Patent Publication Number: US-2023154744-A1

Title: Method and apparatus for forming silicon carbide-containing film

Description:
TECHNICAL FIELD 
     The present disclosure relates to a method and apparatus for forming a silicon carbide-containing film. 
     BACKGROUND 
     In multi-gate type fin-field effect transistors (Fin-FETs) or the like, which are semiconductor elements, the degree of integration is further increased, and film types may be exposed in openings formed in hard masks. Therefore, there is an increasing need for a hard mask material capable of etching a desired film with a high selectivity between films exposed in a fine opening. As a material satisfying this demand, inventors have developed a film forming technology for a silicon carbide-containing film (hereinafter, referred to as a “SiC film”). 
     Regarding a SiC film, Patent Document 1 describes a method of obtaining a SiC film at a high temperature of 900 degrees C. to 1,100 degrees C. by alternately supplying acetylene gas and dichlorosilane gas into a reaction tube. In addition, Patent Document 2 describes a method of forming a SiC film by simultaneously supplying triethylamine gas and disilane gas into a processing chamber. In this method, a pressure regulating valve is closed after the simultaneous supply of both gases, and the triethylamine gas and the disilane gas are enclosed in the processing chamber to improve gas phase reaction efficiency. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     
         
         Patent Document 1: Japanese laid-open publication No. H05-1380 
         Patent Document 2: Japanese laid-open publication No. 2013-30752 
       
    
     The present disclosure provides a technique capable of forming a silicon carbide-containing film having a good film quality and improving a film forming rate. 
     SUMMARY 
     According to one embodiment of the present disclosure, there is provided a method of forming a silicon carbide-containing film on a substrate in a processing container in which vacuum exhaust is performed. The method includes: accommodating the substrate in the processing container; adsorbing an organic compound having an unsaturated carbon bond on the substrate by supplying a carbon precursor gas including the organic compound to the processing container in which the substrate is accommodated; and reacting the organic compound adsorbed on the substrate with a silicon compound by supplying a silicon precursor gas including the silicon compound to the processing container after the carbon precursor gas is supplied. The adsorbing the organic compound on the substrate and the reacting the organic compound with the silicon compound are alternately repeated multiple times to form the silicon carbide-containing film. In the adsorbing the organic compound, the vacuum exhaust is restricted to cause the carbon precursor gas to stay in the processing container, and then the restriction of the vacuum exhaust is released to discharge the carbon precursor gas in the processing container. The supply of the silicon precursor gas to the processing container is stopped during the reacting the organic compound adsorbed on the substrate with the silicon compound, and the vacuum exhaust is not restricted after the supply of the silicon precursor gas is stopped. 
     According to the present disclosure, it is possible to form a silicon carbide-containing film having a good film quality and to improve a film forming rate. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a vertical cross-sectional side view illustrating an example of a film forming apparatus of the present disclosure. 
         FIG.  2    illustrates an example of a chemical reaction formula used in a film forming method of the present disclosure. 
         FIG.  3    illustrates an example of a reaction model related to the chemical reaction formula. 
         FIG.  4 A  is a time chart illustrating an example of a film forming method. 
         FIG.  4 B  is a time chart illustrating another example of the film forming method. 
         FIGS.  5 A and  5 B  illustrate a structural formula illustrating another example of a carbon precursor. 
         FIG.  6    illustrates an example of another chemical reaction formula used in the film forming method. 
         FIG.  7    illustrates an example of a reaction model related to the other chemical reaction formula. 
         FIG.  8    is an explanatory view illustrating a variation of a carbon precursor. 
         FIG.  9    is an explanatory view illustrating a variation of a silicon precursor. 
         FIG.  10    is a time chart illustrating another example of a film forming method. 
         FIG.  11    is a vertical cross-sectional side view illustrating another example of a film forming apparatus. 
         FIG.  12    is a characteristic diagram showing an evaluation result of a film forming method. 
         FIG.  13    is a characteristic diagram showing an evaluation result of a film forming method. 
     
    
    
     DETAILED DESCRIPTION 
     A single-wafer-type film forming apparatus according to an embodiment of an apparatus (hereinafter, referred to as a “film forming apparatus”) for executing a method of forming a silicon carbide-containing film (hereinafter referred to as a “film forming method”) of the present disclosure will be described with reference to  FIG.  1   . The film forming apparatus  1  includes a processing container  10  that accommodates a substrate, for example, a semiconductor wafer (hereinafter, referred to as a “wafer”) W, and the processing container  10  is formed of a metal such as aluminum (Al) in a substantially cylindrical shape. A carry-in/out port  11  for carrying in or out a wafer W is formed in the side wall of the processing container  10  to be openable/closable by a gate valve  12 . 
     An annular exhaust duct  13  having, for example, a rectangular cross section is disposed in an upper portion of the side wall of the processing container  10 . The exhaust duct  13  has a slit  131  along the inner peripheral surface thereof, and an exhaust port  132  is formed in the outer wall of the exhaust duct  13 . A ceiling wall  14  is installed on the top surface of the exhaust duct  13  to close an upper opening of the processing container  10  via an insulating member  15 , and the space between the exhaust duct  13  and the insulating member  15  is hermetically sealed with a seal ring  16 . 
     A stage  2  for horizontally supporting a wafer W is provided inside the processing container  10 , and the stage  2  is made of a ceramic material such as aluminum nitride (AlN) or a metal material such as aluminum or nickel alloy in a disk shape. In this example, a heater  21  forming a heating part for heating the wafer W is embedded in the stage  2 , and the outer peripheral region and the side surface of the top surface of the stage  2  are covered with a cover member  23  made of ceramic such as alumina. 
     The stage  2  is connected to a lifting mechanism  25  installed below the processing container  10  via a support member  24 , and is configured to be moved up and down between a processing position indicated by the solid line in  FIG.  1    and a wafer W delivery position indicated by the alternate long and short dash line below the processing position. In  FIG.  1   , reference numeral  17  indicates a partition member for partitioning the interior of the processing container  10  into upper and lower portions when the stage  2  is raised to the processing position. Three support pins  26  (only two of which are illustrated) are provided below the stage  2  in the processing container  10  to be movable up and down by a lifting mechanism  27  provided below the processing container  10 . The support pins  26  are inserted through through-holes  22  in the stage  2  located at the delivery position to be capable of protruding/sinking with respect to the top surface of the stage  2 , and are used for delivery of a wafer W between an external transport mechanism (not illustrated) and the stage  2 . Reference numerals  28  and  29  in the figure denote bellows that partition the atmosphere inside the processing container  10  from the outside air and expand/contract according to the moving-up/down operations of the stage  2  and the support pins  26 , respectively. 
     A shower head  3  for supplying a processing gas in a shower form in the processing container  10  is installed in the processing container  10  to face the stage  2 . The shower head  3  includes a main body  31  fixed to the ceiling wall  14  of the processing container  10  and a shower plate  32  connected under the main body  31 , and the interior thereof forms a gas diffusion space  33 . An annular protrusion  34  protruding downward is formed at the peripheral edge of the shower plate  32 , and gas ejection holes  35  are formed in the flat surface inside the annular protrusion  34 . A gas supply system  5  is connected to the gas diffusion space  33  via a gas introduction hole  36 . 
     The gas supply system  5  includes a carbon precursor supplier configured to supply a carbon precursor gas to the processing container  10  and a silicon precursor supplier configured to supply a silicon precursor gas. The carbon precursor supplier includes a carbon precursor gas source  51  and a gas supply path  511 , and the gas supply path  511  is provided with a flow rate regulator  512 , a storage tank  513 , and a valve  514  from the upstream side. 
     The carbon precursor contains an organic compound having an unsaturated carbon bond. For example, bis(trimethylsilyl)acetylene (BTMSA) having a triple bond is used. Hereinafter, the carbon precursor gas may be referred to as carbon precursor gas or BTMSA gas. The carbon precursor gas supplied from the source  51  is temporarily stored in the storage tank  513 , pressurized to a predetermined pressure in the storage tank  513 , and then supplied into the processing container  10 . BTMSA is a liquid at room temperature, and the gas obtained by heating the BTMSA is supplied to and stored in the storage tank  513 . The supplying and stopping of the carbon precursor gas from the storage tank  513  to the processing container  10  is performed by opening and closing the valve  514 . 
     The silicon precursor supplier includes a silicon precursor gas source  52  and a gas supply path  521 , and the gas supply path  521  is provided with a flow rate regulator  522 , a storage tank  523 , and a valve  524  from the upstream side. The silicon precursor contains a silicon compound, and, for example, disilane (Si 2 H 6 ) is used. Here, the gas of the silicon precursor may be referred to as silicon precursor gas or disilane gas. The silicon precursor gas supplied from the source  52  is temporarily stored in the storage tank  523 , pressurized to a predetermined pressure in the storage tank  523 , and then supplied into the processing container  10 . The supplying and stopping of the silicon precursor gas from the storage tank  523  to the processing container  10  is performed by opening and closing the valve  524 . 
     In addition, the gas supply system  5  includes sources  53  and  54  of an inert gas such as argon (Ar) gas. In this example, the Ar gas supplied from one source  53  is used as a purge gas for carbon precursor gas. The source  53  is connected from the upstream side to the downstream side of the valve  514  in the gas supply path  511  of the carbon precursor gas via a gas supply path  531  provided with a flow rate regulator  532  and a valve  533 . 
     The Ar gas supplied from the other source  54  is used as a purge gas for silicon precursor gas. The source  54  is connected from the upstream side to the downstream side of the valve  524  in the gas supply path  521  of the silicon precursor gas via a gas supply path  541  provided with a flow rate regulator  542  and a valve  543 . The supplying and stopping of the Ar gas to the processing container  10  is performed by opening and closing the valves  533  and  543 . 
     The processing container  10  is connected to a vacuum exhaust path  62  via an exhaust port  132 , and a vacuum exhauster  61  configured to execute vacuum exhaust of the gas in the processing container  10  and including, for example, a vacuum pump, is installed on the downstream side of the vacuum exhaust path  62 . In the vacuum exhaust path  62 , for example, an auto pressure controller (APC) valve  63  is interposed between the processing container  10  and the vacuum exhauster  61 , as a pressure control valve. 
     The interior of the processing container  10  is configured such that the pressure is regulated by a pressure regulating mechanism. The pressure regulating mechanism of this example includes a vacuum exhauster  61 , a vacuum exhaust path  62 , and an APC valve (pressure regulating valve)  63 . The APC valve  63  is constituted with, for example, a butterfly valve, and provided to be capable of opening/closing the vacuum exhaust path  62 , and has a role of regulating the pressure in the processing container  10  by increasing or decreasing the conductance of the vacuum exhaust path  62  by regulating the opening degree of the same. 
     As described above, the APC valve  63  is opened and closed to regulate the pressure in the processing container  10 , and the exhaust in the processing container  10  is hindered and the exhaust flow rate is decreased by reducing the opening degree of the APC valve  63 . In the vacuum exhaust path  62 , for example, a pressure detector  64  is installed between the exhaust port  132  and the APC valve  63 . The pressure detector  64  is installed in the immediate vicinity of the exhaust port  132 , and the pressure detection value thereof may be regarded as the pressure detection value in the processing container  10 . 
     The APC valve  63  in this example has a pressure regulating function and an opening degree setting function. The pressure regulating function is a function of controlling the pressure by regulating the opening degree based on the pressure detection value by the pressure detector  64  and a preset pressure target value. The opening degree setting function is a function of fixing the opening degree of the valve body to a preset opening degree. Then, in the film forming process of a SiC film to be described later, the pressure regulating function and the opening degree setting function are switched based on a command from a controller  100 . 
     The controller  100  is constituted with, for example, a computer, and includes a data processor including a program, a memory, and a CPU. In the program, commands (respective steps) are incorporated such that the controller  100  sends control signals to each part of the film forming apparatus  1  so as to proceed with a film forming process of a SiC film to be described later. The program is stored in a storage, such as a computer storage medium such as a flexible disk, a compact disk, a hard disk, a magneto-optical disk (MO), or the like, and is installed in the controller  100 . 
     Specifically, the controller  100  is configured to control the film forming process for forming a SiC film on a wafer W. In the film forming process of this example, an adsorption step of adsorbing BTMSA on a wafer W by supplying BTMSA gas as a carbon precursor is performed. Next, a reaction step of reacting BTMSA adsorbed on the wafer W with disilane is executed by supplying disilane gas as a silicon precursor. Then, control of forming a SiC film by an atomic layer deposition (ALD) method is executed by alternately repeating the adsorption step and the reaction step multiple times. 
     In the adsorption step, the controller  100  is configured to temporarily restrict the vacuum exhaust in the processing container  10  by controlling the vacuum exhaust performed by the vacuum exhauster  61 . In this vacuum exhaust control, after making the carbon precursor gas stay in the processing container  10 , the restriction on the vacuum exhaust is released, and the control is executed such that the carbon precursor gas in the processing container  10  is discharged. 
     Further, the controller  100  is configured to perform control of initiating the restriction of vacuum exhaust during the period of supplying the carbon precursor gas to the processing container  10  and terminating the restriction after a lapse of a preset time after the stop of the supply of the gas. The controller  100  is also configured to perform control of stopping the supply of the silicon precursor gas to the processing container  10  during the reaction step and continuing the vacuum exhaust by the vacuum exhauster  61  such that the restriction of the vacuum exhaust is not performed after the stopping of the supply. 
     Subsequently, the film forming method executed by the film forming apparatus  1  will be described. As described above, the film forming method of the present disclosure forms a SiC film by an ALD method using a carbon precursor gas and a silicon precursor gas and by a thermal reaction of 500 degrees C. or low without using plasma.  FIG.  2    illustrates an example in which BTMSA, which is a carbon precursor and has a triple bond, and disilane, which is a silicon precursor, are thermally reacted at a temperature in the range of, for example, 300 degrees C. or higher and 500 degrees C. or lower. 
     The mechanism that is capable of forming a SiC film by such a thermal reaction at a low temperature will be considered by using Reaction Model 1 illustrated in  FIG.  3   . Disilane is thermally decomposed by heating at a temperature near 400 degrees C. to generate a SiH 2  radical having an unpaired electron in the Si atom, wherein the SiH 2  radical has an empty p-orbital. In Reaction Model 1, this empty p-orbital acts as an electrophile that attacks a π bond of an unsaturated carbon bond of electron-rich BTMSA and acts on the triple bond of BTMSA. Then, Reaction Model 1 is a model in which C forming the triple bond reacts with Si of the SiH 2  radical to form a SiC bond. 
     Since the π bond of the BTMSA triple bond has a smaller bond force than a σ bond, it is presumed that if a SiH 2  radical attacks this π bond, a thermal reaction proceeds even at a temperature of 500 degrees C. or lower, forming a SiC bond. Reaction Model 1 is for presuming the reason why the formation of SiC film at a low temperature, which has been considered difficult in the past, is enabled and does not limit an actual reaction route. If it is possible to form the SiC film at a temperature of 500 degrees C. or lower without using plasma, the SiC film may be formed via another reaction path. 
     Next, an example of the film forming method of the present disclosure will be described with reference to the time charts of  FIGS.  4 A and  4 B .  FIGS.  4 A and  4 B  each illustrate the timing of initiating and stopping the supply of each of BTMSA gas, Ar gas, and disilane gas, and the timing of opening and closing the APC valve  63 . For BTMSA gas and disilane gas, “ON” and “OFF” on the vertical axis indicate the supply state and the supply stop state, respectively. In addition, Ar(1) indicated in  FIGS.  4 A and  4 B  refers to Ar gas for purging BTMSA gas, and Ar(2) in  FIG.  4 B  refers to Ar gas for purging disilane gas. 
     In addition, “ON” of the APC valve  63  means that the pressure regulating function of the APC valve  63  is set to “ON” and the opening degree is regulated to approach the pressure target value based on the pressure detection value. Meanwhile, “OFF” of the APC valve  63  means that the pressure regulating function is set to “OFF” and the opening degree of the APC valve  63  is regulated to the set opening degree by the opening degree setting function. “OFF(0)” means that the opening degree is set to 0%, that is, the fully closed state, and “OFF(12)” means that the opening degree is set to 12%. 
     The film forming process will be described with reference to  FIG.  4 A . First, the step of accommodating a wafer W in the processing container  10  by carrying the wafer W into the processing container  10  and closing the gate valve  12  of the processing container  10  is performed. Then, the heating of the wafer W by the heater  21  is initiated, and the vacuum exhauster  61  executes vacuum exhaust in the processing container  10 . In addition, the APC valve  63  controls the interior of the processing container  10  to a pressure target value of, for example, 1,000 Pa by setting the pressure regulating function to “ON” and performing opening/closing control based on the pressure detection value detected by the pressure detector  64 . 
     At time t 0 , a first pressure regulating step S 1  is executed by supplying each of Ar(1) and Ar(2), which are purge gases, into the processing container  10  at a first flow rate r 1 , for example, 50 sccm. Ar(1) and Ar(2) are introduced into the processing container  10  via the shower head  3 , flow toward the exhaust port  132  on the side of the wafer W placed on the stage  2  located at the processing position, and are discharged from the processing container  10  via the vacuum exhaust path  62 . 
     Next, at time t 1 , the valve  514  is opened to initiate the supply of the BTMSA gas, which is a carbon precursor, to the processing container  10 , and the adsorption step of adsorbing BTMSA on the wafer W is initiated. First, a BTMSA supply step S 2  is executed by opening the valve  512  to supply the BTMSA gas stored in the storage tank  513  into the processing container  10  in a short time. At this time, for example, Ar(1) and Ar(2) continue to be supplied at the first flow rate r 1 . 
     Next, at time t 2 , a BTMSA enclosing step S 3  is performed by closing the valve  514  to stop the supply of BTMSA. At this time, for example, the supply of Ar(1) and Ar(2) is stopped. In this example, the adsorption step includes the BTMSA supply step S 2  and the BTMSA enclosing step S 3 . In this adsorption step, the heater  21  heats the wafer W to a temperature in the range of 300 degrees C. or higher and 500 degrees C. or lower, for example, 410 degrees C. 
     In this adsorption step, the BTMSA enclosing step S 3  is provided after the BTMSA supply step S 2 , and during the periods of these steps, the BTMSA gas is caused to stay in the processing container  10  by temporarily limiting the vacuum exhaust in the processing container  10 . In this example, at time t 1 , the control of the APC valve  63  is switched to the opening degree setting function, and the opening degree is set to “0%”, that is, to the fully closed state. As a result, during the periods of the BTMSA supply step S 2  and the BTMSA enclosing step S 3 , the exhaust of the gas in the processing container  10  is temporarily substantially stopped. Therefore, by performing the above operation, it is possible to maintain the state in which the BTMSA gas sufficiently stays in the processing space formed between the shower head  3  and the stage  2 . 
     In general, the APC valve  63  does not have a function of separating the upstream side and the downstream side thereof, and even if the APC valve  63  is set to the fully closed state, gas may continue to be discharged from the processing container  10  although the amount is small. Even in such a case, it has been found that the effect of causing the BTMSA gas to stay in the processing container  10  is obtained compared with the case where the APC valve  63  is in the opened state. 
     By the above-mentioned restriction of vacuum exhaust, compared with the case where vacuum exhaust is continued, the time in which the BTMSA gas stays in the processing container  10  is extended so that the time for bringing the BTMSA gas into contact with the wafer W can be lengthened. As a result, even when the chemisorption between the surface of the wafer W and the BTMSA proceeds relatively slowly, it is possible to sufficiently secure the time required for the chemisorption, so that a sufficient amount of BTMSA can be adsorbed on the surface of the wafer W. 
     As described above, the temporary restriction of the vacuum exhaust in the processing container  10  is executed by making the opening degree of the APC valve  63  smaller than that before the restriction is initiated. Therefore, not only the case where the APC valve  63  is fully closed as in the above-mentioned example, but also the case where the opening degree of the APC valve  63  is made smaller than that before the restriction is initiated is included. When the opening degree of the APC valve  63  is made smaller than that before the initiation of the restriction, the exhaust of the carbon precursor gas in the processing container  10  is suppressed and the exhaust flow rate is lowered, so that the gas stays in the processing container  10 . Therefore, depending on the type of the carbon precursor gas and the film quality of the target SiC film, the organic compound in the gas may be sufficiently adsorbed on the wafer W even if the APC valve  63  is not fully closed. 
     Then, at time t 3  after the set time elapses from time t 1  when the APC valve  63  is fully closed, the restriction on vacuum exhaust is released and the BTMSA gas staying in the processing container  10  is discharged. Specifically, at time t 3 , a first purge step S 4  is performed by setting the opening degree of the APC valve  63  to, for example, 12%, and supplying each of Ar(1) and Ar(2) at a second flow rate r 2 , for example, 500 sccm. In step S 4 , by fixing the opening degree of the APC valve  63  at 12%, the forced exhaust in the processing container  10  proceeds. 
     As a result, the excess BTMSA gas and Ar gas in the processing container  10  are quickly discharged from the processing container  10 , and the atmosphere in the processing container  10  is replaced with Ar gas. Next, at time t 4 , the pressure regulating function of the APC valve  63  is switched to “ON”, Ar(1) and Ar(2) are supplied at the first flow rate r 1 , and the second pressure regulating step S 5  is performed. In step S 5 , the opening degree of the APC valve  63  is regulated based on the pressure detection value such that the interior of the processing container  10  approaches the pressure target value. The second pressure regulating step in step S 5  may be omitted in order for throughput improvement or the like. 
     In this example, the adsorption step is from time t 1  to time t 3  when the purging of Ar gas is initiated. Then, the temporary restriction of the vacuum exhaust is initiated at time t 1  during the period of supplying the BTMSA gas to the processing container  10  and is terminated at t 3  after a lapse of the preset time. Therefore, the period after the supply of the BTMSA gas is stopped at time t 2  is also included in the period in which the vacuum exhaust is restricted. 
     Time t 3  is appropriately set depending on the type of carbon precursor gas, the target SiC film quality, and the like. As an example, the supply time of the BTMSA gas is 1 second, and the time for temporarily restricting the vacuum exhaust is 3 seconds or more, preferably 10 seconds or more. 
     In the adsorption step, the pressure inside the processing container  10  fluctuates by temporarily restricting the vacuum exhaust of the processing container  10 , but as described above, the time of supplying the BTMSA gas and the time of temporarily restricting the vacuum exhaust are short. Therefore, the amount of pressure fluctuation in the processing container  10  is not so large, and does not have a large effect of deteriorating the film quality of the formed SiC film. 
     Next, at time t 5 , the disilane supply step S 6  is executed by opening the valve  524  to initiate the supply of disilane gas, which is the silicon precursor. This step S 6  is a reaction step of reacting the BTMSA adsorbed on the wafer W with disilane. The disilane gas is supplied for a relatively short time, for example, 1 second, until the valve  524  is closed and the supply is stopped at time t 6 . By the operation of opening the valve  524 , the disilane gas stored in the storage tank  523  is supplied into the processing container  10  in a short time. At this time, for example, Ar(1) and Ar(2) are supplied at the first flow rate r 1 . 
     In the disilane gas supply step S 6 , the disilane gas is caused to stay in the processing container  10  by temporarily restricting the vacuum exhaust in the processing container  10 . In this example, at time t 5 , the control of the APC valve  63  is switched to the opening degree setting function and the opening degree is set to “0%”, that is, to the fully closed state. That is, the exhaust in the processing container  10  is temporarily and substantially stopped for a relatively short time from time t 5  at which the supply of the disilane gas is initiated to time t 6  at which the supply is stopped. Therefore, by performing the above operation, in the state of being filled in the processing space formed between the shower head  3  and the stage  2 , the disilane gas comes into contact and reacts with the BTMSA adsorbed on the wafer W to form SiC. 
     Then, at time t 6 , a second purge step S 7  is performed by setting the opening degree of the APC valve  63  to, for example, 12%, and supplying each of Ar(1) and Ar(2) at the second flow rate r 2 . In this step S 7 , the forced exhaust in the processing container  10  proceeds by fixing the opening degree of the APC valve  63  to 12%. As a result, the excess disilane gas and Ar gas in the processing container  10  are quickly discharged from the processing container  10 . Thereafter, steps 2 to 7 are repeated again. 
     In this reaction step, as illustrated in  FIG.  4 B , the vacuum exhaust of the processing container  10  may be controlled to be continued without temporarily restricting the vacuum exhaust. Since the time chart of  FIG.  4 B  is the same as that of  FIG.  4 A  except for the control of the APC valve  63  in the disilane supply step S 6 , the description other than the APC valve  63  of step S 6  will be omitted. In this example, the APC valve  63  switches the pressure regulating function to “ON” at time t 4  when the second pressure regulating step S 5  is started, and in the disilane supply step S 6 , the opening degree is also regulated such that the interior of the processing container  10  approaches the pressure target value based on the pressure detection value. The disilane gas introduced from the shower head  3  comes into contact and reacts with the BTMSA adsorbed on the wafer W while flowing through the processing container  10  toward the exhaust port  132 , thereby forming SiC. 
     When the excess disilane gas is decomposed on the surface of the wafer W, amorphous Si may be deposited and an amorphous Si film may be formed. Therefore, as illustrated in  FIG.  4 A , purging is performed immediately after the supply of the disilane gas is stopped, or as shown in  FIG.  4 B , the vacuum exhaust in the processing container  10  is continued during the supply period of the disilane gas. In other words, in the case of disilane gas, by not providing the enclosing step in the case of BTMSA and not performing the restriction of vacuum exhaust after the supply the disilane gas is stopped, it is possible to suppress the formation of an amorphous Si film. 
     In this way, the supply of the BTMSA gas, which is the carbon precursor of step S 2 , is initiated again, and the step of adsorbing BTMSA on the wafer W and the step of reacting BTMSA with disilane are alternately performed multiple times as in the above-described method to form a SiC film having a predetermined thickness. The SiC film formed in this way by an ALD method is surely formed with a Si—C bond. As described in the Examples to described later, when the chemical bond state was analyzed by X-ray Photoelectron Spectroscopy (XPS), the formation of a bond between Si and C (Si—C bond) was observed. 
     According to the above-described embodiment, in the step of adsorbing BTMSA on a substrate by supplying a carbon precursor, for example, BTMSA gas, the vacuum exhaust in the processing container  10  is restricted to cause the BTMSA gas to stay in the processing container  10 . Therefore, as described above, the chemisorption of BTMSA on the wafer surface is promoted so that a SiC film having good film quality can be formed and the film forming rate can be improved. 
     The SiC film having a good film quality is a film having a good ratio of a silicon (Si) component and a carbon (C) component (Si/C ratio) in the SiC film, and specifically, a film having a Si/C ratio close to 1. From the examples to described later, it has been recognized that the method of the present disclosure increases the number of carbon atoms (C) having a Si—C bond in the SiC film. 
     Meanwhile, in the step of reacting the BTMSA adsorbed on the wafer W with disilane by supplying a silicon precursor, for example, disilane gas, the restriction of vacuum exhaust in the processing container  10  is not performed at least after the supply stop of disilane gas (step S 7  in  FIGS.  4 A and  4 B ). Therefore, the excess disilane gas not used for the reaction with the BTMSA is rapidly discharged from the processing container  10 , and the formation of the above-mentioned amorphous Si film is suppressed. Therefore, from this point as well, since the increase of the Si component in the SiC film is suppressed, it is possible to suppress the formation of the amorphous Si film and to form a film having a good Si/C ratio. 
     In addition, the SiC film formed by thermally reacting the carbon precursor and the silicon precursor at a relatively low temperature of 300 degrees C. or higher and 500 degrees C. or lower by using the ALD method is of high quality, and has properties suitable for a hard mask material, an insulating film, a low dielectric constant film, or the like. When a SiC film is used for a transistor of a semiconductor element, it may be required that the allowable temperature during the film forming process be 500 degrees C. or lower in order to suppress the diffusion of metal from a metal wiring layer. Meanwhile, even if it is possible to form a film at a low temperature of 400 degrees C. or lower, the method of forming a SiC film by using plasma may cause a problem because other films and wiring layers constituting the semiconductor element may be greatly damaged by plasma. Therefore, it is effective to be able to form a SiC film at a temperature of 500 degrees C. or lower without using plasma by the film forming method of the present disclosure, which leads to the expansion of applications of the SiC film. 
     Here, BTMSA has less intramolecular polarization (localization of electric charge), and is less likely to be chemisorbed on the surface of the wafer W compared with a molecule having more polarization. Therefore, in a method such as an ALD method in which the supply of BTMSA gas is repeated for a short time, when vacuum exhaust is performed in the adsorption step, BTMSA may be discharged from the processing container  10  before being sufficiently chemisorbed. As a result, there are problems that since C components in the SiC film are reduced, it is impossible to form a desired SiC film having a Si/C ratio and the film forming rate is low. 
     In order to solve the above problems, a method of increasing the supply flow rate and supply time of BTMSA gas in the adsorption step to increase the total amount of BTMSA to be supplied to the surface of the wafer W may also be considered. However, this method leads to a large amount of consumption of BTMSA gas and increases the time required for the adsorption step, so there is a concern that the productivity decreases. In contrast, according to the method of the present disclosure, since it is not necessary to lengthen the supply time of BTMSA gas, it is possible to improve the film forming rate while forming a SiC film having good film quality. 
     In the above example, since the restriction of vacuum exhaust in the processing container  10  is executed by reducing the opening degree of the APC valve  63 , it is easy to control the restriction. Furthermore, when BTMSA is used as the carbon precursor, the BTMSA does not form a thermal decomposition film by itself. Thus, there is an advantage in that a SiC film can be easily formed by an ALD method. 
     Subsequently, another example of the carbon precursor containing an organic compound having an unsaturated carbon bond will be described with reference to  FIGS.  5 A to  8   . The carbon precursor illustrated in  FIG.  5 A  is trimethylsilylacetylene (TMSA) having a triple bond. The carbon precursor illustrated in  FIG.  5 B  is [(trimethylsilyl)methyl]acetylene (TMSMA) having a triple bond. A SiC film may also be formed by thermally reacting these TMSA gas and TMSMA gas with a silicon precursor, for example, disilane gas, at a temperature in the range of 300 degrees C. or higher and 500 degrees C. or lower. 
     In these TMSA and TMSMA as well, an empty p-orbital of a SiH 2  radical obtained by thermal decomposition of disilane attacks a π bond of a triple bond. Then, it is presumed that the empty p-orbital acts on the triple bond of TMSA and TMSMA, and the C of the triple bond reacts with the Si of the SiH 2  radical, thereby forming a SiC bond. In addition, TMSA and TMSMA also have less intramolecular polarization and are less likely to cause chemisorption on a wafer surface, but by temporarily restricting vacuum exhaust in the adsorption step, chemisorption with the wafer can be promoted. 
     Next, the carbon precursor illustrated in  FIG.  6    is bis(chloromethyl)acetylene (BCMA) having a triple bond which is an unsaturated carbon bond and containing a halogen.  FIG.  6    illustrates an example in which a BCMA gas and a silicon precursor, for example, disilane gas, are thermally reacted at a temperature in the range of 300 degrees C. or higher and 500 degrees C. or lower. Regarding this thermal reaction, it is presumed that Reaction Model 1 illustrated in  FIG.  3    and Reaction Model 2 illustrated in  FIG.  7    proceed at the same time. Reaction Model 2 has nucleophilicity in which BCMA is polarized by having a halogen group (Cl group) and the positive polarization site (σ+) of a SiH 2  radical attacks the negative polarization site (σ−). In this way, the SiH 2  radical reacts with C at a molecular end where Cl is bonded, forming a SiC bond. 
     The carbon precursor containing an organic compound having an unsaturated carbon bond is not limited to the above-mentioned BTMSA, TMSA, TMSMA, and BCMA. Another carbon precursor may be used if it thermally reacts with the silicon precursor at a temperature of 500 degrees C. or lower to form a SiC film. As the carbon precursor, a combination of skeletons and side chains illustrated in  FIG.  8    may be used. The skeleton of the carbon precursor is an unsaturated bond portion of an organic compound, and may be, for example, an unsaturated carbon bond of a triple bond or a double bond of C. The side chain of the carbon precursor is a portion that is bonded to the skeleton. Assuming that the skeleton is a triple bond, the side chain that is bonded to one C is X, and the side chain that is bonded to another C is Y. These side chains X and Y may be the same as or different from each other. 
     Examples of side chains include hydrogen (H) atoms, halogens, alkyl groups with a C number of 5 or less, triple bonds of C, double bonds of C, Si(Z), C(Z), N(Z), O(Z), and the like. In the tables illustrating the variations of side chains of  FIGS.  8  and  9   , Si(Z), C(Z), N(Z), and O(Z) are substances in which the sites bonded to C of the skeleton are Si, C, N, and O, respectively, and (Z) indicates an arbitrary atomic group. 
     As the silicon precursor, a combination of the skeletons and the side chains illustrated in  FIG.  9    may be used. The skeleton of the silicon precursor is a Si—Si bond in terms of disilane. The side chain of the silicon precursor is a portion that is bonded to the skeleton. Assuming that the skeleton is Si—Si, the side chain X that is bonded to one Si and the side chain Y that is bonded to the other Si may be the same as or different from each other. Examples of the skeleton include Si—Si, Si, Si—C, Si—N, Si—O, and the like. Examples of side chains include hydrogen atoms, halogens, alkyl groups with a C number of 5 or less, triple bonds of C, double bonds of C, Si(Z), C(Z), N(Z), O(Z), and the like. Examples of silicon precursors that thermally decompose at a temperature of 500 degrees C. or lower to generate SiH 2  radicals include disilane, monosilane (SiH 4 ), and trisilane (Si 3 H 8 ). 
     Subsequently, another example of the film forming method executed by the above-mentioned film forming apparatus will be described with reference to  FIG.  10   .  FIG.  10    is a time chart illustrating the timing of starting and stopping the supply of BTMSA gas, which is a carbon precursor, and disilane gas, which is a silicon precursor, and the timing of opening/closing control of the APC valve  63 . Illustration of each of the Ar(1) and Ar(2), which are purge gases, is omitted, but since these purge gases are supplied in the same manner as in the time charts illustrated in  FIGS.  4 A and  4 B , a description thereof is omitted. In addition, how to read the time chart is the same as in  FIGS.  4 A and  4 B . 
     In this example, control is performed such that the temporary restriction of vacuum exhaust is initiated after stopping the supply of a carbon precursor gas to the processing container  10  and then terminated after a lapse of a preset time. Specifically, the supply of BTMSA gas is initiated by opening the valve  514  at time t 1 , and the supply is stopped by closing the valve  514  at time t 2 . Meanwhile, the supply of disilane gas is initiated by opening the valve  524  at time t 4 , and the supply is stopped by closing the valve  524  at time t 5 . The pressure regulating function of the APC valve  63  is set to “ON” until time t 2 , that is, while the BTMSA gas is being supplied, and the control pressure of the interior of the processing container  10  is executed. 
     Then, at time t 2 , the supply of BTMSA gas is stopped, the APC valve  63  is fully closed, and the temporary restriction of vacuum exhaust is initiated. As a result, in the processing container  10 , the exhaust flow rate decreases, the BTMSA gas stays, and the chemisorption of BTMSA on the wafer W proceeds. 
     Thereafter, at time t 3 , which is after a preset time has elapsed since the temporary restriction of vacuum exhaust was initiated at time t 2 , the opening degree of the APC valve  63  is set to, for example, “12%”, the temporary restriction of vacuum exhaust is terminated, and the interior of the processing container  10  is forcibly evacuated. 
     In the example illustrated in  FIG.  10   , the pressure regulating function of the APC valve  63  is set to “ON” when the disilane gas is supplied, but as in  FIG.  4 A , the APC valve  63  may be switched to the opening degree setting function to be fully closed only when the disilane gas is supplied. In this case, the supply of the disilane gas is stopped, the opening degree of the APC valve  63  is set to, for example, “12%”, purging is performed, and the interior of the processing container  10  is forcibly evacuated to discharge the excess disilane gas. 
     Here, in the film forming method of the present disclosure, the vacuum exhaust of the processing container  10  may be temporarily restricted in the adsorption step of adsorbing the organic compound of the carbon precursor on the wafer W. Therefore, it is not essential to initiate the restriction of vacuum exhaust in conjunction with the operations of supplying the carbon precursor and stopping the supply of the carbon precursor. For example, the restriction of vacuum exhaust may be initiated slightly later than time t 1  in  FIGS.  4 A and  4 B , which is the timing for initiating the supply of the carbon precursor gas to the processing container  10 . In addition, the restriction of vacuum exhaust may be initiated slightly later than time t 2  in  FIG.  10   , which is the timing for stopping the supply of the carbon precursor gas to the processing container  10 . 
     Subsequently, an example in which a batch-type vertical heat treatment apparatus, which is another embodiment of the film forming apparatus of the present disclosure, is applied to the film forming apparatus will be briefly described with reference to  FIG.  11   . In the film forming apparatus  7 , a wafer boat  72  in which a large number of wafers W are loaded in a shelf shape is airtightly accommodated inside the reaction tube  71 , which is a processing container made of quartz glass, from the lower side. Inside the reaction tube  71 , two gas injectors  73  and  74  are disposed to face each other across the wafer boat  72  in the length direction of the reaction tube  71 . 
     The gas injector  73  is connected to a gas source  811  of a carbon precursor, for example, BTMSA gas, via, for example, a gas supply path  81 . In addition, the gas injector  73  is connected to a source  821  of a purge gas, for example Ar gas, via, for example, a branch path  82  branching from the gas supply path  81 . The gas supply path  81  is provided with a flow rate regulator  812 , a storage tank  813 , and a valve  814  from the upstream side, and the branch path  82  is provided with a flow rate regulator  822  and a valve  823  from the upstream side. In this example, the carbon precursor supplier that supplies the carbon precursor gas to the reaction tube  71  includes the gas supply path  81  and the BTMSA gas source  811 . 
     The gas injector  74  is connected to a source  831  of a silicon precursor, for example, disilane gas, via, for example, a gas supply path  83 . In addition, the gas injector  74  is connected to a source  841  of Ar gas as a purge gas via, for example, a branch path  84  branching from the gas supply path  83 . The gas supply path  83  is provided with a flow rate regulator  832 , a storage tank  833 , and a valve  834  from the upstream side, and the branch path  84  is provided with a flow rate regulator  842  and a valve  843  from the upstream side. In this example, the silicon precursor supplier that supplies the silicon precursor gas to the reaction tube  71  includes the gas supply path  83  and the disilane gas source  831 . 
     An exhaust port  75  is formed at the upper end of the reaction tube  71 , and the exhaust port  75  is connected to a vacuum exhauster  852  including a vacuum pump via a vacuum exhaust path  85  provided with an APC valve  851  that forms a pressure control valve. The vacuum exhaust path  85  is provided with a pressure detector  853  on the upstream side of the APC valve  851 . The function of the APC valve  851  is the same as the configuration example illustrated in  FIG.  1    described above. 
     In  FIG.  11   , reference numeral  76  indicates a lid configured to open/close the lower end opening of the reaction tube  71 , and reference numeral  77  indicates a rotation mechanism configured to rotate the wafer boat  72  around a vertical axis. Heaters  78  are provided around the reaction tube  71  and in the lid  76  to heat the wafers W loaded on the wafer boat  72  to a temperature within a range of, for example, 300 degrees C. or higher and 500 degrees C. or lower. 
     In this film forming apparatus  7  as well, for example, a film forming process for forming a SiC film is performed according to the time chart illustrated in  FIG.  4 A ,  FIG.  4 B  or  FIG.  10   . For example, the step of accommodating wafers W into the reaction tube  71  is executed by carrying the wafer boat  72  mounted with wafers W and closing the lid  76  of the reaction tube  71 . Next, the interior of the reaction tube  71  is vacuumized, and while supplying Ar gas by opening the valves  823  and  843 , the interior of the reaction tube  71  is controlled to each of a pressure target value of, for example, 400 Pa, and a set temperature of 300 degrees C. or higher and 500 degrees C. or lower, for example, 390 degrees C. 
     Next, the step of adsorbing BTMSA on the wafer W is executed by opening the valve  814  and supplying the BTMSA gas, which is a carbon precursor, into the reaction tube  71 . Subsequently, after closing the valve  814  and stopping the supply of BTMSA gas, the interior of the reaction tube  71  is purged with Ar gas. Next, the step of forming a SiC film is executed by opening the valve  834  to supply disilane gas, which is a silicon precursor, and reacting the BTMSA adsorbed on the wafer W with the disilane. Thereafter, after closing the valve  834  and stopping the supply of disilane gas, the interior of the reaction tube  71  is purged with Ar gas. By alternately repeating multiple times the BTMSA adsorbing step and the step of reacting BTMSA with disilane, a SiC film having a predetermined film thickness is formed. 
     Then, in the BTMSA adsorbing step, the APC valve  851  is fully closed to temporarily restrict the vacuum exhaust in the reaction tube  71 , and the BTMSA gas is caused to stay in the reaction tube  71 . Thereafter, the APC valve  851  is opened to release the temporary restriction on vacuum exhaust, and the BTMSA gas is discharged from the reaction tube  71 . During the reaction step, the supply of disilane gas to the reaction tube  71  is stopped, and after stopping the supply, the restriction of vacuum exhaust is not performed, and the pressure regulating function of the APC valve  63  is set to “ON” to perform pressure control of the interior of the reaction tube pipe  71 . Specifically, for example, supply of various gases and regulation of the opening degree of the APC valve  851  are performed according to the time chart of  FIG.  4 A ,  FIG.  4 B  or  FIG.  10    described above. After executing the SiC film forming process in this way, the pressure inside the reaction tube  71  is restored to the pressure at the time of carry-in/out of the wafers W, then the lid  76  of the reaction tube  71  is opened, and the wafer boat  72  is lowered and carried out. 
     In this embodiment as well, in the step of adsorbing BTMSA on the wafers W, the vacuum exhaust of the reaction tube  71  is temporarily restricted. On the other hand, in the step of reacting the BTMSA adsorbed on the wafer W with the disilane, the temporary restriction of vacuum exhaust is not performed after stopping the supply of the disilane gas. Therefore, as in the embodiment described with reference to  FIGS.  1 ,  4 A,  4 B,  10    and the like, it is possible to form a SiC film having good film quality at a high film forming rate. 
     In each of the above-described embodiments, the temporary limitation of vacuum exhaust is not limited to the case where the vacuum exhaust is executed by controlling the opening degree of the APC valve  63 . For example, the temporary restriction of vacuum exhaust may be performed by reducing the exhaust amount of the vacuum exhauster, or by stopping the vacuum exhauster. 
     The embodiments disclosed herein should be considered to be exemplary in all respects and not restrictive. The embodiments described above may be omitted, replaced, or modified in various forms without departing from the scope and spirit of the appended claims. 
     EXAMPLES 
     Evaluation Experiment 1 
     Evaluation experiments of the film forming method of the present disclosure will be described.  FIG.  12    is a characteristic diagram showing an amount of a film formed when a SiC film is formed by an ALD method by using BTMSA as a carbon precursor, disilane as a silicon precursor, and Ar gas as a purge gas in the film forming apparatus  1  illustrated in  FIG.  1   . In order to form a SiC film, a wafer W was heated while supplying Ar gas into the processing container  10 , the pressure in the processing container  10  was regulated to a pressure target value, and then steps 1 to 8 illustrated below are executed in order from step 1 to step 8. 
     Step 1: the step of vacuumizing the interior of the processing container  10  for 3 seconds while the pressure regulating function of the APC valve  63  is set to “ON”, and then switching the pressure regulating function of the APC valve  63  to “OFF” (the fully closed state). 
     Step 2: the step of adsorbing BTSMA on the wafer by supplying BTMSA gas for 1 second while the APC valve  63  is set to the “OFF” state (the fully closed state). 
     Step 3: the step of stopping the supply of BTMSA gas while the APC valve  63  is set to the “OFF” state (fully closed state), and causing the BTMSA gas to stay in the processing container  10  for x seconds. 
     Step 4: the step of purging the interior of the processing container  10  by switching the pressure regulating function of the APC valve  63  to “ON”, and supplying Ar gas for 5 seconds while performing pressure control of the interior of the processing container  10 . 
     Step 5: the step of stopping supply of Ar gas and vacuumizing the interior of the processing container  10  for 3 seconds while the pressure regulating function of the APC valve  63  is set to “ON”, and then switching the pressure regulating function of the APC valve  63  to “OFF” to set the APC valve  63  to the fully closed state. 
     Step 6: the step of reacting BTMSA adsorbed on the wafer with disilane by supplying disilane gas for 1 second while the APC valve  63  is set to the “OFF” state (the fully closed state). 
     Step 7: the step of causing the disilane gas to stay for y seconds while the APC valve  63  is set to the “OFF” state (the fully closed state). 
     Step 8: the step of purging the interior of the processing container  10  by switching the pressure regulating function of the APC valve  63  to “ON”, and supplying Ar gas for 5 seconds while performing pressure control of the interior of the processing container  10 . 
     The film forming process is performed under the process conditions described above, and the times for setting the APC valve  63  to the fully closed state (valve closing time) in step 3 and step 7 were set to the staying time of BTMSA gas (x seconds) and the staying time of disilane gas (y seconds), respectively. 
     In Example 1, a SiC film was formed under the condition that the staying times was provided only for the BTMSA gas (x seconds in step 3: 3 seconds and 10 seconds, y seconds in step 7: 0 seconds). 
     In Comparative Example 1, a SiC film was formed under the condition that the staying time was provided for both BTMSA gas and disilane gas (x seconds in step 3: 3 seconds, y seconds in step 7: 3 seconds). 
     In Comparative Example 2, a SiC film was formed by a method in the related arts, i.e., under the condition that the staying time was not provided for both BTMSA gas and disilane gas (x seconds in step 3: 0 seconds, y seconds in step 7: 0 seconds). 
     In Comparative Example 3, a SiC film was formed under the condition that the staying time was provided only for the disilane gas (x seconds in step 3: 0 seconds, y seconds in step 7: 3 seconds and 10 seconds). 
     The results are shown in  FIG.  12   . In  FIG.  12   , the horizontal axis represents valve closing time, and the vertical axis represents film thickness (film thickness (A) per cycle). Film thicknesses for calculating film forming amounts were measured by a scanning electron microscope (SEM). These film forming amounts are indicated by ◯ in Example 1, □ in Comparative Example 1, and Δ in Comparative Example 3. Since the data of Comparative Example 2 corresponds to the data of Comparative Example 3 when the valve closing time is 0 seconds, the illustration is omitted. 
     According to  FIG.  12   , in Example 1, it was found that the film forming amounts are increased by setting the valve closing time longer. From this, it is understood that it is possible to improve the film forming rate by temporarily restricting the vacuum exhaust in the processing container  10  to cause BTMSA gas to stay. Compared to Example 1, each of Comparative Examples 1 and 3 has a larger film forming amount. As is clear from Evaluation Experiment 2 below, this is because an amorphous Si film was formed in addition to the SiC film, and thus the apparent film forming amount was increased. 
     Evaluation Experiment 2 
     For a SiC film formed by Example 1 under the condition of 10 seconds of step 3, a SiC film formed by Comparative Example 1 under the condition of 3 seconds of step 3 and the condition of 3 seconds of step 7, a SiC film of Comparative Example 2, and a SiC film formed by Comparative Example 3 under the condition of 10 seconds of step 7, the components of the SiC films were analyzed by an X-ray photoelectron spectroscopy (XPS). In  FIG.  13   , C1, C2, Si1, Si2, and Si3 indicate the following components. 
     C1: carbon atoms having a C—C bond and a C—H bond 
     C2: carbon atoms having a Si—C bond 
     Si1: Silicon atoms having a Si—C bond 
     Si2: Silicon atoms having a Si—Si bond 
     Si3: Silicon atoms having SiO x    
     As the results of the component analysis are shown in  FIG.  13   , it was found that the SiC film of Example 1 has more Si and C based on Si—C bonds than the SiC film of Comparative Example 2 formed by the conventional method, and the Si/C ratio is almost 1. As a result, it was confirmed that, by temporarily restricting vacuum exhaust in the processing container  10  and causing the BTMSA gas to stay, the Si—C bonds in the film are increased, so it is possible to obtain a SiC film having good film quality with an ideal Si/C ratio. Even when a carbon precursor such as BTMSA, which has less intramolecular polarization and is less likely to be chemisorbed on a wafer surface, was used, it was possible to form a SiC film having good film quality. In addition, it was also possible to improve the film forming rate. 
     In addition, in Comparative Examples 1 and 3 in which the vacuum exhaust in the processing container  10  was temporarily restricted in the disilane gas supply step to cause disilane gas to stay, the proportion of Si2 (Si atoms having a Si—Si bond) was much larger compared with Example 1. It is presumed that this is because the excess disilane gas generated due to the staying is thermally decomposed and forms an amorphous Si film. Accordingly, it is understood that it is preferable not to perform the restriction of vacuum exhaust in the processing container  10  in the disilane gas supply step. 
     Furthermore, focusing on film densities, Example 1 was 1.67 g/cm 3 , Comparative Example 1 was 2.01 g/cm 3 , Comparative Example 2 was 2.08 g/cm 3 , and Comparative Example 3 was 2.13 g/cm 3 . The film density of Example 1 is smaller than those of Comparative Examples 1 to 3, but it is presumed that since the larger the proportion of Si2 (silicon atoms having a Si—Si bond), the higher the film density in Comparative Examples 1 to 3, the differences in film density are caused due to the formation of an amorphous Si film. 
     EXPLANATION OF REFERENCE NUMERALS 
     W: semiconductor wafer,  10 : processing container,  2 : stage,  51 : carbon precursor source,  52 : silicon precursor source,  61 : vacuum exhauster,  62 : vacuum exhaust path,  63 : APC valve