etched off to finish a semiconductor
layer on each of the gate electrodes 21, 22. After that, a source
electrode, a drain electrode, a storage capacitor 20, and an
insulating protective film are formed in this order on the
semiconductor layer. In this way, a TFT substrate for organic EL
applications including a plurality of driver TFTs 10 and a
plurality of selector TFTs 15 as shown in FIG. 9 is manufactured
such that the crystalline state in the polysilicon semiconductor
layer of each driver TFT 10 differs from that of each selector TFT
15.
[0074] In this TFT substrate, the polysilicon film of each driver
TFT 10 (first TFT formation portion 23), which receives a greater
irradiation dose or a greater cumulative energy of the pulse laser
beam L, has a larger crystal grain size than that of the
polysilicon film of each selector TFT 15 (second TFT formation
portion 24), which receives a smaller irradiation dose or a smaller
cumulative energy of the pulse laser beam L. Accordingly, as shown
in FIG. 10A, each driver TFT 10 has electronic properties that
permit a somewhat large off-state leakage current (approximately
1.times.10.sup.-9 A) but allow greater electron mobility
(approximately 30 cm.sup.2/Vs), and is capable of supplying a large
current to the organic EL device.
[0075] On the other hand, because the crystal grain size of the
polysilicon film of each selector TFT 15 (second TFT formation
portion 24) is smaller than the crystal grain size of the
polysilicon film of each driver TFT 10 (first TFT formation portion
23), the selector TFT 15 has electronic properties that allow only
small electron mobility (approximately 2 cm.sup.2/Vs) but permit a
smaller off-state leakage current (1.times.10.sup.-HA), and is
capable of maintaining the gate voltage of the corresponding driver
TFT 10 at a constant level, as shown in FIG. 10B.
[0076] Thus, with the laser annealing method of the present
invention, the first and second TFT formation portions 23, 24 on
the substrate 6 can be irradiated with the pulse laser beams L at
different irradiation doses between the first TFT formation portion
23 and the second TFT formation portion 24 in a single laser
annealing step. As a result, the amorphous silicon film in the
first TFT formation portions 23 can be crystallized into a
polysilicon film having a crystalline state, and the amorphous
silicon film in the second TFT formation portions 24 can be
crystallized into a polysilicon film having another crystalline
state that is different from that of the polysilicon film in the
first TFT formation portions 23. Therefore, when a thin film
transistor substrate for organic EL applications is manufactured by
using the laser annealing method according to the present
invention, it is possible to provide the driver TFTs 10 with
electronic properties required therefor and provide the selector
TFTs 15 with different electronic properties that are required
therefor.
[0077] During laser annealing performed on the substrate 6 while it
is scanned, the imaging means 3 constantly captures an image of the
data lines 8, and the image processing part 34 performs image
processing on this image and detects the position of a specific
data line 8 based on the luminance variation in the direction
orthogonal to the scanning direction of the substrate 6. Meanwhile,
based on the information on the detected position of this data line
8 and the information on a reference position preset for the
imaging means 3, the operation part 37 calculates the distance
between these two positions. Then, the operation part 37 compares
the thus-calculated distance with a reference distance stored in
the memory 36 and calculates the amount of lateral misalignment of
the substrate 6. Then, the alignment means drive controller 35
drives the alignment means 4 to move the microlens array 27
integrally with the imaging means 3 in fine increments in the
direction orthogonal to the substrate scanning direction so as to
reduce the amount of this lateral misalignment to zero. As a
result, the lateral misalignment of the substrate 6 is corrected,
and annealing is performed by irradiating the pulse laser beams L
onto the first and second TFT formation portions 23, 24 on the
substrate 6 with high positional accuracy.
[0078] In the first embodiment, the microlens array 27 contains a
plurality of mask patterns 29 and a plurality of microlenses 31,
which are arranged in a matrix with columns extending in the
scanning direction of the substrate 6 and rows extending in the
direction orthogonal to this scanning direction, and the numbers of
the mask patterns 29 and the microlenses 31 that are lined up in
the scanning direction of the substrate 6 so as to correspond to
the second TFT formation portions 24 are adjusted so as to be
smaller than the numbers of the mask patterns 29 and the
microlenses 31 that are lined up in this scanning direction so as
to correspond to the first TFT formation portions 23. However, the
present invention is not limited to this. Alternatively, as shown
in FIGS. 11A and 11B, a dimmer film 40 with a predetermined light
transmittance may be formed on the mask patterns 29 corresponding
to the second TFT formation portions 24 so as to adjust the amount
of light transmitted therethrough to be smaller than the amount of
light transmitted thorough the mask patterns 29 corresponding to
the first TFT formation portions 23. In this case, both the first
and second TFT formation portions 23, 24 may be annealed with
multiple irradiation of pulse laser beams L through the microlenses
31. However, when the annealing of the first and second TFT
formation portions 23, 24 is to be completed by a single shot of
irradiation of the pulse laser beams L, the microlens array 27 may
have a single mask pattern and microlens row in which a plurality
of mask patterns 29 and a plurality of microlenses 31 are lined up
in the direction orthogonal to the substrate scanning
direction.
[0079] FIG. 12 is an enlarged front view of substantial portions
for illustrating a second embodiment of a laser annealing apparatus
according to the present invention. Here, portions that differ from
those of the first embodiment will be described. In the first
embodiment, through the microlenses 31, which are provided
individually corresponding to the mask patterns 29 formed on the
light shielding mask 30, reduced-size images of the mask patterns
29 are projected onto the substrate 6. Instead, in this second
embodiment, reduced-size images of the mask patterns 29 are
projected onto the substrate 6 through a single projection lens
(projecting optical system) 41. The projection lens 41 may have a
lens configuration that forms either an inverted image or an erect
image of the light shielding mask 30 on the substrate 6.
[0080] When the projection lens 41 has a lens configuration that
forms an inverted image, annealing may be performed using the light
shielding mask 30 having the mask patterns 29 that are arranged in
180.degree. rotational symmetry about the center of the light
shielding mask 30 with respect to the mask patterns 29 shown in
FIGS. 2A and 2B or FIGS. 11A and 11B. For example, the light
shielding mask 30 shown in FIGS. 13A and 13B corresponds to the
mask obtained by rotating the light shielding mask 30 shown in
FIGS. 11A and 11B by 180.degree. about its center. In other words,
as shown in FIGS. 13A and 13B, in the light shielding mask 30
according to the second embodiment, the dimmer film 40 is provided
on the mask patterns 29 corresponding to the second TFT formation
portions 24 so that the amount of light transmitted through the
mask patterns 29 corresponding to the second TFT formation portions
24 can be smaller than the amount of light transmitted through the
mask patterns 29 corresponding to the first TFT formation portions
23. Needless to say, the array pitch of the mask patterns 29 is set
to a value obtained by converting the longitudinal and lateral
array pitch of the first and second TFT formation portions 23, 24
using the magnification of the projection lens 41.
[0081] In this case, the irradiation of the pulse laser beams L
starts when the first and second TFT formation portions 23, 24 that
are positioned furthest downstream in the substrate scanning
direction arrive at the focal positions of a row of the mask
patterns 29 positioned furthest downstream in the substrate
scanning direction among the mask patterns 29 formed on the light
shielding mask 30 so as to be arranged in rows extending in the
direction orthogonal to the substrate scanning direction, such as
the mask pattern row 29A of the mask pattern rows 29A, 29B, 29C
shown in FIG. 13. Thereafter, in the same manner as in the first
embodiment, the substrate 6 is irradiated with the pulse laser
beams L each time the substrate 6 has traveled by a distance
equivalent to the array pitch W of the first and second TFT
formation portions 23, 24 in the substrate scanning direction,
thereby laser annealing the amorphous silicon film in the first and
second TFT formation portions 23, 24 and crystallizing the
amorphous silicon film into polysilicon films.
[0082] On the other hand, when the projection lens 41 has a lens
configuration that forms an erect image, annealing may be performed
using the light shielding mask 30 having the mask patterns 29 that
are arranged in the same manner as the mask patterns 29 shown in
FIGS. 2A and 2B or FIGS. 11A and 11B. In this case also, the array
pitch of the mask patterns 29 is set to a value obtained by
converting the longitudinal and lateral array pitch of the first
and second TFT formation portions 23, 24 using the magnification of
the projection lens 41. Furthermore, the irradiation of the pulse
laser beams L starts when the first and second TFT formation
portions 23, 24 that are positioned furthest downstream in the
substrate scanning direction arrive at the focal positions of a row
of the mask patterns 29 positioned furthest downstream in the
substrate scanning direction among the mask patterns 29 formed on
the light shielding mask 30 so as to be arranged in rows extending
in the direction orthogonal to the substrate scanning direction.
The subsequent irradiation timings of the pulse laser beams L are
the same as those in the first embodiment.
[0083] In the first and second embodiments, the substrate 6 is
laser annealed while the substrate 6 is scanned, but the present
invention is not limited to this. Alternatively, the substrate 6
placed to be stationary may be laser annealed with a single shot or
multiple shots of laser irradiation. In this case, the substrate 6
may be laser annealed by irradiating the TFT formation portions
with pulse laser beams L at different irradiation doses through the
mask patterns 29 provided corresponding to the TFT formation
portions on the substrate 6, and through the microlenses 31 or the
projection lens 41. Such different irradiation doses of the pulse
laser beams L may be realized by adjusting the amount of light to
be transmitted through the mask patterns 29.
[0084] Furthermore, in the first and second embodiments, the first
and second TFT formation portions 23, 24 are irradiated with the
pulse laser beams L emitted from a single laser source 25 at
different irradiation doses. However, the present invention is not
limited to this. Alternatively, two laser sources with different
irradiation energies may be used, and the first TFT formation
portions 23 may be irradiated with pulse laser beams L with an
irradiation energy emitted from one of these laser sources, and the
second TFT formation portions 24 may be irradiated with pulse laser
beams L with a different irradiation energy emitted from the other
of these laser sources.
[0085] Furthermore, in the above description, the present invention
is applied to the production of a TFT substrate for organic EL
applications. However, the application of the present invention is
not limited to this. The present invention may also be applied to
any laser annealing processes performed on amorphous silicon films
to produce a plurality of TFTs with polysilicon semiconductor
layers having different crystalline states.
[0086] It should be noted that the entire contents of Japanese
Patent Application No. 2016-032469, filed on Feb. 23, 2016, based
on which convention priority is claimed herein, is incorporated
herein by reference.
[0087] It should also be understood that many modifications and
variations of the described embodiments of the invention will be
apparent to a person having an ordinary skill in the art without
departing from the spirit and scope of the present invention as
claimed in the appended claims.
* * * * *