JPH0411626B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to an amorphous silicon film that exhibits good film characteristics as an electrophotographic photoreceptor and has a fast film formation rate. Regarding the method.

[Technical background of the invention and its problems]

Amorphous silicon film is used for electrophotographic photoreceptors,
It is expected to be applied to solar cells or photoelectric conversion elements, and the CVD method using glow discharge is generally known as the film forming method.

That is, in a conventional method for forming an amorphous silicon film, for example, an amorphous silicon photoreceptor, a conductive substrate and a counter electrode are provided in a reaction vessel that is reduced to a vacuum state, and SiH ₄ (silane) or Si ₂
A gas containing silicon (hereinafter abbreviated as Si) such as H ₆ disilane is introduced into the reaction vessel, and DC power or 13.56MHz high frequency power is applied between the counter electrode and the conductive substrate to generate Si. An amorphous silicon photoreceptor was formed on a conductive substrate by generating a plasma of the gas contained therein and causing a reaction. However, by simply applying power between the counter electrode and the conductive substrate, Si
In the method of forming a film by generating plasma of a gas containing .

Therefore, amorphous silicon (hereinafter referred to as a
-Si) film, at least 6
This method required several hours of film formation time, which caused problems in mass production. Therefore, if the applied power is increased in order to increase the film formation rate, powdery Si by-products may be generated due to the gas phase reaction of the Si-containing gas, clogging the exhaust system, or the high power may cause problems. There was a problem in that more Si--H ₂ bonds were generated than Si--H bonds in the a-Si film that was formed, resulting in poor photoelectric properties.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for forming an a-Si film that can be formed at high speed and has good film characteristics even when used as an electrophotographic photoreceptor.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention enables high-speed film formation while maintaining good film characteristics by introducing a previously excited gas into a reaction vessel.

[Embodiments of the invention]

The present invention will be explained in detail below.

That is, at the same time, a gas containing Si such as SiH ₄ or Si ₂ H ₆ is introduced into a reaction vessel reduced in pressure to a vacuum state, and at the same time, previously excited H radicals or SiHn (n= 1, 2, 3)
By introducing this into the reaction vessel, a reaction such as H ^* +SiH ₄ →SiH ^* +H ₂ +2H can be carried out, including Si, without applying direct current or alternating current to the counter electrode in the vacuum reaction vessel. It can generate gas radicals and form a film.

Si-containing gas and pre-excited H radicals or
By introducing SiHn ^* (n = 1, 2, 3) radicals into the reaction vessel and applying direct current or alternating power between the conductive substrate and the counter electrode, more radicals of Si-containing gas are generated. Furthermore, since the radicals contain many Si--H radicals, high-speed film formation is possible, and an a-Si photoreceptor with good photoconductivity and a useful amorphous silicon film can be formed.

Furthermore, if a gas containing Si and pre-excited H radicals and N radicals are introduced into the reaction vessel, and direct current or alternating current power is applied between the conductive substrate and the counter electrode, H radicals can be generated. Many radicals of the Si-containing gas are generated in the reaction vessel due to the reaction between the Si-containing gas and the Si-containing gas.
Since N radicals, which are difficult to generate when electric power is applied to N ₂ gas, are pre-excited and introduced into the reaction vessel, it is possible to efficiently incorporate N atoms into the formed film. By efficiently incorporating N atoms into this film, normal a-
A film with high resistance required for an electrophotographic photoreceptor, which could not be achieved with a Si:H film, can be formed.

As a method for pre-exciting the gas, excitation by electromagnetic waves such as high frequency waves, microwaves or laser beams, or excitation by application of DC power is suitable, but in the examples shown below, excitation was performed by microwaves.

Next, an outline of the film forming apparatus used in this example will be explained with reference to FIG.

Inside the reaction vessel 1, there are first a diffusion pump (not shown),
A rotary pump is brought to a vacuum of 10 ^-6 torr.

The reaction container 1 is isolated from the outside, and inside the reaction container 1, a conductive substrate 2 (made of an aluminum plate) is supported on a heater 3. The conductive base 2 is electrically grounded and heated to 220° C. by a heater 3.

A counter electrode 4 is provided facing the base 2 . A high frequency power source 5 of 13.56 MHZ is connected to this counter electrode 4.

A first introduction pipe 5 is connected above the reaction vessel 1, and a first gas containing Si is introduced into the reaction vessel 1 via a valve 6.

Furthermore, on the right side of the reaction vessel 1 is a second introduction pipe 7.
is connected, and the second gas is introduced through this introduction pipe 7. This introduction pipe 7 is connected to a microwave waveguide 8 , and the second gas is introduced into the introduction pipe 7 via the microwave waveguide 8 .
When the second gas is transported through the waveguide 8,
Microwaves are applied by the microwave application unit 9, and the second gas is decomposed and excited.

On the other hand, an exhaust pipe 10 is provided below the reaction chamber 1, and this exhaust pipe 10 is connected to a mechanical booster pump 12 and a rotary pump 13 via a valve 11.
It is connected to the.

(Example 1) First, the exhaust system is switched to the diffusion pump and rotary pump (not shown) side, and the inside of the reaction vessel 1 is brought into a vacuum state of 10 ^-6 torr. Next, operate the heater 3,
The temperature of the substrate 2 is set to 220°C. However,
Open valve 6 and flow pure silane SiH ₄ gas
It is introduced from the introduction tube 5 into the reaction vessel 1 at 150 SCCM. At the same time, the exhaust system is switched from the diffusion pump and rotary pump side to the mechanical booster pump 12 and rotary pump 13 side, and the valve 11 is fully opened.

On the one hand, hydrogen _H2 with purity 99.99% flow rate 50SCCM
Then, the sample is introduced into the reaction vessel 1 through the microwave waveguide 8. At this time, the frequency of the microwave applied from the microwave application section 9 was 2450MHz, and the power was 300W. As a result, the hydrogen gas introduced through the microwave waveguide 8 is excited and generates H radicals. Normally, the H radicals excited by microwaves are approximately 30 cm/sec in an atmosphere with a degree of vacuum of 0.1 to 1 torr. We have confirmed that it will be transported to a certain extent. In Example 1, the power source 5 was cut off and the film was formed without applying a high frequency voltage to the electrode 4. Then, the valve 11 is closed and the reaction vessel 1 is closed.
The internal pressure was adjusted to 0.5 torr and film formation was carried out for 1 hour. After that, the valve 6 is closed, and the introduction of hydrogen gas into the waveguide 8 is stopped, and the reaction vessel 1 is closed.
Re-evacuate to 10 ^-4 torr. Furthermore, heater 3
The operation of the substrate 2 was stopped, and the substrate 2 was taken out into the atmosphere after waiting for the temperature to drop below 100°C. At this time, an a-Si:H film 14 having a thickness of 1.2 μm was obtained on the substrate 2.

In this example, since the film is formed without applying the high frequency power source 5 to the electrode 4, no plasma is generated in the reaction chamber 1. Therefore, although there is a possibility that the film formation rate will be significantly reduced, as mentioned above, a film formation rate of 1.2 μm/hour has been obtained.

Furthermore, the a-Si;H film formed by the above method
14 was comparable in terms of electrophotographic properties to conventional ones.

(Example 2) Pure silane gas SiH ₄ and pre-excited H radicals were introduced into the reaction vessel 1 under the same conditions as in Example 1, and a power supply of 13.56MHz was applied between the conductive substrate 2 and the counter electrode 4 by the power source 5. A high frequency power of 50 W was applied to form a film for 1 hour. Thereafter, in the same manner as in Example 1, the introduction of gas was stopped, the operation of the heater 3 was stopped, and the conductive substrate 2 was taken out into the atmosphere after waiting for the temperature to reach 100° C. or lower. The thickness of the a-Si:H film 14 at this time is
It was 8 μm.

Also, only normal _SiH4 gas (pre-excited H
SiH ₄ generated under plasma when a high frequency of 50W or more is applied (without introducing radicals)
Powdered Si by-products due to radical plasma polymerization were hardly observed during film formation in Example 2.

When we measured the electrical properties of the sample on which the a-Si:H film 14 was formed in this way, we found that the dark resistance was
When irradiated with light of 10 ¹⁵ photons/cm ² at 10 ¹¹ Ωcm and a wavelength of 633 nm, it showed a good bright resistance of 10 ⁸ Ωcm.

(Example 3) As in Examples 1 and 2, the inside of the reaction vessel 1 was heated to 10 ^-6 torr.
After vacuuming the conductive substrate 2 and raising the temperature to 220°C, open the valve 6 to supply pure silane SiH ₄ gas at a flow rate.
Introduce into reaction vessel 1 at 180 SCCM.

In addition, H radicals pre-excited with microwaves were added at a flow rate of 50 SCCM, and SiHn radicals were added at a flow rate of 50 SCCM.
Both were introduced into the reaction vessel 1 via the waveguide 8 at 100 SCCM.

Adjust the exhaust capacity with the valve 11, wait until the pressure inside the reaction vessel 1 reaches 0.4 torr, and then remove the counter electrode 4.
13.56MHz high frequency power between
Film formation was performed for 1 hour by applying 50W.

Next, in the same manner as in Examples 1 and 2, the gas was turned off, and after waiting for the temperature of the conductive substrate 2 to cool down to 100° C. or less, it was taken out into the atmosphere.

When the a-Si:H film 14 formed in this way was measured, the film thickness was 15 μm, and the electrical properties were as follows.
Dark resistance is 10 ¹⁰ Ωcm, 10 ¹⁵ at 633 nm wavelength
When irradiated with photons/cm ² , it exhibited a bright resistance of 10 ⁷ Ω, cm.

(Example 4) As in Examples 1, 2, and 3, the inside of reaction vessel 1 was heated to 10 ^-6
After drawing a vacuum of torr and raising the temperature of the conductive substrate 2 to 220°C, the valve 6 was opened and pure silane SiH ₄ gas was introduced at a flow rate of 180 SCCM, and further, B _{2 H 6 / B 2} H ₆ /
A B ₂ H ₆ /H ₂ gas of SiH ₄ =2×10 ⁻⁶ diluted with H ₂ is introduced into the reaction vessel 1 .

Under the same microwave excitation conditions as in Example 1, the pre-excited H radicals were heated at a flow rate of 50 SCCM, and N
Radicals were introduced into the reaction vessel 1 through the waveguide 8 at a flow rate of 50 SCCM.

After adjusting the opening and closing of the valve 11 and waiting until the pressure inside the reaction vessel 1 reached 0.5 torr, a high frequency wave of 50 W at 13.56 MHz was applied between the counter electrode 4 and the conductive substrate 2, and the mixture was heated for 1 hour. I performed a membrane.

The gas was stopped in the same manner as in Examples 1, 2, and 3, and the conductive substrate 2 was taken out into the atmosphere after waiting for the temperature to drop to 100° C. or less. The thickness of the obtained a-Si film 14 was 15 μm, the same as in Example 3, but when its electrical properties were measured, it had a high dark resistance of 10 ¹³ Ω, cm, and furthermore, it had a high resistance at a wavelength of 633 nm. It exhibited a bright resistance of 10 ⁸ Ω, cm against light irradiation of 10 ¹⁵ photonS/cm ² .

In Examples 1 to 4 described above, the film forming apparatus shown in FIG. 1 for forming the a-Si film 14 on the flat substrate 2 was used. A cylindrical substrate is often used. In this case, it is more advantageous to use the apparatus shown in FIG. 2 to form the film than the apparatus shown in FIG.

That is, a cylindrical casing 17 forming a reaction chamber 16 is detachably attached to the base 15. On the base 15,
Further, a substrate mounting table 18 is rotatably supported. A gear 2 is connected to the mounting table 18 via a shaft 19.
0 is attached. This gear 20 meshes with a gear 22 attached to a motor 21.

On the other hand, a gas introduction pipe 23 is provided along the inner surface of the casing 17. The gas introduction pipe 23 communicates with an introduction pipe 24 which is a first introduction system,
A plurality of gas jet ports 2 are provided toward the center of the reaction chamber 16.
3a. Further, introduction pipes 25 and 26, which are a second introduction system, communicate with the reaction chamber 16. Furthermore, this introduction tube 23 also serves as an electrode, and is connected to a high frequency power source 27.

Further, a conductive cylindrical base, for example, an aluminum drum 28 is placed on the mounting table 18, and this base 28 is electrically grounded. Furthermore, a heater 29 is provided on the mounting table 18, and the base 28
It is designed to heat from the inside.

On the other hand, the introduction pipe 28 is connected to a gas cylinder (not shown) via a valve 30.

In this case, pure silane gas alone or a mixed gas of pure silane gas and B ₂ H ₆ gas is introduced into the introduction pipe 24 .

On the other hand, microwave applying sections 31 and 32 are provided in the middle portions of the introduction tubes 25 and 26, respectively. These microwave application parts 31 and 32 are connected to the introduction pipe 3.
Connected to 3. Then, from the introduction pipe 33,
Hydrogen _H2 gas, silane (monosilane or disilane)
Gas or nitrogen N ₂ gas is supplied and decomposition is performed by the microwave application parts 31 and 32, so
H radicals, SiHn radicals, or N radicals are introduced into the reaction chamber 16 from the introduction pipes 25 and 26.

Further, the base 15 is provided with an opening 34, and an exhaust system 35 is connected to the opening 34.
This exhaust system 35 is connected via a dust trap 37 with a filter 36 to a mechanical booster pump 38 and a rotary pump 39.

The operation of the film forming apparatus having such a configuration will now be described.

First, the heater 29 is operated to heat the substrate 28, the motor 21 is operated to rotate the mounting table 18, and the inside of the reaction chamber 16 is brought into a vacuum state by the exhaust system 35. In this state, the base body 28 is rotated as the mounting table 18 rotates, and the valve 30 is opened to introduce silane gas into the introduction pipe 2.
H radicals introduced into the reaction chamber 16 via 4 and excited via introduction pipes 25 and 26,
SiHn radicals or N radicals are also present in the reaction chamber 16.
to be introduced.

The gas introduced through the introduction pipe 24 is uniformly sprayed onto the circumferential surface of the base 28 from the injection port of the introduction pipe 23.

On the other hand, the aforementioned H radicals, SiHn radicals, or N radicals are directly introduced into the reaction chamber 16 from the introduction pipes 25 and 26.

In this state, a high frequency power of 13.56 MHz and 50 W is applied to the introduction tube 23 as an electrode by the high frequency power supply 27, thereby generating a glow discharge, generating plasma, and causing a film forming reaction.

At this time, since the base body 28 is being rotated, a uniform a-Si film is formed on its surface.

Using such a film forming apparatus shown in FIG.
When films were formed under the same reaction conditions as in Examples 1 to 4, good samples as described above were obtained in all cases.

In FIG. 2, a dust trap 37 uses a filter 36 to trap powder generated during film formation to prevent it from interfering with the exhaust system.

Although microwaves are used as excitation means in the examples shown in FIGS. 1 and 2 above, excitation can be performed in the same way as microwaves by forming a DC electric field.

Furthermore, the film formation efficiency can be increased by mixing argon gas with the excitation gas.

Furthermore, in the reaction chamber (reaction vessel), high-frequency power was applied between the substrate and the counter substrate, but the film formation reaction can be performed in the same way even if DC power is applied, and DC and AC can be superimposed. By doing so, the reaction efficiency can be increased.

〔Effect of the invention〕

The present invention enables high-speed film formation while maintaining good film properties (photoconductive properties) by introducing a previously excited gas into a reaction vessel.

Furthermore, since the previously excited gas is introduced into the reaction vessel via a second introduction system that is different from the first introduction system that directly introduces the first gas containing silicon into the reaction vessel, the excitation Since the reaction caused by the state gas does not occur outside the reaction vessel, the reaction efficiency within the reaction vessel can be increased.

Further, since hydrogen gas is used as the second gas and introduced into the reaction vessel in an excited state, high-speed film formation is possible and the photoconductive properties of the a-Si film can be improved.

Furthermore, by using a mixed gas of nitrogen and hydrogen as the second gas, the a-Si film formed has a high resistance. If silane gas and nitrogen gas were introduced into a reaction vessel and film formation was performed using plasma generated by glow discharge, a large amount of electric power would be required to decompose the gases, leading to the generation of impurities. In this point, if a mixed gas of hydrogen and nitrogen is used, such a drawback does not exist.

Furthermore, the film formation rate can be increased by pre-exciting silane gas or silane gas and hydrogen gas and introducing them into the reaction vessel. in this case,
By mixing argon gas with hydrogen gas, the decomposition efficiency of silane gas can be increased, thereby enabling high-speed film formation.

Furthermore, in addition to a gas containing silicon such as silane, a gas containing a group A element (e.g. B) or a group A element (e.g. p) may be introduced directly into the reaction vessel. Then,
The semiconductor characteristics (P type or N type) of the a-Si film formed can be controlled.

Further, by providing an electrode in the reaction vessel and applying direct or high power to the electrode, the film formation rate can be increased compared to the case where the reaction of the gas in the pre-excited state is performed. In this case, by applying DC and AC power to the electrodes in a superimposed manner,
The film formation rate can be further increased.

As described above, according to the present invention, high-speed film formation is possible while improving film characteristics.

The a-Si film formed according to the present invention has high electrical resistance in the dark, so it has excellent charge retention.
In particular, the most suitable photoreceptor for electrophotography can be obtained, but other applications such as controlling the semiconductor properties and forming a multilayer a-Si film are also possible.In this case, not only the electrophotographic photoreceptor, Applications to solar cells and optical sensors are also possible.

[Brief explanation of drawings]

FIG. 1 is a schematic longitudinal sectional front view showing a film forming apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic longitudinal sectional front view showing a film forming apparatus according to another embodiment of the present invention. 1...Reaction container, 2...Substrate, 4...Electrode, 5
...High frequency power supply, 7a, 7b...Introduction pipe, 9...
Microwave application section, 16... Reaction chamber, 28... Stem body, 23, 24, 25, 26... Introductory pipe, 27...
...High frequency power supply, 31, 32...Microwave application section.

Claims (1)

[Scope of Claims] 1. A method for forming an amorphous silicon film on a substrate using radicals of a silicon-containing gas, in which a silicon-containing gas is used as a base material and an element of Group B or Group VB of the periodic table is used. A first step of introducing a first gas containing gas into a reaction vessel under reduced pressure via a first introduction system, and a mixed gas of hydrogen gas and nitrogen gas before being introduced into the reaction vessel. a second step of generating a second gas by radicalizing in advance by applying microwaves;
a third step of introducing the second gas into the reaction vessel via a second introduction system different from the first introduction system; and a third step of introducing the second gas into the reaction vessel through a second introduction system different from the first introduction system; A fourth step of forming an amorphous silicon film on the base by reacting the gas by applying either DC power or AC power between the base and a counter electrode provided opposite to the base. A method for forming an amorphous silicon film comprising the steps of. 2. The method of forming an amorphous silicon film according to claim 1, wherein the second gas is a gas containing silicon or a mixed gas of a gas containing silicon and hydrogen gas or argon gas. 3. The method of forming an amorphous silicon film according to claim 1, wherein the base has conductivity and an electrode is provided facing the base. 4. The method for forming an amorphous silicon film according to claim 1, characterized in that AC power and DC power are applied in a superimposed manner between the counter electrode and the conductive substrate.