There have been proposed a number of electrophotographic photosensitive members having a light receiving layer composed of a non-crystalline material containing silicon atoms as the main component, the so-called amorphous silicon (hereinafter referred to as "a-Si") disposed on a substrate.
And there have been proposed various methods for the preparation of such light receiving layer for the electrophotographic member using vacuum evaporation technique, heat chemical vapor deposition technique, plasma chemical vapor deposition technique, reactive sputtering technique, ion plating technique and light chemical vapor deposition technique.
Among those methods, the method using plasma vapor deposition technique (hereinafter referred to as "plasma CVD method") has been generally recognized as being the most preferred and is currently used to manufacture said light receiving layer.
However, for any of the known light receiving layers, even if an acceptable one is obtained by plasma CVD method and that exhibits almost satisfactory characteristics, there still remain problems unsolved in satisfying totally the points for its characteristics, particularly electric and optical characteristics, photoconductive characteristics, deterioration resistance upon repeating use and use-environmental characteristics. Other points relating to its homogeneity, reproducibility and mass-productivity and further points relating to its lasting stability and durability, are required to be satisfied for the photoelectric conversion layer to be a durable one.
The reasons are largely due to the fact that the light receiving layer can not be easily prepared by a simple layer deposition procedure but skill is are required in the process operations in order to obtain a desirable light receiving layer while having due regards for the starting materials.
For example, in the case of forming a film composed of an amorphous silicon material (hereinafter referred to as "a-Si") according to heat chemical vapor deposition technique (hereinafter referred to as "CVD method"), after the gaseous material containing silicon atoms being diluted, appropriate impurities are introduced thereinto and the thermal decomposition of related materials is carried out at an elevated temperature between 500.degree. and 650.degree. C.
Therefore, in order to obtain a desirable a-Si film by CVD method, precise process operation and control are required, and because of this, the apparatus in which the process according to CVD method is practiced will be eventually complicated and costly.
However, even in that case, it is extremely difficult to stably obtain a desirable light receiving layer composed of an a-Si material having abundant practically applicable characteristics on an industrial scale.
Now, although the plasma CVD method is widely used nowadays as above mentioned, it is still accompanied with problems relating to process operations and to facility investment.
Regarding the former problems, the operation conditions to be employed under the plasma CVD method are much more complicated than the known CVD method, and it is extremely difficult to generalize them.
That is, there already exist a number of variations even in correlated parameters concerning the temperature of a substrate, the amount and the flow rate of gases to be introduced, the degree of pressure and the high frequency power for forming a layer, the structure of an electrode, the structure of a reaction chamber, the flow rate of gases to be exhausted, and the plasma generation system. Besides said parameters, there also exist other kinds of parameters. Under these circumstances, in order to obtain a desirable deposited film product it is required to choose precise parameters from a great number of varied parameters. And sometimes serious problems occur. For instance, because of the precisely chosen parameters, a plasma is apt to be in an unstable state which invites problems in a deposited film to be formed.
And for the apparatus in which the process using the plasma CVD method is practiced, its structure will be eventually complicated since the parameters to be employed are precisely chosen as above stated. Whenever the scale or the kind of the apparatus to be used is modified or changed, the apparatus must be so structured as to cope with the precisely chosen parameters.
In this regard, even if a desirable deposited film should be fortuitously mass-produced, the film product becomes unavoidably costly because (1) a heavy investment is firstly necessitated to set up a particularly appropriate apparatus therefor; (2) a number of process operation parameters even for such apparatus still exist and the relevant parameters must be precisely chosen from the existing various parameters for the mass-production of such film. In accordance with such precisely chosen parameters, the process must then be carefully practiced.
Against this background, an electrophotographic photosensitive member has become diversified nowadays. And there is an increased demand to stably provide a relatively inexpensive electrophotographic photosensitive member having a light receiving layer with a normal square measure or a large square measure composed of an a-Si material which has a relevant uniformity and many applicable characteristics and which is suited for the use purpose and the application object.
Consequently, there is an earnest desire to develop an appropriate method and apparatus to satisfactorily meet the above demand.
Likewise, there is a similar situation which exists with respect to other kinds of non-monocrystalline light receiving layers for electrophotographic photosensitive member, for example, those composed of an a-Si material containing at least one kind selected from oxygen atoms, carbon atoms and nitrogen atoms [hereinafter referred to as "a-Si(H,X)(O,C,N)"].