JPH0666272B2 - Method for forming silicon-based amorphous film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for forming a silicon-based amorphous film on a substrate, for example, a conductive substrate, and particularly to a silicon-based film using electron cyclotron resonance plasma and having excellent photoconductive characteristics. The present invention relates to a method for forming an amorphous film.

[Conventional technology]

Regarding formation of a silicon-based amorphous film using electron cyclotron resonance plasma, there is a known example described in JP-A-59-159167. In the above-mentioned known example, H ₂ gas or H ₂ -H ₂ mixed gas is excited by plasma in the magnetic field by resonance of electron cyclotron motion and microwave in a gas pressure range of 0.2 to 05 Worr, and this is brought into contact with a silicon atom-containing gas. A silicon-based amorphous film is formed on the substrate heated to 300 ° C.

[Problems to be solved by the invention]

The above-mentioned prior art uses electron cyclotron resonance plasma, but uses low-energy electron plasma such that the H ₂ gas is not decomposed even if a H ₂ —H ₂ mixed gas is used. For this reason, the obtained silicon-based amorphous film has a dark conductivity of 10 ⁻¹¹ S / cm (S: Ω · cm ⁻¹ ) and a photoconductivity of about 10 ⁻⁷ S / cm. It is hard to say that an amorphous film is obtained.

The present invention provides a method for forming a silicon-based amorphous film having a higher photoconductivity than that of the above-described known silicon-based amorphous film and a large ratio of photoconductivity to dark conductivity and excellent photoconductivity. is there.

[Means for solving problems]

The above invention is achieved by forming a silicon-based amorphous film under a plasma condition in which electron energy is higher than in the above-mentioned known example. More specifically, lower than the above known example
It is achieved by using electron cyclotron resonance plasma at a film formation pressure of 0.1 Torr or less.

The energy of the electrons in the plasma increases as the film forming pressure decreases, and the energy is such that N ₂ molecules and the like are easily decomposed. Although it is not preferable that the electron energy is too large, the use of plasma having a relatively high electron energy is effective for producing a silicon-based amorphous film having high characteristics. Based on this finding, the inventors of the present invention decompose a gas containing silicon atoms and hydrogen atoms or halogen atoms by a plasma generated by electron cyclotron resonance at a film forming pressure of 0.1 mTorr or less to form a silicon-based amorphous film. It has been found that it is effective to use hydrogen or halogen gas generated as a result of decomposition of the silicon atom-containing gas as the non-film forming gas for generating the primary plasma flow in the above-mentioned known example. The present invention was found to be effective in improving the film quality, and the present invention has been achieved.

More specifically, the purpose is to form a magnetic field in at least a part of the vacuum chamber, introduce a microwave into the vacuum chamber, and introduce the silicon atom-containing gas introduced into the vacuum chamber into the magnetic field and the microwave. In the method of forming a silicon-based amorphous film, which is decomposed by the plasma generated by the above, and forms a silicon-based amorphous film on the substrate placed in the vacuum chamber, the magnetic field strength formed in the vacuum chamber is the microwave introduction path. A gas containing silicon atoms and hydrogen or halogen atoms is introduced into a region where the magnetic field strength is smaller than the electron cyclotron resonance magnetic field and decreases below the resonance magnetic field to become smaller than the resonance magnetic field, and the magnetic field strength is smaller than the electron cyclotron resonance magnetic field. The magnetic field strength is set in a smaller region, and the film is formed on a substrate heated to 100 ° C to 400 ° C. It is achieved.

According to a preferred embodiment of the present invention, in the method for forming a silicon-based amorphous film of the present invention, the gas pressure in the vacuum chamber during the plasma discharge is 2 × 10 ⁻⁴ to 1 ×.
A gas containing silicon atoms and hydrogen or halogen atoms, which is 10 ⁻¹ Torr and is introduced into the vacuum chamber, is supplied toward the film-forming substrate in a direction in which the magnetic field strength decreases, A silicon-based amorphous film having good film characteristics can be obtained.

[Action]

In the present invention, as described above, the gas pressure during film formation is set to 1 ×.
It was able to increase the film characteristics of the silicon-based amorphous film by increasing the electron energy of 10 ^-1 Torr in by following the low plasma. Although the reason why the film characteristics are improved by the increase of electron energy in plasma is not clear, the energy required for the decomposition reaction of the source gas such as SiH ₂ depends on the following formulas (1) to (4). ), It is considered that the film mechanism is changed by the energy of electrons in the plasma.

SiH ₄ → Si + 2H ₂ ; 4.4eV ………… (1) SiH ₄ → SiH + H ₂ + H; 5.9eV ………… (2) SiH ₄ → SiH ₂ + H ₂ ; 2.1eV ………… (3) SiH ₄ → SiH ₃ + H; 4.1eV ………… (4) Generally, an amorphous silicon film is a film with few SiH ₂ type bonds, which has good photoconductivity, but the increase in electron energy depends on the reaction ratio of the above formula (3). It is considered that good results can be obtained by lowering it.

As a preparation of a silicon-based amorphous film utilizing electron cyclotron resonance, the present inventors first introduced hydrogen or He or Ne or Ar or Kr or Xe into a region where the magnetic field strength in the vacuum chamber is larger than the electron cyclotron resonance magnetic field. Then, a primary plasma flow is formed by the microwaves introduced into the above region, and the film formation pressure of 5 is obtained by the method of decomposing the silicon atom-containing gas introduced into the region where the magnetic field strength in the vacuum chamber is smaller than the electron cyclotron resonance magnetic field. × 10 ^-5 ~
It has been found that a good silicon-based amorphous film can be obtained when the film is formed at 1 × 10 ^-1 Torr, but as a result of diligent studies, it was found that the inside of the vacuum chamber could be stored without using the non-film-forming gas that was pre-excited. , Along the microwave introduction path, a magnetic field distribution is formed in which the magnetic field strength is smaller than the resonance magnetic field and smaller than the resonance magnetic field, and becomes smaller than the resonance magnetic field. The contained silicon atom-containing gas at a pressure of 2 × 10 ⁻⁴ to 1 × 10 ⁻¹ Torr,
It has been found that good results can be obtained by the method of supplying the film toward the film-forming substrate in the direction in which the magnetic field strength decreases. This is because in this pressure region hydrogen or halogen gas generated as a result of the decomposition of the silicon atom-containing gas selectively diffuses into a region where the magnetic field strength is larger than the resonance magnetic field and is plasma excited in this region to form a primary plasma flow. This is because the primary plasma flow decomposes the silicon atom-containing gas that is supplied later.When the silicon atom-containing gas is supplied to a region where the magnetic field strength is large, good results are not obtained, and the overall magnetic field strength is reduced. Even when the maximum magnetic field strength in the vacuum chamber is the electron cyclotron resonance magnetic field, good results cannot be obtained.

In order to obtain a good silicon-based amorphous film, the substrate should be
It is necessary to heat it to 100 ° C or more, but compared to the case of ordinary parallel plate type R lower claw discharge plasma and the above-mentioned known examples.
A silicon-based amorphous film having the same film quality can be obtained at a temperature as low as 50 to 100 ° C., and particularly when the substrate is heated to 200 ° C. or higher, a silicon-based amorphous film having good characteristics which is difficult to obtain by the conventional method can be obtained.

〔Example〕

 The present invention will be described below with reference to examples.

FIG. 1 is a configuration explanatory view of an electron cyclotron plasma film forming apparatus used in an embodiment of the method for forming a silicon-based amorphous film of the present invention. In FIG, 1 is a magnetron to generate microwaves of normal 0.1~10GH _z. The generated microwave is guided into the vacuum chamber 3 through the circular waveguide 2. Reference numeral 4 denotes a discharge tube, which is made of an insulating material (for example, quartz glass, alumina, etc.) for passing microwaves. Reference numeral 5 is a solenoid coil for forming a magnetic field in the vacuum chamber. The gas inlet 6 is arranged so as to supply gas to the low magnetic field region in the vacuum chamber 3. Reference numeral 7 denotes a film-forming substrate, which is installed so that the gas supplied from the gas inlet 6 enters the surface. Reference numeral 8 is a sample table equipped with a heating mechanism. 9
Is an exhaust port and is connected to a decompression pump (not shown) having a large exhaust speed such as a turbo molecular pump or an oil diffusion pump.

When the discharge gas is introduced into the vacuum chamber at a predetermined pressure and microwave power is supplied, microwave discharge occurs due to the interaction between the microwave electric field and the magnetic field, but the setting conditions of the magnetic field and the arrangement of the gas inlets described above. Will be described. The electrons in the magnetic field make an electron cyclotron motion around the lines of magnetic force, but the electron cyclotron frequency fce depends on the magnetic field strength. However, it is determined that B: magnetic flux density [T] m: electron mass [Kg] e: electronic charge [Coulomb]. Electron cyclotron resonance excitation occurs at a magnetic field strength where fce matches the incident microwave frequency. In FIG. 1, the region of the discharge tube 4 of the vacuum chamber 3 is made larger than the magnetic field strength at which the electron cyclotron resonance occurs, and the gas is directed from the gas inlet 6 toward the film-forming substrate 7 in the region where the magnetic field strength is smaller than the electron cyclotron resonance magnetic field. To supply.
In the first stage of film formation, plasma discharge starts in this region, but when a silicon atom-containing gas containing hydrogen or halogen atoms is used, film forming components such as silicon atoms disappear due to film formation. Hydrogen or halogen gas generated as a secondary diffuses into the region of the discharge tube 4, and high-density plasma is generated in this region, which is transported to the low magnetic field side along the lines of magnetic force due to the diamagnetic property of the generated plasma. A plasma stream is formed. The film-forming gas containing silicon atoms, which is supplied from the gas inlet 6 with a delay with time, is decomposed by ionizing electrons in the primary plasma flow, and a silicon-based amorphous film is formed on the surface of the substrate 7. In this case, the gas pressure in the vacuum chamber 3 during plasma discharge is 2 × 10 ⁻⁴ to 1 × 10 ⁻¹ Torr.
And When the gas pressure is 1 × 10 ^-1 Torr or less, the energy of the electrons in the plasma rises, but the gas pressure is 2 × 10 ^-1.
When it is lower than ^{-4, the} gas pressure becomes lower than that required to maintain the plasma discharge, and film formation cannot be performed. On the other hand, when the gas pressure is higher than 1 × 10 ^-1 Torr, the mean free path in the plasma becomes small, so that the electron temperature of the plasma decreases and the energy sufficient to decompose the raw material gas is insufficient. Therefore, by setting the gas pressure within the above range,
A silicon-based amorphous film can be obtained on the surface of the substrate 7 with good film characteristics.

When the silicon-based amorphous film contains different kinds of atoms such as BPCGe, a gas containing different kinds of atoms may be simultaneously supplied from the gas introduction port 6.

Next, a method for forming a silicon-based amorphous film of the present invention using the plasma film forming apparatus described above will be described with reference to a typical embodiment.

SiH ₄ was used as the silicon atom-containing gas, and 15 sccm was supplied from the gas inlet 6. Microwave frequency = 2.4
5, CH _z , microwave input = 200 W, discharge gas pressure = 1 × 10 ^-3 T
orr, substrate temperature = 200 ° C. The magnetic field distribution was set so that the maximum of the discharge tube 4 was 1750 G, and the exhaust side end of the discharge tube 4 was 875 G (electron cyclotron resonance magnetic field strength). A turbo molecular pump with an exhaust speed of 500 l / sec was used for the exhaust system. The amorphous silicon film formed under these conditions has a photoconductivity of 10 ^−4.
S / cm. The film had a high characteristic that the ratio of photoconductivity to dark conductivity was 10 ⁶ .

In this example, Si ₂ H ₄ was used as the gas containing silicon atoms.
Although other gas containing silicon atom can be used, for example, SiH ₆ .SiF _{4 and the} like can be mentioned.

〔The invention's effect〕

As described above, according to the present invention, it is possible to form amorphous silicon having better photoconductivity than that of the conventional one, or it is possible to form a relatively good amorphous silicon film at a low temperature. It can be applied to various devices that operate.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of an electron cyclotron resonance plasma deposition apparatus used for forming a silicon-based amorphous film of the present invention. DESCRIPTION OF SYMBOLS 1 ... Magnetron, 2 ... Waveguide, 3 ... Vacuum chamber, 4 ... Discharge tube, 5 ... Solenoid coil, 6 ... Gas inlet, 7 ... Substrate, 8 ... Sample stand, 9 ... Exhaust port.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Nakatani 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefectural Institute of Industrial Science and Technology, Ltd. (72) Inventor Tadashi Sonobe, 3-chome, Hitachi-shi, Ibaraki No. 1 Stock company Hitachi Ltd. Hitachi factory (56) Reference JP 61-283112 (JP, A) JP 62-143418 (JP, A) JP 60-117712 (JP, A) JP Sho 61-281519 (JP, A)

Claims (2)

[Claims] 1. A magnetic field is formed in at least a part of a vacuum chamber,
A microwave is introduced into the vacuum chamber, the silicon atom-containing gas introduced into the vacuum chamber is decomposed by the magnetic field and plasma generated by the microwave, and a silicon-based amorphous film is formed on a substrate placed in the vacuum chamber. In the method for forming a silicon-based amorphous film, the magnetic field strength formed in the vacuum chamber becomes smaller than the electron cyclotron resonance magnetic field along the introduction path of the microwave and becomes smaller than the resonance magnetic field by decreasing the resonance magnetic field. , A gas containing silicon atoms and hydrogen or halogen atoms is introduced into a region where the magnetic field strength is smaller than the electron cyclotron resonance magnetic field, and the gas pressure in the vacuum chamber is set to 2 × 10 ⁻⁴ to 1 ×.
A method for forming a silicon-based amorphous film, characterized in that the film is formed on a substrate heated to 100 ° C. to 400 ° C., the magnetic field strength is set to 10 ⁻¹ Torr, and the magnetic field strength is set to a smaller region. 2. The gas containing silicon atoms and hydrogen or halogen atoms, which is introduced into the vacuum chamber during the plasma discharge, is supplied toward the film-forming substrate in a direction in which the magnetic field strength decreases. The method for forming a silicon-based amorphous film according to claim 1.