Abstract:
In the disclosed vapor deposition method, by using a structure wherein an inner diameter of a group-V source gas introduction piping is greater than an outer diameter a group-III source gas introduction piping, and the group-III source gas introduction piping is inserted one-to-one into the interior of the group-V source gas introduction piping, the group-III source gas piping is thereby prevented from being cooled by a cooling mechanism, and hardening of metallic materials upon the surface of the wall of the piping is alleviated. It is thus possible to provide a vapor deposition device, a vapor deposition method, and a semiconductor element manufacturing method, which are capable of efficaciously introducing easily hardening metallic materials into a reactor without the metallic materials adhering to a showerhead or a piping, and to carry out efficacious doping.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a vapor deposition device such as vertical showerhead type MOCVD (Metal Organic Chemical Vapor Deposition) or the like, for example, a vapor deposition method and a semiconductor element manufacturing method. 
       BACKGROUND ART 
       [0002]    In general, a thin film of a group III-V semiconductor crystal of GaAs, InGaP or the like is employed in a device such as a light-emitting diode, a semiconductor laser or the like. In recent years, a nitride crystal represented by InGaN or InGaNAs, referred to as a III-V nitride-based semiconductor crystal, has been particularly watched with interest. 
         [0003]    InGaN or InGaNAs referred to as the aforementioned III-V nitride-based semiconductor crystal has a band gap of 0.8 eV to 1.0 eV absent in semiconductor crystals other than the aforementioned III-V nitride-based semiconductor crystal such as InGaP or InGaAs, and hence high-efficiency light emission and photoreceiving become possible. 
         [0004]    Further, a technique of varying the band gap with the composition of doped nitride has also been reported, and attention to a high-quality nitride-based semiconductor crystal is paid from various types semiconductor application fields. In particular, expectation has increased in the field of a solar cell to which streamlining is earnestly desired. 
         [0005]    In manufacturing of these semiconductor crystals, MOCVD (Metal Organic Chemical Vapor Deposition) growing a compound semiconductor crystal by introducing an organic metal gas such as trimethyl gallium (TMG) or trimethyl aluminum (TMA) and a hydrogen compound gas such as ammonia (NH3), phosphine (PH3) or arsine (AsH3) or a hydrocarbon compound gas such as tertiary butyl arsine (TBAs) into a growth chamber as source gases contributing to film formation is widely known. 
         [0006]    MOCVD is a method introducing the aforementioned source gases into the growth chamber along with an inert gas, heating the same and vapor-phase-reacting the same on a prescribed substrate thereby growing a compound semiconductor crystal on the substrate. 
         [0007]    In manufacturing of the compound semiconductor crystal employing MOCVD, it is regularly highly required how to ensure a yield and productive capacity to the maximum by suppressing the cost while improving the quality of the growing compound semiconductor crystal. In other words, film forming efficiency indicating how many crystals could be film-formed from source gases is desirably higher. In order to apply the same as an excellent device, the film thickness and the composition ratio are desirably uniform. 
         [0008]      FIG. 12  shows a schematic structure of an example of a conventional vertical showerhead type MOCVD device  200  employed for MOCVD. In MOCVD device  200 , a gas pipe  203  for introducing source gases and an inert gas is connected from a gas supply source  202  to a growth chamber  211  in a reactor  201 . A shower plate  210  having a plurality of gas discharge ports for introducing the source gases and the inert gas into growth chamber  211  is set as a gas introducing portion in an upper portion of growth chamber  211  in reactor  201 . 
         [0009]    A rotating shaft  212  rotatable by an unshown actuator is set at the center of a lower portion of growth chamber  211  in reactor  201 . A susceptor  208  is mounted on the forward end of rotating shaft  212 , to be opposed to shower plate  210 . A heater  209  for heating susceptor  208  is mounted on a lower portion of aforementioned susceptor  208 . 
         [0010]    Further, a gas discharge portion  204  for discharging the gases from growth chamber  211  in reactor  201  is set on a lower portion of reactor  201 . Gas discharge portion  204  is connected to an exhaust gas treater  206  for detoxifying the discharged gas through a purge line  205 . 
         [0011]    In a case of growing a compound semiconductor crystal in vertical showerhead type MOCVD device  200  having the aforementioned structure, one or a plurality of substrates  207  are set on susceptor  208 , and susceptor  208  is thereafter rotated by rotation of rotating shaft  212 . Then, substrates  207  are heated to a prescribed temperature through susceptor  208  by heating of heater  209 . The source gases and the inert gas are introduced from the plurality of gas discharge ports formed in shower plate  210  into growth chamber  211  in reactor  201 . 
         [0012]    As a method of forming thin films by supplying a plurality of source gases and reacting the same on substrates  207 , a method of mixing the plurality of gases in shower plate  210  and injecting the source gases from the gas discharge ports provided in shower plate  210  in a large number to substrates  207  has been adopted in general. 
         [0013]    In recent years, a method of providing buffer areas for respective ones of a plurality of supplied gases and supplying the respective source gases from these buffer areas into the growth chamber in separated states through the gas discharge ports of shower plate  210  has been frequently employed in general. This is in order to avoid occurrence of gas phase reaction in the showerhead. 
         [0014]    For example,  FIG. 13  shows a reaction vessel  300  disclosed in Japanese Patent Laying-Open No. 8-91989 (FIG. 2) (PTL 1). In reaction vessel  300 , such a multilayer structure is employed that a buffer area  301  for a group III source gas and a buffer area  302  for a group V source gas are vertically arranged and gas passages are separated from each other so that the respective gases do not get mixed in portions other than a growth chamber  303 . In the case of reaction vessel  300 , the aforementioned group III source gas discharge ports and group V source gas discharge ports are alternately approximately arranged on a shower plate. 
         [0015]    In Japanese Patent Laying-Open 2000-144432 (PTL 2), there is disclosed a structure for preventing prereaction and injecting a mixed gas toward a substrate in a stable state by arranging a nozzle member communicating with a second gas space in a gas injection port communicating with a first gas space. 
         [0016]    For the purposes of ensuring uniformity of a film and suppressing adhesion of products to a showerhead, a temperature control mechanism or a cooling mechanism is frequently provided on a gas introducing pipe immediately above the showerhead. For example, a passage in which cooling water flows is provided on a shower surface in the aforementioned PTL 1. 
         [0017]      FIG. 14  shows a film forming device  400  disclosed in Japanese Patent Laying-Open No. 2007-273747 (FIG. 1) (PTL 3). In film forming device  400 , an annular temperature control chamber  405  is provided on the periphery of a gas passage  404 , and a gas in gas passage  404  can be kept at a constant temperature by feeding a coolant or a heating medium into temperature control chamber  405  thereby controlling the temperature in gas passage  404 . 
         [0018]    As described above, the MOCVD device is a device frequently employed for preparing a compound semiconductor crystal. In order that a semiconductor crystal obtains desired characteristics, a semiconductor may be doped with impurities in preparation. Therefore, various dopant gases may be used for source gases also in the MOCVD device. 
         [0019]    At this time, there is such a problem that a partial metallic material such as Cp2Mg (biscyclopentadienyl magnesium) coagulates in a pipe in the showerhead or on a wall surface in the showerhead due to a temperature drop caused by insufficient temperature control. Thus, a problem such as deterioration of material efficiency, clogging of the showerhead, deterioration of controllability of a doping concentration or the like is caused. 
         [0020]    With respect to this problem, a method of raising the temperature of a doping gas in advance before introducing the same into a growth chamber is disclosed in relation to an MOCVD device  500  disclosed in Japanese Patent Laying-Open No. 4-11419 (FIG. 1) (PTL 4) shown in  FIG. 15 , for example. 
         [0021]    Plurally present source gases are introduced into a showerhead  507  arranged on an upper portion of a growth chamber  503  storing a susceptor  501  and a substrate  502  through introducing pipes  508   a  to  508   d  separate from each other respectively. At this time, a preheater  506  for temperature rising is provided on introducing pipe  508   d  introducing material hard to decompose. Thus, the material hard to decompose can be heated in advance, and improvement of a doping concentration can be attained. The technique of raising the temperature of the gas in advance in this manner can be conceivably expected as effective also for prevention of coagulation in the pipe or on the wall surface in the showerhead resulting from the aforementioned insufficient temperature. 
       CITATION LIST 
     Patent Literature 
       [0022]    PTL 1: Japanese Patent Laying-Open No. 8-91989 
         [0023]    PTL 2: Japanese Patent Laying-Open No. 2000-144432 
         [0024]    PTL 3: Japanese Patent Laying-Open No. 2007-273747 
         [0025]    PTL 4: Japanese Patent Laying-Open No. 4-111419 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0026]    However, the cooling mechanism has been frequently provided on the gas introducing pipe immediately above the showerhead in recent years as described above, and the metallic material is cooled again in the showerhead, particularly in a stage immediately in front of the growth chamber in this case even if the temperature has been raised in advance, to result in problems such as coagulation of the metallic material, deterioration of material efficiency resulting therefrom, clogging of the showerhead, deterioration of controllability of a doping concentration and the like. 
         [0027]    The present invention has been proposed in consideration of the aforementioned conventional problems, and an object thereof is to provide a vapor deposition device capable of performing effective doping by effectively introducing a metallic material easy to coagulate into a reactor without making the same adhere to a showerhead or a wall surface of a pipe, a vapor deposition method and a semiconductor element manufacturing method. 
       Solution to Problem 
       [0028]    A vapor deposition device according to the present invention is a vapor deposition device supplying a group III source gas and a group V source gas into a growth chamber storing a film-formed substrate through a showerhead type gas supply mechanism in which a group III source gas introducing pipe having a plurality of group III source gas discharge ports and a group V source gas introducing pipe having a plurality of group V source gas discharge ports, individually discharging the gases respectively, are arranged, and mixing the gases with each other in the aforementioned growth chamber for film-forming the aforementioned film-formed substrate, and includes the following structure: 
         [0029]    A group V source gas buffer area and a group III source gas buffer area, isolated from each other, introducing the respective ones of the aforementioned group V source gas and the aforementioned group III source gas are stacked and arranged in the aforementioned showerhead type gas supply mechanism, the aforementioned showerhead type gas supply mechanism includes a shower plate in contact with the aforementioned growth chamber, a cooling mechanism for cooling the aforementioned shower plate is provided in the aforementioned showerhead type gas supply mechanism between the aforementioned shower plate and the aforementioned group V source gas buffer area, the inner diameter of the aforementioned group V source gas introducing pipe is greater than the outer diameter of the aforementioned group III source gas introducing pipe, and the aforementioned group III source gas introducing pipe is positioned in the aforementioned group V source gas introducing pipe in a one-to-one manner. 
       Advantageous Effects of Invention 
       [0030]    According to the present invention, the group V source gas buffer area and the group III source gas buffer area, isolated from each other, filling up the showerhead gas supply mechanism with the respective ones of the aforementioned group V source gas and the group III source gas are stacked so that the group V source gas buffer area is on a gas discharge side. 
         [0031]    Thus, the group III source gas and the group V source gas do not get mixed with each other until the same are introduced into the growth chamber and mixed with each other, and form no products in the showerhead. Therefore, such phenomena are prevented that the source gases react with each other in the showerhead and products adhere to the inner portion when the temperature of the group III source gas buffer area is raised with a temperature raising mechanism so that no metallic material coagulates in the showerhead. 
         [0032]    As to the positional relation between the group III source gas buffer area and the group V source gas buffer area, the group V source gas buffer area is stacked as the gas discharge side for employing a section adjacent to the cooling mechanism for cooling a shower surface as the group V source gas buffer area, thereby preventing such phenomena that the group III source gas buffer area is cooled by the cooling mechanism and a metallic material introduced into the group III source gas buffer area coagulates in the showerhead. 
         [0033]    Also with respect to such a problem that the aforementioned group III source gas introducing pipe and the group V source gas introducing pipe pass through the aforementioned cooling mechanism to introduce the source gases into the growth chamber at the time of gas introduction and hence the metallic material passing through the pipe is cooled by the cooling mechanism to easily coagulate on the wall surface of the pipe, in addition, the group III source gas pipe is prevented from being cooled by the cooling mechanism and coagulation of the metallic material on the pipe wall surface is suppressed by rendering the inner diameter of the group V source gas introducing pipe greater than the outer diameter of the group III source gas introducing pipe and adopting the structure in which the aforementioned group III source gas introducing pipe is inserted into the aforementioned group V source gas introducing pipe in a one-to-one manner. 
         [0034]    According to the above effects, a metallic material, easy to coagulate, such as Cp2Mg (biscyclopentadienyl magnesium), for example, can be properly guided into the growth chamber without coagulating the same in the showerhead in the pipe, and effective film formation can be efficiently performed. 
         [0035]    Further, the source gas introducing pipes are doubled, and the group III source gas containing a large quantity of carrier gas and the group V source gas containing a small quantity of carrier gas are introduced from the inner pipe having a small passage sectional and from the outer side having a large passage sectional area respectively, whereby loadings of the carrier gases on the whole can be reduced, and the cost can be suppressed. 
         [0036]    In this specification, the metallic material easy to coagulate denotes a material such as Cp2Mg, for example, solid at room temperature, and a metallic material kept in a cylinder, exhibiting a small takeout quantity at a time of being introduced by a technique, referred to as bubbling, of passing a carrier gas into an inner portion and taking out part of the material by vapor pressure equilibrium, or coagulating by a slight temperature drop even if the same can be taken out. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0037]      FIG. 1  is a schematic block sectional view of a vertical showerhead type vapor deposition device which is an example of a vapor deposition device in an embodiment. 
           [0038]      FIG. 2  is a schematic sectional view showing the structures of a shower plate and a cooling mechanism. 
           [0039]      FIG. 3  is a plan view showing an example of arrangement of gas discharge ports prepared on the shower plate. 
           [0040]      FIG. 4  is a plan view showing another example of arrangement of gas discharge ports prepared on the shower plate. 
           [0041]      FIG. 5  is a plan view showing still another example of arrangement of gas discharge ports prepared on the shower plate.  FIG. 6  is a schematic sectional view showing the structure of a group III source gas buffer area. 
           [0042]      FIG. 7  is a sectional view showing a structure at a time of assembling the showerhead. 
           [0043]      FIG. 8  is a diagram showing another positional relation between group V source gas discharge ports and group III source gas discharge ports. 
           [0044]      FIG. 9  is a diagram showing still another positional relation between the group V source gas discharge ports and the group III source gas discharge ports. 
           [0045]      FIG. 10  is a perspective view showing the structure of a group V source gas outer reflux passage. 
           [0046]      FIG. 11  is a sectional view showing an example of a semiconductor element having a film formed on a film-formed substrate by metal organic chemical vapor deposition by employing the vapor deposition device in this embodiment. 
           [0047]      FIG. 12  is a schematic block sectional view of an example of a conventional vertical showerhead type vapor deposition device employed for vapor deposition. 
           [0048]      FIG. 13  is a schematic block sectional view showing an example of a vertical showerhead type vapor deposition device, employed for vapor deposition, separating a plurality of source gases from each other by buffer areas and separately introducing the same into a growth chamber. 
           [0049]      FIG. 14  is a schematic block sectional view of an example of a vertical showerhead type vapor deposition device, employed for vapor deposition, having a mechanism of keeping the temperature in a pipe at a constant level. 
           [0050]      FIG. 15  is a schematic block sectional view of an example of a vertical showerhead type vapor deposition device, employed for vapor deposition, having a mechanism of raising the temperatures of source gases in advance. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0051]    When describing one embodiment of the present invention on the basis of  FIGS. 1 to 11 , the same is as follows. In the drawings of this embodiment, it is assumed that the same reference signs denote the same portions or corresponding portions. 
         [0052]    When numbers, quantities and the like are mentioned in the embodiment described below, the range of the present invention is not necessarily restricted to the numbers, the quantities and the like, except a case where description is particularly made. The same reference numerals are assigned to the same components and corresponding components, and there is a case where redundant description is not repeated. 
         [0053]    (Basic Structure of Device) 
         [0054]      FIG. 1  shows an example of a schematic structure of a vertical showerhead type MOCVD device  100  which is an example of an MOCVD (Metal Organic Chemical Vapor Deposition) device as a vapor deposition device in an embodiment based on the present invention. 
         [0055]    As shown in  FIG. 1 , MOCVD device  100  according to this embodiment includes a reactor  2  having a growth chamber  1  which is a hollow portion, a susceptor  4  receiving a film-formed substrate  3 , and a showerhead type gas supply mechanism (hereinafter simply referred to as a showerhead)  20  opposed to aforementioned susceptor  4  and having a shower plate  21  in contact with growth chamber  1  on the bottom surface. 
         [0056]    A heater  5  heating film-formed substrate  3  and a support  6  are provided on a lower side of aforementioned susceptor  4 , and a rotating shaft  7  mounted on support  6  rotates by an unshown actuator or the like, so that aforementioned susceptor  4  rotates while keeping a state where the upper surface (surface on the side of shower plate  21 ) of susceptor  4  is parallel to opposed shower plate  21 . 
         [0057]    On the peripheries of aforementioned susceptor  4 , heater  5 , support  6  and rotating shaft  7 , a covering plate  8  which is a heater cover is provided to surround susceptor  4 , heater  5 , support  5  and rotating shaft  7 . 
         [0058]    Further, MOCVD device  100  has a gas discharge portion  11  for discharging gases from growth chamber  1 , a purge line  12  connected to gas discharge portion  12 , and an exhaust gas treater  13  connected to purge line  12 . 
         [0059]    Thus, gases introduced into growth chamber  1  are discharged from growth chamber  1  through gas discharge portion  11 , and the discharged gases are introduced into exhaust gas treater  13  through purge line  12 , to be detoxified in exhaust gas treater  13 . 
         [0060]    (Basic Structure of Showerhead  20 ) 
         [0061]    The structure of showerhead  20  is now described with reference to  FIGS. 1 and 4 . Showerhead  20  is constituted of shower plate  21 , a cooling mechanism  22 , a group V source gas buffer area  23 , a group III source gas buffer area  24  and a temperature-raising mechanism  25  in order from the side of growth chamber  1 . 
         [0062]    A group III source gas containing a group III element supplied from a group III source gas supply source  34  is introduced into group III source gas buffer area  24  through a group III source gas pipe  35  and a mass flow controller  36 . Similarly, a group V source gas containing a group V element supplied from a group V source gas supply source  31  is introduced into group V source gas buffer area  23  through a group V source gas pipe  32  and a mass flow controller  33 . Aforementioned mass flow controllers  33  and  36  are to be controlled by an unshown control portion. 
         [0063]    In this embodiment, at least one type of a gas containing a group III element such as Ga (gallium), Al (aluminum) or In (indium), for example, such as an organic metal gas such as trimethyl gallium (TMG) or trimethyl aluminum (TMA), for example, can be employed as the group III source gas. At this time, it is assumed that a dopant gas such as biscyclopentadienyl magnesium (Cp2Mg), monosilane (SiH4) or dimethyl zinc (DMZn) can also be contained in the group III source gas. 
         [0064]    Further, at least one type of a gas containing a group V element such as N (nitrogen), P (phosphorus) or As (arsenic), for example, such as a hydrogen compound gas such as ammonia (NH 3 ), phosphine (PH 3 ) or arsine (AsH 3 ), for example, or a hydrocarbon compound gas such as tertiary butyl arsine (TBAs) can be employed as the group V source gas. 
         [0065]    Cold water is to be supplied to cooling mechanism  22  from a water cooler  38  through a cold water-system pipe  37 . While cooling mechanism  22  is to supply cooling water in this embodiment, the supplied substance is not necessarily restricted to the water, but it is possible to employ a coolant prepared from another liquid and a gas. 
         [0066]    Temperature-raising mechanism  25  has a structure obtained by spreading a silicon rubber heater all over the upper surface of group III source gas buffer area  24 , and is energized by an unshown power supply system for raising the temperature. While the heater is employed for temperature-raising mechanism  25  in this embodiment, the temperature of group III source gas buffer area  24  may be raised by providing a passage on group III gas buffer area  24  similarly to cooling mechanism  22  and feeding a heat medium from an external device in place of the coolant. 
         [0067]    (Structural Description of Inner Portion of Showerhead  20 ) 
         [0068]      FIG. 2  shows a schematic diagram of the structures of shower plate  21  and cooling mechanism  22 . A plurality of group V source gas discharge ports  41  are provided on shower plate  21 , and lead up to group V source gas buffer area  23  provided above aforementioned shower plate  21  through group V source gas introducing pipes  42 . 
         [0069]    The directions of arrangement of plurally provided group V source gas discharge ports  41  and group V source gas introducing pipes  42  are horizontal and vertical directions, i.e., in the form of a lattice, as shown in  FIG. 3 . However, this lattice is not restricted to a tetragonal lattice, but may be a rhomboidal lattice, as shown in  FIG. 4 . Further, the same may be radially provided, as shown in  FIG. 5 . In addition, the sections of group V source gas introducing pipes  42  and group V source gas discharge ports  41  are not necessarily restricted to circular shapes, but may be in the form of rectangular pipes, elliptic pipes, or other sections. 
         [0070]    Cooling mechanism  22  is provided immediately above shower plate  21  on the peripheries of group V source gas introducing pipes  42 . Cooling mechanism  22  has a coolant supply passage  51 , so that cooling water flows into coolant supply passage  51  from a side portion of showerhead  20  and flows out from an opposite side portion of showerhead  20 , for example. Shower plate  21  is cooled to not more than a constant temperature by aforementioned cooling mechanism  22 . 
         [0071]      FIG. 6  shows a schematic sectional view expressing the structure of group III source gas buffer area  24 . A plurality of group III source gas introducing pipes  44  extend from group III source gas buffer area  24 , and the group III source gas is introduced from group III source gas discharge ports  43  provided on forward ends into growth chamber  1 . 
         [0072]    The directions of arrangement of plurally provided group V source gas discharge ports  41  and group III source gas introducing pipes  44  are horizontal and vertical directions, i.e., in the form of a lattice correspondingly to the arrangement of group V source gas discharge ports  41  shown in  FIG. 3 . However, this lattice is not restricted to a tetragonal lattice, but may be a rhomboidal lattice, correspondingly to the arrangement of group V source gas discharge ports  41  shown in  FIG. 4 . Further, the same may be radially provided, correspondingly to the arrangement of group V source gas discharge ports  41  shown in  FIG. 5 . In addition, the sections of group III source gas introducing pipes  44  and group III source gas discharge ports  43  are not necessarily restricted to circular shapes, but may be in the form of rectangular pipes, elliptic pipes, or other sections. 
         [0073]    Temperature-raising mechanism  25  is provided on an upper portion of group III source gas buffer area  24 , to raise the temperature of group III source gas buffer area  24  to at least ordinary temperature from the upper surface. 
         [0074]      FIG. 7  shows a sectional view at a time of assembling showerhead  20 . Cooling mechanism  22  and group III source gas buffer area  24  are fastened to each other on outer peripheral portions, to constitute showerhead  20 . At this time, group V source gas buffer area  23  is defined by a concave space on the upper surface side of cooling mechanism  22 , the bottom surface of group III source gas buffer area  24  and a constituted space. 
         [0075]    Cooling mechanism  22  and group III source gas buffer area  24  are fastened to each other by using an unshown O-ring, a gasket and the like, whereby the group V source gas supplied to group V source gas buffer area  23  does not leak out to an external portion. 
         [0076]    The inner diameter (W 1 ) of aforementioned group V source gas introducing pipes  42  is greater than the outer diameter (W 2 ) of aforementioned group III source gas introducing pipes  44 , and group III source gas introducing pipes  44  are inserted into group V source gas introducing pipes  42  in a one-to-one manner. Thus, spaces are formed between group III source gas introducing pipes  44  and cooling mechanism  22 , to prevent the group III source gas from being cooled. 
         [0077]    In addition, the passage of the group V source gas becomes larger as compared with the passage of the group III source gas when employing this pipe structure (assuming that the radio between the diameters of group III source gas introducing pipes  42  and group V source gas introducing pipes  42  is 1:2, for example, the area ratio between the passages of the group III source gas and the group V source gas becomes 1:3). Therefore, the flow rate of a required carrier gas can be rendered small. 
         [0078]    It is known that, in a case of performing film formation in an MOCVD device in general, a ratio, referred to as a V/III ratio, between mole numbers of a group V raw material and a group III raw material exerts a remarkable influence on film quality. In order to form a high-quality film, this value frequently becomes at least 500. 
         [0079]    If the group V raw material is fed in a flow rate 500 times that of the group III raw material in practice, however, the group V material whose flow velocity is high reaches film-formed substrate  3  in advance, diffuses onto film-formed substrate  3  and inhibits arrival of the group III gas whose flow velocity is low such that it becomes difficult to control the VIII ratio in reaction. Therefore, the V/III ratio must be controlled to be constant by feeding a carrier gas irrelevant to the reaction to the group III raw material side in a large quantity and equalizing the gas flow rates to each other. 
         [0080]    At this time, an introducing passage for the group V source gas having the large flow rate enlarges and the flow rate of the group V source gas necessary for obtaining a certain flow velocity inevitably increases in the pipe structure of this embodiment, whereby the necessary carrier gas flow rate can be reduced as compared with a case where the magnitudes of the introducing passages of the group III•group V source gases are equal to each other. 
         [0081]    While group V source gas discharge ports  41  and group III source gas discharge ports  43  are provided to be positioned on the same plane in this embodiment as shown in  FIG. 7 , the positional relation between group V source gas discharge ports  41  and group III source gas discharge ports  43  may not necessarily be on the same plane, but either V source gas discharge ports  41  or group III source gas discharge ports  43  may be present on positions protruding with respect to either group III source gas discharge ports  43  or V source gas discharge ports  41 , as shown in  FIGS. 8 and 9 . 
         [0082]    Group V source gas buffer area  23  includes a group V source gas outer reflux passage  61  on a buffer area sidewall portion, in order to uniformly guide the group V source gas supplied from a peripheral portion, for example, of showerhead  20  into group V source gas introducing pipes  42 . 
         [0083]    On the other hand, group III source gas buffer area  24  similarly includes a group III source gas outer reflux passage  62  on a buffer area sidewall portion, in order to uniformly guide the source gas supplied from the peripheral portion, for example, of showerhead  20 .  FIG. 10  is a perspective view of group V source gas outer reflux passage  61  (group III source gas outer reflux passage  62  is also identical in structure and hence description is omitted). 
         [0084]    For example, the group V source gas supplied from a lateral direction of group V source gas outer reflux passage  61  is supplied into group V source gas buffer area  23  uniformly in the circumferential direction, through a plurality of group V source gas supply ports  63  uniformly arranged on an inner peripheral side of group V source gas outer reflux passage  61 . The group V source gas in group V source gas buffer area  23  is supplied from group V source gas discharge ports  41  into growth chamber  1 , through aforementioned plurality of group V source gas introducing pipes  42 . 
         [0085]    (Semiconductor Element Manufacturing Method employing MOCVD Device  100 ) 
         [0086]    A semiconductor element manufacturing method based on vapor deposition employing MOCVD device (vapor deposition device)  100  is now described. 
         [0087]    At least one type of a gas containing a group III element such as Ga (gallium) or Al (aluminum), for example, such as an organic metal gas such as trimethyl gallium (TMG) or trimethyl aluminum (TMA), for example, is introduced into MOCVD device  100  in this embodiment as the group III source gas. 
         [0088]    Further, at least one type of a gas containing a group V element such as N (nitrogen), P (phosphorus) or As (arsenic), for example, such as a hydrogen compound gas such as ammonia (NH 3 ), phosphine (PH 3 ) or arsine (AsH 3 ), for example, or a hydrocarbon compound gas such as tertiary butyl arsine (TBAs) is introduced into MOCVD device  100  in this embodiment as the group V source gas. 
         [0089]    At this time, it is assumed that a dopant gas, easy to coagulate, such as biscyclopentadienyl magnesium (Cp2Mg), for example, is also contained in the group III source gas. 
         [0090]    The group III source gas introduced into MOCVD device  100  is introduced from group III source gas buffer area  24  into growth chamber  1  through group III source gas introducing pipes  44 , while the group V source gas is introduced from group V source gas buffer area  23  into growth chamber  1  through group V source gas introducing pipes  42 . 
         [0091]    The group III source gas and the group V source gas introduced into growth chamber  1  are sprayed onto film-formed substrate  3  set on susceptor  4  in growth chamber  1 . The temperature of film-formed substrate  3  has been raised to a prescribed temperature by heater  5  provided under susceptor  4 , the source gases sprayed onto film-formed substrate  3  are decomposed by this heat to react, and a desired film  70  is formed on film-formed substrate  3 , as shown in  FIG. 11 . 
         [0092]    Source gases having not contributed to the reaction are discharged from growth chamber  1  through gas discharge portion  11 , and the discharged gases are introduced into exhaust gas treater  13 , to be detoxified in exhaust gas treater  13 . A semiconductor element of a prescribed structure is formed on film-formed substrate  3  which is a semiconductor substrate by repeatedly carrying out the aforementioned steps. 
         [0093]    (Functions•Effects) 
         [0094]    Thus, according to MOCVD device  100  in this embodiment, the structure in which group V source gas buffer area  23  and group III source gas buffer area  24 , isolated from each other, filling the respective ones of the group V source gas and the group III source gas are stacked with each other so that group V source gas buffer area  23  serves as a gas discharge side is employed for the shower head  20 . 
         [0095]    Thus, the group III source gas and the group V source gas do not get mixed with each other until the same are introduced into growth chamber  1  and mixed with each other, and do not form products in showerhead  20 . When the temperature of group III source gas buffer area  24  is raised by the temperature-raising mechanism  25  so that no metallic material coagulates in showerhead  20 , therefore, such phenomena are prevented that the source gases react with each other in the showerhead and products adhere to the inner portion. 
         [0096]    As to the positional relation between group III source gas buffer area  24  and group V source gas buffer area  23 , group V source gas buffer area  23  is stacked as the gas discharge side for employing a section adjacent to cooling mechanism  22  for cooling a shower surface of shower plate  21  as group V source gas buffer area  23 , thereby preventing such phenomena that group III source gas buffer area  24  is cooled by cooling mechanism  22  and a metallic material introduced into group III source gas buffer area  24  coagulates in showerhead  20 . 
         [0097]    Also with respect to such a problem that aforementioned group III source gas introducing pipes  44  and group V source gas introducing pipes  42  pass through aforementioned cooling mechanism  22  to introduce the source gases into growth chamber  1  at the time of gas introduction and hence the metallic material passing through the pipes is cooled by cooling mechanism  22  to easily coagulate on the wall surfaces of the pipes, in addition, group III source gas pipes  44  are prevented from being cooled by the cooling mechanism and coagulation of the metallic material onto the pipe wall surfaces is suppressed by rendering the inner diameter (W 1 ) of group V source gas introducing pipes  42  greater than the outer diameter (W 2 ) of group III source gas introducing pipes  44  and adopting the structure in which aforementioned group III source gas introducing pipes  44  are inserted into aforementioned group V source gas introducing pipes  42  in a one-to-one manner. 
         [0098]    According to the above effects, a metallic material, easy to coagulate, such as Cp2Mg (biscyclopentadienyl magnesium), for example, can be properly guided into the growth chamber without coagulating the same in the showerhead in the pipes, and effective film formation can be efficiently performed. 
         [0099]    Further, the source gas introducing pipes are doubled so that the group III source gas containing a large quantity of carrier gas and the group V source gas containing a small quantity of carrier gas are introduced from the inner pipe having a small passage sectional and from the outer side having a large passage sectional area respectively, whereby loadings of the carrier gases on the whole can be reduced, and the cost can be suppressed. 
         [0100]    While the embodiment of the present invention has been described, the embodiment disclosed this time must be considered as illustrative in all points and not restrictive. The range of the present invention is shown by the scope of claims for patent, and it is intended that all modifications within the meaning and range equivalent to the scope of claims for patent are included. 
       INDUSTRIAL APPLICABILITY 
       [0101]    The present invention can be utilized for a vapor deposition device such as a vertical MOCVD device employing a metallic material easy to coagulate and a material hard to decompose as raw materials and a semiconductor element manufacturing method employing the same. 
       REFERENCE SIGNS LIST 
       [0102]      1  growth chamber,  2  reactor,  3  film-formed substrate,  4  susceptor,  5  heater,  6  support,  7  rotating shaft,  8  covering plate,  11  gas discharge portion,  12  purge line,  13  exhaust gas treater,  20  showerhead,  21  shower plate,  22  cooling mechanism,  23  group V source gas buffer area,  24  group III source gas buffer area,  25  temperature-raising mechanism,  31  group V source gas supply source,  32  group V source gas pipe,  33  mass flow controller,  34  group III source gas supply source,  35  group III source gas pipe,  36  mass flow controller,  37  water-cooled-system pipe,  38  water cooler,  41  group V source gas discharge port,  42  group V source gas introducing pipe,  43  group III source gas discharge port,  44  group III source gas introducing pipe,  51  coolant supply passage,  61  group V source gas outer reflux passage,  62  group III source gas outer reflux passage,  63  group V source gas supply port,  70  thin film.