Patent Publication Number: US-2018033640-A1

Title: Heat treatment method for p-type semiconductor

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a heat treatment method for a p-type semiconductor containing germanium or silicon germanium as a major component. 
     Description of the Background Art 
     As material of a semiconductor device, silicon (Si) is mainly used, but germanium (Ge) is also used in some cases. Since germanium is high in mobility compared with silicon, it has been proposed to be used as channel material of a field effect transistor (FET) (refer to US2016/0197076, for example). 
     As for a p-type semiconductor (p-Ge) in which a minute amount of trivalent dopant such as boron (B) is added to high-purity germanium, an activation rate of the dopant at the time of activation annealing is higher than that of an n-type semiconductor (n-Ge) in which a pentavalent dopant such as phosphorus (P) or arsenic (As) is added thereto. Meanwhile, the germanium p-type semiconductor has the problem that the diffusion of the dopant is very slow compared with the n-type semiconductor, and control of the diffusion at the time of activation annealing is difficult. This is because phosphorus and arsenic arc diffused through vacancies in crystals of germanium, but boron, etc. is diffused through gaps between lattices in the crystals. Since there are many vacancies in the crystal of germanium, phosphorus and arsenic are easily diffused through the vacancies, but in contrast, boron, etc. is not likely to be diffused due to the many vacancies serving as a barrier. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a heat treatment method for a p-type semiconductor containing germanium or silicon germanium as a major component. 
     According to one aspect of the present invention, a heat treatment method for a p-type semiconductor includes the steps of: (a) carrying a dopant-doped germanium or silicon germanium semiconductor layer into a chamber; (b) introducing a treatment gas containing hydrogen or ammonia to the chamber; (c) preheating the semiconductor layer at a preheating temperature; and (d) heating the semiconductor layer by irradiation with a flash light from a flash lamp, at a treatment temperature. 
     Thus, the flash heating is performed in a state in which vacancies provided near a surface of the semiconductor layer have been eliminated, and the dopant can be relatively easily diffused. As a result, by adjusting a condition of the flash light irradiation, diffusion of the dopant can be appropriately controlled. 
     Therefore, an object of the present invention is to appropriately control the diffusion of the dopant. 
     These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical cross-sectional view illustrating a configuration of a heat treatment apparatus to be used in a heat treatment method in the present invention; 
         FIG. 2  is a perspective view illustrating an overall appearance of a retention unit; 
         FIG. 3  is a plan view of a susceptor; 
         FIG. 4  is a cross-sectional view of the susceptor; 
         FIG. 5  is a plan view of a transfer mechanism; 
         FIG. 6  is a side view of the transfer mechanism; 
         FIG. 7  is a plan view illustrating a layout of a plurality of halogen lamps; 
         FIG. 8  is a view illustrating a drive circuit of a flash lamp; and 
         FIG. 9  is a view schematically illustrating a structure of a substrate to be treated in the heat treatment apparatus in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, the preferred embodiment of the present invention will be described in detail with reference to the drawings. 
     First, a heat treatment apparatus to implement a heat treatment method according to the preset invention will be described.  FIG. 1  is a vertical cross-sectional view illustrating a configuration of a heat treatment apparatus  1  to be used in the heat treatment method according to the present invention. The heat treatment apparatus  1  in  FIG. 1  is a flash lamp annealer for heating a disk-shaped substrate W by irradiating the substrate W with flash light. A diameter size of the substrate W to be treated is not limited in particular, and it is 300 mm or 450 mm, for example. Furthermore, in  FIGS. 1 to 9 , a dimension of a component and the number of the components are exaggerated or simplified as needed to be easily understood. 
     The heat treatment apparatus  1  includes a chamber  6  for accommodating the substrate W, a flash heating unit  5  incorporating a plurality of flash lamps FL, a halogen heating unit  4  incorporating a plurality of halogen lamps HL. The flash heating unit  5  is provided above the chamber  6 , and the halogen heating unit  4  is provided below the chamber  6 . Furthermore, in the chamber  6 , the heat treatment apparatus I includes a retention unit  7  for horizontally retaining the substrate W, and a transfer mechanism  10  for transferring the substrate W between the retention unit  7  and an outside of the apparatus. Furthermore, the heat treatment apparatus  1  includes a control unit  3  for controlling each of operation mechanisms provided in the halogen heating unit  4 , the flash heating unit  5 , and the chamber  6  to perform the heat treatment for the substrate W. 
     The chamber  6  is formed by attaching chamber windows made of quartz on an upper and a lower sides of a cylindrical chamber lateral part  61 . The chamber lateral part  61  has a roughly tubular shape with the open top and bottom. An upper chamber window  63  is attached to close the upper opening and a lower chamber window  64  is attached to close the lower opening. The upper chamber window  63  is a disk-shaped member made of quartz serving as a ceiling portion of the chamber  6  and functions as the quartz window which transmits the flash light emitted from the flash heating unit  5  to the chamber  6 . Furthermore, the lower chamber window  64  is also a disk-shaped member made of quartz serving as a floor portion of the chamber  6  and functions as the quartz window which transmits a light from the halogen heating unit  4  to the chamber  6 . 
     Furthermore, a reflection ring  68  and a reflection ring  69  are attached to an upper and a lower portions of an inner wall surface of the chamber lateral part  61 , respectively. Both of the reflection rings  68  and  69  are formed into annular shapes. The upper reflection ring  68  is attached by engagement from an upper side of the chamber lateral part  61 . Meanwhile, the lower reflection ring  69  is attached by engagement from a lower side of the chamber lateral part  61  and fixed by a screw (not shown). Thus, both of the reflection rings  68  and  69  are detachably attached to the chamber lateral part  61 . The inner space of the chamber  6 , that is, the space surrounded by the upper chamber window  63 , the lower chamber window  64 , the chamber lateral part  61 , and the reflection rings  68  and  69  is defined as a heat treatment space  65 . 
     When the reflection rings  68  and  69  are attached to the chamber lateral part  61 , a recessed part  62  is formed on the inner wall surface of the chamber  6 . That is, the recessed part  62  is formed so as to be surrounded by a center portion to which the reflection rings  68  and  69  are not attached on the inner wall surface of the chamber lateral part  61 , a lower end surface of the reflection ring  68  and an upper end surface of the reflection ring  69 . The recessed part  62  is annularly formed on the inner wall surface of the chamber  6  along a horizontal direction and surrounds the retention unit  7  for retaining the substrate W. The chamber lateral part  61  and the reflection rings  68  and  69  are formed of metal material (such as stainless steel) which is superior in strength and heat resistance. 
     Furthermore, a conveyance opening (furnace opening)  66  is formed in the chamber lateral part  61  to carry the substrate W into or from the chamber  6 . The conveyance opening  66  can be opened and closed with a gate valve  185 . The conveyance opening  66  is communicated with and connected to an outer peripheral surface of the recessed part  62 . Therefore, while the gate valve  185  is set to open the conveyance opening  66 , the substrate W can be carried into the heat treatment space  65  from the conveyance opening  66  through the recessed part  62 , and the substrate W can be carried out from the heat treatment space  65 . Furthermore, when the conveyance opening  66  is closed with the gate valve  185 , the heat treatment space  65  in the chamber  6  becomes a sealed space. 
     In addition, a gas supply hole  81  is formed in an upper portion of the inner wall of the chamber  6  to supply a treatment gas into the heat treatment space  65 . The gas supply hole  81  is provided above the recessed part  62  and may be provided in the reflection ring  68 . The gas supply hole  81  is communicated with and connected to a gas supplying pipe  83  through a buffer space  82  which is annularly formed in a sidewall of the chamber  6 . The gas supplying pipe  83  is connected to a treatment-gas supply source  85 . Furthermore, a valve  84  is inserted in an intermediate part of a path of the gas supplying pipe  83 . When the valve  84  is opened, a treatment gas is supplied from the treatment-gas supply source  85  to the buffer space  82 . The treatment gas flowed into the buffer space  82  flows and spreads in the buffer space  82  having fluid resistance smaller than that of the gas supply hole  81  and is supplied to the heat treatment space  65  through the gas supply hole  81 . As the treatment gas, hydrogen (H 2 ), ammonia (NH 3 ), and a mixture gas of hydrogen and nitrogen (N 2 ) is used. 
     Meanwhile, a gas exhaust hole  86  is provided in a lower portion of the inner wall of the chamber  6  to exhaust the gas in the heat treatment space  65 . The gas exhaust hole  86  is provided below the recessed part  62  and may be provided in the reflection ring  69 . The gas exhaust hole  86  is communicated with and connected to a gas exhaust pipe  88  through a buffer space  87  which is annularly formed in the sidewall of the chamber  6 . The gas exhaust pipe  88  is connected to an exhaust unit  190 . Furthermore, a valve  89  is inserted in an intermediate part of the path of the gas exhaust pipe  88 . When the valve  89  is opened, the gas in the heat treatment space  65  is exhausted from the gas exhaust hole  86  to the gas exhaust pipe  88  through the buffer space  87 . Here, a plurality of gas supply holes  81  and a plurality of gas exhaust holes  86  may be provided along a circumferential direction of the chamber  6 , or they may have a slit shape. Furthermore, the treatment-gas supply source  85  and the exhaust unit  190  may be mechanisms provided in the heat treatment apparatus  1  or may be utilities in a factory where the heat treatment apparatus  1  is installed. 
     Furthermore, a gas exhaust pipe  191  is connected to an end of the conveyance opening  66  to exhaust the gas in the heat treatment space  65 . The gas exhaust pipe  191  is connected to the exhaust unit  190  through a valve  192 . When the valve  192  is opened, the gas in the chamber  6  is exhausted through the conveyance opening  66 . 
       FIG. 2  is a perspective view illustrating an overall appearance of the retention unit  7 . The retention unit  7  includes a base ring  71 , coupling parts  72 , and a susceptor  74 . Each of the base ring  71 , the coupling parts  72 , and the susceptor  74  is formed of quartz. That is, the entire retention unit  7  is formed of quartz. 
     The base ring  71  is an arc-shaped quartz member in which one portion is missing from an annular shape. This missing portion is provided to prevent interference between later-described transfer arms  11  of the transfer mechanism  10  and the base ring  71 . The base ring  71  is placed on a bottom surface of the recessed part  62  and is supported by the wall surface of the chamber  6  (refer to  FIG. 1 ). A plurality of coupling parts  72  (four in this preferred embodiment) are provided to rise from the upper surface of the base ring  71  along the circumferential direction of the annular shape of the base ring  71 . The coupling part  72  is also made of quartz and fixed to the base ring  71  by welding. 
     The susceptor  74  is supported by the four coupling parts  72  provided on the base ring  71 .  FIG. 3  is a plan view of the susceptor  74 .  FIG. 4  is a cross-sectional view of the susceptor  74 . The susceptor  74  includes a retention plate  75 , a guide ring  76 , and a plurality of substrate support pins  77 . The retention plate  75  is a roughly circular plate-shaped member formed of quartz. The diameter of the retention plate  75  is larger than a diameter of the substrate W. That is, the retention plate  75  has a planar size larger than the substrate W. 
     The guide ring  76  is placed on an upper-surface peripheral portion of the retention plate  75 . The guide ring  76  is an annular member having an inner diameter larger than the diameter of the substrate W. For example, when the diameter of the substrate W is 300 mm, the inner diameter of the guide ring  76  is 320 mm. An inner circumference of the guide ring  76  is formed into a tapered surface which is enlarged upward from the retention plate  75 . The guide ring  76  is formed of quartz similarly to the retention plate  75 . The guide ring  76  may be welded to the upper surface of the retention plate  75 , or may be fixed to the retention plate  75  with a pin separately processed. Alternatively, the retention plate  75  and the guide ring  76  may be processed as one integrated member. 
     The region of the upper surface of the retention plate  75  that is in the inside of the guide ring  76  serves as a planar retention surface  75   a , which retains the substrate W. The plurality of substrate support pins  77  are provided to rise from the retention surface  75   a  of the retention plate  75 . In this preferred embodiment, in total, twelve substrate support pins  77  are provided to rise from the retention surface  75   a  at every 30 degrees along the circumference of a concentric circle of the outer circumference circle of the retention surface  75   a  (inner circumferential circle of the guide ring  76 ). The diameter of the circle on which the twelve substrate support pins  77  are disposed (a distance between the opposite substrate support pins  77 ) is smaller than the diameter of the substrate W, and when the diameter of the substrate W is 300 mm, it ranges from 270 mm to 280 mm (280 mm in this preferred embodiment). Each of the substrate support pins  77  is formed of quartz. The plurality of substrate support pins  77  may be provided to the upper surface of the retention plate  75  by welding or may be integrally processed with the retention plate  75 . 
     Referring to  FIG. 2  again, the four coupling parts  72  provided to rise from the base ring  71  are fixed to the periphery of the retention plate  75  of the susceptor  74  by welding. That is, the susceptor  74  and the base ring  71  are fixedly coupled with the coupling parts  72 . The retention unit  7  is attached to the chamber  6  with base ring  71  of the retention unit  7  supported by the wall surface of the chamber  6 . When the retention unit  7  is attached to the chamber  6 , the retention plate  75  of the susceptor  74  is kept in a horizontal state (in which its normal line coincides with a vertical direction). That is, the retention surface  75   a  of the retention plate  75  is a horizontal surface. 
     The substrate W carried in the chamber  6  is placed and retained in the horizontal state on the susceptor  74  of the retention unit  7  attached to the chamber  6 . At this point, the substrate W is retained by the susceptor  74  by being supported by the twelve substrate support pins  77 , which are provided to rise from the retention plate  75 . More precisely, upper ends of the twelve substrate support pins  77  are in contact with a lower surface of the substrate W to support the substrate W. Since a height of the twelve substrate support pins  77  (a distance from the upper end of the substrate support pin  77  to the retention surface  75   a  of the retention plate  75 ) is uniform, the substrate W can be supported by the twelve substrate support pins  77  in the horizontal state. 
     Thus, the substrate W is supported by the plurality of substrate support pins  77  at a predetermined distance from the retention surface  75   a  of the retention plate  75 . Here, a thickness of the guide ring  76  is larger than the height of the substrate support pin  77 . Therefore, horizontal direction misalignment of the substrate W which is supported by the plurality of substrate support pins  77  is prevented by the guide ring  76 . 
     Furthermore, as illustrated in  FIGS. 2 and 3 , a vertically penetrating opening  78  is formed in the retention plate  75  of the susceptor  74 . The opening  78  is provided so that a radiation thermometer  120  (refer to  FIG. 1 ) can receive a radiated light (infrared light) emitted from the lower surface of the substrate W retained by the susceptor  74 . That is, the radiation thermometer  120  receives the light emitted from the lower surface of the substrate W retained by the susceptor  74  through the opening  78 , and a temperature of the substrate W is measured by a detector separately provided. Furthermore, four through-holes  79  are formed in the retention plate  75  of the susceptor  74  so that lift pins  12  of the transfer mechanism  10  which will be described below penetrate them to transfer the substrate W. 
       FIG. 5  is a plan view of the transfer mechanism  10 .  FIG. 6  is a side view of the transfer mechanism  10 . The transfer mechanism  10  includes two transfer arms  11 . The transfer arm  11  has an arc shape which is along approximately annular recessed part  62 . The two lift pins  12  are provided to rise from each of the transfer arms  11 . Each transfer arm  11  is pivotably moved by a horizontal movement mechanism  13 . The horizontal movement mechanism  13  horizontally moves the pair of transfer arms  11  between a transfer operation position (solid-line position in  FIG. 5 ) in which the substrate W is transferred to the retention unit  7  and a retreat position (two-dot chain line in  FIG. 5 ) in which the transfer arm  11  does not overlap with the substrate W retained by the retention unit  7  in planar view. The horizontal movement mechanism  13  may turn the transfer arms  11  separately by respective motors or may turn the pair of transfer arms  11  in conjunction with each other by one motor using a link mechanism. 
     Furthermore, the pair of transfer arms  11  is vertically moved together with the horizontal movement mechanism  13  by an elevating mechanism  14 . When the elevating mechanism  14  moves up the pair of transfer arms  11  in the transfer operation position, the four lift pins  12  pass through the through-holes  79  (refer to  FIGS. 2 and 3 ) provided in the susceptor  74 , and upper ends of the lift pins  12  project from the upper surface of the susceptor  74 . Meanwhile, when the elevating mechanism  14  moves down the pair of transfer arms  11  in the transfer operation position, the lift pins  12  are pulled out of the through-holes  79 , and then when the horizontal movement mechanism  13  moves the pair of transfer arms  11  outwardly, the transfer arms  11  are moved to the retreat position. The retreat position of the pair of transfer arms  11  is provided right above the base ring  71  of the retention unit  7 . Since the base ring  71  is placed on the bottom surface of the recessed part  62 , the retreat position of the transfer arms  11  is inside the recessed part  62 . Also, in the vicinity of the part at which a drive unit (horizontal movement mechanism  13  and the elevating mechanism  14 ) of the transfer mechanism  10  is provided, an exhaust mechanism (not shown) is provided and is configured so as to discharge the atmosphere around the drive unit of the transfer mechanism  10  to outside of the chamber  6 . 
     Referring to  FIG. 1  again, the flash heating unit  5  provided above the chamber  6  includes the light source composed of a plurality of (30 in this preferred embodiment) xenon flash lamps FL, and a reflector  52  provided so as to cover the light source from above, in a housing  51 . Furthermore, a lamp-light radiation window  53  is attached to a bottom portion of the housing  51  of the flash heating unit  5 . The lamp-light radiation window  53  constituting a floor part of the flash heating unit  5  is a plate-shaped quartz window formed of quartz. Since the flash heating unit  5  is provided above the chamber  6 , the lamp-light radiation window  53  faces the upper chamber window  63 . The flash lamps FL emits the flash light from above the chamber  6  toward the heat treatment space  65  through the lamp-light radiation window  53  and the upper chamber window  63 . 
     Each of the plurality of flash lamps FL is a rod-shaped lamp having a longitudinal cylindrical shape, and they are planarly arranged so that their longitudinal directions become parallel to each other over a main surface of the substrate W retained by the retention unit  7  (that is, along the horizontal direction). Thus, a planar surface formed by the arranged flash lamps FL is also a horizontal surface. 
       FIG. 8  is a view illustrating a drive circuit of the flash lamp FL. As illustrated in  FIG. 8 , a capacitor  93 , a coil  94 , the flash lamps FL, and an insulated gate bipolar transistor (IGBT)  96  arc connected in series. Furthermore, as illustrated in  FIG. 8 , the control unit  3  includes a pulse generator  31  and a waveform setting unit  32 , and is connected to an input unit  33 . The input unit  33  includes various well-known input devices such as keyboard, mouse, and touch panel. The waveform setting unit  32  sets a waveform of a pulse signal based on input contents from the input unit  33 , and the pulse generator  31  generates a pulse signal based on the waveform. 
     The flash lamp FL includes a rod-shaped glass tube (discharge tube)  92  containing sealed xenon gas and having an anode and a cathode at its both ends, and a trigger electrode  91  provided above an outer circumferential surface of the glass tube  92 . A predetermined voltage is applied to the capacitor  93  from an electric-power-source unit  95 , and an electric charge corresponding to the applied voltage (charge voltage) is accumulated therein. In addition, a high voltage can be applied to the trigger electrode  91  from the trigger circuit  97 . The timing for applying the voltage from the trigger circuit  97  to the trigger electrode  91  is controlled by the control unit  3 . 
     The IGBT  96  is the bipolar transistor incorporating a metal oxide semiconductor field effect transistor (MOSFET) in a gate portion, and is a switching element suitable for handling large electric power. The pulse signal is applied to the gate of the IGBT  96  from the pulse generator  31  of the control unit  3 . When a voltage (high voltage) having a predetermined value or higher is applied to the gate of the IGBT  96 , the IGBT  96  becomes an on-state, and when a voltage (low voltage) having a value lower than the predetermined value is applied, the IGBT 96  becomes an off-state. In this way, the drive circuit including the flash lamp FL is turned on/off by the IGBT  96 . When the IGBT  96  is turned on/off, the flash lamp FL is connected to and disconnected from the corresponding capacitor  93 , and a current flowing to the flash lamp LF is subjected to on/off control. 
     Even when the IGBT  96  becomes the on-state and the high voltage is applied to the both electrodes of the glass tube  92  in the state that the capacitor  93  is charged, a current does not flow in the glass tube  92  in a normal state because the xenon gas is an electrical insulator. However, in a case where the high voltage is applied to the trigger electrode  91  from the trigger circuit  97  to cause insulation breakdown, a current instantaneously flows in the glass tube  92  due to the discharge between the both-end electrodes, and a light is emitted due to excitation of atoms or molecules of xenon. 
     The drive circuit illustrated in  FIG. 8  is individually provided for each of the plurality of flash lamps FL provided in the flash heating unit  5 . In this preferred embodiment, the  30  flash lamps FL are planarly arranged, and accordingly the  30  drive circuits illustrated in  FIG. 8  are provided. Thus, the current flowing in each of the  30  flash lamps FL is subjected to individual on/off control by the corresponding IGBT  96 . 
     Furthermore, the reflector  52  is provided above the plurality of flash lamps FL so as to cover all of them. The reflector  52  basically functions to reflect the flash light emitted from the flash lamps FL toward the heat treatment space  65 . The reflector  52  is formed of an aluminum alloy plate, and its surface (surface facing the flash lamps FL) has been undergone surface roughening process by blast treatment. 
     The halogen heating unit  4  provided below the chamber  6  incorporates the plurality of ( 40  in this preferred embodiment) halogen lamps HL in a housing  41 . The halogen heating unit  4  is a light irradiation unit which carries out light irradiation to the heat treatment space  65  from below the chamber  6  through the lower chamber window  64  by the plurality of halogen lamps HL and heats the substrate W. 
       FIG. 7  is a planar view illustrating the layout of the plurality of halogen lamps HL. The  40  halogen lamps HL are disposed separately in upper/lower two stages. Thus, the  20  halogen lamps HL are disposed in an upper stage closer to the retention unit  7 , and the  20  halogen lamps I IL are disposed in a lower stage farther from the retention unit  7  than the upper stage. Each halogen lamp HL is a rod-shaped lamp having a longitudinal cylindrical shape. The  20  halogen lamps HL in each of the upper stage and the lower stage are arranged so that their longitudinal directions become parallel to each other over the main surface of the substrate W retained by the retention unit  7  (that is. along the horizontal direction). Thus, a planar surface formed by the arranged halogen lamps HL in each of the upper and lower stages is a horizontal surface. 
     Furthermore, as illustrated in  FIG. 7 , a density of the disposed halogen lamps HL is higher in a region facing a peripheral portion of the substrate W retained by the retention unit  7  than in a region facing a center thereof in each of the upper and lower stages. That is, both in the upper and lower stages, a pitch of the disposed halogen lamps HL is shorter in the peripheral portion than in the center portion. Therefore, irradiation with larger amount of light can be performed for the peripheral portion of the substrate W in which temperature reduction easily occurs in a case of heating by the light irradiation from the halogen heating unit  4 . 
     Furthermore, the lamp group composed of the halogen lamps HL in the upper stage and the lamp group composed of the halogen lamps HL in the lower stage are arranged to intersect with each other in the form of a lattice. That is, the 40 halogen lamps HL in total are arranged in such a manner that the longitudinal direction of the 20 halogen lamps HL arranged in the upper stage intersects with the longitudinal direction of the 20 halogen lamps HL arranged in the lower stage. 
     The halogen lamp HL is a filament-type light source in which light is emitted by allowing a filament to be incandescent by distributing electricity to the filament disposed in the glass tube. In the glass tube, a gas of an inert gas such as nitrogen or argon to which a minute amount of halogen element (such as iodine or bromine) is introduced is sealed. As a result of introducing the halogen element, the temperature of the filament can be set to a high temperature while inhibiting breaking of the filament. Therefore, the halogen lamp HL has characteristics of having a long life and being able to continuously emit intense light compared with a normal incandescent lamp. That is, the halogen lamp HL is a continuously lighting lamp which emits light continuously for at least one second. Furthermore, since the halogen lamp HL is the rod-shaped lamp, it has long life, and when the halogen lamps HL are disposed along the horizontal direction, a radiation efficiency to the substrate W provided above can be excellent. 
     Also in the housing  41  of the halogen heating unit  4 , a reflector  43  is also provided below the two-stage halogen lamps HL (refer to  FIG. 1 ). The reflector  43  reflects the light emitted from the plurality of halogen lamps HL toward the heat treatment space  65 . 
     The control unit  3  controls the above-described various operation mechanisms provided in the heat treatment apparatus  1 . A configuration of the control unit  3  as a hardware is similar to that of a general computer. That is, the control unit  3  includes a CPU serving as a circuit for performing various arithmetic processing, a ROM serving as a read-only memory for storing a basic program, a RAM serving as a readable/writable memory for storing various information, and a magnetic disk for storing controlling software and data. The CPU of the control unit  3  carries out a predetermined processing program, so that the process proceeds in the heat treatment apparatus  1 . 
     Other than the above-described configurations, the heat treatment apparatus  1  has various cooling structures to prevent the halogen heating unit  4 , the flash heating unit  5 , and the chamber  6  from being excessively increased in temperature due to thermal energy generated from the halogen lamp HL and flash lamp FL during the heat treatment for the substrate W. For example, a water-cooled tube (not shown) is provided in a wall of the chamber  6 . Furthermore, each of the halogen heating unit  4  and the flash heating unit  5  has an air-cooling structure which forms a gas flow inside it to exhaust heat. Furthermore, air is supplied to a gap between the upper chamber window  63  and the lamp-light radiation window  53  to cool the flash heating unit  5  and the upper chamber window  63 . 
     Next, a heat treatment method for the semiconductor in the present invention will be described. In this preferred embodiment, the heat treatment apparatus  1  performs an annealing process to activate a boron-doped germanium p-type semiconductor. 
       FIG. 9  is a view schematically illustrating a structure of the substrate W to be processed in the heat treatment apparatus  1 . In this preferred embodiment, a germanium semiconductor layer  102  is formed in one region on an upper surface of a silicon base material  101 . The semiconductor layer  102  is made of single-crystal germanium. The semiconductor layer  102  is extremely thin and its film thickness is several 10 nm. Methods for forming the semiconductor layer  102  include various well-known methods such as CVD. 
     Prior to the heat treatment according to the present invention, boron is doped as a dopant in a surface of the germanium semiconductor layer  102 . The dopant is doped by an ion implantation device different from the heat treatment apparatus  1 . Acceleration energy and a dose amount at the time of ion implantation can be appropriately set. When a minute amount of boron is doped, the semiconductor layer  102  becomes a p-type semiconductor containing germanium as a major component. 
     Here, boron which has been just doped by the ion implantation is inactive because it does not conform to the crystal of germanium, and a lattice defect is generated in the crystal of germanium due to the ion implantation, so that those need to be recovered. Thus, the flash lamp annealing is performed in the heat treatment apparatus  1  for the germanium semiconductor layer  102  in which the minute amount of boron is doped. The heat treatment apparatus  1  performs the heat treatment for the substrate W in which the semiconductor layer  102  is formed on the silicon base material  101 . Hereinafter, the heat treatment for the substrate W in the heat treatment apparatus  1  will be described. The process procedure in the heat treatment apparatus  1  in the following description is performed while the control unit  3  controls each operation mechanism of the heat treatment apparatus  1 . 
     First, the gate valve  185  is set to open the conveyance opening  66 , and the substrate W is carried into the heat treatment space  65  in the chamber  6  by a carrier robot provided outside the apparatus through the conveyance opening  66 . That is, the semiconductor layer  102  is carried into the chamber  6 . The substrate W carried by the carrier robot is moved to the position just above the retention unit  7  and stops. Then, the pair of transfer arms  11  of the transfer mechanism  10  is horizontally moved from the retreat position to the transfer operation position and raised, and the lift pins  12  project from the upper surface of the retention plate  75  of the susceptor  74  through the through-holes  79  to receive the substrate W. Here, the lift pins  12  are raised to be higher than the upper ends of the substrate support pins  77 . 
     After the substrate W is placed on the lift pins  12 , the carrier robot exits from the heat treatment space  65 , and the conveyance opening  66  is closed with the gate valve  185 . After that, the pair of transfer arms  11  is lowered, and the substrate W is transferred from the transfer mechanism  10  to the susceptor  74  of the retention unit  7  and supported from below in the horizontal state. The substrate W is retained by the susceptor  74  while it is supported by the plurality of substrate support pins  77  provided on the retention plate  75  to rise therefrom. Furthermore, the substrate W is retained by the retention unit  7  with its front surface having the semiconductor layer  102  formed facing upward. A predetermined space is provided between the back surface of the substrate W supported by the plurality of substrate support pins  77  (the main surface opposite to the front surface) and the retention surface  75   a  of the retention plate  75 . The pair of transfer arms  11  lowered below the susceptor  74  is moved to the retreat position by the horizontal movement mechanism  13 , that is, it retreats into the recessed part  62 . 
     Furthermore, after the conveyance opening  66  is closed with the gate valve  185  and the heat treatment space  65  becomes the sealed space, an atmosphere in the chamber  6  is adjusted. More specifically, the valve  84  is opened and the treatment gas is supplied from the gas supply hole  81  to the heat treatment space  65 . In this preferred embodiment, a mixed gas of hydrogen and nitrogen (forming gas) is supplied as the treatment gas to the heat treatment space  65  in the chamber  6 . Furthermore, the valve  89  is opened and the gas in the chamber  6  is exhausted from the gas exhaust hole  86 . Thus, the treatment gas supplied from the upper portion of the heat treatment space  65  in the chamber  6  flows downward and is exhausted from the lower portion of the heat treatment space  65 , so that the atmosphere in the heat treatment space  65  is replaced with the atmosphere containing hydrogen. Furthermore, when the valve  192  is opened, the gas in the chamber  6  is also exhausted from the conveyance opening  66 . In addition, the atmosphere around the drive unit of the transfer mechanism  10  is also exhausted through an exhaust mechanism (not shown). 
     After the atmosphere in the chamber  6  is replaced with that containing hydrogen, and the substrate W is retained by the susceptor  74  of the retention unit  7  in the horizontal state from below, the  40  halogen lamps HL are turned on at the same time in the halogen heating unit  4  to start preheating (assist heating). The halogen light emitted from the halogen lamp HL is applied to the back surface of the substrate W through the lower chamber window  64  and the susceptor  74  made of quartz. The substrate W is preheated by receiving the light irradiation from the halogen lamp HL and increased in temperature. Furthermore, since the transfer arms II of the transfer mechanism  10  are retreated in the recessed part  62 , and therefore, do not hinder the preheating by the halogen lamp HL. 
     While the preheating is performed by the halogen lamp HL, the temperature of the substrate W is measured by the radiation thermometer  120 . That is, the increasing temperature of the substrate is measured when the radiation thermometer  120  receives the infrared light emitted from the back surface of the substrate W retained by the susceptor  74  through the opening  78 . The measured temperature of the substrate W is transmitted to the control unit  3 . The control unit  3  monitors whether or not the temperature of the substrate W which rises due to the light irradiation from the halogen lamp HL reaches a preheating temperature T 1 , to control an output of the halogen lamp HL. That is, the control unit  3  performs feedback control on the output of the halogen lamp HL, based on the value measured by the radiation thermometer  120  so that the temperature of the substrate W can reach the preheating temperature T 1 . The preheating temperature TI is set between 200° C. and 500° C. (500° C. in this preferred embodiment). 
     After the temperature of the substrate W has reached the preheating temperature T 1 , the control unit  3  keeps the substrate W at the preheating temperature T 1  for a while. More specifically, when the temperature of the substrate W measured by the radiation thermometer  120  reaches the preheating temperature T 1 , the control unit  3  adjusts the output of the halogen lamp HL to keep the temperature of the substrate W at roughly the preheating temperature T 1 . 
     Thus, the preheating is performed by the halogen lamp HL, so that the substrate W is uniformly heated up to the preheating temperature T 1  as a whole. Therefore, the semiconductor layer  102  is also heated at the preheating temperature T 1 . Here, while the preheating is performed by the halogen lamp HL, a temperature at the peripheral portion of the substrate W is likely to drop because heat is easily released compared with that in the center. However, in the halogen heating unit  4 , the density of the arranged halogen lamps HL is higher in the region facing the peripheral portion than in the region facing the center portion of the substrate W. Therefore, the larger amount of light is applied to the peripheral portion of the substrate W in which the heat is easily released, so that a uniform in-plane temperature distribution can be provided in the substrate W during the preheating. 
     As described above, there are many vacancies in the crystals of germanium in semiconductor layer  102 . When the semiconductor layer  102  is preheated to the preheating temperature T 1  in the atmosphere having the treatment gas containing hydrogen, the vacancies provided near the surface of the semiconductor layer  102  are terminated by hydrogen and disappear. 
     At the point of time when predetermined time has passed after the temperature of the substrate W has reached the preheating temperature T 1 , the surface of the substrate W is irradiated with the flash light from the flash lamp FL in the flash heating unit  5 . Prior to the flash light irradiation by the flash lamp FL, the electric charge is previously accumulated in the capacitor  93  by the electric-power-source unit  95 . In the state in which the electric charge is accumulated in the capacitor  93 , the pulse signal is output from the pulse generator  31  of the control unit  3  to the IGBT  96  to turn the IGBT  96  on and off. 
     The waveform of the pulse signal can be defined by inputting a recipe which has been sequentially set using parameters of a pulse width time (on time) and a pulse interval time (off time) from the input unit  33 . When an operator inputs the above recipe from the input unit  33  to the control unit  3 , the waveform setting unit  32  of the control unit  3  sets a pulse waveform which repeats on/off based on the recipe. Thus, based on the pulse waveform set by the waveform setting unit  32 , the pulse generator  31  outputs the pulse signal. As a result, the pulse signal having the set waveform is applied to the gate of the IGBT  96 , whereby the on/off drive of the IGBT  96  is controlled. More specifically, when the pulse signal input to the gate of the IGBT  96  is on, the IGBT  96  becomes an on-state, and when the pulse signal is off, the IGBT  96  becomes an off-state. 
     In synchronization with the timing at which the pulse signal output from the pulse generator  31  becomes on, the control unit  3  controls the trigger circuit  97  and applies a high voltage (trigger voltage) to the trigger electrode  91 . In the state in which electric charge is accumulated in the capacitor  93 , the pulse signal is input to the gate of the IGBT  96 , and the high voltage is applied to the trigger electrode  91  in synchronization with the timing at which the pulse signal becomes on. Thus, when the pulse signal is on, a current surely flows between the electrodes at both ends of the glass tube  92 , so that the light is emitted due to the excitation of atoms or molecules of xenon at that time. 
     Thus, the light is emitted from the 30 flash lamps FL in the flash heating unit  5 , and the flash light is applied to the surface of the substrate W retained by the retention unit  7 . Here, in a case where the light is emitted from the flash lamps FL without using the IGBT  96 , the electric charge accumulated in the capacitor  93  is consumed by one light emission, and the output waveform from the flash lamp FL becomes a simple single-pulse having a width of 0.1 milliseconds to 10 milliseconds. Meanwhile, in this preferred embodiment, the IGBT  96  serving as the switching element is connected in the circuit and the pulse signal is output to the gate of the IGBT  96 , so that the electric charge is intermittently supplied from the capacitor  93  to the flash lamp FL by the IGBT  96 , and on/off control of the current which flows to the flash lamp FL is carried out. As a result, the light emission of the flash lamp FL is controlled by chopper control, so that the electric charge accumulated in the capacitor  93  is divided and consumed and the flash lamp FL repeats blinking in an extremely short period of time. In addition, before a value of current flowing in the circuit becomes completely “0”, the next pulse is applied to the gate of the IGBT  96  to increase the value of current again, so that the light emission output does not become completely “0” even while the flash lamp FL is repeating blinking. 
     By subjecting the current flowing in the flash lamp FL to the on/off control by the IGBT  96 , a light emission pattern of the flash lamp FL (time waveform of the light emission output) can be freely defined, so that the light emission time and light emission intensity can be freely adjusted. The pattern of the on/off drive of the IGBT  96  is defined by the pulse width time and the pulse interval time input from the input unit  33 . That is, when the IGBT  96  is incorporated in the drive circuit of the flash lamp FL, the light emission pattern of the flash lamp FL can be freely defined only by appropriately setting the pulse width time and the pulse interval time input from the input unit  33 . 
     More specifically, when a ratio of the pulse width time is increased with respect to the pulse interval time input from the input unit  33 , the current flowing in the flash lamp FL is increased and the light emission intensity becomes strong. Meanwhile, when the ratio of the pulse width time is reduced with respect to the pulse interval time input from the input unit  33 , the current flowing in the flash lamp FL is reduced and the light emission intensity becomes weak. In addition, by appropriately adjusting the ratio of the pulse interval time and the pulse width time input from the input unit  33 , the light emission intensity of the flash lamp FL can be maintained constant. Still furthermore, by increasing a total time of the combination of the pulse width time and the pulse interval time input from the input unit  33 , the current keeps flowing to the flash lamp FL for a relatively long period of time, so that the light emission time of the flash lamp FL is increased. In this preferred embodiment, the light emission time of the flash lamp FL is set between 0.1 milliseconds to 100 milliseconds. 
     In this way, the substrate W is heated with its front surface irradiated with the flash light from the flash lamp FL for the irradiation time of 0.1 milliseconds to 100 milliseconds. Since the intense flash light is applied for the extremely short irradiation time of 0.1 milliseconds to 100 milliseconds, the front surface of the substrate W including the germanium semiconductor layer  102  can be instantaneously heated up to a treatment temperature T 2 . The treatment temperature T 2  which is a maximum temperature (peak temperature) of the front surface of the substrate W reached by the flash light irradiation ranges from 600° C. to 900° C., and in this preferred embodiment, it is 800° C. In the flash heating, since the irradiation time of the flash light is as extremely short as  100  milliseconds or less, the front surface temperature of the substrate W reaches the treatment temperature T 2  instantaneously and then drops close to the preheating temperature Tl. 
     When the front surface of the substrate W is irradiated with the flash light, the germanium semiconductor layer  102  is also heated up to the treatment temperature T 2 . When the semiconductor layer  102  having boron serving as dopant doped in its surface is instantaneously heated up to the treatment temperature T 2 , the dopant is activated. Furthermore, the lattice defect generated in the crystal of germanium due to the ion implantation is recovered. Still furthermore, the dopant doped in semiconductor layer  102  is appropriately diffused. 
     Since there are many vacancies in the crystals of germanium, the dopant such as boron in the p-type semiconductor is not likely to be diffused because of the many vacancies. However, in this preferred embodiment, since the semiconductor layer  102  is preheated in the atmosphere containing hydrogen, the vacancies provided near the surface of the semiconductor layer  102  are eliminated. Therefore, even when the semiconductor layer  102  is the p-type semiconductor, the dopant such as boron can be relatively easily diffused. As a result, by appropriately adjusting the light emission time and the light emission intensity of the flash lamp FL, the diffusion of the dopant can be appropriately controlled. 
     After a predetermined time has passed after the flash heating treatment is finished, the halogen lamps HL are turned off. Thus, the temperature of the substrate W rapidly drops from the preheating temperature T 1 . In addition, the hydrogen supply into the chamber  6  is stopped, and only nitrogen is supplied and the atmosphere in the chamber  6  is replaced with a nitrogen atmosphere. The dropping temperature of the substrate W is measured by the radiation thermometer  120 , and its measurement result is transmitted to the control unit  3 . The control unit  3  monitors whether or not the temperature of the substrate W drops to a predetermined temperature, based on the measurement result of the radiation thermometer  120 . Thus, when the temperature of the substrate W drops to the predetermined temperature or lower, the pair of transfer arms  11  of the transfer mechanism  10  is horizontally moved again from the retreat position to the transfer operation position and raised, as a result, the lift pins  12  project from the upper surface of the susceptor  74  and receive the heat-treated substrate W from the susceptor  74 . After that, the conveyance opening  66  closed with the gate valve  185  is opened, and the substrate W placed on the lift pins  12  is carried out by the carrier robot provided outside the apparatus, whereby the heat treatment for the substrate W by the heat treatment apparatus  1  is completed. 
     In this preferred embodiment, by subjecting the germanium semiconductor layer  102  doped with a dopant such as boron to preheating at the preheating temperature T 1  in the atmosphere containing hydrogen, the vacancies provided near the surface of the semiconductor layer  102  are eliminated with hydrogen. Thus, after that, the semiconductor layer  102  is irradiated with the flash light from the flash lamp FL, so that the semiconductor layer  102  is heated up to the treatment temperature T 2 . Since the vacancies provided near the surface of the semiconductor layer  102  have been eliminated before the flash heating, the dopant can be relatively easily diffused at the time of flash heating, so that by appropriately adjusting the light emission time and the light emission intensity of the flash lamp FL, the diffusion of the dopant can be appropriately controlled. 
     Especially, in a case where the FET has a Fin structure, it is difficult to uniformly dope the dopant in a required region at the time of ion implantation in many cases. However, even in this case, by appropriately controlling the dopant diffusion, the dopant can be doped into a region in which the dopant cannot be doped at the time of ion implantation. 
     The preferred embodiment of the present invention has been described in the above, but the present invention can be variously modified other than the above-described ones, without departing from the scope of the present invention. For example, in the above preferred embodiment, the mixed gas of hydrogen and nitrogen is supplied to the chamber  6  to form the atmosphere containing hydrogen, but instead of this, the mixed gas of ammonia and nitrogen may be supplied to form an atmosphere containing ammonia in the chamber  6 . When the semiconductor layer  102  doped with the dopant is preheated to the preheating temperature T 1  in the atmosphere containing ammonia, similar to the above preferred embodiment, the vacancies provided near the surface of the semiconductor layer  102  can be eliminated. As a result, the diffusion of the dopant can be appropriately controlled at the time of flash heating. 
     Furthermore, in the above preferred embodiment, boron is doped in the germanium semiconductor layer  102  as the dopant, but the present invention is not limited to this, and a trivalent dopant such as indium (In) may be doped. That is, the dopant only needs to form the p-type semiconductor when added to germanium. 
     Furthermore, in the above preferred embodiment, the substrate W is subjected to the heat treatment in the chamber  6  under normal pressure, but the preheating and the flash heating may be performed in the chamber  6  under reduced pressure. More specifically, the preheating and the flash heating for the substrate W may be performed in the chamber  6  under pressure from 20 Pa to atmospheric pressure (about 101325 Pa). 
     Furthermore, in the above preferred embodiment, the semiconductor layer  102  is formed of germanium, but the present invention is not limited to this, and the semiconductor layer  102  may be formed of silicon germanium. When the dopant such as boron is doped in the silicon germanium semiconductor layer  102 , the semiconductor layer  102  becomes a p-type semiconductor containing silicon germanium as its major component. Thus, the heat treatment is performed on the silicon germanium semiconductor layer  102  similarly to the above preferred embodiment, so that the diffusion of the dopant can be appropriately controlled. 
     Furthermore, in the above preferred embodiment, the germanium semiconductor layer  102  is formed in the region of the upper surface of the silicon base material  101 , but a semiconductor wafer made of single-crystal germanium may be used as the substrate. 
     Furthermore, in the above preferred embodiment, 30 flash lamps FL are provided in the flash heating unit  5 , but the present invention is not limited to this, and the number of the flash lamps FL may be any number. Furthermore, the flash lamp FL is not limited to the xenon lamp, and it may be a krypton flash lamp. Furthermore, the number of the halogen lamp HL provided in the halogen heating unit  4  is not limited to 40 and it may be any number. 
     In addition, in the above preferred embodiment, the substrate W is preheated by irradiation with the halogen light from the halogen lamp HL, but the present invention is not limited to this preheating method, and the substrate W may be preheated by being placed on a hot plate. 
     While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention.