JP2675323B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a semiconductor device, and more particularly to a method for manufacturing a semiconductor device such as a solar cell, an optical sensor, an electrophotographic photosensitive member and the like.

(B) Conventional technology In a so-called heterojunction type semiconductor device having a semiconductor junction composed of two semiconductor layers having different energy band gaps, a notch or a spike occurs in the heterojunction portion, and a defect such as an interface state is generated. There are levels. Due to this interface state, carriers of electrons or holes are likely to be recombined at the junction, and as a result, the carrier lifetime is reduced. In a photovoltaic device, photoexcited carriers are likely to disappear before generating photovoltaic power, and the output cannot be increased.

As a technique for solving such a problem, JP-A-55-13938
According to the publication, the semiconductor layer is made amorphous, and an additive such as carbon, nitrogen or oxygen is added in the formation transition process from the first amorphous semiconductor layer to the second amorphous semiconductor layer. Is added while continuously changing the energy band gap from the first amorphous semiconductor to the second amorphous semiconductor, thereby preventing notches, spikes, and interface states from being generated. ing.

In general, a photovoltaic device has a structure in which a transparent electrode film, a pin-type amorphous semiconductor layer, and a back electrode film are formed in this order, but the optical energy band gap is almost the same in the i layer and the n layer. In addition, since the energy level at the upper end of the valence band and the energy level at the lower end of the conduction band are gradually inclined toward the back electrode film side, they are originally collected in the transparent electrode film. The positive holes move to the back electrode side and recombine with the electrons collected there, resulting in deterioration of photovoltaic characteristics.

In order to solve such a problem, according to Japanese Patent Application Laid-Open No. 61-90476, the energy band gap of the n layer is increased by adding carbon or nitrogen to the n layer so as to increase gradually toward the back electrode film side. Are sequentially increased toward the back electrode film.

Furthermore, as one of the photovoltaic devices, a plurality of photoelectric conversion layers each including an amorphous semiconductor layer (more specifically, a pin-type amorphous semiconductor layer) are stacked in the light incident direction and the energy of each photoelectric conversion layer is increased. JP-A-58-116779 discloses a structure in which the band gap is gradually reduced from the light incident side. In this case, in order to adjust the energy band gap, an amorphous semiconductor layer made of silicon is formed. It contains germanium (Ge) and tin (Sn).

(C) Problems to be Solved by the Invention Accordingly, the junction between the first amorphous semiconductor layer and the second amorphous semiconductor layer or its vicinity or the n layer of the pin-type amorphous semiconductor layer is a semiconductor carbide, Since it becomes a nitride or an oxide, it tends to be insulated, thus lowering the electrical conductivity, and in a photovoltaic device, it acts as a series resistance loss of the output.

Further, it is not preferable to mix germanium or tin into the amorphous semiconductor layer, because it causes deterioration of film quality.

(D) Means for Solving the Problems The present invention provides a first amorphous semiconductor layer having a first energy band gap formed by a CVD method and a second energy band different from the first energy band gap. A method of manufacturing a semiconductor device having a semiconductor junction with a second amorphous semiconductor layer having a gap, comprising forming a junction between the first amorphous semiconductor layer and the second amorphous semiconductor layer or a vicinity thereof. Argon (Ar) as raw material gas in the process
The first feature is that the gas is added while changing its addition amount.

Further, a transparent electrode film, a pin type amorphous semiconductor layer formed by a CVD method, and a back surface electrode film are formed in this order, and the energy band gap of the n layer of the amorphous semiconductor layer is located on the back surface electrode film side. In the method for manufacturing a semiconductor device, the n layer of the amorphous semiconductor layer is
The second characteristic is that the raw material gas is formed by adding argon (Ar) gas while gradually increasing the amount of addition thereof toward the back electrode film side.

Further, it is a method for manufacturing a semiconductor device in which a plurality of photoelectric conversion layers formed of an amorphous semiconductor layer formed by a CVD method are stacked in the light incident direction and the energy band gaps of the photoelectric conversion layers are sequentially reduced from the light incident side. The third feature is that each of the photoelectric conversion layers is formed by adding argon (Ar) gas to the raw material gas while gradually decreasing the amount of addition thereof from the light incident side.

According to the present invention, when the first amorphous semiconductor layer and the second amorphous semiconductor layer are sequentially formed, the process of forming the first amorphous semiconductor layer into the second amorphous semiconductor layer In addition, when the n layer of the pin type amorphous semiconductor layer is formed and when the plurality of photoelectric conversion layers are formed, Ar gas is added to the source gas while changing the addition amount, so that the energy band gap is increased. Change.

(F) Example FIGS. 1 (A) to 1 (E) are cross-sectional views by process when a photovoltaic device is manufactured by using the first manufacturing method of the present invention.

In FIG. 1 (A), tin oxide (SnO ₂ ), indium oxide (In ₂ O ₃ ), or indium tin oxide (ITO) is formed on a substrate (1) such as glass or heat-resistant plastic that has a light-transmitting and insulating property. A transparent electrode film (2) made of a translucent conductive oxide (TCO) having a thickness of 300 to 3000 Å is formed by a thermal CVD method, a sputtering method, an electron beam evaporation method or the like.

In FIG. 1 (B), a p-type hydrogenated amorphous silicon carbide (a-SiC: H) layer (3) having a film thickness of about 300Å is formed on the transparent electrode film (2) by a plasma CVD method using glow discharge. Is formed by. Such p-type a-SiC: H layer (3)
The reaction conditions are as follows: reaction pressure: 0.2 to 1 Torr substrate temperature: 250 to 300 ° C. power density: 0.01 to 0.1 w / cm ² , silane (SiH ₄ ) gas, methane (CH ₄ ) gas, and diborane as source gases. (B ₂ H ₆ ) gas and Argon (Ar) gas are used as balance gas. Thus, p-type a-Si with an energy band gap of 1.9 to 2.2 eV
A C: H layer (3) is formed.

In FIG. 1 (C), the i-type hydrogenated amorphous silicon (a-Si: H) layer (4) having a film thickness of 3000 to 6000Å is formed on the p-type a-SiC; H layer (3) as described above. Is formed by the plasma CVD method under the formation conditions of. In this case, SiH ₄ gas is first used as the source gas and Ar gas is used as the balance gas, and the amount of Ar gas is gradually reduced as the film formation is advanced. As a result, as shown in FIG. 2, the graded i-type a-Si: H layer (4a) whose energy band gap continuously changes from about 1.85 eV to 1.65 eV is changed to the p-type a-
It is formed adjacent to the SiC: H layer (3). Subsequently, only SiH ₄ gas was used as the source gas, and the energy band gap was about 1.65 eV. The constant gap i-type a-Si: H layer (4
b) is formed.

In FIG. 1 (D), an n-type a-Si: H layer (5) having a film thickness of 300 to 800 Å is formed on the i-type a-Si: H layer (4) under the same formation conditions as described above. It is formed by the plasma CVD method.
In this case, SiH ₄ gas and phosphine (PH
₃ ) Gas and Ar gas are used as balance gas. Thus, the energy band gap is 1.6-1.75 eV
N-type a-Si: H layer (5) is formed.

Finally, in FIG. 1 (E), aluminum (Al), silver (Ag), titanium (Ti), chromium (Cr), magnesium (Mg) are formed on the n-type a-Si: H layer (5). Alternatively, the back electrode film (6) made of a simple metal such as nickel (Ni) or an alloy thereof is formed by a resistance heating method, an electron beam evaporation method, a sputtering method, or the like.

Thus, on the substrate (1), the transparent electrode film (2), the p-type a-SiC: H layer (3), the i-type a-Si: H layer (4), and the n-type a-S.
A photovoltaic device in which the i: H layer (5) and the back electrode film (6) are laminated is formed, and its energy band gap, particularly the p-type a-SiC: H layer (3) and the i-type a-Si: The energy band gap at or near the junction with the H layer (4) is
As shown in FIG. 3, it changes continuously.

FIG. 4 shows the relationship between the Ar gas addition ratio and the electrical conductivity, specifically, the photoconductivity σph and the dark conductivity σd. From the figure, it can be seen that the addition of Ar gas has almost no adverse effect on the photoconductivity σph and the dark conductivity σd.

FIG. 5 is a cross-sectional view showing a photovoltaic device manufactured by the second manufacturing method of the present invention. In such a photovoltaic device, instead of the n-type a-Si: H layer (5) in the above-mentioned device, a graded n-type a-Si: whose energy band gap gradually increases toward the back electrode film (6). The point is that the H layer (5) (see FIG. 6) is formed.

The graded n-type a-Si: H layer (5) is formed by the plasma CVD method under the same formation conditions as described above. In this case, SiH ₄ gas is used as the source gas, Ar gas is used as the balance gas, and Ar gas is used as the film formation progresses.
The amount of gas is gradually increased, so that the energy band gap changes continuously from about 1.65 eV to 1.7 eV.

The open circuit voltage Voc (V), the short circuit current Isc (μA), and the form factor FF (for the photovoltaic device of the present invention thus manufactured and the conventional photovoltaic device in which the n layer is not graded are compared. %) Was measured and the results are shown in the table below.

As described above, according to the present invention, in Isc and FF,
Has been greatly improved.

Further, FIGS. 7 (A) to 7 (H) show the third embodiment of the present invention.
FIG. 7 is a cross-sectional view for each step when a photovoltaic device is manufactured by the manufacturing method of.

In FIG. 7 (A), SnO ₂ , In is formed on a substrate (10) having a light-transmitting property and an insulating property, such as glass or heat-resistant plastic.
A transparent electrode film (11) made of TCO such as ₂ O ₃ or ITO and having a film thickness of 300 to 6000 Å is formed by a thermal CVD method, a sputtering method, an electron beam evaporation method or the like.

In FIG. 7 (B), a first p-type a-SiC: H layer (12) having a film thickness of about 300Å is formed on the transparent electrode film (11) by the plasma CVD method using glow discharge. Such first p-type a-Si
The conditions for forming the C; H layer (12) are: reaction pressure: 0.2 to 1 Torr substrate temperature: 200 to 250 ° C. power density: 0.01 to 0.1 W / cm ² , and SiH ₄ gas, CH ₄ gas and B ₂ H ₆ gas and Ar gas are used as balance gas. Thus, the first p-type a-SiC: H layer (12) having an energy band gap of 2.2 to 2.3 eV is formed.

In FIG. 7 (C), the first i-type a-Si: H layer (13) having a film thickness of 3000 to 6000Å is formed on the first p-type a-SiC: H layer (12) under the same formation conditions as described above. Is formed by plasma CVD method. In this case, SiH ₄ gas as the starting material gas,
Ar gas is used as the balance gas, and the amount of Ar gas is gradually reduced to a certain amount as the film formation proceeds. As a result, as shown in Fig. 8, the energy band gap continuously changes from about 2.15 eV to 2.05 eV.
The graded i-type a-Si: H layer (13a) is the first p-type a-SiC: H
Formed adjacent to the layer (12). Subsequently, the SiH ₄ gas as the source gas and a fixed amount of the balance gas
Energy band gap of Ar gas is about 2.05eV
A first constant gap i-type a-Si: H layer (13b) is formed. In FIG. 7 (D), the first n-type a-Si: H layer (14) having a film thickness of 300 to 800 Å is formed on the first i-type a-Si: H layer (13) under the same formation conditions as described above. It is formed below by the plasma CVD method. In this case, SiH ₄ gas and PH ₃ gas are used as the source gas, and Ar gas is used as the balance gas. Thus, the first n-type a with an energy band gap of 2.0 to 2.1 eV
-Si: H layer (14) is formed.

In FIG. 7 (E), the film thickness is about 300Å and the energy band gap is 2.0 to 2.1e on the first n-type a-Si: H layer (14).
The second p-type a-SiC: H layer (15) of V is the first p-type a-SiC: H layer (1
It is formed by the plasma CVD method under the same forming conditions and used gas as in 2).

In FIG. 7 (F), a second i-type a-Si: H layer (16) having a film thickness of 3000Å to 1 μm is formed on the second p-type a-Si: H layer (15) under the same formation conditions as described above. Is formed by plasma CVD method. In this case, SiH ₄ gas is used as the source gas, the above-mentioned fixed amount of Ar gas is used as the balance gas, and the amount of Ar gas is gradually reduced as the film formation proceeds, and finally becomes 0. This results in an energy bandgap of about
Second graded i that continuously changes from 2.05 to 1.95 eV
A type a-Si: H layer (16a) is formed adjacent to the second p-type a-Si: H layer (15). Subsequently, only SiH ₄ gas was used as the source gas, and the energy band gap was about 1.95 eV.
A second constant gap i-type a-Si: H layer (16b) is formed.

In FIG. 7 (G), a film thickness of 300 to 800Å and an energy band gap of 1.9 are formed on the second i-type a-Si: H layer (16).
The second n-type a-Si: H layer (17) of ~ 2.0 eV has the same formation conditions as the first n-type a-Si: H layer (14) and the plasma CV under the used gas.
It is formed by the D method.

Finally, in FIG. 7 (H), aluminum (Al), silver (Ag), titanium (Ti), chromium (Cr), magnesium (Mg) is formed on the second n-type a-Si: H layer (17). ) Or a simple metal such as nickel (Ni) or an alloy thereof, a back electrode film (18) is formed by a resistance heating method, an electron beam evaporation method, a sputtering method or the like.

Thus, the transparent electrode film (11) and the first p-layer are formed on the substrate (10).
Type a-SiC: H layer (12) and 1st i-type a-Si: H layer (13) and 1n
Type a-Si: H layer (14), first p-type photoelectric conversion layer, second p-type a-SiC: H layer (15), second i-type a-Si: H layer (16) and second n-type a- A photovoltaic device in which a second photoelectric conversion layer composed of a Si: H layer (17) and a back electrode film (18) are laminated is formed,
Type a-Si: H layer (13) energy band gap Eg
_As shown in FIG. 9, ₁ is larger than Eg _{2 of the second} i-type a-Si: H layer (16).

The photoelectric conversion layer is not limited to the two layers as described above and may be three or more layers.

Further, as seen from FIGS. 2 and 8, when the substrate temperature is changed in addition to the change of the addition amount of Ar gas, the change width of the energy band gap can be increased. Therefore, it is possible to form a photovoltaic device having high photoelectric conversion efficiency by stacking more photoelectric conversion layers having energy band gaps that become smaller from the light incident side.

By the way, as an accompanying effect of adding Ar gas, there is an effect of increasing the film formation rate as shown in FIG.
Thereby, productivity can be improved.

It should be noted that FIG. 10 shows, as a reference example, JP-A-56-88377.
As shown in the publication, the relationship between the amount of hydrogen (H ₂ ) gas added as an additive for forming a film having a graded energy band gap as in the present invention and the film formation rate is shown. ing. As is clear from the figure, addition of H ₂ gas is not preferable because it lowers the film formation rate and deteriorates productivity.

(G) Effect of the Invention According to the present invention, since the argon gas is added while changing the addition amount thereof, the energy band gap is arbitrarily changed without lowering the electrical conductivity or degrading the film quality. be able to. as a result,
The photovoltaic device can have good output characteristics.

[Brief description of the drawings]

1 (A) to 1 (E) are cross-sectional views showing steps in the case where a photovoltaic device is manufactured by the first manufacturing method of the present invention, and FIG. 2 is at a substrate temperature of 250 to 300 ° C. Characteristic diagram showing the relationship between the amount of Ar gas added and the energy band gap, No. 3
FIG. 4 is a schematic diagram showing the band profile of the photovoltaic device manufactured by the first manufacturing method of the present invention, and FIG. 4 shows the relationship between the additive amount of Ar gas and the photoconductivity σph and dark conductivity σd. FIG. 5 is a characteristic view, FIG. 5 is a cross-sectional view of a photovoltaic device manufactured by the second manufacturing method of the present invention, and FIG.
Schematic diagrams showing band profiles of photovoltaic devices manufactured by the manufacturing method of FIG. 7, FIGS. 7 (A) to 7 (H)
Is a cross-sectional view showing steps in the case of manufacturing a photovoltaic device by the third manufacturing method of the present invention, and FIG. 8 is a substrate temperature of 200 to 250.
FIG. 9 is a characteristic diagram showing the relationship between the amount of Ar gas added and the energy band gap at 0 ° C., FIG. 9 is a schematic diagram showing a band profile of a photovoltaic device manufactured by the third manufacturing method of the present invention, and FIG. The figure is a characteristic diagram showing the relationship between the amount of Ar gas and H ₂ gas added and the film formation rate. (3) (12) (15) ... p-type a-SiC: H layer, (4a) (13
a) (16a) ... Graded i-type a-Si: H layer, (4b)
(13b) (16b) ... Constant gap i-type a-Si: H layer,
(5) (5 ') (14) (17) ... n-type a-Si: H layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-155180 (JP, A) JP-A-58-116779 (JP, A) JP-A-56-88377 (JP, A) JP-A-58- 220478 (JP, A) JP-A-56-138970 (JP, A)

Claims (6)

(57) [Claims] 1. A first amorphous semiconductor layer having a first energy bandgap formed by a CVD method and a second amorphous semiconductor having a second energy bandgap different from the first energy bandgap. A method of manufacturing a semiconductor device having a semiconductor junction by layers, wherein argon (Ar) is used as a source gas in the process of forming the junction between the first amorphous semiconductor layer and the second amorphous semiconductor layer or in the vicinity thereof.
A method of manufacturing a semiconductor device, characterized in that a gas is added while changing its addition amount. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the first amorphous semiconductor layer is amorphous silicon carbide. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the second amorphous semiconductor layer is amorphous silicon. 4. A transparent electrode film, a pin formed by a CVD method
A method of manufacturing a semiconductor device, wherein an amorphous semiconductor layer and a back electrode film are formed in this order, and the energy band gap of the n-layer of the amorphous semiconductor layer is increased toward the back electrode film side. The n layer of the amorphous semiconductor layer is formed by adding argon (Ar) gas to a source gas while gradually increasing the amount of addition of the argon gas toward the back electrode film side. Production method. 5. A method of manufacturing a semiconductor device in which a plurality of photoelectric conversion layers made of an amorphous semiconductor layer formed by a CVD method are stacked in the light incident direction and the energy band gaps of the photoelectric conversion layers are sequentially reduced from the light incident side. A method for manufacturing a semiconductor device, wherein each of the photoelectric conversion layers is formed by adding argon (Ar) gas to a raw material gas while sequentially decreasing the amount of addition thereof from the light incident side. 6. The CVD method is plasma C using glow discharge.
The method for manufacturing a semiconductor device according to any one of items 1, 4, or 5, which is a VD.