JPH0793269B2 - Amorphous semiconductor manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an amorphous semiconductor containing silicon and other atoms in addition to hydrogen as a terminator of a dangling bond thereof.

[Conventional technology]

Amorphous silicon consisting only of silicon hydrogen (hereinafter a-Si
H) is created by using silane, disilane, and their derivatives as source gases and forming films by glow discharge plasma CVD, photo-CVD, electron cyclotron resonance CVD, microwave CVD, etc. ing. Further, in order to improve characteristics such as an optical gap or to impart p or n conductivity type, CnHm, GeH ₄ , B
By mixing gases such as ₂ H ₆ and PH ₃ and performing CVD, amorphous silicon containing atoms other than silicon and hydrogen as constituent atoms is created.

[Problems to be Solved by the Invention]

For example, FIG. 2 shows the characteristic change due to the C concentration in the gas when CnHm is added to produce a-SiC: H. The optical gap Eg ^opt increases with the C concentration, but the photoconductivity σph decreases significantly. FIG. 3 shows the case where a-SiGe: H was prepared by mixing GeH _4, and the dark conduction concentration σ _d increased as the Ge concentration in the gas increased, showing an increase in defects in the film. Figure 4 shows C
nHm and B ₂ H ₆ were mixed with SiH ₄ gas to form a-SiC: H used for the p-layer of the photoelectric conversion element, and the characteristic change due to the mixing ratio of B ₂ H ₆ to SiH ₄ was shown. Even if boron is doped, more than half of them do not have 4-coordination bonds in the film and do not have 3-coordination bonds, so that the doping efficiency is poor, and the incorporation of B causes the optical gap Eg ^opt of the film to increase. There were drawbacks such as narrow width. Also, the activation energy Ea becomes constant around 0.55. This is because the position of the Fermi level is fixed by the defect created by B in a-SiC: H.

An object of the present invention is to reduce the defect density in the formed film when forming a film containing other atoms in addition to Si and H, and to obtain an amorphous semiconductor of good quality. It relates to a manufacturing method.

[Means for Solving the Problems]

To achieve the above object, according to the present invention, in the production of an amorphous semiconductor composed of silicon, hydrogen, and atoms of germanium, boron, one of carbon or a combination thereof, A gas containing the excluded constituent atoms after decomposing a gas consisting of constituent atoms excluding at least one of germanium, boron, and carbon atoms other than silicon and hydrogen to form an amorphous semiconductor film. A method for producing an amorphous semiconductor, in which the constituent atoms are plasma decomposed to enter the inside of the amorphous semiconductor film,
The penetration of the constituent atoms into the inside of the amorphous semiconductor film is performed by plasma doping.

[Action]

Occurrence of defects in an amorphous semiconductor film by removing all constituent atoms other than silicon and hydrogen, or excluding a part (selected from germanium, boron, and carbon) that adversely affects film formation In that case, when the excluded constituent atoms are introduced into the film by plasma doping after that, no defect is generated and good film quality can be maintained.

〔Example〕

FIG. 5 shows an example of an apparatus used for plasma CVD and plasma doping for carrying out the present invention, in which an upper electrode 21 and a lower electrode 22 are arranged to face each other inside a vacuum chamber 1.
The substrate 3 is placed on the lower electrode 22 and heated to a predetermined temperature by the heater 4 below the lower electrode. The power supply 5 is connected to the upper electrode 21, and the lower electrode 22 is grounded. The vacuum chamber 1 is provided with an exhaust port 61 and a gas introduction port 62.

1 (a) to (c) show a-SiG of one embodiment of the present invention.
The manufacturing process of the e: H film is shown, and the substrate 3 shown in FIG. 1 (a) is placed on the lower electrode 22 of the same device as shown in FIG. 5, and the inside of the vacuum chamber 1 is exhausted from the exhaust port 61. Evacuate, introduce a mixed gas of SiH ₄ and H ₂ from the gas inlet 62, apply a high frequency or DC electric field between both electrodes 21, 22 to generate glow discharge, and as shown in FIG. 1 (b). Then, an a-Si: H film 7 with few defects was formed on the substrate 3 by plasma CVD. Next, glow discharge is generated in a gas in which 100 ppm to 1% GeH ₄ gas is mixed with H ₂ or He gas as a base gas, so that Ge atoms generated by decomposition are doped in the film 7. As shown in Fig. 1 (c), a-Si has few defects in the film.
A Ge: H film 71 is obtained. Fig. 6 shows H ₂ gas as the base gas
Fig. 7 shows changes in film characteristics with plasma doping time when a gas containing Ge 1000ppm is used. Although the optical gap Eg ^opt is lowered by the Ge gas entering the a-Si: H film,
The photoconductivity σ _ph and the dark conductivity σ _d increase to the same extent, indicating that the defects in the film do not increase so much. The improvement in film quality can be better understood by comparing with FIG.

FIG. 7 shows another embodiment of the present invention. Similar to the above embodiment, first, an a-Si: H film is formed, and then CH ₄ 1% of H ₂ gas group is prepared.
The relationship between doping time and characteristics when plasma doping is performed using gas is shown. A good a-SiC: H film having a high Eg ^opt of 2.1 eV and a σ _ph of 10 ⁻⁶ (Ωcm) ⁻¹ was obtained.

8 (a) to (d) show a manufacturing process of a solar cell as an embodiment of the present invention, in which a transparent conductive film 12 is formed on a transparent substrate 11 and SiH ₄ and C ₂ H are formed thereon. _A -SiC: H film with few defects by plasma CVD using ₂ or CH ₄ and H ₂ mixed gas
13 is formed (Fig. A). After that, plasma 14 is generated in a gas in which 10 ppm to about 1% of B ₂ H ₆ is mixed with H ₂ or He, whereby the a-SiC: H film 13 is doped with boron 15. As a result, p-type a-SiC: H film 16 with few defects
Is obtained (Fig. B). Undoped a-Si: H film after that
7. Phosphorus-doped n-type a-Si: H in the same manner as in the past
Layer 17 is sequentially formed (Fig. C), and electrodes 18 and 19 are formed by vapor deposition, sputtering, etc. (Fig. D). As a result, an amorphous silicon solar cell in which an electromotive force is generated by the light 10 is obtained.
FIG. 9 shows a change in film quality of the p-type a-SiC: H film formed as described above depending on the doping time. The doping gas used was H ₂ mixed with 1000 ppm of B ₂ H ₆ . It is a thing. The activation energy Ea decreases as the doping time increases, reaching 0.38 eV in 25 minutes, which is a value smaller than 0.1 eV as compared with the case where doping is performed simultaneously with film formation. The optical gap Eg ^opt remains 2.0eV and σ
The values of _d and σ _ph are 10 ⁻⁴ and 10 ³ (Ωcm) ⁻¹ , which are also high values that could not be obtained conventionally.

FIG. 10 shows the AM of the amorphous solar cell in which the p-layer is formed by the conventional method and the amorphous solar cell according to the embodiment described with reference to FIG.
/ 100 mW / cm ^{2 This} shows the photoelectric conversion characteristics under solar simulator light, and in the solar cell according to the example shown by the line 31 with an area of 1 cm ² , the activation energy of the p layer 16 was reduced, so that p-i-n Since the diffusion potential of the junction increases and the number of defect levels inside the p layer is small, the open circuit voltage V _oc and short circuit current J
Both _sc increased from the conventional solar cell indicated by line 32, and the form factor also improved from 9.3% to 11.3%.

11 (a) to 11 (c) show a manufacturing process of a solar cell in still another embodiment, in which an n-type a-Si: H layer film 17, which is sequentially doped with phosphorus on a metal substrate 20, is not doped. An a-Si: H film 7 is laminated, and a non-doped a-SiC: H film 13 is further formed thereon.
(FIG. A), and then plasma-doping the same as in FIG. 8 (b) to form a p-type a-SiC: H film 16 (FIG. B). It was deposited on top of 16 (Fig. C). This solar cell produces an electromotive force by the light 10 from the electrode 18 side, and when compared with the element of the embodiment shown in FIG.
The a-Si: H film 7 and the a-SiC: H film 13 with few defects are formed on the interface in advance.
The difference is that a p-i interface with few defects can be obtained because the doping is performed after the formation.

In the above solar cell manufacturing examples, plasma CVD
The a-SiC: H film formed by
As for the iC: H film itself, the characteristics are further improved by using a film formed by adding C to the a-Si: H film by plasma doping as described in FIG. Further, by appropriately controlling the source gas, it is possible to plasma-dope both C and B into the a-Si: H film.

In the embodiment shown in FIGS. 12 (a) to 12 (c), the non-doped a-Si: H layer 13 is not formed and the non-doped a-Si: H is not formed as shown in FIG. 12 (b). Unlike the case of the embodiment shown in FIG. 11 in that the surface layer of the layer 7 is directly plasma-doped to form the p-type doped a-Si: H layer 26, the conventional method uses a-Si: H. Although the open-circuit voltage V _oc is not much different from that of the solar cell having the p-i-n junction, the short-circuit current J _sc is remarkably increased because the p-layer having few defects becomes the photoelectric conversion active region.

〔The invention's effect〕

According to the present invention, another atom is added to the a-Si: H film composed of silicon and hydrogen atoms to form an a-SiC: H film,
When the optical gap is widened like an a-SiGe: H film, or when a p-type a-Si: H film or a-SiC: H film is formed, constituent atoms that cause defects are formed during film formation. Except for forming an amorphous semiconductor film with few defects by CVD using a gas consisting of silicon, hydrogen, and constituent atoms with less adverse effects, other necessary constituent atoms (germanium, boron, or carbon are selected). Since it is introduced into the film by plasma doping, an amorphous semiconductor with few defects can be manufactured, and if a plasma CVD device is applied as CVD, it can be manufactured using the same plasma generation device. In particular, it can be effectively applied to the production of photoelectric conversion elements such as solar cells.

[Brief description of drawings]

1 (a) to (c) show a-SiGe: H of one embodiment of the present invention.
Sectional views showing the film manufacturing process in sequence, FIGS. 2 and 3 are diagrams showing the relationship between film quality and gas concentration during film formation using a mixed source gas by the conventional method, and FIG. 4 is a diagram by the conventional method. FIG. 5 is a diagram showing the relationship between film quality and doping gas concentration during elementary doping, FIG. 5 is a cross-sectional view of a plasma generator used to practice the present invention, and FIGS. 6 and 7 show two examples of the present invention. Diagrams showing the relationship between plasma doping time and film quality, FIGS. 8 (a) to 8 (d) are cross-sectional views sequentially showing a manufacturing process of a solar cell according to an embodiment of the present invention, and FIG. 9 is an implementation of FIG. FIG. 10 is a diagram showing the relationship between the film quality of the p-layer film and the plasma doping time in the example, FIG. 10 is a photoelectric conversion characteristic diagram of the solar cell manufactured by the process of FIG. 8 and the solar cell by the conventional method, FIG. (A)-(c), FIG. 12 (a)-
(C) is sectional drawing which shows the manufacturing process of the solar cell in a different Example of this invention one by one. 1: vacuum chamber, 21, 22: electrode, 3: substrate, 61: exhaust port, 62: gas inlet port, 7: a-Si: H film, 71: a-SiGe: H film, 13: a-SiC: H film,
16: p-type a-SiC: H film, 26: p-type a-Si: H film.

Claims (1)

[Claims] 1. When manufacturing an amorphous semiconductor composed of silicon, hydrogen, and an atom of germanium, boron, or one or a combination thereof, germanium other than silicon and hydrogen, boron, After forming an amorphous semiconductor film by decomposing a gas composed of constituent atoms excluding at least one of carbon atoms, the gas containing the excluded constituent atoms is plasma decomposed to form the constituent atoms A method of manufacturing an amorphous semiconductor which penetrates into an amorphous semiconductor film, wherein the constituent atoms are introduced into the amorphous semiconductor film by plasma doping. Manufacturing method.