Abstract:
The invention provides a group III nitride semiconductor manufacturing system which is free from interruption to rotation of a rotational shaft. The group III nitride semiconductor manufacturing system has a reacting vessel having an opening, a crucible disposed in an interior of the reaction vessel and containing a melt including at least a group III metal and an alkali metal, a holding unit supporting the crucible and having a rotational shaft extending from the interior of the reaction vessel to an exterior of the reaction vessel through the opening, a rotational shaft cover covering a part of the rotational shaft positioned at the exterior of the reacting vessel and connected to the reacting vessel at the opening, a rotational driving unit disposed at an outside of the reacting vessel and regulating the rotational shaft and a supply pipe connected to the rotational shaft cover and supplying a gas including at least nitrogen into a gap between the rotational shaft and the rotational shaft cover, wherein the gas and the melt react to grow a group III nitride semiconductor crystal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a group III nitride semiconductor manufacturing system and more particularly to a group III nitride semiconductor manufacturing system based on a fluxing method using an alkali metal. 
         [0002]    There has conventionally been known a group III nitride semiconductor crystal growing method based on an Na (sodium) fluxing method. This method is a crystal growth of GaN (Gallium Nitride) on a surface of a seed crystal. The process is reaction under several tenth of atmospheric pressure between nitrogen and melted Na and Ga kept around 800° C. 
         [0003]    In the crystal growing method based on the Na fluxing method, in order to increase crystal uniformity and crystal growth stability, such an approach as rotating a crucible or rotating a seed crystal is adopted (refer to JP-A-2005-187317 and JP-A-2007-254161). In order to realize the rotation of the crucible or seed crystal, a rotational shaft is provided on the manufacturing system which holds the crucible or the seed crystal. 
         [0004]    In this method, however, there are problems caused by the fact that Na evaporated during crystal growth enters a gap between the reaction vessel and the rotational shaft. The first example problem is interruption of rotation of the rotational shaft liquefied or solidified Na. Another one is the rotational shaft cannot be moved up and down vertically. This deficiency makes it difficult for the crucible or crystal to be taken out of the reaction vessel. In particular, in the case of Na being solidified, the rotational shaft has to be heated to melt the solidified Na. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention has been made in view of the situations and an object thereof is to provide a group III nitride semiconductor manufacturing system which is free from interruption to rotation and movement of a rotational shaft. 
         [0006]    With a view to attaining the object, according to a first aspect of the invention, a group III nitride semiconductor manufacturing system including a reacting vessel having an opening, a crucible disposed in an interior of the reaction vessel and containing a melt including at least a group III metal and an alkali metal, a holding unit supporting the crucible and having a rotational shaft extending from the interior of the reaction vessel to an exterior of the reaction vessel through the opening, a rotational shaft cover covering a part of the rotational shaft positioned at the exterior of the reacting vessel and connected to the reacting vessel at the opening, a rotational driving unit disposed at an outside of the reacting vessel and regulating the rotational shaft and a supply pipe connected to the rotational shaft cover and supplying a gas including at least nitrogen into a gap between the rotational shaft and the rotational shaft cover, wherein the gas and the melt react to grow a group III nitride semiconductor crystal. 
         [0007]    According to a second aspect of the invention, there is provided a group III nitride semiconductor manufacturing system including a reacting vessel having an opening, a crucible disposed in an interior of the reaction vessel and containing a melt including at least a group III metal and an alkali metal, a holding unit holding a seed crystal and having a rotational shaft extending from the interior of the reaction vessel to an exterior to the reaction vessel through the opening, a rotational shaft cover covering a part of the rotational shaft positioned at the exterior of the reacting vessel and connected to the reacting vessel at the opening, a rotational driving unit disposed at an outside of the reacting vessel and regulating the rotational shaft and a supply pipe connected to the rotational shaft cover and supplying a gas including at least nitrogen into a gap between the rotational shaft and the rotational shaft cover, wherein the gas, the seed crystal and the melt react to grow a group III nitride semiconductor crystal. 
         [0008]    In the first and second aspects of the invention, although Na is normally used as alkali metal, K (potassium) can be used. In addition, alkaline-earth metals such as Mg (magnesium) and Ca (calcium), or Li (lithium) may be mixed therewith. In addition, the gas containing nitrogen means a single or mixed gas which contains nitrogen molecules or nitrogen compound gas and may include inactive gas such as rare gas. 
         [0009]    In addition, a single or a plurality of supply pipes which connect to the reaction vessel may be provided in addition to the supply pipe which connects to the rotational shaft cover. 
         [0010]    According to a third aspect of the invention set froth in the first or second aspect of the invention, the rotational shaft has a first magnet and the rotational driving unit has a second magnet so as to rotate and move the rotational shaft by magnetic coupling between the first and the second magnet. 
         [0011]    According to the first and second aspects of the invention, the gas containing at least nitrogen continues to flow into the gap between the rotational shaft and the rotational shaft cover during crystal growth so that evaporated Na can be prevented from entering the gap. Therefore the rotation and movement of the rotational shaft is not interrupted. As a result, crystal uniformity is increased, thereby making it possible to manufacture a high-quality group III nitride semiconductor. In addition, since the movement of the rotational shaft is not interrupted after the crystal growth, the removal of the crucible or group III nitride semiconductor crystal can be facilitated. 
         [0012]    In addition, according to the third aspect of the invention, the configuration of the rotational driving unit is simple, and the rotational shaft can be controlled in such a state that communication between the interior and exterior of the reaction vessel is cut off by the rotational shaft cover. 
         [0013]    The fourth aspect of the invention set forth in the second and first aspect, the reaction vessel has a dual structure including an inner vessel and an outer vessel. Preferably, a heater is mounted on an inside of the outer vessel and an outside of the inner vessel. Preferably, the outer vessel has an opening. Preferably, the opening is shared by the outer vessel and the inner vessel. Preferably, the inside of the outer vessel is pressured by gas including nitrogen. 
         [0014]    According to the fourth aspect of the invention, as the outer vessel  31  is responsible for the pressure and the inner vessel  32  is heated by the heater inside of the reaction vessel  30 , the efficient crystal growth is performed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  shows the configuration of a group III nitride semiconductor manufacturing system of Embodiment 1. 
           [0016]      FIG. 2  shows the configuration of a group III nitride semiconductor manufacturing system of Embodiment 2. 
           [0017]      FIG. 3  shows the configuration of a group III nitride semiconductor manufacturing system of Embodiment 3. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0018]    Hereinafter, specific embodiments of the invention will be described by reference to the drawings, but the invention is not limited to the embodiments. 
         [0019]      FIG. 1  is a diagram showing the configuration of a group III nitride semiconductor manufacturing system of Embodiment 1. As is shown in  FIG. 1 , the group III nitride semiconductor manufacturing system is made up of following components. A reaction vessel  10  and a rotation shaft cover  15  are connected through an opening each other. The reaction vessel  10  is heated by a heater  12 . In the reaction vessel  10 , a crucible  11  containing a mixed melt  19  of Ga and Na is disposed. The crucible  11  is supported by a holding unit  14  which is provided with a rotational shaft  13 . The rotational shaft cover  15  covers the part of the rotational shaft  13  exposed to the exterior of the reaction vessel  10  through the opening. A supply pipe for supplying nitrogen gas is connected to the rotational shaft cover  15 . An exhaust pipe  17  for expelling gasses from the reaction vessel  10  is connected to the reaction vessel  10 . 
         [0020]    The reaction vessel  10  is made of stainless steel and has pressure resistance and heat resistance. The crucible  11  which is held by the holding unit  14  is disposed in the interior of the reaction vessel  10 . 
         [0021]    The crucible  11  is made from BN (boron nitride) and is disposed on a tray  20  in the interior of the reaction vessel  10 . The mixed melt  19  of Ga and Na and a seed crystal  23  are held in an interior of the crucible  11 . 
         [0022]    The heater  12  is disposed to lie round external side and bottom portions of the reaction vessel  10 . The temperature in the interior of the reaction vessel  10  is controlled by the heater  12 . 
         [0023]    The holding unit  14  is made up of the tray  20  on which the crucible  11  is disposed and the rotational shaft  13  which connects to the tray  20  and penetrates the reaction vessel  10  from an internal lower portion to an outside of the reaction vessel  10 . At a distal end of the rotational shaft  13  of exterior side, a magnet  21  is provided. 
         [0024]    The rotational shaft cover  15  covers an exterior the rotational shaft  13  in the reaction vessel  10  and connects to the reaction vessel  10  in such a manner as to be made to open thereto. The interior and exterior of the reaction vessel  10  are separated by the rotational shaft cover  15 , forming a continuous space defined by a gap  24  between the rotational shaft  13  and the rotational shaft cover  15  and the interior of the reaction vessel  10 . 
         [0025]    The rotational driving unit  18  has a magnet  22  provided on a external side portion of the rotational shaft cover  15 . The rotational shaft  13  can be rotated via the magnet  21  by rotating the magnet  22 . In addition, the magnet  22  can be moved up and down in vertical direction. By this vertical motion, the rotational shaft  13  can also be moved up and down in the vertical direction. By the use of the magnets described above, the rotation and movement of the rotational shaft  13  can be controlled under the condition that the interior and the exterior of the reaction vessel  10  is sealed by the rotational shaft cover  15 . 
         [0026]    The supply pipe  16  connects to the rotational shaft cover  15  with a valve  16   v.  Nitrogen gas is supplied from the supply pipe  16  into the interior of the reaction vessel  10  through the gap  24  between the rotational shaft  13  and the rotational shaft cover  15 . 
         [0027]    The discharge pipe  17  connects to the reaction vessel  10  with a valve  17   v.  The valve  17   v  controls the amount of gases that are discharged to the outside of the reaction vessel  10  through the discharge pipe  17 . By controlling the amounts of nitrogen gas supplied and discharge by the valves  16   v,    17   v  of the supply pipe  16  and the discharge pipe  17 , an internal pressure of the reaction vessel  10  is controlled. 
         [0028]    Next, manufacturing of a GaN crystal using the group III nitride semiconductor manufacturing system of Embodiment 1 is described. 
         [0029]    Firstly, the rotational shaft  13  is moved vertically upwards by the rotational driving unit  18  so that the tray  20  moves upside of the reaction vessel  10 . In this state, a seed crystal  23 , Ga, Na are placed in the interior of the crucible  11 , and the crucible  11  is disposed on the tray  20 . After that the rotational shaft  13  is moved vertically downwards by the rotational driving unit  18  so as to move the crucible  11  into the interior of the reaction vessel  10 . Then a lid is mounted on the reaction vessel  10 . 
         [0030]    Next, the valve  16   v  is closed, and the valve  17   v  is opened, so that gases in the atmosphere of the reaction vessel  10  are exhausted. Thereafter, the valve  16   v  is opened so as to supply nitrogen into the interior of reaction vessel  10  through the gap  24  between the rotational shaft  13  and the rotational shaft cover  15 . In addition, the valves  16   v,    17   v  are controlled so that the internal pressure of the reaction vessel  10  becomes 50 atm. 
         [0031]    Next, the interior of the reaction vessel  10  is heated by the heater  12 . For crystal growth of GaN on the seed crystal, the condition in the interior of the reaction vessel  10  is kept 50 atm and 800° C. In addition, by the rotational shaft  13  being rotated by the rotational driving unit  18 , the crucible  11  placed on the tray  20  is caused to rotate so as to stir the mixed melt  19 . During this process, nitrogen gas is supplied from the supply pipe  16  to the interior of the reaction vessel  10  at all times. 
         [0032]    Since nitrogen continues to flow towards the interior of the reaction vessel  10  through the gap between the rotational shaft  13  and the rotational shaft cover  15  at all times during growth of GaN crystal, no evaporated Na enters the gap. Consequently, a smooth rotation of the crucible  11  is implemented and the mixed melt  19  is stirred well by the rotating crucible. As a result the uniform composition of the mixed melt  19  and uniform growth of GaN crystal are attained. 
         [0033]    Thereafter, the temperature of the reaction vessel is decreased down to the ordinary room temperature, ending the manufacturing of GaN crystal. Then, the lid of the reaction vessel  10  is opened, and the rotational shaft  13  is moved vertically upwards by the rotational driving unit  18  so as to draw the crucible  11  and the grown GaN crystal is drawn out. At this stage, as described above, since no evaporated Na enters the gap defined between the rotational shaft  13  and the rotational shaft cover  15 , the upward movement of the rotational shaft  13  is implemented in a smooth fashion, and the crucible  11  can easily be removed from the reaction vessel  10 . 
         [0034]    As described heretofore, in the group III nitride semiconductor manufacturing system of Embodiment 1, evaporated Na is prevented from entering the gap defined between the rotational shaft  13  and the rotational shaft cover  15  during the growth of GaN crystal. Consequently, the rotation of the crucible  11  is not interrupted. This advantage makes the composition of the mixed melt  19  to be uniform. As a result, crystal uniformity is increased, and a high quality group III nitride semiconductor is manufactured. In addition, the crucible  11  can easily be removed after the completion of crystal growth. This means that operating efficiency of this invention is improved. 
         [0035]      FIG. 2  shows the configuration of a group III nitride semiconductor manufacturing system of Embodiment 2. In the group III nitride semiconductor manufacturing system of Embodiment 2, a holding unit  114  is substituted for the holding unit  14  which holds the crucible  11  in the above mentioned Embodiment 1. The holding unit  114  is used to hold a seed crystal  123 . 
         [0036]    The holding unit  114  is made up of a rotational shaft  113  and a fixing part  20  on which the seed crystal  123  is fixed. The rotational shaft  113  penetrates a reaction vessel  10  from an internal upper portion to an outside through a opening. A magnet  121  is provided at a distal end of the rotational shaft  113  which lies outside the reaction vessel  10 . In addition, a rotational shaft cover  115  is connected to the upper end of the reaction vessel at the opening. The rotational shaft cover  115  covers an exterior of the rotational shaft  113  in the reaction vessel  10  and connects to the reaction vessel  10  in such a manner as to be made to open thereto. The interior and exterior of the reaction vessel  10  are separated by the rotational shaft cover  15 , forming a continuous space defined by a gap  124  between the rotational shaft  113  and the rotational shaft cover  115  and the interior of the reaction vessel  10 . A supply pipe  116  connects to the rotational shaft cover  115 . The supply pipe  116  has a valve  116   v  along the length thereof. 
         [0037]    A rotational driving unit  118  is provided above the reaction vessel  10  for controlling the rotation and movement of the rotational shaft  113 . The rotational driving unit  118  has a magnet  122 . The rotational shaft  113  rotates via the magnet  121  by rotating the magnet  122 . In addition, as the magnet  122  moves vertically upwards and downwards, the rotational shaft  113  also moves vertically upwards and downwards. 
         [0038]    Other configurations of the group III nitride semiconductor manufacturing system of Embodiment 2 than the constituent elements or portions that are described above are similar to corresponding elements described in the group III nitride semiconductor manufacturing system of Embodiment 1. 
         [0039]    Next, manufacturing of a GaN crystal using the group III nitride semiconductor manufacturing system of Embodiment 2 is described. 
         [0040]    Firstly, the rotational shaft  113  is moved vertically upwards by the rotational driving unit  118  so that the holding unit  114  moves upwards. In this state, Ga and Na are placed in the interior of the crucible  11 , and the crucible  11  is disposed in the interior of the reaction vessel  10 . In addition, a seed crystal  123  is fixed to the fixing part  120  of the holding unit  114 , and then the reaction vessel  10  is closed. 
         [0041]    Next, the valve  16   v  is closed, and the valve  17   v  is opened, so that gases in the reaction vessel  10  are discharged. Thereafter, the valve  16   v  is opened so as to supply nitrogen into the interior of reaction vessel  10  through the gap  124 . In addition, the valves  16   v,    17   v  are controlled so that the internal pressure of the reaction vessel  10  becomes 50 atm. 
         [0042]    Next, the interior of the reaction vessel  10  is heated by the heater  12 . At this stage, condition in the reaction vessel  10  is kept 50 atm and 800° C. During this process, nitrogen gas is supplied from the supply pipe  116  into the interior of the reaction vessel  10  at all times. 
         [0043]    Next, the rotational shaft  113  is moved vertically downwards so as to submerge the seed crystal  123  in the mixed melt  19  by the rotational driving unit  118 . Then the rotational shaft  113  rotates by the rotational driving unit  118  for growing a GaN crystal. 
         [0044]    Since nitrogen continues to flow towards the interior of the reaction vessel  10  through the at all times during growth of GaN crystal, no evaporated Na enters the gap. Consequently, a smooth rotation of the seed crystal  123  is implemented. Therefore uniform growth of GaN crystal is attained. 
         [0045]    Following above, the rotational shaft  113  is moved vertically upwards by the rotational driving unit  118  so as to pick up the seed crystal  123  from the mixed melt  19 . Then, the temperature of the reaction vessel  10  is decreased to the ordinary room temperature, ending the manufacturing of GaN crystal. At this time, as described above, since no evaporated Na enters the gap  124 , the vertically upward movement of the rotational shaft  113  is implemented in a smooth fashion, and the resulting GaN crystal can easily be removed from the reaction vessel  10 . 
         [0046]    As described heretofore, in also the group III nitride semiconductor manufacturing system of Embodiment 2, since evaporated Na is prevented from entering the gap  124  by the continuous flow of nitrogen gas supplied through the gap  124 , the smooth rotation of the seed crystal is maintained. This advantage makes it possible to obtain a uniform crystal. In addition, since the manufactured GaN crystal is easily removed from the reaction vessel  10 , an operating efficiency is qualified. 
         [0047]      FIG. 3  shows the third embodiment. In the following explanation of this embodiment, detail description of the elements same as the first embodiment are omitted. The distinct feature of the third embodiment is the structure of the reaction vessel  30 . The reaction vessel  30  has a dual structure including an inner vessel and an outer vessel. As shown in  FIG. 3 , the outer vessel  31  encloses the inner vessel  32 . The inner vessel  32  covers the crucible  11  and the upper part of the holding unit  14 . The inner vessel  32  is fixed in the outer vessel  31  at the inner wall of the outer vessel  31  and has a lid (not shown) through which a seed crystal  23 , Na, Ga and other source materials are supplied. The opening of the reaction vessel  30  is formed on bottom of the outer vessel  31  shared by the outer vessel  31  and the inner vessel  32 . Through the opening, the lower part of the holding unit  14  is extended to the rotational shaft cover  15 . In a space between the inner vessel  32  and the outer vessel  31 , the heater  12  is mounted. The discharge pipe  171  for the inner vessel  32  is connected to the inner vessel  32  penetrating the outer vessel  31  and the supply pipe  161  for the inner vessel  32  is connected to the rotational shaft cover  24 . Additionally, a discharge pipe  172  for the outer vessel  31  is connected to a upper part of the outer vessel and a supply pipe  162  for the outer vessel  31  is connected to a lower part of the outer vessel. 
         [0048]    The outer vessel  31  are pressured preferably about 5 MPa by nitrogen gas which is supplied through the supply pipe  162  for the outer vessel  31 . This pressure is spread into the inner vessel  32  so as to make nitrogen gas be dissolved into the mixed melt  19 . Another way to pressure the inner vessel  32  is to supply nitrogen gas to the inner vessel  32  through the supply pipe  161  for the inner vessel  32 . Using the two supply pipes  161  and  162 , the inner vessel  32  and the outer vessel  31  are able to be pressured individually. Thus in this configuration, as the outer vessel  31  is responsible for the pressure and the inner vessel  32  is heated by the heater inside of the reaction vessel  30 , the efficient crystal growth is performed. 
         [0049]    In  FIG. 3 , though the opening is shared by the inner vessel  31  and the outer vessel  32 , configurations are not restricted in the type of  FIG. 3 . It is possible that the opening is placed only at the outer vessel or inner vessel in other example embodiments. 
         [0050]    While in the embodiments Na is used as the flux, alkali metals such as Li and K, alkaline-earth metals such as Mg and Ca or mixtures thereof can also be used. And also, while nitrogen is supplied into the interior of the reaction vessel in the embodiments, a compound such as ammonia which contains nitrogen can be used. Alternatively, an inert gas such as argon can be mixed to the supplied gas. 
         [0051]    In addition, while in the embodiments, the supply pipe is provided and connected only to the rotational shaft cover, another one or more supply pipe can be provided which is connected to the reaction vessel. 
         [0052]    Additionally, while in the embodiments, only the rotational shaft for rotating the seed crystal or the rotational shaft for rotating the crucible is used, there may be provided a group III nitride semiconductor manufacturing system which has both the shafts. A rotational shaft cover is provided for each of the rotational shafts, and nitrogen is supplied from supply pipes which connect, respectively, to the rotational shaft covers so provided, whereby a uniform group III nitride semiconductor crystal can be manufactured which is similar to those manufactured by the embodiments. 
         [0053]    The invention can be applied to the manufacturing of a group III nitride semiconductor based on the Na fluxing method.