JPH01164022A - Formation of silicon germanium amorphous alloy film - Google Patents

Abstract

PURPOSE:To make a rapid formation of a silicon germanium amorphous alloy film which has a high photo-conductivity, by using electron cyclotron resonance plasma generated interaction of a magnetic field and a micro-wave, and by using, as a raw gas, a compound which has Si and Ge atoms in one molecule. CONSTITUTION:A raw compound which has Si and Ge atoms in one molecule is supplied from a gas supply port 7 and is decomposed by high-energy electrons among the primary plasma flow, to be formed into a silicon germanium amorphous alloy film on the surface of a basic material 8. In the case that non-film formation gas is not supplied, non-film formation gas such as hydrogen, etc., which is generated as a result of decomposition of film formation gas is supplied from the gas supply port 7, is diffused in a discharge tube to be turned into high-density plasma which generates a quasi-primary plasma flow. A film formation raw gas, which is drawn in from the gas supply port 7 after a some time, is decomposed by this quasi-primary plasma flow, to be turned into a silicon geranium amorphous alloy film formed on the surface of the base material 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for forming a silicon-based amorphous alloy film on a substrate, and particularly to a method for forming an amorphous silicon germanium alloy film with excellent photoconductive properties.

[Conventional technology]

Amorphous silicon germanium alloy films can be selectively etched by using them in place of the n+ layer for amorphous silicon TFTs (thin film transistors), and are also attracting attention as long-wavelength sensitive electrophotographic materials for laser printers.・It is a material.

Conventionally, silicon-germanium-based amorphous alloy films have been formed by mixing silane gas and germane gas, for example, and using RF
Alternatively, a method using DC glow discharge decomposition is common. An example of using the RF Douglow discharge method is the Journal of Non-Crystalline Solids 77 & 7B (1985).
) No. 9CN page to No. 904 page (Journal of
Non Cr7atalline 5olids 77
&78, (1985) P901-904).

[Problem that the invention seeks to solve]

When an amorphous silicon germanium alloy film is formed from silane and germane, there is a problem in that only a non-uniform alloy film is obtained because the chemical reactivity of silane and germane is different.

Therefore, in the above conventional technology, parallel plate plasma CVD
By using mesh electrodes between the electrodes, long-life G, H,
By selectively extracting radicals to the substrate surface, the difference in reactivity between silane and germane is improved.

However, in this method, the film formation rate was very slow at about CLIA/second, which was a practical problem.

Further, in the glow discharge plasma CVD method, since the film forming pressure range is relatively high, there is a problem that fine powder is likely to be generated during film forming. Therefore, as a method to increase the film formation rate and prevent the generation of fine powder, a CVD method using electron cyclotron resonance plasma, which forms a film at high plasma density in a high vacuum region, has recently been studied.

By this method, an amorphous silicon germanium alloy film formed from silane and germane has been improved in terms of increasing the film formation speed and preventing the generation of fine powder. However, it is desired that this method be further improved in terms of the electro-optical properties of the resulting film.

The purpose of the present invention is to make it possible to form a silicon-germanium-based amorphous alloy film with excellent photoconductivity at high speed, and to apply it to 'I'F'l' ID or electrophotography. An object of the present invention is to provide a method for forming a silicon germanium-based amorphous alloy film.

[Means for solving problems]

The purpose is to create a magnetic field in at least a portion of the vacuum chamber;
Microwaves are introduced into the vacuum chamber, the gas introduced into the vacuum chamber is plasma excited by electron cyclotron resonance caused by the magnetic field and the microwave, and the film-forming gas introduced into the vacuum chamber is decomposed. Forming a silicon-germanium-based amorphous alloy film on a substrate placed on a silicon-germanium-based amorphous alloy film In the method for forming a silicon-germanium-based amorphous alloy film, a compound having a silicon atom and a germanium atom in one molecule is used as the film-forming gas. is achieved.

As a compound having a silicon atom and a germanium atom in one molecule used as the film forming gas of the present invention, general 2GeHx (""Hs)4-x (x=Ot' +
2+3).

According to a preferred embodiment of the present invention, in the method for forming a silicon germanium-based amorphous alloy film of the present invention, the magnetic field strength formed in the vacuum chamber is lower than the electron cyclotron resonance magnetic field along the microwave introduction path. The magnetic field decreases from a large state, passes through a resonant magnetic field, becomes smaller than the resonant magnetic field, and forms a film made of a compound containing silicon atoms and germanium atoms in one molecule in a region where the magnetic field strength is smaller than the electron cyclotron resonant magnetic field. A silicon-germanium-based amorphous alloy film with good film properties can be obtained by introducing a gas and forming a film on a substrate placed in a region where the magnetic field strength is smaller than the electron cyclotron resonance magnetic field.

According to a further preferred embodiment of the present invention, in the method for forming a silicon germanium-based amorphous alloy film of the present invention, hydrogen, helium, neon, argon,
A non-film-forming gas such as xenon or krypton is introduced to generate a partial plasma flow of the non-film-forming gas, and one molecule is introduced into a region where the magnetic field strength is smaller than the electron cyclotron resonance magnetic field. By decomposing a compound containing silicon atoms and germanium atoms and forming a film on a substrate placed in a region where the magnetic field strength is low, the photoconductive properties are particularly improved under low-pressure film forming conditions. Uniform film formation rate and film properties are achieved.

In the method for forming a silicon-germanium-based amorphous alloy film of the present invention, when the compound containing silicon atoms and germanium atoms in one molecule contains silicon atoms and germanium atoms in a ratio of 1:10, The optical bandgap of the formed film is approximately 1.3 eV, although it varies somewhat depending on the film forming conditions.

If a larger optical band gear is required, an appropriate amount of silane gas as a film-forming gas should be mixed into the compound containing silicon atoms and germanium atoms in one molecule. A silicon germanium-based amorphous alloy film having a desired optical bandgap in the range from V to about 1.8 eV is obtained. for example,
The wavelength of semiconductor lasers used in laser printers is currently about 830 nm, and a silicon germanium-based amorphous alloy film of about 1.4 ev can be used as a photoreceptor corresponding to this wavelength.

According to a further preferred embodiment of the present invention, in the method for forming a silicon-germanium-based amorphous alloy film of the present invention, the film formation may be performed under the condition that the film-forming substrate is heated to 100°C to 400°C. , is effective in improving the photoconductive properties of the film.

According to a further preferred embodiment of the present invention, in the method for forming a silicon germanium-based amorphous alloy film of the present invention, the gas pressure in the vacuum chamber during the plasma discharge is 5 x 10-5 to 5 x 10-2 Torr. It is desirable to perform film formation in view of the photoelectric properties of the film. Gas pressure is 5 x 1
In the case of 0-2 Torr jd, the quality of the formed silicon germanium film deteriorates as the electron energy in the plasma decreases due to the pressure increase. On the other hand, when the gas pressure is 5 x 10-5 Torr DA, plasma discharge becomes unstable and the film formation rate and film properties tend to become non-uniform.

According to a further preferred embodiment of the present invention, in the method for forming a silicon germanium-based amorphous alloy film of the present invention, the power of the microwave introduced into the vacuum chamber is 1 sccm of the film-forming gas introduced into the vacuum chamber. In view of the photoelectric properties of the film, it is desirable to set the power to J95W or more.If the power of the introduced microwave is low, the amount of hydrogen in the film is large and the photoelectric properties are deteriorated.

[Effect]

In the present invention, as described above, photoconductivity is achieved by utilizing electron cyclotron resonance plasma generated by the interaction of a magnetic field and microwave, and by using a compound having Ksi atoms and Go atoms in one molecule as a raw material gas. A silicon germanium-based amorphous alloy film with good properties can be formed at high speed. Electron cyclotron resonance plasma is characterized in that it can be generated at a deposition pressure of 3.times.10@-2 Torr H, which is significantly lower than in the case of ordinary radio wave glow discharge plasma, and that a plasma with high electron energy can be obtained. When forming a silicon germanium-based amorphous alloy film, as in the past, G,
Only H4 is decomposed and the composition does not become non-uniform, and since the raw material gas itself has 8l-Go bonds, the composition tends to be uniform when it is decomposed to form a film. The silicon-germanium-based amorphous alloy film obtained in this way is formed at high speed and is still under a sufficiently high degree of vacuum, so there are fewer collisions between molecules in the gas phase, and there is less generation of fine powder that can cause pinholes. .

The present invention will be explained below using examples.

〔Example〕

FIG. 1 is an explanatory diagram of the configuration of an electron cyclotron plasma film forming apparatus used for forming the silicon germanium-based amorphous alloy film of the present invention.

In the figure, 1 is a magnetron, usually 01 to 10
Generates GHz microwaves. The generated microwaves are guided into the vacuum chamber 3 through the circular waveguide 2.

4 is a discharge tube made of an insulating material (for example, quartz glass, alumina, etc.) to transmit microwaves.

5 is a solenoid coil for forming a magnetic field within the vacuum chamber.

6.7 is a gas inlet of a different system. The gas introduction port 6 is arranged to supply gas to the high magnetic field region within the vacuum chamber 3, and the gas introduction lower is arranged to supply gas to the low magnetic field region within the vacuum chamber 3.

Reference numeral 8 denotes a substrate to be film-formed, which is arranged so that the gas supplied from the gas introduction lower is incident on the surface.

9 is a sample stage equipped with a heating mechanism.

Reference numeral 10 designates an exhaust port to which a decompression pump (not shown) with a high exhaust speed, such as a turbo molecular pump or an oil diffusion pump, is connected.

When a discharge gas is introduced into a vacuum chamber at a predetermined pressure and microwave power is supplied, a microwave discharge is generated due to the interaction between the microwave electric field and the magnetic field.

Here, the setting conditions of the magnetic field and the arrangement of the gas inlets will be explained.

Electrons in a magnetic field move in a cyclotron around magnetic lines of force, and the cyclotron frequency fce of the electron is determined by the magnetic field strength as follows: B: @flux density [T] m: electron mass CKg) e: electron charge (Coulomb) Electron cyclotron resonance excitation occurs at the position of the magnetic field strength where fee coincides with the incident microwave frequency. ], gas is supplied from the gas introduction port 6 to this region, and another system of gas is supplied from the gas introduction lower to the region where the magnetic field strength is smaller than the electron cyclotron resonance.

In such a configuration, hydrogen, He, Ne, Ar.

When using a partial plasma flow of a non-film-forming gas such as Xs, these non-film-forming gases are introduced from the gas inlet 6. As a result, high-density plasma is generated in the discharge tube 4. Since the generated plasma has diamagnetic properties, it is transported toward the lower magnetic field side along the lines of magnetic force and partially forms a plasma flow.

Raw material compound 1 having 81 and Geji molecules in one molecule is
The gas is supplied from the gas introduction lower and is decomposed by high-energy electrons in the secondary plasma flow to form a silicon-germanium-based amorphous alloy film on the surface of the base 8.

When a non-film-forming gas is not introduced, non-film-forming gas such as hydrogen, which is generated as a by-product as a result of the decomposition of the film-forming gas supplied from the gas introduction lower, diffuses into the region of the discharge tube 4. A high-density plasma 9 forms a quasi-order plasma flow. This pseudo-
Due to the subsequent plasma flow, the film-forming raw material gas introduced from the gas introduction lower is decomposed with a time delay, and a silicon-germanium-based amorphous alloy film is formed on the surface of the substrate 8.

When it is desired to contain doping atoms such as B and P in the film, it is efficient to supply a gas containing these atoms from the gas introduction lower.

Next, a method for forming a silicon germanium-based amorphous alloy film of the present invention using the above-mentioned plasma film forming apparatus will be described with reference to representative examples.

<Example 1> H5GsSiH was used as the film-forming raw material gas, and was supplied from a 4 sccm gas introduction lower. Here, the synthesis of the raw material gas H5GeSiH5 is as follows: sila/ and germane 1:
The mixed gas of No. 1 was reacted by silent discharge and purified by vacuum distillation. 65 cans of Ar gas was supplied from the gas inlet 6.

Microwave frequency 2.45GHz, microwave input 20
0W, discharge gas pressure of 4×10-' Torr, and substrate temperature of 190°C. The magnetic field distribution was set to 875 G at the exhaust side end of the discharge tube 4. A turbo molecular pump with an exhaust speed of 5 oot/sec was used for the exhaust system. Under these conditions, an amorphous silicon germanium film with a band gap of 1.30 θV was obtained at a deposition rate of 6 A/sec. This film was of good quality with a photoconductivity ratio of 2.0×10′.

<Example 2> H2Ge (S i H5)2 was used as the film-forming raw material gas.
't- was used, and this was supplied from the 680Off+ gas introduction lower. Here, the raw material gas H2Ge (SiJ)2 is obtained by using a 2:1 mixed gas of silane and germane by silent discharge.
The product was reacted, separated and purified by vacuum distillation, and then used.

Hydrogen was supplied at 12 sccm from the gas inlet 6, the discharge gas pressure was 9, and the other conditions were set as in Example 1 to form an amorphous silicon germanium film. At this time, film formation speed 1 & 5
Although an alloy film with a band gap of 1.48 eV was obtained at A/sec, this film was of good quality with a photoconductivity of 2.5 x 10-50-5S' and a ratio of photoconductivity to dark conductivity of 8 x 10s. . In addition, without introducing a non-film forming gas, H2Go (SiH,
) When a similar film was formed using only 2, similarly good results were obtained.

In addition, when He, Ne, Kr, or Xs f gases are supplied from the gas inlet 6, the optimum film forming pressure will vary; A germanium film was obtained.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to form a silicon germanium-based amorphous alloy film with excellent photoconductivity characteristics at high speed, and it is possible to apply it to TPT (thin film transistor), electrophotography, etc. .

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of an electron cyclotron resonance plasma deposition apparatus used for forming a silicon germanium-based amorphous alloy film of the present invention. 1... Magnetron 2... Waveguide 3... Vacuum chamber 4... Discharge tube 5... Solenoid coil 6.7... Gas inlet 8... Substrate 9... Sample stage 10... Exhaust boat 1. − Agent: Patent Attorney Katsuo Ogawa

Claims (1)

[Claims] 1. A magnetic field is formed in at least a part of the vacuum chamber, microwaves are introduced into the vacuum chamber, and the gas introduced into the vacuum chamber is subjected to electron cyclotron resonance by the magnetic field and the microwaves. In the method for forming a silicon-germanium-based amorphous alloy film, in which plasma is excited, a film-forming gas introduced into the vacuum chamber is decomposed, and a silicon-germanium-based amorphous alloy film is formed on a substrate placed in the vacuum chamber. A method for forming a silicon-germanium-based amorphous alloy film, characterized in that the film gas is a compound having a silicon atom and a germanium atom in one molecule. 2. The film forming gas has the general formula H_xGe(SiH_3)
_4_-_x (x = 0, 1, 2, 3)
The method for forming a silicon germanium-based amorphous alloy film according to claim 1, characterized in that the film is a compound represented by: