JPH0650729B2 - Method for forming amorphous semiconductor film - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an amorphous semiconductor film containing a compensating element such as silicon, germanium, carbon, etc., which reduces the localized density of states.

2. Description of the Related Art Conventionally, a plasma CVD method capable of forming a thin film at a relatively low temperature has been used for forming an amorphous semiconductor film such as amorphous silicon for a solar cell or an electrophotographic photoreceptor, amorphous germanium, or amorphous carbon. Is most commonly used. This method is used as a source gas when forming an amorphous silicon film, for example.
SiH ₄ (silane gas) or mixed gas of SiH ₄ and H ₂ is used, the substrate temperature is 200 to 350 ° C., and the gas pressure is
This is a method of applying high frequency power between the substrates facing the electrodes to generate plasma while controlling to 0.1 to 10 Torr to decompose silane gas to form a film on the substrate. In this case, the deposition rate is as slow as about 3 μm / h, and it takes 6 hours or more to manufacture an electrophotographic photosensitive member requiring about 20 μm or more, which makes rapid mass production difficult. Further, when the high frequency power is increased to increase the deposition rate, a large amount of powdery silicon is generated due to a gas phase reaction in the raw material gas, which causes a problem in the exhaust system of the manufacturing apparatus, which is a big problem in mass production.

Electron cyclotron resonance (EC) has been proposed as a means for solving the problems of the above-mentioned plasma CVD apparatus.
It is a plasma CVD apparatus using R). (JP-A-56-
No. 155535, Japanese Patent Laid-Open No. 59-159167) FIG. 1 shows the basic configuration of this device. Reference numeral 1 is a plasma generation chamber, 2 is a film formation chamber, and the plasma generation chamber 1 is connected to a magnetron power source (not shown) through a waveguide 3 and a waveguide window 4, and a magnetic coil 5 is provided on the outer periphery thereof. Is installed. The plasma generation chamber 1 is cooled by a water cooling pipe 6 arranged outside the plasma generation chamber 1. A plasma excitation gas is introduced into the plasma generation chamber 1 through the first gas inlet 7, plasma is excited in the plasma generation chamber 1 by microwaves, and a magnetic field is further applied to cause electron cyclotron resonance in the plasma. , Plasma introduction port 8 by diffusion magnetic field
Substrate 1 on substrate holder 9 arranged in film formation chamber 2
Lead to 0. The raw material gas is introduced into the film forming chamber 2 through the second gas introduction ports 11 and 11A and brought into contact with plasma, and the raw material gas 12
To decompose and deposit a film.

Since this method uses electron cyclotron resonance, discharge can be sustained even under a low pressure of 2 × 10 ^{−5 to} 0.1 Torr, and energy used for film formation is incident on the substrate. Given by the energy of the ions, the collision of ions on the film surface causes the film to honey,
A good film can be obtained even when the substrate temperature is set to room temperature. It has been shown that this method can form a good quality insulating layer such as Si ₃ N ₄ or SiO ₂ or Si for a semiconductor process at a low temperature. It is believed that this is because only the very surface rises to a high temperature due to ion energy and breaks the Si—H bond.

On the other hand, Japanese Patent Application Laid-Open No. 59-159167 discloses that an amorphous silicon film is deposited by using a gas containing an inert gas and hydrogen as an exciting gas. However, this is deposited at 0.1 Torr or more in order to avoid the influence of plasma, and the conventional CVD that requires substrate heating is used.
Due to the same deposition mechanism as in the method, silicon powder is often generated, and it is 20 μm like the electrophotographic photoreceptor using amorphous silicon.
When the above thickness is required, processing of powder has been a very important issue in manufacturing.

Problems to be Solved by the Invention While the CVD method using ECR as described above allows an insulating film to be deposited at a low temperature and at a high speed, substrate heating is required to form a good-quality semiconductor film. The generation of silicon powder, which was a drawback, is still unsolved.

That is, it is unknown whether or not a high-quality amorphous semiconductor film containing hydrogen, which is a monovalent compensating element that reduces the localized density of states by the incidence of ions, can be formed at room temperature.

It is an object of the present invention to realize a method for depositing an amorphous semiconductor film in which the amount of powder generated is extremely small and a good quality amorphous semiconductor film can be obtained uniformly at room temperature even in a large area.

Means for Solving Problems A method for forming an amorphous film in which gasified molecules, which are a raw material for a film to be deposited, are introduced into a decompression container in which a substrate to be deposited is placed and then deposited on the substrate. And pre-exciting an excited gas using an electric discharge to bring the excited gas containing ions into contact with the raw material gas introduced into the container, radicalize the raw material gas and deposit it on the substrate. Including the steps, the distance between the substrate and the inlet for introducing the plasma containing the ions and radicals (d) is d <with respect to the mean free path of the molecules existing in the container (λ).
The gas pressure is 100 λ, and the gas flow ratio is Fm / (Fa + Fm) <0.9 when the flow rates of the excitation gas and the raw material gas are Fa and Fm, respectively.

When the excited gas that is excited and ionized by the electric discharge is introduced into the container in which the substrate is installed, the ions attract electrons and come into contact with the raw material gas to generate a large amount of radicals. These radicals diffuse to the surface of the substrate and react with the film material on the substrate to be deposited.

At that time, the lifetime of the ions is relatively short, and energy is lost before they are attached to the substrate due to collision with neutral molecules existing in the sheath where plasma is not present. Therefore, it is considered that the reason why the deposition rate is slowed is that the amount of ions generated in a large amount reaches the substrate is extremely small. Also at this time,
In the gas phase, a large amount of gas phase reaction is induced by collision of ions and radicals, and a polymer of semiconductor material is generated,
The powder is deposited in the reaction vessel.

Therefore, by controlling the pressure of the molecules in the reaction vessel so that the mean free path of the molecules becomes sufficiently large with respect to the distance between the plasma inlet and the substrate, the generation of powder can be significantly reduced. Further, by making the ions of the excited gas plasma incident on the substrate in a state having sufficient energy, a high-quality semiconductor film with high photosensitivity containing monovalent atoms that reduces the localized density of states is formed even at room temperature. can do.

Further, at this time, the amount of incident ions needs to be a certain amount or more with respect to the deposited molecules, so that it is considered necessary that the flow rate of the source gas with respect to the excited gas be made a certain amount or less.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

Example 1 A film deposition apparatus similar to the conventional one shown in FIG. 1 was used. A gas containing hydrogen as an exciting gas was introduced into the ion source through the exciting gas inlet 7. 2.45GHz to generate plasma
Plasma generation chamber 1 which forms a cavity resonator
To excite the excited gas. A magnetic field was applied to the plasma generation chamber 1 from the external magnetic coil 5 to form a divergent magnetic field for guiding plasma into the reaction vessel 2 (the magnetic field becomes weaker as it approaches the reaction vessel from the cavity resonator). This magnetic field was set to satisfy the electron cyclotron resonance condition near the center of the plasma generation chamber 1. Due to the divergent magnetic field, plasma is introduced into the film forming chamber 2 forming the reaction vessel through the inlet 8 and contacts the silane gas (SiH ₄ ) introduced from the source gas introduction 11A in the film forming chamber 2 to radicalize the silane gas. Turned into The maximum magnetic field at this time was about 1 KG. At this time, in the film forming chamber 2, a sheath is formed between the plasma and the electrically insulated substrate 10 so that a self-negative bias of about 20 is obtained.
V is induced. Therefore, the positive ions in the plasma are accelerated to the substrate. At this time, the pressure in the reaction chamber is 5
Exhausted by a pump to × 10 ^{−2 to} 3 × 10 ⁻⁴ Torr,
Controlled. The distance from the plasma inlet 8 to the substrate 10 was set to about 15 cm. The mean free path of the gas molecules introduced at this time is 0.15 to 20 cm. Dark conductivity and photoconductivity (1.4 μW / c at 546 nm light) of the amorphous silicon film deposited on the substrate 10 in such a state at room temperature.
m ² ), and hydrogen content were determined from the absorbance of infrared absorption. The temperature of the substrate was controlled from room temperature to 350 ° C. by the heater 13, but no dependency on the substrate temperature was recognized.

Further, it was confirmed that the deposition rate at this time was as high as 11 μm / h.

Figure 2 shows the results of dark conductivity and photoconductivity. 21 in the figure
a and 21b are SiH ₄ and H for the source gas and the excitation gas, respectively.
₂ and the respective flow rate ratios SiH ₄ / (SiH ₄ + H ₂ ) are 67%, 22a and 22b are prepared under the condition that the flow rate ratio is 34%, and 21b and 22b are dark conductivity, 21
a and 22a represent photoconductivity. Since the distance between the gas inlet and the substrate is 15 cm, it is 100 times the mean free path λ (0.15 cm) of the molecules in the film formation chamber.
The photoconductivity becomes equal to the dark conductivity near 0 ⁻² Torr. Further, at 1 × 10 ^{−3 which} is about 20 times λ, sufficiently good photosensitivity can be obtained. On the other hand, the amount of hydrogen contained in the amorphous silicon film changes depending on the ratio of the flow rates of the source gas and the excitation gas at 5 × 10 ⁻⁴ Torr. This is shown in FIG. 61 is the case where hydrogen is used as the exciting gas, and 62 is the case where He is used as the exciting gas.
It was found that it changed from 0 to 14 atm% and 13 to 5 atm%. Despite this change in the amount of hydrogen, an amorphous semiconductor film with high photosensitivity and high quality could be formed.

Further, under such a deposition condition, unlike the ordinary plasma CVD method, the amount of silicon powder generated in the deposition container is remarkably small, and even if the film is deposited to a film thickness of 20 μm or more required for the electrophotographic photoreceptor, the powder is not produced. Since the generation of the body is extremely small, the time required for the maintenance of the device is not required, and the productivity can be remarkably improved.

Next, the deposition rate and photosensitivity were measured by changing the ratio of the excitation gas and the source gas. 31a and 31b in FIG. 3 show the results when hydrogen was used as the excitation gas and SiH ₄ was used as the source gas. The horizontal axis represents the raw material gas flow rate / (raw material gas flow rate + excitation gas flow rate) in percent. 31b shows dark conductivity at room temperature, and 31a shows photoconductivity. 5 × 10 ^-4 To
When rr is 90%, the photosensitivity is remarkably reduced, and when it is 60% or less, good photosensitivity is obtained.

Further, FIG. 4 shows the results of the film deposition rate. In 41 in the figure, although it is saturated at around 50%, a deposition rate of 10 μm / H or more is obtained. When it is less than 50%, it rapidly decreases and approaches O directly. The lower limit is constrained by the deposition rate which limits manufacturing time.

Although SiH ₄ was used as the source gas, other SiF ₄ , SiC
In addition to silicon-based gases such as l ₄ , Si ₂ H ₆ , Si ₂ F ₆ , SiH ₂ H ₂ , SiH ₃ F, and SiHCl ₃ , GeH ₄ , GeF ₄ , GeH ₂ F ₂ , Ge ₂ F ₆ , GeH
Amorphous germanium or amorphous silicon or germanium semiconductor film can be formed by using germanium-based gas such as ₃ F or GeHF ₃ .

_{Further, CH 4, C 2 H 6} , C 2 H 4, C 3 H 6, n-C 4 H 10, i-C
₄ H ₁₀ , C ₄ H ₈ , CH ₃ Cl, C ₂ H ₅ Cl, CH ₃ Br, Si (C ₂ H ₅ ) ₄ , Si (C
_{H 3) 4, SiCl (CH} 3) 3, SiCl 2 (CH 3) amorphous carbon film by using the _2, SiCl ₃ CH _3, or mixed with the silicon, germanium gas, an amorphous germanium carbide, non Semiconductor films such as crystalline silicon carbide and amorphous germanium silicon carbide can also be formed.

Example 2 Next, the case where B ₂ H ₆ is added as a doping gas into the deposition container using the apparatus shown in FIG. 1 will be described.

In Figure 5, 5x10 ^-4 Torr, SiH ₄ / H ₂ at 34% B ₂
The results of measuring the dark conductivity 51b and the photoconductivity 51a by changing the amount of H ₆ are shown as in FIG. On the other hand, 5 × 10
^{At -2} Torr, the sensitivity is low as shown by 52b and 52a, and the amount of silicon powder generated is remarkably increased.

[Example 3] Next, He gas was used as the excitation gas, but the deposition rate is high as in the case of H ₂ gas as shown in FIG. Moreover, as shown in FIGS. 32a and 32b, a high-quality semiconductor film having high photosensitivity can be obtained. In the figure, 32a indicates photoconductivity and 32b indicates dark conductivity at room temperature. Similar results can be obtained by mixing hydrogen as the exciting gas.

As the doping material, it is clear that in addition to B, all gasifiable materials such as P, As and Ga can be applied.

EFFECTS OF THE INVENTION According to the present invention, a good quality amorphous semiconductor film can be deposited at a very high deposition rate and at a low temperature with almost no powder generated in the reaction vessel. Furthermore, an amorphous semiconductor film containing a monovalent element that reduces the localized density of states in the semiconductor film and capable of controlling valence electrons can be easily obtained.

As a result, a functional device using an amorphous semiconductor film, such as an electrophotographic photoreceptor or a solar cell, can be manufactured more easily at a lower cost than the conventional CVD method.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing one embodiment of a deposition apparatus used in the present invention, and FIGS. 2 and 3 are characteristic diagrams showing dark conductivity and photoconductivity of an amorphous semiconductor film according to the present invention, FIG. 4 is a characteristic diagram showing the deposition rate of an amorphous semiconductor film according to the present invention,
FIG. 5 is a characteristic diagram showing changes in dark conductivity and photoconductivity due to B doping, and FIG. 6 is a characteristic diagram showing a relationship between gas flow rate ratio and hydrogen concentration in the film. 1 ... Plasma generation chamber, 2 ... Film formation chamber, 3 ... Waveguide, 4 ... Waveguide window, 5 ... Magnetic coil, 6 ... Water cooling pipe, 7 ... Excitation gas inlet, 8 ...... Plasma inlet,
9 ... Substrate holder, 10 ... Substrate, 11, 11A ... Raw material gas inlet, 12 ... Raw material gas, 13 ... Heater.

Claims (3)

[Claims] 1. A method for forming an amorphous semiconductor film, comprising introducing a gasified raw material gas of an adhered film raw material into a depressurized container in which a substrate to be adhered is placed and depositing the gas on the substrate. , Pre-exciting an excited gas using an electric discharge in a space adjacent to the container, contacting the excited gas containing ions with the raw material gas introduced into the container, radicalizing the raw material gas and a substrate Including depositing on,
A gas pressure at which the distance (d) between the substrate and the inlet for introducing the plasma containing the ions and radicals is d <100λ with respect to the mean free path (λ) of the molecules in the container; In addition, when the flow rates of the excitation gas and the raw material gas are Fa and Fm, respectively, Fm / (Fa
A method for forming an amorphous semiconductor film, characterized in that the deposition step is performed at a gas flow rate ratio of + Fm) <0.9. 2. A gas containing silicon is used as a raw material gas,
The method for forming an amorphous semiconductor film according to claim 1, wherein a gas containing hydrogen is used as an exciting gas to deposit an amorphous silicon film containing hydrogen. 3. The method for forming an amorphous semiconductor film according to claim 1, wherein an inert gas is used as the exciting gas, and the gas flow rate ratio is Fm / (Fa + Fm) <0.6.