JPH0541990B2 - - Google Patents

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for manufacturing an electrophotographic photoreceptor.

Conventional technology Conventionally, the photoconductive layer of an electrophotographic photoreceptor is made of CdS,
Fine powder such as ZnO dispersed and coated in organic matter,
Amorphous Se added with As or Te, organic semiconductors such as polyvinylcarbazole, and trinitrofluon, etc. have been used. However, it is difficult to control the material composition of amorphous Se-based materials, and there is also the problem that their properties change due to crystallization in high-temperature environments.Furthermore, it cannot be said that the materials themselves are not harmful to the human body, so they cannot be used for used materials. Problems such as the need to collect and centrally process photosensitive plates remain. Resin dispersion materials such as CdS and ZnO have the disadvantage that it is difficult to obtain high-quality images in a humid atmosphere because of their humidity dependence.
Organic photosensitive plates have the disadvantage of toxicity and poor printing durability.

Amorphous Si (hereinafter abbreviated as a-Si) has recently attracted attention as a promising material that can improve the drawbacks of these conventional technologies.
Its expected usefulness is disclosed in Publications No. 78135 and No. 54-86341.

Problems to be Solved by the Invention However, although both of the above-mentioned publications emphasize the usefulness of this material, there is no description of why it became possible to obtain the characteristics of a material useful as a photosensitive plate. That is, although conventional a-Si has excellent photoconductivity, its room temperature resistivity is n-type with 10 ⁸ to ^{10 10} Ω·cm in the non-doped state, and B ₂ H ₆ is
10 ¹² when added about 10 ^-4 mol% to SiH ₄
There have only been reports of resistance increasing up to about Ω·cm, and when the concentration is further increased, the specific resistance decreases rapidly. On the other hand, in order to obtain the chargeability required for an electrophotographic photosensitive plate, the room temperature dark specific resistance must be at least about 10 ¹³ Ω・cm or more.
It is not disclosed at all why it is possible to obtain such a dark specific resistance and maintain high photoconductivity.

The present invention is based on the development of a technique that overcomes this major problem in material technology. In other words, in addition to the previously proposed impurities for controlling the valence electrons of a-Si, such as B, P, and As, at least one group element such as oxygen is added to the a-Si, while maintaining excellent photoconductivity. This is based on the fact that it has become possible to maintain a high room temperature dark specific resistance.

Furthermore, from the viewpoint of light resistance, corona resistance, and abrasion resistance, it is described in JP-A-54-145537 that silicon nitride or silicon oxide is formed as a surface coating layer. It cannot be said that the electrophotographic properties including these are improved to a satisfactory degree.

Furthermore, the biggest drawback is that the film forming speed is extremely slow compared to other photoreceptors, making it expensive.

The purpose of the present invention is to rapidly form an electrophotographic photoreceptor having a low residual potential, excellent dark decay characteristics, corona ion resistance, and light fatigue resistance, and which does not deteriorate even after repeated use over a long period of time. .

Means for Solving the Problems The conductive support of the photoconductive layer is provided with a photoconductive layer containing amorphous silicon as a main component and at least one of group elements on a conductive support. a layer containing amorphous silicon carbide as a main component as a charge blocking layer for stabilizing the surface potential on a main surface portion on a side different from that of the photoconductive layer; An electrophotographic photoreceptor having a dark decay prevention layer mainly composed of amorphous silicon into which valence electron control impurities are introduced at a high concentration is sequentially formed by glow discharge decomposition of a raw material gas.

By mixing a raw material gas containing group elements with silane gas and forming a film on a conductive support by glow discharge decomposition, the film formation speed is seven times faster than the conventional film formation speed of amorphous silicon. We discovered that it is possible to form a film. In addition, by forming a layer mainly composed of amorphous silicon into which valence electron control impurities are introduced at a high concentration on the support side, we can simultaneously improve the dark decay characteristics and solve the new problem of residual potential generation. can do. Furthermore, by forming a layer containing amorphous silicon carbide as a main component on the surface, it is possible to provide a photoreceptor having excellent stability that can withstand repeated use.

Embodiments The present invention will be described below with reference to embodiments and drawings.

FIG. 1 is a diagram schematically showing an embodiment of an apparatus for carrying out the present invention. Reference numeral 1 designates the outer wall of the deposition apparatus, in which substrates 3, 3', etc. are installed in contact with a heating substrate holder 2, a counter electrode 4 is installed facing the substrate holder 2, and a gap between the substrate holder 2 and the counter electrode 4 is installed. A high frequency voltage or DC voltage is applied to the The raw material gas is introduced into the deposition apparatus from each container, and is ejected from distribution pipes 5, 5', etc., which have a large number of small holes (not shown) and have a large gas conductance inside to uniformly distribute the gas. The air is then exhausted from the exhaust pipe 6. When the raw material gas is introduced, the temperature inside the outer wall 1 is 10 ^-2 Torr ~
A glow discharge is performed in the range of 10 ^-7 Torr to deposit the desired amorphous film on the substrate.

7 to 13 are raw material gas cylinders, which in numerical order are SiH ₄ , CaH ₄ , PH ₃ , Ga(CH ₃ ) ₃ , B ₂ H ₅ , respectively.
Contains N ₂ O and NH ₃ . For comparison, SiH ₄ diluted with He and diluted with Ar were used interchangeably, and the container 12 contained O ₂ , N ₂ O, CO ₂
are used interchangeably for comparison, PH ₃ , B ₂ H ₆ is
For He-diluted containers and Ga(CH ₃ ) ₃ containers, the amount of gas introduced can be controlled by controlling the temperature and bubbling He. 14 to 20 are flow meters, 21 to 27 are flow control needle valves, and 28 to 34 are shutoff valves.

Using the apparatus shown in Figure 1, first Ar-diluted SiH ₄ and He
Nondoped a-Si was deposited by conventional methods using diluted SiH ₄ . The dark specific resistance of the film was distributed in the range of 10 ⁸ to 10 ¹⁰ Ω cm with no particular difference depending on the diluting gas, but the photoconductivity was about twice as high in the He diluted film as compared to the Ar diluted film. When Al was used as the substrate, the frequency of film peeling was lower with He dilution. Furthermore, when the deposited film was heated and the mass distribution of the emitted gas was analyzed, it was found that the deposited film made of Ar-diluted SiH ₄ released Ar, as previously known, but the analysis showed that Ar was emitted from the film made of He-diluted SiH ₄ . No He was detected above the background of the device.
Based on the above, the following experiment used SiH ₄ diluted with He.

Next, calculate the PH ₃ and B ₂ H ₆ concentrations for the amount of SiH ₄ .
The relationship between doping concentration and room temperature dark resistivity (ρ _D ) was investigated by varying the amount of addition from 10 ppm to 3%.
Report by Spear et al. (solid state communication)
Comminucation) 17, 1193 (1975)), and in particular, the maximum value of the room temperature dark resistivity (ρ _D ) is on the order of 10 ¹² Ω cm, and the manufacturing conditions are
It was reconfirmed that it can only be obtained within a very limited range of B ₂ H ₆ /SiH ₄ = (1±0.5)×10 ² ppm.

After verifying the conventional techniques for a-Si deposition as described above, the present invention was implemented.

Reference example In the apparatus shown in Figure 1, quartz glass, Al-deposited quartz glass, and high-purity Si single crystal plate are installed as substrates, and B ₂ H ₆ /SiH ₄ = 100ppm, N ₂ O /
A-Si doped by normal glow discharge under the conditions of SiH ₄ = approx. 5% and substrate temperature of 250°C is approximately 10 μm thick.
Deposited. Room temperature dark specific resistance from a sample in which parallel electrodes were formed by chromium vapor deposition on a deposited film on quartz glass.
10 ¹³ to 10 ¹⁴ Ω·cm was obtained. Infrared absorption measurements of samples deposited on high-purity Si single crystal plates revealed a strong absorption spectrum unique to SiO in addition to Si-H absorption. Here, FIG. 2 shows the dependence of the electrical conductivity (σ) of the amorphous silicon (a-Si) samples obtained in this reference example and the preliminary experiment described above on the amount of irradiation light.
Lines a, b, and c in the figure are respectively a non-doped sample deposited from SiH ₄ alone, a sample deposited with B ₂ H ₆ added to SiH ₄ and doped with B, and a sample deposited with B ₂ H ₆ and N ₂ O added to SiH _4. ShiB
The characteristics of the sample doped with and O are shown. The circle mark on the vertical axis of the figure indicates the dark conductivity (σ _D ). As is clear from the figure, σ _D is 10 ^-12 by doping with B.
By further doping B and O to the extent of
It has decreased to about 10 ^-14 . However, even with the addition of these impurities, each sample maintained sufficient photoconductivity.

On the other hand, as shown in FIG.
When the sample deposited with 100% is placed in a normal corona charge/photodischarge tester and a corona discharge of -7000V is performed, -
An initial dark charging surface potential of 500V was observed. Subsequently, when exposure is performed at 1ιx・sec, the surface potential attenuates,
Only a residual potential of -30V remained.

Example A substrate was placed in the apparatus shown in FIG. 1 in the same manner as in Reference Example 1, and an n ⁺ layer was deposited at a thickness of about 500 A at a substrate temperature of 250° C. by glow discharge of a mixed gas of PH ₃ /SiH ₄ =3%. Subsequently, a film doped with boron and oxygen was deposited to a thickness of about 10 μm under the conditions of Reference Example 1. In this way, as shown in FIG. 4, a photoconductive element having an n ⁺ layer 45 and a boron and oxygen doped layer 46 was formed on a quartz substrate 44 having an Al deposited film 43. When corona charging and photoconductive discharge tests were performed in the same manner as the sample in Figure 4, the initial dark band surface potential was almost the same as Reference Example 1, but subsequent exposure to 1ιx·sec showed almost no residual potential. The surface potential attenuated without any damage.
An even more remarkable difference was the difference in the dark decay characteristics of the surface charge potential. Curves d and e in FIG. 5 show the attenuation characteristics of the surface potential of the device of this example as a reference example in the dark, respectively. By introducing the highly doped layer 45 as in the device shown in FIG. 4, the dark decay characteristics during negative charging were improved, and the residual potential after light irradiation was further reduced.

However, an electrophotographic photoreceptor with such a structure,
Although it has excellent dark decay characteristics, when the charged surface potential was measured by corona discharge in the dark after repeated corona discharge and light irradiation, the initial charged potential decreased as shown by curve g in FIG.

The device structure shown in FIG. 4 was formed by the same process as in the above example, and SiH ₄ and C ₂ H ₄ gas
Glow discharge decomposition is performed by introducing it into the deposition apparatus shown in the figure.
A silicon carbide film (a-Si _1-x C _x,X ~0.7) was deposited at about 1000A. (The element structure of this example is shown in Fig. 6.
The layer 49 is made of a-Si _1-x C _x . ) Regarding the device of this example, when the dependence of the initial charging potential immediately after negative corona charging on the number of charging/photodischarge repetitions was measured, it was found that the characteristics were stabilized as shown in Figure 7f. .

The application characteristics of the film when oxygen is added to a-Si have been described in detail above. This effect of increasing dark resistance due to oxygen addition increases the flow rate of B ₂ H ₆ /SiH ₄ by approximately
When set to 100ppm, the flow rate ratio of N ₂ O/SiH ₄ is approximately 1.
It was recognized in the range of 10 ¹ from ×10 ^-4 . In other words, it is possible to continuously change the oxygen concentration from the state in which oxygen is incorporated into a-Si as a trace amount of impurity to the state as amorphous silicon oxide, and the dark resistance can be changed by adding oxygen. has increased. On the other hand, from the viewpoint of maintaining the necessary photoconductivity, N ₂ O/
It has been found that the flow rate ratio of SiH ₄ is preferably in the range of 1×10 ⁻⁴ to 4, and more preferably in the range of 10 ⁻³ to 2. On the other hand, when the flow rate ratio of N ₂ O / SiO ₄ was kept constant at about 5 × 10 ^-2 and the flow rate ratio of B ₂ H ₆ /SiH ₄ was changed, the latter became B ₂ H ₆ from 0 to about 10 ^-4 . The dark resistance increased as the value increased, and the dark resistance remained almost constant in the range from 10 ^-4 to 10 ^-2 . However, the photoconductivity hardly depended on the above-mentioned flow rate ratio of B ₂ H ₆ /SiH ₄ (0 to 10 ⁻² ) and remained almost constant within an error range.

The same effect as above was also observed when Ga(CH ₃ ) ₃ , which is considered to be another p-type dopant, was added.

The effect of adding oxygen to amorphous silicon not only improves the electrical and optical properties described above, but also brings about an engineeringly desirable effect of increasing the film growth rate. In other words, when N ₂ O is not added, the growth rate is usually about 1 μm per hour, but when N ₂ O is added to SiH ₄ at a growth rate of 10%
By adding this material, even after high-speed deposition of 7 μm for more than 1 hour, a film that maintained good specularity could be grown on the substrate instead of a film that was made up of fine powder.

In the above embodiments, N ₂ O gas was used as a source of oxygen to amorphous silicon (a-Si). However, the gas for the oxygen supply source is not limited to the upper limit, and gases that contain oxygen and cause silane (SiH ₄ ) to react with oxygen in the plasma, such as CO ₂ , can also be used. . Of course, purified oxygen may also be used.

When depositing a-Si by glow discharge decomposition, an oxygen-containing gas and a p-type impurity gas are added to the raw material gas silane (SiH ₄ ) to increase the dark resistance of the deposited a-Si. It was also revealed that the a-Si film can maintain sufficient photoconductivity, indicating that this a-Si film with high dark resistance is optimal for use as a means of converting a two-dimensional optical image into an electrostatic image. .

Conventional attempts to add oxygen to amorphous silicon include (1) PG Recomber, etc.: Proceedings (Proc), 5th International
Conference on Amorphous and Liquid Semiconductors (Intern.
Conf.on Amorphous and Liquid
Semiconductors), Taylor and Francis, London 1974,
Page245, (2) MA Passler etc.: Physical
Review Letters (Phys.Rev.Letters.41
1492, (1978), (3) Kiyohide Kamono: Institute of Electronics and Communication Engineers, Electronic Components Study Group Material CPM79-22 (1979) (4) Kazumi Maruyama et al.: Institute of Electronics and Communication Engineers, Electronic Components Study Group Material CPM79-25 (1979), etc. Some have already been reported. However, none of the above-mentioned documents describes that the dark specific resistance of amorphous silicon at room temperature can be 10 ¹³ Ω·cm or more. Furthermore, the effects of oxygen addition have only been investigated using the sputtering method and the ion beam sputtering method.If oxygen is added during deposition using these methods, the film quality obtained by the sputtering method described above is improved, and the a. -The only interpretation is that it approaches the properties of a Si film. However, in the above, there are four reasons why the properties of a-Si produced by the sputtering method, etc., which are originally inferior to those produced by the glow discharge method, are improved by oxygen addition.
Introducing two-coordinated oxygen into Si, which has a gonally coordinated structure, gives flexibility to the amorphous structure, reduces defect density, and further recombines the recombination lifetime of carriers (generated by light). It is stated that there is a possibility that the period may be extended.

As mentioned above, this is not expected with the conventional technology,
The present invention revealed that by simultaneously adding p-type impurities and oxygen to a-Si, it was possible to increase the dark specific resistance of a-Si and maintain photoconductivity, and that the above-mentioned two configurations of oxygen Considering the potential, two-coordinate additives other than oxygen, for example group elements such as sulfur, selenium, and tellurium, whose effects have not been reported so far, can also be used as material elements for the photoconductive element of the present invention. Can be used. Moreover, their addition concentrations can also be increased to concentrations leading to so-called chalcogen glasses.

In the above description of the present invention, a-Si containing hydrogen produced by glow discharge decomposition of SiH ₄ has been described. However, instead of hydrogen, it may contain other monovalent elements, such as halogen group elements.

Effects of the Invention According to the present invention, an electrophotographic photoreceptor having excellent dark decay characteristics, almost no residual potential, and excellent repeated use characteristics can be formed at a speed approximately 7 times faster than conventional methods. , high-performance photoreceptors can be provided at low cost.

[Brief explanation of drawings]

FIG. 1 is a diagram showing one embodiment of the apparatus for carrying out the present invention, FIG. 2 is a diagram showing the dependence of the electrical conductivity of undoped and doped samples on the irradiation light amount, and FIG.
4 and 4 are cross-sectional views of an electrophotographic photoreceptor in a reference example, FIG. 5 is a view showing the dark decay characteristics of the surface charge potential, and FIG. 6 is a cross-sectional view of an electrophotographic photoreceptor in an embodiment of the present invention. , FIG. 7 is a diagram showing changes in initial charging potential during repeated charging. DESCRIPTION OF SYMBOLS 1... Deposition apparatus outer wall, 2... Temperature-controlled substrate holder, 3... Substrate, 4... Electrode, 5... Gas distribution piping, 6... Exhaust hole, 7-13... Raw material gas cylinder, 1
4-20...Flowmeter, 21-27...Needle valve, 28-34...Shutoff valve, 41, 44...Substrate, 4
0, 43... Conductive film, 45... Highly doped layer, 46
...Photoconductive film, 49...Amorphous SiC.

Claims (1)

[Claims] 1. A photoconductive layer containing amorphous silicon as a main component and at least one group element is provided on a conductive support, and a main surface portion of the photoconductive layer on a side different from the conductive support is provided. In addition to having a layer mainly composed of amorphous silicon carbide as a charge blocking layer for stabilizing the surface potential, impurities for controlling valence electrons are added to the main surface of the photoconductive layer on the side in contact with the conductive support. A method for manufacturing an electrophotographic photoreceptor having a dark decay prevention layer mainly containing amorphous silicon introduced in a concentration, characterized in that the layers having the above structure are sequentially formed by glow discharge decomposition of a raw material gas. A method for manufacturing a photographic photoreceptor.