JPS5935016A - Preparation of hydrogen-containing silicon layer - Google Patents

Abstract

PURPOSE:To obtain the titled layer capable of providing a solar cell having both merits of amorphous and crystalline silicons, by making a silicon layer at a temperature including a temperature wherein silicon is made into crystallite, treating it with hydrogen plasma at a temperature approximately the crystallite formation temperature. CONSTITUTION:In the preparation of silicon layer by vacuum metallizing of silicon-containing solid substance or chemical decomposition method or plasma decomposition method of silane-containing gas mixture under reduced pressure, the preparation consists of the first stage wherein the silicon layer is prepared at a temperature including a temperature (480-540 deg.C in the vacuum metallizing and plasma decomposition method under reduced pressure, and 560-600 deg.C in chemical decomposition method under reduced pressure) at which it is converted into crystalline, and the second stage wherein heat-treatment in a plasma atmosphere containing hydrogen or its isotope is carried out at a temperature approximately the crystallite formation temperature of silicon. By making the silicon layer containing both of amorphous and crystalline silicons, a hydrogen-containing silicon layer useful for a solar cell having characteristics of both merits is prepared.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydrogen-containing silicon layer for use in electronic devices incorporating a layer of silicon or one of its alloys, particularly solar cells that can be used to convert photon radiation into electrical energy. The present invention relates to a manufacturing method.

Crystalline silicon has generally been used as a material for conventional solar cells, but although it has good cell characteristics, it has the drawback of high manufacturing costs. On the other hand, amorphous silicon, which has been attracting attention recently, has the advantage of being able to be made thin due to its high light absorption and can be produced in a low-temperature process.
There are also problems with reliability in long-term use. Also, from the perspective of sunlight spectrum, the wavelength sensitivity range is narrow, so it cannot be considered an optimal material.

An object of the present invention is to provide a solar cell having characteristics that have the advantages of both amorphous silicon and microcrystalline silicon by using a silicon film containing both amorphous silicon and microcrystalline silicon. This film is a material with wavelength sensitivity close to the sunlight spectrum and high light absorption, and because it has small localized levels and high mobility, it exhibits high photoelectric conversion efficiency and exhibits long-term stable characteristics. .

In order to use amorphous silicon as a solar cell, it is essential to include hydrogen in the film in order to give it light guiding properties, and it is usually formed by a glow discharge method. The formation temperature is 200 to 300C, and those formed at temperatures higher than this have an extremely low hydrogen content and are not suitable as solar cells. It is also known that hydrogen is released by heat treatment at 300C or higher when hydrogen is added during the formation of the silicon film. 30
Heating above 0C has been considered to have negative effects.

However, when hydrogen plasma treatment is performed after forming a silicon film, the higher the treatment temperature, the better.
Sufficient photoconduction was obtained up to a temperature of C. On the other hand, if a silicon film is formed by vacuum evaporation or chemical decomposition or plasma decomposition under reduced pressure, it is not possible to form a film containing both amorphous silicon and microcrystalline silicon depending on the relationship between pressure and formation temperature. It's easy. If the film thus formed is treated with hydrogen plasma at a temperature near the microcrystallization temperature,
It exhibits high light guiding properties and light absorption similar to that of amorphous silicon, and its wavelength sensitivity is intermediate between that of crystalline silicon and amorphous silicon. Historically, this results in a much more reliable film than those formed at low temperatures by glow discharge methods. The temperature for microcrystallization varies slightly depending on the silicon film formation method and conditions, but it is 480C to 540C for vacuum evaporation and reduced pressure plasma decomposition, and 560C to 600C for chemical decomposition under reduced pressure. there were.

The light absorption rate of a silicon film depends on the size of crystal grains. The absorption coefficient value at a wavelength of 0.5 μm is 1. I x 10'cm-'', and the amorphous silicon vacuum-deposited at 250C without doping with impurities had 2X1011Crn-', whereas the silicon microcrystallized at 500C had 4X10'crn''1. As the temperature increases, this value approaches that of crystalline silicon and becomes smaller, reaching 2.5 x 10'cm-'' at 550G. In other words, if formed at a temperature higher than this,
As a solar cell, a film thickness of several μm or more is required, so the advantage is small.

The effect of hydrogen plasma treatment after film formation depends on the crystallinity of the film, and the smaller the crystal grains, the better the low temperature treatment. This effect can be confirmed by measuring the amount of hydrogen in the film by infrared absorption measurement or the like and by changing the conductivity. As a result of investigating this effect on various silicon films, it was found that for amorphous silicon films, a temperature range of 400 to 500 C was most effective, and for other films containing microcrystalline silicon, the temperature range of 400 to 500 C was the most effective. A temperature range of ±50C was most effective. Furthermore, if this hydrogen plasma treatment is once exposed to the atmosphere after film formation, the silicon on the surface tW will be oxidized and cannot bond with hydrogen, reducing its effectiveness.

Example 1 A silicon film was deposited on a heated quartz substrate by irradiating an electron beam onto crystalline silicon as a deposition source under a pressure of 10'''J'orr. At this time, when the substrate temperature is 450C, the deposited silicon film is amorphous;
Then it becomes microcrystalline. First, amorphous silicon is deposited to a thickness of 0.5 μm at a rate of 1 nm per second at a temperature of 450 C, and then microcrystalline silicon is deposited to a thickness of 0.5 μm at a rate of 1.5 nm per second at a temperature of 500 C. did.

Then 30 at a pressure of 46 (I', 0.1'l'Orr)
Hydrogen plasma treatment was performed for 1 minute. As a result, while the dark conductivity is 3×10''QΩ−”an−”, the light irradiation conductivity at the intensity of AMI is 5×10”Ω−1·cln−1 and 1
It was found that the change was more than 0.01' times, and that sufficient self-contained carriers usable as solar cells were generated. Also,
The absorption coefficient value for a wavelength of 0.5 μm was 6.5×10′f −1, which is an intermediate value between amorphous silicon and crystalline silicon.

Example 2 Figure 1r;): Overall view of a reduced pressure plasma CVI) apparatus for forming silico/membranes. Reaction tube 1 is furnace 2
The stainless steel substrate 3 is held by the electrode 4. Reference numeral 5 indicates a high frequency power supply, and reference numeral 6 indicates a vacuum pump. After drawing the inside of the reaction tube 1 into a high vacuum, siH
, and PH3 were flowed at a ratio of 8'H4:PHs=10:1, and the total pressure was set to tlTOr'. In this state, a high frequency voltage was applied to the electrode 4 to cause plasma discharge inside the reaction tube. First, an n-type layer is grown to a thickness of 39 nm on the substrate 3, and then PH is applied.

After adjusting the pressure f to I Torr, a doped layer f of 3000 m was grown. Next, the temperature in the reactor was set to 5000, which is near the microcrystallization temperature, and a non-doped layer was subsequently grown to a thickness of 400 nm. Finally, at this temperature, 8iH, and B, H6 are 8' 84: B x H
A single layer of 10 nm of pm was grown at a pressure of I Torr (D pressure). In this state, the reaction tube was evacuated to a high vacuum, and then hydrogen was flowed to a pressure of 0.1 TOrr to cause plasma discharge. , hydrogen plasma treatment was performed for 15 minutes.

After taking it out from the reactor, a transparent conductive film was deposited on the surface to form a solar cell, and under the simulated sunlight of AMI, the open voltage was 0.81 V and the short circuit current was 7.8 mA/lyn''
fI: Obtained. Furthermore, 35Qn for the sunlight spectrum
It exhibited sensitivity to wavelengths from m to 9001 m, and exhibited characteristics intermediate between crystalline silicon solar cells and amorphous solar cells.

The present invention is useful in chemical or plasma decomposition methods.

According to the present invention, it is possible to produce a solar cell that takes advantage of the advantages of both amorphous silicon solar cells and crystalline silicon solar cells. In other words, since the absorption of light is large, the film thickness is several microns.
m or less, and by changing the ratio of the thicknesses of the amorphous layer and the microcrystalline layer depending on the application, any wavelength sensitivity can be obtained. In terms of photoelectric conversion efficiency, by microcrystallizing the surface-side junction layer, the localized level density in the depletion layer is reduced, making it possible to achieve a current density close to that of a crystalline silicon solar cell, resulting in high conversion efficiency. Furthermore, since the device is subjected to heat treatment near the microcrystallization temperature, the reliability of the device is significantly improved.

[Brief explanation of the drawing]

Figure 1 shows low-pressure plasma CV for forming a silicon film.
It is an overall view of D device. 1... Reaction furnace, 2... Heating furnace, 3... Substrate, 4...
...High frequency electrode, 5...High frequency power supply. Patent applicant Makoto Ishizaka, Director of the Agency of Industrial Science and Technology -- VJ 1 (2)

Claims (1)

[Claims] 1. In the production of a silicon layer by vacuum evaporation of a silicon-containing solid or by a chemical decomposition method or a plasma decomposition method of a silane-containing gas mixture under reduced pressure, a temperature including the temperature at which silicon microcrystallizes is applied. a first step of manufacturing a silicon layer using hydrogen, and a second step of performing heat treatment in a plasma atmosphere containing hydrogen or one of its isotopes at a temperature near the microcrystallization temperature of silicon. Method for manufacturing a hydrogen-containing silicon layer. The method of manufacturing a hydrogen-containing silicon layer according to claim 1, characterized in that the second step is performed at a temperature between T and T+50d. 3. The hydrogen-containing silicon layer according to claim 1, characterized in that the second step is carried out in a temperature range of T-501:' and T+5(l), where T is the temperature at which silicon microcrystallizes. Manufacturing method: 4. The method for manufacturing a hydrogen-containing silicon layer according to claim 1, characterized in that the first step and the second step are performed consecutively without exposure to the atmosphere.