JPH06105688B2 - Method for manufacturing semiconductor thin film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a semiconductor thin film, and more particularly to a method for producing a silicon-based semiconductor thin film having excellent photoelectric characteristics.

[Background technology]

Amorphous semiconductor thin films are widely used in solar cells, photosensors, photosensitive drums, image display device drive circuits, etc., and are being actively researched. As a method for forming the thin film, glow discharge decomposition, thermal decomposition, photodecomposition, etc. are appropriately used depending on the purpose.

In forming a semiconductor device suitable for various uses from the thin film, the substrate on which the thin film is formed is desired to be kept under mild conditions such as low temperature as much as possible in order to maintain its original function. It is rare. However, in order to maintain good quality of the thin film, there has been a contradictory request in the prior art that the substrate must be maintained at a high temperature of at least 300 to 400 ° C.

Further, many techniques for forming the thin film at high speed have been studied for the purpose of cost reduction. From these studies, it has been proposed that the substrate temperature needs to be further increased in order to maintain the high quality of the thin film as the forming speed increases.

In order to solve this problem, a photolysis method (photo CVD method) has been proposed. However, in the photolysis method, the raw material absorbs light and decomposes it.Therefore, not only the type of light but also the type of raw material is limited.To increase the decomposition efficiency, a toxic substance such as mercury is used as a sensitizer. Was forced to use. Further, the formation rate in the photolysis method is lower than that in the conventional technique, and there are many problems such that it is difficult to use for a long time due to a phenomenon of a thin film adhering to the light incident window.

In order to solve these problems, the present inventor firstly proposed a method of superposing CO ₂ laser light on glow discharge decomposition (Japanese Patent Application No.
However, the present invention proposes a new method.

[Disclosure of Invention]

In the production method of the present invention, a silicon compound as a raw material gas is decomposed substantially only by glow discharge to form a thin film on a substrate, and the thin film is formed by irradiating the main surface of the thin film with the light. It is carried out while absorbing at least a thin film or a substrate.

Light that can be effectively used in the present invention is such that a thin film is not formed only by irradiation with light. In other words, it is characterized by using light that is not absorbed by the source gas, specifically, light having a wavelength of 200 nm or more and up to infrared light.
Further, this light is always absorbed by the thin film and / or the substrate to be formed. It is preferably light that is absorbed and efficiently converted into heat, and particularly preferably light that has a large absorption in the formed thin film and is efficiently converted into heat.

Further, in the present invention, it is preferable to change the irradiation intensity of light according to the formation rate of the thin film. When increasing the thin film formation rate, it is preferable to increase the light irradiation intensity.
As a concrete example, in the glow discharge decomposition of a silicon compound, the thin film formation rate is changed from 4 to 5Å / S to 8 to 10Å
When irradiating light with a wavelength of 10.6 μm when increasing twice to / S, 10 ^-5 S / cm by increasing the irradiation intensity from 1w / cm ² to 1.5w / cm ² by about 1.5 times A photoconductivity exceeding ² is obtained, and the photosensitivity expressed by photoconductivity / dark conductivity is
It is possible to obtain a high quality hydrogenated amorphous silicon film (a-Si: H film) exceeding 10 ⁶ without particularly heating the substrate. When the substrate is heated, the effect of the present invention can be achieved by appropriately reducing the irradiation intensity.

Further, when light having high energy, that is, light having a short wavelength is used, the light is effectively absorbed by the thin film. Therefore, the irradiation intensity may be appropriately adjusted according to the wavelength. For example, light of 10.6 μm requires about 10 ³ or more photons (photons) per silicon atom, while light of 250 nm, which has a shorter wavelength, has more than 10 photons per silicon atom. Therefore, the quality can be improved.

However, in the present invention, it is not always necessary to use monochromatic light. Therefore, light with excellent monochromaticity such as laser light, mercury lamp, tungsten lamp, halogen lamp, rare gas lamp, hydrogen discharge tube, deuterium discharge tube,
Any polychromatic light such as a mercury-rare gas lamp can be effectively used as long as the above-mentioned conditions are satisfied. For example, laser light is useful in increasing the number of irradiation photons in addition to monochromaticity, while other light is excellent in that a large area can be irradiated at one time.

The silicon compound used in the present invention means monosilane (SiH ₄ ), disilane (Si ₂ H ₆ ), trisilane (Si ₃ H ₈ ).
Silicon hydride such as monofluorosilane (SiH ₃ F),
Difluorosilane (SiH ₂ F ₂ ), trifluorosilane (SiH
Fluorinated silanes such as F ₃ ), hexafluorodisilane (Si ₂ F ₆ ), etc., and a particularly preferred silicon compound is disilane capable of forming a thin film at high speed with low glow discharge power. Furthermore, diborane (B ₂ H ₆ ) and phosphine (PH
By mixing an impurity gas such as ₃ ) with a silicon compound, it is possible to form a semiconductor thin film having a different conductivity type or a semiconductor junction. These silicon compounds and the like can be used alone or as a mixture, or can be diluted with a gas such as hydrogen or helium and used.

The production method of the present invention is not limited to silicon compounds, it can be easily conjectured by those skilled in the art to substitute for other source gases such as germane (GeH ₄ ) and germanium tetrafluoride (GeF ₄ ), Included within the scope of the invention as equivalents.

As the substrate used in the present invention, a conductive or electrically insulating material is used. Specifically, not only a metal plate, a metal foil, a glass plate, a ceramics plate, a polymer film, and a semiconductor material, but also those on which a thin film such as a conductor, a semiconductor, or an insulator is formed in advance are effectively used.

As described above, in the present invention, there is the convenience that the heating of the substrate is not always necessary. Therefore, the substrate installation position only needs to consider the uniform formation of the thin film and is relatively freely determined, so that the glow discharge of either the capacitive coupling method or the inductive coupling method can be effectively used.

The conditions of glow discharge used in the present invention are not significantly different from the conventional method except for the substrate temperature. Reaction pressure is 5 Torr
The low pressure is the following, preferably 2 Torr or less, and 0.01 Torr or more is preferable for high-speed formation of a thin film.

The substrate temperature adopted in the present invention is 300 in the conventional method.
A lower temperature may be used as compared to a temperature of ~ 400 ° C. Under the selected light irradiation conditions, a high quality thin film can be formed without heating the substrate.

[Preferred modes for carrying out the invention]

 Next, preferred embodiments of the present invention will be described.

A light irradiation means is provided outside or / and inside the reaction chamber capable of glow discharge. A substrate on which a semiconductor thin film is to be formed is placed in a reaction chamber and heated and held at room temperature or a low temperature of 300 ° C. or lower under reduced pressure. Then, a silicon compound and, if necessary, an impurity gas and a diluent gas are introduced while controlling the flow rate so that the pressure becomes 5 Torr or less, and glow discharge is performed. The semiconductor thin film may be formed by superimposing on the glow discharge and irradiating the main surface on which the thin film is formed with the selected light as described above.

The present invention can be implemented by the apparatus shown in FIGS. 1 to 4, for example. Here, 1 , 21 , 41 , 61 are thin film forming devices, 3, 23, 43,
63 is a light irradiation means (including a scanning means), 5, 6, 2
5,26,45,46,65,66 are glow discharge electrodes, 9,29,49,69 are bases, and 77 is a thin film deposition means.

Here, FIG. 2 shows the equipment in which the glow discharge means and the base are separated from each other to facilitate light irradiation to the base.
Further, the position of the raw material gas introduction means can be adjusted so that the glow discharge in the vicinity of the substrate can be kept uniform.

Further, FIG. 1 shows that the beam light can be scanned by the scanning means 3 by the variation of the apparatus shown in FIG.

FIG. 4 is also a variation of the device shown in FIG. 2, in which a light source (light irradiation means) is installed inside the device.

FIG. 3 is one of the examples in the case of introducing beam light. The beam-like light irradiates the substrate directly from the light generating means or through the beam scanning means. This is a preferable example when laser light is used as the beam-like light.

[Action / effect]

As described above, the semiconductor thin film obtained by the present invention has excellent photoelectric characteristics. Further, in the present invention, it is possible to reduce the temperature of the process, and a semiconductor device such as a solar cell, a thin film transistor, a photosensitive drum, an image sensor, which is composed of various interfaces such as a semiconductor junction interface, a semiconductor insulator interface, and a semiconductor conductor interface. Greatly improve the characteristics such as. It is considered that this is because the interface damage is reduced due to the low temperature of the process.

Further, in the conventional method, particularly in the case of continuous production, the substrate must be heated first before the formation of the thin film,
The time lag is large. It has even been proposed to install a preheating device for this solution, but according to the method of the invention, there is no need for such substrate preheating, and one after the other immediately starts forming thin films on new substrates. Productivity is dramatically improved, and its industrial significance is extremely large.

〔Example〕

In the plasma CVD apparatus 1 capable of light irradiation shown in FIG. 1, a thin film was formed using disilane as a silicon compound. A glass substrate 9 was placed on a substrate holder 10 and exhausted through an exhaust hole 7 or 8 connected to a vacuum exhaust means so that the pressure in the reaction chamber was on the order of 10 ⁻⁷ Torr. Disilane was supplied into the reaction chamber 13 through the gas introduction portion 14 or 15 provided in the electrode 5 or 6, and the pressure was maintained at 0.25 Torr or 0.5 Torr while exhausting by the exhaust means. A light 2 having a wavelength of 10.6 μm is introduced through a light entrance window 4 provided in a reaction chamber through an irradiation means 3 to irradiate a substrate 9, and a high frequency power of 13.56 MHz is applied between electrodes 5 and 6 to glow. The discharge started. When the required film thickness was reached, discharge and light irradiation were stopped and the substrate was taken out of the reaction chamber. The thin film thickness on the substrate was divided by the glow discharge time to obtain an average thin film formation rate. The conductivity and the optical bandgap (Eg) of the obtained thin film were measured. The results obtained by variously changing the irradiation light intensity are shown in Table 1. Table 1 also shows the properties of the thin film prepared without light irradiation. As is clear from this example, in the present invention, it was demonstrated that irradiation with light tends to slightly reduce the formation rate, and that light does not substantially contribute to the decomposition of the silicon compound.
However, a remarkable effect of improving the film characteristics was observed. As described above, the remarkable effect is obvious without comparing with the comparative example. For example, in Example 4, the photoconductivity and the dark conductivity were 2.0 × 10 ⁻⁵ S / cm and 1.9 × 1 respectively.
0 ^-12 S / cm, and the photosensitivity expressed by this ratio is
This shows that an amorphous silicon thin film having an extremely high value of 1.1 × 10 ⁷ was obtained at a high formation rate of 7.6 Å / S. In this example, the photoconductivity is measured under the light irradiation of AMI and 100 mw / cm ² .

[Brief description of drawings]

FIGS. 1, 2, 3, and 4 are schematic views showing an example of a thin film forming apparatus suitable for embodying the present invention. In the figure, 1 , 21 , 41 , 61 ... thin film forming apparatus, 3, 23, 43, 63 ... light irradiation means (including scanning means), 5, 6, 25, 26, 4
5,46,65,66 …… Glow discharge electrode, 9,29,49,69 …… Substrate,
77 …… Indicates thin film deposition means.

Claims (2)

[Claims] 1. A silicon compound is decomposed only by glow discharge so that a thin film is not formed only by irradiation of light to form a thin film on a substrate, and at the same time, on the main surface on which the thin film is formed, the light is formed. Thin film is not formed only by irradiation
While irradiating light with an irradiation intensity of 0.8 to 6 W / cm ² and at least absorbing the light into the thin film or the substrate, the thin film having a photoconductivity / dark conductivity value of 1.0 × 10 ⁴ or more is formed. A method of manufacturing a semiconductor thin film, which is characterized in that 2. The method for producing a semiconductor thin film according to claim 1, wherein the irradiation speed of light is changed according to the forming speed of the thin film.