JPH07201741A - Manufacturing device of amorphous semiconductor thin film - Google Patents

Abstract

PURPOSE:To enable the photoelectric conversion efficiency of an amorphous solar battery to be improved by a method wherein a thin film forming substrate is arranged in a magnetic field formed mainly in the parallel direction with the substrate surface so as to deposit the amorphous semiconductor thin film on the substrate using a material gas in plasma state. CONSTITUTION:As for a thin film forming device, a parallel flat plate type plasma CVD device is used. Besides, a 5cm square transparent conductive substrate 3 is arranged on the side of an electrode 5 with a substrate heater in an i-layer forming chamber to be impressed with a magnetic field, on the other hand, in order to impress the magnetic field, a bar type samarium cobalt permanent magnet 2 is arranged in parallel with the substrate on the position 5cm distant from both sides of the substrate end so that a parallel magnetic field with the substrate surface may be formed. An i-type semiconductor thin film is formed into a hydride amorphous silicon thin film 5500Angstrom thick by cracking silane using high-frequency power at the substrate temperature of 180 deg.C. Successively, an n type semiconductor thin film is formed into an n-type fine crystal silicon thin film 400Angstrom thick at the substrate temperature of 180 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high quality amorphous semiconductor thin film manufacturing apparatus suitable for manufacturing high efficiency amorphous solar cells, which are promising as alternative energy sources for the next generation.

[0002]

2. Description of the Related Art Nowadays, there is an urgent need to develop and popularize alternative energy sources because of the danger of depletion of fossil fuels, safety of fuels for nuclear power generation, and destruction of the global environment due to an increase in atmospheric CO ₂ concentration. High-efficiency amorphous solar cells are regarded as promising alternative energy sources.

In most of the photoactive layers of amorphous solar cells, hydrogenated amorphous silicon thin films have been formed by glow discharge decomposition of monosilane and disilane gas using a plasma CVD (chemical vapor deposition) apparatus. in this case,
The glow discharge is induced in the vacuum reaction chamber by using a high frequency power source and a DC power source, and the gas becomes a plasma state. In a plasma CVD apparatus having parallel plate electrodes, a DC voltage or a cross voltage is applied to the electrodes, and the charged particles drift along the electric field generated by the voltage. As a result, ions, electrons and neutral particles having various energies enter the substrate. Among them, it is said that the high-energy-charged particles irradiate the formed film to deteriorate the film characteristics. However, in the conventional parallel plate plasma CVD apparatus, the charged particles are not exposed to the surface of the film. The incident was unavoidable.

[0004]

SUMMARY OF THE INVENTION The present invention is a plasma C
For the purpose of developing an apparatus for preventing the deterioration of the electrical characteristics of the amorphous semiconductor thin film due to the incidence of high-energy charged particles on the film formation surface when forming a hydrogenated amorphous silicon thin film using a VD apparatus. There is. When the amorphous semiconductor thin film is a hydrogenated amorphous silicon thin film and is used as a photoactive layer of an amorphous solar cell, the film characteristics of this hydrogenated amorphous silicon thin film are improved to improve the photoelectric conversion efficiency of the amorphous solar cell. Is an important issue.

[0005]

According to the present invention, a thin film-formed substrate is placed in a magnetic field formed mainly in a direction parallel to the substrate surface, and plasma is turned into a raw material gas to form a thin film-formed substrate on the substrate. An apparatus for producing an amorphous semiconductor thin film configured to deposit an amorphous semiconductor thin film, wherein the maximum static magnetic field strength of a component parallel to the substrate surface is equal to that of the substrate and the gas decomposition power application electrode. The above device, which is more than 5 Gauss in between,
And the maximum static magnetic field strength of the component perpendicular to the substrate surface is 1 between the substrate and the gas decomposition power application electrode.
The device is Gaussian or less, and is a hydrogenated amorphous silicon thin film composed of an amorphous semiconductor thin film formed by using the device, and the formed hydrogenated amorphous silicon thin film is photoactive. An amorphous silicon solar cell used as a layer.

The present invention will be described in detail below.

The charged particles incident on the substrate include electrons, raw material gas molecular ions and their dissociation product molecular ions and atomic ions. In the present invention, a magnetic field is formed parallel to the film formation incident substrate surface in order to suppress the drifting charged particles from entering the substrate by the electric field applied in the direction perpendicular to the substrate, and the charged particles to be eliminated are The magnetic field strength is adjusted according to the valence and mass.

When forming a magnetic field, the Curie point of a ferrite magnet, a samarium cobalt magnet, etc. is set to 200.
Both a permanent magnet at a temperature of not less than 0 ° C. and a permanent magnet of which current is supplied to the coil of the electromagnet can be used, but the permanent magnet and the electromagnet may be used in combination. The magnetic field strength can be adjusted so that the larma radius in the magnetic field of the charged particles, which is considered to cause the deterioration of the electrical characteristics of the amorphous semiconductor thin film, is the same or smaller than the inter-electrode distance. preferable. For example, when electrons accelerated to 100 eV enter the substrate, 1 at 30 gauss
Incident can be blocked by forming a magnetic field having a width of cm or more. When hydrogen ions accelerated to 100 eV are incident on the substrate, the incidence can be suppressed by forming a magnetic field having a width of 3 cm or more at 500 Gauss. Even when the charged particles are not completely blocked, the movement in the vertical direction of the substrate is suppressed and converted into the movement in the horizontal direction with respect to the surface of the substrate, so that the entrance of the charged particles into the film is suppressed. It is expected to be done.

FIG. 1 is a diagram showing an example of an amorphous semiconductor thin film manufacturing apparatus of the present invention. In the figure, 1 is a chamber,
2 is a permanent magnet or electromagnet, 3 is a thin film forming substrate, 4 is a substrate / magnet support, 5 is an electrode with a substrate heating heater, 6
Is a gas decomposition power application electrode, 7 is a discharge suppressing electrode (shield), 8 is an electrical insulator, 9 is a gas supply system, 10 is a gas decomposition power supply power source, and 11 is an exhaust system.

It is desirable that the chamber-1 and the components in the apparatus in the apparatus for manufacturing an amorphous semiconductor thin film shown in FIG. 1 are made of a non-magnetic material. In particular, the thin film forming substrate 3, substrate / magnet support 4, substrate heating heater-equipped electrode 5
Is preferably a non-magnetic material in order to prevent generation of a magnetic field component in the direction perpendicular to the substrate.

The hydrogenated amorphous silicon thin film, which is the photoactive layer, is formed by glow discharge decomposition of pure gas of monosilane or disilane gas, or monosilane or a mixed gas of disilane gas and hydrogen gas. The formation temperature of the photoactive layer is 100 to 250 ° C, preferably 150 to 2 ° C.
25 ° C, forming pressure is 0.01 to 1 Torr, preferably 0.03 to 0.
Done at 3 Torr.

As a power source used in the plasma CVD method, it is preferable to mainly use a DC power source or a power source for generating an alternating electric field of 50 Hz or more. Industrially, a frequency of 13.56 MHz and 2.45 GHz is preferably used, and the frequency is appropriately set according to the purpose of film formation.

The amorphous semiconductor thin film is a hydrogenated amorphous silicon thin film, a hydrogenated amorphous silicon germane thin film, a hydrogenated silicon carbon thin film, etc., and forms a photoactive layer of an amorphous solar cell. These amorphous semiconductor thin films are compounds having silicon in the molecule,
It is easily formed by applying the plasma CVD method to a raw material gas appropriately selected from a compound having germanium in the molecule such as germane and silylgermane, a hydrocarbon gas and the like in accordance with a target semiconductor thin film. The use of the raw material gas diluted with hydrogen, helium, or the like, addition of a very small amount of diborane to the raw material gas, or the like, does not hinder the effect of the present invention when used in combination with conventional techniques for forming an amorphous semiconductor thin film. Not a thing.

FIG. 2 is a diagram showing the layer structure of a solar cell using the amorphous semiconductor thin film of the present invention as a photoactive layer. In the figure, 100 is a transparent substrate, 200 is a transparent electrode, 300 is a p-type semiconductor thin film, 400 is an i-type semiconductor thin film, and 500 is n.
A semiconductor thin film, 600 is a metal electrode.

The film thickness of the i-type semiconductor thin film as the photoactive layer is appropriately determined according to the application of the photoelectric conversion element,
It is not a limiting condition of the invention. In order to achieve the effect of the present invention, 1000 to 10000Å is sufficient.

The transparent substrate, transparent electrode, metal electrode, etc. are not particularly limited. As the translucent substrate, conventionally used glass substrate materials such as soda lime glass, borosilicate glass, and quartz glass are useful, but metal and plastics can also be used as the substrate material. As a plastic material, a material that can withstand a temperature of 100 ° C. or higher can be effectively used.

As the transparent electrode, a metal oxide such as tin oxide, indium oxide, zinc oxide, or a translucent metal can be effectively used.

Since the metal electrode does not necessarily have to be translucent, a metal such as aluminum, chromium, nickel-chromium, silver, gold or platinum or a metal oxide such as tin oxide, indium oxide or zinc oxide is used. It can be appropriately selected and used from the inside.

[0019]

The present invention will be described in more detail with reference to the following examples. Example 1 An amorphous solar cell in which p-type, i-type, n-type semiconductors and metal electrodes were formed on a 5 cm square transparent conductive substrate was produced. As a thin film forming apparatus, a parallel plate type plasma CVD
The device was used. The gas decomposition was performed by applying high frequency power to the gas decomposition power application electrode. A glass substrate with a transparent electrode made of tin oxide is installed in the film forming apparatus, vacuum exhaust and substrate heating are performed, the substrate temperature is 180 ° C, the silane gas flow rate is 1 sccm, the methane gas flow rate is 1 sccm, and the hydrogen gas flow rate is 20 sc.
cm,% hydrogen diluted diborane gas flow rate 3 sccm, pressure 0.15 Torr
At 60, a p-type a-SiC: H film was formed at 60 Å.

Next, a hydrogenated amorphous silicon carbide (a-SiCx: H) film having a thickness of 150 liters was formed. a-Si
Cx: H film is produced by using silane / methane /
Hydrogen was introduced at a rate of 2/2/5, and at a pressure of 0.15 Torr,
A high frequency power was applied to form a thin film. The flow rate was controlled so that the flow rate of methane was 0 at the end of formation.

Next, a 5 cm square transparent conductive substrate was placed on the electrode side with a substrate heating heater in the i-layer forming chamber, and a magnetic field was applied. In order to apply a magnetic field, a rod-shaped samarium-cobalt permanent magnet is placed in parallel with the substrate at a position as shown in FIG. Arranged as formed. When the magnetic field strength was measured, it was about 110 gauss at the center of the substrate and 1 cm on the substrate surface. The magnetic field component in the direction perpendicular to the substrate was almost 0 Gauss. As the i-type semiconductor thin film, silane was decomposed with high frequency power to form a hydrogenated amorphous silicon (a-Si: H) thin film having a thickness of 5500Å at a substrate temperature of 180 ° C. Subsequently, an n-type semiconductor thin film was formed at a substrate temperature of 180 ° C. to form an n-type microcrystalline silicon thin film of 400 Å. After that, the film was taken out from the thin film forming apparatus, the Ag electrode was vapor-deposited, and the amorphous solar cell shown in FIG. 2 was produced. AM (air mass) 1.5, 100 mW / cm
As a result of measuring the photoelectric characteristics of the amorphous solar cell under the pseudo sunlight of ^2, the photoelectric conversion element characteristics have a fill factor of 0.790.
A very high value was obtained, the effect of the present invention was confirmed, and a short-circuit photocurrent of 18.9 mA / cm ² and an open-ended voltage of O.920 V were obtained, resulting in an extremely high photoelectric conversion efficiency of 13.7%. It was confirmed that the value was obtained. The results are shown in Table 1.

Example 2 In Example 1, the samarium-cobalt permanent magnet was replaced with a ferrite magnet, and a parallel static magnetic field of about 5 gauss was formed at the center of the thin film forming substrate surface and further 1 cm above the substrate surface. Further, the magnetic field component in the direction perpendicular to the thin film formation substrate was almost 0 Gauss. AM (air mass) 1.5,
As a result of measuring the photoelectric characteristics of the solar cell under simulated sunlight of 100 mW / cm ^2, the photoelectric conversion element characteristics showed a very high fill factor of 0.772, and the effect of the present invention was confirmed. It was confirmed that a short circuit photocurrent of 18.9 mA / cm ² and an open end voltage of O.914 V were obtained, and as a result, a high value of photoelectric conversion efficiency of 13.3% was obtained. The results are shown in Table 1.

Comparative Example 1 In Example 1, the i-type semiconductor thin film was formed and the solar cell was formed without removing the Samarium cobalt permanent magnet and applying a static magnetic field to the thin film forming substrate. As a result, the AM-1.5, 100 mW / cm2 photoelectric conversion element characteristics under simulated sunlight have a low fill factor of 0.750, a short-circuit photocurrent of 18.5 mA / cm ² and an open-ended voltage of O.915 V. As a result, the photoelectric conversion efficiency was 12.7%, which was about 1% lower than that of the example, and the characteristics were remarkably deteriorated as compared with the thin film forming substrate parallel static magnetic field application film formation of the example 1. The results are shown in Table 1.

Comparative Example 2 In Example 2, in the center of the substrate surface, and further on the substrate surface 1
At i cm, the i-type semiconductor thin film was formed by adjusting the distance to the substrate so that it was about 1 gauss, and a solar cell was produced. As a result, the photoelectric conversion element characteristics under AM-1.5 and 100 mW / cm ² of simulated sunlight have a fill factor of 0.748,
Similar to Comparative Example 2, a short-circuit photocurrent of 18.6 mA / cm ² and an open-circuit voltage of O.916V were obtained. As a result, the photoelectric conversion efficiency was 12.7%, which was almost the same as that of Comparative Example 1 in the absence of a magnetic field. And was judged to be ineffective. The results are shown in Table 1.

COMPARATIVE EXAMPLE 3 In Example 1, an experiment was conducted in which a rod-shaped samarium-cobalt permanent magnet was placed at a position of 0 cm from the edge of the substrate in parallel contact with only one side of the substrate. When the magnetic field strength was measured, the magnetic field component parallel to the substrate surface was about 150 gauss at the center of the substrate and 1 cm above the substrate surface.
The magnetic field component in the substrate vertical direction was about 15 Gauss.
In this state, an i-type semiconductor thin film was formed to manufacture a solar cell. As a result, the photoelectric conversion element characteristics under AM-1.5 and 100 mW / cm ² of pseudo sunlight were as low as 0.677 due to the fill factor,
Short circuit photocurrent of 18.0mA / cm ² and open end voltage of O.903V are obtained.
As a result, the photoelectric conversion efficiency was 11.0% and the solar cell characteristics were lower than in the case where the magnetic field of Comparative Example 1 was not installed. The results are shown in Table 1.

[0026]

[Table 1]

[0027]

As described above, by using the apparatus capable of forming a parallel magnetic field of 5 gauss or more between the substrate and the gas decomposition power applying electrode of the i-type semiconductor thin film forming apparatus by the plasma CVD method, The characteristics of the produced amorphous solar cells were improved in conversion efficiency as compared with those in which a parallel magnetic field was not applied to the surface of the thin film-formed substrate and those in which there was a magnetic field component perpendicular to the substrate surface. That is, the present invention greatly contributes to the formation of an amorphous semiconductor thin film at a practical level and the improvement of the photoelectric conversion efficiency of an amorphous solar cell produced using the amorphous semiconductor thin film, and its industrial applicability is extremely great. I have to say.

[Brief description of drawings]

FIG. 1 is a diagram showing an amorphous semiconductor thin film manufacturing apparatus of the present invention.

FIG. 2 is a diagram showing an example of the layer structure of an amorphous solar cell of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 chamber-2 permanent magnet or electromagnet 3 substrate for thin film formation 4 substrate / magnet support 5 electrode with substrate heating heater 6 gas decomposition power application electrode 7 discharge suppression electrode (shield) 8 electrical insulator 9 gas supply System 10 Gas decomposition power supply power supply 11 Exhaust system 100 Transparent substrate 200 Transparent electrode 300 p-type semiconductor thin film 400 i-type semiconductor thin film 500 n-type semiconductor thin film 600 metal electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyuki Yanagawa 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd. (72) Shin Fukuda 1190 Kasama-cho, Sakae-ku, Yokohama, Kanagawa Mitsui Toatsu Chemical Incorporated (72) Inventor Nobuhiro Fukuda 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd.

Claims (5)

[Claims] 1. A thin film formation substrate is installed mainly in a magnetic field formed in a direction parallel to the substrate surface, and an amorphous semiconductor thin film is deposited on the substrate by plasma-forming source gas. An apparatus for manufacturing an amorphous semiconductor thin film configured as described above. 2. The maximum static magnetic field strength of the component parallel to the substrate surface is 5 between the substrate and the gas decomposition power application electrode.
The device of claim 1, which is Gaussian or better. 3. The maximum static magnetic field strength of the component perpendicular to the substrate surface is 1 between the substrate and the gas decomposition power application electrode.
The device according to claim 2, which is Gaussian or less. 4. A hydrogenated amorphous silicon thin film comprising an amorphous semiconductor thin film formed by using the apparatus according to claim 1. 5. An amorphous silicon solar cell using the formed hydrogenated amorphous silicon thin film according to claim 4 as a photoactive layer.