METHOD FOR FORMING DEPOSITED FILM

Abstract: A method for forming deposited film, which comprises effecting a step [A] and another step [B] at least one time, the step [A] being the introduction of a starting material (A) which is either one of a gaseous starting material (I) for formation of a deposited film and a gaseous halogenic oxidizing agent (II) having the property of oxidative action on said starting material into a film forming space in which a substrate of which at least the surface to be filmed thereon has crystal orientability is previously arranged to have said starting material absorbed onto the surface of said substrate to form an adsorbed layer (I) and the step [B] being the introduction of the other starting material (B) into said film forming space, thereby causing the surface reaction on said absorption layer (I) to occur and form a deposited film.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a method for formation of a deposited film, which is useful for the preparation of a functional film, particularly a semiconductive deposited film being useful for uses such as semiconductor device, electronic device such as optical input sensor device for optical image inputting device, photosensitive device for electrophotography, etc. Description of the Related Art Hitherto, for functional films, particularly crystalline semiconductor films, individually suitable film forming methods have been employed from the standpoint of desired physical characteristics, uses, etc. For example, for formation of silicon deposited films such as amorphous or polycrystalline non-single crystalline silicon which are optionally compensated for lone pair electrons with a compensating agent such as hydrogen atoms (H) or halogen atoms (X), etc., (hereinafter abbreviated as "NON-Si (H,X)", particularly "A-Si (H,X)" when indicating an amorphous silicon and "poly-Si (H,X)" when indicating a polycrystalline silicon) (the so called microcrystalline silicon is included within the category of A-Si (H,X) as a matter of course), there have been attempted the vacuum vapor deposition method, the plasma CVD method, the thermal CVD method, the reactive sputtering method, the ion plating method, the optical CVD method, etc. Generally, the plasma CVD method has been used as the optimum method and industrialized. However, the reaction process in formation of a silicon deposited film according to the plasma CVD method which has been generalized in the prior art is considerably complicated as compared with the CVD method of the prior art, and its reaction mechanism involves not a few ambiguous points. Also, there are a large number of parameters for formation of a deposited film such as substrate temperature, flow rate and flow rate ratio of the introduced gases, pressure during formation, high frequency power, electrode structure, structure of the reaction vessel, speed of evacuation, plasma generating system, etc. On a count of the use of a combination of such a large number of parameters, the plasma may sometimes become unstable state, whereby marked deleterious influences were exerted frequently on the deposited film formed. Besides, the parameters characteristic of the device must be selected for each device and therefore it has been difficult to generalize the production conditions under the present situation. Also, in the case of the plasma CVD method, since plasma is generated by high frequency or microwave, etc., in the film forming space in which a substrate on which film is formed is arranged, electrons or a number of ion species generated thereby may give damages to the film in the film forming process to cause lowering in film quality or unevenness of film quality. Moreover, the conditions for crystallization of deposited film are narrow and therefore it has been deemed to be difficult to produce polycrystalline deposited films having stable characteristics. Whereas, for formation of an epitaxial deposited film such as of silicon, germanium, the group II-VI and the group III-V semiconductors, etc., there have been used the gas phase epitaxy and the liquid phase epitaxy as classified broadly (generally speaking, the strict definition of epitaxy is to grow another single crystal on a single crystal, both having the same single crystal axes, but here epitaxy is interpreted in a broader sense and it is not limited to the growth onto a single crystal substrate). The liquid phase epitaxy is a method for the deposition of a semiconductor crystal on a substrate by dissolving a starting material for semiconductor at an elevated temperature to a supersaturated state in a solvent of a metal which is molten to a liquid and cooling the solution. According to this method, since the crystals are prepared under the state most approximate to thermal equilibrium among various epitaxy techniques, crystals having high perfectness can be obtained, but on the other hand, mass productivity is poor and also the surface state is bad. For such reasons, in an optical device which requires an epitaxial layer which is thin and also uniform in thickness, problems are accompanied such as yield in device production, or influences exerted on the device characteristics, etc., and therefore this method is not frequently used. On the other hand, the gas phase epitaxy has been attempted by physical methods such as the vacuum vapor deposition method, the sputtering method, etc., or chemical methods such as hydrogen reduction of a metal chloride, or thermal pyrolysis of an organic metal or a metal hydride. Among them, the molecular ray epitaxy which is a kind of the vacuum vapor deposition method is a dry process under ultra-high vacuum, and therefore high purification and low temperature growth of crystals are possible, whereby there is the advantage that composition and concentration can be well controlled to give a relatively even deposited film. However, in addition to an enormous cost required for the film forming device, the surface defect density is great, and no effective method for controlling directionality of molecular ray has been developed, and also enlargement of area is difficult and mass productivity is not so good. Due to such many problems, it has not been industrialized yet. The hydrogen reduction method of a metal chloride or the thermal pyrolysis method of an organic metal or a metal hydride are generally called the halide CVD method, the hydride CVD method, the MO-CVD method. For these methods, since the film forming apparatus can be manufactured with relative ease and also metal chloride, metal hydrides, and organic metals being the starting materials, those with high purities are now readily available, they have been studied widely at the present time and application for various devices has been investigated. However, in these methods, it is required to heat the substrate to at least an elevated temperature at which the reduction reaction or thermal pyrolysis reaction can occur and therefore the scope of choice of the substrate material is limited, and also contamination with impurities such as carbon or halogen, etc., is liable to be caused if decomposition of the starting material is insufficient, thus having the drawback that controllability of doping is poor. Also, depending on the application use of the deposited film, it is desired to effect mass production having reproducibility with full satisfaction of enlarged area, uniformization of film thickness as well as uniformness of film quality and yet at a high speed film formation, under the present invention. However, no technique which enables mass production while maintaining practical characteristics satisfying such demands has been established yet. The present invention is directed to a solution of the problem of providing a crystalline film having uniform characteristics over a large area and exhibiting satisfactory semiconductive characteristics. It is directed to a process which is conservative in the expenditure of energy and which also is suited to simple process control. In accordance with the present invention there is provided a method for forming crystalline film on the surface of a substrate, which method comprises: providing a substrate having a crystalline surface, the lattice constant and thermal expansion coefficient characteristic of this surface being either identical with or so closely matched to those characteristic of the film material as to be able to effect crystalline orientation in said crystalline film; introducing a first gaseous material into a film forming space containing the substrate, and adsorbing an amount of said first gaseous material at the surface of the substrate; removing a surplus amount of said first gaseous material while retaining a sufficient amount of said first gaseous material adsorbed at the surface of said substrate; introducing a second gaseous material into said film forming space and reacting this with said sufficient amount of said first gaseous material adsorbed at the surface of said substrate to form the crystalline film, and which method is characterised in that: the first and second gaseous materials are one and the other of: a gaseous starting material containing a major constituent of the film to be formed, and a gaseous halogenic oxidising agent having the property of oxidating action on said gaseous starting material; and wherein flow rates of said first and second gaseous materials and temperatures and pressures during adsorption and reaction are appropriately chosen such that said reacting of said first and second gaseous materials results in the growth of film in a poly- crystalline form. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic illustration of the film forming apparatus used in Examples of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method for forming deposited film of the present invention, the gaseous starting material to be used for formation of a deposited film (hereinafter called "gaseous starting material (I)") is a material which receives oxidation action through contact with a gaseous halogenic oxidizing agent (hereinafter called "halogenic oxidizing agent (II)"), and may be selected suitably as desired depending on the kind, the characteristics, uses, etc. of the desired deposited film. In the method of the present invention, the above gaseous starting material (I) and the halogenic oxidizing agent (II) are gaseous when introduced,but may be any of gaseous, liquid or solid under ordinary state. In the case when the gaseous starting material (I) or the halogenic oxidizing agent (II) is liquid or solid under ordinary state, a carrier gas such as Ar, He, N₂, H₂, etc., is used and bubbling is effected optionally with heating to introduce either one of the gaseous starting material (I) or the halogenic oxidizing agent (II) in the gaseous state into the film forming space to form an adsorbed layer on the substrate having a crystalline surface to be subjected to a film-forming treatment, and then the other material is introduced in the gaseous state. During this operation, the introducing pressure of the above gaseous starting material (I) or the halogenic oxidizing agent (II) may be set by controlling the flow rate of the carrier gas or the vapor pressure of the gaseous starting material (I) and the halogenic oxidizing agent (II). When the gaseous starting material (I) or the halogenic oxidizing agent (II) is a gas under normal state, it can be also introduced as diluted with a carrier gas such as Ar, He, N₂, H₂, etc., if necessary. As the gaseous starting material (I) to be used in the method of the present invention, for example, for obtaining a deposited film of silicon belonging to the group IV of the periodic table, there may be employed straight and branched chain silane compounds, cyclic silane compounds, etc. As one capable of being such gaseous starting material (I), specifically, examples of the straight chain silane compounds may include Si n H 2n+2 ( n = 1, 2, 3, 4, 5, 6, 7, 8), examples of branched chain silane compounds SiH₃SiH(SiH₃)SiH₂SiH₃, and examples of cyclic silane compounds Si n H 2n ( n = 3, 4, 5, 6), etc. Of course, these silicon compounds may be used individually or two or more may be mixed together and used. The halogenic oxidizing agent (II) to be used in the method of the present invention is gaseous when introduced into the film forming space and at the same time has a property of exerting oxidation action effectively on the gaseous starting material (I) for formation of deposited film merely through contact therewith. Halogenic gases such as F₂, Cl₂, Br₂, I₂, ClF, etc., for example, are effective. Either one of these gaseous starting materials (I) or halogenic oxidizing agent (II) is first introduced in the form of a gas with desired flow rate and feeding pressure given into a film forming space in which a substrate for formation of deposited film is arranged to form an adsorbed layer on said substrate having a crystalline surface, and then the other is introduced after desired time with desired flow rate and feeding pressure given, whereby the both are collided against each other on the surface of the above adsorbed, layer to cause a surface chemical reaction to occur, whereby the above halogenic oxidizing agent (II) exerts oxidation reaction on the above gaseous starting material to form a deposited film on the substrate having the crystalline surface as mentioned above. Such deposited film forming process can proceed with better efficiency and with more saving of energy, whereby a deposited film having desired good physical characteristics over the whole film surface can be formed at a lower substrate temperature than hitherto. In the prior art technique of plasma CVD, spurious etching and/or abnormal discharge can arise during film formation. Since in this present method the deposited film is formed by a reaction with a gaseous halogenic oxidizing agent, such deleterious effects are obviated. This method for forming deposited film, which utilizes a redox reaction of a gaseous starting material (I) containing an element which is to become a major constituent element of the deposited film, with a gaseous halogenic oxidizing agent (II), thus requires no high temperature for deposition. Accordingly there is no disturbance of the film structure by heat. No heating installation is required for production and none of the expense of running the same is incurred. The film therefore can be made at a lower cost. Also it becomes possible to select the substrate material from a wide range of materials, since this choice is not dictated by the heat resistant properties of the material chosen as hitherto. Since the present method relies upon adsorption and surface reaction enlargement of area is possible and is not restricted to specific shapes and sizes of substrate. In general, the starting materials employed need only be introduced in small amounts. Accordingly, the film forming space can be chosen smaller and the yield can be improved dramatically. To summarise, energy saving during formation of deposited film can be effected and at the same time management of film quality can be easily done, whereby it becomes possible to form a good crystalline deposited film having uniform film quality and characteristics over a large area. Further, it is possible to obtain efficiently a crystalline film which is excellent in productivity and mass productivity, of high quality and also excellent in various characteristics such as electrical, optical, semiconductive characteristics, etc. So that the deposited film forming process may proceed smoothly and a film having desired physical characteristics of high quality may be formed, as the film forming factors, the kinds and combinations of the starting material (I) for formation of deposited film and the halogenic oxidizing agent (II), the pressure during the reaction, the flow rate, the inner pressure in the film forming space, the kind of the substrate, the pressure during adsorption, the flow rates of the gases, the adsorption temperature and the film forming temperature (substrate temperature and atmosphere temperature) are selected as appropriate. These film forming factors are interrelated and therefore they are not determined in isolation but are determined collectively. The process of adsorption and reaction of the gaseous starting material (I) for formation of deposited film and the gaseous halogenic oxidizing agent (II) to be introduced into the film forming space may be determined as appropriate and in relation to the film forming factors mentioned above. In adsorption of gas molecules onto a solid surface, there exists intramolecular force, and the chemical adsorption with valence energy is greater in its intramolecular force than the physical adsorption with dispersion energy (corresponding to Van der Waals force). Also, while physical adsorption is liable to become a multi-layer adsorption, a chemical adsorption is a monomolecular layer adsorption. Therefore for controlling deposition of a homogeneous thin film, chemical adsorption is preferred. However, physical adsorption and chemical adsorption of gas molecules may be considered to be inter-related in a complicated way in the processes from the formation of an adsorbed layer to the formation of a deposited film by a reaction of said adsorbed layer, and the form of adsorption is not necessarily limited. On the other hand, the factors which determine the adsorption state may include the kind of the adsorbed molecules, the kind of the solid surface and the surface state, and further temperature and pressure as controlling factors, and it is at least necessary to determine these controlling factors so that the reaction may be carried out to give a desired deposited film. That is to say, if the pressure in the vacuum chamber is too low in the course from adsorption to reaction, desorption from the state of physical adsorption is liable to occur, while if the temperature is too high, dissociating adsorption from the state of chemical adsorption is liable to occur. The reaction process therefore must be selected with care. In one cycle for formation of a deposited film the forming of an adsorbed layer and the reacting of the adsorbed layer with a starting material, prior to uniform formation of a desired deposited film on the substrate surface, can be performed by the following steps. There is a step of introducing the starting material A into the film forming space and permitting it in a suitable amount adsorbed on the substrate (a first step: Step [A]) form an adsorbed layer. And, there is further a step of permitting the starting material A to remain in the adsorbed layer and discharging superfluous starting material A (a second step). In these steps, the pressures may be set suitably for the above reasons, and the pressure in the first step [A] may be preferably higher for sufficient progress of adsorption, preferably 1.33 x 10⁻⁵ to 1.33 x 10³ Pa (1 x 10⁻⁷ to 10 Torr), more preferably 1.33 x 10⁻² to 1.33 x 10² Pa (1 x 10⁻⁴ to 1 Torr). The pressure in the second step may be preferably lower for discharging superfluous starting material A, preferably 1.33 x 10⁻⁸ to 1.33 x 10² Pa (1 x 10⁻¹⁰ to 1 Torr), more preferably 1.33 x 10⁻⁷ to 1.33 Pa (1 x 10⁻⁹ to 1 x 10⁻²) Torr. Further, one cycle for formation of the deposited film comprises subsequent to these steps a step of introducing the starting material B into the film forming space to cause the surface reaction with the adsorbed layer on the substrate to form the deposited film (a third step: Step [B]), and next a step of discharging the by-products formed other than the deposited film at this time (a fourth step), and the pressure during the reaction in the third step may be preferably higher in order to enhance the probability of contact between the starting materials A and B, but the final value is determined suitably as desired in view of reactivity. The pressure in the third step may be preferably 1.33 x 10⁻⁶ to 1.33 x 10³ Pa (1 x 10⁻⁸ to 10 Torr), more preferably 1.33 x 10⁻⁴ to 1.33 x 10² Pa (1 x 10⁻⁶ to 1 Torr). The pressure in the fourth step may be preferably 1.33 x 10⁻¹⁰ to 1.33 x 10² Pa (1 x 10⁻¹² to 1 Torr). In the method thus far described, the said steps [A] and [B] are carried out at least once. However, in some cases, the steps [A] and [B] may be repeated a desired number of times in cyclic order. At this case, the periods for the steps [A] and [B] may be equal or unequal in each cycle. For the substrate material having a crystalline surface, the following conditions are necessary for effecting crystal growth if the substrate is of different material to that of the film to be deposited: (1) The lattice constant of the single crystalline or poly-crystalline material of the substrate surface should be identical with or very approximate to the lattice constant of the deposited film; (2) The coefficients of thermal expansion of the single crystalline or poly-crystalline material of the substrate surface and the deposited film should be identical with each other or at least very nearly so. Hence, for example, as the material which would constitute the surface of a suitable substrate for obtaining a deposited film of crystalline Si, there may be used CaF₂, ZnS, Yb, Mn₃Ga, NaCoF₃, Ni₃Sn, Fe₃C, NiTe x ( x < 0.7), CoMnO₃, NiMnO₃, CuCl, AlP, Si, etc. Even when the above two conditions are barely met, by selecting the deposition conditions more adequately, a crystalline deposited film can be also obtained, and the present invention is not limited only to the materials as described above. The method of the present invention now will be considered in more detail with reference to examples. This is by way of illustration only and it is not intended that the invention should be limited by these examples. Fig. 1 shows one Example of a preferred apparatus for performing the method for formation of deposited film of the present invention. The apparatus for forming deposited film shown in Fig. 1 is classified broadly into the three parts: the main device; the discharging system; and the gas feeding system. The main device is provided with a film forming space. 101 to 108 are respectively bombs filled with the gases to be used during film formation, 101a-108a are respectively gas feeding pipes, 101b-108b are respectively mass flow controllers for controlling the flow rates of the gases from the respective bombs, 101c-108c are respectively gas pressure gauges, 101d-108d and 101e-108e are respectively valves, and 101f-108f are respectively pressure gauges indicating the pressures in the corresponding gas bombs. 120 is a vacuum chamber, having a structure such that a pipeline for introduction of gas is provided at the upper portion and a reaction space is formed downstream of the pipeline, and also having a structure such that a film forming space provided with a substrate holder 112 may be formed so that a substrate 118 may be placed as opposed to the gas introducing inlet of said pipeline. The pipeline for introduction of gas has a three-tubular arrangement structure, having from the innerside a first gas introducing pipe 109 for introducing gases for the gas bombs 101 and 102, a second gas introducing pipe 110 for introducing the gases from the gas bombs 103-105, and a third gas introducing pipe 111 for introducing the gases from the gas bombs 106-108. Feeding of the gases from the bombs to the respective introducing pipes is done through the gas feeding pipelines 123-125, respectively. The respective gas introducing pipes, the respective gas feeding pipelines, and the vacuum chamber 120 are evacuated to vacuum by a vacuum evacuating device not shown through the main vacuum valve 119. The substrate 118 can be set freely at any desired position from the respective gas introducing pipes by moving the substrate holder 112 vertically and in the directions of X and Y. The distance between the substrate and the gas introducing inlet of the gas introducing pipe may be determined appropriately in view of the kinds of the deposited film to be formed, its desired characteristics, gas flow rates, the inner pressure in the vacuum chamber, etc., but it should preferably several mm to 20 cm, more preferably about 5 mm to 15 cm. 130 is a cooling pipe for making the gas molecules of the starting material A easily adsorbable onto the substrate 118, and it is connected to the flow rate controller 131. Cooling can be also used during film formation or after film formation other than in the first and the second steps in which adsorption is effected. 113 is a heater for heating the substrate, which heats the substrate 118 to an appropriate temperature during film formation, preheats the substrate 118 before film formation, and further, after film formation, heats the film for annealing. To the heater 113 for heating the substrate is fed power from the power source 115 through the wire 114. 116 is a thermocouple for measuring the temperature of the substrate (Ts) and is connected electrically to the temperature display apparatus 117. 126 and 127 are bubblers for liquid starting materials, and used with filling of liquid starting materials 128 and 129 for formation of deposited film, respectively. When the starting materials for formation of deposited film are gases under ordinary state, it is not necessary to use bubblers for liquid starting materials. Example 1 By means of the film forming apparatus having a constitution similar to one shown in Fig. 1, a deposited film having good quality was prepared as described below. First, the vacuum chamber 120 was evacuated under sufficient baking by means of an evacuating apparatus not shown to 7x10⁻⁷ Pa (5 x 10⁻⁹ Torr). The SiH₄ filled in the bomb 101 was permitted to flow at a flow rate of 4 sccm through the gas introducing pipe 109 into the vacuum chamber 120 for 0.2 sec under the state maintained at an evacuating speed of 1.3 x 10⁻² Pa/s (0.1 mTorr/sec) by controlling the evacuating valve 119. Subsequently, the valve 101d was closed to stop feeding of the SiH₄ gas, and the evacuation valve 119 was controlled to a vacuum degree of 1.3 Pa (10 mTorr). The F₂ gas (diluted to 10% with He) filled in the bomb 107 was introduced at 5 sccm through the gas introducing pipe 111 into the vacuum chamber 120. The evacuation rate at this time was controlled to 1.1 x 10⁻¹ Pa/s (0.8 mTorr/sec) by controlling the evacuating valve 119, and after this state was maintained for 0.2 sec, the valve 107a was closed to stop feeding of F₂ gas,and the vacuum degree was maintained at 5 x 10⁻¹ Pa (4 mTorr) for 2 sec. by controlling the evacuation valve 119. As the substrate, a single crystalline silicon was used, and the substrate temperature was 340°C. For the respective samples obtained by the repetition of the above procedure, crystallinity of the deposited film was evaluated by the X-ray diffraction method and the electron beam diffraction method, whereby they were confirmed to be polycrystalline silicon films. Further, the grain size of the polycrystalline silicon determined by the Scherrar method was found to be 3.5 µm. There was substantially no variance in crystal grain sizes over the whole surface of the substrate. When the surface state of each sample was observed by a scanning type electron microscope, the smoothness was good without wavy pattern, etc., and the film thickness irregularity t was ±5% or less. Also, concerning electrical characteristics, they were formed to be superior to the polycrystalline silicon prepared according to the prior art, as summarized in Table 1. Example 2 By the use of a substrate of 5 cm x 5 cm CaF₂ single crystal, a polycrystalline Si of good quality was formed as described below by means of the deposited film forming apparatus having a constitution similar to one shown in Fig. 1. First, the vacuum chamber 120 was evacuated under sufficient baking by means of an evacuating apparatus not shown to 7 x 10⁻⁷ Pa (5 x 10⁻⁹ Torr). The SiH₄ filled in the bomb 101 was permitted to flow at a flow rate of 6 sccm through the gas introducing pipe 109 into the vacuum chamber 120 for 0.4 sec under the state maintained at an evacuating speed of 1.3 x 10⁻² Pa/s (0.1 mTorr/sec) by controlling the evacuating valve 119. Subsequently, the valve 101d was closed to stop feeding of the SiH₄ gas, and the state controlled to a vacuum degree of 5.3 x 10⁻¹ Pa (40 mTorr) by controlling the evacuating valve 119 was maintained for 3 sec. The F₂ gas (diluted to 10% with He) filled in the bomb 107 was introduced at 8 sccm through the gas introducing pipe 111 into the vacuum chamber 120. The evacuation rate at this time was controlled to 1.0 x 10⁻² Pa/s (0.8 mTorr/sec) by controlling the evacuating valve 119, and after this state was maintained for 0.4 sec, the valve 107a was closed to stop feeding of F₂ gas, and the vacuum degree was maintained at 7 x 10⁻¹ Pa (5 mTorr) for 4 sec by controlling the evacuating valve 119. The substrate temperature was 350 o C. For the respective samples obtained by the repetition of the above procedure, crystallinity of the deposited film was evaluated by the X-ray diffraction method and the electron beam diffraction method, whereby they were confirmed to be polycrystalline silicon films. Further, the grain size of the polycrystalline silicon determined by the Scherrar method was found to be about 3.3 µm. There was substantially no variance in crystal grain sizes over the whole surface of the substrate. When the surface state of each sample was observed by a scanning type electron microscope, the smoothness was good without wavy pattern, etc., and the film thickness irregularity t was ± 5% or less. Also, concerning electrical characteristics, they were formed to be superior to the polycrystalline silicon prepared according to the prior art, as summarized in Table 1. Example 3 By the use of a substrate of 5 cm x 5 cm ZnS single crystal, a polycrystalline Si of good quality was formed as described below by means of the deposited film forming apparatus having a constitution similar to one shown in Fig. 1. First, the vacuum chamber 120 was evacuated under sufficient baking by means of an evacuating device not shown to 7 x 10⁻⁷ Pa (5 x 10⁻⁹ Torr). The SiH₄ filled in the bomb 101 was permitted to flow at a flow rate of 7 sccm through the gas introducing pipe 109 into the vacuum chamber 120 for 0.5 sec under the state maintained at an evacuating speed of 1.3 x 10⁻² Pa/s (0.1 mTorr/sec) by controlling the evacuating valve 119. Subsequently, the valve 101d was closed to stop feeding of the SiH₄ gas, and the vacuum degree was maintained at 8.0 Pa (60 mTorr) for 3 sec by controlling the evacuating valve 119. The F₂ gas (diluted to 10% with He) filled in the bomb 107 was introduced at 9 sccm through the gas introducing pipe 111 into the vacuum chamber 120. The evacuation rate at this time was controlled to 1.1 x 10⁻¹ Pa/s (0.8 mTorr/sec) by controlling the evacuating valve 119, and after this state was maintained for 0.7 sec, the valve 107a was closed to stop feeding of F₂ gas, and the vacuum degree was maintained at 8.0 x 10⁻¹ Pa (6 mTorr) for 5 sec by controlling the evacuating valve 119. The substrate temperature was 370 o C. For the respective samples obtained by the repetition of the above procedure, crystallinity of the deposited film was evaluated by the X-ray diffraction method and the electron beam diffraction method, whereby they were confirmed to be polycrystalline silicon films. Further, the grain size of the polycrystalline silicon determined by the Scherrar method was found to be about 3 µm. There was substantially no variance in crystal grain sizes over the whole surface of the substrate. When the surface state of each sample was observed by a scanning type electron microscope, the smoothness was good without wavy pattern, etc., and the film thickness irregularity t was ± 5% or less. Also, concerning electrical characteristics, they were formed to be superior to the polycrystalline silicon prepared according to the prior art, as summarized in table 1. As described above, the method for forming deposited film of the present invention can form a deposited film merely by contacting a gaseous starting material with a gaseous halogenic oxidizing agent, and has the advantage of requiring particularly no reaction exciting energy from the outside. Accordingly, it becomes possible to lower the substrate temperature. Also, by heat treatment of the deposited film during film formation by means of an excited energy generating device, any desired crystalline deposited film can be formed. Further, simultaneously with saving of energy, it is possible to obtain a crystalline deposited film having uniform film quality and characteristics over a large area with easy management of the film quality. Further, a crystalline film excellent in productivity, mass productivity and having high quality with excellent electrical, optical, semiconductive, and other physical properties can be obtained with ease. Example σd (S · cm⁻¹) Electron mobility (cm/V · sec) 1 5 x 10⁻⁵ 400 2 4 x 10⁻⁵ 370 3 1 x 10⁻⁵ 310

Claims: A method for forming crystalline film on the surface of a substrate, which method comprises: providing a substrate having a crystalline surface, the lattice constant and thermal expansion coefficient characteristic of this surface being either identical with or so closely matched to those characteristic of the film material as to be able to effect crystalline orientation in said crystalline film; introducing a first gaseous material into a film forming space containing the substrate, and adsorbing an amount of said first gaseous material at the surface of the substrate; removing a surplus amount of said first gaseous material while retaining a sufficient amount of said first gaseous material adsorbed at the surface of said substrate; introducing a second gaseous material into said film forming space and reacting this with said sufficient amount of said first gaseous material adsorbed at the surface of said substrate to form the crystalline film, and which method is characterised in that: the first and second gaseous materials are one and the other of: a gaseous starting material containing a major constituent of the film to be formed, and a gaseous halogenic oxidising agent having the property of oxidating action on said gaseous starting material; and wherein flow rates of said first and second gaseous materials and temperatures and pressures during adsorption and reaction are appropriately chosen such that said reacting of said first and second gaseous materials results in the growth of film in a poly- crystalline form. A method according to claim 1, wherein it is the gaseous halogenic oxidising agent that is adsorbed onto the substrate surface. A method according to claim 1, wherein it is the gaseous starting material that is adsorbed onto the substrate surface. A method according to any preceding claim, wherein the steps of: introducing said first gaseous material; removing said surplus amount of first gaseous material; and introducing said second material, are performed repeatedly following a step of removing any surplus amount of said second gaseous material and any surplus reaction products. A method according to any preceding claim, wherein the gaseous starting material is a chain silane compound. A method according to claim 5, wherein the chain silane compound is a straight chain silane compound. A method according to claim 6, wherein the straight chain silane compound is represented by the formula Si n H 2n+2 wherein n is an integer of 1 to 8. A method according to claim 5, wherein the chain silane compound is a branched chain silane compound. A method according to any preceding claim 1 to 4, wherein said gaseous starting material is a cyclic silane compound. A method according to any preceding claim, wherein the gaseous halogenic oxidising agent comprises a halogenic gas. A method according to claim 10, wherein the gaseous halogenic oxidising agent comprises fluorine gas. A method according to claim 10, wherein the gaseous halogenic oxidising agent comprises chlorine gas. A method according to claim 10, wherein the gaseous halogenic oxidising agent is a gas containing fluorine atoms. A method claimed in any preceding claim wherein the adsorption step is carried out at a pressure of 1 x 10⁻⁴ to 1 Torr (1.33 x 10⁻² to 1.33 x 10² Pa). A method according to claim 14, wherein the pressure in the reaction space is reduced to 1 x 10⁻⁹ to 1 x 10⁻² Torr (1.33 x 10⁻⁷ to 1.33Pa) to discharge superfluous first gaseous starting material before introduction of the second gaseous starting material. A method according to claim 14 or 15, wherein the pressure in the reaction space during the reaction of the first and second gaseous starting materials is 1 x 10⁻⁶ to 1 Torr (1.33 x 10⁻⁴ to 1.33 x 10² Pa). A method as claimed in any preceding claim, wherein the substrate is monocrystalline.

Inventors: HIRAI, YUTAKA, MATSUYAM, JINSO, SAKAI, AKIRA, UEKI, MASAO
Applicants: CANON KABUSHIKI KAISHA
Application year: 1987
Main classification: C23C16
IPC codes: C23C16, H01L31, H01L21