Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
1999-01-21
2001-07-31
Christianson, Keith (Department: 2813)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
Reexamination Certificate
active
06268235
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing a photoelectric conversion device, typified by a solar cell or an image input sensor, which uses roll-to-roll system production means, and to a roll-to-roll system apparatus for manufacturing the photoelectric conversion device.
2. Description of the Related Art
As compared with a crystalline silicon material, an amorphous silicon film has such features that a film with a large area can be formed at a low temperature not higher than 400° C., and a thickness of about 1 &mgr;m is sufficient for the film as a photoelectric conversion layer to absorb light. Thus, the amorphous silicon film presents saving of silicon resources and lowering of manufacturing energy, and has hitherto attracted attention as a low cost material.
In a conventional technique, it has been common that a photoelectric conversion layer of a solar battery, an image sensor, a photosensor, or the like uses a diode structure in which a PIN junction is formed, so as to raise a photoelectric conversion efficiency or light responsibility. Although it is possible to form all of p-type and n-type semiconductor films and a substantially intrinsic i-type semiconductor film from amorphous silicon films, it is known that if a microcrystalline silicon material is used for the p-type and n-type semiconductor films, excellent photoelectric conversion characteristics can be obtained.
The reason is that in the photoelectric conversion layer of the PIN junction structure, since light absorption and generation of electric charges due to the light absorption occur in the i-type amorphous silicon film, the p-type and n-type semiconductor films are required to have high light transmissivity and to have such high conductivity that an excellent contact with an electrode can be achieved. For such requirements, the microcrystalline silicon film has properties of both low light absorption and high conductivity, so that it is a material suitable for the p-type layer and the n-type layer of the photoelectric conversion layer.
The amorphous silicon film is formed by a chemical deposition method (plasma CVD method) using a glow discharge plasma under a reduced pressure. The plasma CVD method uses a plasma CVD apparatus including a reaction chamber, exhaust means for keeping the reaction chamber under a reduced pressure, gas introduction means for introducing a raw material gas, means for generating a glow discharge plasma in the reaction chamber, and means for holding and heating a substrate. Although a silane (SiH
4
) gas is generally used as a raw material gas of an amorphous silicon film, it is also possible to use a disilane (Si
2
H
6
) gas. Further, it is also possible to use a gas obtained by diluting the foregoing raw material gas with a hydrogen (H
2
) gas.
On the other hand, as a raw material gas of a microcrystalline silicon film, a mixture gas of a SiH
4
gas and a H
2
gas is used, and the film can be obtained when film formation is carried out under such a state that a diluting ratio of the H
2
gas to the SiH
4
gas has been raised. It is known that a microcrystalline silicon film itself to which a p-type or n-type conductivity determining impurity element is not added, shows n-type conductivity. However, in general, in order to control its conductivity of p-type or n-type and to raise its electrical conductivity, an impurity gas containing a p-type or n-type conductivity determining impurity element is added to the raw material gas and the film is manufactured.
In a technical field of semiconductor, an element of group III of the periodic table, typified by boron (B), aluminum (Al), gallium (Ga), and indium (In) is known as the p-type conductivity determining impurity element, and an element of group Vb of the periodic table, typified by phosphorus (P), arsenic (As), and antimony (Sb) is known as the n-type conductivity determining impurity element. In a general plasma CVD method, an impurity gas typified by B
2
H
6
or PH
3
is mixed to the raw material gas and a film is formed. The addition amount of the mixed impurity gas at this time is about 0.1% to 5% of SiH
4
, and is not higher than 10% at most.
As described above, since the process temperature of the microcrystalline silicon film or amorphous silicon film is low, an organic resin film in addition to a glass material can be used as a substrate of a photoelectric conversion device. Since the thickness of several tens to several hundreds &mgr;m suffices for the organic resin substrate and the organic resin film has flexibility, a roll-to-roll system production means can be applied. The roll-to-roll system can be applied to any step of the photoelectric conversion device, and it can be applied to a laser scribing step and a printing step for patterning, in addition to a step of forming an electrode by a sputtering method and a step of forming a photoelectric conversion layer by a plasma CVD method.
Basic steps relating to a photoelectric conversion layer of a solar battery, an image sensor, or the like manufactured on a substrate include a step of forming a first electrode on the substrate, a step of forming a photoelectric conversion layer which is made of a PIN junction and is in close contact with the first electrode, and a step of forming a second electrode which is in close contact with the photoelectric conversion layer. At the time of manufacturing the PIN junction which becomes the photoelectric conversion layer, the film formation is generally carried out without breaking a vacuum so as to improve the characteristics of a contact interface.
It is known that at this time, when the foregoing impurity gas is added to the foregoing raw material gas in order to form a p-type or n-type semiconductor film, a very small amount of impurity gas and its reaction product remain and are attached to a reaction chamber and a discharge electrode as a part of glow discharge plasma producing means.
For example, after the formation of an n-type silicon film, when a substantially intrinsic i-type amorphous silicon film is formed continuously in the same reaction chamber without adding an impurity gas, there has been a problem that the remaining impurity separates from the n-type silicon film and is newly taken in the i-type film. Since the substantially intrinsic i-type amorphous silicon film is manufactured such that the defect density in the film is made not higher than about 1×10
16
/cm
3
, there has been a problem that even if the impurity element with a concentration of several tens ppm to several hundreds ppm is taken in, an impurity level is generated so that the characteristics of the film is changed.
In order to solve such problems, a multi-chamber separation type plasma CVD apparatus in which a plurality of reaction chambers are provided and gas separation means are provided between the respective reaction chambers, is put to practical use. In order to form the PIN junction, it has been necessary to provide at least three independent reaction chambers to form p-type, i-type and n-type semiconductor films.
Although the roll-to-roll system has a merit that productivity is excellent through a continuous process of an elongate substrate, various contrivances have been necessary to solve the foregoing problems in the plasma CVD apparatus.
FIG. 2
is a schematic view of a conventional plasma CVD apparatus for a solar battery by a roll-to-roll system. An elongate substrate
212
wound on a bobbin
205
is disposed in a feeding chamber
210
. The elongate substrate
212
fed from this chamber is rewound on a rewinding bobbin
206
provided in a rewinding chamber
211
through a coupling slit
209
a
, an n-type film forming chamber
201
a
, a coupling slit
209
b
, an i-type film forming chamber
201
b
, a coupling slit
209
c
, a p-type film forming chamber
201
c
, and a coupling slit
209
d
. At this time, the coupling slits
209
a
to
209
d
have functions to enable continuous movement of the elongate substrate
212
while a reduced pressure state is maint
Arai Yasuyuki
Sakakura Masayuki
Yamazaki Shunpei
Christianson Keith
Fish & Richardson P.C.
Semiconductor Energy Laboratory Co,. Ltd.
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