Patent Publication Number: US-2002000200-A1

Title: Chemical vapor deposition apparatus

Description:
RELATED APPLICATION DATA  
       [0001] The present application claims priority to Japanese Application No. P2000-120743 filed Apr. 21, 2000, which application is incorporated herein by reference to the extent permitted by law.  
       BACKGROUND OF THE INVENTION  
       [0002] The present invention relates to chemical vapor deposition apparatuses (hereinafter, chemical vapor deposition is referred to as CVD) and particularly to a thermal CVD apparatus for depositing a monocrystalline semiconductor thin-film by epitaxial growth.  
       [0003] A thermal CVD apparatus is known as one of the apparatuses for epitaxial growth. In general, the epitaxial growth apparatuses facilitate epitaxial growth on substrates which are placed on susceptors and heated together therewith. The epitaxial growth apparatuses are classified into horizontal apparatuses, vertical apparatuses, cylindrical apparatuses, hot wall apparatuses, cluster apparatuses, single-wafer processing apparatuses, and the like. These apparatuses are disclosed in pages 411 to 414 of “Science of Silicon” (Realize Inc.) (Chapter 5, Section 3 “Epitaxial Wafer Production Technology”).  
       [0004] Apparatuses using electromagnetic waves such as etching apparatuses by microwave plasma and plasma enhanced CVD apparatuses are also disclosed. For example, microwaves are confined in a cavity resonator or a ring cavity resonator, as disclosed in Japanese Unexamined Patent Application Publication No. 9-270386.  
       [0005] However, these epitaxial growth apparatuses have the following problems: A common problem in these apparatuses is low energy efficiency, since a substrate placed on a susceptor is indirectly heated by heating the susceptor. In other words, the susceptor must also be heated. Moreover, only the face away from the susceptor of the substrate is cooled by gas flow; hence, the substrate thermally deforms and slip defects occur in the epitaxial layer. In addition, individual apparatuses have the following problems.  
       [0006] Horizontal apparatuses and vertical apparatuses are not suitable for mass production since substrates cannot be stacked due to the structures thereof. Since cylindrical apparatuses require a considerably large reaction chamber for single-wafer processing, it is difficult to construct an apparatus large enough to meets trends towards an increase in size of the substrate. Hot wall apparatuses strongly heat the periphery of the substrate by the skin effect in high-frequency induction heating. Although the temperature gradient is moderated by heat conduction in the substrate and heat radiation from the upper and lower substrates, it takes a significant amount of time for the temperature distribution to become uniform, thus impairing volume efficiency. Since radiant heating using a halogen lamp strongly heats the periphery of the substrate, it takes a significant amount of time for the temperature distribution to become uniform, thus impairing volume efficiency. The single-wafer process which basically processes a single wafer at a time does not have volume efficiency.  
       SUMMARY OF THE INVENTION  
       [0007] Accordingly, it is an object of the present invention to provide a chemical vapor deposition apparatus which does not have the above problems.  
       [0008] According to a first aspect of the present invention, a chemical vapor deposition apparatus comprises a reaction chamber for forming a thin film on a face of a substrate placed therein; and a substrate heater having an electromagnetic wave generator connecting to the reaction chamber for supplying electromagnetic waves to the reaction chamber.  
       [0009] The chemical vapor deposition apparatus according to the first aspect has the electromagnetic wave generator which connects to the reaction chamber and supplies electromagnetic waves to the reaction chamber. The substrate placed in the reaction chamber is heated by electromagnetic waves which are supplied from the electromagnetic wave generator. The heating source using electromagnetic waves simultaneously and uniformly heats a plurality of substrates placed in the reaction chamber in a short time.  
       [0010] Preferably, the chemical vapor deposition apparatus further comprises a holder for holding the substrate in the reaction chamber, the holder having an opening in a region the substrate is placed.  
       [0011] In this chemical vapor deposition apparatus, the substrate is held on the holder having the opening so that the back face of the substrate lies at the opening. Thus, the two faces of the substrate held on the holder are exposed. Since the substrate selectively consumes electromagnetic wave energy in the region in which it is held, the substrate can be heated using less energy.  
       [0012] Preferably, the substrate and the holder are arranged such that a structure constituted by the substrate and the holder confines the electromagnetic waves.  
       [0013] A plurality of substrates may be arrayed three-dimensionally in this configuration and may be treated simultaneously.  
       [0014] According to a second aspect of the present invention, a chemical vapor deposition apparatus comprises a cavity resonator for placing a substrate therein; and a substrate heater having an electromagnetic wave generator connecting to the cavity resonator for supplying electromagnetic waves to the cavity resonator.  
       [0015] The chemical vapor deposition apparatus according to a second aspect has the electromagnetic wave generator which connects to the cavity resonator and supplies electromagnetic waves to the cavity resonator. The substrate placed in the cavity resonator is heated by electromagnetic waves which are supplied from the electromagnetic wave generator to the cavity resonator. The heating source using electromagnetic waves can simultaneously and uniformly heat a plurality of substrates placed in the cavity resonator in a short time.  
       [0016] Preferably, the chemical vapor deposition apparatus further comprises a holder for holding the substrate in the cavity resonator, the holder being provided with an opening in the region the substrate is placed.  
       [0017] In this chemical vapor deposition apparatus, the substrate is held on the holder having the opening so that the back face of the substrate lies at the opening. Thus, the two faces of the substrate held on the holder are exposed. Since the substrate selectively consumes electromagnetic wave energy in a region holding the substrate, the substrate can be heated by reduced energy.  
       [0018] Preferably, the substrate and the holder are arranged so that a structure constituted by the substrate, the holder, and the cavity resonator confines the electromagnetic waves.  
       [0019] In such a configuration, a plurality of substrates may be arrayed three-dimensionally and may be treated simultaneously.  
       [0020] Preferably, the internal face of the cavity resonator is covered with a coating film which comprises a corrosion-resistant material and which reflects radiation (primarily infrared radiation) from the heated substrate.  
       [0021] The coating applied on the internal face of the cavity resonator enhances confinement effects of radiation (primarily infrared radiation) from the heated substrate. Thus, the input energy is more effectively used for heating the substrate. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0022]FIG. 1 is a partially cut-away isometric view of an overall configuration of a first CVD apparatus according to the first aspect of the present invention;  
     [0023]FIG. 2 is a partially enlarged cross-sectional view of a holder of the first thermal CVD apparatus shown in FIG. 1;  
     [0024]FIG. 3 is a partially cut-away isometric view of an overall configuration of a second thermal CVD apparatus according to a second aspect of the present invention;  
     [0025]FIG. 4A is a partially cut-away isometric view of an overall configuration of a third thermal CVD apparatus according to the second aspect of the present invention; and FIG. 4B is an enlarged cross-sectional view taken from line IVB-IVB in FIG. 4A;  
     [0026]FIG. 5 is a partially cut-away isometric view of an overall configuration of a fourth thermal CVD apparatus according to the second aspect of the present invention;  
     [0027]FIG. 6 is an outline diagram illustrating a configuration of an electromagnetic wave generator;  
     [0028]FIG. 7 is another outline diagram illustrating a configuration of an electromagnetic wave generator;  
     [0029]FIG. 8 is a partially cut-away isometric view of an overall configuration of an eighth thermal CVD apparatus according to the second aspect of the present invention; and  
     [0030]FIG. 9 is a partially cut-away isometric view of an overall configuration of a ninth thermal CVD apparatus according to the second aspect of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0031] First Thermal CVD Apparatus  
     [0032] The chemical vapor deposition apparatus according to the first aspect in accordance with the present invention (hereinafter referred to as a first thermal CVD apparatus) will be described with reference to FIG. 1 which is a partially cut-away view of an overall configuration thereof and FIG. 2 is a partially enlarged cross-sectional view of a component.  
     [0033] With reference to FIG. 1, the first thermal CVD apparatus  1  heats a substrate (hereinafter referred to as a silicon substrate) in a reaction chamber to an elevated temperature of approximately 1,000° C. and supplies a silicon-containing compound to the reaction chamber. Thin-film monocrystalline silicon is formed and is deposited onto the silicon substrate by pyrolysis of the silicon-containing compound.  
     [0034] As shown in FIG. 1, the thermal CVD apparatus  1  is provided with a reaction chamber  11  formed of, for example, synthetic quartz. In the interior of the reaction chamber  11 , a plurality of holders, for example, five holders  21  are vertically arranged so that a plurality of silicon substrates  51  may be placed thereon. These holders  21  are arranged at predetermined intervals by a holder supporter  26 . The holders  21  will be described below in detail. An electromagnetic wave generator  12  is connected to a side face of the reaction chamber  11 . The electromagnetic wave generator  12  supplies electromagnetic waves to the interior of the reaction chamber  21 . For example, a magnetron is used as the electromagnetic wave generator  12 . The oscillation frequency thereof is in the microwave or millimeter band. In this embodiment, 2.46 GHz microwaves are generated as an example. The reaction chamber  11  is connected to a gas supply pipe  13  and a gas exhaust pipe  14  The holders  21  will now be described. With reference to FIG. 2, each holder  21  supported by the holder supporter  26  has an opening  22  at a position for placing each silicon substrate  51 . Each holder  21  is formed of a conductive material such as silicon carbide (SiC) which is durable at elevated temperatures such as 1,000° C. When the holder  21  is composed of a material having an electric conductivity which is substantially the same as that of the silicon substrate  51 , the holder  21  is heated together with the silicon substrate  51  without heat being dissipated from the silicon substrate  51 . Thus, a state in which the silicon substrate  51  has a uniform temperature can be readily achieved.  
     [0035] When the silicon substrate  51  is circular, the diameter of the opening  22  formed in each holder  21  is several mm to ten and several mm shorter than the diameter of the silicon substrate  51 . When the substrate is rectangular, the length is several mm to ten and several mm shorter than the length of the substrate, although this is not clearly indicated on the drawing.  
     [0036] The arrangement of the silicon substrates  51  is such that the vertical distance between the silicon substrates  51  is, for example, ½ or ¼ of the wavelength of electromagnetic waves, or an integral multiple of the wavelength of the electromagnetic waves, in which case the distance would actually be 61 mm. The horizontal distance between the silicon substrates  51  is, for example, an integral multiple of the wavelength or ½ or ¼ of the wavelength of the electromagnetic waves, in which case the distance would actually be 61 mm.  
     [0037] The silicon substrates  51  placed in the reaction chamber  11  are arrayed three-dimensionally in the first thermal CVD apparatus  1 ; hence the silicon substrates  51  are irradiated and heated with electromagnetic waves supplied from the electromagnetic wave generator  12 . The electromagnetic waves scattered from the silicon substrates  51  are interfered to form a photonic band. Thus, electromagnetic waves are confined in the vicinity of the silicon substrates  51  to effectively heat the silicon substrates  51 .  
     [0038] In the formation of the thin-film monocrystalline silicon in the first thermal CVD apparatus  1 , the silicon substrate  51  is supported on each holder  21  in the reaction chamber  11  which is hated to an elevated temperature of approximately 1,000° C. by electromagnetic waves supplied from the electromagnetic wave generator  12  while a silicon-containing compound is fed to the reaction chamber  11  through the gas supply pipe  13  so as to deposit silicon on the silicon substrate  51  by pyrolysis. As the siliconcontaining compounds, gases, such as SiCl 4 , SiHCl 3 , SiH 2 Cl 2 , and SiH 4 , are generally used. These gases are diluted with hydrogen gas and are fed into the reaction chamber  11 , while the excess silicon-containing gas in the reaction chamber  11  is expelled through the gas exhaust pipes  14  provided on a side wall of the reaction chamber  11 .  
     [0039] The first thermal CVD apparatus  1  does not require a susceptor, which is essential for holding the silicon substrates in conventional chemical vapor deposition apparatuses. Since energy required for heating the susceptor can be used for heating the silicon substrate, the energy can be more effectively used. Moreover, the holder  21  having the opening  22  is used instead of the susceptor. Thus, thin-film monocrystalline silicon can be simultaneously formed on the upper and lower faces of the silicon substrate  51 , resulting in high volume efficiency.  
     [0040] In contrast, in other deposition apparatuses which place silicon substrates on susceptors, the front face of each silicon substrate is primarily cooled by a hydrogen carrier, resulting in deformation of the substrate. For example, a known hot wall apparatus of an induction heating system heats only the periphery of the silicon substrate by the skin effect; hence, a large temperature gradient occurs in the silicon substrate, causing deformation. The gradient results in stresses which induce slip defects.  
     [0041] The first thermal CVD apparatus  1 , however, holds the silicon substrate  51  on the periphery of the opening  22  of the holder  21 ; hence, the two faces of the silicon substrate  51  are exposed. Since the two faces of the silicon substrate  51  are simultaneously heated by electromagnetic waves (for example, microwaves), only slight deformation occurs in the silicon substrate  51 . Moreover, the faces of the silicon substrate  51  can be heated by electromagnetic waves with a uniform intensity distribution. Thus, high-quality thin-film monocrystalline silicon having fewer defects can be formed.  
     [0042] In an induction heating type CVD apparatus which has high volume efficiency by stacking silicon substrates as in the first thermal CVD apparatus  1 , only the periphery of each silicon substrate is heated by the skin effect. Thus, a large temperature gradient occurs in the silicon substrate. Although this temperature gradient is moderated by thermal conduction of the silicon substrate and radiant heat from the silicon substrate, it takes too long to make the temperature of the silicon substrate uniform, thus the problem of reduced volume efficiency arises.  
     [0043] Since in the first thermal CVD apparatus  1 , the silicon substrates  51  can be stacked on the holders  21 , many silicon substrates  51  can be subjected to deposition simultaneously. Accordingly, this deposition apparatus has remarkably high volume efficiency.  
     [0044] The silicon substrate is held horizontally in this embodiment. Alternatively, the silicon substrate may be tilted at an appropriate angle by rotating the overall apparatus. When the silicon substrate is held perpendicularly, the formation of slip defects caused by flexure stress which occurs due to the weight of the silicon substrate is suppressed at elevated temperatures such as 1,0000° C.  
     [0045] Second Thermal CVD Apparatus  
     [0046] A first embodiment of the chemical vapor deposition apparatus according to a second aspect in accordance with the present invention (hereinafter referred to as a second thermal CVD apparatus) will be described with reference to FIG. 3 which is a partially cut-away view of an overall configuration thereof. The same components illustrated in the former embodiment are referred to as the same reference numerals.  
     [0047] The second thermal CVD apparatus heats the substrate (hereinafter referred to as a silicon substrate) to an elevated temperature of approximately 1,000° C. and supplies a silicon-containing compound into the cavity resonator. Thin-film monocrystalline silicon is deposited on the silicon substrate by pyrolysis. In this embodiment, the reaction chamber  11  in the first thermal CVD apparatus  1  is replaced with a cylindrical cavity resonator.  
     [0048] With reference to FIG. 3, the second thermal CVD apparatus  2  is provided with a ring cavity resonator  31 . The cavity resonator  31  is formed of, for example, aluminum, copper, or stainless steel having an electrical conductivity, which is higher than that of the silicon substrate  51 . However, the use of the cavity resonator  31  of aluminum and copper restricts the types of gases used in the film deposition. That is, gases which do not contain corrosive components are used. The internal face of the cavity resonator  31  of aluminum or copper may be coated with gold. However, in a cavity resonator formed of stainless steel having high corrosion resistance, gold coating is unnecessary except that gas containing a component causing corrosion of stainless steel is used.  
     [0049] Holders  21  are arranged into a plurality of layers (for example, eight layers), each supporting a silicon substrate  51 , in the interior of the cavity resonator  31 . These holders  21  are supported by holder supporters  26  at a predetermined interval. In this embodiment, the silicon substrates  51  are unidimensionally arranged. Of course, the silicon substrates  51  may be arrayed two-dimensionally or three-dimensionally.  
     [0050] An electromagnetic wave generator  12  for supplying electromagnetic waves to the cavity resonator  31  via a waveguide  36  is connected to a side wall of the cavity resonator  31 . This means the electromagnetic wave generator  12  is placed at the incident end of the waveguide  36 . A magnetron is used, for example, as the electromagnetic wave generator  12 . The oscillation frequency thereof is in the microwave or millimeter band. In this embodiment, 2.46 GHz microwaves, for example, are used. In order to prevent reflection of the electromagnetic waves towards the electromagnetic wave generator  12  as the electromagnetic wave source, the waveguide  36  connecting the electromagnetic wave generator  12  and the cavity resonator  31  is provided with an isolator  38 .  
     [0051] A plurality of gas supply pipes  13  and a plurality of gas exhaust pipes  14  are connected to the side wall of the cavity resonator  31 . It is preferable that the diameters of each gas supply pipe  13  and each gas exhaust pipe  14  be smaller than the wavelength of the electromagnetic waves in order to prevent leakage of the electromagnetic waves from the cavity resonator  31 . The position of the connection of each pipe in the cavity resonator  31  preferably corresponds to a position of an antinode having a maximum amplitude of the standing wave of the electromagnetic waves, that is, a position with minimized current flow in the wall of the cavity resonator  31 . Thus, each gas supply pipe  13  and each gas exhaust pipe  14  are connected at an intermediate height between the upper and lower silicon substrates  51  in the second thermal CVD apparatus  2 . The diameters of each gas supply pipe  13  and each gas exhaust pipe  14  are, for example, 10 mm or less.  
     [0052] The holders  21  will be described. Each holder  21  is provided with an opening  22  at a position for placing the silicon substrate  51 . Each holder  21  is formed of a conductive material such as silicon carbide (SiC) which is durable at elevated temperatures such as 1,000° C. When the holder  21  is composed of a material having an electric conductivity which is lower than that of the cavity resonator  31  and is substantially the same as that of silicon, the holder  21  is heated together with the silicon substrate  51  without heat being dissipated from the silicon substrate  51 . Thus, a state in which the silicon substrate  51  has a uniform temperature can be readily achieved.  
     [0053] When the silicon substrate  51  is circular, the diameter of the opening  22  formed in each holder  21  is several mm to ten and several mm shorter than the diameter of the silicon substrate  51 . When the substrate is rectangular, the length is several mm to ten and several mm shorter than the length of the substrate, although this is not clearly indicated on the drawing.  
     [0054] The arrangement of the silicon substrates  51  is such that the vertical distance between the silicon substrates  51  is, for example, ½ or ¼ of the wavelength of electromagnetic waves, or an integral multiple of the wavelength of the electromagnetic waves, in which case the distance would actually be 61 mm. When the silicon substrates  51  are also arrayed in the horizontal direction, the horizontal distance between the silicon substrates  51  is, for example, an integral multiple of the wavelength or ½ or ¼ of the wavelength of the electromagnetic waves.  
     [0055] The silicon substrates  51  placed in the reaction chamber  11  are arrayed three-dimensionally in the second thermal CVD apparatus  2 ; hence the silicon substrates  51  are irradiated and heated with electromagnetic waves supplied from the electromagnetic wave generator  12  via the waveguide  36 . The electromagnetic waves leaked from the silicon substrates  51  are confined in the cavity resonator  31  and are used for heating the silicon substrates  51 . Thus, electromagnetic waves are confined in the vicinity of the silicon substrates  51  to effectively heat the silicon substrates  51 .  
     [0056] In order to prevent heating of the cavity resonator  31  by radiation from the silicon substrates  51  which are heated to an elevated temperature, the inner face of the cavity resonator  31  is polished so that the surface roughness is {fraction (1/10)} or less the wavelength of the electromagnetic waves. Since the inner face of the cavity resonator  31  is polished, radiant waves are confined in the cavity resonator  31  and are used for heating the silicon substrates  51 .  
     [0057] The resonance mode in the cavity resonator  31  is determined by the silicon substrates  51  and the cavity resonator  31 . The electromagnetic waves induce a current I which flows in the silicon substrates  51  and the cavity resonator  31  and heats the silicon substrates  51  and the cavity resonator  31 . Supposing the resistance is R, then the heat divergence is in proportion to RI 2 . Thus, the heat divergence in the silicon substrates  51  is larger than that in the cavity resonator  31 . As a result, the energy of the electromagnetic waves is effectively absorbed in the silicon of the silicon substrates  51  and is not substantially absorbed in the cavity resonator  31 . Since the temperature of the cavity resonator  31  is not substantially elevated, amorphous silicon etc. is not substantially deposited on the side wall of the cavity resonator  31  during the film deposition.  
     [0058] In other methods for placing silicon substrates on susceptors, a face of each silicon substrate is cooled by primarily a hydrogen carrier, causing deformation of the silicon substrate. An induction heating type hot wall apparatus heats only the periphery of a silicon substrate by the skin effect; hence, the silicon substrate has a large temperature gradient which generates deformation. Moreover, the stress generated by the deformation induces slip defects. Since the holders  21  are used in the second thermal CVD apparatus  2  such that the two sides of each silicon substrate  51  are exposed on each holder, the two faces of the silicon substrate  51  are simultaneously cooled. Thus, deformation barely forms in the silicon substrate  51 . Moreover, the faces of the silicon substrate  51  can be heated by electromagnetic waves with a uniform intensity distribution. Thus, high-quality thin-film monocrystalline silicon having fewer defects can be formed on the silicon substrate  51 .  
     [0059] In the formation of the thin-film monocrystalline silicon in the second thermal CVD apparatus  2 , the silicon substrate  51  is supported on each holder  21  in the cavity resonator  31  which is hated to an elevated temperature of approximately 1,000° C. by electromagnetic waves supplied from the electromagnetic wave generator  12  while a silicon-containing compound is fed to the reaction chamber  11  through the gas supply pipe  13  so as to deposit silicon on the silicon substrate  51  by pyrolysis. As the siliconcontaining compounds, gases, such as SiCl 4 , SiHCl 3 , SiH 2 Cl 2 , and SiH 4 , are generally used. These gases are diluted with hydrogen gas and are fed into the cavity resonator  31 , while the excess silicon-containing gas in the cavity resonator  31  is expelled through the gas exhaust pipes  14  provided on a side wall of the cavity resonator  31 .  
     [0060] It is preferable that the diameters of each gas supply pipe  13  and each gas exhaust pipe  14  be smaller than the wavelength of the electromagnetic waves in order to prevent leakage of the electromagnetic waves. The positions of the connections of each gas supply pipe  13  and each gas exhaust pipe  14  in the cavity resonator  31  preferably correspond to the position of an antinode having a maximum amplitude of the standing wave of the electromagnetic waves, that is, positions showing a minimized current flow in the wall of the cavity resonator  31 . Thus, each gas supply pipe  13  and each gas exhaust pipe  14  are connected at an intermediate height between the upper and lower silicon substrates  51  in the second thermal CVD apparatus  2 . The diameters of each gas supply pipe  13  and each gas exhaust pipe  14  are, for example, 10 mm or less.  
     [0061] The second thermal CVD apparatus  2  does not require a susceptor, which is essential for holding the silicon substrates in conventional chemical vapor deposition apparatuses. Since energy required for heating the susceptor can be used for heating the silicon substrate, the energy can be more effectively used. Moreover, the holder  21  having the opening  22  is used instead of the susceptor. Thus, thin-film monocrystalline silicon can be simultaneously formed on the upper and lower faces of the silicon substrate  51 , resulting in high volume efficiency.  
     [0062] Meanwhile, an induction heating type CVD apparatus having high volume efficiency by stacking silicon substrates as in the second thermal CVD apparatus  2 , the silicon substrates have large temperature gradients since only the peripheries thereof are heated by the skin effect. Although this temperature gradient is moderated by thermal conduction of the silicon substrate and radiant heat from the silicon substrate, it takes too long to make the temperature of the silicon substrate uniform, thus the problem of reduced volume efficiency arises.  
     [0063] The second thermal CVD apparatus  2 , however, holds the silicon substrate  51  on the periphery of the opening  22  of the holder  21 ; hence, the two faces of the silicon substrate  51  are exposed. Since the two faces of the silicon substrate  51  are simultaneously heated by electromagnetic waves (for example, microwaves), only slight deformation occurs in the silicon substrate  51 . Moreover, the faces of the silicon substrate  51  can be heated by electromagnetic waves with a uniform intensity distribution. Thus, high-quality thin-film monocrystalline silicon having fewer defects can be formed.  
     [0064] Since in the above second thermal CVD apparatus  2 , the silicon substrates  51  are stacked on the holders  21 , many silicon substrates  51  can be simultaneously subjected to deposition. Thus, the deposition apparatus has high volume efficiency.  
     [0065] The use of a material, having a resistivity which is smaller than that of the silicon substrate  51 , in the cavity resonator  31  enables effective heating of the silicon substrate  51  without substantially heating the cavity resonator  31 . Thus, the silicon substrate  51  can be heated using less energy.  
     [0066] In the cavity resonator  31  formed of a material having high reflectance for radiation (mainly infrared rays) from the heated silicon substrates  51 , the radiation from the silicon substrates  51  can be effectively confined in the cavity resonator  31 . Since the confined radiation is thereby used for heating the silicon substrates  51 , the utilization efficiency of energy is enhanced.  
     [0067] The silicon substrate is held horizontally in this embodiment. Alternatively, the silicon substrate may be tilted at an appropriate angle by rotating the overall apparatus. When the silicon substrate is held perpendicularly, the formation of slip defects caused by flexure stress which occurs due to the weight of the silicon substrate is suppressed at elevated temperatures such as  
     [0068] Third Thermal CVD Apparatus  
     [0069] A second embodiment of the chemical vapor deposition apparatus according to the second aspect in accordance with the present invention (hereinafter referred to as a third thermal CVD apparatus) will be described with reference to FIG. 4A which is a partially cut-away cross-sectional view of an overall configuration thereof and FIG. 4B which is an enlarged cross-sectional view taken from line IVB-IVB in FIG. 4A. The same components illustrated in the former embodiments are referred to using the same reference numerals.  
     [0070] The third thermal CVD apparatus heats the substrate (hereinafter referred to as a silicon substrate) to an elevated temperature of approximately 1,000° C. and supplies a silicon-containing compound into the cavity resonator. Thin-film monocrystalline silicon is deposited on the silicon substrate by pyrolysis. In this embodiment, the cavity resonator is of a ring type, and the ring cavity resonator is connected to a waveguide with a T-shaped coupler to transmit the electromagnetic waves to the ring cavity resonator.  
     [0071] With reference to FIG. 4A, the third thermal CVD apparatus  3  is provided with a ring cavity resonator  33 . The ring cavity resonator  33  is formed of, for example, aluminum, copper, or stainless steel, which has an electrical conductivity higher than that of the silicon substrate  51 . However, the ring cavity resonator  33  of aluminum and copper restricts the types of gases used in the film deposition. That is, gases which do not contain corrosive components are used. Thus, in the ring cavity resonator  33  of aluminum or copper, the internal face thereof is coated with gold. However, in a ring cavity resonator formed of stainless steel having high corrosion resistance, gold coating is unnecessary except that gas containing a component causing corrosion of stainless steel is used.  
     [0072] Holders  21  are arranged at a plurality of places (for example, three places) into a plurality of layers (for example, seven layers), each supporting a silicon substrate  51 , in the interior of the ring cavity resonator  33 . These holders  21  are supported by holder supporters (not shown in the drawings) at a predetermined interval. In this embodiment, the silicon substrates  51  are rectangular and are unidimensionally arranged in one holder group. Of course, the silicon substrates  51  may be arrayed two-dimensionally or three-dimensionally in the same holder group.  
     [0073] The output end of the waveguide  36  is connected to a side wall of the ring cavity resonator  33  with the T-shaped coupler  40  while the input end of the waveguide  36  is connected to an electromagnetic wave generator  12  for supplying electromagnetic waves to the ring cavity resonator  33 . A magnetron is used, for example, as the electromagnetic wave generator  12 . The oscillation frequency thereof is in the microwave or millimeter band. In this embodiment, 2.46 GHz microwaves, for example, are used. In order to prevent reflection of the electromagnetic waves from the ring cavity resonator  33  to the electromagnetic wave generator  12  as the electromagnetic wave source, the waveguide  36  is provided with an isolator  38 .  
     [0074] A plurality of gas supply pipes  13  is connected to a side wall of the ring cavity resonator  33  at the position of each holder group including a plurality of stacked holders  21 , whereas a plurality of gas exhaust pipes  14  is connected to another side wall of the ring cavity resonator  33  at the position opposing the plurality of gas supply pipes  13 .  
     [0075] It is preferable that the diameters of each gas supply pipe  13  and each gas exhaust pipe  14  be smaller than the wavelength of the electromagnetic waves in order to prevent leakage of the electromagnetic waves from the ring cavity resonator  33 . The position of the connection in the ring cavity resonator  33  preferably corresponds to the position of an antinode having a maximum amplitude of the standing wave of the electromagnetic waves, that is, a position showing a minimized current flow in the wall of the ring cavity resonator  33 . Thus, each gas supply pipe  13  and each gas exhaust pipe  14  are connected at an intermediate height between the upper and lower silicon substrates  51  in this third thermal CVD apparatus  3 . The diameters of each gas supply pipe  13  and each gas exhaust pipe  14  are, for example, 10 mm or less. The position of each silicon substrate  51  and the positions of each gas supply pipe  13  and each gas exhaust pipe  14  may have an appropriate angle to the central axis of the waveguide  36 .  
     [0076] The silicon substrate is held horizontally in this embodiment. Alternatively, the silicon substrate may be tilted at an appropriate angle by rotating the overall apparatus. When the silicon substrate is held perpendicularly, the formation of slip defects caused by flexure stress which occurs due to the weight of the silicon substrate is suppressed at elevated temperatures such as 1,000° C.  
     [0077] The holders  21  will be described. Each holder  21  is provided with an opening  22  at a position for placing the silicon substrate  51 . Each holder  21  is formed of a conductive material such as silicon carbide (Sic) which is durable at elevated temperatures such as 1,000° C. When the holder  21  is composed of a material having an electric conductivity which is lower than that of the ring cavity resonator  33  and is substantially the same as that of silicon, the holder  21  is heated together with the silicon substrate  51  without heat being dissipated from the silicon substrate  51 . Thus, a state in which the silicon substrate  51  has a uniform temperature can be readily achieved.  
     [0078] When the silicon substrate  51  is circular, the diameter of the opening  22  formed in each holder  21  is several mm to ten and several mm shorter than the diameter of the silicon substrate  51 . When the substrate is rectangular, the length is several mm to ten and several mm shorter than the length of the substrate, although this is not clearly indicated on the drawing.  
     [0079] The arrangement of the silicon substrates  51  is such that the vertical distance between the silicon substrates  51  is, for example, ½ or ¼ of the wavelength of electromagnetic waves, or an integral multiple of the wavelength of the electromagnetic waves, in which case the distance would actually be 61 mm. When the silicon substrates  51  are also arrayed in the horizontal direction, the horizontal distance between the silicon substrates  51  is, for example, an integral multiple of the wavelength or ½ or ¼ of the wavelength of the electromagnetic waves.  
     [0080] In order to prevent heating of the ring cavity resonator  33  by radiation from the silicon substrates  51  which are heated to an elevated temperature, the inner face of the ring cavity resonator  33  is polished so that the surface roughness is {fraction (1/10)} or less the wavelength of the electromagnetic waves. Since the inner face of the ring cavity resonator  33  is polished, radiant waves are confined in the ring cavity resonator  33  and are used for heating the silicon substrates  51 .  
     [0081] The resonance mode in the ring cavity resonator  33  is determined by the silicon substrates  51  and the ring cavity resonator  33 . The electromagnetic waves induce a current I which flows in the silicon substrates  51  and the ring cavity resonator  33 , and heats the silicon substrates  51  and the ring cavity resonator  33 . Supposing the resistance is R, then the heat divergence is in proportion to RI 2 . Thus, the heat divergence in the silicon substrates  51  is larger than that in the ring cavity resonator  33 . As a result, the energy of the electromagnetic waves is effectively absorbed in the silicon of the silicon substrates  51  and is not substantially absorbed in the ring cavity resonator  33 . Since the temperature of the ring cavity resonator  33  is not substantially elevated, amorphous silicon etc. is not substantially deposited on the side walls of the ring cavity resonator  33  during the film deposition.  
     [0082] In the formation of the thin-film monocrystalline silicon in the third thermal CVD apparatus  3 , the silicon substrate  51  is supported on each holder  21  in the ring cavity resonator  33  which is hated to an elevated temperature of approximately 1,000° C. by electromagnetic waves supplied from the electromagnetic wave generator  12  while a silicon-containing compound is fed to the reaction chamber  11  through the gas supply pipe  13  so as to deposit silicon on the silicon substrate  51  by pyrolysis. As the silicon-containing compounds, gases, such as SiCl 4 , SiHCl 3 , SiH 2 Cl 2 , and SiH 4 , are generally used. These gases are diluted with hydrogen gas and are fed into the ring cavity resonator  33 , while the excess silicon-containing gas in the ring cavity resonator  33  is expelled through the gas exhaust pipes  14  provided on a side wall of the cavity resonator  33 .  
     [0083] It is preferable that the diameters of each gas supply pipe  13  and each gas exhaust pipe  14  be smaller than the wavelength of the electromagnetic waves in order to prevent leakage of the electromagnetic waves. The positions of the connections of each gas supply pipe  13  and each gas exhaust pipe  14  in the ring cavity resonator  33  preferably correspond to the position of an antinode having a maximum amplitude of the standing wave of the electromagnetic waves, that is, positions showing a minimized current flow in the wall of the ring cavity resonator  33 . Thus, each gas supply pipe  13  and each gas exhaust pipe  14  are connected at an intermediate height between the upper and lower silicon substrates  51  in the third thermal CVD apparatus  3 . The diameters of each gas supply pipe  13  and each gas exhaust pipe  14  are, for example, 10 mm or less.  
     [0084] The gas supplied through these gas supply pipes  13  flows as layered streams between the silicon substrates  51  and is pyrolyzed on the silicon substrates  51  to form thin-film monocrystalline silicon. In this third thermal CVD apparatus  3 , the gas flows in the direction perpendicular to the arrangement or the longitudinal direction of the substrate, instead of a flow in the direction of the arrangement or the longitudinal direction of the substrate, as in a transverse epitaxial deposition apparatus; hence, thin-film monocrystalline silicon having a uniform thickness is readily obtainable. By depositing the film by reversing the directions of the inlet and outlet of the gas, the resulting thin-film monocrystalline silicon has a more uniform thickness.  
     [0085] The third thermal CVD apparatus  3  does not require a susceptor, which is essential for any conventional chemical vapor deposition apparatus. Since energy required for heating the susceptor can be used for heating the silicon substrate, the energy can be more effectively used. Moreover, the holder  21  having the opening  22  is used instead of the susceptor. Thus, thin-film monocrystalline silicon can be formed simultaneously on the upper and lower faces of the silicon substrate  51 , resulting in high volume efficiency, as in the above embodiments.  
     [0086] Fourth Thermal CVD Apparatus  
     [0087] A third embodiment of the chemical vapor deposition apparatus according to the second aspect in accordance with the present invention (hereinafter referred to as a fourth thermal CVD apparatus) will be described with reference to FIG. 4 which is a partially cut-away cross-sectional view of an overall configuration thereof. The same components illustrated in the former embodiments are referred to using the same reference numerals. This chemical vapor deposition apparatus also includes a ring cavity resonator, as in the third thermal CVD apparatus  3 .  
     [0088] With reference to FIG. 5, the fourth thermal CVD apparatus  4  has a waveguide  36  connected to a ring cavity resonator  33  with a directional coupler  42  which is used instead of the T-shaped coupler  40  used in the third thermal CVD apparatus  3 . The directional coupler  42  transmits electromagnetic waves to a ring cavity resonator  33 . The T-shaped coupler  40  guides electromagnetic waves both in the right and left directions of the ring cavity resonator  33  in the third thermal CVD apparatus  3 , whereas the directional coupler  42  guides electromagnetic waves only in one direction in the fourth thermal CVD apparatus  4 . The other components, such as the electromagnetic wave generator  12 , the isolator  38 , the holder  21 , the holder support (not shown in the drawing), the gas supply pipes  13 , and the gas exhaust pipes  14 , are the same as those in the third thermal CVD apparatus  3 .  
     [0089] The fourth thermal CVD apparatus  4  is provided with a ring cavity resonator  33 . The ring cavity resonator  33  is formed of, for example, aluminum, copper, or stainless steel, which has an electrical conductivity higher than that of the silicon substrate  51 . However, the ring cavity resonator  33  of aluminum and copper restricts the types of gases used in the film deposition. That is, gases which do not contain corrosive components are used. Thus, in the ring cavity resonator  33  of aluminum or copper, the internal face thereof is coated with gold. However, in a ring cavity resonator formed of stainless steel having high corrosion resistance, gold coating is unnecessary except that gas containing a component causing corrosion of stainless steel is used.  
     [0090] Holders  21  are arranged at a plurality of places (for example, three places) into a plurality of layers (for example, seven layers), each supporting a silicon substrate  51 , in the interior of the ring cavity resonator  33 . These holders  21  are supported by holder supporters (not shown in the drawings) at a predetermined interval. In this embodiment, the silicon substrates  51  are rectangular and are unidimensionally arranged in one holder group. Of course, the silicon substrates  51  may be arrayed two-dimensionally or three-dimensionally in the same holder group.  
     [0091] An electromagnetic wave generator  12  is connected to a side wall of the ring cavity resonator  33  for generating electromagnetic waves to the ring cavity resonator  33  via the directional coupler  42  and a waveguide  36 . That is, the electromagnetic wave generator  12  is placed at the incident end of the waveguide  36 . A magnetron is used, for example, as the electromagnetic wave generator  12 . The oscillation frequency thereof is in the microwave or millimeter band. In this embodiment,  2 . 46  GHz microwaves, for example, are used. In order to prevent reflection of the electromagnetic waves from the ring cavity resonator  33  to the electromagnetic wave generator  12  as the electromagnetic wave source, the waveguide  36  is provided with an isolator  38 .  
     [0092] A plurality of gas supply pipes  13  is connected to a side wall of the ring cavity resonator  33  at the position of each holder group including a plurality of stacked holders  21 , whereas a plurality of gas exhaust pipes  14  is connected to another side wall of the ring cavity resonator  33  at the position opposing the plurality of gas supply pipes  13 .  
     [0093] It is preferable that the diameters of each gas supply pipe  13  and each gas exhaust pipe  14  be smaller than the wavelength of the electromagnetic waves in order to prevent leakage of the electromagnetic waves from the ring cavity resonator  33 . The position of the connection in the ring cavity resonator  33  preferably corresponds to the position of an antinode having a maximum amplitude of the standing wave of the electromagnetic waves, that is, a position with minimized current flow in the wall of the ring cavity resonator  33 . Thus, each gas supply pipe  13  and each gas exhaust pipe  14  are connected at an intermediate height between the upper and lower silicon substrates  51  in this third thermal CVD apparatus  3 . The diameters of each gas supply pipe  13  and each gas exhaust pipe  14  are, for example, 10 mm or less. The position of each silicon substrate  51  and the positions of each gas supply pipe  13  and each gas exhaust pipe  14  may have an appropriate angle to the central axis of the waveguide  36 .  
     [0094] The silicon substrate is held horizontally in this embodiment. Alternatively, the silicon substrate may be tilted at an appropriate angle by rotating the overall apparatus. When the silicon substrate is held perpendicularly, the formation of slip defects caused by flexure stress which occurs due to the weight of the silicon substrate is suppressed at elevated temperatures such as 1,000° C.  
     [0095] The holders  21  will be described. Each holder  21  is provided with an opening  22  at a position for placing the silicon substrate  51 . Each holder  21  is formed of a conductive material such as silicon carbide (SiC) which is durable at elevated temperatures such as 1,000° C. When the holder  21  is composed of a material having an electric conductivity which is lower than that of the ring cavity resonator  33  and is substantially the same as that of silicon, the holder  21  is heated together with the silicon substrate  51  without heat being dissipated from the silicon substrate  51 . Thus, a state in which the silicon substrate  51  has a uniform temperature can be readily achieved.  
     [0096] When the silicon substrate  51  is circular, the diameter of the opening  22  formed in each holder  21  is several mm to ten and several mm shorter than the diameter of the silicon substrate  51 . When the substrate is rectangular, the length is several mm to ten and several mm shorter than the length of the substrate.  
     [0097] The arrangement of the silicon substrates  51  is such that the vertical distance between the silicon substrates  51  is, for example, ½ or ¼ of the wavelength of electromagnetic waves, or an integral multiple of the wavelength of the electromagnetic waves, in which case the distance would actually be 61 mm. When the silicon substrates  51  are also arrayed in the horizontal direction, the horizontal distance between the silicon substrates  51  is, for example, an integral multiple of the wavelength or ½ or ¼ of the wavelength of the electromagnetic waves.  
     [0098] In order to prevent heating of the ring cavity resonator  33  by radiation from the silicon substrates  51  which are heated to an elevated temperature, the inner face of the ring cavity resonator  33  is polished so that the surface roughness is {fraction (1/10)} or less the wavelength of the electromagnetic waves. Since the inner face of the ring cavity resonator  33  is polished, radiation is confined in the ring cavity resonator  33  and are used for heating the silicon substrates  51 .  
     [0099] The resonance mode in the ring cavity resonator  33  is determined by the silicon substrates  51  and the ring cavity resonator  33 . The electromagnetic waves induce a current I which flows in the silicon substrates  51  and the ring cavity resonator  33  and heats the silicon substrates  51  and the ring cavity resonator  33 . Supposing the resistance is R, then the heat divergence is in proportion to RI 2 . Thus, the heat divergence in the silicon substrates  51  is larger than that in the ring cavity resonator  33 . As a result, the energy of the electromagnetic waves is effectively absorbed in the silicon of the silicon substrates  51  and is not substantially absorbed in the ring cavity resonator  33 . Since the temperature of the ring cavity resonator  33  is not substantially elevated, amorphous silicon etc. is not substantially deposited on the side walls of the ring cavity resonator  33  during the film deposition.  
     [0100] In the formation of the thin-film monocrystalline silicon in the fourth thermal CVD apparatus  4 , the electromagnetic waves generated by the electromagnetic wave generator  12  are introduced in one direction through the directional coupler  42 , and the silicon substrates  51  supported on the holders  21  in the ring cavity resonator  33  are hated to an elevated temperature of approximately 1,000° C. In this state, a silicon-containing compound is fed to the reaction chamber  11  through the gas supply pipes  13  so as to deposit silicon on the silicon substrates  51  by pyrolysis. As the silicon-containing compounds, gases, such as SiCl 4 , SiHCl 3 , SiH 2 Cl 2 , and SiH 4 , are generally used. These gases are diluted with hydrogen gas and are fed into the ring cavity resonator  33 , while the excess silicon-containing gas in the ring cavity resonator  33  is expelled through the gas exhaust pipes  14  provided on a side wall of the cavity resonator  33 .  
     [0101] The gas supplied through these gas supply pipes  13  flows as layered streams between the silicon substrates  51  and is pyrolyzed on the silicon substrates  51  to form thin-film monocrystalline silicon. In this fourth thermal CVD apparatus  4 , the gas flows in the direction perpendicular to the arrangement or the longitudinal direction of the substrate, instead of a flow in the direction of the arrangement or the longitudinal direction of the substrate, as in a transverse epitaxial deposition apparatus; hence, thin-film monocrystalline silicon having a uniform thickness is readily obtainable. By depositing the film by reversing the directions of the inlet and outlet of the gas, the resulting thin-film monocrystalline silicon has a more uniform thickness.  
     [0102] A susceptor, which is essential in conventional chemical vapor deposition apparatuses is not required in the fourth thermal CVD apparatus  4 . Since energy required for heating the susceptor can be used for heating the silicon substrate, the energy can be more effectively used. Moreover, the holder  21  having the opening  22  is used instead of the susceptor. Thus, thin-film monocrystalline silicon can be simultaneously formed on the upper and lower faces of the silicon substrate  51 , resulting in high volume efficiency, as in the above second thermal CVD apparatus  2 .  
     [0103] Fifth Thermal CVD Apparatus  
     [0104] A fourth embodiment of the chemical vapor deposition apparatus according to the second aspect in accordance with the present invention (hereinafter referred to as a fifth thermal CVD apparatus) will be described.  
     [0105] The basic configuration of the fifth thermal CVD apparatus is the same as that of the above fourth thermal CVD apparatus  4 . In this fifth thermal CVD apparatus, the ring cavity resonator  33  is designed so that the resonant mode slightly shifts, for example, by 0.001% to 1% to the incident electromagnetic waves. Thus, the electromagnetic waves in the ring cavity resonator  33  are not standing waves but are propagating waves. Since the heat divergence distribution on the silicon substrate  51  becomes more uniform in this apparatus compared to the above fourth thermal CVD apparatus  4 , the temperature distribution on the silicon substrate  51  becomes uniform in a short time.  
     [0106] The ring cavity resonator  33  is heated by not only electromagnetic waves but also by radiation from the heated silicon substrate  51 . Thus, a rise in temperature due to radiant heat can be suppressed by heating the silicon substrate  51  in a short time, maintaining the ring cavity resonator  33  at low temperature. As a result, energy supplied as electromagnetic waves is more effectively used for heating the ring cavity resonator  33 . Since pyrolytic deposition of the silicon material on the walls of the ring cavity resonator  33  is reduced, the silicon material is more effectively deposited on the substrate  51 .  
     [0107] Such a ring cavity resonator  33  having a resonant mode which slightly shifts, for example, by 0.001% to 1% is also applicable to other cavity resonators in the first thermal CVD apparatus  1  and the second thermal CVD apparatus  2 . Modification of First to Fourth Thermal CVD Apparatuses (Sixth Thermal CVD Apparatus)  
     [0108] A modification of the electromagnetic wave generator  12  in accordance with the first to fourth thermal CVD apparatuses  1  to  4  will be described with reference to FIG. 6. The same components illustrated in the former embodiments are referred to using the same reference numerals.  
     [0109] The electromagnetic wave source of the electromagnetic wave generator  12  is replaced with oscillators  15  which are linearly arranged on a plane parallel to a silicon substrate (not shown in the drawing). Each oscillator  15  consists of an independent magnetron. The frame represents a waveguide  36 .  
     [0110] Electromagnetic waves emitted from these oscillators  15  heat silicon substrates as in the fifth thermal CVD apparatus. Since frequencies thereof are slightly different from each other, the intensity distribution changes over time due to the formation of the interference beat. However, the mode in the direction perpendicular to the silicon substrates is the same as that in the fifth thermal CVD apparatus. Since the time required for heating the silicon substrates is significantly longer than the beat period, the changes in electromagnetic waves are averaged so that the intensity distribution becomes uniform. Thus, a sixth thermal CVD apparatus provided with the electromagnetic wave generator shown in FIG. 6 can heat the silicon substrates in a shorter time than the fifth thermal CVD apparatus. Accordingly, the sixth thermal CVD apparatus utilizes energy and a silicon material more effectively.  
     [0111] Another feature of the sixth thermal CVD apparatus is that the mode in the direction perpendicular to the silicon substrates is the same as that in the fifth thermal CVD apparatus. Thus, leakage of electromagnetic waves from the ring cavity resonator can be reduced by providing holes at an intermediate height between the silicon substrates, as in the third and fourth thermal CVD apparatuses  3  and  4 , respectively.  
     [0112] Modification of First to Fourth Thermal CVD Apparatuses (Seventh Thermal CVD Apparatus)  
     [0113] Another modification of the electromagnetic wave generator  12  in accordance with the first to fourth thermal CVD apparatuses  1  to  4  will be described with reference to FIG. 7. The same components illustrated in the former embodiments are referred to using the same reference numerals.  
     [0114] The electromagnetic wave source of the electromagnetic wave generator  12  is replaced with a plurality of oscillators  15  which is two-dimensionally arranged. Each oscillator  15  consists of an independent magnetron. The frame represents a waveguide  36 .  
     [0115] Electromagnetic waves emitted from the plurality of oscillators  15  heat silicon substrates as in the fifth thermal CVD apparatus. Since frequencies thereof are slightly different between the oscillators  15 , the intensity distribution changes over time due to the formation of interference beat. A seventh thermal CVD apparatus provided with the electromagnetic wave generator shown in FIG. 7 (the basic configurations other than the electromagnetic wave generator are the same as those of the fifth thermal CVD apparatus) differs from the sixth CVD apparatus in that the mode in the direction perpendicular to the silicon substrates is not the standing wave which is the mode in the fifth thermal CVD apparatus. However, the silicon substrates can be more uniformly heated by averaging the electromagnetic waves by increasing the number of the oscillators  15  (magnetrons). Since more oscillators  15  (magnetrons) compared with the sixth thermal CVD apparatus are used, heating is performed with higher energy. Since the time required for heating the silicon substrates is significantly longer than the beat period, the changes in electromagnetic waves are averaged so that the intensity distribution becomes uniform. Accordingly, in the seventh thermal CVD apparatus, the silicon substrates can be heated within a further decreased time compared with the sixth thermal CVD apparatus. As a result, this apparatus utilizes energy and the silicon material more effectively.  
     [0116] However, the mode in the direction perpendicular to the silicon substrates is not the standing wave mode in this seventh thermal CVD apparatus. Thus, leakage of electromagnetic waves from the cavity resonator does not attenuate even when a hole is provided at an intermediate height between the silicon substrates. Thus, the diameter of the gas supply pipe and the diameter of the gas exhaust pipe must be sufficiently smaller than the wavelengths of the electromagnetic waves. For example, these are {fraction (1/10)} or less of the wavelengths of the electromagnetic waves.  
     [0117] Eighth Thermal CVD Apparatus  
     [0118] An eighth thermal CVD apparatus according to the second aspect in accordance with the present invention will be described with reference to FIG. 8 which is a partially cutaway cross-sectional view of an overall configuration thereof. The same components illustrated in the former embodiments are referred to using the same reference numerals.  
     [0119] This eighth thermal CVD apparatus  8  corresponds to a modification of the second thermal CVD apparatus  2  and is provided with a plurality of waveguides  36  (for example, four) for introducing electromagnetic waves into the cavity resonator  31 . Electromagnetic waves are supplied from independent electromagnetic wave generators  12  to these waveguides  36 . In order to prevent reflection of the electromagnetic waves from the cavity resonator  31  to the electromagnetic wave generators  12  as the electromagnetic wave sources, an isolator  38  is connected to each waveguide  36  which connects the corresponding electromagnetic wave generator  12  and the cavity resonator  31 . A radial arrangement of the waveguides  36  from the cavity resonator  31  heats each substrate  51  with a uniform temperature distribution. Since many electromagnetic wave generators  12  (magnetrons) are connected, the electromagnetic wave energy required for heating increases. As a result, the temperature distribution in the silicon substrate  51  held by the holder  21  will become uniform in a short time. Thus, this apparatus utilizes the energy and the silicon material more effectively.  
     [0120] A ninth thermal CVD apparatus according to the second aspect in accordance with the present invention will be described with reference to FIG. 9 which is a partially cutaway cross-sectional view of an overall configuration thereof. The same components illustrated in the former embodiments are referred to using the same reference numerals.  
     [0121] The ninth thermal CVD apparatus  9  is provided with the ring cavity resonator  33  used in the fourth thermal CVD apparatus  4  and a plurality of waveguides  36  (for example, two) for introducing electromagnetic waves into the ring cavity resonator  33 . The ring cavity resonator  33  and each waveguide  36  are connected with a unidirectional coupler  42 .  
     [0122] The electromagnetic waves are absorbed and attenuated by the silicon substrates  51  held on the holders  21  in the ring cavity resonator  33 . The introduction of electromagnetic waves from the plurality of waveguides  36  compensates for this attenuation. Thus, the temperature distribution in the ring cavity resonator  33  becomes uniform. Moreover, the plurality of electromagnetic wave generators  12  (for example, two) heat the substrates  51  with increased energy. Accordingly, in the ninth thermal CVD apparatus  9 , the time required for heating the silicon substrates  51  is reduced compared with the fourth thermal CVD apparatus  4 . As a result, the apparatus utilizes energy and the silicon material more effectively.  
     [0123] Each electromagnetic wave generator  12  of the ninth thermal CVD apparatus  9  preferably consists of a plurality of oscillators  15 , as shown in FIGS. 6 and 7. The gas supply pipes  13 , the gas exhaust pipes  14 , and the holders  21  are the same as those in the third thermal CVD apparatus  3 .  
     [0124] Tenth Thermal CVD Apparatus  
     [0125] A tenth thermal CVD apparatus according to the second aspect in accordance with the present invention will be described. The same components illustrated in the former embodiments are referred to using the same reference numerals.  
     [0126] In the tenth thermal CVD apparatus, the holder  21  for holding the silicon substrate  51  is composed of an insulating material in the configuration shown in the second thermal CVD apparatus  2 . When the holder  21  does not come into close contact with the silicon substrate  51  in the second thermal CVD apparatus  2 , the contact resistance may significantly increase. Thus, large heat dissipation may occur at the point of the contact between the holder  21  and the silicon substrate  51 . In such a case, the uniformity of the temperature of the silicon substrate  51  may decrease. The insulating holder  21  solves the heat dissipation caused by the contact resistance. This insulating holder  21  is also applicable to the ring cavity resonator  33  described in the third to fifth thermal CVD apparatuses  3  to  5 .  
     [0127] Eleventh Thermal CVD Apparatus  
     [0128] An eleventh thermal CVD apparatus according to the second aspect in accordance with the present invention will be described. The same components illustrated in the former embodiments are referred to using the same reference numerals.  
     [0129] In the eleventh thermal CVD apparatus (see FIG. 3), the holder  21  for holding the silicon substrate  51 , as well as the cavity resonator  31 , is composed of a material having low electrical resistance in the configuration shown in the second thermal CVD apparatus  2 . Since the holder  21  is formed of an insulating material in the tenth thermal CVD apparatus, the propagation mode of the electromagnetic waves may become unstable at the edge of the silicon substrate  51 . In the eleventh thermal CVD apparatus, the propagation mode is stabilized; hence, the intensity of the electromagnetic waves on the silicon substrate  51  is constant. Thus, the temperature distribution on the silicon substrate  51  is uniform. This holder  21  is also applicable to the above ring cavity resonator  33 .  
     [0130] Twelfth Thermal CVD Apparatus  
     [0131] A twelfth thermal CVD apparatus according to the second aspect in accordance with the present invention will be described. The same components illustrated in the former embodiments are referred to using the same reference numerals.  
     [0132] In the twelfth thermal CVD apparatus (see FIG. 3), a reaction chamber  11  formed of synthetic quartz is placed in the cavity resonator  31  of the second thermal CVD apparatus  2 . Although highly reactive silicon-containing gas corrodes the metal of the cavity resonator  31 , the synthetic quartz reaction chamber  11  is resistive to corrosion by the gas. Such a configuration is also applicable to the eighth thermal CVD apparatus  8 .  
     [0133] The first thermal CVD apparatus  1  is not limited to the above-mentioned configuration, as long as the silicon substrate  51  and the holder  21  are arranged so that the electromagnetic waves generated by the electromagnetic wave generator  12  are confined in the structure constituted by the silicon substrate  51  and the holder  21 . The thermal CVD apparatus provided with the cavity resonator  31  or the ring cavity resonator  33  is not limited to the above-described configurations, as long as the silicon substrate  51  and the holder  21  are arranged so that the electromagnetic waves generated by the electromagnetic wave generator  12  are confined in the structure constituted by the silicon substrate  51 , the holder  21 , and the cavity resonator  31  or the ring cavity resonator  33 .  
     [0134] The above embodiments involve the use of the silicon substrate. However, the substrate is not limited to the silicon substrate and may be an insulating substrate, such as a glass substrate or a ceramic substrate, or a semiconductor substrate. Moreover, the substrate may be provided with a thin film thereon.  
     [0135] The holder  21  may have a step along the periphery of the opening  22  for fitting the silicon substrate  51 . When the substrate is placed on the holder having the step, the silicon substrate  51  fits into the step and is firmly held on the holder  21 . Thus, the positioning of the silicon substrate  51  to the holder  21  is easy and the silicon substrate  51  is stably held on the holder  21 .