Title: Film forming apparatus and method of manufacturing light emitting device
Abstract: The problem regarding volatileness of a solvent in an EL forming material, which occurs in adopting printing, are solved. An EL layer is formed in a pixel portion of a light emitting device by printing. Upon formation of the EL layer, a printing chamber is pressurized to reach a pressure equal to or higher than the atmospheric pressure, and the printing chamber is filled with inert gas or set to a solvent atmosphere. Thus the difficulty in forming an EL layer by printing is eliminated.
Patent Number: 6,940,223 Issued on 09/06/2005 to Yamazaki
| Inventors:
|
Yamazaki; Shunpei (Tokyo, JP)
|
| Assignee:
|
Semiconductor Energy Laboratory Co., Ltd. (Kanagawa-Ken, JP)
|
| Appl. No.:
|
898067 |
| Filed:
|
July 5, 2001 |
Foreign Application Priority Data
| Jul 10, 2000[JP] | 2000-209130 |
| Current U.S. Class: |
313/504 |
| Intern'l Class: |
H01R 001/62 |
| Field of Search: |
313/504,506,507,509
257/E51.022,40,99,57,59,72,448
438/30,166,359,46,47,507,508
427/557,66,68,64
345/76,36,45
428/690
315/169.3,169.1
|
References Cited [Referenced By]
U.S. Patent Documents
| 5431800 | Jul., 1995 | Kirchhoff et al.
| |
| 5488266 | Jan., 1996 | Aoki et al.
| |
| 5895692 | Apr., 1999 | Shirasaki et al.
| |
| 6175345 | Jan., 2001 | Kuribayashi et al.
| |
| 6208075 | Mar., 2001 | Hung et al.
| |
| 6329215 | Dec., 2001 | Porowski et al.
| |
| 6373455 | Apr., 2002 | Kuribayashi et al.
| |
| 6384427 | May., 2002 | Yamazaki et al.
| |
| 6420200 | Jul., 2002 | Yamazaki et al.
| |
| 6451391 | Sep., 2002 | Yamada et al.
| |
| Foreign Patent Documents |
| 0 554 117 | Aug., 1993 | EP.
| |
Primary Examiner: Gilman; Alexander
Attorney, Agent or Firm: Fish & Richardson P.C.
Claims
1. A method of manufacturing a light emitting device with an electrode formed
over an insulating surface and an electro luminescence layer in contact with the
electrode, the method comprising the steps of:
making an atmosphere in a processing chamber contain a first solvent;
pressurizing the processing chamber to reach a pressure equal to or higher than
the atmospheric pressure; and
forming the electro luminescence layer in the processing chamber,
wherein the electro luminescence layer is formed by printing.
2. A method of manufacturing a light emitting device according to in claim 1,
wherein the pressure in the processing chamber is 1.1 to 1.5 atm.
3. A method of manufacturing a light emitting device according to claim 1 wherein
the electro luminescence layer is formed by one of letterpress, plate printing,
and screen printing.
4. A light emitting device manufactured by a manufacturing method according to
claim 1.
5. A light emitting device according to claim 4, wherein the light emitting device
is a device selected from the group consisting of a display device, a digital camera,
a notebook computer, a mobile computer, a portable image reproducing device that
is provided with a recording medium, a goggle type display device, a video camera,
and a cellular phone.
6. A method of manufacturing a light emitting device with an electrode connected
to a semiconductor element and an electro luminescence layer in contact with the
electrode, the method comprising the steps of:
making an atmosphere in a processing chamber contain a first solvent;
pressurizing the processing chamber to reach a pressure equal to or higher than
the atmospheric pressure; and
forming the electro luminescence layer in the processing chamber,
wherein the electro luminescence layer is formed by printing.
7. A method of manufacturing a light emitting device according to in claim 6,
wherein the pressure in the processing chamber is 1.1 to 1.5 atm.
8. A method of manufacturing a light emitting device according to claim 6 wherein
the electro luminescence layer is formed by one of letterpress, plate printing,
and screen printing.
9. A light emitting device manufactured by a manufacturing method according to
claim 6.
10. A light emitting device according to claim 9, wherein the light emitting
device is a device selected from the group consisting of a display device, a digital
camera, a notebook computer, a mobile computer, a portable image reproducing device
that is provided with a recording medium, a goggle type display device, a video
camera, and a cellular phone.
11. A method of manufacturing a light emitting device comprising:
introducing a substrate in a chamber;
making an atmosphere in the chamber contain a first solvent; and
forming an electro luminescence layer comprising an organic material by printing
over the substrate in the atmosphere,
wherein said electro luminescence layer is formed in said chamber at a pressure
higher than the atmospheric pressure.
12. A method according to claim 11 wherein the pressure in the chamber is 1.1
to 1.5 atm.
13. A method according to claim 11 wherein the electro luminescence layer is
formed by one of letterpress, plate printing, and screen printing.
14. A method of manufacturing a light emitting device comprising:
introducing a substrate in a chamber;
making an atmosphere in said chamber contain a first solvent; and
printing a layer comprising an electro luminescence material dissolved in a second
solvent over the substrate.
15. A method according to claim 14 wherein the pressure in the chamber is 1.1
to 1.5 atm.
16. A method according to claim 14 wherein the electro luminescence layer is
formed by one of letterpress, plate printing, and screen printing.
17. A method according to claim 14 wherein the first solvent comprises the same
material as the second solvent.
18. A method of manufacturing a light emitting device comprising:
introducing a substrate in a chamber;
making an atmosphere in said chamber contain a first solvent; and
printing a layer comprising an electro luminescence material dissolved in a second
solvent over the substrate,
wherein the first solvent is provided in a tray placed in the chamber.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a film forming apparatus and a film forming
method used to manufacture an EL element composed of an anode, a cathode and a
light emitting material, especially a self-light emitting material, for providing
EL (electro luminescence) (hereinafter referred to as EL material), with the EL
material sandwiched between the anode and the cathode. The EL material herein refers
to a material that provides fluorescence or phosphorescence when an electric field.
In the present invention, a light emitting device refers to an image display
device,
or a light emitting device, that uses an EL element. Also, the following modules
are all included in the definition of the light emitting device: a module obtained
by attaching to an EL element a connector such as an anisotropic conductive film
(FPC: flexible printed circuit), a TAB (tape automated bonding) tape, or a TCP
(tape carrier package); a module in which a printed wiring board is provided at
an end of a TAB tape or a TCP; and a module in which an IC (integrated circuit)
is directly mounted with a light emitting element by the COG (chip on glass) method.
2. Description of the Related Art
In recent years, a technique of forming a semiconductor element on a substrate
has greatly advanced and application of the semiconductor element to active matrix
display devices (light emitting devices) is being developed. The semiconductor
element refers to a single element, or a plurality of elements, formed of a semiconductor
material and having a switching function. Given as an example of the semiconductor
element are transistors, in particular, field effect transistors, typical example
of which are a MOS (metal oxide semiconductor) transistor and a thin film transistor
(TFT). A TFT formed of a polysilicon film can operate at high speed since the TFT
is high in field effect mobility (also called mobility) compared with a conventional
TFT that is formed of an amorphous silicon film. This makes it possible to control
pixels by a driving circuit formed on the same substrate as the pixels instead
of using a driver circuit outside the substrate as in the past.
The active matrix display devices as above have various circuits and elements
formed on the same substrate, whereby a diversity of advantages are obtained including
reduction in manufacture cost, miniaturization of electro-optical devices, raised
yield, and an increase in throughput.
On the other hand, the light emitting device that is being vigorously researched
is an active matrix light emitting device which has an EL element as a self-light
emitting element (also called an EL display).
In this specification, the EL element of the light emitting device has a structure
in which an EL layer is sandwiched between a pair of electrodes (an anode and a
cathode). The EL layer generally takes a laminate structure. A typical example
of the laminate structure is the one proposed by Tang et al. of Eastman Kodak Company,
and consists of a hole transporting layer, a light emitting layer and an electron
transporting layer. This structure has so high a light emission efficiency that
it is employed in almost all of light emitting devices that are under development
at present.
Other examples of the laminate structure include a structure consisting of
a hole injection layer, a hole transporting layer, a light emitting layer, and
an electron transporting layer which are layered in this order on an anode, and
a structure consisting of a hole injection layer, a hole transporting layer, a
light emitting layer, an electron transporting layer, and an electron injection
layer which are layered in this order on an anode. The light emitting layer may
be doped with a fluorescent pigment or the like.
In this specification, all of the layers provided between a cathode and an anode
are collectively called an EL layer. Accordingly, the hole injection layer, a hole
transporting layer, a light emitting layer, an electron transporting layer, an
electron injection layer, etc. mentioned above are all included in the EL layer.
A predetermined voltage is applied to the EL layer with the above structure from
the pair of electrodes, whereby recombination of carriers takes place in the light
emitting layer to emit light. The EL element in this specification refers to a
light emitting element composed of an anode, an EL layer, and a cathode.
The EL layer of the EL element is degraded by heat, light, moisture, oxygen,
etc. Therefore, the EL element is generally formed after wirings and TFTs are formed
in a pixel portion in manufacturing an active matrix light emitting device.
The EL layer described above can be formed by various methods. Examples of the
methods that have been proposed include vacuum evaporation, sputtering, spin coating,
roll coating, casting, the LB method, ion plating, dipping, the ink jet method,
and printing. The printing is a particularly effective method because the EL layer
can be formed selectively.
After the EL element is formed, the substrate over which the EL element is
formed (EL panel) is bonded to a covering member by sealing with a sealing member
or the like (packaging) without exposing the EL element to the outside air.
After the packaging or other processing for enhancing airtightness, a connector
(FPC, TAB, or the like) is attached in order to connect an external signal terminal
to a terminal lead out of an element or a circuit formed on the substrate. The
active matrix light emitting device is thus completed.
When printing is employed to form the EL layer, a print material changes with
time if a solvent for dissolving an EL material is highly volatile. This makes
it difficult to process a large number of substrates.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a means for solving the above
problem in forming an EL layer by printing.
In order to attain the object above, the present invention is characterized in
that an EL layer is formed by printing while setting the pressure in a processing
chamber for forming the EL layer by printing (also called a printing chamber) to
the atmospheric pressure (normal pressure), or to a pressure higher than the atmospheric
pressure, through pressurizing. The processing chamber is connected to a pressure
adjusting mechanism. The pressure adjusting mechanism according to the present
invention has a function of keeping the pressure in the processing chamber at the
atmospheric pressure or near the atmospheric pressure (typically 1 to 2 atm., preferably
1.1 to 1.5 atm.).
Specifically, the mechanism is composed of a compressor for compressing
gas to introduce the compressed gas to the processing chamber, and a sensor for
measuring the pressure in the processing chamber and then opening or closing an
exhaust valve in accordance with the measured pressure. A valve for discharging
the gas from the processing chamber is herein called the exhaust valve. The sensor
in this specification means a device for measuring the pressure in the processing
chamber and inputting a control signal in accordance with the measured value. The
control signal from the sensor here is inputted to the exhaust valve to control
the opening and closing.
Alternatively, the pressure adjusting mechanism may have a heater
that heats the processing chamber to pressurize the processing chamber and set
the pressure in the processing chamber to a desired pressure. In this case, the
signal from the sensor is inputted to a variable resister for controlling electric
power to be given to the heater from a power source.
The present invention is also characterized in that the processing chamber is
filled with inert gas or set to a solvent atmosphere to form the EL layer.
The inert gas is gas with poor reactivity, specifically, noble gas such as argon
and helium, or nitrogen. The solvent atmosphere refers to a state in which a space
or a processing chamber is filled with a solvent in the gaseous state.
The present invention is also characterized by providing a film forming apparatus
equipped with, in addition to the processing chamber for forming the EL layer (the
printing chamber), a processing chamber for drying the EL layer formed by printing
(a drying chamber), a processing chamber for forming a cathode or an anode of the
EL element (an evaporation chamber), and a processing chamber for sealing the completed
EL element (a sealing chamber) so that all the processing can be handled by a single apparatus.
Printing in this specification refers to a method of forming an EL layer
on an electrode adopting a printing method such as letterpress, plate printing,
or screen printing (silkscreen). Letterpress is particularly preferable to form
an EL layer. Now, a description is given with reference to FIGS. 1A to 1C
on printing according to the present invention, which adopts letterpress (a letterpress
printing method).
FIG. 1A shows a processing chamber for forming an EL layer by the letterpress
printing method in accordance with the present invention. In this specification,
the processing chamber provided with a printing device for forming an EL layer
by printing is called a printing chamber. The processing chamber in FIG. 1A is
denoted by 118.
In FIGS. 1A to 1C, reference symbol 110 denotes an anilox roll and
111 denotes a doctor bar (also called a doctor blade). With the doctor bar
111, a mixture of an EL material and a solvent (hereinafter the mixture
is referred to as EL forming material 112) pools about the surface of the
anilox roll 110. The EL material here refers to a fluorescent organic compound,
namely, an organic compound generally called as a hole injection layer, a hole
transporting layer, a light emitting layer, an electron transporting layer, or
an electron injection layer.
On the surface of the anilox roll 110, mesh-like grooves (hereinafter referred
to as mesh) 110
a is provided as shown in FIG. 1B. The mesh
110
a holds the EL forming material 112 to the surface of the
anilox roll through rotation of the anilox roll in the direction indicated by the
arrow A. The dotted line over the surface of the anilox roll 110 in FIG.
1A represents the EL forming material held to the surface of the anilox roll 110.
Reference symbol 113 denotes a printing roll and 114 denotes
a letterpress plate. The letterpress plate 114 has uneven surface obtained
by etching or the like. The uneven surface is shown in FIG. 1C. In FIG.
1C, pixel portion patterns 114
a are formed in different places on
the letterpress plate 114 in order to manufacture plural sheets of light
emitting devices on a single substrate. Looking at the enlarged view of the pixel
portion patterns 114
a, each pattern has convex 114
b at
positions corresponding to positions of a plurality of pixels.
The anilox roll 110 rotates to keep holding the EL forming material 112
in the mesh 110
a. On the other hand, the printing roll 113
rotates in the direction indicated by the arrow B and only the convex 114
b
on the letterpress plate 114 come into contact with the mesh 110
a.
Upon contact, the EL forming material 112 is applied to surfaces of the
convex 114
b.
The EL forming material 112 is printed at positions where the convex 114
b
is brought into contact with a substrate 115 that moves horizontally
(in the direction indicated by the arrow C) at the same speed as the printing roll
113. Thus the EL forming material 112 is printed forming a matrix
on the substrate 115.
Thereafter, the solvent contained in the EL forming material 112
is vaporized to leave the EL material through heat treatment in a nitrogen atmosphere
at the atmospheric pressure in another processing chamber (called a drying chamber
in this specification). Accordingly, the solvent needs to be vaporized at a temperature
lower than the glass transition temperature (Tg) of the EL material. The viscosity
of the EL forming material 112 determines the final thickness of the EL
layer to be formed. The viscosity can be adjusted by choosing a solvent. A preferable
viscosity is 1×10
-3 to 5×10
-2 Pa s (more desirably
1×10
-3 to 2×10
-2 Pa·s).
Typical examples of the solvent for dissolving the EL material include toluene,
xylene, chlorobenzen, dichlorobenzen, anisole, chloroform, dichloromethane, γbutyl
lactone, butyl Cellosolve, cyclohexane, NMP (N-methyl-2-pyrrolidone), cyclohexanone,
dioxane, and THF (tetrahydrofuran).
If the EL forming material 112 contains too many impurities that could
serve as crystal nuclei, the possibility that the EL material is crystallized is
high in vaporizing the solvent. The EL material crystallized is low in light emission
efficiency and hence is undesirable. Therefore, less impurity in the EL forming
material 112 is better.
In order to reduce the impurities, the environment has to be cleaned as much
as
possible in refining the solvent, refining the EL material, and mixing the solvent
with the EL material. An equally important matter in the present invention is that
the atmosphere in the printing device in printing the EL forming material is conditioned
so as to reduce the impurities.
To condition the atmosphere, a chamber in which the printing device is installed
(typically a clean booth) is filled with inert gas such as nitrogen, helium or
argon in printing the EL forming material. Alternatively, the chamber is set to
a solvent atmosphere containing the solvent used to dissolve the EL material.
When the printing chamber 118 is to be set to a solvent atmosphere, the
solvent is put in a solvent tray 117 that is provided in the printing chamber 118.
According to the present invention, a pressure adjusting mechanism 116
provided in the printing chamber 118 keeps the pressure in the printing
chamber 118 filled with inert gas or set to a solvent atmosphere at the
atmospheric pressure or near the atmospheric pressure (typically 1 to 2 atm., preferably
1.1 to 1.5 atm.).
With carrying out the present invention, no apparatus such as a vacuum evaporation,
which needs vacuum exhaust equipment device, is required form the EL material into
a film. Therefore the overall system is simplified and maintenance is easy, making
the present invention advantageous.
The present invention can be embodied in passive matrix (simple matrix) light
emitting devices as well as active matrix light emitting devices.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIGS. 1A to 1C are diagrams illustrating the principle of a letterpress
printing method;
FIG. 2 is a diagram showing a multi-chamber film forming apparatus;
FIGS. 3A to 3C are diagrams showing a process of manufacturing an active
matrix light emitting device;
FIGS. 4A to 4C are diagrams showing the process of manufacturing the
active matrix light emitting device;
FIGS. 5A and 5B are diagrams showing the process of manufacturing the active
matrix light emitting device;
FIGS. 6A and 6B are diagrams showing a structure for sealing a light emitting device;
FIGS. 7A and 7B are diagrams showing an in-line film forming apparatus;
FIGS. 8A to 8D are diagrams illustrating multi-color printing;
FIG. 9 is a diagram showing a multi-chamber film forming apparatus;
FIGS. 10A to 10F are diagrams showing specific examples of electric equipment;
FIGS. 11A to 11C are diagrams showing specific examples of the electric equipment;
FIG. 12 is a diagram illustrating a pressure adjusting mechanism; and
FIG. 13 is a diagram illustrating a pressure adjusting mechanism.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[Embodiment Mode]
Now, an apparatus for performing the present invention will be described with
reference to FIG.
2. The apparatus performs a series of processing from
forming an EL layer by printing to forming an electrode followed by sealing an
EL element. Shown in FIG. 2 is a top view of a multi-chamber film forming apparatus.
In FIG. 2, reference symbol
201 denotes a transfer chamber. The transfer
chamber
201 is provided with a transfer mechanism (A)
202 to transfer
substrates
203. The transfer chamber
201 is set to a reduced pressure
atmosphere and is connected to respective processing chambers through gates. The
transfer mechanism (A)
202 hands the substrates to the respective processing
chambers while the gates are opened. The pressure in the transfer chamber
201
can be reduced by a vacuum pump such as an oil rotary pump, a mechanical booster
pump, a turbomolecular pump, or a cryopump. Preferably, a cryopump is used for
its effectiveness in removing moisture.
The processing chambers will be described below respectively. Of the processing
chambers, those directly connected to the transfer chamber
201 have vacuum
pumps (not shown) since the transfer chamber
201 is set to an atmospheric
atmosphere. Examples of the vacuum pumps are given as above and include an oil
rotary pump, a mechanical booster pump, a turbomolecular pump, and a cryopump.
First, denoted by
204 is a loading chamber in which the substrates
are set and which doubles as an unloading chamber. The loading chamber
204
is connected to the transfer chamber
201 through a gate
200a,
and a carrier (not shown) with the substrates
203 set is placed in the loading
chamber
204. The loading chamber
204 may be divided into two rooms,
one for bringing the substrates in and the other for sending the substrates out.
The loading chamber
204 is provided with, as well as the vacuum pump mentioned
above, a purge line for introducing nitrogen gas or noble gas.
Next, reference symbol
205 denotes a printing chamber for forming an
EL material into a film by printing. The printing chamber
205 is connected
to the transfer chamber
201 through a gate
200b. The printing
chamber
205 has therein a printing unit
206 where a hole injection
layer, a light emitting layer that emits red light, a light emitting layer that
emits green light, and a light emitting layer that emits blue light are formed.
Any material can be used for the hole injection layer, the light emitting layer
that emits red light, the light emitting layer that emits green light, and the
light emitting layer that emits blue light.
The EL layer is formed by printing in the present invention, and therefore an
appropriate EL material is a polymer material. Typical polymer materials are high
molecular materials such as a polyparaphenylene vinylyene (PPV) based material,
a polyvinyl carbazole (PVK) based material, and a polyfluoren (PF) based material.
In order to form a hole injection layer, a hole transporting layer, and a light
emitting layer from polymer materials by printing, a polymer precursor is printed
and then heated to transfer the precursor into a polymer material as an EL material.
Other necessary EL materials are formed into films by evaporation or the like and
the formed films are laminated thereon, thus obtaining the EL layer with a laminate structure.
Specifically, a hole transporting layer is formed by heating polytetrahydrothiophenylphenylene
as a polymer precursor to transform it into polyphenylene vinylene. An appropriate
thickness for the hole transporting layer is 30 to 100 nm (preferably 40 to 80
nm). Preferable materials of light emitting layers are: cyanopolyphenylen vinylene
for a red light emitting layer, polyphenylene vinylene for a green light emitting
layer, and polyphenylene vinylene or polyalkyl phenylene for a blue light emitting
layer. An appropriate thickness for each light emitting layer is 30 to 150 nm (preferably
40 to 100 nm).
It is also effective to form as a buffer layer a copper phthalocyanine film between
an electrode and the EL material film formed thereon.
The materials given above are merely examples of materials that can be used for
the EL material of the present invention, and there is no need to limit the above
EL material. According to the present invention, the EL material is mixed with
a solvent to print the mixture and then the solvent is removed by vaporization
to form the EL layer. Therefore any EL material can be used as long as the combination
of the EL material and the solvent does not cause the temperature for vaporizing
the solvent to exceed the glass transition temperature of the EL layer.
It is also effective to add thereto an additive in order to increase the viscosity
of the EL forming material. The EL material can be a low molecular material if
it is soluble in a solvent.
When the EL layer is formed by printing, the EL layer could easily be degraded
under the presence of moisture and oxygen. Therefore these factors for degrading
have to be removed as much as possible before formation. To eliminate moisture
and oxygen, a printing device is desirably installed in a chamber (the printing
chamber here) filled with inert gas such as argon or helium to print in an inert atmosphere.
The dew point of the inert gas used is desirably -20° C. or lower, more
desirably -50° C. or lower.
In order to form the EL forming material into a uniform film, it is effective
to set the printing chamber to a solvent atmosphere containing a solvent that constitutes
the EL forming material. The solvent atmosphere can be obtained by putting the
solvent in a solvent tray
216.
The pressure in the chamber filled with inert gas or set to a solvent atmosphere
is kept at the atmospheric pressure or the chamber is kept pressurized (to reach
1 to 2 atm. typically, 1.1 to 1.5 atm. preferably). The pressure is adjusted by
a pressure adjusting mechanism
215. In carrying out the present invention,
no apparatus such as a vacuum evaporation device, which needs vacuum exhaust equipment,
is required to form the EL material into a film. Therefore the overall system is
simplified and maintenance is easy, making the present invention advantageous.
The EL material formed into a film in the printing chamber
205 is then
dried in a drying chamber
207. The drying chamber
207 is connected
to the transfer chamber
201 through a gate
200c. The EL material
on the substrate may be dried here by placing the substrate on a hot plate unit
208 that is provided in the drying chamber
207.
The next processing chamber denoted by
209 is an evaporation chamber for
forming a conductive film that is to serve as an anode or a cathode of an EL element
by evaporation. The evaporation chamber
209 is connected to the transfer
chamber
201 through a gate
200d.
The evaporation chamber
209 has therein a film forming unit
210.
A specific example of the conductive film formed in the film forming unit
210
is an MgAg film or an Al—Li alloy film (an alloy film of aluminum and lithium),
which serves as the cathode of the EL element.
Alternatively, aluminum may be subjected to co-evaporation with an
element which belongs to Group 1 or Group 2 in the periodic table. Co-evaporation
is an evaporation method in which plural evaporation cells are simultaneously heated
to mix different substances during film formation.
Next, denoted by
211 is a sealing chamber (also called an enclosing
chamber or a glove box), which is connected to the loading chamber
204 through
a gate
200e. The sealing chamber
211 conducts the final processing
of enclosing the EL element in an airtight space. The processing is carried out
for protecting the completed EL element from oxygen and moisture. Through the processing,
the EL element is automatically enclosed using a sealing member, or is enclosed
using either a thermally curable resin or a UV-curable resin.
The sealing member may be glass, ceramics, plastics, or metals. If the light
is emitted toward the sealing member side, the sealing member has to be transmissive
to light. The sealing member is bonded to the substrate on which the EL element
is formed using a thermally curable resin or a UV-curable resin. The resin is then
cured by heat treatment or ultraviolet ray irradiation treatment to create an airtight
space. It is also effective to put in the airtight space a hygroscopic material,
typical example of which is barium oxide.
The space defined by the sealing member and the substrate on which the EL element
is formed may be filled with a thermally curable resin or a UV-curable resin. In
this case, adding a hygroscopic material, typical example of which is barium oxide,
to the thermally curable resin or the UV-curable resin is effective.
In the film forming apparatus shown in FIG. 2, a mechanism for irradiating ultraviolet
rays (hereinafter referred to as ultraviolet ray irradiation mechanism)
212
is provided in the sealing chamber
211. The ultraviolet ray irradiation
mechanism
212 emits ultraviolet rays to cure the UV-curable resin. The inside
of the sealing chamber
211 may be set to reduced pressure if a vacuum pump
is installed in the sealing chamber
211. When the above enclosing step is
automatically conducted through operation of a robot, the reduced pressure prevents
oxygen and moisture from entering. On the other hand, the inside of the sealing
chamber
211 may be pressurized. In this case, pressurization is carried
out while purging with nitrogen gas or noble gas with high purity to prevent oxygen
or other contaminants from entering from the outside air.
The sealing chamber
211 is connected to a handing-over chamber (pass box)
213. The handing-over chamber
213 is provided with a transfer mechanism
(B)
214, which transfers the substrate whose EL element has been enclosed
in the sealing chamber
211 to the handing-over chamber
213. The handing-over
chamber
213 may also be set to reduced pressure if a vacuum pump is provided
therein. The handing-over chamber
213 is installed to avoid direct exposure
of the sealing chamber
211 to the outside air, and the substrate is taken
out of the handing-over chamber.
With the film forming apparatus described above, a series of processing up through
enclosing the EL element into an airtight space can be achieved without exposure
to the outside air. The apparatus thus can manufacture a light emitting device
with high reliability. The film forming apparatus shown here is merely one mode
of carrying out the present invention and does not limit the present invention.
[Embodiment 1]
Here, a method of simultaneously forming, on the same substrate, a pixel portion
and TFTs (n-channel TFT and p-channel TFT) of a driver circuit provided in the
periphery of the pixel portion, is described in detail with FIGS. 3A to
5B.
First, in this embodiment, a substrate
300 is used, which is made of
glass such as barium borosilicate glass or aluminum borosilicate, represented by
such as Corning #7059 glass and #1737 glass. Note that, as the substrate
300,
there is no limitation provided that it is a substrate with transmittance, and
a quartz substrate may be used. A plastic substrate with heat resistance to a process
temperature of this embodiment may also be used.
Then, a base film
301 formed of an insulating film such as a silicon
oxide film, a silicon nitride film or a silicon nitride oxide film is formed on
the substrate
300. In this embodiment, a two-layer structure is used as
the base film
301. However, a single-layer film or a lamination structure
consisting of two or more layers of the insulating film may be used. As a first
layer of the base film
301, a silicon nitride oxide film
301a
is formed with a thickness of 10 to 200 nm (preferably 50 to 100 nm) with a
plasma CVD method using SiH
4, NH
3, and N
2O as
reaction gas. In this embodiment, the silicon nitride oxide film
301a
(composition ratio Si=32%, O=27%, N=24% and H=17%) with a film thickness of
50 nm is formed. Then, as a second layer of the base film
301, a silicon
nitride oxide film
301b is formed and laminated into a thickness
of 50 to 200 nm (preferably 100 to 150 nm) with a plasma CVD method using SiH
4
and N
2O as reaction gas. In this embodiment, the silicon nitride oxide
film
301b (composition ratio Si=32%, O=59%, N=7% and H=2%) with a
film thickness of 100 nm is formed.
Subsequently, semiconductor layers
302 to
305 are formed
on the base film. The semiconductor layers
302 to
305 are formed
from a semiconductor film with an amorphous structure which is formed by a known
method (such as a sputtering method, an LPCVD method, or a plasma CVD method),
and is subjected to a known crystallization process (a laser crystallization method,
a thermal crystallization method, or a thermal crystallization method using a catalyst
such as nickel). The crystalline semiconductor film thus obtained is patterned
into desired shapes to obtain the semiconductor layers. The semiconductor layers
302 to
305 are formed into the thickness of from 25 to 80 nm (preferably
30 to 60 nm). The material of the crystalline semiconductor film is not particularly
limited, but it is preferable to be formed of silicon, a silicon germanium (Si
xGe
1-x(X=0.0001
to 0.02)) alloy, or the like. In this embodiment, 55 nm thick amorphous silicon
film is formed by a plasma CVD method, and then, a nickel-containing solution is
held on the amorphous silicon film. A dehydrogenation process of the amorphous
silicon film is performed (500° C. for one hour), and thereafter a thermal
crystallization process is performed (550° C. for four hours) thereto. Further,
to improve the crystallinity thereof, a laser annealing treatment is performed
to form the crystalline silicon film. Then, this crystalline silicon film is subjected
to a patterning process using a photolithography method, to obtain the semiconductor
layers
302 to
305.
Further, after the formation of the semiconductor layers
302 to
305,
a minute amount of impurity element (boron or phosphorus) may be doped to control
a threshold value of the
Besides, in the case where the crystalline semiconductor film is manufactured
by the laser crystallization method, a pulse-oscillation type or continuous-wave
type excimer laser, YAG laser, or YVO
4 laser may be used. In the case
where those kinds of laser are used, it is appropriate to use a method in which
laser light radiated from a laser oscillator is condensed by an optical system
into a linear beam, and is irradiated to the semiconductor film. Although the conditions
of the crystallization should be properly selected by an operator, in the case
where the excimer laser is used, a pulse oscillation frequency is set as 300 Hz,
and a laser energy density is set as 100 to 400 mJ/cm
2 (typically 200
to 300 mJ/cm
2). In the case where the YAG laser is used, it is appropriate
that the second harmonic is used to with a pulse oscillation frequency of 30 to
300 Hz and a laser energy density of 300 to 600 mJ/cm
2 (typically, 350
to 500 mJ/cm
2). Then, laser light condensed into a linear shape with
a width of 100 to 1000 μm, for example, 400 μm is irradiated to the
whole surface of the substrate, and an overlapping ratio (overlap ratio) of the
linear laser light at this time may be set as 50 to 90%.
A gate insulating film
306 is then formed for covering the semiconductor
layers
302 to
305. The gate insulating film
106 is formed
of an insulating film containing silicon by a plasma CVD method or a sputtering
method into a film thickness of from 40 to 150 nm. In this embodiment, the gate
insulating film
306 is formed of a silicon nitride oxide film into a thickness
of 110 nm by a plasma CVD method (composition ratio Si=32%, O=59%, N=7%, and H=2%).
Of course, the gate insulating film is not limited to the silicon nitride oxide
film, and an other insulating film containing silicon may be used as a single layer
or a lamination structure.
Besides, when the silicon oxide film is used, it can be possible to be formed
by a plasma CVD method in which TEOS (tetraethyl orthosilicate) and O
2
are mixed and discharged at a high frequency (13.56 MHZ) power density of 0.5 to
0.8 W/cm
2 with a reaction pressure of 40 Pa and a substrate temperature
of 300 to 400° C. Good characteristics as the gate insulating film can be
obtained in the manufactured silicon oxide film thus by subsequent thermal annealing
at 400 to 500° C.
Then, as shown in FIG. 3A, on the gate insulating film
306, a first
conductive film
307 with a thickness of 20 to 100 nm and a second conductive
film
308 with a thickness of 100 to 400 nm are formed and laminated. In
this embodiment, the first conductive film
307 of TaN film with a film thickness
of 30 nm and the second conductive film
308 of a W film with a film thickness
of 370 nm are formed into lamination. The TaN film is formed by sputtering with
a Ta target under a nitrogen containing atmosphere. Besides, the W film is formed
by the sputtering method with a W target. The W film may be formed by a thermal
CVD method using tungsten hexafluoride (WF
6). Whichever method is used,
it is necessary to make the material have low resistance for use as the gate electrode,
and it is preferred that the resistivity of the W film is set to less than or equal
to 20 μΩcm. By making the crystal grains large, it is possible to make
the W film have lower resistivity. However, in the case where many impurity elements
such as oxygen are contained within the W film, crystallization is inhibited and
the resistance becomes higher. Therefore, in this embodiment, by forming the W
film by a sputtering method using a W target with a purity of 99.9999%, and in
addition, by taking sufficient consideration to prevent impurities within the gas
phase from mixing therein during the film formation, a resistivity of from 9 to
20 μΩcm can be realized.
Note that, in this embodiment, the first conductive film
307 is made
of TaN, and the second conductive film
308 is made of W, but the material
is not particularly limited thereto, and either film may be formed of an element
selected from the group consisting of Ta, W, Ti, Mo, Al, Cu, Cr, and Nd, or an
alloy material or a compound material containing the above element as its main
constituent. Besides, a semiconductor film, typified by a polycrystalline silicon
film doped with an impurity element such as phosphorus, may be used. Further, an
AgPdCu alloy may be used. Besides, any combination may be employed such as a combination
in which the first conductive film is formed of tantalum (Ta) and the second conductive
film is formed of W, a combination in which the first conductive film is formed
of titanium nitride (TiN) and the second conductive film is formed of W, a combination
in which the first conductive film is formed of tantalum nitride (TaN) and the
second conductive film is formed of Al, or a combination in which the first conductive
film is formed of tantalum nitride (TaN) and the second conductive film is formed
of Cu.
Next, masks
309 to
313 made of resist are formed using a photolithography
method, and a first etching process is performed in order to form electrodes and
wirings. This first etching process is performed with the first and second etching
conditions. In This embodiment, as the first etching conditions, an ICP (inductively
coupled plasma) etching method is used, a gas mixture of CF
4, Cl
2
and O
2 is used as an etching gas, the gas flow rate is set to 25/25/10
sccm, and plasma is generated by applying a 500 W RF (13.56 MHZ) power to a coil
shape electrode under 1 Pa. A dry etching device with ICP (Model E645-ICP) produced
by Matsushita Electric Industrial Co. Ltd. is used here. A 150 W RF (13.56 MHZ)
power is also applied to the substrate side (test piece stage) to effectively apply
a negative self-bias voltage. The W film is etched with the first etching conditions,
and the end portion of the second conductive layer is formed into a tapered shape.
In the first etching conditions, the etching rate for W is 200.39 nm/min, the etching
rate for TaN is 80.32 nm/min, and the selectivity of W to TaN is about 2.5. Further,
the taper angle of W is about 26° with the first etching conditions.
Thereafter, the first etching conditions are changed into the second
etching conditions without removing the masks
309 to
312 made of
resist, a mixed gas of CF
4 and Cl
2 is used as an etching
gas, the gas flow rate is set to 30/30 sccm, and plasma is generated by applying
a 500 W RF (13.56 MHZ) power to a coil shape electrode under 1 Pa to thereby perform
etching for about 30 seconds. A 20 W RF (13.56 MHZ) power is also applied to the
substrate side (test piece stage) to effectively a negative self-bias voltage.
The W film and the TaN film are both etched on the same order with the second etching
conditions in which CF
4 and Cl
2 are mixed. In the second
etching conditions, the etching rate for W is 58.97 nm/min, and the etching rate
for TaN is 66.43 nm/min. Note that, the etching time may be increased by approximately
10 to 20% in order to perform etching without any residue on the gate insulating film.
In the first etching process, the end portions of the first and second conductive
layers are formed to have a tapered shape due to the effect of the bias voltage
applied to the substrate side by adopting masks of resist with a suitable shape.
The angle of the tapered portions may be set to 15° to 45°. Thus, first
shape conductive layers
314 to
318 (first conductive layers
314a
to
318a and second conductive layers
314b to
318b)
constituted of the first conductive layers and the second conductive layers are
formed by the first etching process. The width of the first conductive layers in
a channel length direction corresponds to W
1 shown in the embodiment mode.
Reference numeral
319 denotes a gate insulating film, and regions of the
gate insulating film which are not covered by the first shape conductive layers
314 to
318 are made thinner by approximately 20 to 50 nm by etching.
Then, a first doping process is performed to add an impurity element for imparting
an n-type conductivity to the semiconductor layer without removing the mask made
of resist (FIG.
3B). Doping may be carried out by an ion doping method or
an ion injecting method. The condition of the ion doping method is that a dosage
is 1×10
13 to 5×10
15 atoms/cm
2, and an
acceleration voltage is 60 to 100 keV. In this embodiment, the dosage is 1.5×10
15
atoms/cm
2 and the acceleration voltage is 80 keV. As the impurity
element for imparting the n-type conductivity, an element which belongs to group
15 of the periodic table, typically phosphorus (P) or arsenic (As) is used, and
phosphorus is used here. In this case, the conductive layers
314 to
318
become masks to the impurity element for imparting the n-type conductivity, and
high concentration impurity regions
320 to
323 are formed in a self-aligning
manner. The impurity element for imparting the n-type conductivity is added to
the high concentration impurity regions
320 to
323 in the concentration
range of 1×10
20 to 1×10
21 atoms/cm
3.
Thereafter, the second etching process is performed without removing
the masks made of resist as shown in FIG.
3C. Here, a mixed gas of CF
4,
Cl
2 and O
2 is used as an etching gas, the gas flow rate is
set to 25/25/10 sccm, and plasma is generated by applying a 500 W RF (13.56 MHZ)
power to a coil shape electrode under 1 Pa to thereby perform etching. A 20 W RF
(13.56 MHZ) power is also applied to the substrate side (test piece stage) to effectively
apply a negative self-bias voltage. In the second etching process, the etching
rate for W is 124.62 nm/min, the etching rate for TaN is 20.67 nm/min, and the
selectivity of W to TaN is 6.05. Accordingly, the W film is selectively etched.
The taper angle of W is 70° in the second etching. Second conductive layers
324b to
327b are formed by the second etching process.
On the other hand, the first conductive layers
314a to
318a
are hardly etched, and first conductive layers
324a to
327a
are formed.
Next, a second doping process is performed. Second conductive layers
122b
to
125b are used as masks to an impurity element, and doping
is performed such that the impurity element is added to the semiconductor layer
below the tapered portions of the first conductive layers. In this embodiment,
phosphorus (P) is used as the impurity element, and plasma doping is performed
with the dosage of 3.5×10
12 atoms/cm
2 and the acceleration
voltage of 90 keV. Thus, low concentration impurity regions
329 to
332,
which overlap with the first conductive layers, are formed in a self-aligning manner.
The concentration of phosphorus (P) in the low concentration impurity regions
329
to
332 is 1×10
17 to 1×10
18 atoms/cm
3,
and has a gentle concentration gradient in accordance with the film thickness of
the tapered portions of the first conductive layers. Note that, in the semiconductor
layer that overlaps with the tapered portions of the first conductive layers, the
concentration of the impurity element slightly falls from the end portions of the
tapered portions of the first conductive layers toward the inner portions. The
concentration, however, keeps almost the same level. Further, the impurity element
is added to the high concentration impurity regions
333 to
336 to
form high concentration impurity regions
333 to
336.
Thereafter, a third etching process is performed without removing the
masks made of resist as shown in FIG.
4A. The tapered portions of the first
conductive layers are partially etched to thereby reduce the regions that overlap
with the semiconductor layer in the third etching process. Here, CHF
3
is used as an etching gas, and a reactive ion etching method (RIE method) is used.
In this embodiment, the third etching process is performed with the chamber pressure
of 6.7 Pa, the RF power of 800 W, the CHF
3 gas flow rate of 35 sccm.
Thus, first conductive layers
341 to
344 are formed.
In the third etching process, the insulating film
319 is etched at the
same time, a part of the high concentration impurity regions
333 to
336
is exposed, and insulating films
346a to
346d are formed.
Note that, in this embodiment, the etching condition by which the part of the high
concentration impurity regions
333 to
336 is exposed is used, but
it is possible that a thin layer of the insulating film is left on the high concentration
impurity regions if the thickness of the insulating film or the etching condition
is changed.
In accordance with the third etching process, impurity regions (LDD regions)
337a
to
340a are formed, which do not overlap with the first conductive
layers
341 to
344. Note that, impurity regions (GOLD regions)
337b
to
340b remain overlapped with the first conductive layers
341
to
344.
The electrode formed of the first conductive layer
341 and the second
conductive layer
324b becomes a gate electrode of an n-channel TFT
of a driver circuit to be formed in the later process. The electrode formed of
the first conductive layer
342 and the second conductive layer
325b
becomes a gate electrode of a p-channel TFT of the driver circuit to be formed
in the later process. Similarly, the electrode formed of the first conductive layer
343 and the second conductive layer
326b becomes a gate electrode
of an n-channel TFT of a pixel portion to be formed in the later process, and the
electrode formed of the first conductive layer
344 and the second conductive
layer
327b becomes one of electrodes of a storage capacitor of the
pixel portion to be formed in the later process.
In accordance with the above processes, in this embodiment, the difference between
the impurity concentration in the impurity regions (GOLD regions)
337b
to
340b that overlap with the first conductive layers
341
to
344 and the impurity concentration in the impurity regions (LDD regions)
337a to
340a that do not overlap with the first conductive
layers
341 to
344 can be made small, thereby improving the TFT characteristics.
Next, the masks of resist are removed, masks
348 and
349 are
newly formed of resist, and a third doping process is performed. In accordance
with the third doping process, impurity regions
350 to
355 are formed,
in which the impurity element imparting a conductivity (p-type) opposite to the
above conductivity (n-type) is added to the semiconductor layer that becomes an
active layer of the p-channel TFT (FIG.
4B). The first conductive layers
342 and
344 are used as masks to the impurity element, and the impurity
element that imparts the p-type conductivity is added to thereby form impurity
regions in a self-aligning manner. In this embodiment, the impurity regions
350
to
355 are formed by an ion doping method using diborane (B
2H
6).
Note that, in the third doping process, the semiconductor layer to become the n-channel
TFT is covered with the masks
145 and
146 formed of resist. Although
phosphorus is added to the impurity regions
348 and
349 to become
the p-channel TFT of the source region and the drain region at different concentrations
in accordance with the first and second doping processes, the doping process is
performed such that the concentration of the impurity element imparting p-type
conductivity is in the range of 2×10
20 to 2×10
21 atoms/cm
3
in any of the impurity regions. Thus, the impurity regions function as a
source region and a drain region of the p-channel TFT with no problem. In this
embodiment, a part of the semiconductor that becomes an active layer of the p-channel
TFT is exposed, and thus, there is an advantage that an impurity element (boron)
is easily added.
In accordance with the above-described processes, the impurity regions are formed
in the respective semiconductor layers.
Subsequently, the masks
348 and
349 of resist are removed,
and a first interlayer insulating film
356 is formed. This first interlayer
insulating film
356 is formed of an insulating film containing silicon by
a plasma CVD method or a sputtering method into a thickness of 100 to 200 nm. In
this embodiment, a silicon nitride oxide film with a film thickness of 150 nm is
formed by a plasma CVD method. Of course, the first interlayer insulating film
356 is not particularly limited to the silicon nitride oxide film, but an
other insulating film containing silicon may be formed into a single layer or a
lamination structure.
Then, as shown in FIG. 8C, a step of activating the impurity elements added
in the respective semiconductor layers is performed. This step is carried out by
thermal annealing using a furnace annealing oven. The thermal annealing may be
performed in a nitrogen atmosphere containing an oxygen content of 1 ppm or less,
preferably 0.1 ppm or less, at 400 to 700° C., typically 500 to 550°
C. In this embodiment, a heat treatment at 550° C. for 4 hours is carried
out. Note that, except the thermal annealing method, a laser annealing method,
or a rapid thermal annealing method (RTA method) can be applied thereto.
Note that, in this embodiment, at the same time as the above activation process,
nickel used as the catalyst in crystallization is gettered to the impurity regions
(
333,
335,
350,
353) containing phosphorous at a high
concentration. As a result, nickel concentration of the semiconductor layer which
becomes a channel forming region is mainly lowered. The TFT with a channel forming
region thus formed has an off current value decreased, and has high electric field
mobility because of good crystallinity, thereby attaining satisfactory characteristics.
Further, an activation process may be performed before forming the first
interlayer insulating film. However, in the case where a wiring material used is
weak to heat, it is preferable that the activation process is performed after an
interlayer insulating film (an insulating film containing silicon as its main ingredient,
for example, silicon nitride oxide film) is formed to protect the wiring or the
like as in this embodiment.
In addition, heat treatment at 300 to 550° C. for 1 to 12 hours is performed
in an atmosphere containing hydrogen of 3 to 100%, to perform a step of hydrogenating
the semiconductor layers. In this embodiment, the heat treatment is performed at
410° C. for 1 hour in an atmosphere containing hydrogen of about 3 %. This
step is a step of terminating dangling bonds in the semiconductor layer with hydrogen
in the interlayer insulating film. As another means for hydrogenation, plasma hydrogenation
(using hydrogen excited by plasma) may be carried out.
Besides, in the case of using a laser annealing method as the activation
process, it is preferred to irradiate laser light such as an excimer laser or a
YAG laser after the hydrogenating process.
Next, as shown in FIG. 5A, a second interlayer insulating film
357 is
formed on the first interlayer insulating film
356 from an organic insulating
material. In this embodiment, an acrylic resin film with a thickness of 1.6 μm
is formed. Patterning is then performed to form contact holes respectively reaching
the impurity regions
333,
335,
350, and
353.
A film of an insulating material containing silicon or of a film of an organic
resin can be used as the second interlayer insulating film
357. Examples
of the usable insulating mat
