U.S. patent application number 13/334757 was filed with the patent office on 2012-04-19 for method for manufacturing wiring, thin film transistor, light emitting device and liquid crystal display device, and droplet discharge apparatus for forming the same.
This patent application is currently assigned to SEMICONDUCTOR ENERGY LABORATORY CO., LTD.. Invention is credited to Osamu NAKAMURA, Klyofumi Ogino.
Application Number | 20120094412 13/334757 |
Document ID | / |
Family ID | 34537918 |
Filed Date | 2012-04-19 |
United States Patent
Application |
20120094412 |
Kind Code |
A1 |
NAKAMURA; Osamu ; et
al. |
April 19, 2012 |
METHOD FOR MANUFACTURING WIRING, THIN FILM TRANSISTOR, LIGHT
EMITTING DEVICE AND LIQUID CRYSTAL DISPLAY DEVICE, AND DROPLET
DISCHARGE APPARATUS FOR FORMING THE SAME
Abstract
As a semiconductor device, specifically, a pixel portion
included in a semiconductor device is made to have higher precision
and higher aperture ratio, it is required to form a smaller wiring
in width. In the case of forming a wiring by using an ink-jet
method, a dot spreads on a wiring formation surface, and it is
difficult to narrow width of a wiring. In the present invention, a
photocatalytic substance typified by TiO.sub.2 is formed on a
wiring formation surface, and a wiring is formed by utilizing
photocatalytic activity of the photocatalytic substance. According
to the present invention, a narrower wiring, that is, a smaller
wiring in width than a diameter of a dot formed by an ink-jet
method can be formed.
Inventors: |
NAKAMURA; Osamu; (Atsugi,
JP) ; Ogino; Klyofumi; (Atsugi, JP) |
Assignee: |
SEMICONDUCTOR ENERGY LABORATORY
CO., LTD.
Atsugi-si
JP
|
Family ID: |
34537918 |
Appl. No.: |
13/334757 |
Filed: |
December 22, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13034771 |
Feb 25, 2011 |
8105945 |
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13334757 |
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12432503 |
Apr 29, 2009 |
7919411 |
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13034771 |
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11970318 |
Jan 7, 2008 |
7534724 |
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12432503 |
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10946649 |
Sep 22, 2004 |
7332432 |
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11970318 |
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Current U.S.
Class: |
438/30 ;
257/E21.295; 257/E33.053; 438/676 |
Current CPC
Class: |
H01L 21/76838 20130101;
H01L 21/288 20130101; H01L 27/3276 20130101; H01L 51/0022 20130101;
H01L 2251/5315 20130101; G09G 2300/0814 20130101; H01L 51/56
20130101; H01L 2251/5323 20130101; H01L 27/3244 20130101 |
Class at
Publication: |
438/30 ; 438/676;
257/E21.295; 257/E33.053 |
International
Class: |
H01L 33/08 20100101
H01L033/08; H01L 21/3205 20060101 H01L021/3205 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 2003 |
JP |
2003-344202 |
Claims
1. A method for manufacturing a wiring comprising: forming a
substance having a photocatalytic function over a substrate; and
discharging a solvent comprising a conductive material onto the
substance having the photocatalytic function by an application
method.
2. The method for manufacturing a wiring according to claim 1,
wherein the conductive material comprises at least one selected
from the group consisting of gold, silver, copper, platinum,
palladium, tungsten, nickel, tantalum, bismuth, lead, indium, tin,
zinc, titanium, and aluminum, an alloy thereof, and a dispersive
nanoparticle thereof.
3. The method for manufacturing a wiring according to claim 1,
wherein the application method is an ink-jet method.
4. A method for manufacturing a wiring comprising: forming a
substance having a photocatalytic function over a substrate;
selectively irradiating the substance having the photocatalytic
function with light to be hydrophilic; and discharging a conductive
material mixed into a water-based solvent to a region irradiated
with the light by an application method.
5. The method for manufacturing a wiring according to claim 4,
wherein the water-based solvent is added with a surfactant.
6. The method for manufacturing a wiring according to claim 4,
wherein the conductive material comprises at least one selected
from the group consisting of gold, silver, copper, platinum,
palladium, tungsten, nickel, tantalum, bismuth, lead, indium, tin,
zinc, titanium, and aluminum, an alloy thereof, and a dispersive
nanoparticle thereof.
7. The method for manufacturing a wiring according to claim 4,
wherein the application method is an ink-jet method.
8. A method for manufacturing a thin film transistor comprising:
forming a substance having a photocatalytic function over an
insulating surface; selectively irradiating the substance with
light to be hydrophilic; discharging a conductive material mixed
into a water-based solvent to a region irradiated with the light by
an ink-jet method to form a gate electrode; sequentially forming a
semiconductor film and a first protective film over the gate
electrode; patterning the first protective film using the gate
electrode; forming a semiconductor film having one conductivity to
cover the patterned first protective film; forming a mask over the
semiconductor film having one conductivity by an ink-jet method;
patterning the semiconductor film and the semiconductor film having
one conductivity using the mask; and forming a wiring over the
patterned semiconductor film having one conductivity by an ink-jet
method.
9. The method for manufacturing a thin film transistor according to
claim 8, wherein the semiconductor film having one conductivity is
formed by adding an impurity element.
10. The method for manufacturing a thin film transistor according
to any one of claim 8, further comprising the steps of: forming an
electrode connected to the wiring; and forming a second protective
film by an ink-jet method to cover the semiconductor film, the gate
electrode, and a part of the electrode.
11. The method for manufacturing a thin film transistor according
to claim 8, further comprising the steps of forming an
electroluminescent layer and an electrode over the
electroluminescent layer.
12. The method for manufacturing a thin film transistor according
to claim 8, further comprising the steps forming an orientation
film, dropping a liquid crystal over the orientation film, and
attaching an opposing substrate provided with an electrode, a color
filter, and the orientation film.
13. The method for manufacturing a thin film transistor according
to claim 8, wherein the thin film transistor is incorporated in at
least one selected from the group consisting of a video camera, a
digital camera, a goggle type display, a navigation system, an
audio reproducing device, a personal computer, a game machine, a
personal digital assistance, and an image reproducing device.
14. A method for manufacturing a thin film transistor comprising:
forming a crystalline semiconductor film over an insulating
surface; forming a gate insulating film comprising a substance
having a photocatalytic function to cover the crystalline
semiconductor film; selectively irradiating the gate insulating
film with light to be hydrophilic; discharging a conductive
material mixed into a water-based solvent to a region irradiated
with the light by an ink-jet method to form a gate electrode;
etching the gate insulating film using the gate electrode; forming
a metal film to cover the gate electrode; and reacting the
crystalline semiconductor film and the metal film to form a
silicide.
15. The method for manufacturing a thin film transistor according
to claim 14, further comprising the steps of forming an
electroluminescent layer and an electrode over the
electroluminescent layer.
16. The method for manufacturing a thin film transistor according
to claim 14, further comprising the steps forming an orientation
film, dropping a liquid crystal over the orientation film, and
attaching an opposing substrate provided with an electrode, a color
filter, and the orientation film.
17. The method for manufacturing a thin film transistor according
to claim 14, wherein the thin film transistor is incorporated in at
least one selected from the group consisting of a video camera, a
digital camera, a goggle type display, a navigation system, an
audio reproducing device, a personal computer, a game machine, a
personal digital assistance, and an image reproducing device.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for manufacturing
a wiring and a method for manufacturing a semiconductor device such
as a light emitting device or a liquid crystal display device by a
droplet discharge (ink-jet) method utilizing a photocatalytic
reaction. In addition, the invention relates to a droplet discharge
apparatus for forming them.
[0003] 2. Related Art
[0004] A droplet discharge technique typified by a piezo method or
a thermal jet method, or a continuous droplet discharge technique
has attracted attention. This droplet discharge technique has been
used in printing a type and drawing an image. However, an attempt
to apply it to a semiconductor field, for example, micropattern
formation or the like has begun in recent years.
[0005] On the other hand, there is a method for forming a patterned
metal film made of only an absorption metal atom by soaking a base
material provided with a substance having a photocatalytic function
over its surface in a metal-ion-containing aqueous solution
including alcohol, by drawing on the base material with a
predetermined pattern by laser light, and by soaking the base
material in an aqueous solution capable of forming a complex to
remove the absorption metal ion, as a conventional method for
forming a metal wiring by a photocatalytic reaction (for example,
Reference 1: Japanese Patent Laid-Open No. 9-260808).
[0006] In addition, titanium oxide (TiO.sub.2) used as a
photocatalytic material is an N-type semiconductor. It is known
that a photocatalytic reaction is caused on its surface when the
surface is irradiated with light of a wavelength in an ultraviolet
region and it has an effect such as deodorization, mildew proofing,
antifouling, or antibacterial due to activated species generated on
the surface, There are three types of titanium oxide called a
rutile type, an anatase type, a brookite type, each of which has a
different crystal structure. It is the anatase type that has the
highest photocatalytic activity among them.
[0007] In the case of forming a wiring by using an ink-jet method
as described above, a droplet (a dot) discharged from an ink-jet
nozzle spreads on a wiring formation surface, and it is difficult
to narrow a line width (simply referred to as a width) of a wiring.
On the other hand, as a semiconductor device, specifically, a pixel
portion included in a semiconductor device is made to have higher
precision and higher aperture ratio, it is required to form a
narrower wiring.
[0008] Further, in the case where the wiring formation surface is
liquid-repellent, a landed dot easily rolls on the surface and
coheres. Therefore, it is difficult to draw a continuous line in a
desired region.
[0009] Thus, it is difficult to form a small wiring in width and to
control a position of a wiring to be formed in a designated
position by an ink jet method.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide a method
for forming a wiring which is narrower and of which position is
easily controlled in forming a wiring by an ink jet method. In
addition, it is an object to provide a thin film transistor and a
semiconductor device having the wiring and a manufacturing method
thereof.
[0011] In view of the above object, a wiring is formed by utilizing
photocatalytic activity of a substance having a photocatalytic
function (hereinafter, simply referred to as a photocatalytic
substance) according to the present invention. Specifically, a
wiring material mixed into a solvent (including a wiring material
(conductive material) dissolved or dispersed in a solvent) is
formed over the photocatalytic substance or at opposite ends
thereof by an application method or the like, thereby forming a
wiring. For example, a conductive, material mixed into a solvent is
discharged onto the photocatalytic substance by an ink jet method.
The conductive material mixed into a solvent may be formed over the
photocatalytic substance by a spin coating method, a dipping
method, or another application method besides an ink-jet
method.
[0012] It is preferable to use titanium oxide (TiO.sub.2),
strontium titanate (SrTiO.sub.3), cadmium selenide (CdSe),
potassium tantalite (KTaO.sub.3), cadmium sulfide (CdS), zirconium
oxide (ZrO.sub.2), niobium oxide (Nb.sub.2O.sub.3), zinc oxide
(ZnO), iron oxide (Fe.sub.2O.sub.3), tungsten oxide (WO.sub.3), or
the like as the photocatalytic substance. The photocatalytic
substance is irradiated with light of an ultraviolet light region
(wavelength: equal to or less than 400 nm, preferably, equal to or
less than 380 nm) to be photocatalytically activated. At this time,
a width of a light irradiation region can be made narrower than a
diameter of a dropped droplet (also referred to as a dot), and
minute drawing can be performed.
[0013] For example, TiO.sub.2 is not hydrophilic but oleophilic,
that is, water-repellent before being irradiated with light. Light
irradiation causes photocatalytic activity, and TiO.sub.2 is
converted into hydrophilic and non-oleophilic, that is,
oil-repellent. Note that TiO.sub.2 can be at once hydrophilic and
oleophilic depending on a length of irradiation time.
[0014] Note that "hydrophilic" means a state which is easy to be
got wet with water and has a contact angle of equal to or less than
30.degree.. Specifically, a state having a contact angle of equal
to or less than 5.degree. is referred to as "super-hydrophilic". On
the other hand, "water-repellent" means a state which is hard to be
got wet with water and has a contact angle of equal to or more than
90.degree.. Similarly, "oleophilic" means a state which is easy to
be got wet with oil, and "oil-repellent" means a state which is
hard to be got wet with oil. Note that the contact angle means an
angle made by a formation face and a tangent to a droplet on the
edge of a dropped dot.
[0015] Namely, a region irradiated with light (hereinafter,
referred to as an irradiation region) becomes hydrophilic or
super-hydrophilic (simply collectively referred to as hydrophilic).
At this time, light irradiation is performed so that a width of an
irradiation region is a desired width of a wiring. Thereafter, a
dot including a conductive material mixed into a water-based
solvent is discharged from above the irradiation region to the
irradiation region by an ink-jet method. Then, a smaller wiring in
width, that is, a narrower wiring than a diameter of a dot
discharged merely by an ink-jet method can be formed. This is
because the irradiation region is formed to have a desired width of
a wiring, and then, a discharged dot can be prevented from
spreading on a formation surface. Further, a wiring can be formed
along the irradiation region even in the case where a dot is
discharged out of alignment to some extent. Thus, a position of a
wiring to be formed can be controlled with accuracy.
[0016] In the case of using a water-based solvent, it is preferable
to add a surfactant in order to smoothly discharge a droplet from a
nozzle of an inkjet apparatus.
[0017] In the case of discharging a conductive material mixed into
an oil (alcohol) based solvent, a wiring can be similarly formed by
discharging a conductive material onto a region which is not
irradiated with light (hereinafter, referred to as a
non-irradiation region) and discharging a dot from above the
non-irradiation region to the non-irradiation region. Namely,
opposite ends of a region where a wiring is to be formed, that is,
the periphery surrounding the region where a wiring is to be formed
may be irradiated with light, thereby forming an irradiation
region. Since the irradiation region is oil-repellent at this time,
a dot including a conductive material mixed into an oil (alcohol)
based solvent is selectively formed in the non-irradiation region.
Namely, light irradiation is performed so that a width of the
non-irradiation region is a desired width of a wiring.
[0018] Note that a nonpolar solvent or a low polar solvent can be
used as the oil (alcohol) based solvent. For example, terpineol,
mineral spirit, xylene, toluene, ethyl benzene, mesitylene, hexane,
heptane, octane, decane, dodecane, cyclohexane, or cyclooctane can
be used.
[0019] Further, photocatalytic activity can be improved by doping a
transition metal (such as Pd, Pt, Cr, Ni, V, Mn, Fe, Ce, Mo, or W)
into the photocatalytic substance, and photocatalytic activity can
be caused by light of a visible light region (wavelength: from 400
nm to 800 nm). This is because the transition metal can form a new
level within a forbidden band of an active photocatalyst having a
wide band gap and can expand a light absorption range to a visible
light region. For example, an acceptor type such as Cr or Ni, a
donor type such as V or Mn, an amphoteric type such as Fe, or other
types such as Ce, Mo, and W can be doped. A wavelength of light can
thus be determined depending on the photocatalytic substance.
Therefore, light irradiation means to irradiate with light having
such a wavelength that photocatalytically activates the
photocatalytic substance.
[0020] When the photocatalytic substance is heated and reduced in a
vacuum or under reflux of hydrogen, an oxygen defect is generated
in crystal. Without doping a transition element, an oxygen defect
plays a similar role to an electron donor in this way.
Specifically, in the case of forming by a sol-gel method, the
photocatalytic substance may not be reduced since an oxygen defect
exists from the beginning. In addition, an oxygen defect can be
formed by doping a gas of N.sub.2 or the like.
[0021] Gold, silver, copper, platinum, palladium, tungsten, nickel,
tantalum, bismuth, lead, indium, tin, zinc, titanium, aluminum, an
alloy thereof, a dispersive nanoparticle thereof, or a silver
halide particle can be used as the conductive material.
Specifically, silver or copper which is low resistant is preferably
used. However, in the case of using copper, an insulating film
containing nitrogen is formed as a barrier film to prevent copper
from spreading in a semiconductor film or the like. In addition,
ITO (indium tin oxide), IZO (indium zinc oxide) in which zinc oxide
(ZnO) of from 2% to 20% is mixed into indium oxide, ITSO in which
silicon oxide (SiO.sub.2) of from 2% to 20% is mixed into indium
oxide, organic indium, organotin, titanium nitride (TIN), or the
like can also be used its a transparent conductive material.
[0022] A piezo method can be employed as an ink-jet method. The
piezo method is utilized also for an inkjet printer since it has
superior ink-droplet controllability and a high degree of freedom
for ink selection. Note that the piezo method has an MLP (Multi
Layer Piezo) type and an MLChip (Multi Layer Ceramic Hyper
Integrated Piezo Segments) type. Alternatively, an ink-jet method
using a so-called thermal method which makes a heating element
generate heat to generate bubbles, thereby pushing out a solution
may be employed depending on a solvent material.
[0023] The thus formed wiring is provided with a conductive film
with the photocatalytic substance therebetween.
[0024] The thus formed wiring can be used as a gate electrode, a
source electrode, or a drain electrode of a thin film transistor
(also referred to as a MI a wiring connected to the electrode, or a
wiring to which a source signal, a drain signal, or a gate signal
is inputted. Then, a semiconductor device having such a thin film
transistor can be formed.
[0025] In addition, a photocatalystic substance that is formed
except below the conductive film, that is, an unnecessary
photocatalytic substance for forming a wiring may be removed. This
is because TiO.sub.2 is prevented from unnecessarily reacting when
irradiated with light such as external light after forming a thin
film transistor or a semiconductor device. A wet etching method or
a dry etching method using the conductive film as a mask can be
employed as a removing method. For example, TiO.sub.2 can be
removed by a wet etching method using an HF based etchant.
[0026] On the contrary, the photocatalytic substance may be left
when a harmful organic material attaches to a thin film transistor
or the like due to transfer between film formation chambers while
forming a thin film transistor or the like since it becomes
possible to remove the organic material. Therefore, the
photocatalytic substance may be formed on the periphery (border,
edge) of a display portion.
[0027] According to the present invention, a narrower wiring, that
is, a smaller wiring in width than a diameter of a dot formed by an
ink-jet method can be formed. Further, a wiring can be formed along
a region in which photocatalytic activity is improved even in the
case where a dot is discharged out of alignment to some extent.
Thus, a position of a wiring to be formed can be controlled with
accuracy. In addition, adjacent dots can be prevented from
cohering, and thus, a wiring can be prevented from breaking by
controlling a photocatalytic substance to be hydrophilic,
oil-repellent, or the like. Further, a film thickness of a wiring
can be made thick since a dot does not spread in a width
direction.
[0028] As described above, large area patterning and high precision
patterning becomes easy; use of a mask can be reduced;
manufacturing steps can be simplified since a photolithography step
can be omitted; and a material can be utilized efficiently,
according to a method for manufacturing a wiring by an ink-jet
method utilizing a photocatalytic reaction of the present
invention. When an ink-jet method is used, a wiring can be formed
even on a large substrate with low cost and with manufacturing
steps shortened.
[0029] These and other objects, features and advantages of the
present invention will become more apparent upon reading of the
following detailed description along with the accompanied
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIGS. 1A and 1B show a method for forming a wiring of the
present invention.
[0031] FIGS. 2A and 2B show a method for forming a wiring of the
present invention.
[0032] FIGS. 3A to 3D are cross-sectional views showing a step of
manufacturing a thin film transistor of the present invention.
[0033] FIGS. 4A to 4C are cross-sectional views showing a step of
manufacturing a thin film transistor of the present invention.
[0034] FIGS. 5A to 5D are cross-sectional views showing a step of
manufacturing a thin film transistor of the present invention.
[0035] FIGS. 6A to 6D are cross-sectional views showing a step of
manufacturing a thin film transistor of the present invention.
[0036] FIG. 7 is a top view showing a thin film transistor of the
present invention.
[0037] FIGS. 8A to 8C are cross-sectional views showing a step of
manufacturing a thin film transistor of the present invention.
[0038] FIGS. 9A to 9C are cross-sectional views showing a step of
manufacturing a thin film transistor of the present invention.
[0039] FIGS. 10A to 10C are cross-sectional views showing a step of
manufacturing a thin film transistor of the present invention.
[0040] FIGS. 11A to 11C are cross-sectional views showing a step of
manufacturing a thin film transistor of the present invention.
[0041] FIGS. 12A to 12D are cross-sectional views showing a step of
manufacturing a thin film transistor of the present invention.
[0042] FIGS. 13A to 13D are cross-sectional views showing a step of
manufacturing a thin film transistor of the present invention.
[0043] FIGS. 14A to 14C are cross-sectional views showing a step of
manufacturing a thin film transistor of the present invention.
[0044] FIGS. 15A and 15B show a droplet discharge apparatus of the
present invention.
[0045] FIGS. 16A to 16C show an electronic device of the present
invention.
[0046] FIGS. 17A to 17C are cross-sectional views showing a step of
manufacturing a thin film transistor of the present invention.
[0047] FIG. 18 is a top view of a module of the present
invention.
[0048] FIGS. 19A and 19B are cross-sectional views of a display
device of the present invention.
[0049] FIGS. 20A and 20B are top views showing a thin film
transistor of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0050] Embodiment modes of the present invention are hereinafter
described with reference to attached drawings. Note that the same
reference numeral is given to the same portion or a portion having
a similar function throughout whole diagrams for explaining
embodiment modes, and repetitive description is omitted.
Embodiment Mode 1
[0051] A specific method for manufacturing a wiring is described in
this embodiment mode.
[0052] As shown in FIG. 1A, a photocatalytic substance 101 is
formed over a region 100 where a wiring is to be formed. The
photocatalytic substance can be formed by a dip coating method of a
sol-gel method, a spin coating method, an ink-jet method, an ion
plating method, an ion beam method, a CVD method, a sputtering
method, an RF magnetron sputtering method, a plasma spraying
method, or an anodic oxidation method. In addition, the
photocatalytic substance can be formed by mixing and melting a salt
of a constituent element, in the case of a photocatalytic substance
made of an oxide semiconductor including a plurality of metals. A
solvent may be baked or dried when it is necessary to remove the
solvent in the case of forming the photocatalytic substance by an
application method such as a dip coating method or a spin coating
method. Specifically, it may be heated at a predetermined
temperature (for example, equal to or more than 300.degree. C.),
preferably, in an atmosphere including oxygen. For example, Ag is
used as conductive paste and baking is performed in an atmosphere
including oxygen and nitrogen; then, an organic material such as a
thermosetting resin is decomposed. Therefore, Ag without containing
an organic material can be obtained. Accordingly, planarity on the
surface of Ag can be increased.
[0053] According to the heat treatment, the photocatalytic
substance can have a predetermined crystal structure. For example,
it has an anatase type or a rutile-anatase mixed type. The anatase
type is preferentially formed in a low temperature phase.
Therefore, the photocatalytic substance may be heated when it does
not have a predetermined crystal structure. In addition, the
photocatalytic substance can be formed plural times to obtain a
predetermined film thickness in the case of being formed by an
application method.
[0054] The case of forming TiO.sub.2 crystal having a predetermined
crystal structure by a sputtering method as a photocatalytic
substance is described in this embodiment mode. Sputtering is
performed using a metal titanium tube as a target and using an
argon gas and oxygen. Further, a He gas may be introduced. The
atmosphere is made to include much oxygen and formation pressure is
set high to form TiO.sub.2 having high photocatalytic activity. It
is preferable to form TiO.sub.2 while heating a film formation
chamber or a substrate provided with an object to be treated.
[0055] Thus formed TiO.sub.2 has a photocatalytic function even
when it is a very thin film (approximately 1 .mu.m).
[0056] Subsequently, light is converged by using an optical system
to form an irradiation region by selectively performing light
irradiation. For example, light 104 is converged by a lens 103.
Then, light irradiation is selectively performed by relatively
moving TiO.sub.2 and the light. For example, the photocatalytic
substance 101 may be moved in a direction of an arrow 108.
Accordingly, an irradiation region 105 and a non-irradiation region
106 can be formed. TiO.sub.2 in the irradiation region 105 shows a
hydrophilic property. Note that it can be at once hydrophilic and
oleophilic depending on a length of irradiation time.
[0057] A lamp (for example, an ultraviolet lamp, so-called black
light) and laser light (for example, a XeCl excimer, laser having
an oscillation wavelength of 308 nm, a XeF excimer laser having an
oscillation wavelength of 351 nm, a KrF excimer laser having an
oscillation wavelength of 248 nm, or the like) can be used as the
light. It is preferable to use laser light which can oscillate a
particular wavelength. In addition, the light is only necessary to
be light having such a wavelength that photocatalytically activates
TiO.sub.2, and TiO.sub.2 can be selectively irradiated with light
by using external light.
[0058] In this step, light irradiation is performed in a dark room
or in a reaction room where at least a photocatalytically
activating wavelength is removed or reduced to selectively perform
light irradiation. At least a reaction chamber of an apparatus
itself may be a dark room, or at least a photocatalytically
activating wavelength may be removed or reduced.
[0059] In addition, light irradiation can be entirely performed by
selectively forming TiO.sub.2 in a region where a conductive
material is to be formed. For example, TiO.sub.2 is selectively
formed by an ink-jet method, or a spin coating method with a metal
mask having a desired shape arranged; thereafter, light irradiation
may be entirely performed by using a lamp, laser light, or the
like. Accordingly, selectively formed TiO.sub.2 becomes
hydrophilic.
[0060] TiO.sub.2 can be prevented from unnecessarily reacting when
irradiated with light such as external light after forming a thin
film transistor or a-semiconductor device by selectively forming
TiO.sub.2 in this way. Namely, a wet etching method or a dry
etching method using a conductive film as a mask need not be used
to remove TiO.sub.2 which is formed except below the conductive
film, that is, unnecessary TiO.sub.2 for forming a wiring.
[0061] In addition, TiO.sub.2 in a desired region where the
conductive material is to be formed can be made hydrophilic by
forming a protective film, selectively removing the protective
film, and performing light irradiation after entirely forming
TiO.sub.2. A dry etching method or a wet etching method can be
employed as a method for selectively removing the protective film.
Alternatively, the protective film may be removed by laser ablation
using laser light having equal to or more than certain power and
having such a wavelength that photocatalytically activates
TiO.sub.2. In this case, selective removal of the protective film
and photocatalytic activation of TiO.sub.2 can be simultaneously
performed. Subsequently, a material which absorbs or reflects light
having equal to or less than certain power and a photocatalytically
activating wavelength is selected for the protective film so that
TiO.sub.2 is not irradiated with light having a photocatalytically
activating wavelength. Namely, the protective film is selected in
consideration of being irradiated with light having a
photocatalytically activating wavelength included in external
light. As a result, TiO.sub.2 can be prevented from being
irradiated with light having a photocatalytically activating
wavelength during transfer between reaction chambers or during use
as a product. In addition, a material used as the protective film
can absorb or reflect light having a photocatalytically activating
wavelength by controlling a film thickness. Further, the protective
film can be formed by laminating a plurality of materials.
Accordingly, it can widely absorb or reflect light having a
photocatalytically activating wavelength.
[0062] In this way, TiO.sub.2 can be selectively made hydrophilic.
A width of a hydrophilic region can be a desired width of a wiring,
and a light irradiation region can be narrowed by the optical
system.
[0063] Thereafter, a dot 109 is discharged from above the
irradiation region as shown in FIG. 1B. A dot discharge means has a
head provided with one or a plurality of solution inlets and one or
a plurality of nozzles. A composition to be a material of a dot is
injected from the solution inlet, and the composition is discharged
from the nozzle. At this time, the composition is discharged to be
a dot shape or a linear shape of a series of dots; however, they
are collectively referred to as a dot. In other words, discharging
a dot means to continuously discharge a plurality of dots;
therefore, dots may be discharged to be a linear shape without
being recognized as a dot.
[0064] A diameter of the nozzle is preferably set from 0.02 .mu.m
to 100 .mu.m (preferably, equal to or less than 30 .mu.m), and the
quantity of the composition discharged from the nozzle is
preferably set from 0.001 pl to 100 pl (preferably, equal to or
less than 10 pl). The quantity to be discharged can be controlled
by the diameter size of the nozzle. Therefore, the diameter of the
nozzle can be designed in accordance with a desired width of a
wiring. In addition, a distance between a surface of a hydrophilic
region, that is, a surface of an object to be treated and an outlet
of the nozzle is preferably close to drop at a desired position.
Preferably, it is set about from 0.1 mm to 3 mm (preferably, from
0.5 mm to 2 mm).
[0065] A conductive material mixed into a solvent is used as the
composition discharged from the outlet. Gold, silver, copper,
platinum, palladium, tungsten, nickel, tantalum, bismuth, lead,
indium, tin, zinc, titanium, aluminum, an alloy thereof, a
dispersive nanoparticle thereof, or a silver halide particle can be
used as the conductive material. Specifically, silver or copper
which is low resistant is preferably used. However, in the case of
using copper, an insulating film containing nitrogen is formed as a
barrier film to prevent copper from spreading in a semiconductor
film or the like. In addition, ITO (indium tin oxide), IZO (indium
zinc oxide) in which zinc oxide (ZnO) of from 2% to 20% is mixed
into indium oxide, ITSO in which silicon oxide (SiO.sub.2) of from
2% to 20% is mixed into indium oxide, organic indium, organotin,
titanium nitride (TiN), or the like can also be used as a
transparent conductive material.
[0066] A water-based or oil (alcohol) based solvent can be used as
the solvent. In the case of using a water-based solvent, it is
preferable to add a surfactant in order to smoothly discharge the
composition from the nozzle. In this embodiment mode, the
photocatalytic substance is controlled to be hydrophilic;
therefore, a detail of an oil (alcohol) based solvent is described
in the following embodiment mode.
[0067] The surface tension of the composition is preferably equal
to or less than 40 mN/m. The viscosity of the composition is
preferably equal to or less than 50 cp. This is because the
composition is prevented from drying or the composition is smoothly
discharged from the outlet. Note that the viscosity of the
composition and the like may be appropriately adjusted in
accordance with a solvent to be used and intended use. For example,
the viscosity of a composition in which ITO, organic indium, or
organotin is dissolved or dispersed in the solvent is from 5 mPaS
to 50 mPaS, the viscosity of a composition in which silver is
dissolved or dispersed in the solvent is from 5 mPaS to 20 mPaS,
and the viscosity of a composition in which gold is dissolved or
dispersed in the solvent is from 10 mPa5 to 20 mPaS.
[0068] The diameter of a particle of the conductive material is
preferably smaller for the purpose of preventing clogged nozzles
and manufacturing a high-definition pattern, although it depends on
the diameter of each nozzle, a desired width of a pattern, and the
like. Preferably, the diameter of the particle of the conductive
material is equal to or less than 0.1 .mu.m.
[0069] The composition is formed by an electrolyzing method, an
atomizing method, a wet reducing method, or the like, and the
particle size thereof is typically about from 0.5 .mu.m to 10
.mu.m. However, in the case of using a gas evaporation method, each
nanomolecule protected with a dispersing agent is minute, about 7
nm. When each surface of particles is covered with a coating, the
nanoparticles do not cohere in the solvent but are uniformly
dispersed in the solvent at a room temperature, and show a property
similar to that of liquid.
[0070] The step of discharging the composition is preferably
performed under reduced pressure. The solvent of the composition is
evaporated during a period from discharging the composition until
the composition lands on an object to be treated, and thus, steps
of drying and baking the composition can be both omitted. It is
preferable to perform the step under reduced pressure, since an
oxide film or the like is not formed on the surface of the
conductive material.
[0071] After discharging the composition, one step of or both steps
of drying and baking is/are performed. Each step of drying and
baking is a step of heat treatment. For example, drying is
performed for three minutes at 100.degree. C. and baking is
performed for from 15 minutes to 30 minutes at a temperature of
from 200.degree. C. to 350.degree. C. The steps of drying and
baking are performed at normal pressure or under reduced pressure
by laser light irradiation, rapid thermal annealing, a heating
furnace, or the like.
[0072] The substrate may be heated to efficiently perform the steps
of drying and baking. The temperature of the substrate at the time
depends on a material of the substrate or the like, but it is
typically from 100.degree. C. to 800.degree. C. (preferably, from
200.degree. C. to 350.degree. C.). According to the steps, fusion
between nanoparticles to be in contact with one another is
accelerated by hardening and shrinking as well as evaporating
solvent or solution in the composition or chemically removing the
dispersing agent.
[0073] Thus, a narrower wiring, that is, a smaller wiring in width
than a diameter of a dot can be formed by an ink-jet method
utilizing a photocatalytic reaction. Further, a wiring can be
formed along the region in which photocatalytic activity is
increased even in the case where a dot is discharged out of
alignment to some extent. Thus, a position of a wiring to be formed
can be controlled with accuracy.
[0074] Further, a semiconductor film or an insulating film may be
formed by an ink-jet method utilizing a photocatalytic reaction,
and metal sulfide of Cd or Zn, or oxide of Fe, Ti, Si, Ge, Zr, Ba,
or the like can be dropped.
[0075] In addition, a plug for connecting wirings can be formed by
an ink-jet method utilizing a photocatalytic reaction. An opening
is formed in the insulating film to be provided with the plug; a
photocatalytic substance is formed only on a side face of the
opening or on the surface of the insulating film in the vicinity of
the opening; the photocatalytic substance is controlled to be
hydrophilic or the like by light irradiation; and a plug material
can be actively dropped into the opening.
Embodiment Mode 2
[0076] The case of using an oil (alcohol) based solvent as a
solvent of a conductive material is described in this embodiment
mode.
[0077] A photocatalytic substance 101 is formed over a region 100
where a wiring is to be formed as described in Embodiment Mode 1
and as shown in FIG. 2A. Subsequently, light is converged by using
an optical system to selectively irradiate with light. For example,
light irradiation is selectively performed by converging light 104
with a lens 103 and relatively moving TiO.sub.2 and the light. For
example, the photocatalytic substance 101 may be moved in a
direction of an arrow 108. Accordingly, an irradiation region 105
and a non-irradiation region 106 can be formed. Then, TiO.sub.2 in
the irradiation region 105 shows an oil-repellent property.
[0078] Thereafter, a dot 109 is discharged from above the
non-irradiation region as shown in FIG. 2B. An oil (alcohol) based
solvent is used as the solvent of the conductive material in this
embodiment mode; therefore, a dot is discharged from above the
non-irradiation region provided between the irradiation regions to
the non-irradiation region. Note that discharging a dot means to
continuously discharge a plurality of dots; therefore, dots may be
discharged to be a linear shape without being recognized as a
dot.
[0079] A nonpolar solvent or a low polar solvent can be used as the
oil (alcohol) based solvent. For example, terpineol, mineral
spirit, xylene, toluene, ethyl benzene, mesitylene, hexane,
heptane, octane, decant, dodecane, cyclohexane, or cyclooctane can
be used. Tetradecane is used for the solvent in this embodiment
mode. In addition, a similar material to that in the above
embodiment mode can be used as the conductive material.
[0080] Subsequently, a wiring is formed by drying or baking as in
the above embodiment mode.
[0081] Thus, a narrower wiring, that is, a smaller wiring in width
than a diameter of a dot can be formed by an ink-jet method
utilizing a photocatalytic reaction. Further, a wiring can be
formed along the region in which photocatalytic activity is
increased even in the case where a dot is discharged out of
alignment to some extent. Thus, a position of a wiring to be formed
can be controlled with accuracy.
[0082] Height of the wiring can be increased by making the region
where a wiring is to be formed oil-repellent. In other words, the
height of the wiring can be more heightened compared to the above
embodiment mode since a dot including a conductive material mixed
into the oil (alcohol) based solvent is dropped between the
non-irradiation regions.
[0083] Further, a semiconductor film or an insulating film may be
formed by an ink-jet method utilizing a photocatalytic reaction,
and metal sulfide of Cd or Zn, or oxide of Fe, Ti, Si, Ge, Zr, Ba,
or the like can be dropped.
[0084] In addition, a plug for connecting wirings can also be
formed by an ink-jet method utilizing a photocatalytic reaction. An
opening is formed in the insulating film to be provided with the
plug; a photocatalytic substance is formed only on a side face of
the opening or on the surface of the insulating film in the
vicinity of the opening; the photocatalytic substance is controlled
to be hydrophilic or the like by light irradiation; and a plug
material can be actively dropped into the opening.
Embodiment Mode 3
[0085] An example of forming a thin film transistor by using a
method for manufacturing a wiring described in the above embodiment
mode is described in this embodiment mode. Note that TiO.sub.2 is
used as a photocatalytic substance.
[0086] First, a base film 201 is formed over a substrate 200 having
an insulating surface (over an insulating surface) as shown in FIG.
3A. A glass substrate such as barium borosilicate glass or
aluminoborosilicate glass, a quartz substrate, a stainless steel
substrate, or the like can be used as the substrate 200. Although a
substrate made of a flexible synthetic resin such as plastics
typified by polyethylene-terephthalate (PET),
polyethylenenaphthalate (PEN), or polyeter sulfone (PES) or acrlyic
generally tends to have a lower heat resistance temperature
compared to other substrates, it can be used as the substrate 200
as long as it can withstand the process temperature in the
manufacturing step.
[0087] The base film 201 is formed in order to prevent an alkaline
metal such as Na or an alkaline earth metal, contained in the
substrate 200 from spreading in a semiconductor film and exerting
an adverse influence on semiconductor element characteristics. The
base film 201 is therefore formed by using an insulating film, such
as silicon oxide, silicon nitride, or silicon nitride oxide,
capable of suppressing the spread of an alkaline metal or an
alkaline earth metal into the semiconductor film. Note that the
base film 201 can have a laminated structure. In this embodiment
mode, a silicon oxynitride film formed as a rust base film by a
plasma CVD method with SiH.sub.4, N.sub.2O, NH.sub.3, or N.sub.2
used as a material gas, pressure of 0.3 Torr (39.9 Pa), RF power of
50 W, an RF frequency of 60 MHz, a substrate temperature of
400.degree. C. to be from 10 nm to 200 nm, (preferably, from 50 nm
to 200 nm) in thickness, and a silicon oxynitride film formed as a
second base film by a plasma CVD method with SiH.sub.4 or N.sub.2O
used as a material gas, pressure of 0.3 Torr (39.9 Pa), RF power of
150 W, an RF frequency of 60 MHz, a substrate temperature of
400.degree. C. to be from 50 nm to 200 nm (preferably, from 150 nm
to 200 nm) in thickness are sequentially laminated.
[0088] It is effective to provide a base film in order to prevent
impurity spread in the case of using a substrate that contains a
certain amount of an alkaline metal or an alkaline earth metal,
such as a glass substrate or a plastic substrate. However, a base
film is not necessarily required to be provided when using a quartz
substrate or the like, with which impurity spread does not cause a
problem.
[0089] TiO.sub.2 is formed as a photocatalytic substance 202 over
an entire surface of the base film. In addition, TiO.sub.2 can be
used as the base film; in this case, the base film can be omitted.
TiO.sub.2 may be formed as in the above embodiment mode. In this
embodiment mode, TiO.sub.2 having a predetermined crystal structure
is formed by baking or drying after forming TiO.sub.2 by a spin
coating method. For example, it has an anatase type or a
rutile-anatase mixed type.
[0090] Subsequently, an irradiation region 203 is formed by
irradiating TiO.sub.2 in a desired region with light having a
photocatalytically activating wavelength. Then, the irradiation
region shows a hydrophilic property.
[0091] A dot including a conductive material dispersed in a solvent
is dropped from above the irradiation region to the irradiation
region by an ink-jet method. In this embodiment mode, a dot is
dropped on the irradiation region by using a water-based solvent
and using Ag as the conductive material. Subsequently, it is baked
by being heated at from 150.degree. C. to 400.degree. C., thereby
forming a wiring 204. The wiring 204 functions as a so-called
source electrode or drain electrode.
[0092] A semiconductor film having one conductivity, for example, a
semiconductor film having N-type conductivity 206 is formed by a
plasma CVD method as shown in FIG. 3B. Thereafter, the
semiconductor film having N-type conductivity is patterned to
prevent a short circuit between wirings.
[0093] Subsequently, a semiconductor film 207 is formed by a plasma
CVD method. A film thickness of the semiconductor film 207 is from
25 nm to 200 nm (preferably, from 30 nm to 60 nm). In addition,
silicon germanium as well as silicon can be used for an amorphous
semiconductor. In the case of using silicon germanium, a
concentration of germanium is preferably set about from 0.01 atomic
% to 4.5 atomic %. In addition, either semiconductor film selected
from a semi-amorphous semiconductor in which a crystal grain is
dispersed in the amorphous semiconductor and a microcrystal
semiconductor in which a crystal grain of from 0.5 nm to 20 nm can
be observed in the amorphous semiconductor may be used. A crystal
in which a crystal grain of from 0.5 nm to 20 nm can be observed is
referred to as so-called microcrystal (.mu.c). In this embodiment
mode, an amorphous semiconductor film containing silicon as its
main component (also referred to as an amorphous silicon film) is
used.
[0094] Thereafter, a photomask 208 is formed, and the semiconductor
film and the semiconductor film having N-type conductivity are
patterned by using the mask. For example, the photomask can be
formed by dropping polyimide, polyvinyl alcohol, or the like by an
ink-jet method.
[0095] An insulating film, that is, a so-called gate insulating
film 210 is formed as shown in FIG. 3C. In this embodiment mode,
TiO.sub.2 is applied by a spin coating method to be used as the
gate insulating film. TiO.sub.2 is suitable for the gate insulating
film since it has a high dielectric constant. Then, an irradiation
region 209 is formed by irradiating a desired wiring formation
region, that is, a region where the gate insulating film is to be
formed with light having a photocatalytically activating
wavelength. The irradiation region 209 shows a hydrophilic
property.
[0096] A dot including a conductive material mixed into a solvent
is dropped from above the irradiation region to the irradiation
region by an ink-jet method. In this embodiment mode, a dot is
dropped on the irradiation region by using a water-based solvent
and using Ag as the conductive material. Subsequently, it is heated
at from 150.degree. C. to 400.degree. C. to form a gate electrode
211.
[0097] Alternatively, a dot including a conductive material mixed
into an oil (alcohol) based solvent may be dropped. In this case,
opposite ends of a region where the gate electrode is formed may be
irradiated with light having a photocatalytically activating
wavelength to be more oil-repellent.
[0098] An interlayer insulating film 213 is formed if necessary as
shown in FIG. 3D. An inorganic material (silicon oxide, silicon
nitride, silicon oxynitride, or the like), a photosensitive or
non-photosensitive organic material (polyimide, acrylic, polyamide,
polyimidamide, a resist, or benzocyclobutene), a material in which
a skeletal structure is configured by a bond of silicon (Si) and
oxygen (O) and which contains at least hydrogen as a substituent,
or which further contains at least one kind of fluorine, an alkyl
group, and aromatic hydrocarbon as a substituent, that is,
so-called siloxane, or a laminated structure thereof can be used as
the interlayer insulating film. A positive photosensitive organic
resin or a negative photosensitive organic resin can be used as the
organic material. For example, when a positive photosensitive
acrylic is used as the organic material, an opening having a
curvature in its top edge portion can be formed by etching the
photosensitive organic resin with light-exposure treatment. In this
embodiment mode, a silicon oxynitride film is formed by a plasma
CVD method using SiH.sub.4 or N.sub.2O as a material gas to be 600
nm in thickness.
[0099] Subsequently, an opening, that is, a so-called contact hole
is formed in the interlayer insulating film 213. A wiring 214 is
formed in the contact hole and is electrically connected to the
wiring 204. The wiring 214 can be formed by an ink-jet method. The
wiring 214 functions as a so-called source wiring or drain
wiring.
[0100] Note that the wiring 214 may be laminated first by an
ink-jet method, and then, an insulating film having high viscosity
may be formed to form the interlayer insulating film. In addition,
the insulating film and the wiring may be appropriately alternately
dropped by an ink-jet method. In other words, an insulating film
material is dropped; then, a wiring material is dropped in a region
where the wiring is to be formed. When surface planarity at this
time becomes a problem, a planarization step such as CMP (Chemical
Mechanical Polishing) or etchback may be performed. As described
above, a photomask formation step for opening a contact hole, an
etching step using the mask, a washing step for removing the mask
can be reduced.
[0101] Thereafter, an electrode 215 is formed to be in contact with
the wiring 214. The electrode 215 can be formed by an ink-jet
method. The electrode 215 functions as a so-called pixel electrode
in a liquid crystal display device and functions as a so-called
anode or cathode of a light emitting element in a light emitting
device. A dot including a conductive material mixed into a
water-based solvent can be used as the electrode 215. Specifically,
a transparent conductive film can be formed by using a dot
including a transparent conductive material mixed into the solvent.
In addition, TiO.sub.2 is formed on a top face of the interlayer
insulating film 213, and a desired region where the electrode 215
is to be formed may be irradiated with light having a
photocatalytically activating wavelength to be hydrophilic.
[0102] Alternatively, a dot including a conductive material mixed
into an oil (alcohol) based solvent may be dropped. In this case,
opposite ends of the region where the electrode 215 is to be formed
may be irradiated with light having a photocatalytically activating
wavelength to be more oil-repellent.
[0103] In addition, it is preferable to form the interlayer
insulating film 213 since planarity is enhanced; on the other hand,
manufacturing steps are increased. Therefore, a contact hole may be
formed in the gate insulating film 210 without forming the
interlayer insulating film 213 and the electrode 215 may be
formed.
[0104] Thus, a thin film transistor having a narrower wiring, that
is, a smaller wiring in width than a diameter of a dot can be
formed by an ink-jet method utilizing a photocatalytic reaction.
The thin film transistor of this embodiment mode is a so-called top
gate thin film transistor in which a gate electrode is provided
above a semiconductor film.
[0105] In addition, unnecessary TiO.sub.2 may be removed in this
embodiment mode. An unnecessary region means a region where a
wiring is not formed; therefore, TiO.sub.2 can be removed by dry
etching or wet etching using a wiring as a mask.
Embodiment Mode 4
[0106] An example of forming a thin film transistor by a different
method from that of the above embodiment mode is described in this
embodiment mode. Note that TiO.sub.2 is used as a photocatalytic
substance.
[0107] First, a base film 201 is formed over a substrate 200 as in
the above embodiment mode and as shown in FIG. 4A. TiO.sub.2 is
formed as the photocatalytic substance 202 over an entire surface
of the base film. In addition, TiO.sub.2 can be used as the base
film; in this case, the base film can be omitted. TiO.sub.2 may be
formed as described in the above embodiment mode.
[0108] Subsequently, an irradiation region 203 is formed by
irradiating TiO.sub.2 in a desired region with light having a
photocatalytically activating wavelength. Then, the irradiation
region shows a hydrophilic property.
[0109] A dot including a conductive material mixed into a solvent
is dropped from above the irradiation region to the irradiation
region by an ink-jet method to form a wiring 204. A semiconductor
film having one conductivity, for example, a semiconductor film
having N-type conductivity 206 is formed, and the wiring 204 and
the semiconductor film having N-type conductivity 206 are
simultaneously patterned.
[0110] A semiconductor film 207 is formed over the semiconductor
film having N-type conductivity and is patterned as shown in FIG.
4B. For example, an amorphous semiconductor film is used as the
semiconductor film, a mask made of polyimide, polyvinyl alcohol, or
the like is formed over the amorphous semiconductor film by an
ink-jet method, and the amorphous semiconductor film is patterned
by using the mask. At this time, the semiconductor film having
N-type conductivity may be patterned at the same time. Thereafter,
a gate insulating film 210 is formed to cover the semiconductor
film and the like. An irradiation region 209 is formed by using
TiO.sub.2 as the gate insulating film and irradiating a desired
region with light having a photocatalytically activating
wavelength. Then, the irradiation region 209 shows a hydrophilic
property.
[0111] A dot including a conductive material mixed into a solvent
is dropped from above the irradiation region to the irradiation
region by an ink-jet method to form a gate electrode 211. A
water-based solvent is used to selectively drop a dot on the
hydrophilic region.
[0112] Alternatively, a dot including a conductive material
dispersed in an oil (alcohol) based solvent may be dropped. In this
case, opposite ends of a region where the gate electrode 211 is to
be formed may be irradiated with light having a photocatalytically
activating wavelength to be more oil-repellent.
[0113] As shown in FIG. 4C, an interlayer insulating film 214 is
formed, a contact hole is formed in a desired region, and a wiring
214 is formed in the contact hole. The wiring 214 can be formed by
an ink-jet method. Then, an electrode 215 is formed to connect to
the wiring 214. The electrode 215 can be formed by an ink jet
method.
[0114] The electrode 215 functions as a pixel electrode in a liquid
crystal display device and functions as an anode or a cathode of a
light emitting element in a light emitting device. A conductive
material dispersed in a water-based solvent can be used as the
electrode 215. Specifically, a transparent conductive film can be
formed by using a transparent conductive material. In addition,
TiO.sub.2 is formed on a top face of the interlayer insulating film
213, and a desired region where the electrode 215 is to be formed
may be irradiated with light having a photocatalytically activating
wavelength.
[0115] Alternatively, a dot including a conductive material mixed
into an oil (alcohol) based solvent may be dropped. In this case,
opposite ends of the region where the electrode 215 is to be formed
may be irradiated with light having a photocatalytically activating
wavelength to be more oil-repellent.
[0116] In addition, it is preferable to form the interlayer
insulating film 213 since planarity is enhanced; on the other hand,
manufacturing steps are increased. Therefore, a contact hole may be
formed in the gate insulating film 210 without forming the
interlayer insulating film 213 and the electrode 215 may be
formed.
[0117] Thus, a thin film transistor having a narrower wiring, that
is, a smaller wiring in width than a diameter of a dot can be
formed by an ink-jet method utilizing a photocatalytic reaction.
The thin film transistor of this embodiment mode is a so-called top
gate thin film transistor in which a gate electrode is provided
above a semiconductor film.
[0118] In addition, unnecessary TiO.sub.2 may be removed in this
embodiment mode. An unnecessary region means a region where a
wiring is not formed; therefore, TiO.sub.2 can be removed by dry
etching or wet etching using a wiring as a mask.
[0119] As described above, top gate thin film transistors having
various structures can be formed.
Embodiment Mode 5
[0120] An example of forming a thin film transistor by a different
method from that of the above embodiment mode is described in this
embodiment mode. Note that TiO.sub.2 is used as a photocatalytic
substance.
[0121] First, a base film 201 is formed over a substrate 200 as
described in the above embodiment mode and as shown in FIG. 4A. An
electrode 215 is formed over the base film. The electrode 215 can
be formed by an ink-jet method. In addition, a photocatalytic
substance is used for the base film, and is irradiated with light
to be hydrophilic or oil-repellent. Then, the electrode 215 may be
dropped by an ink-jet method.
[0122] A wiring 204 is entirely formed, and a semiconductor film
having one conductivity, for example, a semiconductor film having
N-type conductivity 206 is formed. The wiring 204 can be formed by
a sputtering method or an ink-jet method. Thereafter, TiO.sub.2 is
formed as the photocatalytic substance 202 over the semiconductor
film having N-type conductivity. An irradiation region 203 is
formed by irradiating TiO.sub.2 in a desired region with light. The
irradiation region shows a hydrophilic property.
[0123] Then, a mask 208 made of polyimide, polyvinyl alcohol, or
the like is formed over the semiconductor film having N-type
conductivity by an ink-jet method. At this time, a mask is formed
over the irradiation region. Therefore, the mask is formed by
dropping a dot having a water-based solvent. Accordingly, a
narrower mask than a diameter of a dot can be formed and minute
patterning can be performed. Further, heat treatment may be
performed if necessary to bake the mask.
[0124] The wiring, the semiconductor film having N-type
conductivity, and the photocatalytic substance are patterned by
using the mask as shown in FIG. 17B. The electrode 215 appears by
the patterning. Subsequently, washing is performed to remove the
mask. Further, the photocatalytic substance is removed by wet
etching or dry etching.
[0125] A semiconductor film 207 is formed and is patterned by using
the mask, as shown in FIG. 17C. Although not shown, the mask may be
formed by dropping polyimide, polyvinyl alcohol, or the like on the
semiconductor film by an ink-jet method. When the semiconductor
film is patterned, the semiconductor film having N-type
conductivity may be patterned at the same time.
[0126] Then, an insulating film which functions as a gate
insulating film 210 is formed to cover the semiconductor film. At
this time, the insulating film is not formed over the electrode
215. In this embodiment mode, the gate insulating film is formed by
using TiO.sub.2 which is the photocatalytic substance. An
irradiation region 209 is formed by irradiating TiO.sub.2 in a
desired region with light. The irradiation region shows a
hydrophilic property. Then, a conductive film which functions as a
gate electrode 211 is formed over the irradiation region.
Therefore, the conductive film is formed by dropping a dot
including a conductive material mixed into a water-based solvent.
Accordingly, a smaller gate electrode in width than a diameter of a
dot can be formed, and miniaturization can be achieved. Further,
heat treatment may be performed if necessary to bake the gate
electrode.
[0127] As described above, top gate thin film transistors having
various structures can be formed.
Embodiment Mode 6
[0128] An example of forming a thin film transistor by a different
method from that of the above embodiment mode is described in this
embodiment mode. Note that TiO.sub.2 is used as a photocatalytic
substance.
[0129] First, a base film 201 is formed over a substrate 200 as
described in the above embodiment mode and as shown in FIG. 5A.
TiO.sub.2 is entirely formed over the base film as the
photocatalytic substance 202. In addition, TiO.sub.2 can be used as
the base film; in this case, the base film can be omitted.
TiO.sub.2 may be formed as in the above embodiment mode.
[0130] Subsequently, an irradiation region 203 is formed by
irradiating TiO.sub.2 in a desired region with light having a
photocatalytically activating wavelength. Then, the irradiation
region shows a hydrophilic property.
[0131] A conductive film which functions as a gate electrode 211 is
formed by dropping a dot including a conductive material mixed into
a solvent from above the irradiation region, using an ink jet
method.
[0132] A gate electrode 210 is formed to cover the gate electrode
as shown in FIG. 5B. Thereafter, a semiconductor film 207 and a
semiconductor film having one conductivity, for example, a
semiconductor film having N-type conductivity 206 are formed by a
plasma CVD method or the like. At this time, the semiconductor film
207 and the semiconductor film having N-type conductivity 206 can
be continuously formed by changing a material gas and a flow rate
thereof. A mask 208 made of polyimide, polyvinyl alcohol, or the
like is formed over the semiconductor film having N-type
conductivity by an ink-jet method, and the semiconductor film and
the semiconductor film having N-type conductivity are patterned by
using the mask. Thereafter, washing is performed to remove the
mask.
[0133] A wiring 204 is formed as shown in FIG. 5C. The wiring 204
can be formed by an ink-jet method. The wiring 204 functions as a
so-called source electrode or drain electrode.
[0134] At this time, TiO.sub.2 is formed in a region where the
wiring 204 is to be formed and is irradiated with light having a
photocatalytically activating wavelength to be hydrophilic, and the
wiring may be formed by dropping a dot having a water-based
solvent.
[0135] Alternatively, the wiring can be formed by forming TiO.sub.2
at opposite ends where the wiring is to be formed, irradiating
TiO.sub.2 with light having a photocatalytically activating
wavelength to be oil-repellent, and dropping a dot having an oil
(alcohol) based solvent.
[0136] Thereafter, the wiring 204 is separated by using the wiring
204 as a mask and etching the semiconductor film having N-type
conductivity. At this time, the semiconductor film may be etched to
some extent. Preferably, a protect film is formed to cover the
etched semiconductor film. For example, polyimide or the like may
be dropped by an ink-jet method on the etched region of the
semiconductor film.
[0137] As shown in FIG. 5D, an interlayer insulating film 213 is
formed, a contact hole is formed in a desired region, and a wiring
214 is formed in the contact hole. The wiring 214 can be formed by
an ink-jet method. Then, an electrode 215 is formed to connect to
the wiring 214. The electrode 215 can be formed by an ink-jet
method.
[0138] The electrode 215 functions as a pixel electrode in a liquid
crystal display device and functions as an anode or a cathode of a
light emitting element in a light emitting device. A dot including
a conductive material mixed into a water-based solvent can be used
as the electrode 215. Specifically, a transparent conductive film
can be formed by using a transparent conductive material. In
addition, TiO.sub.2 is formed on a top face of the interlayer
insulating film 213, and a desired region where the electrode 215
is to be formed may be irradiated with light having a
photocatalytically activating wavelength.
[0139] In addition, a dot including a conductive material dispersed
in an oil (alcohol) based solvent may be dropped. In this case,
opposite ends of the region where the electrode 215 is to be formed
may be irradiated with light having a photocatalytically activating
wavelength to be more oil-repellent.
[0140] In addition, it is preferable to form the interlayer
insulating film 213 since planarity is enhanced; on the other hand,
manufacturing steps are increased. Therefore, a contact hole may be
formed in the gate insulating film 210 without forming the
interlayer insulating film 213 to form the electrode 215.
[0141] Thus, a thin film transistor having a narrower wiring, that
is, a smaller wiring in width than a diameter of a dot can be
formed by an ink-jet method utilizing a photocatalytic reaction.
The thin film transistor of this embodiment mode is a so-called
bottom gate thin film transistor in which a gate electrode is
provided below a semiconductor film and a so-called channel etch
thin film transistor in which a channel region is etched.
[0142] In addition, unnecessary TiO.sub.2 may be removed in this
embodiment mode. An unnecessary region means a region where a
wiring is not formed; therefore, TiO.sub.2 can be removed by dry
etching or wet etching using a wiring as a mask.
Embodiment Mode 7
[0143] An example of forming a thin film transistor by a different
method from that of the above embodiment mode is described in this
embodiment mode. Note that TiO.sub.2 is used as a photocatalytic
substance.
[0144] First, a base film 201 is formed over a substrate 200 as
described in the above embodiment mode and as shown in FIG. 6A.
TiO.sub.2 is entirely formed over the base film as the
photocatalytic substance 202. In addition, TiO.sub.2 can be used as
the base film; in this case, the base film can be omitted.
TiO.sub.2 may be formed as described in the above embodiment
mode.
[0145] Subsequently, an irradiation region 203 is formed by
irradiating TiO.sub.2 in a desired region, in this embodiment mode,
at opposite sides of a region where a wiring is to be formed with
light having a photocatalytically activating wavelength. Then, the
irradiation region shows an oil-repellent property.
[0146] A conductive film which functions as a gate electrode 211 is
formed by dropping a dot including a conductive material mixed into
a solvent from above a non-irradiation region to a non-irradiation
region, using an ink-jet method.
[0147] A gate insulating film 210 is formed to cover the gate
electrode as shown in FIG. 6B. Thereafter, a semiconductor film 207
is formed by a plasma CVD method or the like. An insulating film is
formed by, for example, a plasma CVD method, and is patterned to
have a desired shape in a desired region in order to form a channel
protective film 220. At this time, the channel protective film 220
can be formed by exposing a back of a substrate to light using the
gate electrode as a mask. In addition, polyimide, polyvinyl
alcohol, or the like may be dropped as the channel protective film
by an ink-jet method. Consequently, the light-exposure step can be
omitted.
[0148] Thereafter, a semiconductor film having one conductivity,
for example, a semiconductor film having N-type conductivity 206 is
formed by a plasma CVD method or the like.
[0149] A mask 208 made of polyimide is formed by an ink-jet method
over the N-type semiconductor film as shown in FIG. 6C. The
semiconductor film 207 and the semiconductor film having N-type
conductivity 206 are patterned by using the mask. Thereafter,
washing is performed to remove the mask.
[0150] A wiring 204 is formed as shown in FIG. 6D. The wiring 204
can be formed by an ink-jet method. The wiring 204 functions as a
so-called source electrode or drain electrode.
[0151] At this time, TiO.sub.2 is formed in a region where the
wiring 204 is to be formed and is irradiated with light having a
photocatalytically activating wavelength to be hydrophilic, and the
wiring may be formed by dropping a dot having a water-based
solvent.
[0152] Alternatively, the wiring can be formed by forming TiO.sub.2
at opposite ends where the wiring is to be formed, irradiating
TiO.sub.2 with light having a photocatalytically activating
wavelength to be oil-repellent, and dropping a dot having an oil
(alcohol) based solvent.
[0153] Then, an electrode 215 is formed to connect to the wiring
204. The electrode 215 can be formed by an ink-jet method.
[0154] The electrode 215 functions as a pixel electrode in a liquid
crystal display device and functions as an anode or a cathode of a
light emitting element in a light emitting device. A dot including
a conductive material mixed into a water-based solvent can be used
as the electrode 215. Specifically, a transparent conductive film
can be formed by using a transparent conductive material. In
addition, the gate insulating film is formed by using TiO.sub.2,
TiO.sub.2 is formed on a desired top face of the gate insulating
film, and a desired region where the electrode 215 is to be formed
may be irradiated with light having a photocatalytically activating
wavelength.
[0155] In addition, a dot including a conductive material dispersed
in an oil (alcohol) based solvent may be dropped. In this case,
opposite ends of the region where the electrode 215 is to be formed
may be irradiated with light having a photocatalytically activating
wavelength to be more oil-repellent.
[0156] In addition, the interlayer insulating film 213 may be
formed, a contact hole may be formed in the interlayer insulating
film, a wiring may be formed in the contact hole, and the wiring
and the electrode 215 may be connected to each other, as described
in the above embodiment mode. It is preferable to form the
interlayer insulating film since planarity is enhanced.
[0157] FIG. 7 is a top view of a thin film transistor shown in
FIGS. 6A to 6D. Note that FIG. 6D corresponds to a cross-sectional
view taken along a line A-A' in FIG. 7.
[0158] The gate electrode 211 is formed on the same layer as a
scanning line 502 by an ink-jet method. The irradiation region 203
where TiO.sub.2 formed at opposite ends of a region where at least
the gate electrode and the scanning line are to be formed is
irradiated with light having a photocatalytically activating
wavelength is formed, in order to make TiO.sub.2 more
oil-repellent.
[0159] Thereafter, the semiconductor film 207 or the like is formed
over the gate electrode. A channel protective film is formed over
the semiconductor film, and is irradiated with light from a back by
using the gate electrode to perform light exposure as described
above, although not shown. Then, the semiconductor film having
N-type conductivity is formed, and the semiconductor film and the
semiconductor film having N-type conductivity are patterned by
using a mask formed by an ink-jet method.
[0160] The wiring 204 is formed over the semiconductor film having
N-type conductivity, and the wiring is formed by an ink jet method
on the same layer as a signal line 501 to which a video signal or
the like is inputted. At this time, the gate insulating film may be
formed by using TiO.sub.2, or TiO.sub.2 is formed on a desired top
face of the gate insulating film, and opposite ends of a region
where a gate insulating film wiring and the signal line are to be
formed may be irradiated with light having a photocatalytically
activating wavelength to be more oil-repellent. At least opposite
ends of a region where the signal line is to be formed is
preferably irradiated with light having a photocatalytically
activating wavelength. Accordingly, a position of a wiring to be
formed can be controlled with accuracy.
[0161] Then, the electrode 215 is formed to connect to the wiring
204. The electrode 215 can be formed by an ink-jet method. In
addition, the electrode 215 can be formed by dropping a dot having
a water-based solvent or a dot having an oil (alcohol) based
solvent. Specifically, a dot having a water-based solvent is
dropped and a region thereof may be irradiated with light having a
photocatalytically activating wavelength to be hydrophilic, in the
case of making the electrode 215 thin. On the other band, a dot
having an oil (alcohol) based solvent is dropped and the periphery
of a region thereof (referred to as opposite ends in the
cross-sectional view) may be irradiated with light having a
photocatalytically activating wavelength to be oil-repellent, in
the case of making the electrode 215 thick. At this time, a film
thickness of the electrode 215 can be controlled in accordance with
the quantity of a dot to be dropped.
[0162] Thus, a thin film transistor having a narrower wiring, that
is, a smaller wiring in width than a diameter of a dot can be
formed by an ink-jet method utilizing a photocatalytic reaction.
The thin film transistor of this embodiment mode is a so-called
bottom gate thin film transistor in which a gate electrode is
provided below a semiconductor film and a so-called channel
protective thin film transistor in which a channel protective film
is formed.
[0163] In addition, unnecessary TiO.sub.2 may be removed in this
embodiment mode. An unnecessary region means a region where a
wiring is not formed; therefore, TiO.sub.2 can be removed by dry
etching or wet etching using a wiring as a mask.
Embodiment Mode 8
[0164] The case of forming a protective film to cover a thin film
transistor by an ink-jet method is described in this embodiment
mode.
[0165] FIG. 8A shows a top gate thin film transistor, in which a
wiring 204 and an electrode 215 are connected to each other without
forming an interlayer insulating film. An irradiation region 203
with respect to TiO.sub.2 is formed at opposite ends of a region
where the wiring 204 is to be formed, and the wiring 204 is formed
by dropping a dot having an oil (alcohol) based solvent. In
addition, the irradiation region 203 may be formed also in a region
where the electrode 215 is to be formed. In that case, the
electrode 215 may be formed by dropping a dot having a water-based
solvent.
[0166] Since an interlayer insulating film is not formed in the
thin film transistor shown in FIG. 8A, the thin film transistor can
be formed very thinly. In this state, a protective film 221 is
formed to cover a gate electrode 211 and a part of the electrode
215. For example, polyimide, polyvinyl alcohol, or the like may be
dropped by an ink-jet method. When such an interlayer insulating
film is not formed, the thin film transistor can be protected from
outside by forming a protective film.
[0167] FIG. 8B shows a channel etch thin film transistor, in which
a wiring 204 and an electrode 215 are connected to each other
without forming an interlayer insulating film. An irradiation
region 203 with respect to TiO.sub.2 is formed at opposite ends of
a region where a gate electrode 211 is to be formed, and the gate
electrode 211 is formed by dropping a dot having an oil (alcohol)
based solvent. In addition, the irradiation region 203 may be
formed also in a region where the electrode 215 is to be formed. In
that case, the electrode 215 may be formed by dropping a dot having
a water-based solvent.
[0168] Since an interlayer insulating film is not formed in the
thin film transistor shown in FIG. 8B, the thin film transistor can
be formed very thinly. In this state, a protective film 221 is
formed to cover the wiring 204 and a part of the electrode 215. For
example, polyimide or the like may be dropped by an ink-jet method.
When such an interlayer insulating film is not formed, the thin
film transistor can be protected from outside by forming a
protective film. Note that the protective film may be formed to
cover at least an etched channel formation region.
[0169] FIG. 8C shows a channel protective thin film transistor, in
which a wiring 204 and an electrode 215 are connected to each other
without forming an interlayer insulating film. An irradiation
region 203 with respect to TiO.sub.2 is formed at opposite ends of
a region where a gate electrode 211 is to be formed, and the gate
electrode 211 is formed by dropping a dot having an oil (alcohol)
based solvent. In addition, the irradiation region 203 may be
formed also in a region where the electrode 215 is to be formed. In
that case, the electrode 215 may be formed by dropping a dot having
a water-based solvent.
[0170] Since an interlayer insulating film is not formed in the
thin film transistor shown in FIG. 8C, the thin film transistor can
be formed very thinly. In this state, a protective film 221 is
formed to cover the wiring 204 and a part of the electrode 215. For
example, polyimide or the like may be dropped by an ink-jet method.
When such an interlayer insulating film is not formed, the thin
film transistor can be protected from outside by forming a
protective film.
[0171] The thin film transistor can be protected from outside by
forming a protective film with an ink-jet method in this way.
Further, it is preferable to form a protective film by an ink-jet
method since a light-exposure step of a photomask, an etching step
using the mask, and a removal step of the mask can be omitted.
Embodiment Mode 9
[0172] A light emitting device having a thin film transistor
described in the in above embodiment mode is described in this
embodiment mode.
[0173] As shown in FIG. 9A, a top gate N-channel type TFT is formed
in a driver circuit portion 310 and a pixel portion 311 based on
the above embodiment mode. Specifically, an N-channel type TFT
connected to a light emitting element formed in the pixel portion
311 is referred to as a driving TFT 301. An insulating film 302
referred to as a bank or a partition wall is formed to cover an
edge portion of an electrode (referred to as a first electrode) 215
included in the driving TFT 301. An inorganic material (silicon
oxide, silicon nitride, silicon oxynitride, or the like), a
photosensitive or non-photosensitive organic material (polyimide,
acrylic, polyamide, polyimidamide, a resist, or benzocyclobutene),
a material in which a skeletal structure is configured by a bond of
silicon (Si) and oxygen (O) and which contains at least hydrogen as
a substituent, or which contains at least one kind of fluorine, an
alkyl group, and aromatic hydrocarbon as a substituent, that is,
so-called siloxane, or a laminated structure thereof can be used as
the insulating film 302. A positive photosensitive organic resin or
a negative photosensitive organic resin can be used as the organic
material.
[0174] An opening is formed in the insulating film 302 over the
first electrode 215. The opening is provided with an
electroluminescent layer 303, and a second electrode 304 of a light
emitting element is provided to cover the electroluminescent layer
and the insulating film 302.
[0175] Note that a singlet excited state and a triplet excited
state can be given as the kind of a molecular exciton generated in
the electroluminescent layer. A ground state is normally a singlet
state; therefore, luminescence from a siglet excited state is
referred to as fluorescence and luminescence from a triplet excited
state is referred to as phosphorescence. Luminescence from the
electroluminescent layer includes the case where either excited
state contributes. In addition, fluorescence and phosphorescence
can be combined and used, and can be selected in accordance with a
luminescence property (such as light-emitting luminance or life) of
each RGB.
[0176] The electroluminescent layer 303 is formed by sequentially
laminating an HIL (hole injection layer), an HTL (hole transport
layer), an EML (emission layer), an ETL (electron transport layer),
and an EIL (electron injection layer) in this order from a side of
the first electrode 215. Note that the electroluminescent layer can
have a single layer structure or a combined structure as well as a
laminated structure.
[0177] In the case of full color display, a material showing light
of red (R), green (G), and blue (B) may be selectively formed as
the electroluminescent layer 303 by an evaporation method using an
evaporation mask for each, an ink-jet method, or the like. It is
preferable to form it by an ink-jet method since RGB can be
separately colored without using a mask. Obviously, a monochrome
electroluminescent layer may be formed by an ink-jet method.
[0178] Specifically, CuPc or PEDOT is used as the HIL; .alpha.-NPD,
as the HTL; BCP or Alq.sub.3, as the ETL; BCP:Li or CaF.sub.2, as
the EIL respectively. In addition, Alq.sub.3 doped with a dopant in
accordance with the respective colors of R, G, and B (DCM or the
like in the case of R, and DMQD or the like in the case of G) may
be used as the EML, for example. Note that the electroluminescent
layer is not limited to a material having the above laminated
structure. For example, a hole injection property can be enhanced
by co-evaporating oxide such as molybdenum oxide (MoOx: x=2 to 3)
and a-NPD or rubrene. An organic material (including a low
molecular weight material or a high molecular weight material) or a
composite material of an organic material and an inorganic material
can be used as the material.
[0179] In the case of forming an electroluminescent layer of each
RGB, high-definition display can be performed by using a color
filter.
[0180] In the case of forming an electroluminescent layer showing
white light-emission, full color display can be performed by
separately providing a color filter, a color filter and a color
conversion layer, or the like. The color filter or the color
conversion layer may be formed over a second substrate (sealing
substrate) for example, and then, attached. The color filter or the
color conversion layer can be formed by an ink-jet method.
Obviously, monochrome light emitting device may be formed by
forming an electroluminescent layer which shows light-emission
except white. In addition, an area color type display device which
can perform monochrome display may be formed. A passive matrix
display portion is suitable for the area color type and can mainly
display characters and symbols.
[0181] In addition, it is necessary to select materials of the
first electrode 215 and the second electrode 304 in consideration
of a work function. However, both the first electrode and the
second electrode can be an anode or a cathode depending on a pixel
structure. Since polarity of the driving TFT is an N-channel type,
the first electrode is preferably a cathode and the second
electrode is preferably an anode in this embodiment mode. When
polarity of the driving TFT is a P-channel type, the first
electrode is preferably an anode and the second electrode is
preferably a cathode.
[0182] Hereinafter, an electrode material used for an anode and a
cathode is described.
[0183] It is preferable to use a metal, an alloy, a conductive
compound, a mixture thereof, or the like having a high work
function (work function: 4.0 eV) as an electrode material used for
the anode. ITO (indium tin oxide), IZO (indium zinc oxide) in which
zinc oxide (ZnO) of from 2% to 20% is mixed into indium oxide, ITSO
in which silicon oxide (SiO.sub.2) of from 2% to 20% is mixed into
indium oxide, gold (Au), platinum (Pt), nickel (Ni), tungsten (W),
chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper
(Cu), palladium (Pd), nitride (TiN) of a metal material, or the
like can be used as a specific material.
[0184] On the other band, it is preferable to use a metal, an
alloy, a conductive to compound, a mixture thereof, or the like
having a low work function (work function: equal to or less than
3.8 eV) as an electrode material used for the cathode. An element
belonging to Group 1 or 2 in the periodic table, that is, alkaline
metal such as Li or Cs, alkaline earth metal such as Mg, Ca, or Sr,
an alloy (Mg:Ag or Al:Li) or a compound (LiF, CsF, or CaF.sub.2)
including them, or a transition metal including a rare-earth metal
can be used as a specific material. However, the second electrode
can be formed by very thinly forming the metal or an alloy
including the metal and by laminating ITO, IZO, ITSO, or another
metal (including an alloy) thereover, since the second electrode is
not light transmitting in this embodiment mode.
[0185] The first electrode and the second electrode can be formed
by an evaporation method, a sputtering method, an ink-jet method,
or the like.
[0186] In the case of forming a conductive film, ITO or ITSO, or a
lamination body thereof as the second electrode by a sputtering
method, the electroluminescent layer may be damaged. In order to
reduce damage due to a sputtering method, oxide such as molybdenum
oxide (MoOx: x=2 to 3) is preferably formed on a top surface of the
electroluminescent layer. Therefore, oxide such as molybdenum oxide
(MoOx: x=2 to 3) which functions as the HIL or the like is formed
on a top face of the electroluminescent layer. An EIL (electron
injection layer), an ETL (electron transport layer), an EML
(emission layer), an HTL (hole transport layer), an HIL (hole
injection layer), and the second electrode may be laminated in this
order from a side of the first electrode. At this time, the first
electrode functions as a cathode and the second electrode functions
as an anode.
[0187] Since polarity of the driving TFT is an N-channel type in
this embodiment mode, the first electrode is preferably a cathode,
and the EIL (electron injection layer), the ETL (electron transport
layer), the EMI, (emission layer), the HTL (hole transport layer),
the HIL (hole injection layer), and the second electrode are
preferably an anode in consideration of a moving direction of an
electron.
[0188] Thereafter, a passivation film containing nitrogen, a DLC,
or the like is preferably formed by a sputtering method or a CVD
method. Accordingly, penetration of moisture and oxygen can be
prevented. In addition, penetration of oxygen or moisture can be
prevented by covering a side of a display means with the first
electrode, the second electrode, or another electrode.
Subsequently, a sealing substrate is attached. A space formed by
the sealing substrate may be encapsulated with nitrogen or may be
provided with a drying agent. In addition, a light transmitting and
high absorbent resin may be filled.
[0189] In addition, a polarizing plate or a circular polarizing
plate may be provided to increase contrast. For example, one side
of or both sides of a display surface can be provided with a
polarizing plate or a circular polarizing plate.
[0190] The first electrode and the second electrode are light
transmitting in the light emitting device having a thus formed
structure. Therefore, light is emitted in both arrow directions 305
and 306 from the electroluminescent layer with luminance in
accordance with a video signal inputted from a signal line.
[0191] A structure of a light emitting device shown in FIG. 9B is
based on the above embodiment mode, and a channel etch N-channel
type TFT is formed in the driver circuit portion 310 and the pixel
portion 311. As described in FIG. 9A, an N channel TFT connected to
a light emitting element formed in the pixel portion 311 is
referred to as the driving TFT 301. The light emitting device is
different from that in FIG. 9A in the way that the first electrode
215 is a non-light-transmitting, preferably, highly reflective
conductive film and the second electrode 304 is a light
transmitting conductive film. Therefore, a light emitting direction
is only on a sealing substrate side.
[0192] In the case of using a light transmitting conductive film
formed by a sputtering method as the second electrode in FIG. 9B,
the electroluminescent layer may be damaged as described above. In
order to reduce damage due to a sputtering method, oxide such as
molybdenum oxide (MoOx: x=2 to 3) is preferably formed on a top
surface of the electroluminescent layer. Therefore, oxide such as
molybdenum oxide (MoOx: x=2 to 3) which functions as an HIL or the
like is formed on a top surface of the electroluminescent layer,
and an EIL (electron injection layer), an ETL (electron transport
layer), an EML (emission layer), an HTL (hole transport layer), an
HIL (hole injection layer), and the second electrode may be
sequentially laminated in this order from a side of the first
electrode. Since polarity of the driving TFT is an N-channel type
specifically in this embodiment mode, the first electrode is
preferably a cathode, and the EIL (electron injection layer), the
ETL (electron transport layer), the EML (emission layer), the HTL
(hole transport layer), the JUL (hole injection layer), and the
second electrode are preferably an anode. Since other structures
are similar to that in FIG. 9A, description is omitted.
[0193] A structure of a light emitting device shown in FIG. 9C is
based on the above embodiment mode, and a channel protective
N-channel type TFT is formed in the driver circuit portion 310 and
the pixel portion 311. As in FIG. 9A, an N-channel type TFT
connected to a light emitting element formed in the pixel portion
311 is referred to as the driving TFT 301. The light emitting
device is different from that in FIG. 9A in the way that the first
electrode 215 is a light transmitting conductive film and the
second electrode 304 is a non-light-transmitting, preferably,
highly reflective conductive film. Therefore, a light emitting
direction 306 is only on a sealing substrate side.
[0194] In the case of using a non-light-transmitting conductive
film formed by a sputtering method as the second electrode in FIG.
9C, the electroluminescent layer may be damaged as described above.
In order to reduce damage due to a sputtering method, oxide such as
molybdenum oxide (MoOx: x=2 to 3) is preferably formed on a top
surface of the electroluminescent layer. Therefore, oxide such as
molybdenum oxide (MoOx: x=2 to 3) which functions as an HIL or the
like is formed on a top surface of the electroluminescent layer,
and an EIL (electron injection layer), an ETL (electron transport
layer), an EML (emission layer), an HTL (hole transport layer), an
HIL (hole injection layer), and the second electrode may be
sequentially laminated in this order from a side of the first
electrode. Since polarity of the driving TFT is an N-channel type
specifically in this embodiment mode, the first electrode is
preferably a cathode, and the EIL (electron injection layer), the
ETL (electron transport layer), the EML (emission layer), the HTL
(hole transport layer), the HIL (hole injection layer), and the
second electrode are preferably an anode. Since other structures
are similar to that in FIG. 9A, description is omitted.
[0195] Light can be efficiently utilized by using a highly
reflective conductive film as a non-light-transmitting electrode
provided on a side which does not become a light emitting direction
as in FIGS. 9B and 9C.
[0196] In this embodiment mode, a non-light-transmitting conductive
film is thinly formed to be light transmitting in order to obtain a
light transmitting conductive film, and a light-transmitting
conductive film may be laminated thereover.
[0197] Hereinbefore, a structure of a light emitting device is
described using each thin film transistor; however, a structure of
a thin film transistor and a structure of a light emitting device
may be combined anyhow.
[0198] Note that digital gradation display and analog gradation
display can be performed in a light emitting device; however,
analog gradation display is preferably performed in a light
emitting device using an amorphous semiconductor film.
Embodiment Mode 10
[0199] A light emitting device different from a light emitting
device having a thin film transistor described in the above
embodiment mode is described in this embodiment mode. Specifically,
an, insulating film 302 referred to as a bank or a partition wall
is formed to cover the electrode 215 without forming an interlayer
insulating film.
[0200] In a light emitting device shown in FIGS. 10A to 10C, a top
gate N-channel type TFT (referred to as a driving TFT 301) is
formed in the pixel portion, based on the above embodiment mode. An
electrode (referred to as a first electrode) 215 connected to the
driving TFT 301 is formed. At this time, an irradiation region 203
or a gate electrode 211 is oil-repellent, and a dot including a
conductive material mixed into an oil (alcohol) based solvent is
used as a dot for forming the wiring 204. Then, a dot including a
conductive material mixed into a water-based solvent may be used as
a dot for forming the electrode 215. In other words, a
photocatalytic substance can be at once hydrophilic and
oil-repellent when light irradiation is continued. In this way, a
solvent of a dot to be a wiring material can be separately used in
accordance with a photocatalyst substance.
[0201] Thereafter, the insulating film 302 referred to as a bank or
a partition wall is formed to cover the electrode 215, and an
opening is formed in the insulating film 302 over the electrode
215.
[0202] At this time, the insulating film 302 is formed without
forming an interlayer insulating film; therefore, a very thin
lightweight light emitting device can be formed. In addition, the
insulating film 302 has a function as a protective film 221
described in the above embodiment mode; therefore, a step of
forming a protective film of polyimide, polyvinyl alcohol, or the
like can be reduced.
[0203] An opening is formed in the insulating film 302 over the
first electrode 215. The opening is proved with an
electroluminescent layer 303, and a second electrode 304 of a light
emitting element is provided to cover the electroluminescent layer
and the insulating film 302.
[0204] Steps thereafter are similar to those shown in FIGS. 9A to
9C described in the above embodiment mode; therefore, description
is omitted.
[0205] As described above, this embodiment mode can form a very
thin lightweight light emitting device.
Embodiment Mode 11
[0206] An equivalent circuit diagram and a top view of a light
emitting device including a thin film transistor having an
amorphous semiconductor film described in the above embodiment mode
are described in this embodiment mode. Although a TFT has three
terminals, that is, a gate, a source, and a drain, a source
terminal (source electrode) and a drain terminal (drain electrode)
cannot be clearly distinguished because of a transistor structure.
Therefore, one of a source electrode and a drain electrode is
referred to as a first electrode, and the other is referred to as a
second electrode, when connection between terminals is
described.
[0207] FIG. 20A shows an equivalent circuit diagram of a pixel
portion of a light emitting device. One pixel includes a TFT for
switching (switching TFT) 1000, a TFT for driving (driving TFT),
and a TFT for controlling current (current controlling TFT) 1002,
and these TFTs are N-channel types. One electrode and a gate
electrode of the switching TFT 1000 are connected to a signal line
1003 and a scanning line 1005, respectively. One electrode of the
current controlling TFT 1002 is connected to a first power supply
line 1004, and a gate electrode is connected to the other electrode
of the switching TFT.
[0208] A capacitor element 1008 may be provided to hold gate-source
voltage of the current controlling TFT. In this embodiment mode,
when electric potential of the first power supply line is low and
that of a light emitting element is high, the current controlling
TFT is an N-channel type. Therefore, the source electrode and the
first power supply line are connected. Therefore, the capacitor
element can be provided between the gate electrode and a source
electrode of the current controlling TFT, that is, the first power
supply line. When the switching TFT, the driving TFT, or the
current controlling TFT has a large gate capacity and leak current
from each TFT is tolerance, the capacitor element 1008 does not
need to be provided.
[0209] One electrode of the driving TFT 1001 is connected to the
other electrode of the current controlling TFT, and the gate
electrode is connected to a second power supply line 1006. The
second power supply line 1006 has fixed electric potential.
Therefore, gate electric potential of the driving TFT can be fixed
electric potential, and the driving TFT can be operated so that
gate-source voltage Vgs by parasitic capacitance or wiring
capacitance does not change.
[0210] Then, a light emitting element 1007 is connected to the
other electrode of the driving TFT. In this embodiment mode, when
electric potential of the first power supply line is low and that
of the light emitting element is high, a cathode of the light
emitting element is connected to a drain electrode of the driving
TFT. Therefore, it is preferable to sequentially laminate a
cathode, an electroluminescent layer, and an anode as described
above. At this time, in order to reduce damage due to a sputtering
method during forming the second electrode, oxide such as
molybdenum oxide (MoOx: x=2 to 3) is preferably formed on a top
surface of the electroluminescent layer. Therefore, it is more
preferable to form oxide such as molybdenum oxide (MoOx: x=2 to 3)
which functions as an HIL or the like on a top surface of the
electroluminescent layer. In this way, it is preferable to connect
the drain electrode and the cathode of the TFT and to laminate an
EIL, an ETL, an EML, an HTL, an HIL, and an anode in this order, in
the case of a TFT having an amorphous semiconductor film and an
N-channel type.
[0211] Hereinafter, operation of such a pixel circuit is
described.
[0212] When the scanning line 1005 is selected and the switching
TFT is turned ON, a charge begins to be stored in the capacitor
element 1008. The charge in the capacitor element 1008 is stored
until it becomes equal to gate-source voltage of the current
controlling TFT. When it gets equal, the current controlling TFT is
turned ON, and then, a serially connected driving TFT is turned ON.
At this time, gate potential of the driving TFT is fixed potential.
Therefore, constant gate-source voltage Vgs which does not depend
on the parasitic capacitance or the wiring capacitance can be
applied to the light emitting element. Namely, current for the
constant gate-source voltage Vgs can be supplied.
[0213] Since the light emitting element is a current driving type
element, it is preferable to employ analog driving in the case of
having few characteristic variation of the TFT in the pixel,
specifically, Vth variation. As in this embodiment mode, a TFT
having an amorphous semiconductor film has few characteristics
variation; therefore, analog driving can be employed. On the other
hand, a constant current value can be supplied to the light
emitting element even with digital driving by operating the driving
TFT in a saturation region (region satisfying
|Vgs-Vth|<|Vds|).
[0214] FIG. 20B shows an example of a top view of a light emitting
device having the above equivalent circuit.
[0215] First, a gate electrode, a scanning line, and a second power
supply line of each TFT are formed on the same layer by an ink jet
method. An irradiation region 1009 which is irradiated with light
having a photocatalytically activating wavelength is formed within
TiO.sub.2 formed at opposite ends of a region where at least the
gate electrode and the scanning line are to be formed, in order to
make the irradiation region 1009 more oil-repellent.
[0216] Then, a semiconductor film of each TFT is formed. The
semiconductor film is entirely formed by a plasma CVD method to be
a semiconductor film of each TFT by using a mask, in this
embodiment mode. Although not shown, a gate insulating film is
subsequently formed.
[0217] Then, a source electrode, a drain electrode, a signal line,
and a first power supply line are formed on the same layer. The
source electrode, the drain electrode, the signal line, and the
first power supply line can be formed by an ink-jet method, a
plasma CVD method, or the like.
[0218] A contact hole is formed in the gate insulating film to
connect one wiring of the switching TFT to the gate electrode of
the current controlling TFT.
[0219] In this embodiment mode, the capacitor element 1008 is made
up of a gate wiring and a source-drain wiring which are disposed
with the gate insulating film therebetween.
[0220] An electrode 1010 of the light emitting element 1007 is
formed to connect to one electrode of the driving TFT.
[0221] Since the driving TFT has an amorphous semiconductor film,
it is designed to have a wide channel width (W).
[0222] In this way, a pixel portion of a light emitting device can
be formed.
[0223] In this embodiment mode, an active matrix light emitting
device where one pixel is provided with each TFT is described;
however, a passive matrix light emitting device where a TFT is
provided every line can be formed. The passive matrix light
emitting device has a high aperture ratio since each pixel is not
provided with the TFT. Therefore, the passive matrix display device
is preferably used in the case of a light emitting device which
emits light to both sides of the electroluminescent layer. When
pixel density is increased, the active matrix light emitting device
is considered to have an advantage over low voltage driving since
each pixel is provided with the TFT.
[0224] Such a thin film transistor having a narrower wiring, that
is, a smaller wiring in width than a diameter of a dot can be
formed by an ink-jet method utilizing a photocatalytic
reaction.
[0225] In addition, unnecessary TiO.sub.2 may be removed in this
embodiment mode. An unnecessary region means a region where a
wiring is not formed; therefore, TiO.sub.2 can be removed by dry
etching or wet etching using a wiring as a mask.
Embodiment Mode 12
[0226] A structure of a top gate thin film transistor in which a
semiconductor film having one conductivity is formed without a
plasma CVD method is described in this embodiment mode.
[0227] A base film 201, a photocatalytic substance 202, an
irradiation region 203, a wiring 204 formed by an ink-jet method, a
semiconductor film 207, a gate insulating film 210 made of
TiO.sub.2, an irradiation region 209 within the gate insulating
film, and a gate electrode 211 formed by an ink-jet method are
formed over a substrate 200 having an insulating surface as
described in the above embodiment mode and as shown in FIG. 11A. In
order to form the wiring 204 and the gate electrode 211 in the
irradiation regions 203 and 209 respectively by an ink-jet method,
a water-based solvent is used as a solvent thereof. Note that they
may be formed by using a dot having an oil (alcohol) based solvent;
in that case, an irradiation region may be formed at opposite ends
of a region where the wiring or the gate electrode is to be
formed.
[0228] Thereafter, instead of forming a semiconductor film having
one conductivity, for example, a semiconductor film having N-type
conductivity, an impurity element having N-type conductivity, for
example, phosphorus (P) is added using the gate electrode as a
mask. Accordingly, a connection resistance between the
semiconductor film and the wiring (corresponding to a source
electrode and a drain electrode) 204 can be decreased. In addition,
steps can be reduced since it becomes unnecessary to pattern the
semiconductor film having N-type conductivity formed between the
wirings 204.
[0229] An interlayer insulating film 213 is formed to cover the
gate electrode 211 as shown in FIG. 11B. A contact hole is formed
in the interlayer insulating film 213 formed over the wiring 204. A
wiring 214 is formed in the contact hole, and an electrode 215 is
formed to connect to the wiring 214. The electrode 215 can be
formed by an ink-jet method.
[0230] An insulating film 302 referred to as a bank or a partition
wall is formed to cover the electrode 215, and an opening is formed
in the insulating film 302 over the electrode 215, as shown in FIG.
11C. Since a material of the insulating film is similar to that in
the above embodiment mode, description is omitted. An
electroluminescent layer 303 is formed in the opening to be in
contact with the electrode 215. Then, a second electrode 304 is
formed to cover the electroluminescent layer. Since a structure of
the electroluminescent layer is similar to that in the above
embodiment mode, description is omitted. Since structures of the
first electrode 215 and the second electrode 304 are similar to
those in the above embodiment mode, description is omitted.
[0231] Connection resistance between the semiconductor film and the
source wiring and the drain wiring can be decreased by adding an
impurity element instead of forming a semiconductor film having
N-type conductivity as described above. Further, a step of
patterning the semiconductor film having N-type conductivity can be
omitted.
Embodiment Mode 13
[0232] A thin film transistor using a crystalline semiconductor
film is described in this embodiment mode.
[0233] A base film 401 is formed over a substrate 400 having an
insulating surface as shown in FIG. 12A. The base film 401 may have
a laminated structure. In this embodiment mode, a silicon
oxynitride film formed as a first base film 401a to be from 10 nm
to 200 nm (preferably, from 50 nm to 200 nm) in thickness by a
plasma CVD method with SiH.sub.s, N.sub.2O, NH.sub.3, or N.sub.2
used as a material gas, pressure of 0.3 Torr (39.9 Pa), RF power of
50 W, an RF frequency of 60 MHz, and a substrate temperature of
400.degree. C., and a silicon oxynitride film formed as a second
base film 401b to be from 50 nm to 200 nm (preferably, from 150 nm
to 200 nm) in thickness by a plasma CVD method with SiH.sub.s or
N.sub.2O used as a material gas, pressure of 0.3 Torr (39.9 Pa), RF
power of 150 W, an RF frequency of 60 MHz, and a substrate
temperature of 400.degree. C. are sequentially laminated.
[0234] An amorphous semiconductor film is formed over the base film
401. A film thickness of the amorphous semiconductor film is from
25 nm to 100 nm (preferably, from 30 nm to 60 nm). In addition,
silicon germanium as well as silicon can be used for the amorphous
semiconductor. In the case of using silicon germanium, a
concentration of germanium is preferably set about from 0.01 atomic
% to 4.5 atomic %. In this embodiment mode, a semiconductor film
containing silicon as its main component (also referred to as an
amorphous silicon film) having a thickness of 66 nm is used.
[0235] Subsequently, the amorphous semiconductor film is
crystallized to form a crystalline semiconductor film. As a
crystallizing means, a metal element which promotes crystallization
can be added and be heated. It is preferable to form a metal
element since crystallization can be performed at low temperature.
However, a step of removing the metal element is required. One of
or a plurality of Ni, Fe, Co, Pd, Pt, Cu, Au, Ag, In, and Sn can be
used as the metal element.
[0236] In addition, the amorphous semiconductor film may be
irradiated with laser light. A continuous wave laser (CW laser) or
a pulsed oscillation laser (pulsed laser) can be used. One of or a
plurality of an Ar laser, a Kr laser, an excimer laser, a YAG
laser, a Y.sub.2O.sub.3 laser, a YVO.sub.4 laser, a YLF laser, a
YAlO.sub.3 laser, a glass laser, a ruby laser, an alexandrite
laser, a Ti:sapphire laser, a copper vapor laser, and a gold vapor
laser can be used as the laser.
[0237] For example, a Ni solution (including an aqueous solution
and an acetic acid solution) is applied onto the amorphous
semiconductor film by an application method such as a spin coating
method or a dip method. At this time, in order to improve
wettability of the surface of the amorphous semiconductor film and
to coat all over the surface thereof with the solution, it is
desirable to form an oxide film to be from 1 nm to 5 nm by UV light
radiation in the oxygen atmosphere, by a thermal oxidation method,
by treatment using ozone water or hydrogen peroxide including a
hydroxyl radical, or the like. Alternatively, a Ni ion can be
injected to the amorphous semiconductor film by an ion implantation
method; heat treatment can be performed in the water vapor
atmosphere including Ni; or the sputtering can be performed using a
Ni material as a target under Ar plasma. In this embodiment mode,
an aqueous solution containing Ni acetate by 10 ppm is applied by a
spin coating method.
[0238] Thereafter, the amorphous semiconductor is heated at a
temperature of from 500.degree. C. to 550.degree. C. for 2 hours to
20 hours to crystallize the amorphous semiconductor film, so that
the crystalline semiconductor film is formed. In the heat
treatment, it is preferable to gradually change the heating
temperature. The initial low-temperature heat treatment can extract
hydrogen or the like in the amorphous semiconductor film.
Accordingly, so-called dehydrogenation which reduces the roughness
of the film in the crystallization can be performed. Alternatively,
a magnetic field may be applied to crystallize the semiconductor
film in combination with its magnetic energy, or a microwave of
high output may also be used. In this embodiment mode, the heat
treatment is performed at a temperature of 550.degree. C. for 4
hours after heat treatment at a temperature of 500.degree. C. for
one hour by using a vertical furnace.
[0239] Then, the crystalline semiconductor film is patterned to
form an island-shaped semiconductor film 402.
[0240] An insulating film which functions as a gate insulating film
404 is formed to cover the island-shaped semiconductor film 402 as
shown in FIG. 12B. In this embodiment mode, TiO.sub.2 which is a
photocatalytic substance is used for the gate insulating film.
TiO.sub.2 can be manufactured by the method described in the above
embodiment mode.
[0241] Then, an irradiation region 405 is formed over TiO.sub.2 in
a region where a conductive film which functions as a gate
electrode is to be formed. The irradiation region shows a
hydrophilic property. Therefore, a dot including a conductive
material mixed into a water-based solvent is used in this
embodiment mode in the case of forming the gate electrode by an
ink-jet method. The conductive film can be selected from the
material described in the above embodiment mode, and Al is used in
this embodiment mode. Then, a dot is dropped from above the
irradiation region to the irradiation region. Thereafter, a gate
electrode 406 is formed by performing heat treatment for baking or
the like as described in the above embodiment mode.
[0242] Subsequently, an impurity element is added in a self-aligned
manner by using the gate electrode 406. For example, phosphorus (P)
is added to the semiconductor film to be an N channel thin film
transistor and boron (B) is added to the semiconductor film to be a
P channel thin film transistor.
[0243] An insulating film 407 containing nitrogen is formed to
cover the gate electrode 406 as shown in FIG. 12C. In this
embodiment mode, the insulating film 407 can be formed by an
ink-jet method. Subsequently, a dangling bond of the semiconductor
film can be reduced by thereafter heating with the insulating film
407 provided.
[0244] An interlayer insulating film 408 is formed to cover the
insulating film 407 as shown in FIG. 12D. An inorganic material
(silicon oxide, silicon nitride, silicon oxynitride, or the like),
a photosensitive or non-photosensitive organic material (polyimide,
acrylic, polyamide, polyimidamide, a resist, or benzocyclobutene),
a material in which a skeletal structure is configured by a bond of
silicon (Si) and oxygen (O) and which contains at least hydrogen as
a substituent, or which contains at least one kind of fluorine, an
alkyl group, and aromatic hydrocarbon as a substituent, that is,
so-called siloxane, or a laminated structure thereof can be used as
the interlayer insulating film. A positive photosensitive organic
resin or a negative photosensitive organic resin can be used as the
organic material. For example, when positive photosensitive acrylic
is used as the organic material, an opening having a curvature in
its top edge portion can be formed by etching the photosensitive
organic resin with light-exposure treatment.
[0245] A contact hole is opened in the interlayer insulating film
408 over an impurity region to form an electrode 409. The electrode
409 can also be formed by an ink jet method.
[0246] A thin film transistor can be formed as described above. A
semiconductor device having such a thin film transistor is, for
example, an integrated circuit or a semiconductor display device.
The thin film transistor formed as described in the above
embodiment mode can be used particularly in a pixel portion and in
a driver circuit portion of the semiconductor display device such
as a liquid crystal display device, a DMD (Digital Micromirror
Device), a PDP (Plasma Display Panel), or an FED (Field Emission
Display).
[0247] Thus, a narrower wiring, that is, a smaller wiring in width
than a diameter of a dot can be formed using a dot by an ink-jet
method utilizing a photocatalytic reaction for a wiring or an
electrode of a thin film transistor having a crystalline
semiconductor film. Further, a wiring can be formed along a region
in which photocatalytic activity is increased even in the case
where a dot is discharged out of alignment to some extent. Thus, a
position of a wiring to be formed can be controlled with
accuracy.
Embodiment Mode 14
[0248] A thin film transistor using a crystalline semiconductor
film, manufactured by a different method from the above embodiment
mode is described in this embodiment mode.
[0249] Base films 401a and 401b, an island-shaped semiconductor
film 402, a gate insulating film 404 containing TiO.sub.2, an
irradiation region 405, and a gate electrode 406 are formed over a
substrate 400 having an insulating surface as described in the
above embodiment mode and as shown in FIG. 13A. Then, the gate
insulating film 404 containing TiO.sub.2 is etched, using the gate
electrode 406 as a mask. Wet etching or dry etching may be used as
an etching means. Accordingly, TiO.sub.2 except a region where the
gate electrode is formed can be removed. As for TiO.sub.2,
TiO.sub.2 can be prevented from being photocatalytically activated
by a later step or external light by removing TiO.sub.2 since it
has a photocatalytic function.
[0250] A metal film 410 is formed to cover the island-shaped
semiconductor film 402 as shown in FIG. 13B. Then, silicide is
formed by reacting the metal film and silicon contained in the
island-shaped semiconductor film. The metal film is preferably such
a material that silicide to be formed later can have an ohmic
contact or close to ohmic contact which is low resistance with the
semiconductor. Specifically, molybdenum (Mo), tungsten (W),
platinum (Pt), chromium (Cr), titanium (Ti), or cobalt (Co) is
preferable. At least one of the above metal materials is reacted
with silicon to be silicide. In addition, a laser is emitted from
above or a substrate side or heating is performed by an electric
furnace to form silicide.
[0251] Thereafter, the metal film 410 is removed, and silicide 411
can be formed in a source region and a drain region as shown in
FIG. 13C. At this time, it is necessary to control a film thickness
of the gate insulating film and a film thickness of silicide to
prevent silicide in the source region and the drain region and the
gate electrode from short-circuiting.
[0252] Subsequently, an insulating film 407 and an interlayer
insulating film 408 are formed as described in the above embodiment
mode and as shown in FIG. 13D. Etching is performed so that the
insulating film 407 and the interlayer insulating film 408, and the
island-shaped semiconductor film 402 can have a selection ratio,
and an electrode (also referred to as a source wiring or a drain
wiring) 409 connected to the silicide 411 is formed. The electrode
409 can be formed by an ink-jet method.
[0253] With the use of such silicide, a contamination element can
be prevented from adhering to the island-shaped semiconductor film
in a region where the gate insulating film is removed in a
manufacturing step. Further, resistance of the source region and
the drain region can be reduced by the silicide.
[0254] In addition, a photocatalytic substance can be prevented
from being photocatalytically activated in an unnecessary region by
removing the photocatalytic substance as described in this
embodiment mode.
Embodiment Mode 15
[0255] An example of using a thin film transistor using a
crystalline semiconductor film in a light emitting device is
described in this embodiment mode.
[0256] A thin film transistor using a crystalline semiconductor
film as in the above embodiment mode can be used in a light
emitting device as described in the above embodiment mode. A light
emitting direction from an electroluminescent layer can be
determined by controlling a light transmitting property of a first
electrode and a second electrode as described in the above
embodiment mode.
[0257] In addition, one pixel is preferably provided with a
plurality of thin film transistors in the case of using the
crystalline semiconductor film. Each thin film transistor functions
as a switching transistor connected to a signal line to which a
video signal is inputted, a driving transistor connected to a light
emitting element, and a current controlling transistor connected to
the driving transistor. A characteristic of each thin film
transistor can be either enhancement mode or depletion mode.
[0258] Preferably, the switching transistor is an N channel
transistor, and the driving transistor and the current controlling
transistor are P channel transistors. Since the driving transistor
is a P channel transistor, the light emitting element may be formed
by sequentially laminating an HIL (hole injection layer), an HTL
(hole transport layer), an EML (emission layer), an ETL (electron
transport layer), and an EIL (electron injection layer) in this
order from the first electrode side. At this time, the first
electrode functions as an anode, and the second electrode functions
as a cathode.
[0259] In a light emitting device equipped with a thin film
transistor having a crystalline semiconductor film, an EIL
(electron injection layer), an ETL (electron transport layer), an
EML (emission layer), an HTL (hole transport layer), and an HIL
(hole injection layer) may be sequentially laminated in this order
from the first electrode side, and the first electrode may function
as a cathode, and the second electrode may function as an
anode.
[0260] Since other structures such as a specific material of an
electroluminescent layer are described in the above embodiment
mode, description is omitted.
[0261] Note that digital gradation display and analog gradation
display can be performed in a light emitting device; however,
digital gradation display is preferably performed in a light
emitting device using a crystalline semiconductor film.
Embodiment Mode 16
[0262] An example of forming a liquid crystal display device having
a thin film transistor described in the above embodiment mode is
described in this embodiment mode.
[0263] FIG. 14A shows a liquid crystal display device using a top
gate thin film transistor having an amorphous semiconductor film
described in the above embodiment mode as a switching transistor
601.
[0264] A pixel electrode 602 which is electrically connected to the
thin film transistor is formed. When a light transmitting
conductive film (for example, ITO or ITSO) is used as the pixel
electrode 602, a transmissive liquid crystal display device can be
formed. When a non-light-transmitting, that is, highly reflective
conductive film (for example, Al) is used, a reflective liquid
crystal display device can be formed. Subsequently, an orientation
film 603 is formed to cover the pixel electrode 602.
[0265] In addition, an opposing substrate 608 is provided with a
color filter 607, an opposite electrode 606, and an orientation
film 605. The color filter, the opposite electrode, or the
orientation film can be formed by an ink-jet method. Further, a
black matrix can be formed by an ink-jet method, although not
shown. Thereafter, the opposing substrate 608 is attached using a
sealant, and a cell having a liquid crystal element is completed by
injecting liquid crystal 604 therebetween. Note that liquid crystal
may be dropped to form it. Liquid crystal may be dropped by an ink
jet method.
[0266] Subsequently, an FPC (Flexible Printed Circuit) is attached
using an anisotropic conductive film, and may be used as an
external terminal.
[0267] Liquid crystal display devices shown in FIGS. 14B and 14C
each show an example of using a thin film transistor having a
channel protective amorphous semiconductor film and an example of
using a thin film transistor having a crystalline semiconductor as
a switching transistor.
[0268] Thus, a liquid crystal display device having a narrower
wiring, that is, a smaller wiring in width than a diameter of a dot
formed by an ink-jet method can be formed. Further, a liquid
crystal display device having a wiring formed along a region in
which photocatalytic activity is increased can be formed even in
the case where a dot is discharged out of alignment to some
extent.
Embodiment Mode 17
[0269] An ink-jet apparatus (droplet discharge apparatus) for
forming the above thin film transistor is described in this
embodiment mode.
[0270] A droplet discharge apparatus shown in FIG. 15A includes a
droplet discharge means 701 and a means (light irradiation means)
of irradiating with light having such a wavelength that
photocatalytically activates a photocatalytic substance from a
window 706. A lamp (for example, an ultraviolet lamp or so-called
black light) or a laser light (for example, a XeCl excimer laser
having an oscillation wavelength of 308 nm, a XeF excimer laser
having an oscillation wavelength of 351 nm, a KrF excimer laser
having an oscillation wavelength of 248 nm, or the like) oscillator
can be used as the light irradiation means.
[0271] Although not shown, the droplet discharge apparatus
incorporates a nozzle driving power source and a nozzle heater for
discharging a droplet and a moving means of moving the droplet
discharge means.
[0272] A hydrophilic property or an oil-repellent property can be
controlled by light applied from the window (for example, a quartz
window) 706. A desired pattern of a wiring or the like can be
obtained over a substrate 702 by discharging a dot with the droplet
discharge means. Preferably, a desired pattern of a wiring or the
like may be formed in a region where a hydrophilic property or an
oil-repellent property is controlled. Further, a photocatalytic
substance is discharged from the droplet discharge means and can be
photocatalytically activated by light applied from the window
706.
[0273] In such a droplet discharge apparatus, the substrate 702 is
carried into a reaction chamber 704 from a carrying entrance 703.
The substrate 702 is placed on the conveyance table having a moving
means in an X-Y axis direction and can be moved to an optional
point on an X-Y plane. Droplet discharge treatment begins when the
substrate 702 reaches a predetermined position where the droplet
discharge means 701 is waiting by move of the conveyance table. The
droplet discharge treatment is accomplished by relative move of the
droplet discharge means 701 and the substrate 702 and predetermined
timing of droplet discharge, and a desired pattern can be drawn
over the substrate 702 by adjusting each movement speed and cycles
of discharging a droplet from the droplet discharge means 701.
Since droplet discharge treatment specifically requires high
accuracy, it is preferable to stop movement of the substrate on the
conveyance table and to make only the highly controllable droplet
discharge means 701 scan. In addition, it is conceivable that the
droplet discharge means and the substrate on the conveyance table
are simultaneously moved to prevent a clot of a dot from being
formed at a starting point and at an end point.
[0274] The reaction chamber 704 is provided with the window 706,
and light from the light irradiation means 707 provided outside a
chassis enters through the quartz window 706. An optical system 710
made up of a shutter 708, a reflecting mirror 709, a cylindrical
lens or a convex lens, or the like is provided in the light path.
In the droplet discharge apparatus of this embodiment mode, light
can be made incident on the substrate 702 obliquely from above by
adjusting the optical system. A distance between a tip of a droplet
discharge portion of the droplet discharge means 701 and the
substrate 702 is approximately several mm. Therefore, incident
light is preferably at an angle of equal to or more than 45.degree.
toward a normal line direction of the substrate 702. In the case of
using a light transmitting material as the substrate 702, light can
be applied from a bottom face of the substrate 702. In this case, a
window is provided on the bottom face of the reaction chamber.
[0275] Further, it is preferable to provide an exhaust port 505 of
the reaction chamber 704 with a pressure reducing device 711 and to
vacuum evacuate the chamber to hasten drying of a landed droplet
and to remove a solvent component of the droplet. However, it can
be performed under atmospheric pressure. In the case of performing
under atmospheric pressure or the like, the reaction chamber or the
quartz window is not necessarily required. Although not shown, a
sensor or a CCD camera for alignment to the pattern on the
substrate, a means of heating the substrate and a means for
measuring various physical properties such as temperature and
pressure may be provided, if necessary. In addition, these means
can be collectively controlled by a controlling means provided
outside the reaction chamber 704. When the controlling means is
further connected to a production management system or the like
with a LAN cable, a wireless LAN, an optical fiber, or the like,
steps can be collectively controlled from outside, thereby
improving the productivity.
[0276] Although not shown, a beam shape and a beam course can be
adjusted by providing an optical system such as a microlens array
between a laser oscillator corresponding to the light irradiation
means 707 and the substrate 702.
[0277] According to the above structures, a droplet discharged from
the droplet discharge means 701 is irradiated with a semiconductor
laser beam at predetermined timing.
[0278] FIG. 15B shows a droplet discharge apparatus in which the
light irradiation means 707 is mounted on the droplet discharge
means 701, that is, they are integrally formed. Light irradiation
position controllability or droplet discharge controllability can
be improved by integrally forming. Therefore, a photocatalytic
substance is preferably dropped from the droplet discharge means
and is preferably irradiated with light having a photocatalytically
activating wavelength from the integrally formed light irradiation
means. Since other structures are similar to that in FIG. 15A,
description is omitted.
[0279] In this embodiment mode, droplet discharge is performed by a
so-called piezo method using a piezoelectric element; however, a
so-called thermal ink-jet method which makes a heating element
generate heat to generate bubbles, thereby pushing out a solution
may be employed depending on a solution material. In this case, the
piezoelectric element is replaced with a heating element. In
addition, wettability of a solution with a liquid chamber channel,
a spare liquid chamber, a fluid resistance portion, a compression
chamber, and a solution outlet (a nozzle or a head) is important
for droplet discharge. Therefore, a carbon film, a resin film, or
the like for adjusting wettability with a material may be formed in
each flow path.
[0280] According to the above structure of the apparatus, a pattern
can be formed with high accuracy over a substrate to be treated by
using a droplet discharge means, and further, a photocatalytic
substance can be efficiently irradiated with light having a
photocatalytically activating wavelength. In addition, a droplet
discharge method includes a so-called sequential method for forming
a continuous linear pattern by continuously discharging a solution
and a so-called on-demand method for discharging a solution to be
dot-shaped, and either of them can be employed.
Embodiment Mode 18
[0281] A mode of a module such as a light emitting device or a
liquid crystal display device described in the above embodiment
mode is described in this embodiment mode.
[0282] FIG. 18 shows an appearance of a module on which a control
circuit 901 and a power supply circuit 902 are mounted. A pixel
portion 903 in which a light emitting element or a liquid crystal
element is provided for each pixel is provided over a substrate
900. A thin film transistor included in the pixel portion 903 can
be formed by an ink-jet method utilizing a photocatalytic reaction
as described in the above embodiment mode. A scanning line driver
circuit 904 for selecting a pixel included in the pixel portion 903
and a signal line driver circuit 905 for supplying the selected
pixel with a video signal are mounted with an IC chip. Further, the
length of a long side and a short side of an IC to be mounted and
the number thereof are not limited to those in this embodiment
mode.
[0283] A printed wiring board 907 is provided with the control
circuit 901 and the power supply circuit 902. Various kinds of
signals and power supply voltage outputted from the control circuit
901 or the power supply circuit 902 are supplied through an FPC 906
to the scanning line driver circuit 904 and the signal line driver
circuit 905, and further to the pixel portion 903.
[0284] The power supply voltage and various kinds of signals of the
printed wiring board 907 are supplied through an interface (VF)
portion 908 in which a plurality of input terminals, is
disposed.
[0285] Note that the printed wiring board 907 is mounted with using
the FPC 906 in this embodiment mode; however, the present invention
is not necessarily limited to this structure. The control circuit
901 and the power supply circuit 902 may be mounted directly on the
substrate by a COG (Chip On Glass) method. In addition, a mounting
method of an IC chip such as the signal line driver circuit and the
scanning line driver circuit is not limited to this embodiment
mode, and an IC chip formed over the substrate may be connected to
a wiring in a pixel portion by a wire bonding method.
[0286] Further, in the printed wiring board 907, noise may be
caused in the power supply voltage or signals, or the rise of the
signal may become slow due to capacitance formed between lead
wirings, resistance of the wiring itself, and the like. Thus,
various kinds of elements such as a capacitor and a buffer may be
provided on the printed wiring board 907, thereby preventing noise
from being caused in the power supply voltage or signals, or
preventing the rise of the signal from becoming slow.
[0287] As described above, a module having a thin film transistor
formed by an ink-jet method utilizing a photocatalytic reaction can
be formed.
Embodiment Mode 19
[0288] A sealed state of a light emitting device or a liquid
crystal display device described in the above embodiment mode is
described in this embodiment mode.
[0289] FIG. 19A shows a light emitting device and corresponds to a
cross-sectional view taken along a line B-B' in FIG. 18. In a pixel
portion 903, an N channel driving TFT 914 is provided over a
substrate (referred to as a first substrate for convenience) 911
with a base film and a photocatalytic substance 912 therebetween.
The photocatalytic substance has an irradiation region 913, and a
driving TFT is formed by an ink-jet method utilizing a
photocatalytic reaction as described in the above embodiment mode.
An anode 915 is connected to a wiring which functions as a source
electrode or a drain electrode included in the driving TFT. An
electroluminescent layer 916 and a cathode 917 are sequentially
formed, over the anode.
[0290] Further, a protective film 918 is provided to cover the
cathode. The protective film is formed to have an insulating film
which mainly contains silicon nitride or silicon nitride oxide
obtained by a sputtering method (a DC method or an RF method) or a
DLC film (Diamond Like Carbon) which contains hydrogen. In
addition, the protective film can have a single layer structure or
a laminated structure of the above described film. The protective
film can prevent the electroluminescent layer from being
deteriorated by moisture, oxygen, or the like.
[0291] The cathode and the protective film are provided to a first
connection region 920. The cathode is connected to a connection
wiring 919 in the connection region 920.
[0292] In a sealing region 923, the first substrate 911 and an
opposing substrate (referred to as a second substrate for
convenience) 922 are attached to each other with a sealant 921
therebetween. The sealant is made of a thermosetting resin or an
ultraviolet curing resin, and attaches and fixes the first
substrate and the second substrate to each other by being heated
with pressure applied or being irradiated with an ultraviolet ray.
For example, an epoxy-based resin can be used as the sealant. The
sealant is mixed with a spacer, and holds an interval, that is, a
so-called gap between the first substrate and the second substrate.
As the spacer, the one having a spherical shape or a columnar shape
is used. In this embodiment mode, a cylindrical spacer is laid down
and used, and a diameter of a circle is a gap.
[0293] In a second connection region 926, the connection wiring 919
is connected to a signal line driver circuit formed with an IC chip
927 with an anisotropic conductive film 924 therebetween. Note that
the IC chip is provided over an FPC 925. When the anisotropic
conductive film is attached by pressurizing or heating, an
attention should be paid so that crack is not generated due to
flexibility of a film substrate or softening by heating it. For
example, the substrate having high hardness may be disposed as a
support in the region to be attached. In this way, a video signal
or a clock signal is received from the connected IC chip.
[0294] When the first substrate is sealed with the second substrate
922, a space is formed between the second substrate and the
protective film 918. The space is filled with an inert gas, for
example, a nitrogen gas or provided with a material having a high
moisture-absorbing property in order to prevent moisture or oxygen
from penetrating thereinto. Alternatively, a light-transmitting
resin having a high moisture-absorbing property may be formed.
Since the resin is light-transmitting, transmittance does not
decrease even when light from the light-emitting element is emitted
to a second substrate side.
[0295] FIG. 19B shows the case of sealing without using the second
substrate, differently from FIG. 19A. Since other structures are
similar, description is omitted.
[0296] In FIG. 19B, a second protective film 930 is provided to
cover the protective film 918. As the second protective film, an
organic material such as an epoxy resin, a urethane resin, or a
silicone resin can be used. In this embodiment mode, an epoxy resin
is dropped by using a dispenser and is dried.
[0297] When deterioration of the electroluminescent layer due to
moisture, oxygen, or the like does not cause a problem, the
protective film 918 may not be provided. Further, a second
substrate may be provided over the second protective film for
sealing.
[0298] As described above, the display device can be more
lightweight, miniaturized, and thinned by sealing without using the
second substrate.
Embodiment Mode 20
[0299] Examples of electronic devices using a display device
described in the above embodiment mode can be given as follows: a
video camera; a digital camera; a goggle type display (head mounted
display); a navigation system; an audio reproducing device (car
audio, an audio component, or the like); a laptop personal
computer; a game machine; a personal digital assistance (a mobile
computer, a cellular phone, a portable game machine, an electronic
book, or the like); an image reproducing device including a
recording medium (specifically, a device capable of reproducing a
recording medium such as a Digital. Versatile Disc (DVD) and having
a display that can display the image of the data); and the like.
Specifically, an ink-jet method described in the above embodiment
mode is preferably employed for a large television having a large
screen, or the like. Practical examples of these electronic devices
are shown in FIGS. 16A to 16C.
[0300] FIG. 16A shows a large display device, which includes a
chassis 2001, a supporting section 2002, a display portion 2003,
speaker portions 2004, a video input terminal 2005, and the like.
The display portion 2003 is provided with a module including a
pixel portion and a driver circuit portion. The pixel portion has a
light emitting element or a liquid crystal element and a TFT formed
by an ink-jet method described in the above embodiment mode. Note
that the display device includes all display devices for displaying
information, including ones for personal computers, for TV
broadcasting reception, and for advertisement.
[0301] FIG. 16B shows a cellular phone that is one of mobile
terminals, which includes a main body 2101, a chassis 2102, a
display portion 2103, an audio input portion 2104, an audio output
portion 2105, operation keys 2106, an antenna 2107, and the like.
The display portion 2103 is provided with a module including a
pixel portion and a driver circuit portion. The pixel portion has a
light emitting element or a liquid crystal element and a TFT formed
by an ink-jet method described in the above embodiment mode. In
addition, costs of the cellular phone can be reduced by forming the
display portion 2103 with gang printing.
[0302] FIG. 16C shows a sheet-shaped cellular phone, which includes
a main body 2301, a display portion 2303, an audio input portion
2304, an audio output portion 2305, a switch 2306, an external
connection port 2307, and the like. A separately prepared earphone
2308 can be connected to the cellular phone through the external
connection port 2307. A touch panel display screen having a sensor
is used for the display portion 2303. A continuous stream of
operation can be performed by touching a touch panel operation key
2309 displayed on the display portion 2303. The display portion
2303 is provided with a module having a pixel portion and a driver
circuit portion. The pixel portion has a light emitting element or
a liquid crystal element and a TFT formed by an ink-jet method
described in the above embodiment mode. In addition, costs of the
sheet-shaped cellular phone can be reduced by forming the display
portion 2303 with gang printing.
[0303] As described above, an applicable range of the present
invention is so wide that the present invention can be applied to
electronic devices of various fields. In addition, the electronic
device of this embodiment mode can employ any structure described
in the above embodiment mode.
[0304] This application is based on Japanese Patent Application
serial no. 2003-344202 filed in Japan Patent Office on Oct. 2,
2003, the contents of which are hereby incorporated by
reference.
[0305] Although the present invention has been fully described by
way of example with reference to the accompanied drawings, it is to
be understood that various changes and modification will be
apparent to those skilled in the art. Therefore, unless otherwise
such changes and modification depart from the scope of the present
invention hereinafter defined, they should be construed as being
included therein.
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