Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2000-01-25
2001-11-13
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192220, C204S192260, C204S298200
Reexamination Certificate
active
06315874
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to film deposition methods by a magnetron sputtering apparatus, and particularly to improvements in methods of depositing a thin film of metal oxide by a magnetron sputtering apparatus with a mobile magnet for creating a magnetic field moving across a film deposition region.
2. Description of the Related Art
A typical example of depositing a thin film of metal oxide by a magnetron sputtering apparatus is deposition of a conductive thin film of metal oxide on a photoelectric conversion layer of semiconductor in a thin-film solar battery. Particularly, a thin-film solar battery for large power to be installed on a roof of a house, the top of a building and the like is required to have a larger area to provide larger power efficiently at low cost.
In depositing a thin film of a large area, a magnetron sputtering apparatus with a mobile magnet is used more preferably than that with fixed magnets, since if the magnetron sputtering apparatus with fixed magnets is used to deposit a thin film on a fixed substrate of a large area, a large number of magnets must be arranged across the entirety of a large film deposition region and thus the apparatus with fixed magnets becomes complex and expensive. Furthermore, even if a large number of magnets are used, it is difficult to create a uniform magnetic field across the entirety of the large film deposition region, so that a target tends to be unevenly consumed and a film tends to be unevenly deposited. Incidentally, there also exists a magnetron sputtering apparatus with fixed magnets, wherein a substrate is moved relative to the fixed magnets, though such an apparatus with fixed magnets requires a large vacuum chamber and a large vacuum pump to move a large substrate in the chamber and also requires a large installation area therefor.
In a magnetron sputtering apparatus with a magnet for creating a magnetic field reciprocating across a film deposition region, conventionally the magnet typically reciprocates across the entirety of the film deposition region multiple times to provide a uniform quality to a film deposited on a fixed substrate. For example, Japanese Patent Laying-Open No. 10-158833 discloses on page 5, paragraph [0034] that a magnet is exemplarily reciprocated eleven times to deposit an ITO (indium-tin oxide) film having a thickness of 60nm.
However, when a magnetron sputtering apparatus with a mobile magnet is used with the magnet being reciprocated multiple times to deposit a transparent conductive oxide (TCO) layer of metal oxide such as ITO, SnO
2
, or ZnO on a photoelectric conversion layer of semiconductor in a thin-film solar battery, the obtained thin-film solar battery cannot have sufficiently satisfactory characteristics and in particular tends to have a fill factor, as a well-known output characteristic, of insufficient level.
FIGS. 2 and 3
are illustrative, schematic cross sections of thin-film solar batteries each with a TCO layer deposited on a photoelectric conversion layer of semiconductor. In the
FIG. 2
thin-film solar battery, successively stacked on a transparent glass substrate
1
are a SnO
2
layer as a first electrode layer
2
, a photoelectric conversion layer
3
of semiconductor, and a ZnO layer as a second electrode layer
4
. Photoelectric conversion layer
3
of semiconductor includes a p-type sublayer
3
p
, an i-type sublayer
3
i
, and an n-type sublayer
3
n
that are stacked successively. Relatively thick i-type sublayer
3
i
provides photoelectric conversion, while p- and n-type layers
3
p
and
3
n
much thinner than i-type sublayer
3
i
create an electric field. The sublayers may also be formed of either amorphous semiconductor or crystalline semiconductor.
In the
FIG. 3
thin-film solar battery also, first electrode layer
2
of SnO
2
and photoelectric conversion layer
3
of semiconductor are stacked successively on transparent glass substrate
1
. The
FIG. 3
thin-film solar battery, however, includes a ZnO layer
4
a
and an Ag layer
5
that are stacked successively on photoelectric conversion layer
3
of semiconductor , as disclosed in Japanese Patent Laying-Open No. 55-108780. ZnO layer
4
a
acts to enable a second electrode layer to have a high light reflectivity to provide an improved conversion efficiency, and Ag layer
5
acts as the second electrode layer. Ag layer
5
is preferable as a back electrode layer, since it is highly light reflective and highly conductive. ZnO layer
4
a
between semiconductor layer
3
and Ag layer
5
is much less thick than the
FIG. 2
ZnO electrode layer
4
, but it can act to realize an enhanced reflectivity of Ag layer
5
and also prevent Ag atoms from diffusing into semiconductor layer
3
.
As such, it is known that a thin-film solar battery preferably includes a TCO layer deposited on a photoelectric conversion layer of semiconductor. As has been described, however, if a magnetron sputtering apparatus with a mobile magnet is used with the magnet being reciprocated multiple times to provide a thin-film solar battery with a TCO layer deposited on a photoelectric conversion layer of semiconductor, the obtained solar battery as shown in
FIG. 3
can hardly have satisfactory output characteristics and in particular tends to have a degraded fill factor.
SUMMARY OF THE INVENTION
In view of such issues in the prior art, the present invention contemplates a method of depositing a high-quality thin film of metal oxide by a magnetron sputtering apparatus with a mobile magnet. In particular, the present invention also contemplates a film deposition method capable of improving output characteristics of a thin-film solar battery of a large area including a thin film of metal oxide deposited on a photoelectric conversion layer of semiconductor by magnetron sputtering.
In accordance with the present invention, the method of depositing a thin film of metal oxide by a magnetron sputtering apparatus with a mobile magnet reciprocating to create a magnetic field, is characterized in that the magnet reciprocates no more than twice in depositing a single thin film of metal oxide.
More specifically, the magnet may reciprocate once, or it may do so a half time, i.e., move one way.
The thin film of metal oxide to be formed may be a transparent conductive film of any one of ITO, SnO
2
and ZnO.
When the thin film of metal oxide is transmissive to visible light, the thin film of metal oxide can overlie, e.g., on a semiconductor layer included in the thin-film solar battery, with at least an outermost surface layer of the semiconductor layer being an amorphous silicon layer, an amorphous silicon based alloy layer, a crystalline silicon layer or a crystalline silicon based alloy layer.
Furthermore in accordance with the present invention, the method of depositing a thin film of metal oxide by magnetron sputtering is characterized in that the magnet moves at no more than 50 mm/second.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4221652 (1980-09-01), Kuriyama
patent: 4622120 (1986-11-01), Gillery
patent: 5833815 (1998-11-01), Kim et al.
patent: 19701575 (1998-07-01), None
patent: 55-108780 (1980-08-01), None
patent: 06010127 (1994-01-01), None
patent: 08274375 (1996-10-01), None
patent: 9-59772 (1997-03-01), None
patent: 10158833 (1998-06-01), None
Nishio Hitoshi
Suzuki Takayuki
Hogan & Hartson L.L.P.
Kaneka Corporation
McDonald Rodney G.
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