JPS6214414A - Semiconductor thin film - Google Patents

Abstract

PURPOSE:To make an amorphous silicon/amorphous germanium multilayer thin film having excellent characteristics by a method wherein, in the formation of the amorphous germanium thin films, the energy to be directed on the thin film forming surfaces is decreased and the film quality of the amorphous germanium thin films is improved. CONSTITUTION:Two layers or more of amorphous silicon layers and two layers or more of amorphous germanium layers, which contain hydrogen and/or fluorine in the films thereof, are alternately laminated on the substrate [glass (a)] and the amorphous silicon/amorphous germanium multilayer thin film is formed on the substrate. When these silicon layers and germanium layers are respectively deposited on the substrate by a decomposition to be caused by the glow discharge of the raw gas containing a silicon compound and by a decomposition to be caused by the glow discharge of the raw gas containing a germanium compound, the irradiation intensities of the lights to be directed on the silicon layers and the germanium layers and the wavelengths of the lights are respectively changed and the film-forming conditions thereof shall be respectively a condition suitable to each layer of the layers. By this way, the film quality of the amorphous germanium films is improved. As a result, the amorphous silicon/amorphous germanium multilayer thin film having excellent characteristics is made.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a semiconductor thin film, and more particularly to an amorphous silicon/amorphous germanium multilayer thin film with excellent photocharging properties.

[Background technology]

Amorphous multilayer thin films made of multiple elements can have various changes in optical bandgap and photoelectric properties by changing the thickness of the thin film, so they have recently been considered as candidates for new photoelectric materials.
It's starting to get attention. A-8i so far: H/
a-8i, xNx:H, a-8iN:H/a-8
iC: H, a-si, -xcx, / a-8i,
There is a report on a-8i:H/a-8iGe:H, etc. (1985 Spring Applied Physics Society). In this way a-
8i:H/a-8ide: Although there have been publications on the H multilayer structure, there have been no reports on the amorphous silicon/amorphous germanium multilayer thin film proposed by the present inventors. However, in this case, it is thought that it is extremely difficult to improve the film quality of a multilayer film at present, where improvement in the film quality of an amorphous germanium film has not been realized.

Many attempts have been made to prepare an a-8iGe:H film by glow discharging a mixture of a silicon compound and a germanium compound, but no satisfactory results have been obtained.

In an amorphous germanium film, the bond between germanium and hydrogen is weak, so it is difficult to remove dangling bonds caused by hydrogen. As a result of our research, the inventors found that
It has been found that in the formation of germanium thin films by glow discharge of germanium compounds, it is possible to improve the film quality by lowering the energy on the thin film formation surface.

However, in the formation of a silicon thin film by glow discharge of a silicon compound, such germanium thin film formation conditions actually caused a deterioration in film quality.

As a result of intensive studies to solve these problems, the present inventors discovered a method for forming thin films suitable for silicon compounds and germanium compounds, which perform glow discharge while being irradiated with light. We were able to obtain a multilayer thin film of amorphous silicon/amorphous germanium.

[Disclosure of the invention]

As shown in FIG. 1, the present invention is made by alternately laminating two or more amorphous silicon layers and amorphous germanium layers (hereinafter simply referred to as silicon layers and germanium layers) on a substrate (for example, glass). It is a semiconductor thin film with a multilayer structure. The thickness of each of the silicon layer and the germanium layer is 100X or less, preferably 50A or less and 5A or more. These thin layers are alternately laminated to the required thickness. Each of these layers contains hydrogen and/or fluorine, and is mainly amorphous. In the present invention, since the silicon layer and the germanium layer can be deposited separately, the deposition conditions can be optimized for each.

The silicon layer and the germanium layer are deposited on the substrate by glow discharge decomposition of raw material gases containing a silicon compound and a germanium compound, respectively, and during the deposition of these thin films, light is irradiated onto the main surface on which the thin film is formed. . When depositing the silicon layer and the germanium layer, the irradiation intensity and the wavelength of the light are respectively changed so that the film forming conditions are set to conditions suitable for each.

As mentioned above, germanium has a weaker covalent bond than silicon (Ge-H and Ge-F are difficult to form), so in order to improve the film quality of an amorphous germanium film, it is necessary to fabricate an amorphous silicon film. Milder conditions are required.In practice, it is desirable to equalize the plasma conditions, so during the deposition of the silicon layer, the intensity of the light is increased, and during the deposition of the germanium layer, In some cases, it is preferable to lower the intensity of the light than during the deposition of the silicon layer.

Furthermore, it is preferable to change the wavelength of light in order to optimize the conditions. If the wavelength of light is made shorter, the absorption coefficient of light becomes larger, and most of the light is absorbed only by the film forming surface (the main surface on which the thin film is formed), and the energy of the light is relaxed. The influence on the lower layer region is reduced, leading to improved performance of the device when applied to a semiconductor device.

Now, as a concrete example, we will consider an amorphous solar cell as a semiconductor device. The cell typically comprises a substrate, a first electrode, a film of a first conductivity type, a photoactive layer, a film of a second conductivity type, and a second electrode.

In this case, for example, when forming the photoactive layer,
Even if we try to optimize the film formation conditions using only glow discharge, the formation conditions of the photoactive layer are limited in order to reduce the influence on the first electrode and first conductivity type film that have been formed previously. Therefore, it is difficult to arbitrarily change the glow discharge conditions to optimize the conditions. Furthermore, in the case of multilayer film formation using a variety of raw materials, optimizing the conditions becomes increasingly difficult due to the constraint that the film that has already been formed must not be affected. In order to solve this problem, the present invention is characterized by reinforcing the glow discharge conditions by superimposing light irradiation, which makes it possible to balance the energy necessary to form a high-quality film. It is something that

The film thicknesses of the silicon layer and the germanium layer are each 100A or less, preferably 50X or less and 5A or more. By reducing the film thickness within this range, the optical bandgap of the obtained semiconductor thin film can be arbitrarily changed. As the film thickness decreases, the optical bandgap approaches that of the silicon layer.

The semiconductor thin film having a multilayer structure obtained by the present invention is an amorphous semiconductor thin film in which each thin film layer contains hydrogen and/or fluorine, and these hydrogen and/or fluorine are present in the amorphous semiconductor thin film. This compensates for dangling bonds.

In the present invention, the silicon compounds to be decomposed by glow discharge include silicon hydrides represented by the general formula 5inH2n+2, silicon fluorides represented by the general formula ''mFzm+2, and fluorine-substituted silicon hydrides represented by the general formula SiH,F4□. In silicon hydride and silicon fluoride, preferably n is gaseous at room temperature.
Monosilane and disilane represented by 21 and 2, and m-2 hexafluorodisilane. The fluorine-unsubstituted silicon hydride is difluorosilane (SiH2F2) in which a = 1 to 3, particularly preferably a = 2
) and monofluorosilane (5iH
8F).

Particularly preferred are monosilane and disilane.

Further, as the germanium compound to be decomposed by glow discharge, germane (GeH, ) and germane tetrafluoride (GeF4) are used.

In the present invention, the irradiation intensity and/or wavelength of light is changed, and it is preferable to change the irradiation intensity of light in relation to the film formation rate. The higher the film formation rate, the thicker the irradiation intensity (preferably. Also, the irradiation intensity of light is also related to the substrate temperature, and the lower the substrate temperature is, the higher the irradiation intensity is, the better. Also, regarding the wavelength of light, Can be used from the ultraviolet region to the infrared region.When the wavelength of light differs, the absorption coefficient changes, so the optimal irradiation intensity differs.The monochromaticity of the wavelength is not particularly limited.Coherent light such as laser and mercury lamp , tungsten lamps, hydrogen discharge tubes, deuterium discharge tubes, rare gas lamps, mercury-rare gas lamps, etc., can all be effectively used.Laser light has the advantage of increasing the number of irradiated photons. This is useful, and when a pulsed laser is used, the pulsed interval can be adapted to the film formation rate.

On the other hand, 1n coherent light is superior in that it can irradiate a large area without scanning it.

Substrates used in the present invention include thin films and plate-like materials such as glass, stainless steel, aluminum, brass, and polymers, as well as those on which electrodes, conductive thin films, other semiconductor devices, etc. are formed. It will be done.

In the present invention, the heating temperature of the substrate on which the thin film is formed may be relatively low as shown in Examples below.

By selecting the irradiation intensity and/or wavelength of light, a high-quality film can be formed even at room temperature without heating the substrate.

In the present invention, it is preferable to use hydrogen or helium μ as a diluent gas together with the source gas mentioned above. By using hydrogen or helium, glow discharge during thin film formation can be stably maintained, making it possible to further improve film quality.

The present invention can be implemented, for example, by the apparatus shown in FIGS. 2 and 3. Here, 1.11 is a light generation means, 2 and 12 are light introduction means, and 3゜1
3 is a base body; 4. (4 is a substrate heating means, 5 and 15 are raw material gas introduction means, 6, 6', 16, and 16' are evacuation means, 7.17 is a glow discharge means, and 8 and 18 are substrate holding means.

Here, FIG. 2 shows an arrangement in which the glow discharge means and the base are separated from each other to facilitate light irradiation onto the base.

Furthermore, it is possible to adjust the position of the raw material gas introducing means in order to maintain a uniform glow discharge near the base.

FIG. 3 shows one embodiment in which beam-shaped light is introduced. The beam-shaped light is irradiated onto the substrate directly from the light generating means or via the beam scanning means. This is a preferred example when laser light is used as a beam of light.

[Preferred form for carrying out the invention] The present invention can be carried out, for example, as shown in FIG. installing the substrate in a light irradiation glow discharge decomposition reactor having at least a light generation means, a light irradiation means, a substrate introduction means, a substrate holding means, a substrate heating means, a raw material gas introduction means, a vacuum evacuation means, and a glow discharge means; The substrate is heated to a low temperature of 300° C. or lower under vacuum evacuation. While introducing the first raw material gas consisting of a silicon compound, the light generated by the light generation means is appropriately selected and adjusted to irradiate the main surface of the substrate on which the thin film is to be formed by the light irradiation means, and the reactor is evacuated by the evacuation means. The pressure is set to 2 Tow or less, glow discharge is performed, and thin film formation is started. Since the formation of a thin film starts at the same time as the discharge starts, the discharge is stopped when the required film thickness is reached, taking into consideration the film formation rate.

After adjusting the irradiation light (stop the introduction of the first raw material gas and reduce the pressure to 10-' Tow or less using a vacuum evacuation means, introduce the second raw material gas consisting of a germanium compound and generate a glow discharge. When the required film thickness is reached, the introduction of the second raw material gas is stopped, the irradiation light is adjusted, and the pressure is evacuated to 10-5 Torr or less using a vacuum evacuation means.The above operation is repeated as many times as necessary to form amorphous silicon. A semiconductor thin film having a multilayer structure in which amorphous germanium films are laminated is obtained.

Although the semiconductor thin film obtained by the present invention has a narrow optical bandgap of 1.6 ev or less, the spin density obtained by electron spin resonance method is 10"°.

It has excellent properties such as a small ratio of photoconductivity to dark conductivity of 103 to 104.

The thin film of the present invention having high photosensitivity on the long wavelength side is extremely useful for manufacturing photoelectric conversion elements, thin film solar cells, photoreceptors, and the like.

[Brief explanation of the drawing]

FIG. 1 is one of the embodiments of the present invention, and is a cross-sectional view showing a state in which glass plates (H) films are laminated in multiple layers. FIGS. 2 and 3 are explanatory diagrams showing a light irradiation glow discharge decomposition reactor suitable for carrying out the present invention. In the figure, 1, II... light generation means, 2, 12... light introducing means, 3, 13... substrate, 4, 14... substrate heating means, 5, 15... ...Means for introducing raw material gas, 6, 6
', 16°16'...Evacuation means, 7.7',
17.17'...Glow discharge means, 8,18...
- Indicates the substrate holding means.

Claims (6)

[Claims] (1) A semiconductor thin film with a multilayer structure, characterized in that it is formed by alternately laminating two or more amorphous silicon layers and amorphous germanium layers on a substrate. (2) Silicon layer thickness and germanium layer thickness are each 1
The semiconductor thin film according to claim 1, which has a thickness of 00 Å or less. (3) The semiconductor thin film according to claim 1, wherein the silicon layer contains hydrogen and/or fluorine. (4) The semiconductor thin film according to claim 1, wherein the germanium layer contains hydrogen and/or fluorine. (5) Alternating glow discharge of a silicon compound and a germanium compound to alternately laminate two or more silicon layers and germanium layers on a substrate, and perform the laminate while irradiating light onto the main surface on which the thin film is formed. A method for forming a semiconductor thin film with a characteristic multilayer structure. (6) The method for forming a semiconductor thin film according to claim 5, wherein the irradiation intensity of light and/or the wavelength of light are changed during formation of the silicon layer and during formation of the germanium layer.