Method of producing solar cell device

Details Method of producing solar cell device Method of producing solar cell device

1999-09-24

2001-03-27

Smith, Matthew (Department: 2825)

Semiconductor device manufacturing: process

Making device or circuit responsive to nonelectrical signal

Responsive to electromagnetic radiation

C438S690000, C438S720000, C438S722000

Reexamination Certificate

active

06207471

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a fabricating method for a solar cell device for giving a required amount of transmitted light to semiconductor layers by obtaining a clean insulating substrate surface and transparent oxide electrode surface.
BACKGROUND TECHNOLOGY
FIG. 10
is a sectional view showing the structure of a conventional solar cell device
102
.
The solar cell device
102
has a structure in which a transparent oxide electrode
12
is formed on the surface of an insulating substrate
10
which is a transparent glass substrate, and a p-type semiconductor layer
18
, a buffer layer
20
, an intrinsic semiconductor layer
22
, an n-type semiconductor layer
24
, and a metal electrode
26
are laminated in order on to the surface of the transparent oxide electrode
12
into a laminated structure.
The insulating substrate
10
transmits light incident from the surface on the side thereof (the lower side in the drawing), on which the transparent oxide electrode
12
is not formed, to the transparent oxide electrode
12
.
The transparent oxide electrode
12
is formed to lead light (mainly sunlight) incident through the insulating substrate
10
to the intrinsic semiconductor layer
22
through the p-type semiconductor layer
18
and the buffer layer
20
and to keep ohmic contact with the p-type semiconductor layer
18
.
The p-type semiconductor layer
18
is a layer composed of a p-type semiconductor, which is provided to lead carriers, produced in the intrinsic semiconductor layer
22
by the incident light, to the transparent oxide electrode
12
. The buffer layer
20
functions as a buffer layer for preventing a forbidden band width of the intrinsic semiconductor layer
22
from narrowing due to the mixing of p-type impurities (boron) contained in the p-type semiconductor layer
18
, into the intrinsic semiconductor layer
22
. The intrinsic semiconductor layer
22
is a layer made of an intrinsic semiconductor for producing carriers by absorbing the incident light. The n-type semiconductor layer
24
is a layer made of an n-type semiconductor provided to lead the carriers produced in the intrinsic semiconductor layer
22
to the metal electrode
26
. The metal electrode
26
is connected with an interconnection for taking out electromotive force.
Next, the fabricating method for the aforesaid conventional solar cell device will be described using FIG.
11
through FIG.
15
.
First, tin oxide film is formed on the insulating substrate
10
to form a transparent oxide electrode
12
, and thereafter a photoresist
13
is applied on the entire surface of the tin oxide film. The photoresist
13
is exposed and developed with a predetermined mask to remain in a region which is to be the solar cell device
102
.
Next, as shown in
FIG. 11
, the transparent oxide electrode
12
is etched by means of a reactive ion etching system with the above photoresist
13
as an etching mask and with hydrogen iodide (HI) and argon (Ar) used as the raw material gas. Removing the photoresist
13
makes a state where the transparent oxide electrode
12
is provided on the surface of the insulating substrate
10
as shown in FIG.
12
.
Subsequently, the p-type semiconductor layer
18
is formed on the entire surface of the insulating substrate
10
so as to cover the transparent oxide electrode
12
, as shown in
FIG. 13
, by the plasma CVD (chemical-vapor deposition) method. At this time, mono-silane (SiH
4
) and diborane (B
2
H
6
) are used as the raw material gas. Methane gas (CH
4
) is simultaneously introduced to form silicon carbide in the p-type semiconductor layer
18
, thereby preventing the forbidden band width of the p-type semiconductor layer
18
from narrowing and the light converting efficiency from lowering. The buffer layer
20
is then formed over the entire surface of the p-type semiconductor layer
18
. This is carried out by the plasma CVD method with mono-silane (SiH
4
) and methane gas (CH
4
). The intrinsic semiconductor layer
22
is next formed on the entire surface of the buffer layer
20
. This is also carried out by the plasma CVD method with mono-silane (SiH
4
) as the raw material gas.
Moreover, as shown in
FIG. 14
, the n-type semiconductor layer
24
is formed on the entire surface of the intrinsic semiconductor layer
22
. This is performed by the plasma CVD method with mono-silane (SiH
4
) and phosphine (PH
3
) as the raw material gas. Thereafter, a metal film
25
which becomes the metal electrode
26
is formed on the entire surface of the n-type semiconductor layer
24
by the sputtering method and a photoresist
15
is applied on the entire surface of the metal film
25
.
The photoresist
15
is exposed and developed with a predetermined mask, as shown in
FIG. 15
, to remain only in a region which is to be the solar cell device
102
. Then, the metal film
25
and the respective layers laminated thereunder are etched and removed by the reactive ion etching method using the photoresist
15
as an etching mask, and the photoresist
15
used for the etching mask is also removed.
Consequently, the solar cell device
102
can be fabricated as shown in
FIG. 10
, in which all layers from the p-type semiconductor layer
18
, the buffer layer
20
, the intrinsic semiconductor layer
22
, the n-type semiconductor layer
24
to the metal electrode
26
are laminated in order on the transparent oxide electrode
12
.
Although the solar cell device
102
can be fabricated by the above fabricating method, the solar cell device
102
has the following disadvantages which are due to the use of tin oxide as a material for the transparent oxide electrode
12
. Tin oxide can be etched by means of the reactive ion etching system with hydrogen iodide (HI), hydrogen bromide (HBr), hydrogen chloride (HCl) or the like as the raw material gas. Hydrogen iodide is especially superior in etching properties, thus obtaining a high etching rate. However, there is a disadvantage that the use of hydrogen iodide produces tin iodide series compounds
11
through the etching, which adhere to the inside of a reaction chamber of the reactive ion etching system and to the insulating substrate
10
and the transparent oxide electrode
12
as shown in
FIG. 10
to
FIG. 15
to cause contamination, thereby reducing yields of the solar cell device. When contamination of the insulating substrate
10
and the transparent oxide electrode
12
occurs, the amount of transmitted light is decreased, which lowers electric power taken out. Therefore, the eliminating of the above contamination is an extremely important subject in terms of enhancement of output characteristics of a solar cell.
The object of the present invention is to fabricate a solar cell device for giving a required amount of transmitted light to semiconductor layers by solving the above disadvantages to obtain a clean insulating substrate surface and transparent oxide electrode surface in a fabricating method for a solar cell device.
DISCLOSURE OF THE INVENTION
To achieve the above object, the present invention is characterized by a fabricating method which comprises the steps of: forming a transparent oxide electrode by etching a metal film formed on an insulating substrate; cleaning the surfaces of the insulating substrate and the transparent oxide electrode with a halogen gas having a saturated vapor pressure higher than that of etching gas in the step of forming the transparent oxide electrode; forming a p-type semiconductor layer, an intrinsic semiconductor layer, and an n-type semiconductor layer over the surface of the transparent oxide electrode in order; and forming a metal electrode on the n-type semiconductor layer.
When a solar cell device is fabricated by the above fabricating method, the surfaces of the insulating substrate and the transparent oxide electrode are made clean so as to be high in transparency. Therefore, a required amount of transmitted light can be obtained.
Moreover, it is possible that a fabricating method for a solar cell device comprises the steps of: forming a transparent oxide elect

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