Abstract:
A film-forming method and apparatus for performing vapor phase growth reaction avoiding a substrate becoming adhered to a substrate supporting portion, comprising: 
     placing a substrate on a substrate supporting portion in a film-forming chamber, supplying a source gas into the film-forming chamber while the substrate is rotating on a cylindrical portion for supporting the substrate supporting portion thereon, supplying a purge gas into the cylindrical portion and forming a film on the substrate while at least a part of the substrate is vibrating up and down on the substrate supporting portion by discharge of the purge gas from between the substrate and the substrate supporting portion. The vibration allowing the substrate to not become adhered to the substrate supporting portion, and thus increase throughput of the operation.

Description:
CROSS-REFERENCE TO THE RELATED APPLICATION 
       [0001]    The entire disclosure of the Japanese Patent Applications No. 2011-238285, filed on Oct. 31, 2011 including specification, claims, drawings, and summary, on which the Convention priority of the present application is based, are incorporated herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a film-forming method and a film-forming apparatus. 
       BACKGROUND ART 
       [0003]    Epitaxial growth technique for used depositing a monocrystalline film on a substrate such as a wafer is conventionally used to produce a semiconductor device such as a power device (e.g., IGBT (Insulated Gate Bipolar Transistor)) requiring a relatively thick crystalline film. 
         [0004]    In the case of film-forming apparatus used in an epitaxial growth technique, a wafer is placed inside a film-forming chamber maintained at an atmospheric pressure or a reduced pressure, and a source gas is supplied into the film-forming chamber while the wafer is heated. As a result of this process, a pyrolytic reaction or a hydrogen reduction reaction of the source gas occurs on the surface of the wafer so that an epitaxial film is formed on the wafer. 
         [0005]    In order to produce a thick epitaxial film in high yield, a fresh source gas needs to be continuously brought into contact with the surface of a grown on a wafer while the wafer is rotated uniformly heated substrate to increase a film-forming rate. Therefore, in the case of a conventional film-forming apparatus, a film is epitaxially at a high speed (see, for example, Japanese Patent Application Laid-Open No. H05-152207). 
         [0006]      FIG. 5  is a schematic cross-sectional view of a conventional film-forming apparatus. 
         [0007]    A conventional film-forming apparatus  1100  includes a chamber  1103  used as a film-forming chamber for forming an epitaxial film on a wafer  1101  as a semiconductor substrate by vapor phase growth reaction. A gas supply portion  1123  used for supplying a source gas for growing the crystalline film on the surface of the heated wafer  1101  is provided in the upper part of the chamber  1103 . The gas supply portion  1123  is connected with a shower plate  1124  on which has a plurality of through-holes for the source gas. 
         [0008]    A plurality of gas discharge portions  1125  that discharge the source gas subjected to reaction, are provided in the bottom of the chamber  1103 . The gas discharge portions  1125  are connected with a discharge system  1128  comprising of an adjustment valve  1126  and a vacuum pump  1127 . A ring-shaped susceptor  1102  for holding the wafer  1101  is provided above a rotating portion  1104  in the chamber  1103 . The susceptor  1102  has a counterbore provided thereon so that the outer periphery of the wafer  1101  can be positioned in the counterbore. 
         [0009]    The rotating portion  1104  has a cylindrical portion  1104   a  and a rotating shaft  1104   b.  The rotating shaft  1104   b  rotates, and then the susceptor  1102  will be rotated via the cylindrical portion  1104   a.    
         [0010]    As seen in  FIG. 5 , the cylindrical portion  1104   a  includes an opening in the upper part of the portion. The susceptor  1102  is positioned in the opening of the cylindrical portion  1104   a;  the wafer  1101  is placed on the susceptor  1102 . As the opening is covered with the susceptor  1102  and the wafer  1101  a hollow area (herein after area P 12 ) is formed that is separated from the area P 11  in the chamber  1103 . 
         [0011]    A heater  1120  is provided in area P 12 . Electricity is conducted to the heater  1120  via wires  1109  in a cylindrical shaped shaft  1108  within the rotating shaft  1104   b,  as a result the back surface of the wafer  1101  is heated by the heater  1120 . 
         [0012]    The rotating shaft  1104   b  of the rotating portion  1104  is connected with the rotating system (not shown) positioned outside of the chamber  1103 . The cylindrical portion  1104   a  is rotated, as a result the susceptor  1102  is rotated via the cylindrical portion  1104   a,  and the wafer  1101  is rotated with the susceptor  1102 . 
         [0013]    A transfer robot (not shown) is used for transferring the wafer  1101  into, or out of the chamber  1103  as seen in  FIG. 5 . In this case, a substrate rising means (not shown) is used for moving the wafer  1101  up and down. When the wafer  1101  is transferred out of the chamber  1103 , for example, the wafer  1101  is moved in an upwards direction via the substrate rising means to take it away from the susceptor  1102 . The wafer  1101  is then transferred to the transfer robot, and then the wafer  1101  is transferred out of the chamber  1103 . When the wafer  1101  is transferred into the chamber  1103 , the wafer  1101  is transferred from the transfer robot to the substrate rising means, and then the wafer  1101  is lowered via the substrate rising means by the elevator to be placed on the susceptor  1102 . 
         [0014]    In the conventional film-forming apparatus  1100  as seen in  FIG. 5 , when vapor phase growth reaction is performed in the chamber  1103  thin film created by the source gas is formed not only on the wafer  1101  but also on the susceptor  1102  supporting the wafer  1101 . If vapor phase growth reaction is performed on another wafer  1101  newly transferred into the chamber  1103 , a new thin film tends to be produced on the former thin film, as this process continues the wafer  1101  can become stuck to the susceptor  1102 . 
         [0015]    If the wafer  1101  becomes stuck to the susceptor  1102 , it becomes difficult to move the wafer  1101  away from the susceptor  1102  and transfer the wafer  1101  out from the chamber  1103 . As a result, the adhesion between the wafer  1101  and the susceptor  1102  causes a decrease in the speed of forming epitaxial film on the wafer  1101 . 
         [0016]    The present invention has been made to address the above issues. That is, an object of the present invention is to provide a film-forming apparatus and a film-forming method, the purpose of which can prevent adhesion between a substrate such as the wafer and the susceptor that the substrate is placed upon. 
         [0017]    Other challenges and advantages of the present invention are apparent from the following description. 
       SUMMARY OF THE INVENTION 
       [0018]    In a first embodiment of this invention, a film-forming method comprising: placing a substrate on a susceptor in a film-forming chamber, supplying a source gas into the film-forming chamber while the substrate is rotating on a cylindrical portion for supporting the susceptor thereon, supplying a purge gas into the cylindrical portion and forming a film on the substrate while at least a part of the substrate is vibrating up and down on the susceptor by discharge of the purge gas from between the substrate and the susceptor. 
         [0019]    In a second embodiment of this invention, a film-forming apparatus comprising: a film-forming chamber, a source gas supply portion for supplying a source gas into the film-forming chamber, a susceptor for holding a substrate in the film-forming chamber, a rotating portion having a cylindrical portion for supporting the susceptor, a purge gas supply portion for supplying the purge gas into the cylindrical portion, and a control unit for controlling the supply of the source gas and the purge gas so that the purge gas is discharged from between the substrate and the susceptor, thereby at least a part of the substrate rises on the susceptor. 
     
    
     
       BRIEF DESCRIPTION OF THE DIAGRAMS 
         [0020]      FIG. 1  is a schematic cross-sectional view of a single wafer film-forming apparatus according to the present embodiment. 
           [0021]      FIG. 2  is a schematic cross-sectional view of a susceptor of a film-forming apparatus according to the present embodiment. 
           [0022]      FIG. 3  shows an example of the film-forming method according to the present embodiment. 
           [0023]      FIG. 4  shows another example of the film-forming method according to the present embodiment. 
           [0024]      FIG. 5  is a schematic cross-sectional view of a conventional film-forming apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiment 1 
       [0025]      FIG. 1  is a schematic cross-sectional view of a single wafer film-forming apparatus according to the present embodiment. 
         [0026]      FIG. 1  is a schematic cross section of a film-forming apparatus according to the present embodiment. 
         [0027]    In the present embodiment, a substrate  101  may be a wafer, as one example of a substrate, is used to form a film thereon. The substrate  101  is placed on the susceptor  102  of the film-forming apparatus  100  according to the present embodiment as shown in  FIG. 1 . 
         [0028]    The film-forming apparatus  100  includes a chamber  103  to be used for forming an epitaxial film on the substrate  101  via vapor phase growth reaction. 
         [0029]    A gas supply portion  123 , used for supplying a source gas is provided at the upper of the chamber  103  of the film-forming apparatus  100 . Gas pipes  131  and  132  are connected to the gas supply portion  123 . The other end of the gas pipes  131  and  132  are connected to gas storing portions  133  and  134  comprising of, for example, a gas cylinder. Gas valves  135 ,  136  for adjusting the supply of the gas, are connected along the gas pipe  131 ,  132 . The source gas  137  for forming the epitaxial film on the substrate  101  is stored in the gas storing portion  133 . The carrier gas  138  is stored in the gas storing portion  134 . The gas valve  135  is provided to control the supply of the source gas  137  that is supplied from the gas supply portion  123  to the chamber  103 . The gas valve  136  is provided to control the supply of the carrier gas  138  that is supplied from the gas supply portion  123  to the chamber  103 . 
         [0030]    The film-forming apparatus  100  includes a gas control unit  140  for controlling the supply of the gas that is supplied to the chamber  103 . The gas control unit  140  is connected with the gas valves  135 ,  136 . The gas control unit  140  controls the gas valves  135 ,  136 , and thereby controls the supply of the source gas  137  and the carrier gas  138  that are supplied from the gas supply portion  123  to the chamber  103 . The source gas  137  for forming the epitaxial film is supplied on the surface of the substrate  101  that is heated to a high temperature. 
         [0031]    The gas supply portion  123  is connected with a shower plate  124  on which has a plurality of through-holes for the source gas  137  etc. The shower plate  124  is provided at the upper portion of the chamber  103  so that it faces the surface of the substrate  101 , thereby the source gas  137  can be supplied to the surface of the substrate  101 . 
         [0032]    A plurality of gas discharge portions  125  for discharging the source gas  137 , carrier gas  138 , and other gases resulting from the epitaxial reaction, are provided at the bottom of the chamber  103 . The gas discharge portions  125  are connected to a discharge system  128  comprising an adjustment valve  126  and a vacuum pump  127 . The discharge system  128  is controlled by a control system (not shown) to adjust the pressure in the chamber  103 . 
         [0033]    A susceptor  102  is provided above the rotating portion  104  in the chamber  103 . The susceptor  102  is a ring-shape with a counterbore provided within the opening so that the outer periphery of the substrate  101  can be positioned in the counterbore. As the susceptor  102  is used under high temperatures, a susceptor obtained by coating the surface of isotropic graphite with SiC, of a high degree of purity and a high resistance to heat, by CVD (Chemical Vapor Deposition) is used (as one example). 
         [0034]    The shape of the susceptor  102  is not limited to the example of  FIG. 1 . 
         [0035]      FIG. 2  is a schematic cross-sectional view of another susceptor in a film-forming apparatus according to the present embodiment. 
         [0036]    Another example of a susceptor  102 , as seen in  102   a,  has an overhanging portion  150  that overhangs the counterbore of the susceptor  102   a.  The overhanging portion  150  is provided to control the up-and-down motion of the substrate  101  on the susceptor  102   a  so that the substrate  101  doesn&#39;t come out of the susceptor  102   a  while the substrate  101  is rotating. 
         [0037]    The rotating portion  104  includes a cylindrical portion  104   a  and a rotating shaft  104   b.  The susceptor  102  is held above the cylindrical portion  104   a  in the rotating portion  104 . A motor (not shown) rotates the rotating shaft  104   b  resulting in the susceptor  102  rotating via the cylindrical portion  104   a.  Accordingly the substrate  101  can be rotated after the substrate  101  is placed on the susceptor  102 . 
         [0038]    As seen in  FIG. 1 , the cylindrical portion  104   a  has an opening in the upper part of the portion. The susceptor  102  can be positioned in the opening, or on the opening of the cylindrical portion  104   a,  and then the substrate  101  is placed on the susceptor  102 . This results in the opening being covered with the susceptor  102  and the substrate  101 , and a hollow area (herein after area P 2 ) is formed. Inside the chamber  103  the area P 2  is substantially separated from area P 1  by the substrate  101  and the susceptor  102 . 
         [0039]    Therefore, it is possible to prevent contamination of the substrate  101  by a contaminant generated around an in-heater  120  and an out-heater  121  (described later). It is also possible to prevent the source gas  137 , and the carrier gas  138  in the area P 1 , from coming into the area P 2  and contacting with the in-heater  120  and the out-heater  121 . 
         [0040]    In the film-forming apparatus  100  according to the present embodiment, the top portion of a gas supply pipe  111  is positioned in the area P 2 . A purge gas  151  is supplied to the area P 2  by the gas supply pipe  111 . 
         [0041]    In the film-forming apparatus  100 , a through-hole can be provided at the sidewall around the bottom of the cylindrical portion  104   a  so that the through-hole is bored through the sidewall, as shown in  FIG. 1 . The through-hole is a discharge portion  155  which discharges the purge gas  151  supplied to the area P 2 . The purge gas  151  is supplied to the area P 2  according to the amount that can be discharged from the discharge portion  155  in the cylindrical portion  104   a,  thereby the purge gas  151  can purge around the in-heater  120  and the out-heater  121 . In this case, the purge gas  151  that was supplied to the area P 2  will be discharged from the discharge portion  155  and the state of separation of the area P 2  from the area P 1  can be substantially maintained. 
         [0042]    The in-heater  120  and the out-heater  121  used as heaters are provided in the area P 2 . For use as the in-heater  120  and the out-heater  121 , resistive heaters can be used; the material of these are obtained by coating the surface of carbon material with SiC of a high resistance to heat. Electricity is conducted to these heaters via wires  109  positioned in a cylindrical shaped shaft  108 , wherein the cylindrical shaped shaft  108  consists of quartz, contained in the rotating shaft  104   b;  thereby these heaters heat the back surface of the wafer  101  placed on the susceptor  102 . The out-heater  121  mainly heats the periphery of the substrate  101 , as the heat in the outer periphery of the substrate  101  easily escapes. The out-heater  121  is provided as well as the in-heater  120 , and the substrate  101  can be uniformly heated by the double heaters. 
         [0043]    The surface temperature of the substrate  101  is measured by radiation thermometers  122  provided at upper portion of the chamber  103 . It is preferred that the shower plate  124  be formed of quartz, because the use of quartz prevents the shower plate  124  affecting the temperature measurement of the radiation thermometers  122 . The measured data of the temperature is sent to a control system (not shown), and then the control system provides feedback to an output control system of the in-heater  120  and the out-heater  121 . Accordingly the substrate  101  can be heated to the desired temperature. 
         [0044]    A pin  110 , capable of moving in an up and down direction, supporting the substrate  101 , is provided in the shaft  108 . The end of the pin  110  extends to a substrate rising means (not shown) provided at the bottom of the shaft  108 . The pin  110  can be moved up and down by the substrate rising means. The pin  110  is used when the substrate  101  is transferred into and out of the chamber  103 . The pin  101  supports the bottom of the substrate  101 , and then rises to move the substrate  101  away from the susceptor  102 . The substrate  101  is then positioned above the rotating portion  104  separate from the susceptor  102  by the pin  110 , allowing a transfer robot (not shown) to remove the substrate  101 . 
         [0045]    A gas supply pipe  111  is provided in the shaft  108 . The opening of the gas supply pipe  111  extends into the area P 2  inside of the cylindrical portion  104   a.  A purge gas  151  is supplied to the area P 2  by the gas supply pipe  111 . The gas supply pipe ill is connected with a gas pipe  152 . The end of the gas pipe  152  is connected with a gas-storing portion  153  comprising of a gas cylinder. The purge gas  151  supplied to the area P 2  is stored in the gas-storing portion  153 . 
         [0046]    A gas valve  154  for adjusting the supply of the gas is connected to the gas pipe  152 . The gas valve  154  is connected with the above-mentioned gas control unit  140 . Therefore the gas control unit  140  controls the gas valve  154 , and thereby the purge gas  151 , which is supplied from the gas pipe  111  to the area P 2 , is controlled in the film-forming apparatus  100 . The gas control unit  140  also controls the source gas  137  for forming the epitaxial film on the surface of the substrate  101 , the carrier gas  138 , and the purge gas  151 , which is supplied to purge the area P 2 . 
         [0047]    The purge gas  151  stored in the gas storing portion  153 , to be supplied from the gas supply pipe  111  to the area P 2  by the gas control unit  140 , is at least one selected from the group consisting of an inert gas such as argon (Ar) gas and helium (He) gas, hydrogen (H 2 ) gas and nitrogen (H 2 ) gas. 
         [0048]    In the film-forming apparatus  100  according to the present embodiment, the source gas  137  that will be supplied to the area P 1  and the purge gas  151  for purging the area P 2  are individually controlled by the gas control unit  140 , in the film-forming process for forming the epitaxial film on the substrate  101 . The purge gas  151  can also be supplied with the source gas  137  in the film-forming apparatus  100 . 
         [0049]    In the film-forming apparatus  100 , the purge gas  151  can be supplied to the area P 2  of the cylindrical portion  104   a  while the substrate  101  on the susceptor  102  is rotating. The purge gas  151  supplied the area P 2  is exhausted from between the substrate  101  and the susceptor  102 , thereby at least a part of the substrate  101  will rise on the susceptor  102 . That is, the epitaxial film is formed using the source gas  137  supplied in the Area P 1  on the substrate  101  while at least a part of the substrate  101  is rising on the susceptor  102  in the film-forming apparatus  100 . 
         [0050]    In the film-forming apparatus  100 , the purge gas  151  is supplied to area P 2  of the cylindrical portion  104   a;  thereby at least a part of the rotating substrate  101  will rise on the susceptor  102 . The discharge portion  155  can be provided in the film-forming apparatus  100  as mentioned above. The amount of purge gas  151  that can be exhausted from the discharge portion  155  may be supplied into the area P 2  and purged around the in-heater  120  and the out-heater  121  before the substrate  101  will rise. In that situation, the amount of the purge gas  151  supplying to the area P 2  can be temporarily increased; thereby at least a part of the substrate  101  can be risen on the susceptor  102 . 
         [0051]    The film-forming apparatus  100  is constructed so that the pressure in the area P 1  of the chamber  103  is almost same as the pressure of the area P 2  in the cylindrical portion  104   a.  Moreover the pressure of the area P 2  is a little higher than the pressure the area P 1  so that the source gas  137  in the area P 1  and the carrier gas  138  used with the source gas  137  cannot be enter into the area P 2 . For example, the pressure of the area P 1  is set to 300 Torr, the pressure of the area P 2  in the cylindrical portion  104   a  can set between 301 Torr to 305 Torr. Therefore the flow rate of the purge gas  151  supplied to the area P 2  can be set at a rate of 5 L/minute or below. In the film-forming apparatus  100 , such flow rate of the purge gas  151  can be always supplied to the area P 2  in the process that the epitaxial film is formed while the substrate is rotating. 
         [0052]    The purge gas  151  is supplied to the area P 2  of the cylindrical portion  104   a  to make at least a part of the rotating substrate  101  rise on the susceptor  102 . In this situation, the supply amount of the purge gas  151  is temporarily increased over the current supply amount by the gas control unit  140 . The supply amount of the purge gas  151  is temporarily increased to  10  times or more, for example, 6 L/minute to 10 L/minute to make a least a part of the substrate  101  rise on the susceptor  102 . 
         [0053]    The substrate  101  can be temporarily raised on the susceptor  102 . The substrate  101  will then be back to the previous position on the susceptor  102  by the exhaustion of the purge gas  151  from between the substrate  101  and the susceptor  102 . This is repeated; thereby the substrate  101  can move slightly up and down. At the same time the substrate  101  is rotated at high speeds via the susceptor  102 . That is, the substrate  101  is rotating at high speeds while slightly moving up and down. 
         [0054]    In the film-forming apparatus  100 , the epitaxial film can be formed on the substrate  101  while the substrate  101  is rotating and vibrating up and down on the susceptor  102 . At that time, the outer periphery of the wafer  101  that is positioned in the counterbore, occasionally contacts the counterbore, therefore the epitaxial film will not be formed on the outer periphery. 
         [0055]    As mentioned above, the thin film caused by the source gas  137  is formed not only on the surface of the substrate  101  but also on the surface of the susceptor  102  supporting the substrate  101  when the vapor phase growth reaction is performed in the chamber  103  of the film-forming apparatus  100 . There is a concern that the substrate will become attached to the susceptor via the thin film on the susceptor in the above-mentioned conventional film-forming apparatus. 
         [0056]    However, if the substrate  101  can be rotated at high speeds while vibrating up and down on the susceptor  102  as a result of the purge gas  151  supplied to the area P 2  of the cylindrical portion  104   a  in the film-forming apparatus  100  according to the present embodiment, the adhesion between the substrate  101  and the susceptor  102  can be prevented, even if a thin film caused by the source gas  137  is formed between the substrate  101  and the susceptor  102 . 
       Embodiment 2 
       [0057]    Next, the film-forming method according to the present embodiment will be described. The film-forming apparatus  100  as shown in  FIG. 1  can perform the film-forming method according to the present embodiment. This will be explained with reference to  FIG. 1 . 
         [0058]    In the film-forming method according to the present embodiment, an epitaxial film is formed on the substrate  101  by vapor phase growth reaction. The adhesion between the substrate  101  and the susceptor  102  can be prevented even if a thin film, caused by the source gas  137 , is formed between the substrate  101  and the susceptor  102 . The diameter of the substrate  101  is 200 mm or 300 mm for example. 
         [0059]    The substrate  101  is transferred into the chamber  103  of the film-forming apparatus  100  by a transfer robot (not sown). The purge gas  151  can be supplied to the area P 2  via the gas supply pipe  111 , which extends into the area P 2 , by the gas control unit  140  when the substrate  101  is transferred. The flow rate of the purge gas  151  is determined so that the substrate  101  can be positioned on the susceptor  102 . That is, the flow rate is preferably determined so that at least a part of the substrate  101  will not rise on the susceptor  102  by the exhaustion of the purge gas  151  supplied to the area P 2  from between the substrate  101  and the susceptor  102 . For example, the flow rate of the purge gas  151  supplied to the area P 2  is determined at a rate of 5 L/minute or below. 
         [0060]    The previously mentioned gas can be used as the purge gas  151 . Further the purge gas  151  is preferably chosen from at least one of argon gas and nitrogen gas that will avoid damaging the in-heater  120  and the out-heater  121  consisting of carbon material if the purge contacts these heaters. 
         [0061]    A pin  110  capable of moving in an up and down direction supporting the substrate  101 , is provided through the rotating shaft  104   b  in the rotating portion  104  of the film-forming apparatus  100  as shown in  FIG. 1 . The substrate  101  is transferred to the pin  110  from the transfer robot. 
         [0062]    The pin  110  rises from the first position to a predetermined position above the susceptor  102  to receive the substrate  101  from the transfer robot, after the substrate  101  is transferred to the pin  110 , the pin  110  descends while the substrate is held by the pin  110 . 
         [0063]    The pin  110  is returned to the first position as shown in  FIG. 1 . Thereby the substrate  101  is positioned on the susceptor  102  on the cylindrical portion  104   a  of the rotating portion  104 . 
         [0064]    Next, the pressure of the chamber  103  is set to a specific atmospheric pressure or a reduced pressure, and then hydrogen gas as a carrier gas  138  is supplied from the gas supply portion  123  to the area P 1  by the gas control unit  140 . The substrate  101  is rotates at about 50 rpm via the rotating portion  104  while the carrier gas  138  is flows. 
         [0065]    The purge gas  151  having the above-mentioned flow rate, is supplied to the area P 2  of the cylindrical portion  104   a.  The purge gas  151  is purged in the area P 2 , and then is exhausted through the discharge portion  155 . The area P 2  is substantially separated from the area P 1 . 
         [0066]    When the cylindrical portion  104   a  for forming the area P 2  doesn&#39;t have the discharge portion  155 , the supply of the purge gas  151  would be stopped or a small amount of the purge gas  151  would be supplied. In this case, the area P 2  can be substantially separated from the area P 1 . As a result the substrate  101  can remain stable on the susceptor  102 . 
         [0067]    Next, the substrate  101  is heated to between 1100 and 1200 degrees by the in-heater  120  and the out-heater  121 . For example, the substrate  101  would be gradually heated to 1150 degrees as a film-forming temperature. 
         [0068]    After it is confirmed that the temperature of the substrate  101  measured by the radiation thermometer  122  has reached 1150° C., the number of revolutions of the substrate  101  positioned on the susceptor  102  is gradually increased to a predetermined speed. The source gas  137  is supplied through the shower plate  124  from the gas supply portion  123  to the chamber  103  by the gas control unit  140 . In the present embodiment, trichlorosilane can be used as a source gas  137 . The source gas  137  that is mixed with hydrogen gas as a carrier gas  138 , is introduced from the gas supply portion  123  into the area P 1  of the chamber  103 . 
         [0069]    In the film-forming method according to the present embodiment, the gas control unit  140  starts supplying the source gas  137  from the gas supply portion  123  to the area P 1 , and increases the supply amount of the purge gas  151  from the gas supply pipe  111  to the area P 2 . Thereby the purge gas  151  can be exhausted through the opening between the substrate  101  and the susceptor  102 , and at least a part of the substrate  101  can be risen while the substrate  101  is rotating. That is, the substrate  101  is rotating at high speed while vibrating up and down as mentioned above. 
         [0070]    If the purge gas  151  is not supplied through the gas supply pipe  111  to the area P 2  before the source gas  137  is supplied through the gas supply portion  123  to the area P 1 , the purge gas  151  is supplied through the gas supply pipe  111  to the area P 2 , at the same time that the source gas  137  is supplied to the area P 1 . Then, at least a portion of the substrate  101  is rising on the susceptor  102  while it is rotating. 
         [0071]    The source gas  137  introduced to the area P 1  in the chamber  103  flows downward toward the substrate  101 . The substrate  101  is rotated at high speed while slightly vibrating up and down as a result of the supply of the purge gas  151  to the area P 2  of the cylindrical portion  104   a  by the gas control unit  140 , as mentioned above. 
         [0072]    While the temperature of the substrate  101  is maintained at 1150 degrees, and the susceptor  102  on the cylindrical portion  104   a  is rotating at  900 rpm or more, the source gas  137  is continuously supplied to the substrate  101  through the shower plate  124  from the gas supply portion  123 . 
         [0073]    As a result, the speed of the vapor phase growth reaction process on the substrate  101  is increased, and then the epitaxial film can be efficiently formed at high speed. 
         [0074]    According to the present embodiment, the susceptor  102  is rotated while the source gas  137  is been flowing, thereby the silicon epitaxial film can be uniformly formed on the substrate  101 . For example, the silicon epitaxial film can have a thickness of 10 μm or more, usually between 10 μm to 100 μm on the substrate having a diameter of 300 mm. The rotation of the substrate is preferable to be fast, for example about 900 rpm as the above-mentioned, to form a thick film during the film-formation. 
         [0075]    In the film-forming method according to the present embodiment, when the vapor phase growth reaction is performed in the film-forming chamber  103 , a thin film formed by the source gas  137  would be formed not only the surface of the substrate  101  but also on the susceptor  102  supporting the substrate  101  as mentioned above. 
         [0076]    The film-forming apparatus  100  of the present embodiment, utilizes the purge gas  151  supplied to the area P 2  of the cylindrical portion  104   a  by the gas control unit  140 . The substrate  101  can be rotated at high speed while slightly vibrating up and down as mentioned above. Accordingly, adhesion between the substrate  101  and the susceptor  102  can be prevented even if a thin film formed by the source gas  137  is formed between the substrate  101  and the susceptor  102 . 
         [0077]    After the epitaxial film having a predetermined thickness is formed on the substrate  101 , the heating by the in-heater  120  and the out-heater  121  is stopped and the supply of the source gas  137  from the gas supply portion  123  is finished. The supply of the carrier gas  138 , controlled by the gas control unit  140 , can be also stopped along with the source gas  137 , or the supply of the carrier gas  138  can continue until the temperature of the substrate  101  reaches, or is below, a predetermined value. 
         [0078]    When the source gas  137  is finished being supplied, the increased level of purge gas  151  should finish, however the purge gas  151  should continue at the previous rate into the area P 2 . 
         [0079]    After the film-formation on the substrate  101  is finished, and the substrate  101  on which the epitaxial film was formed is cooled to the predetermined temperature, the substrate  101  is transferred out of the chamber  103 . In this case, the pin  110  is raised. The pin  110  supports the bottom of the substrate  101 . The pin  110  is further moved in an upward direction to move the substrate  101  away from the susceptor  102 . In the film-forming method according to the present embodiment, the substrate  101  is prevented sticking to the susceptor  102 . Therefore, it is easy for the pin  110  to move the substrate  101  with the epitaxial film  102  away from the susceptor  102 , and the substrate  101  and the epitaxial film on the substrate  101  will not damaged. 
         [0080]    The substrate  101  is transferred to the transfer robot (not shown) by the pin  110 . After that, the robot  101  transfers the substrate  101  out of the chamber  103 . 
         [0081]    In the present embodiment, the gas control unit  140  can increase the amount of purge gas  151  supplied to the area P 2  when the supply of the carrier gas  138  to the area P 2  is started. Moreover the gas control unit  140  can increase the amount of the supply of the purge gas  151  before the supply of the carrier gas  138  to the area P 2  is started. For example, the substrate  101  is rotated at about  50 rpm, and then the supply of the purge gas  151  can be increased while the substrate  101  is gradually heated to the film-forming temperature, by the in-heater  120  and the out-heater  121 . 
         [0082]    In the film-forming method according to the present embodiment, for example, the amount of the purge gas  151  is increased through the gas supply pipe  111  to the area P 2  when the source gas  137  is supplied from the gas supply portion  123  to the area P 1  by the gas control unit  140 . 
         [0083]    In the film-forming method according to the present embodiment, the time of temporarily increasing the supply of the purge gas  151  does not need to be a continuous period. For example, in another example of the film-forming method according to the present embodiment, a plurality of periods of increasing the amount of the supply of the purge gas  151  can be intermittently set while the epitaxial film is formed on the substrate  101 , that has been heated, by the supply of the source gas  137 . 
         [0084]    In another example of the film-forming method, the period of supplying the purge gas  151  at the amount before increasing can be set between the periods for increasing the supply of the purge gas  151 . 
         [0085]    According to another example, the period for rotating the substrate, heated at a high temperature, at high speed while it is slightly vibrating up and down can be set while the supply of the purge gas  151  is increasing. Therefore, the adhesion between the substrate  101  and the susceptor  102  can be prevented even if the thin film caused by the source gas  137  is formed between the substrate  101  and the susceptor  102 . 
         [0086]    In the film-forming method according to the present embodiment, the source gas  137  can be continuously supplied when the substrate  101  is heated to a high temperature and rotated at a high speed to form the epitaxial film on the substrate  101  as mentioned above. The source gas  137  can also be intermittently supplied when the epitaxial film is formed on the substrate  101  that is heated to a high temperature, thereby the speed of film-forming will be higher and the film will be efficiently formed. That is, at least one period for temporarily stopping the supply of the source gas  137  can be set while the source gas  137  is supplied on the substrate  101 , heated to a high temperature, to form the epitaxial film. Thereby the saturation of the vapor phase growth reaction on the substrate  101  can be prevented, as a result the epitaxial film can be more efficiently formed on the substrate  101 . 
         [0087]    In the film-forming method according to the present embodiment, when the period for stopping the supply of the source gas  137  is set by the gas control unit  140  in the above-mentioned example, the period for increasing the amount of the supply of the purge gas  151  can be set while the source gas  137  is stopping. 
         [0088]      FIG. 3  is a diagram for explaining another example of the film-forming method according to the present embodiment. 
         [0089]    In another example of the film-forming method according to the present embodiment, as seen in  FIG. 3 , the flow amount of the purge gas  151  supplied through the gas supply pipe  111  to the area P 2  changes depending on the time by the gas control unit  140 . 
         [0090]    That is, a plurality of periods of supplying the source gas  137  can be intermittently set by the gas control unit  140  in the process for forming the epitaxial film on the substrate  101  that has been heated. The period for temporarily stopping supplying the source gas  137  by the gas control unit  140  can be set between the periods of supplying of the source gas  137 . The period that the purge gas  151  increases is the same length as the period for stopping supplying the source gas  137  or less than the length, while the source gas  137  is stopping, in another example of the film-forming method according to the present embodiment. 
         [0091]    In this case, the substrate  101  can be rotated at high speed while being heated and while slightly vibrating up and down in the period for increasing the purge gas  151 . Therefore the adhesion between the substrate  101  and the susceptor  102  can be prevented even if the thin film caused by the source gas  137  is formed between the substrate  101  and the susceptor  102 . 
         [0092]    The supply of the purge gas  151  will not be increased in the period of supplying the source gas  137 , and the previous amount of the supply of the purge gas  151  will be maintained to control the slight vibration up and down of the substrate  101 . Therefore, the adhesion between the substrate  101  and the susceptor  102  can be prevented and the epitaxial film having high quality can be more efficiently formed in more stable condition. 
         [0093]    As the mentioned above, the supply of the purge gas  151  is stopped or decreased to a smaller amount when the cylindrical portion  104   a  for forming the area P 2  does not have the discharge portion  155 , thereby the area P 2  is substantially separated from the area P 1 . In that case, the period of supplying the purge gas  151  can be set while the supply of the source gas  137  is stopped, as other example of the film-forming method according to the present embodiment. 
         [0094]      FIG. 4  is a diagram showing another example of the film-forming method according to the present embodiment. 
         [0095]      FIG. 4  shows the example in which the gas control unit  140  intermittently sets the period of supplying the purge gas  151  to the area P 2 , and the flow amount of the purge gas  151  supplied to the area P 2  changes depending on the time. 
         [0096]    That is, in another example of the film-forming method according to the present embodiment, the gas control unit  140  in the process for forming the epitaxial film on the substrate  101 , while the substrate is heated, can intermittently set a plurality of periods of supplying the source gas  137 . The period for temporarily stopping supplying the source gas  137  can be set by the gas control unit  140  between the periods of supplying the source gas  137 . The period for temporarily supplying the purge gas  151  to the area P 2  can be set for the same length as the period for stopping supplying the source gas  137  or less while the source gas  137  is stopping in the other example of the film-forming method according to the present embodiment. 
         [0097]    In this case, the substrate  101  can be rotated at high speed while the substrate  101  is heated, and slightly vibrating up and down in the period of supplying the purge gas  151 . Therefore the adhesion between the substrate  101  and the susceptor  102  can be prevented even if the thin film caused by the source gas  137  is formed between the substrate  101  and the susceptor  102 . 
         [0098]    The purge gas  151  will not be supplied in the period of supplying the source gas  137  to control the slight vibration up and down of the substrate  101 . Therefore the adhesion of between the substrate  101  and the susceptor  102  can be prevented and the epitaxial film having high quality can be more efficiently formed in more stable condition according to another example of the film-forming method according to the present embodiment. 
         [0099]    Features and advantages of the present invention can be summarized as follows. 
         [0100]    According to the film-forming method of the present invention, the adhesion between a substrate, such as a wafer, and a unit for supporting the substrate, such as a susceptor, can be prevented. According to the film-forming apparatus of the present invention, the adhesion between a substrate such as a wafer and a unit for supporting the substrate such as a susceptor can be prevented. 
         [0101]    The present invention is not limited to the embodiments described and can be implemented in various ways without departing from the spirit of the invention. 
         [0102]    In addition to the above-mentioned embodiments, an epitaxial growth system cited as the example of a film-forming apparatus for forming epitaxial film in the present invention is not limited to these. Source gas supplied into the film-forming chamber for forming a film on the surface of a semiconductor substrate, while heating the semiconductor substrate, can also be applied to other apparatus such as CVD (Chemical Vapor Deposition) film-forming apparatus.