Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Field effect device in non-single crystal – or...
Reexamination Certificate
2001-01-03
2003-07-15
Zarabian, Amir (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Field effect device in non-single crystal, or...
C257S059000, C257S750000, C428S699000, C428S701000, C428S702000
Reexamination Certificate
active
06593593
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a transparent electrode, a patterning method for the same, and a manufacturing method for a semiconductor element of the same formed on a transparent substrate used in an integrated type photovoltaic device, a liquid crystal display device, and an organic EL device or the like.
2. Description of the Prior Art
A photovoltaic device comprising an amorphous semiconductor of amorphous silicon, amorphous silicon carbide, amorphous silicon germanium or the like has been developed as a solar cell device because it is manufactured at low cost and easily increases in size.
Explanation of a general amorphous photovoltaic device is made by referring to
FIG. 35. A
photovoltaic element
100
of an amorphous semiconductor is formed by laminating a transparent electrode
102
, a photovoltaic conversion layer
103
of a lamination of p-, i-, and n-type amorphous semiconductor layers
103
p
,
103
i
,
103
n
, and a rear surface metal electrode
104
in this order on a glass substrate
101
.
Tin oxide (SnO
2
) and ITO (Indium Tin Oxide) are used conventionally as transparent conductive material for forming the transparent electrode
102
. In recent years, zinc oxide (ZnO) has been examined in order to reduce manufacturing cost and provide a photovoltaic element having high photovoltaic characteristics.
A photovoltaic element using ZnO is manufactured by the following processes. For example, a transparent electrode
102
of ZnO is formed on a glass substrate
101
by sputtering, and a photovoltaic conversion layer
103
formed of a lamination of a p-type layer
103
p
of approximately 150 Å of p-type amorphous silicon carbide, an i-type layer
103
i
of approximately 4000 Å of i-type amorphous silicon, and an n-type layer
103
n
of approximately 200 Å of n-type amorphous silicon is formed by plasma CVD. Then, a rear surface metal electrode
104
of silver (Ag) is sequentially laminated by sputtering to manufacture the photovoltaic element
100
.
Photovoltaic elements including transparent electrodes
102
of ZnO of various thickness are manufactured and the photovoltaic conversion efficiency of them are measured. The results are shown in FIG.
36
. As shown in a characteristic diagram of
FIG. 36
, high photovoltaic conversion efficiency over 10.5% is obtained when a thickness of the transparent electrode
102
is approximately 2100-5000 Å.
The photovoltaic element using the transparent electrode of ZnO can provide high photovoltaic conversion efficiency.
The photovoltaic device comprising the amorphous semiconductor has an integrated structure so as to take out a high voltage from a single substrate.
In order to form the integrated structure, it is necessary to separate the transparent electrode film, the amorphous semiconductor layer, and the metal electrode film on the glass substrate. A laser patterning method is used for the separation.
A structure of a laser patterning device is explained by referring to
FIG. 37. A
laser
11
emitted from an Nd:YAG laser oscillating device
10
changes its direction at a reflection mirror
12
, is condensed by a condensing lens
13
, and irradiates a region to be processed of an object to be processed
20
mounted on a moving table
14
of an XYZ stage. A pattern is controlled by moving the moving table
14
with the object to be processed
20
mounted thereon.
In patterning a transparent electrode by using this device, the transparent substrate
21
with the transparent electrode film
22
formed on the whole surface thereof as the object to be processed is mounted on the moving table
14
. The moving table
14
is controlled to move in XYZ directions so that the region to be processed of the transparent electrode
22
is eliminated by laser as shown in FIG.
38
.
In the meantime, when the ZnO film formed by sputtering as the transparent electrode on the transparent substrate (a glass substrate)
21
is laser-patterned by an Nd:YAG laser (a wavelength of 1064 nm, power 10W, and a beam diameter 50 &mgr;m), phenomena particular to the ZnO film, which is not observed when using material such as SnO
2
and ITO as the transparent electrode, are found. That is, (1) volume expansion of a laser irradiated end part, (2) a crack of a laser irradiated end part, (3) peeling of the ZnO film from the glass substrate, (4) diffusion of a ZnO forming element into the glass substrate, or the like.
These phenomena seem to complicatedly relate to a crystalline structure, heat conductivity, a surface tension in melting or the like of ZnO material. These phenomena may result in short-circuit between electrodes of the photovoltaic device, degraded reliability of the photovoltaic device, separation failure of the ZnO film (insulation failure between adjacent photovoltaic elements), and these problems obstruct commercialization of the ZnO material. The photovoltaic element using the transparent electrode of the ZnO film can not provide sufficient characteristics as an integrated type photovoltaic device while it can provide high photovoltaic conversion efficiency.
It is generally known that the ZnO material has moisture absorption property. Therefore, when the ZnO film is retained in an atmosphere over a day, moisture in the atmosphere penetrates from a surface of the ZnO film and solid state properties change, resulting in significant failure of laser patterning.
FIG. 39
is results of temperature distribution simulation in laser patterning; an Nd:YAG laser (wavelength 1064 nm, power 10W, a beam diameter 50 &mgr;m) is irradiated to an aluminum dope ZnO film(7500 Å in thickness) formed on a glass substrate by sputtering. In this simulation, it is assumed that laser energy injected to the ZnO film (laser energy excluding reflection and transmission loss) is converted into heat energy.
The laser-irradiated ZnO film is required to be evaporated (scattered) with the temperature reaching over the melting point and be completely eliminated so as to obtain complete electrical insulation by laser patterning. The ZnO film is required to melt to an interface of the glass and the ZnO film completely. In this case, a temperature of the ZnO film on a surface side reaches over the melting point and is in a high temperature state.
The excessive energy not only is converted into kinetic energy of a ZnO molecule but also moves to a periphery of a laser irradiated part by heat conduction, resulting in following heat damages; (1) volume expansion of the laser irradiated end part, (2) a crack of the laser irradiated end part, (3) peeling of the ZnO film from the glass substrate, (4) diffusion of the ZnO forming element in the glass substrate.
These problems may cause short-circuit passing through a semiconductor layer later formed, or a crack generated in the ZnO film in other processes may cause loss of a part of the film and degradation of reliability. In addition, diffusion of component elements of the ZnO film to the glass substrate causes separation failure (electrical insulation failure).
The above simulation is made in assumption that all laser energy is converted into heat energy. However, in actually dividing the ZnO film into a plurality of electrodes by laser patterning, absorption of a laser is insufficient when the ZnO film is thin, resulting in incomplete electrical separation.
A ZnO film having various thickness is formed on a glass substrate, and is divided into two electrodes by laser patterning. Then resistance between the two electrodes is measured.
FIG. 40
is a characteristic view showing relations between a thickness of the ZnO film and yields of non-defective item having resistance between the electrodes not less than 10M&OHgr;.
A separation width of the two electrodes is approximately 100 &mgr;m as in the case of using for a photovoltaic device. It is found that high yields of over 90% can be obtained when a thickness of the ZnO film is larger than 5000 Å but as a thickness becomes small, the yield declines. When the thickness is smaller than 4500 &angst
Shinohara Wataru
Yamamoto Yasuaki
Arent Fox Kintner & Plotkin & Kahn, PLLC
Brophy Jamie L.
Sanyo Electric Co,. Ltd.
Zarabian Amir
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