U.S. patent number RE38,466 [Application Number 10/263,070] was granted by the patent office on 2004-03-16 for manufacturing method of active matrix substrate, active matrix substrate and liquid crystal display device.
This patent grant is currently assigned to Seiko Epson Corporation. Invention is credited to Satoshi Inoue, Tatsuya Shimoda.
United States Patent |
RE38,466 |
Inoue , et al. |
March 16, 2004 |
Manufacturing method of active matrix substrate, active matrix
substrate and liquid crystal display device
Abstract
A method of manufacturing an active matrix substrate is provided
that uses a technique of transferring a thin film device. In
forming thin film transistors and pixel electrodes on an original
substrate before transfer, an insulator film such as an interlayer
insulation film or the like, is previously removed before the pixel
electrodes are formed. Further, the original substrate is separated
by exfoliation to transfer the device to a transfer material to
cause the pixel electrodes to partially appear in the surface or
the vicinity of the surface of the device. This portion permits
application of a voltage to a liquid crystal through the pixel
electrode.
Inventors: |
Inoue; Satoshi (Chino,
JP), Shimoda; Tatsuya (Nagano-ken, JP) |
Assignee: |
Seiko Epson Corporation (Tokyo,
JP)
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Family
ID: |
31950712 |
Appl.
No.: |
10/263,070 |
Filed: |
October 3, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCTJP9704110 |
Nov 11, 1997 |
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Reissue of: |
113373 |
Jul 10, 1998 |
06127199 |
Oct 3, 2000 |
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Foreign Application Priority Data
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Nov 12, 1996 [JP] |
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8-315590 |
Nov 22, 1996 [JP] |
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8-327688 |
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Current U.S.
Class: |
438/30; 438/158;
438/160; 438/486; 438/949 |
Current CPC
Class: |
H01L
21/76251 (20130101); H01L 27/1214 (20130101); H01L
27/1266 (20130101); G02F 1/1368 (20130101); H01L
2224/24226 (20130101); H01L 2924/01019 (20130101); H01L
2924/01078 (20130101); H01L 2924/01057 (20130101); H01L
2924/01025 (20130101); H01L 2221/68359 (20130101); G02F
1/13613 (20210101); H01L 2224/76155 (20130101); H01L
2924/13091 (20130101) |
Current International
Class: |
G02F
1/1368 (20060101); G02F 1/13 (20060101); H01L
27/12 (20060101); H01L 21/762 (20060101); H01L
21/84 (20060101); H01L 21/70 (20060101); H01L
021/00 (); H01L 021/48 () |
Field of
Search: |
;438/30,158,160,486,949,157,635,164,459 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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A-61-231714 |
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Oct 1986 |
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JP |
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A-6-291291 |
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Oct 1994 |
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JP |
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A-8-62591 |
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Mar 1996 |
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JP |
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A-8-288522 |
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Nov 1996 |
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JP |
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WO 98/09333 |
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Mar 1998 |
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JP |
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Other References
Sameshima, T. "Laser Beam Application to Thin Film Transistors,"
Applied Surface Science 96-98, (1996), pp. 352-358..
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Primary Examiner: Lebentritt; Michael S.
Attorney, Agent or Firm: Oliff & Berridge, PLC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-Part of international
application PCT/JP97/04110, filed on Nov. 11, 1997, which claims
priority from Japanese application Nos. 8-315590 and 8-327688,
filed on Nov. 12, 1996 and Nov. 22, 1996, respectively.
PCT/JP97/04110 and Japanese application Nos. 8-315590 and 8-327688
are incorporated by reference herein in their entirety.
Claims
What is claimed is:
1. A method of manufacturing an active matrix substrate comprising
a pixel portion including thin film transistors connected to
scanning lines and signal lines arranged in a matrix, and pixel
electrodes connected to terminals of the thin film transistors, the
method comprising the steps of: forming a separation layer on a
substrate; forming the thin film transistors over the separation
layer; forming an insulation film on the thin film transistors and
over the separation layer; selectively removing at least a portion
of the insulation film where each of the pixel electrodes is to be
formed; forming each of the pixel electrodes on the insulation film
and the separation layer in the region where at least a portion of
the insulation film has been removed; adhering the thin film
transistors to a transfer material with an adhesive layer;
producing exfoliation in the separation layer and/or at an
interface of the separation layer and the substrate to separate the
substrate from the separation layer; and removing any portion of
the separation layer remaining on the pixel electrodes to form an
active matrix substrate using the transfer material as a new
substrate.
2. The method of manufacturing an active matrix substrate according
to claim 1, wherein the step of selectively removing at least a
portion of the insulation film comprises forming contact holes for
electrically connecting the pixel electrodes to the thin film
transistors.
3. The method of manufacturing an active matrix substrate according
to claim 2, further comprising connecting the pixel electrodes
directly to an impurity layer which constitutes the thin film
transistors.
4. The method of manufacturing an active matrix substrate according
to claim 2, further comprising the steps of: forming electrodes
connected to an impurity layer which constitutes the thin film
transistors; and connecting the pixel electrodes to the
corresponding electrodes connected to the impurity layers.
5. The method of manufacturing an active matrix substrate according
to claim 1, further comprising the step of forming at least one of
a color filter and a light shielding film after the step of forming
the pixel electrodes.
6. The method of manufacturing an active matrix substrate according
to claim 1, wherein in selectively removing at least a portion of
the insulation film, at least a portion of the insulation film is
selectively removed from a region where an external connection
terminal is to be provided.
7. The method of manufacturing an active matrix substrate according
to claim 6, further comprising the step of forming the external
connection terminal as a conductive layer made of a same material
as the pixel electrodes or a same material as an electrode
connected to an impurity layer which constitutes the thin film
transistors.
8. A method of manufacturing an active matrix substrate comprising
a pixel portion including thin film transistors connected to
scanning lines and signal lines arranged in a matrix, and pixel
electrodes connected to terminals of the thin film transistors, the
method comprising the steps of: forming a separation layer on a
substrate; forming an intermediate layer on the separation layer;
forming the thin film transistors on the intermediate layer;
forming an insulation film on the thin film transistors and the
intermediate layer; selectively removing at least a portion of the
insulation film where each of the pixel electrodes is to be formed;
forming each of the pixel electrodes on the insulation film and the
separation layer in the region where at least a portion of the
insulation film is removed; adhering the thin film transistors to a
transfer material with an adhesive layer; producing exfoliation in
the separation layer and/or at an interface of the separation layer
and the substrate to separate the substrate from the separation
layer; and removing any portion of the separation layer remaining
on the intermediate layer and the pixel electrodes to form an
active matrix substrate using the transfer material as a new
substrate.
9. The method of manufacturing an active matrix substrate according
to claim 8, wherein the step of selectively removing at least a
portion of the insulation film comprises forming contact holes for
electrically connecting the pixel electrodes to the thin film
transistors.
10. The method of manufacturing an active matrix substrate
according to claim 9, further comprising connecting the pixel
electrodes directly to an impurity layer which constitutes the thin
film transistors.
11. The method of manufacturing an active matrix substrate
according to claim 9, further comprising the steps of: forming
electrodes connected to an impurity layer which constitutes the
thin film transistors; and connecting the pixel electrodes to the
corresponding electrodes connected to the impurity layers.
12. The method of manufacturing an active matrix substrate
according to claim 8, further comprising the step of forming at
least one of a color filter and a light shielding film after the
step of forming the pixel electrodes.
13. The method of manufacturing an active matrix substrate
according to claim 8, wherein in selectively removing at least a
portion of the insulation film, at least a portion of the
insulation film is selectively removed from a region where an
external connection terminal is to be provided.
14. The method of manufacturing an active matrix substrate
according to claim 13, further comprising the step of forming the
external connection terminal as a conductive layer made of a same
material as the pixel electrodes or a same material as an electrode
connected to an impurity layer which constitutes the thin film
transistors.
15. A method of manufacturing an active matrix substrate comprising
a pixel portion including thin film transistors connected to
scanning lines and signal lines arranged in a matrix, and pixel
electrodes connected to terminals of the thin film transistors, the
method comprising the steps of: forming a separation layer on a
transmissive substrate; forming the thin film transistors over the
separation layer or on an intermediate layer formed on the
separation layer; forming an insulation film on the thin film
transistors; forming the pixel electrodes made of a conductive
material on the insulation film; forming a light shielding layer
that is overlapped with the thin film transistors, and not
overlapped with at least a portion of the pixel electrodes;
adhering the thin film transistors and the light shielding layer to
a transmissive transfer material with a transmissive adhesive
layer; irradiating the separation layer through the transmissive
substrate to produce exfoliation in the separation layer and/or at
an interface of the separation layer and the transmissive substrate
to separate the transmissive substrate from the separation layer;
forming a photoresist on a surface obtained by separating the
transmissive substrate or the surface of a layer appearing after
removing any remaining portion of the separation layer; irradiating
light to expose only a predetermined portion of the photoresist
using the light shielding layer as a mask, followed by development
to form a desired photoresist mask; selectively removing at least a
portion of the intermediate layer and the insulation film or at
least a portion of the insulation film by using the photoresist
mask; and removing the photoresist mask to form an active matrix
substrate using the transfer material as a new substrate.
16. A method of manufacturing an active matrix substrate comprising
a pixel portion including thin film transistors connected to
scanning lines and signal lines arranged in a matrix, and pixel
electrodes connected to terminals of the thin film transistors, the
method comprising the steps of: forming a separation layer on a
substrate; forming the pixel electrodes over the separation layer
or on an intermediate layer formed on the separation layer; forming
an insulation film on the pixel electrodes, and forming the thin
film transistors on the insulation film to respectively connect the
thin film transistors to the pixel electrodes; adhering the thin
film transistors to a transmissive transfer material with a
transmissive adhesive layer; producing exfoliation in the
separation layer and/or at an interface of the separation layer and
the substrate to separate the substrate from the separation layer;
and removing any portion of the separation layer remaining on the
intermediate layer to form an active matrix substrate using the
transfer material as a new substrate.
17. The method of manufacturing an active matrix substrate
according to claim 16, further comprising forming a conductive
material layer on the separation layer or on the intermediate layer
at a position where an external connection terminal is to be
formed.
18. An active matrix substrate manufactured by the method of
manufacturing an active matrix substrate according to claim 1.
19. An active matrix substrate manufactured by the method of
manufacturing an active matrix substrate according to claim 8.
20. An active matrix substrate manufactured by the method of
manufacturing an active matrix substrate according to claim 15.
21. An active matrix substrate manufactured by the method of
manufacturing an active matrix substrate according to claim 16.
22. A liquid crystal display device comprising an active matrix
substrate manufactured by the method of manufacturing an active
matrix substrate according to claim 1.
23. A liquid crystal display device comprising an active matrix
substrate manufactured by the method of manufacturing an active
matrix substrate according to claim 8.
24. A liquid crystal display device comprising an active matrix
substrate manufactured by the method of manufacturing an active
matrix substrate according to claim 15.
25. A liquid crystal display device comprising an active matrix
substrate manufactured by the method of manufacturing an active
matrix substrate according to claim 16..Iadd.
26. A transfer method for transferring a thin film device formed on
a substrate onto a transcriptional body, the method comprising:
forming a separation layer over a substrate; forming the thin film
device over the separation layer; forming an insulation film over
the thin film device and the separation layer; selectively removing
at least a portion of the insulation film; and forming at least one
of a first electrode connected to the thin film device and an
external connection terminal in an area where the insulation film
is removed..Iaddend..Iadd.
27. The transfer method according to claim 26, further comprising:
adhering the thin film device to a transfer material with an
adhesive layer..Iaddend..Iadd.
28. The transfer method according to claim 27, further comprising:
producing exfoliation in the separation layer and/or at an
interface of the separation layer and the substrate to separate the
substrate from the separation layer..Iaddend..Iadd.
29. The transfer method according to claim 28, further comprising:
removing any portion of the separation layer remaining on the first
electrode to form an active matrix substrate using the transfer
material as a new substrate..Iaddend..Iadd.
30. The transfer method according to claim 26, selectively removing
at least a portion of the insulation film including forming at
least one contact hole for electrically connecting the first
electrode to the thin film device..Iaddend..Iadd.
31. The transfer method according to claim 30, further comprising
connecting the first electrode directly to an impurity layer which
constitutes the thin film device..Iaddend..Iadd.
32. The transfer method according to claim 30, further comprising:
forming at least one of a second electrode connected to an impurity
layer which constitutes the thin film device; and connecting the
first electrode to the corresponding second electrode connected to
the impurity layer..Iaddend..Iadd.
33. The transfer method according to claim 26, further comprising
forming at least one of a color filter and a light shielding film
after forming the first electrode..Iaddend..Iadd.
34. The transfer method according to claim 26, selectively removing
at least a portion of the insulation film includes selectively
removing at least a portion of the insulation film from a region
where an external connection terminal is to be
provided..Iaddend..Iadd.
35. The transfer method according to claim 34, further comprising
forming the external connection terminal as a conductive layer made
of a same material as the first electrode or a same material as a
second electrode connected to an impurity layer which constitutes
the thin film device..Iaddend..Iadd.
36. A transfer method for transferring a thin film device formed
over a substrate onto a transcriptional body, the method
comprising: forming a separation layer over a substrate; forming an
intermediate layer over the separation layer; forming the thin film
device over the intermediate layer; forming an insulation film over
the thin film device and the separation layer; selectively removing
the intermediate layer; and forming at least one of a first
electrode connected to the thin film device and an external
connection terminal in an area where the insulation film is
removed..Iaddend..Iadd.
37. The transfer method according to claim 36, further comprising:
adhering the thin film device to a transfer material with an
adhesive layer..Iaddend..Iadd.
38. The transfer method according to claim 37, further comprising:
producing exfoliation in the separation layer and/or at an
interface of the separation layer and the substrate to separate the
substrate from the separation layer..Iaddend..Iadd.
39. The transfer method according to claim 38, further comprising:
removing any portion of the separation layer remaining on the
intermediate layer and the first electrode to form an active matrix
substrate using the transfer material as a new
substrate..Iaddend..Iadd.
40. The transfer method according to claim 37, selectively removing
at least a portion of the insulation film including forming contact
holes for electrically connecting the electrode to the thin film
device..Iaddend..Iadd.
41. The transfer method according to claim 40, further comprising
connecting the first electrode directly to an impurity layer which
constitutes the thin film device..Iaddend..Iadd.
42. The transfer method according to claim 40, further comprising:
forming at least one second electrode connected to an impurity
layer which constitutes the thin film device; and connecting the
first electrode to the corresponding second electrode connected to
the impurity layer..Iaddend..Iadd.
43. The transfer method according to claim 37, further comprising
forming at least one of a color filter and a light shielding film
after forming the first electrode..Iaddend..Iadd.
44. The transfer method according to claim 37, selectively removing
at least a portion of the insulation film includes selectively
removing at least a portion of the insulation film from a region
where an external connection terminal is to be
provided..Iaddend..Iadd.
45. The transfer method according to claim 44, further comprising
forming the external connection terminal as a conductive layer made
of a same material as the first electrode or a same material as a
second electrode connected to an impurity layer which constitutes
the thin film device..Iaddend..Iadd.
46. A transfer method for transferring a thin film device formed on
a substrate onto a transcriptional body, the method comprising:
forming a separation layer over a substrate; forming the thin film
device over the separation layer; forming an insulation film over
the thin film device and the separation layer; forming at least one
of an electrode connected to the thin film device and an external
connection terminal over the insulation film; transferring at least
one of the thin film device, the electrode, and the external
connection terminal onto a transcriptional body; and selectively
removing the insulation layer to expose at least one of the
electrode and the external connection terminal..Iaddend..Iadd.
47. The transfer method according to claim 46, further comprising:
forming a light shielding layer that is overlapped with the thin
film device, and not overlapped with at least a portion of the
electrode..Iaddend..Iadd.
48. The transfer method according to claim 47, transferring at
least one of the thin film device, the electrode, and the external
connection terminal onto a transcriptional body including: adhering
the thin film device and the light shielding layer to a
transmissive transfer material with a transmissive adhesive layer;
and irradiating the separation layer through the transmissive
substrate to produce exfoliation in the separation layer and the
transmissive substrate to separate the transmissive substrate from
the separation layer..Iaddend..Iadd.
49. The transfer method according to claim 48, selectively
reviewing the insulation layer to expose at least one of the
electrode and the external connection terminal including: forming a
photoresist on a surface obtained by separating the transmissive
substrate; irradiating light to expose only a predetermined portion
of the photoresist using the light shielding layer as a mask,
followed by development to form a desired photoresist mask; and
selectively removing at least a portion of the insulation film by
using the photoresist mask..Iaddend..Iadd.
50. The transfer method according to claim 49, further comprising:
removing the photoresist mask to form an active matrix substrate
using the transfer material as a new substrate..Iaddend..Iadd.
51. A transfer method for transferring a thin film device formed on
a substrate onto a transcriptional body, the method comprising:
forming a separation layer over a substrate; forming at least one
of an electrode connected to the thin film device and an external
connection terminal on the separation layer; forming at least one
of the electrode and the external connection terminal and then
forming the thin film device; and transferring at least one of the
thin film device, the electrode, and the external connection
terminal onto a transcriptional body to expose at least one of the
electrode and the external connection terminal..Iaddend..Iadd.
52. The transfer method according to claim 51, further comprising:
adhering the thin film device to a transmissive transfer material
with a transmissive adhesive layer..Iaddend..Iadd.
53. The transfer method according to claim 52, further comprising:
producing exfoliation in the separation layer to separate the
substrate from the separation layer..Iaddend..Iadd.
54. The transfer method according to claim 51, further comprising
forming a conductive material layer on the separation layer where
an external connection terminal is to be formed..Iaddend..Iadd.
55. A method of manufacturing a device, the method comprising:
forming a separation layer over a substrate; forming the thin film
device over the separation layer; forming an insulation film over
the thin film device and the separation layer; selectively removing
at least a portion of the insulation film; and forming at least one
of a first electrode connected to the thin film device and an
external connection terminal in an area where the insulation film
is removed..Iaddend..Iadd.
56. A method of manufacturing a device, the method comprising:
forming a separation layer over a substrate; forming an
intermediate layer over the separation layer; forming the thin film
device over the intermediate layer; forming an insulation film over
the thin film device and the separation layer; selectively removing
the intermediate layer; and forming at least one of a first
electrode connected to the thin film device and an external
connection terminal in an area where the insulation film is
removed..Iaddend..Iadd.
57. A method of manufacturing a device, the method comprising:
forming a separation layer over a substrate; forming the thin film
device over the separation layer; forming an insulation film over
the thin film device and the separation layer; forming at least one
of an electrode connected to the thin film device and an external
connection terminal over the insulation film; transferring at least
one of the thin film device, the electrode, and the external
connection terminal onto a transcriptional body; and selectively
removing the insulation layer to expose at least one of the
electrode and the external connection terminal..Iaddend..Iadd.
58. A method of manufacturing a device, the method comprising:
forming a separation layer over a substrate; forming at least one
of an electrode connected to the thin film device and an external
connection terminal on the separation layer; forming at least one
of the electrode and the external connection terminal and then
forming the thin film device; and transferring at least one of the
thin film device, the electrode, and the external connection
terminal onto a transcriptional body to expose at least one of the
electrode and the external connection terminal..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing an
active matrix substrate using a method of transferring a thin film
device. The present invention also relates to an active matrix
substrate manufactured by the manufacturing method, and a liquid
crystal display device comprising this active matrix substrate as
one of a pair of substrates.
2. Description of Related Art
For example, a liquid crystal display using thin film transistors
(TFT) is manufactured through the step of forming thin film
transistors on a substrate by CVD or the like. Since the step of
forming thin film transistors on the substrate is accompanied with
high temperature processing, it is necessary to use material for
the substrate which has excellent heat resistance, i.e., material
having a high softening point and melting point. At present, silica
glass is used as a substrate which can resist a temperature of
about 10000C, and heat resistant glass is used as a substrate which
can resist a temperature of about 500.degree. C.
Namely, the substrate on which thin film elements are mounted must
satisfy conditions for producing the thin film transistors.
Therefore, the substrate used is determined so as to satisfy
conditions for manufacturing a device to be mounted thereon.
However, in consideration of only the steps after the substrate
comprising the thin film transistors such as TFT or the like
mounted thereon is completed, in some cases, the above-described
substrate is not always satisfactory.
For example, in the above-described manufacturing process
accompanied with high temperature processing, a quartz substrate, a
heat-resistant substrate, or the like is used. However, these
substrates are very expensive, and thus cause an increase in
product cost.
Also the glass substrate has the properties that it is heavy and
easily broken. A liquid crystal display used for portable
electronic apparatus such as a palm top computer, a portable
telephone, etc. is preferably light weight, can resist a little
deformation, and is hardly broken by dropping. However, in fact,
the glass substrate is generally heavy, less resistant to
deformation and is possibly broken by dropping.
In other words, there are gaps between the limitations caused by
manufacturing conditions and preferable characteristics required
for products, and it is very difficult to satisfy the conditions
and characteristics.
SUMMARY OF THE INVENTION
The present invention has been achieved in consideration of these
problems, and an object of the invention is to provide a novel
technique which permits independent free selection of a substrate
used in producing thin film devices, and a substrate (a substrate
having preferable properties for application of a product) used in,
for example, actual use of a product, and a completely new method
of effectively manufacturing an active matrix substrate having
excellent properties and a liquid crystal display device by using
the technique.
In order to achieve the object, the present invention may include
the following.
(1) The present invention provides a method of manufacturing an
active matrix substrate comprising a pixel portion including thin
film transistors connected to scanning lines and signal lines
arranged in a matrix, and pixel electrodes respectively connected
to terminals of the thin film transistors, the method may include:
forming a separation layer on the substrate; forming the thin film
transistors over the separation layer; forming an insulation film
on the thin film transistors and over the separation layer;
selectively removing at least a portion of the insulation film in a
region where each of the pixel electrodes is to be formed; forming
each of the pixel electrodes on the insulation film and the
separation layer in a region where at least a portion of the
insulation film has been removed; adhering the thin film
transistors to a transfer material with an adhesive layer producing
exfoliation in the separation layer and/or at an interface of the
separation layer and the substrate to separate the substrate from
the separation layer; and removing any portion of the separation
layer remaining on the pixel electrodes and under the insulation
film to form an active matrix substrate using the transfer material
as a new substrate.
In the method of manufacturing an active matrix substrate of the
present invention, the thin film transistors and the pixel
electrodes formed on the substrate are transferred to the desired
transfer material by the device transfer technique developed by the
applicant of the present invention. In this case, the device
transferred onto the transfer material is reverse to a normal
device. In the transferred device, consequently, the pixel
electrode is covered with the insulator layer such as an interlayer
insulation film or the like before transfer. If the insulation film
has a large thickness, a large voltage loss occurs in this portion,
and thus a sufficient voltage cannot be applied to a liquid
crystal.
Therefore, in the manufacturing method of the present invention, in
forming the thin film transistors and pixel electrodes on the
original substrate before transfer, at least a portion of the
insulator layer such as the interlayer insulation film or the like
is removed before the pixel electrodes are formed. In this case,
the entire insulator layer is preferably removed. However, when the
insulation film remaining unremoved is thin, at least a portion of
the insulator layer may be removed because no problem occurs in
application of a voltage to the liquid crystal.
In any case, by separating the original substrate after a device is
transferred onto the transfer material, the pixel electrode
partially appears at least in the vicinity of the surface of the
device. Therefore, a sufficient voltage can be applied to the
liquid crystal layer from this portion.
The insulation film remaining on the pixel electrodes can also be
separately removed in another step (for example, in a step after
transfer of the device).
(2) The present invention provides a method of manufacturing an
active matrix substrate comprising a pixel portion including thin
film transistors connected to scanning lines and signal lines
arranged in a matrix, and pixel electrodes respectively connected
to terminals of the thin film transistors, and the method may
include: forming a separation layer on a substrate; forming an
intermediate layer on the separation layer; forming the thin film
transistors on the intermediate layer; forming an insulation film
on the thin film transistors and the intermediate layer;
selectively removing a portion of the insulation film in a region
where each of the pixel electrodes is to be formed; forming each of
the pixel electrodes on the insulation film and the separation
layer in the region where at least a portion of the insulation film
is removed; adhering the thin film transistors to a transfer
material with an adhesive layer; producing exfoliation in the
separation layer and/or at an interface of the separation layer and
the substrate to separate the substrate from the separation layer;
and removing any portion of the separation layer remaining on the
intermediate layer and the pixel electrodes to form an active
matrix substrate using the transfer material as a new
substrate.
This invention is different from invention (1) in that the
intermediate layer is provided. The intermediate layer can comprise
a single layer film of an insulator, such as an SiO.sub.2 film or
the like, or a multilayered film comprising a laminate of an
insulator and a metal. The intermediate layer functions to
facilitate separation from the separation layer, protect the
transistors from contamination during removal of the separation
layer, ensure insulation properties of the transistors, and
suppress irradiation of the transistors with laser light.
In forming the thin film transistors and the pixel electrodes on
the original substrate before transfer, at least a portion of the
insulator layer such as an interlayer insulation film or the like,
which causes a problem in the later steps, is removed before the
pixel electrodes are formed. In this case, the whole insulation
film and intermediate layer below it are preferably removed at the
same time from the viewpoint of prevention of a loss of the voltage
applied to the liquid crystal. However, where the insulator layer
remaining unremoved is thin, a sufficient voltage can be applied to
the liquid crystal from the pixel electrodes. Therefore, at least a
portion of the insulation film may be removed.
In the present invention, by separating the original substrate
after a device is transferred to the transfer material, the pixel
electrode partially appears at least in the vicinity of the surface
of the device. Therefore, a voltage can sufficiently be applied to
the liquid crystal layer from this portion.
The insulation film remaining on the pixel electrodes can
separately be removed in another step (for example, the step after
transfer of the device).
(3) In invention (2), at least a portion of the insulation film may
be selectively removed in the step of forming contact holes for
electrically connecting the pixel electrodes to the thin film
transistors. Since the same manufacturing step is used for both
purposes, an increase in the number of the manufacturing steps can
be prevented.
(4) In invention (3), the contact holes may be used for connecting
the pixel electrodes directly to an impurity layer which
constitutes the thin film transistors.
Namely, in a structure in which the pixel electrodes are connected
directly to terminals(source layer or drain layer) of the thin film
transistors, the insulator layer such as an interlayer insulation
film or the like may be removed in formation of the contact holes
for connection.
(5) In invention (3), the contact holes may be used for connecting
the pixel electrodes to respective electrodes connected to an
impurity layer which constitutes the thin film transistors.
Namely, in a structure in which the pixel electrodes are connected
to terminals(the source layer or drain layer) of the thin film
transistors through electrodes made of a metal or the like (when
the pixel electrodes are in a layer above the electrodes of the
transistors), the insulator layer such as an interlayer insulation
film or the like may be removed in formation of the contact holes
for connection.
(6) In any one of inventions (1) to (5), at least one of a color
filter and a light shielding film may be after the step of forming
the pixel electrodes.
In the structure of normal thin film transistors, if the color
filter or the light shielding film is formed on the pixel
electrodes, application of a voltage to the liquid crystal layer
from the pixel electrodes is interfered with, and thus such a
structure cannot be used.
However, in the present invention, a device is reversed by
transfer, and thus the region where a voltage is applied to the
liquid crystal layer from the pixel electrode is formed on the side
(i.e., the thin film transistor side) opposite to a conventional
device. Therefore, even if the color filter or the light shielding
film has been previously formed on the original substrate before
transfer, no trouble occurs. In this case, only common electrodes
may be formed on the opposite substrate, and the color filter or
the light shielding film, which is conventionally formed on the
opposite substrate, need not be strictly aligned with the pixel
electrodes, thereby facilitating assembly of a liquid crystal
display device.
(7) In any one of inventions (1) to (6), in selectively removing at
least a portion of the insulation film, at least a portion of the
insulation film may be selectively removed in a region where an
external connection terminal is to be provided.
In an active matrix substrate, where the external connection
terminal (for example, a terminal for connecting a liquid crystal
driving IC) is required, this terminal also must be at a position
near at least the surface of the device.
Therefore, in the region where the external connection terminal is
provided, the insulator film such as an interlayer insulation film
or the like is removed. In this case, the under insulation film
(intermediate layer) must be removed in the same step or a
different step.
(8) In invention (7), in the region where at least a portion of the
insulation film is selectively removed for providing the external
connection terminal, a conductive layer formed from the same
material as the pixel electrodes or an electrode connected to an
impurity layer which constitutes the thin film transistors may be
formed. In this invention, the conductive layer may be used for
forming the external connection terminal.
(9) The present invention also may provide a method of
manufacturing an active matrix substrate having a pixel portion
including thin film transistors connected to scanning lines and
signal lines arranged in a matrix, and pixel electrodes connected
to terminals of the thin film transistors, and the method may
include: forming a separation layer on a transmissive substrate;
forming the thin film transistors over the separation layer or on a
predetermined intermediate layer formed on the separation layer;
forming an insulation film on the thin film transistors; forming
the pixel electrodes comprising a transparent conductive material
on the insulation film; forming a light shielding layer that is
overlapped with the thin film transistors and is not overlapped
with at least a portion of the pixel electrodes; adhering the thin
film transistors and the light shielding layer on a transmissive
transfer material with a transmissive adhesive layer; irradiating
the separation layer with light through the transmissive substrate
to produce exfoliation in the separation layer and/or at an
interface of the separation layer and the transmissive substrate to
separate the transmissive substrate from the separation layer;
forming a photoresist on a surface from which the transmissive
substrate is separated, or on the surface of a layer which appears
after removing any remaining portion of the separation layer;
irradiating light to expose only a predetermined portion of the
photoresist using the light shielding layer as a mask, followed by
development to form a desired photoresist mask; selectively
removing at least a portion of the intermediate layer and the
insulation film or at least a portion of the insulation film using
the photoresist mask; and removing the photoresist mask to form an
active matrix substrate using the transfer material as a new
substrate.
Although, in inventions (1) to (8), at least a portion of the
insulator layer below the pixel electrodes may be removed before
transfer, in this invention, at least a portion of the insulator
layer below the pixel electrodes may be removed in a self alignment
manner using the light shielding film after transfer.
Namely, the light shielding layer may be formed on the original
substrate before transfer, and may be used as an exposure mask
after transfer to form a desired resist pattern by utilizing the
fact that the light shielding layer is formed around the pixel
electrodes. Then, at least a portion of the insulator layer below
the pixel electrodes may be removed by using the resist pattern as
an etching mask.
(10) This invention provides a method of manufacturing an active
matrix substrate having a pixel portion including thin film
transistors connected to scanning lines and signal lines arranged
in a matrix, and pixel electrodes respectively connected to
terminals of the thin film transistors, and the method may include:
forming a separation layer on a substrate; forming the pixel
electrodes over the separation layer or on a predetermined
intermediate layer formed on the separation layer; forming an
insulation film on the pixel electrodes, forming the thin film
transistors on the insulation film, and respectively connecting the
thin film transistors to the pixel electrodes; adhering the thin
film transistors to a transfer material with an adhesive layer;
producing exfoliation in the separation layer and/or at an
interface of the separation layer and the substrate to separate the
substrate from the separation layer; and removing any portion of
the separation layer remaining on the intermediate layer to form an
active matrix substrate using the transfer material as a new
substrate.
In this invention, when the thin film transistors are formed on the
original substrate before transfer, the pixel electrodes are
previously formed. The original substrate before transfer is
separated after transfer to automatically expose the surfaces of
the pixel electrodes or position the pixel electrodes at least at
the surface of the device.
(11) In invention (10), a conductive material layer may be formed
on the separation layer or on the intermediate layer at a position
where an external connection terminal is to be formed.
When the thin film transistors are formed on the original substrate
before transfer, the conductive material layer for forming the
external connection terminal is previously formed as well as the
pixel electrode. The original substrate before transfer is
separated after transfer to automatically expose the surface of the
conductive material layer at the same time as the pixel electrodes,
or position the conductive material layer near the surface, leaving
the intermediate layer. In the latter case, the intermediate layer
is removed in the same step or a different step to expose the
surface of the conductive material layer. The conductive material
layer with the exposed surface serves as the external connection
terminal.
(12) This invention provides an active matrix substrate
manufactured by the method of manufacturing an active matrix
substrate of any one of inventions (1) to (11). Since limitations
due to the manufacturing conditions are eliminated so that the
substrate can freely be selected, a novel active matrix substrate,
which has not yet been realized, can be realized.
(13) This invention provides a liquid crystal display device
comprising an active matrix substrate manufactured by the method of
manufacturing an active matrix substrate of any one of inventions
(1) to (11). For example, it is possible to realize an active
matrix type liquid crystal display device comprising a plastic
substrate and having flexibility.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view showing the first step of a method of
transferring a thin film element.
FIG. 2 is a sectional view showing the second step of a method of
transferring a thin film element.
FIG. 3 is a sectional view showing the third step of a method of
transferring a thin film element.
FIG. 4 is a sectional view showing the fourth step of a method of
transferring a thin film element.
FIG. 5 is a sectional view showing the fifth step of a method of
transferring a thin film element.
FIG. 6 is a sectional view showing the sixth step of a method of
transferring a thin film element.
FIG. 7 is a drawing illustrating the whole configuration of a
liquid crystal display device.
FIG. 8 is a drawing illustrating the configuration of a principal
portion of a liquid crystal display device.
FIG. 9 is a sectional view illustrating the structure of a
principal portion of a liquid crystal display device.
FIG. 10 is a sectional view showing the first step of a method of
manufacturing an active matrix substrate in accordance with a first
embodiment of the present invention.
FIG. 11 is a sectional view showing the second step of the method
of manufacturing an active matrix substrate in accordance with the
first embodiment of the present invention.
FIG. 12 is a sectional view showing the third step of the method of
manufacturing an active matrix substrate in accordance with the
first embodiment of the present invention.
FIG. 13 is a sectional view showing the fourth step of the method
of manufacturing an active matrix substrate in accordance with the
first embodiment of the present invention.
FIG. 14 is a sectional view showing the fifth step of the method of
manufacturing an active matrix substrate in accordance with the
first embodiment of the present invention.
FIG. 15 is a sectional view showing the first step of a method of
manufacturing an active matrix substrate in accordance with a
modified embodiment of the first embodiment.
FIG. 16 is a sectional view showing the second step of the method
of manufacturing an active matrix substrate in accordance with the
modified embodiment of the first embodiment.
FIG. 17 is a sectional view showing the third step of the method of
manufacturing an active matrix substrate in accordance with the
modified embodiment of the first embodiment.
FIG. 18 is a sectional view showing the first step of a method of
manufacturing an active matrix substrate in accordance with a
second embodiment of the present invention.
FIG. 19 is a sectional view showing the second step of the method
of manufacturing an active matrix substrate in accordance with the
second embodiment of the present invention.
FIG. 20 is a sectional view showing the structure of a principal
portion of a liquid crystal display device in accordance with a
third embodiment of the present invention.
FIG. 21 is a drawing showing electrical connection in the liquid
crystal display device shown in FIG. 20.
FIG. 22 is a sectional view showing the first step of a method of
manufacturing an active matrix substrate in accordance with the
third embodiment of the present invention.
FIG. 23 is a sectional view showing the second step of the method
of manufacturing an active matrix substrate in accordance with the
third embodiment of the present invention.
FIG. 24 is a sectional view showing the third step of the method of
manufacturing an active matrix substrate in accordance with the
third embodiment of the present invention.
FIG. 25 is a sectional view showing the fourth step of the method
of manufacturing an active matrix substrate in accordance with the
third embodiment of the present invention.
FIG. 26 is a sectional view showing the fifth step of the method of
manufacturing an active matrix substrate in accordance with the
third embodiment of the present invention.
FIG. 27 is a sectional view showing the sixth step of the method of
manufacturing an active matrix substrate in accordance with the
third embodiment of the present invention.
FIG. 28 is a sectional view showing the first step of a method of
manufacturing an active matrix substrate in accordance with a
modified embodiment of the third embodiment.
FIG. 29 is a sectional view showing the second step of the method
of manufacturing an active matrix substrate in accordance with the
modified embodiment of the third embodiment.
FIG. 30 is a sectional view showing the third step of the method of
manufacturing an active matrix substrate in accordance with the
modified embodiment of the third embodiment.
FIG. 31 is a sectional view showing the first step of a method of
manufacturing an active matrix substrate in accordance with a
fourth embodiment of the present invention.
FIG. 32 is a sectional view showing the second step of the method
of manufacturing an active matrix substrate in accordance with the
fourth embodiment of the present invention.
FIG. 33 is a sectional view showing the third step of the method of
manufacturing an active matrix substrate in accordance with the
fourth embodiment of the present invention.
FIG. 34 is a sectional view showing the fourth step of the method
of manufacturing an active matrix substrate in accordance with the
fourth embodiment of the present invention.
FIG. 35 is a sectional view showing the fifth step of the method of
manufacturing an active matrix substrate in accordance with the
fourth embodiment of the present invention.
FIG. 36 is a sectional view showing the sixth step of the method of
manufacturing an active matrix substrate in accordance with the
fourth embodiment of the present invention.
FIG. 37 is a sectional view showing the seventh step of the method
of manufacturing an active matrix substrate in accordance with the
fourth embodiment of the present invention.
FIG. 38 is a sectional view of a liquid crystal display device in
accordance with the fourth embodiment of the present invention.
FIG. 39 is a sectional view showing the first step of a method of
manufacturing an active matrix substrate in accordance with a fifth
embodiment of the present invention.
FIG. 40 is a sectional view showing the second step of the method
of manufacturing an active matrix substrate in accordance with the
fifth embodiment of the present invention.
FIG. 41 is a sectional view showing the third step of the method of
manufacturing an active matrix substrate in accordance with the
fifth embodiment of the present invention.
FIG. 42 is a sectional view of a liquid crystal display device in
accordance with the fifth embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
An exfoliating method in accordance with an embodiment of the
present invention is described in detail below with reference to
the attached drawings.
In the present invention, an active matrix substrate is formed by
using "the device transfer technique" developed by the applicant of
this invention. Therefore, the contents of "the device transfer
technique" are first described.
(Contents of device transfer technique)
FIGS. 1 to 6 are drawings illustrating the contents of the device
transfer technique.
[Step 1]
As shown in FIG. 1, a separation layer (light absorbing layer) 120
is formed on a substrate 100.
The substrate 100 and the separation layer 120 are described.
(1) Description of the substrate 100
The substrate 100 preferably has transmissivity which allows
transmission of light. In this case, the light transmittance is
preferably 10% or more, and more preferably 50% or more. With too
low transmittance, attenuation (loss) of light is increased, and
thus a large quantity of light is required for exfoliating the
separation layer 120.
Also the substrate 100 is preferably made of a material having high
reliability, particularly a material having excellent heat
resistance. The reason for this is that for example, when a
transferred layer 140 or an intermediate layer 142, which will be
described below, are formed, the process temperature is sometimes
increased (for example, about 350 to 1000.degree. C.) according to
the type and the forming method. However, in this case, in forming
the transferred layer 140 or the like on the substrate 100 having
excellent heat resistance, the ranges of the film forming
conditions such as the temperature condition, etc. are widened.
Therefore, if the highest temperature in formation of the
transferred layer 140 is Tmax, the substrate 100 is preferably made
of a material having a strain point higher than Tmax. Specifically,
the material for forming the substrate 100 preferably has a strain
point of 350.degree. C. or higher, more preferably 500.degree. C.
or higher. Examples of such materials include heat resistant glass
such as quartz glass, Corning 7059, Nihon Denki glass OA-2, and the
like Although the thickness of the substrate 100 is not limited,
the thickness is preferably about 0.1 to 5.0 mm, more preferably
about 0.5 to 1.5 mm. With the substrate 100 having an excessively
small thickness, the strength deteriorates, and with the substrate
100 having an excessively large thickness, attenuation of light
easily occurs when the substrate 100 exhibits low transmittance.
When the substrate 100 exhibits high transmittance, the thickness
thereof may exceed the upper limit. In order to permit uniform
irradiation, the substrate 100 preferably has a uniform
thickness.
(2) Description of the separation layer 120
The separation layer 120 has the property of absorbing light to
produce exfoliation in the layer and/or the interface thereof
(referred to as "internal exfoliation" and "interfacial
exfoliation" hereinafter), and preferably, the adhering strength
between the atoms or molecules of the material which constitutes
the separation layer 120 is reduced or eliminated by irradiation of
light, i.e., internal exfoliation and/or interfacial exfoliation
results from ablation.
Further, in some cases, gases are discharged from the separation
layer 120 by irradiation of light to cause a separating effect.
Namely, the components contained in the separation layer 120 are
discharged as gases, or the separation layer 120 absorbs light to
become a gas for a moment and the vapor is discharged to contribute
to separation. Examples of the composition of the separation layer
120 include the following A to E.
A. Amorphous silicon (a-Si)
Amorphous silicon may contain hydrogen (H). In this case, the H
content is preferably about 2 atomic % or more, more preferably
about 2 to 20 atomic %. When a predetermined amount of hydrogen (H)
is present, hydrogen is discharged by irradiation of light to
generate internal pressure in the separation layer 120, which
serves as the force to exfoliate upper and lower thin films. The
content of hydrogen (H) in amorphous silicon can be adjusted by
appropriately setting film deposition conditions, e.g., the gas
composition, gas pressure, gas atmosphere, gas flow rate,
temperature, substrate temperature, input power, etc. of CVD.
B. Various oxide ceramics such as silicon oxide or silicates,
titanium oxide or titanates, zirconium oxide or zirconates,
lanthanum oxide or lanthanates, and the like, dielectric material
(ferroelectric material) or semiconductor.
Examples of silicon oxides include SiO, SiO.sub.2 and Si.sub.3
O.sub.2, and examples of silicate compounds include K.sub.2
SiO.sub.3, Li.sub.2 SiO.sub.3, CaSiO.sub.3, ZrSiO.sub.4, and
Na.sub.2 SiO.sub.3.
Examples of titanium oxides include Tio, Ti.sub.2 O.sub.3 and
TiO.sub.2, and examples of titanate compounds include BaTiO.sub.4,
BaTiO.sub.3, Ba.sub.2 Ti.sub.9 O.sub.20, BaTi.sub.5 O.sub.1 l,
CaTiO.sub.3, SrTiO.sub.3, PbTiO.sub.3, MgTiO.sub.3, ZrTiO.sub.2,
SnTiO.sub.4, Al.sub.2 TiO.sub.5, and FeTiO.sub.3.
Zirconium oxide is ZrO.sub.2, and examples of zirconate compounds
include BaZrO.sub.3, ZrSiO.sub.4, PbZrO.sub.3, MgZrO.sub.3, and
K.sub.2 ZrO.sub.3.
C. Ceramics such as PZT, PLZT, PLLZT, PBZT and the like, or
dielectric material (ferroelectric material)
D. Nitride ceramics such as silicon nitride, aluminum nitride,
titanium nitride, and the like.
E. Organic polymer material
As an organic polymer material, any material having bonds such as
--CH--, --CO-- (ketone), --CONH-- (amido), --NH-- (imido), COO--
(ester), --N.dbd.N-- (azo), --CH.dbd.N-- (Schiff) or the like
(these bonds are cut by light irradiation), particularly any
material having many bonds of such a type can be used. The organic
polymer material may have an aromatic hydrocarbon (at least one
benzene ring or condensed ring thereof) in the composition
thereof.
Examples of such organic polymer materials include polyolefines
such as polyethylene and polypropylene, polyimide, polyamide,
polyester, polymethylmethacrylate (PMMA), polyphenylenesulfide
(PPS), polyethersulfone (PES), epoxy resins, and the like.
F. Metal
Examples of metals include Al, Li, Ti, Mn, In, Sn, Y, La, Ce, Nd,
Pr, Gd, Sm, and alloys containing at least one of these metals.
Although the thickness of the separation layer 120 depends upon
conditions such as the purpose of exfoliation, the composition of
the separation layer 120, the layer structure, the forming method,
etc., the thickness is preferably about 0.5 nm to 20 pm, more
preferably about 1 nm to 2 .mu.m, most preferably about 5 nm to 1
.mu.m. With the separation layer 120 having an excessively small
thickness, uniformity of film deposition deteriorates, thereby
causing nonuniformity in exfoliation. With the separation layer 120
having an excessively large thickness, the power of light (quantity
of light) must be increased to ensure good exfoliating properties
of the separation layer 120, and much time is required for removing
the separation layer 120 later. The thickness of the separation
layer 120 is preferably as uniform as possible.
The method of forming the separation layer 2 is not limited, and is
appropriately selected according to conditions such as the film
composition, the thickness, and the like. Examples of the forming
method include various vapor phase deposition methods such as CVD
(including MOCVD, low-pressure CVD and ECR-CVD), evaporation,
molecular beam evaporation (MB), sputtering, ion plating, PVD, and
the like; various plating methods such as electroplating, immersion
plating (dipping), electroless plating, and the like; coating
methods such as Langmuir-Blodgett's (LB) technique, spin coating,
spray coating, roll coating, and the like; various printing
methods; a transfer method; an ink jet method; a powder jet method;
and the like. The separation layer may be formed by a combination
of at least two of these methods.
For example, where the composition of the separation layer 120
comprises amorphous silicon (a-Si), the layer is preferably formed
by CVD, particularly low-pressure CVD or plasma CVD.
Where the separation layer 120 is made of ceramic by a sol-gel
method, or an organic polymer material, it is preferably formed by
a coating method, particularly spin coating.
[Step 2]
Next, the transferred layer (thin film device layer) 140 is formed
on the separation layer 120, as shown in FIG. 2.
An enlarged section of portion K (shown by a one-dot chain line in
FIG. 2) of the thin film device layer 140 is shown on the right
side of FIG. 2. As shown in FIG. 2, the thin film device layer 140
comprises TFTs (thin film transistor) formed on, for example, an
SiO.sub.2 film (intermediate layer) 142, and the TFT comprises
source and drain layers 146 formed by introducing N-type impurities
in a polysilicon layer, a channel layer 144, a gate insulation film
148, a polysilicon gate 150, a protecting film 154, and an
electrode 152 made of, for example, aluminum.
Although, in this embodiment, as the intermediate layer provided in
contact with the separation layer 120, the SiO.sub.2 film is used,
another insulation film can also be used. The thickness of the
SiO.sub.2 film (intermediate layer) is appropriately determined
according to the purpose of forming, the degree of the function
exhibited, but the thickness is preferably about 10 nm to 5 .mu.m,
more preferably about 40 nm to 1 .mu.m. The intermediate layer is
formed for various purposes. For example, the intermediate layer is
formed for exhibiting at least one of the functions as a protection
layer for physically or chemically protecting the transferred layer
140, an insulation layer, a conductive layer, laser light shielding
layer, a barrier layer for preventing migration, and a reflecting
layer.
In some cases, the intermediate layer comprising the SiO.sub.2 film
or the like is not formed, and the transferred layer (thin film
layer) 140 may be formed directly on the separation layer 120. An
example of cases in which the intermediate layer need not be
provided is a case in which a TFT in the transferred layer is a
bottom gate structure transistor, and no problem with contamination
occurs even if the bottom gate is exposed to the surface after
transfer.
The transferred layer 140 (thin film device layer) is a layer
containing thin film devices such as TFTs or the like, as shown on
the right hand side of FIG. 2. Besides TFTs, examples of thin film
devices include thin film diodes and other thin film semiconductor
devices, electrodes (for example, transparent electrodes such as
ITO and mesa films), switching devices, memory, actuators such as
piezo-electric devices, micro mirrors (piezo thin film ceramics),
magnetic recording thin film heads, coils, inductors, thin film
materials with high permeability and micro magnetic devices
comprising a combination of these materials, filters, reflecting
films, dichroic mirrors, and the like.
Such a thin film device is generally formed through a relatively
high process temperature in relation to the forming method thereof.
Therefore, in this case, the substrate 100 must-resist the process
temperature and have high reliability, as described above.
[Step 3]
Next, the thin film device layer 140 is adhered to a transfer
material 180 through an adhesive layer 160, as shown in FIG. 3.
Preferable examples of an adhesive which constitutes the adhesive
layer 160 include various curing adhesives such as reactive curing
adhesives, heat curing adhesives, light curing adhesives such as
ultraviolet curing adhesives, anaerobic curing adhesives, and the
like. As the composition of the adhesive, any type such as an epoxy
type, an acrylate type, or a silicone type, may be used. The
adhesive layer 160 is formed by, for example, the coating
method.
In the use of the curing adhesive, for example, the curing adhesive
is coated on the transferred layer (thin film device layer) 140,
the transfer material 180 is adhered to the curing adhesive, and
then the curing adhesive is cured by the curing method according to
the properties of the curing adhesive, to bond and fix the
transferred layer (thin film device layer) 140 and the transfer
material 180.
Unlike the case shown in the drawing, the adhesive layer 160 may be
formed on the transfer material 180 side, and the transferred layer
(thin film device layer) 140 may be adhered to the adhesive layer
160. For example, when the transfer material 180 has the adhesive
function, the formation of the adhesive layer 160 may be
omitted.
Although the transfer material 180 is not limited, a substrate,
particularly a transparent substrate can be used. Such a substrate
may be a flat plate or a curved plate. As the transfer material
180, a material having heat resistance, corrosion resistance, and
the like which are poorer than the substrate 100 may be used. The
reason for this is that in the present invention, since the
transferred layer (thin film device layer) 140 is formed on the
substrate 100 side, and is then transferred to the transfer
material 180, the conditions required for the transferred layer
(thin film device layer) 140, particularly, heat resistance, does
not depend upon the temperature conditions in forming the
transferred layer (thin film device layer) 140.
Therefore, when the highest temperature in formation of the
transferred layer 140 is Tmax, as the material for forming the
transfer material 180, a material having a glass transition point
(Tg) or softening point lower than Tmax can be used. For example,
the transfer material 180 preferably comprises a material having a
glass transition point (Tg) or softening point of 800.degree. C. or
less, more preferably 500.degree. C. or less, most preferably
320.degree. C. or less.
The transfer material 180 may have as a mechanical property some
rigidity (strength), but it may have flexibility and
elasticity.
As the material which constitutes the transfer material 180,
various synthetic resins or various types of glass may be used,
particularly various synthetic resins or inexpensive ordinary glass
materials (low melting point) are preferably used.
Synthetic resins may be either thermoplastic resins or heat curing
resins. Examples of such synthetic resins include polyolefins such
as polyethylene, polypropylene, ethylene-propylene copolymers,
ethylene-vinyl acetate copolymers (EVA), and the like; cyclic
polyolefins; modified polyolefins; polyvinyl chloride;
polyvinylidene chloride; polystyrene; various polyesters such as
polamide, polyimide, polycarbonate, poly-(4-methylpentene-1),
ionomer, acrylic resins, polymethyl methacrylate, acryl-styrene
copolymers (AB resins), butadiene-styrene copolymers, polyolefin
copolymers (EVOH), polyetheyele terephthalate (PET), polubutylene
terephthalate (PBT), polycyclohexane terephthalate (PCT), and the
like; polyethers; polyether ketones (PEK); polyether ether ketones
(PEKK); polyether imide; polyacetal (POM); polyphenylene oxide;
modified polyphenyl oxide; polyacrylate; aromatic polyetsers
(liquid crystal polymers); polytetrafluoroethene; polyvinylene
fluoride; other fluororesins; various thermoplastic elastomers of
styrene, polyolefin, polyvinyl chloride, polyurethane,
fluororubber, chlorinated polyethylene, and the like; epoxy resins;
phenolic resins; urea resins; melamine resins; unsaturated
polyesters; silicone resins; polyurethane; and copolymers, blends
and polymer alloys mainly consisting of these polymers; the like.
These polymers may be used singly or in combination of at least two
of them (for example, as a laminate of at least two layers).
Examples of glass materials include silicate glass (quartz glass),
alkali silicate glass, soda-lime glass, potash lime glass, lead
(alkali) glass, barium glass, borosilicate glass, and the like. Of
these types of glass, glass other than silicate glass is preferable
because it has a melting point lower than silicate glass, is
relatively easily formed and processed, and inexpensive.
When a member made of a synthetic resin is used as the transfer
material 180, there are various advantages that the larger transfer
material 180 can be integrally formed, the member having a
complicated shape such as a curved surface or an unevenness can
easily be produced, and the material cost and production cost are
low. Therefore, the use of a synthetic resin is advantageous for
producing a large low-priced device (for example, a liquid crystal
display).
The transfer material 180 may comprise an independent device, such
as a liquid crystal cell, or a portion of a device, such as a color
filter, an electrode layer, a dielectric layer, an insulation layer
or a semiconductor device.
The transfer material 180 may be made of a material such as a
metal, ceramic, a stone material, wood paper, or the like, or may
comprise any desired surface which constitutes a product (a surface
of a watch, a surface on an air conditioner, a surface of a printed
board, or the like), or a surface of a structure, such as a wall, a
column, a ceiling, a window glass, or the like.
[Step 4]
Next, the substrate 100 is irradiated with light from the back
thereof, as shown in FIG. 4.
The light passes through the substrate 100 and is then applied to
the separation layer 120. This causes internal exfoliation and/or
interfacial exfoliation in the separation layer 120, thereby
decreasing or eliminating the adhering strength.
The principle of occurrence of internal exfoliation and/or
interfacial exfoliation in the separation layer 120 is thought to
be based on ablation occurring in the constituent material of the
separation layer 120, discharge of gases contained in the
separation layer 120 and a phase change such as melting or
vaporization caused immediately after irradiation.
The ablation means that a solid material (the constituent material
of the separation layer 120) which absorbs light is photochemically
or thermally excited to discharge atoms or molecules due to cutting
of bonds in the surface and inside of the material. This mainly
occurs as the phenomenon that a phase change such as melting,
vaporization (evaporation) or the like occurs in the whole or part
of the constituent material of the separation layer 120. Also, in
some cases, the phase change causes a fine foam state, and
decreases the adhering strength.
The type of the exfoliation produced in the separation layer 120,
i.e., internal exfoliation, interfacial exfoliation or both types
of exfoliation, depends upon the composition of the separation
layer 120, and other various factors. One of the factors is the
type, wavelength, strength, arrival depth and the like of
irradiating light.
As the irradiating light, any light can be used as long as it
generates internal exfoliation and/or interfacial exfoliation in
the separation layer 120. Examples of the irradiating light include
X-rays, ultraviolet rays, visible light, infrared light (heat
rays), laser light, millimeter waves, microwaves, electron rays,
radiation (.alpha.-rays, .beta.-rays and .gamma.-rays), and the
like. Of these types of light, laser light is preferable from the
viewpoint that exfoliation (ablation) is easily produced in the
separation layer 120.
As a laser device for generating laser light, various gas lasers,
solid lasers (semiconductor lasers), and the like can be used.
However, an excimer laser, an Nd-YAG laser, an Ar laser, a CO.sub.2
laser, a CO laser, an He--Ne laser and the like are preferably
used, and an eximer laser is particularly preferable.
Since the eximer laser outputs high energy in a short wavelength
region, it can generate ablation in the separation layer 120 within
a very short time, and thus peel off the separation layer 120 with
hardly producing a temperature rise in the transfer material 180
and the substrate 100 adjacent to the separation layer 120, i.e.,
with producing neither deterioration nor damage.
In producing ablation in the separation layer 120, the wavelength
of the irradiating laser light is preferably about 100 to 350 nm.
In regard to the transmittance of the substrate 100 for the light
wavelength, the substrate 100 has the property that transmittance
for a wavelength of 250 nm rapidly increases. In this case,
irradiation is performed with light at a wavelength over 300 nm
(for example, Xe--Cl eximer laser light with 308 nm).
For example, when a phase change such as gas discharge, evaporation
or sublimation is generated in the separation layer 120 to provide
a separation property, the wavelength of the irradiating laser
light is preferably about 350 to 1200 nm.
The energy density of the irradiating laser light, particularly the
energy density of eximer laser, is preferably about 10 to 5000
mJ/cm.sup.2, more preferably about 100 to 500 mJ/cm.sup.2. The
irradiation time is preferably about 1 to 1000 nsec, more
preferably about 10 to 100 nsec. With a low energy density or a
short irradiation time, sufficient ablation does not occur, and
with a high energy density or a long irradiation time, the
irradiating light transmitted through the separation layer 120
might produce adverse effects on the transferred layer 140.
As a measure against the adverse effects caused by arrival of the
irradiating light transmitted through the separation layer at the
transferred layer 140, for example, a metal film of tantalum (Ta)
or the like is formed on the separation layer (laser absorbing
layer) 120. This causes the laser light transmitted through the
separation layer 120 to be totally reflected by the interface of
the metal film, thereby causing no adverse effect on the thin film
element provided thereon.
Irradiation is preferably performed with the irradiating light,
typically laser light, so that the strength is made uniform. The
irradiation direction of the irradiating light is not limited to
the direction perpendicular to the separation layer 120, and the
irradiation direction may be a direction at a predetermined angle
with respect to the separation layer 120.
Where the area of the separation layer 120 is larger than the
irradiation area of the irradiating light in one irradiation, the
total region of the separation layer 120 can be irradiated several
times with the irradiating light. The same position may be
irradiated two times or more, or the same region or different
regions may be irradiated with different types of irradiating light
(laser light) or irradiating light at different wavelengths
(wavelength ranges).
Next, as shown in FIG. 5, force is applied to the substrate 100 to
separate the substrate 100 from the separation layer 120. Although
not shown in FIG. 5, the separation layer sometimes adheres to the
substrate 100 after separation.
Next, as shown in FIG. 6, the remaining separation layer 120 is
removed by, for example, washing, etching, ashing, polishing or a
combination thereof. As a result, the transferred layer (thin film
device layer) 140 is transferred to the transfer material 180.
When part of the separation layer also adheres to the separated
substrate 100, it is removed by the same method as described above.
When the substrate 100 is made of an expensive material such as
quartz glass or a rare material, the substrate is preferably
recycled. Namely, the present invention can be applied to the
substrate 100, which is desired to be recycled, with high
availability.
The transferred layer (thin film device layer) 140 is completely
transferred to the transfer material 180 through the above steps.
Then the SiO.sub.2 film adjacent to the transferred layer (thin
film device layer) 140 may be removed. and a desired protecting
film may be formed.
In the present invention, since the transferred layer (thin film
device layer) 140, which is a layer to be exfoliated, is not
directly exfoliated, but exfoliated through the separation layer
adhered thereto, the transferred layer 140 can easily, securely and
uniformly be exfoliated (transferred) regardless of the properties
of the layer to be exfoliated (the transferred layer 140), and
conditions, etc., without damage to the layer to be exfoliated (the
transferred layer 140) due to the exfoliating operation. Therefore,
it is possible to maintain the high reliability of the transferred
layer 140.
The device transfer technique is summarized above.
Next, an example of the method of manufacturing a liquid crystal
display device using the above device transfer technique is
described.
(First embodiment)
In this embodiment, an example of the process for manufacturing an
active matrix type liquid crystal display device comprising an
active matrix substrate, as shown in FIGS. 7, 8 and 9, using the
thin film device transfer technique is described.
(Configuration of liquid crystal display device)
As shown in FIG. 7, an active matrix type liquid crystal display
device comprises backlights 400, a polarizer 420, an active matrix
substrate 440, a liquid crystal 460, an opposite substrate 480, and
a polarizer 500. In the present invention, when a flexible
substrate is used as each of the active matrix substrate 440 and
the opposite substrate 480, a lightweight active matrix type liquid
crystal panel having flexibility and resistance to shock can be
realized as a reflective liquid crystal panel by using a reflecting
plate in place of the illumination light sources 400.
The active matrix substrate 440 used in this embodiment is an
active matrix substrate with a built-in driver in which TFTs are
arranged in a pixel portion 442, and a driver circuit (a scanning
line driver and data line driver 444) is provided.
Namely, as shown in FIG. 8, the pixel portion 442 on the active
matrix substrate 440 comprises a plurality of TFTs (M1) in which
gates are connected to scanning lines S1, and ends (terminals) are
connected to data lines D1, the other ends being connected to the
liquid crystal 460. Similarly, the driver portion 444 also
comprises TFT (M2).
FIG. 9 is a sectional view showing a principal portion of the
active matrix type liquid crystal display device. As shown in the
left side of FIG. 9, the TFT (M1) in the pixel portion 442
comprises source-drain layers 1100a and 1100b, a gate insulation
film 1200a, a gate electrode 1300a, an insulation film 1500, and
source-drain electrodes 1400a and 1400b. Reference numeral 1700
denotes a pixel electrode comprising an ITO film or a metallic
film. With the ITO film, a transmissive liquid crystal panel is
formed, and with the metallic film, a reflective liquid crystal
panel is formed.
Reference numeral 1702 denotes a region (voltage applied region)
where a voltage is applied to the liquid crystal 460 from the pixel
electrode 1700.
Also, as shown on the right hand side of FIG. 9, the TFT (M2) which
constitutes the driver portion 444 comprises source-drain layers
1100c and 1100d, a gate insulation film 1200b, a gate electrode
1300b, an interlayer insulation film 1500, and source-drain
electrodes 1400c and 1400d.
In FIG. 9, reference numeral 480 denotes, for example, an opposite
substrate (for example, a soda glass substrate), and reference
numeral 482 denotes a common electrode.
Reference numeral 1000 denotes a underlaying SiO.sub.2 film
corresponding to an "intermediate layer". Reference numeral 1600
denotes an insulation film (for example, a CVD SiO.sub.2 film), and
reference numeral 1800 denotes an adhesive layer. Reference numeral
1900 denotes a substrate (transfer material) comprising, for
example, soda glass.
In this embodiment, attention should be given to the point that a
recess (through hole) is selectively formed in the insulation film
1600 and the underlying SiO.sub.2 film, and the pixel electrode
1700 is bent downward along the surface of the recess and has the
exposed back at the bottom thereof to form the voltage applied
region 1702 for the liquid crystal 460. This eliminates
interposition of the insulation films (the underlying SiO.sub.2
film (intermediate layer) 1000 and the interlayer insulation film
1500) between the pixel electrode 1700 and the liquid crystal layer
460, thereby preventing a voltage loss.
If the insulation films remain on the pixel electrode without
causing a problem in driving the liquid crystal, the insulation
films need not be completely removed. For example, although, in
FIG. 9, the underlying SiO.sub.2 film (intermediate layer) 1000 is
completely removed from the region 1702, the underlying SiO.sub.2
film (intermediate layer) 1000 remaining unremoved causes no
problem as long as it is thin and causes a little voltage loss.
A detailed description will now be made.
In this embodiment, the active matrix substrate is manufactured by
transferring, to a desired transfer material, thin film transistors
and pixel electrodes which are formed on the predetermined
substrate. In this case, the device transferred onto the transfer
material is reverse to a normal device. As a result, in the
transferred device, the pixel electrode is covered with an
insulator film in the state before transfer such as the interlayer
insulation film or the like.
In this state, in assembly of a liquid crystal display device
(liquid crystal panel), the insulator layer is interposed between
the pixel electrode and the liquid crystal layer, and thus a
voltage loss in this portion cannot be neglected.
Therefore, in manufacturing the active matrix substrate, a method
is used in which in forming the thin film transistor and the pixel
electrode on the original substrate before transfer, at least a
portion of the insulator layer such as the interlayer insulation
film or the like, which causes a problem in the later steps, is
previously removed before the pixel electrode is formed. This
causes a portion of the pixel electrode to appear in the surface or
the vicinity of the surface by separating the original substrate
after the device is transferred to the transfer material. It is
thus possible to apply a voltage from this portion. Therefore, the
above-described trouble (voltage loss) does not occur.
Even if an unnecessary insulation film remains on the pixel
electrode after the thin film transistor is transferred, the
remaining insulating film is removed in another step, thereby
causing no problem.
FIG. 9 shows a liquid crystal display device manufactured by using
the active matrix substrate produced by the above method. [Process
for manufacturing liquid crystal display device]
The process for manufacturing the principal portion of the liquid
crystal display device shown in FIG. 9 is described below with
reference to FIGS. 10 to 14.
First, as shown in FIG. 10, TFT (M1, M2) are formed on a substrate
(for example, a quartz substrate) 3000 having high reliability and
transmitting laser light through the manufacturing process shown in
FIGS. 1 and 2, and an insulation film 1600 is formed. In FIG. 10,
reference numeral 3100 denotes a separation layer (laser absorbing
layer) comprising, for example, amorphous silicon. Reference
numerals 1400a and 1400b denote electrodes (transistor electrodes)
made of, for example, aluminum which are connected to n.sup.+
layers 1100a and 1100b, respectively, which constitute the TFT of
the pixel portion.
In FIG. 10, both TFTs (M1, M2) are N-type MOSFET. However, the TFT
is not limited to this, p-type MOSFET and CMOS structures may be
used.
Next, as shown in FIG. 11, the insulation film 1600 is selectively
etched to form a contact hole (opening) 1620, and the insulation
film 1600 and the underlying SiO.sub.2 film 1000 are selectively
etched to form an opening (through hole) 1610.
These two openings (1610 and 1620) are simultaneously formed in a
common etching step. Namely, in forming the contact hole 1620 for
connecting the pixel electrode to TFT, the insulation film 1600 and
the underlying SiO.sub.2 film (intermediate layer) 1000 are also
selectively removed. Therefore, the special step for forming the
opening 1610 is unnecessary, and an increase in the number of the
manufacturing steps can thus be prevented.
Although, in FIG. 11, the insulation 1600 and the underlying
SiO.sub.2 film (intermediate layer) 1000 are completely removed
when the opening 1610 is formed, these films may be left as long as
a sufficient voltage can be applied to the liquid crystal. For
example, the underlying SiO.sub.2 film (intermediate layer) 1000
may be left.
Even when the insulation film 1600 and the underlying SiO.sub.2
film (intermediate layer) 1000 are completely removed in formation
of the opening 1610, a method may be used in which these films are
not removed at a time in this step, but these films are partially
left in this step, and the films remaining on the pixel electrode
are removed in a later step (for example, the step after the thin
film transistor is transferred) to expose the surface of the pixel
electrode.
Next, as shown in FIG. 12, the pixel electrode 1700 made of an ITO
film is formed.
Next, as shown in FIG. 13, a substrate 1900 (transfer material) is
adhered through an adhesive layer 1800. Next, as shown in FIG. 13,
the substrate 3000 is irradiated with eximer laser light from the
back thereof, and then is exfoliated.
Next, the separation layer (laser absorbing layer) 3100 is removed
to complete the active matrix substrate shown in FIG. 14. The
bottom (the region 1702) of the pixel electrode 1700 is exposed to
permit application of a sufficient voltage to the liquid
crystal.
Then an alignment film is formed on the inner sides of the opposite
substrate 480 and the active matrix substrate 440 shown in FIG. 14,
followed by rubbing. Both substrates are then adhered with a
sealing agent with a space formed therebetween, and a liquid
crystal is sealed in between the both substrates to complete the
liquid crystal display device shown in FIG. 9.
Although the above description is made on the basis of a device
structure (the pixel electrode is in an upper layer, and the
transistor electrode is in a lower layer) in which the transistors
electrode layers 1400a and 1400b connected to the n.sup.+ layers
1100a and 1100b, respectively, which constitute the pixel TFT, are
in a layer different from the pixel electrode 1700, the device
structure is not limited to this. As shown in FIGS. 15 to 17, even
when the pixel electrode and the transistor electrode are in the
same layer, the above manufacturing method can be applied.
Namely, as shown in FIG. 15, an opening 1612 is formed at the same
time that electrode contact holes 1622 and 1630 of the TFT are
formed. Therefore, the special step for forming the opening 1612 is
unnecessary.
Although, in FIG. 15, the interlayer insulation film 1500 and the
underlying SiO.sub.2 (intermediate layer) 1000 are completely
removed when the opening 1612 is formed, these films may be left as
long as a sufficient voltage can be applied to the liquid crystal.
For example, the underlying SiO.sub.2 film (intermediate layer)
1000 may be left.
Even when the interlayer insulation film 1500 and the underlying
SiO.sub.2 film (intermediate layer) 1000 are completely removed in
formation of the opening 1612, a method may be used in which these
films are not removed at a time in this step, but these films are
partially left in this step, and the films remaining on the pixel
electrode are removed in a later step (for example, the step after
the thin film transistor is transferred) to expose the surface of
the pixel electrode.
Next, as shown in FIG. 16, an aluminum electrode 1402 and a pixel
electrode (ITO) 1702 are formed.
Then, like in the case shown in FIGS. 13 and 14, the thin film
transistor and pixel electrode are adhered to a transfer material
1900 through an adhesive layer 1800, and the substrate 3000 is
separated after light irradiation to complete the active matrix
substrate shown in FIG. 17.
(Second embodiment)
FIGS. 18 and 19 are sectional views showing a device in accordance
with a second embodiment of the present invention.
This embodiment is characterized in that the step of forming a
color filter and a light shielding film (for example, a black
matrix) is added after the step of forming the pixel electrode made
of ITO or a metal to form an active matrix substrate with the color
filter and the light shielding film (for example, a black
matrix).
The case where the black matrix is used as the light shielding film
is described below.
As the structure of an ordinary thin film transistor, a structure
in which the color filter and the black matrix are formed on the
pixel electrode cannot be used because the liquid crystal layer and
the pixel electrode are separated.
However, in the present invention, a device is reverse to a normal
device due to transfer, and thus the contact region between the
pixel electrode and the liquid crystal layer is formed on the side
(i.e., the TFT side) opposite to a conventional device.
Therefore, in the original substrate before transfer, the color
filter and the black matrix can be formed without any trouble. In
this case, only the common electrode is formed on the opposite
substrate, and the color filter and the black matrix, which are
conventionally formed on the opposite substrate side, need not be
strictly aligned with the pixel electrode, thereby causing the
special effect of facilitating assembly of a liquid crystal display
device.
As shown in FIG. 18, a color filter 1770 is formed by a pigment
dispersion method, a dyeing method or an electrodeposition method
to cover the principal portion of the pixel electrode 1700, and a
light shielding black matrix 1750 is formed to cover the TFT.
As shown in FIG. 19, the device is adhered to the transfer material
1900 through the adhesive layer 1800, and then the substrate 3000
(FIG. 18) is separated to complete an active matrix substrate with
the color filter and the black matrix.
As described above, when a liquid crystal display device is formed
by using the active matrix substrate, strict alignment with the
opposite substrate is unnecessary, and assembly is facilitated.
(Third embodiment)
FIG. 20 shows a section of the principal portion of a liquid
crystal display device in accordance with a third embodiment of the
present invention.
The liquid crystal display device shown in FIG. 20 is characterized
in that a terminal (external connection terminal) 1404 (made of ITO
or a metal) for connecting a driver IC 4200 is formed on the active
matrix substrate through the same manufacturing steps as the pixel
electrodes.
Namely, in the active matrix substrate, where the external
connection terminal (for example, a terminal for connecting liquid
crystal driving IC) is required, this terminal must be exposed to
the surface.
Therefore, in the region where the external connection terminal is
provided, the underlying insulation film (intermediate layer) and
the insulator layer such as interlayer insulation film are
moved.
However, the surface of the external connection terminal 1404 need
not be exposed only in the same step as formation of the opening in
the pixel electrode region, and another etching step may be added
for removing the film remaining on the surface of the external
connection terminal 1404 in the etching step, to expose the
surface.
In FIG. 20, "region P1" is a region (bonding pad) to which the lead
4100 of the driver IC 4200 is connected.
Namely, as shown in FIG. 21, the driver IC 4200 is connected to the
data line D1 through the pad P1.
In FIG. 20, the driver IC is a tape carrier package (TCP) type IC,
and a lead 4100 is connected to the pad P1 (the external connection
terminal 1404 ) through an anisotropic conductive film (conductive
anisotropic adhesive) 4000, the other lead 4104 being connected to
a printed board 4300 through solder 4004.
In FIG. 20, reference numeral 484 denotes the sealing material
(sealant), reference numeral 4102 denotes a tape carrier, and
reference numeral 4002 denotes a conductive filler. Reference
numerals 1010 and 1012 each denote an alignment film. The same
portions as FIG. 9 are denoted by the same reference numerals.
The process for manufacturing the active matrix substrate shown in
FIG. 20 is described below with reference to FIGS. 22 to 27. Since
the manufacturing process is common to that shown in FIGS. 10 to
14, the same portions are denoted by the same reference
numerals.
First, as shown in FIG. 22, TFT (M1), the data line D1, and the
scanning line S1 (not shown in the drawing) are formed on the
substrate 3000. In FIG. 22, the pixel portion is shown on the left
side, and the terminal portion where the external connection
terminal is formed is shown on the right side.
Next, as shown in FIG. 23, the openings 1610 and 1640 are formed at
the same time as the contact holes 1620 and 1630. Therefore, the
surface of the separation layer 3100 is exposed at the bottoms of
the openings 1610 and 1640. The special step of forming the
openings 1610 and 1640 is unnecessary.
Although, in FIG. 23, the insulation film 1600, the interlayer
insulation film 1500 and the underlying SiO.sub.2 film
(intermediate layer) 1000 are completely removed when the opening
1610 is formed, these films may partially be left as long as a
sufficient voltage can be applied to the liquid crystal. For
example, the underlying SiO.sub.2 film (intermediate layer) 1000
may be left. However, in the opening 1640, the insulation film
1600, the interlayer insulation film 1500 and the underlying
SiO.sub.2 film (intermediate layer) 1000 must be completely removed
by etching in the same step or another step.
Even when the insulation film 1600, the interlayer insulation film
1500 and the underlying SiO.sub.2 film (intermediate layer) 1000
are completely removed in formation of the opening 1610 (1640), a
method may be used in which these films are not removed at a time
in this step, but these films are partially left in this step, and
the films remaining on the pixel electrode are removed in a later
step (for example, the step after the thin film transistor is
transferred) to expose the surface of the pixel electrode.
Next, as shown in FIG. 24, the pixel electrode made of ITO and the
external connection terminal 1404 made of ITO are simultaneously
formed.
Next, as shown in FIG. 25, a device is adhered to the transfer
material 1900 through the adhesive layer 1800.
Next, as shown in FIG. 26, the substrate 3000 side is irradiated
with laser light to generate ablation in the separation layer
3100.
Next, the substrate 3000 is separated, and the separation layer
3100 is completely removed to form the active matrix substrate
shown in FIG. 27. In FIG. 27, reference numeral 1710 denotes a
voltage applied region for the liquid crystal, and region P1
corresponds to a pad for connecting the region P1 and the driver
IC.
Although the above description is made on the basis of a device
structure (the pixel electrode and the external connection terminal
are in an upper layer, and the transistor electrodes are in a lower
layer) in which the transistor electrode layers 1400a and 1400b
connected to the n.sup.+ layers 1100a and 1100b, respectively,
which constitute the TFT of the pixel, are in a layer different
from the pixel electrode 1700 and the external connection terminal
1404, the device structure is not limited to this. As shown in
FIGS. 28 to 30, even when the pixel electrode, the external
connection terminal and the transistor electrode are in the same
layer, the above manufacturing method can be applied.
Namely, as shown in FIG. 28, openings 1612 and 1642 are formed at
the same time as electrode contact holes 1622 and 1630 of the TFT.
Therefore, the special step for forming the openings 1612 and 1642
is unnecessary.
Next, as shown in FIG. 29, an aluminum electrode 1402, the data
line D1 (and the scanning line not shown in the drawing) made of
aluminum, a pixel electrode (ITO) 1702 made of ITO and an external
connection terminal 1406 made of ITO are formed.
Then, the device is adhered to the transfer material 1900 through
the adhesive layer 1800, and the substrate is separated after light
irradiation to complete the active matrix substrate shown in FIG.
30.
The pixel electrode and the external connection terminal need not
be made of ITO, and may be a metal electrode made of aluminum which
serve as a reflection type pixel electrode. When the pixel
electrode is a metal electrode, there is the advantage of low
wiring resistance. In this case, the external connection terminal
is made of the same metal material, thereby causing an advantage
from the viewpoint of electrical properties.
(Fourth embodiment)
FIGS. 31 to 38 shows the sectional structure of a device in
accordance with a fourth embodiment of the present invention.
Although, in the above embodiments, the insulator layer below the
pixel electrode is previously removed before transfer of the
device, in this embodiment, at least a portion of the insulator
layer below the pixel electrode is removed in self alignment by
using a black matrix after transfer.
Namely, the black matrix is formed on the original substrate before
transfer, and exposure is performed by using the black matrix as an
exposure mask after transfer by utilizing the fact that the black
matrix is formed around the pixel electrode, followed by
development to form a desired resist pattern. The insulator layer
below the pixel electrode is removed by using the resist pattern as
an etching mask.
A detailed description will now be made.
First, as shown in FIG. 31, like in FIG. 10, TFT (M1) is formed,
the insulation film 1600 is then formed to cover the TFT (M1), a
contact hole is formed in the insulation film 1600, and then a
pixel electrode (an ITO film or metal film) 1790 is formed. In this
embodiment, attention should be given to the point that unlike
FIGS. 11 and 15, no additional opening is formed in the insulation
film 1600.
Next, a black matrix 1750 is formed. The black matrix 1750 is
provided to shield the periphery of the principal portion (the
voltage applied region for the liquid crystal) from light except
the principal portion, as shown on the lower side of FIG. 34.
Next, as shown in FIG. 32, a device is adhered to the transfer
material 1900 through the adhesive layer 1800, and the substrate
3000 side is irradiated with laser light.
Next, as shown in FIG. 33, the substrate 3000 is separated, and the
remaining separation layer 3100 is also removed.
Next, as shown in FIG. 34, a photoresist 5000 is formed on the
surface obtained by separating the substrate 3000, followed by
exposure from the transfer material 1900 side. In this case, the
black matrix 1750 serves as an exposure mask to automatically
irradiate only the region of contact between the pixel electrode
and the liquid crystal with light.
Next, as shown in FIG. 35, the photoresist 5000 is patterned by
development.
Next, as shown in FIG. 36, the underlying insulation film
(intermediate layer) 1000, the gate insulation film 1500, the
insulation film 1600 are etched by using the patterned photoresist
5000 as a mask to form an opening 8002. As a result, the surface of
the pixel electrode is exposed.
Like in the above embodiments, the films may be left on the pixel
electrode as long as no trouble occurs in driving the liquid
crystal. Alternatively, the remaining films may be removed in
another step to expose the surface of the pixel electrode.
Next, as shown in FIG. 37, the photoresist 5000 is removed to
complete an active matrix substrate.
The liquid crystal display device shown in FIG. 38 is manufactured
by using the active matrix substrate. In FIG. 38, the same portions
as FIG. 9 are denoted by the same reference numerals.
Although, in this embodiment, only the black matrix is formed, the
color filter may be formed on the active matrix substrate as long
as the exposure conditions for photoresist are satisfied, as in the
case shown in FIGS. 18 and 19.
Like in the above embodiments, not only the pixel electrode but
also the external connection terminal can be formed by the same
method as described above.
(Fifth embodiment)
FIGS. 39 to 42 show the sectional structure of a device in
accordance with a fifth embodiment of the present invention.
In this embodiment, when a thin film transistor is formed on an
original substrate before transfer, a pixel electrode is previously
formed. Therefore, the original substrate before transfer is
separated after transfer of the device to automatically expose the
surface of the pixel electrode.
Namely, as shown in FIG. 39, an aluminum electrode 7100 and a pixel
electrode 7000 made of ITO are formed on a separation layer 3100.
The pixel electrode 7000 may be made of a metal such as aluminum or
the like. In this case, the pixel electrode 7000 can be formed at
the same time as the aluminum electrode 7100.
Next, as shown in FIG. 40, an interlayer insulation film 7200,
source-drain layers 7300a and 7300b, a gate insulation film 7400,
and a gate electrode 7500 are formed, and the device is then
adhered to a transfer material 7700 through an adhesive layer 7600.
Next, the substrate 3000 side is irradiated with laser light.
Next, as shown in FIG. 41, the substrate 3000 is separated, and the
remaining separation layer 3100 is removed to complete an active
matrix substrate.
The liquid crystal display device shown in FIG. 42 is manufactured
by using the active matrix substrate. In FIG. 42, the same portions
as FIG. 9 are denoted by the same reference numerals.
In FIG. 42, reference numeral 4100 denotes a lead of a driver IC;
reference numeral 4102, a tape carrier; reference numeral 4000, a
conductive anisotropic adhesive; and reference numeral 4002, a
conductive filler.
As described above, the present invention is capable of effectively
removing the problems due to reversal of a device which results
from the use of the transfer technique. Therefore, a substrate used
in manufacturing thin film devices and a substrate (for example, a
substrate having preferable properties from the viewpoint of
application of a product) used in, for example, actual use of a
product can be freely individually selected. For example, an active
matrix substrate can be formed by using a flexible plastic
substrate.
The active matrix substrate can be used for not only a liquid
crystal display device but for also other applications. For
example, an active matrix substrate on which an electronic circuit
(a computer or the like) comprising TFTs is mounted can be
formed.
The present invention is not limited to the above embodiments, and
various modifications can be made. For example, although, in each
of the above embodiments, a type (top gate type) in which a gate
electrode is disposed above a channel after the channel is formed
is described as an example of thin film transistor (TFT)
structures, TFT structures of a type (bottom gate type) in which
the gate electrode is formed before the channel is formed can also
be used.
Further, although, in the embodiments, the manufacturing substrate
is separated from the separation layer by irradiation with laser
light or the like, of course, the present invention can be applied
to any cases using other methods of separating the substrate as
long as the methods can separate the manufacturing substrate from
the separation layer.
Industrial Applicability
As described above, the present invention is capable of forming a
liquid crystal display device by forming the thin film transistors
on the substrate and then transferring thin film transistors to any
one of various other substrates, thus providing as an active type
liquid crystal display device a liquid crystal display device using
glass, plastic, films or the like, which cannot be used for
conventional active type liquid crystal display devices.
* * * * *