Abstract:
A heat treatment apparatus is provided which includes heating means for enabling a rapid temperature rise to a temperature of 1600 through 1900° C., and a thermometer capable of accurately measuring temperatures even when rapid temperature rises and drops are repeated, the heat treatment apparatus being capable of performing heat treatment of an SiC substrate with good mass productivity after ion implantation. The heat treatment apparatus enables the heat treatment of a semiconductor substrate at 1600 to 1900° C. by temperature control using a resistance heating element and thermocouple thermometers. The heat treatment apparatus is configured such that the resistance heating element and the thermocouple thermometers include a common constituent metal as a main component.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a heat treatment apparatus which is useful for the heat treatment of an SiC substrate after ion implantation. 
       BACKGROUND ART 
       [0002]    The activation heat treatment of an SiC substrate after ion implantation requires a temperature from 1600 to 1900° C. It is also required to perform the activation heat treatment in a short period of time in order to activate impurities without imparting time for atoms to move. It is further required to reduce variations in the in-plaine temperature distribution of the SiC substrate being heat treated as well as to provide improved mass productivity. 
         [0003]    In response to such a demand, a heat treatment apparatus has been suggested in which a substrate was retained in a tube-shaped body formed of a high melting point material, and the tube-shaped body was heated with an RF coil at a high frequency to thereby create a high-temperature region in the tube-shaped body (Patent Literature 1). The heat treatment apparatus provides a temperature rise rate of about 20 to 30° C. per minute which is two to three times that provided by heating using a conventional infrared lamp, thereby reducing variations in the in-plane temperature distribution. 
       CITATION LIST 
     Patent Literature 
       [0004]    Patent Literature 1: Japanese Patent Application Laid-Open No. 2003-77855 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    However, the aforementioned heat treatment apparatus that employs high-frequency heating is reduced in mass productivity of substrates to be treated because the structure of a jig for retaining the substrate in a high-temperature region restricts the number of substrates to be heat treated at a time to 4 to 8. 
         [0006]    Furthermore, the heat treatment apparatus has conventionally often provided temperature control by measuring the temperature of the substrate with a radiation thermometer. However, the radiation thermometer requires a complicated procedure of determining a calibration curve by another temperature measurement method because the emissivity of thermal radiation differs depending on the substance to be measured. Furthermore, the radiation thermometer is significantly influenced by the surface state of an object being measured, and accurately measures temperatures with difficulty even due to soil on the measurement port. 
         [0007]    In response to this, it is conceivable to use a thermocouple thermometer in place of the radiation thermometer. However, use of the thermocouple thermometer in the high-frequency heating apparatus may lead to inaccurate temperature measurement due to self-heating or noise caused by induction. In this context, the heating method may be changed from the high-frequency heating to resistance heating. In this case, the problem of the self-heating can be resolved. However, the activation heat treatment after ion implantation leads to high temperature rise and drop rates, so that for example, use of the thermocouple thermometer incorporating an iridium rhodium alloy with a ceramic heater serving as heating means would cause the thermocouple to be worn and have a break due to grain boundaries. 
         [0008]    In view of the aforementioned problems associated with the conventional techniques, an object of the present invention is to provide a heat treatment apparatus which includes: heating means enabling a rapid temperature rise to a temperature of 1600 through 1900° C.; and a thermometer which can measure temperatures with accuracy even when a temperature rise and a temperature drop are rapidly repeated, and which is capable of heat treating a large number of substrates at a time and performing heat treatment on an SiC substrate with improved mass productivity after ion implantation. 
       Solution to Problem 
       [0009]    The present inventor has found that when employing resistance heating as the heating method for a heat treatment apparatus and a thermocouple thermometer for temperature control, a heat treatment apparatus is configured to utilize a heating element responsible for the resistance heating and the thermocouple each being formed of a common main component metal, so as to provide a common atmosphere suitable for both. This can configure the heat treatment apparatus which is capable of maintaining accurate heat control due to optimum heat treatment conditions being readily set even when abrupt increases and drops in temperature are repeated. 
         [0010]    That is, the present invention provides a heat treatment apparatus for a semiconductor substrate, in which heat treatment can be performed at 1600 to 1900° C. by temperature control using a resistance heating element and a thermocouple thermometer, wherein the resistance heating element and the thermocouple thermometer include a common constituent metal as a main component. 
       ADVANTAGEOUS EFFECTS OF INVENTION 
       [0011]    The heat treatment apparatus according to the present invention employs a resistance heating element for performing resistance heating and a thermocouple thermometer formed of a main component common to that of the resistance heating element so as to provide temperature control to the heat treatment of a substrate. This makes it possible to provide a rapid temperature rise to a temperature of 1600 through 1900° C. as well as to provide accurate temperature control to heat treatment even in the presence of repeated rapid rises and drops in temperature. Thus, the heat treatment of an SiC substrate after ion implantation can be carried out in an improved manner. 
         [0012]    In addition, since a few tens of substrates can be heat treated at a time, the heat treatment of substrates can be performed with good mass productivity. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]      FIG. 1  is a longitudinal sectional view illustrating a heat treatment apparatus according to an embodiment. 
           [0014]      FIG. 2  is across-sectional view, taken along X-X, illustrating the heat treatment apparatus according to the embodiment. 
           [0015]      FIG. 3  is a view illustrating a change in heat treatment temperature. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0016]    Now, referring to the drawings, the present invention will be described more specifically. 
         [0017]      FIG. 1  is a longitudinal sectional view illustrating a heat treatment apparatus  1  according to an embodiment of the present invention, and  FIG. 2  is across-sectional view taken along X-X. 
         [0018]    This heat treatment apparatus  1  activates an SiC substrate  2  after ion implantation and includes: a vertical type boat  3  which can accommodate 20 or more SiC substrates  2  at the same time; a tube type container (hereafter to be referred to as the SiC tube)  4  formed of a high melting point material (for example, SiC); a transfer device  6  for inserting or drawing out the boat  3  into a heating chamber  5  formed in an upper region within the SiC tube  4 ; a resistance heating element  7  disposed in a tubular shape so as to surround the heating chamber  5 ; a first thermocouple thermometer  8   a  with an end disposed between the resistance heating element  7  and the SiC tube  4 ; and a second thermocouple thermometer  8   b  with an end disposed in the heating chamber  5 . The outer side of the resistance heating element  7  disposed in a tubular shape is surrounded by a reflector  11  formed from a tungsten and molybdenum alloy. 
         [0019]    More specifically, the resistance heating element  7  is made up of three plate type heating elements that are each bent to form three planes, so that these three bent plate type heating elements  7   a,    7   b,  and  7   c  are formed in a tubular shape to surround the outer periphery of the SiC tube  4  that forms the heating chamber  5 . In this case, as shown in  FIG. 2 , the tube-shaped body is an approximately regular dodecagon in cross section, and the three bent plate type heating elements  7   a,    7   b,  and  7   c  occupy nine sides of the generally regular dodecagon. Also provided are three heater electrodes  9  and guide pipes  10  corresponding to the respective three bent plate type heating elements  7   a,    7   b,  and  7   c.    
         [0020]    To dispose a plurality of plate type heating elements in a tubular shape, the heating elements preferably form a circle in cross section from the viewpoint of the thermal uniformity in the cross section of the heating chamber  5 . However, plate type heating elements may be disposed so as to form a regular polygon with six sides or more, for example, around the SiC tube  4  having an outer diameter of 145 mm or more, more preferably 145 to 185 mm, thereby ensuring a sufficient thermal uniformity in the cross section. 
         [0021]    On the other hand, in disposing a plurality of plate type heating elements in a tubular shape, the entire periphery is not always required to be occupied with the heating elements, so that the individual plate type heating elements may be disposed with a gap therebetween. However, when there are too many regions in which no heating element exists, the temperature of the heating chamber  5  cannot be rapidly increased to 1600 through 1900° C. Thus, for example, in employing a plurality of plate type heating elements to form a regular polygon with  12  or more sides, it is preferable to occupy ¾ the number of sides or greater with the heating elements. Thus, the resistance heating element  7  of this embodiment which employs the three bent plate type heating elements  7   a,    7   b,  and  7   c,  each having three continuous rectangular planes, so as to form a generally regular dodecagon provides the heating chamber  5  with an improved thermal uniformity. 
         [0022]    On the other hand, in disposing plate type heating elements so that the heating elements form a tubular polygonal shape in cross section, bent plate type heating elements each having a plurality of adjacent planes, more preferably two to four continuous side surfaces, may be more preferably used because the total number of heating elements can be reduced and the manufacturing costs of heating elements can also be reduced. In this context, although a resistance heating element which is made of tungsten and formed cylindrically in a mesh is conventionally known, bent plate type heating elements can be disposed in a tubular shape as a heating element as in this embodiment, thereby reducing the processing costs of the heating element by 15 to 20%. 
         [0023]    Note that rod-shaped heating elements may also be conceivably disposed in a tubular shape in place of the plate type heating elements, but may lead to an increase in the number of electrodes, thus unpreferably making the processing of the mantle and the structure of the heating chamber  5  complicated. 
         [0024]    On the other hand, as the first thermocouple thermometer  8   a  and the second thermocouple thermometer  8   b,  the heat treatment apparatus  1  includes a tungsten rhenium alloy thermocouple (rhenium 5%, 26%) which has a main component common to that of the aforementioned plate type heating elements  7   a,    7   b,  and  7   c.  Thus, the heat treatment apparatus  1  can be used at a high temperature in a reduction atmosphere. Furthermore, the heat treatment apparatus  1  can maintain a heating accuracy within ±1° C. with respect to 1900° C. even when heat treatments are repeated because heating control is performed not by high-frequency heating but by resistance heating and a thermocouple thermometer. Heating the heating chamber by a conventional combination of the high-frequency heating and the radiation thermometer may cause an error of about ±10° C. It can be thus seen that the heat treatment apparatus  1  of this embodiment provides a significantly improved temperature control accuracy. 
         [0025]    As atmosphere control means, the heat treatment apparatus  1  has a gas inlet pipe  12  for drawing an inert gas such as argon or nitrogen into the SiC tube  4  that forms the heating chamber  5 , and a gas discharge pipe  13  for discharging the gas from the SiC tube  4 . The lower end of the SiC tube  4  is closed with a quartz plate  16  via an O-ring  15 . Note that dummy plates  14  are placed at a lower portion of the heating chamber  5  inside the SiC tube  4  to thermally insulate the heating chamber  5 , and a farther lower region is surrounded by a sub-chamber  17  through which water is passed to cool down the SiC tube  4 . Furthermore, a stainless steel water cooling pipe  18  is provided outside the reflector  11 . 
         [0026]    The heat treatment apparatus  1  is used as follows. At a temperature of 300° C. or lower, in the heating chamber  5 , a substrate  2  placed on the boat  3  is inserted into the heating chamber  5  by actuating the transfer device  6 , an inert gas such as argon is drawn from the upper end of the SiC tube  4  through the gas inlet pipe  12 , and oxygen and water are discharged from the lower end of the SiC tube  4  through the gas discharge pipe  13 . Then, the resistance heating element  7  is used to rapidly heat the heating chamber  5  to a temperature of 1600° C. or higher, heat treatment is completed in a few minutes, and the heating chamber  5  is then cooled down.  FIG. 3  shows an example of changes in temperature inside and outside the heating chamber  5  for this case. As can be seen, the heating apparatus enables a rapid temperature rise at a rate of 100° C. or greater per minute, and preferably at a rate of 200° C. or greater per minute. It is thus possible to perform thermal activation treatment after ion implantation without diffusing impurities in the substrate. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  Heat treatment apparatus 
           2  Substrate 
           3  Boat 
           4  SiC tube 
           5  Heating chamber 
           6  Transfer device 
           7  Resistance heating element 
           7   a,    7   b,    7   c  Plate type heating element 
           8   a,    8   b  Thermocouple thermometer 
           9  Heater electrode 
           10  Heater electrode guide pipe 
           11  Reflector 
           12  Gas inlet pipe 
           13  Gas discharge pipe 
           14  Dummy plate 
           15  O-ring 
           16  Quartz plate 
           17  Sub-chamber 
           18  Water cooling pipe