Abstract:
A heating apparatus which is installed in a low pressure CVD system or annealing equipment for use in semiconductor integrated circuit manufacturing processes for heat-treating wafers on which IC&#39;s are to be formed, wherein wafers are uniformly heated, the temperature of wafers is rapidly raised and lowered, and wafers are processed in high volume, wherein the apparatus comprises a cylindrical body made of glass-like carbon placed inside a reactor, and a high-frequency induction coil which is placed outside the reactor and is for causing the cylindrical body made of glass-like carbon to produce heat and thereby heating wafers in the reactor.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a heating apparatus which is installed in, for example, a low pressure CVD system and is suitable for heat treatment on wafers. 
     2. Description of Related Art 
     As is commonly known, a semiconductor integrated circuit manufacturing process involves a variety of IC process units, including oxidation and dispersion equipment, vapor phase epitaxial growth systems, low pressure CVD systems (LPCVD systems), and annealing equipment. These units are equipped with heating apparatuses for heat-treating silicon wafers (hereafter, simply referred to as “wafers”) on which IC&#39;s are being formed or to be formed. 
       FIG. 2  is a schematic diagram illustrating an example of vertical low pressure CVD systems equipped with a heater based on electric resistance heating as heating apparatus, for the purpose of explanation of prior arts. In low pressure CVD, films are generally formed at temperature of 400 to 800° C. under pressure of 0.1 to 30 Torr (approx. 0.013 kPa to 4.0 kPa). 
     As shown in  FIG. 2 , the batch processing vertical low pressure CVD system is provided with a reactor  51  made of quartz having circular hollow cross-sections and dome-shaped top; a cylindrical inner tube  54  made of quartz placed inside the reactor  51 ; a boat  53  which is placed inside the inner tube  54  and is mounted with a large number (for example, 100 to 150 or so) of vertically arranged wafers  52 ; and a manifold  56 . The vertical low pressure CVD system is further provided with a cylindrical heater  55  concentrically placed around the reactor  51  so that the reactor is encircled with the heater in the case of this example. The reactor  51 , the inner tube  54 , the boat  53 , and the heater  55  are arranged with the axis common thereto. On the manifold  56 , the reactor  51  and the inner tube  54  are placed, and further, the boat  53  is placed with a pedestal (not shown) in-between. The manifold  56  is provided with gas injectors  57   a  and  57   b  for feeding source gas or the like into the inner tube  54  and with a gas exhaust port  58  for letting out reacted gas or unreacted gas from the reactor  51 . 
     An explanation is given below about a case where, for example, a polysilicon film is formed on wafers  52  using the vertical low pressure CVD system provided with the heater  55  based on electric resistance heating. First, wafers  52  are set on the boat  53 , and the boat  53  is inserted into the inner tube  54  from an opening (not shown) located at the lower end of the manifold  56 , together with the pedestal (not shown) with the boat  53  placed thereon. The opening in the manifold  56  is closed with a hatch (not shown). Then the space inside the inner tube  54  is heated to a specified temperature by means of the heater  55  based on electric resistance heating, and further, silane gas is fed into the inner tube  54  through the gas injector  57   a.  The silane gas is heated and pyrolytically decomposed on the surfaces of the wafers  52 , and a polysilicon film is thereby formed on the surfaces of the wafers  52 . The reacted gas or unreacted gas goes through the path between the inner tube  54  and the reactor  51  and externally discharged from the gas exhaust port  58 . As mentioned above, to form films on wafers in the vertical low pressure CVD system, the heater  55  based on electric resistance heating is used as heating apparatus for heat-treating the wafers  52 . 
       FIG. 3  is a schematic diagram illustrating an example of single wafer processing vapor phase epitaxial growth systems equipped with infrared lamps as heating apparatus, for the purpose of explanation of prior arts. The details of the vapor phase epitaxial growth of silicon vary depending on source gas used (four varieties of gases: silicon tetrachloride gas, silane dichloride gas, silane trichloride gas, and silane gas), but in general the reaction occurs at a temperature of 1100 to 1200° C. or so. 
     As shown in  FIG. 3 , a disk-like susceptor designed to support a wafer  62  placed thereon one by one is placed in a reactor  61  made of quartz. The surface of the susceptor  63  is made of a graphite base material coated with silicon carbide. A plurality of infrared lamps  64  as heating apparatus is placed concentrically with the reactor  61  outside the reactor. In the upper space  61   a  in the reactor  61 , source gas (including dopant), fed in through a gas feed port  65  together with hydrogen gas as carrier gas, moves in substantially laminar flow over the surface of the wafer  62 , and is discharged from an exhaust port  66  located on the opposite side. In the lower space  61   b  in the reactor  61 , hydrogen gas as purge gas is fed under a higher pressure than that of the source gas (reactive gas). In this vapor phase epitaxial growth system, a wafer  62  placed in the reactor  61  is radiantly heated to a specified temperature through the reactor  61  by means of infrared lamps  64  located above and beneath the reactor  61 , and thus a silicon epitaxial layer is formed by vapor phase growth. As mentioned above, to form a silicon epitaxial layer in this vapor phase epitaxial growth system by vapor phase growth, infrared lamps  64  are used as heating apparatus for heat-treating the wafer  62 . 
       FIG. 4  is a schematic diagram illustrating an example of single wafer processing vapor phase epitaxial growth system equipped with a high-frequency induction coil as heating apparatus, for the purpose of explanation of prior arts. 
     As shown in  FIG. 4 , a disk-like susceptor  73  made of graphite on which a wafer  72  is to be placed one by one is placed in a reactor  71  made of quartz. A high-frequency induction coil  74  for causing the susceptor  7  with a wafer  72  supported thereon to produce heat and thereby heating the wafer  72  is installed under the susceptor  73  outside the reactor  71 . The high-frequency induction coil  74  and the susceptor  73  form a heating apparatus for heating a wafer  72 . In the reactor  71 , source gas (reactive gas) or the like is fed through a gas feed port  75 . The gas or the like moves in substantially laminar flow over the surface of the wafer  72 , and is discharged from an exhaust port  76  located on the opposite side. In this vapor phase epitaxial growth system, a wafer  72  is heated to a specified temperature by causing the susceptor  73  to produce heat via the high-frequency induction coil  74 , and a silicon epitaxial layer is formed by vapor phase growth. As mentioned above, to form a silicon epitaxial layer in this vapor phase epitaxial growth system by vapor phase growth, the high-frequency induction coil  74  and the susceptor  73  made of graphite are used as heating apparatus for heat-treating a wafer  72 . 
     However, in the above-mentioned heating apparatuses wherein heating is provided by radiant heat or conductive heat from a heater, there is restriction due to thermal conduction between the output of the heater and wafers as objects to be heated. As shown in Table 1, therefore, these apparatuses are theoretically unsuitable for rapidly raising or lowering the temperature. Thus, these apparatuses have a disadvantage that it takes much time to rise and lower the temperature of wafers and this leads to impaired throughput. 
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Required Characteristics 
               
             
          
           
               
                   
                   
                   
                   
                 Rapid 
               
               
                   
                 Conventional 
                 High-volume 
                 Temperature 
                 temperature 
               
               
                   
                 Apparatuses 
                 processing 
                 uniformity 
                 rise/drop 
               
               
                   
                   
               
               
                   
                 Heater 
                 ◯ 
                 ◯ 
                 Δ 
               
               
                   
                 Lamp 
                 X 
                 ◯ 
                 ⊚ 
               
               
                   
                 High-frequency 
                 X 
                 ◯ 
                 ⊚ 
               
               
                   
                 induction coil 
               
               
                   
                   
               
               
                   
                 ⊚: Excellent  
               
               
                   
                 Δ: Considerably restricted  
               
               
                   
                 ◯: Medium  
               
               
                   
                 X: Unsuitable  
               
             
          
         
       
     
     In the above-mentioned heating apparatuses wherein radiant heating is implemented by infrared lamps, the performance greatly depends on the distance between the lamps and wafers as objects to be heated. Therefore, tens of lamps are required for several wafers. As shown in Table 1, these apparatuses have a disadvantage that the apparatuses are incapable of processing wafers in high volume. In the above-mentioned heating apparatuses wherein heating is implemented by a high-frequency induction coil, the susceptor caused to produce heat to heat wafers is formed in disk shape, and such apparatuses are so designed that wafers are placed on the disk-shaped susceptor. Therefore, these apparatuses have a disadvantage that they are incapable of processing wafers in high volume. 
     SUMMARY OF THE INVENTION 
     To cope with these disadvantages, this invention is intended to provide a heating apparatus which is installed in a low pressure CVD system or annealing equipment for use in semiconductor integrated circuit manufacturing processes for heat-treating wafers on which IC&#39;s are to be formed, wherein wafers are uniformly heated, the temperature of wafers is rapidly raised or lowered, and wafers are processed in high volume. 
     To attain the purpose, first aspect of the invention is directed to a heating apparatus comprising a cylindrical body made of glass-like carbon placed in a reactor; and a high-frequency induction coil that is placed outside the reactor and is for causing the cylindrical body made of glass-like carbon to produce heat and thereby heating objects to be heated in the reactor. 
     Second aspect of the invention is directed to the heating apparatus according to first aspect wherein a heat insulating body is placed between the cylindrical body made of glass-like carbon and the high-frequency induction coil or around the high-frequency induction coil. 
     The heating apparatus of the invention is a heating apparatus utilizing high-frequency induction heating, and is provided with the cylindrical body made of glass-like carbon placed inside the reactor and the high-frequency induction coil placed outside the reactor. The heating apparatus is so designed that alternating-current, high-frequency power is supplied to the high-frequency induction coil to cause the cylindrical body made of glass-like carbon with wafers, or objects to be heated, housed, for example, therein to produce heat, and the wafers are thereby heat-treated. 
     The heating apparatus of the invention is provided with the cylindrical body made of glass-like carbon as heating element. Glass-like carbon (GLC) is obtained by curing thermosetting resin as raw material and carbonizing the material in an inert atmosphere or in vacuum. Like ordinary carbon materials, glass-like carbon has such properties as lightness in weight, heat resistance, corrosion resistance, and electrical conductivity. In addition, glass-like carbon has such advantages as high purity, high strength (mirror-polishable), gas impermeability, and low particle and gas emission capability. On this account, the cylindrical body made of glass-like carbon placed in the reactor does not emit impurity particles or gas, and absorbs less gas and is chemically stable. Therefore, wafers are prevented from being contaminated even under high-temperature, corrosive reaction conditions. While glass-like carbon has an amorphous, uniform, continuous, and dense texture, graphite materials have a structure comprising aggregates of carbon powder particles. For this reason, graphite materials pose problems, such as the production of carbon powder and emission of occluded gas during reaction. 
     Since the cylindrical body made of glass-like carbon is caused to produce heat by electrical currents produced by high-frequency induction, the cylindrical body is capable of rapidly raising the temperature. Meanwhile, since the cylindrical body is made of glass-like carbon having a property of low thermal capacity, the cylindrical body is capable of rapidly lowering the temperature. Further, since the cylindrical body is made of glass-like carbon that has an amorphous, uniform, continuous, and dense texture and is excellent in thermal conductivity, the cylindrical body made of glass-like carbon is excellent in temperature uniformity. Further, the cylindrical body made of glass-like carbon can be fabricated in such size that batch processing, in which a large number of wafers are processed at a time, can be implemented. As mentioned above, the heating apparatus of the invention can be installed in low pressure CVD systems, annealing equipment, and the like for use in semiconductor integrated circuit manufacturing processes, and is capable of uniformly heating wafers and rapidly raising and lowering the temperature of wafers as well as processing wafers in high volume. 
     In the heating apparatus with a heat insulating body placed between the cylindrical body made of glass-like carbon and the high-frequency induction coil or around the high-frequency induction coil, the quantity of heat escaping from the cylindrical body made of glass-like carbon to the outside of the reactor can be reduced, and this contributes to the enhancement of heating efficiency (heat utilization). 
     As mentioned above, the heating apparatus of the invention comprises the cylindrical body made of glass-like carbon placed inside a reactor and the high-frequency induction coil that is placed outside the reactor and is for causing the cylindrical body made of glass-like carbon to produce heat and thereby heating objects to be heated in the reactor. Therefore, when the heating apparatus of the invention is installed in a low pressure CVD system or annealing equipment for use in semiconductor integrated circuit manufacturing processes for heat-treating wafers on which IC&#39;s are to be formed, the wafers are uniformly heated, the temperature of wafers is rapidly raised and lowered, and further, wafers are processed in high volume, which is not the case with systems using a conventional heating apparatus based on high-frequency induction heating. Thus, furnishing a low pressure CVD system or annealing equipment with the heating apparatus of the invention significantly shortens time required for high-volume processing of wafers and enhances the productivity, as compared with cases where a conventional electrical resistance heater is used. With the heating apparatus of the invention provided with the heat insulating body, the quantity of heat escaping from the cylindrical body made of glass-like carbon to the outside of the reactor is reduced, and this contributes to the enhancement of heating efficiency (heat utilization). 
     Other and further objects, features and advantages of the invention will appear more fully from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating an example of vertical low pressure CVD systems equipped with the heating apparatus of the invention. 
         FIG. 2  is a schematic diagram illustrating an example of vertical low pressure CVD systems equipped with a heater based on electric resistance heating as heating apparatus, for the purpose of explanation of prior arts. 
         FIG. 3  is a schematic diagram illustrating an example of single wafer processing vapor phase epitaxial growth systems equipped with infrared lamps as heating apparatus, for the purpose of explanation of prior arts. 
         FIG. 4  is a schematic diagram illustrating an example of single wafer processing vapor phase epitaxial growth systems provided with a high-frequency induction coil as heating apparatus, for the purpose of explanation of prior arts. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An explanation is given below about an embodiment of the invention, referring to the accompanying drawing.  FIG. 1  is a schematic diagram illustrating an example of vertical low pressure CVD systems equipped with the heating apparatus of the invention. 
     As shown in  FIG. 1 , this batch processing vertical low pressure CVD system is provided with a reactor  11  made of quartz having circular hollow cross-sections and dome-shaped, closed top; a cylindrical body  1  made of glass-like carbon which is placed in the reactor  11  and is an inner tube formed in cylindrical shape; a boat  13  which is placed inside the cylindrical body  1  made of glass-like carbon and is designed to be mounted with a large number of vertically arranged wafers  12 ; and a manifold  14 . The vertical low pressure CVD system is further provided with a heat insulating body  6  made of carbon fiber felt covering the reactor  11 ; an air-core-type, high-frequency induction coil  2  placed concentrically with the reactor  11  covered with the heat insulating body  6  outside the reactor; a high-frequency, alternating-current power supply  3  which supplies alternating-current, high-frequency power to the high-frequency induction coil  2  through a matching device  4 ; and a controller  5 . The controller  5  uses a thermocouple (not shown) as sensor in the case of this example to detect the temperature in the reactor  11 , and feeds the detected value back to the output of the high-frequency, alternating-current power supply  3  to control the temperature. 
     The reactor  11 , the cylindrical body  1  made of glass-like carbon, the boat  13 , and the high-frequency induction coil  2  are arranged with the axis common thereto. On the manifold  14 , the reactor  11  and the cylindrical body  1  made of glass-like carbon are placed, and further, the boat  13  is placed with a pedestal (not shown) in-between. The manifold  14  is provided with gas injectors  15   a  and  15   b  for feeding source gas or the like into the cylindrical body  1  made of glass-like carbon and with a gas exhaust port  16  for letting out reacted gas or unreacted gas from the reactor  11 . 
     The cylindrical body  1  made of glass-like carbon, the high-frequency induction coil  2 , the high-frequency, alternating-current power supply  3 , the matching device  4 , the controller  5 , and the heat insulating body  6  form the heating apparatus installed in this vertical low pressure CVD system. The cylindrical body  1  made of glass-like carbon can be fabricated using thermosetting resin, for example, phenolic resin as raw material by a publicly known method. A resin molding as a precursor of the cylindrical body  1  made of glass-like carbon is preferably formed by centrifugal molding. The resin molding is carbonized at a temperature not less than 1000° C., preferably a temperature not less than 1500° C. and thereby converted to the cylindrical body  1  made of glass-like carbon. The cylindrical body is then machined to a specified length, inside diameter, and/or outside diameter as required. 
     Then an explanation is given below about a case where, for example, a polysilicon film is formed on wafers  12  using this vertical low pressure CVD system. First, the wafers  12  are set on the boat  13 , and the boat  13  is inserted into the cylindrical body  1  made of glass-like carbon from an opening (not shown) located at the lower end of the manifold  14 , together with the pedestal (not shown) with the boat  13  placed thereon. The opening in the manifold  14  is closed with a hatch (not shown). Then an alternating, high-frequency current is passed through the high-frequency induction coil  2  to cause the cylindrical body  1  made of glass-like carbon to produce heat. Thereby the space in the cylindrical body  1  made of glass-like carbon is heated to a specified temperature, and further, silane gas is fed into the cylindrical body  1  made of glass-like carbon through the gas injector  15   a.  The silane gas is heated and pyrolytically decomposed, and a polysilicon film is consequently formed on the surfaces of the wafers  12 . Reacted gas or unreacted gas goes through the path between the cylindrical body  1  made of glass-like carbon and the reactor  11 , and is externally discharged from the gas exhaust port  16 . When the formation of the polysilicon films completes, power application to the high-frequency induction coil  2  is stopped. 
     As mentioned above, to form films on the surfaces of wafers  12  in this vertical low pressure CVD system, the heating apparatus is used for heat-treating the wafers  12 . The heating apparatus in this embodiment comprises the cylindrical body  1  made of glass-like carbon placed inside the reactor  11  and the high-frequency induction coil  2  is placed outside the reactor  11 . The heating apparatus is so designed that alternating-current, high-frequency power is supplied to the high-frequency induction coil  2  to cause the cylindrical body  1  made of glass-like carbon with wafers  12  housed therein to produce heat, and the wafers  12  are thereby heat-treated. Thus the heating apparatus in this embodiment is capable of uniformly heating wafers, rapidly raising and lowering the temperature of wafers, and further, processing wafers in high volume unlike conventional heating apparatuses based on high-frequency induction heating. When a film is formed on wafers using a vertical low pressure CVD system equipped with the heating apparatus in this embodiment, time required for processing the wafers in high volume is shortened as compared with cases where a system provided with an electrical resistance heater is used. 
     Furnishing a CVD system with the heating apparatus of the invention brings an advantage that the CVD system can be cleaned in situ. An explanation is given about this point. As a CVD (Chemical Vapor Deposition) process is repeated, unwanted films deposit on the component parts, such as an inner tube mentioned above, of the CVD system. When the thickness of the deposited films exceeds a certain limit, particles are formed due to film peeling and the yield of wafers is impaired. To cope with this, the inner tube used is replaced with a new one before this event takes place, and the removed tube is cleaned in chemical, such as hydrofluoric acid. The operation of the system need be interrupted before the replacement of the inner tubes, and after the installation of a new inner tube, idling must be performed to stabilize film formation conditions. A series of these operations reduces uptime and thus degrades productivity. To cope with this, recently, in-situ equipment cleaning (operation of cleaning equipment in situ) has been employed to reduce the downtime of equipment for replacement. In in-situ cleaning, such gas as chlorine trifluoride is fed into the CVD system and reacted with unwanted deposited films to remove the deposited film in gaseous form. However, the conventional inner tubes made of quartz or silicon carbide (SiC) is insufficient in corrosion resistance, and the application of in-situ equipment cleaning is rather limited. 
     Since the cylindrical body made of glass-like carbon is excellent in corrosion resistance, meanwhile, the cylindrical body is not affected by highly corrosive gas, such as chlorine trifluoride mentioned above. Further, since the cylindrical body made of glass-like carbon itself produces heat unlike the conventional inner tubes, noticeable gas cleaning effect is achieved. As mentioned above, furnishing a CVD system with the heating apparatus of the invention brings an advantage that in-situ equipment cleaning is performed with ease. 
     Since the heating apparatus in this embodiment is provided with the heat insulating body  6  made of carbon fiber felt covering the reactor  11 , the quantity of heat escaping from the cylindrical body  1  made of glass-like carbon to the outside of the reactor  11  can be reduced. If the heat insulating body  6  is not installed, approx. ½ of the quantity of heat produced will escape from the cylindrical body  1  made of glass-like carbon to the outside of the reactor  11 . In this embodiment, the heat insulating body  6  is placed between the reactor  11  and the high-frequency induction coil  2 , but the heat insulating body may be placed outside the high-frequency induction coil  2  so that the coil  2  and the reactor  11  are encircled with the heat insulating body. 
     Then the specific result of an experiment is introduced below as an example. The cylindrical body made of glass-like carbon was placed in the reactor made of quartz, and the high-frequency induction coil was placed outside the reactor. While nitrogen gas was passed though the reactor, the cylindrical body made of glass-like carbon was caused to produce heat. The heat insulating body was not installed. In this experiment, the dimensions of the cylindrical body made of glass-like carbon were 2 mm in thickness×60 mm in outside diameter×110 mm in length. The air-core-type, high-frequency induction coil to be water-cooled, 85 mm in inside diameter×4 turns (coil pitch: 10 mm) was fabricated using a water-cooled copper tube, 6 mm in outside diameter. A current was passed through the high-frequency induction coil under the conditions of frequency of 430 kHz, output of 1.2 kW, and current of 6 A. As a result, it only took 3 minutes to raise the temperature of the inner circumferential surface of the cylindrical body made of glass-like carbon in the center in the direction of the length from room temperature to 850° C. 
     Table 2 illustrates a concrete example of the heating apparatus of the invention installed in, for example, a vertical low pressure CVD system. Use of high-frequency induction heating as detailed in the table realizes a heating apparatus which is applicable to high-volume processing of wafers, unlike the conventional heating apparatuses based on high-frequency induction heating using a heating element made of graphite material. 
     
       
         
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Item 
                 Design Specifications 
               
               
                   
               
             
             
               
                 Cylindrical body made 
                 Dimensions: 2.5 mm (thickness) × 270 mm 
               
               
                 of glass-like carbon 
                 (outside diameter) × 1300 mm (length) 
               
               
                   
                 Specific heat: Approx. 0.16 
               
               
                 Heating conditions 
                 Temperature: To be raised from room 
               
               
                   
                 temperature to 1000° C. in 10 minutes. 
               
               
                   
                 Thereafter, this temperature is to be maintained. 
               
               
                   
                 Area to be heated: Substantially whole surface of 
               
               
                   
                 cylindrical body made of glass-like carbon in 
               
               
                   
                 above dimensions 
               
               
                 High-frequency 
                 Water-cooled copper tube used: 20 mm 
               
               
                 induction coil 
                 Dimensions: 350 mm (inside diameter) × 
               
               
                   
                 1100 mm (number of turns: 50 turns) 
               
               
                 High-frequency power 
                 Output: 50 kW 
               
               
                 supply 
                 Frequency: 30 kHz to 100 kHz 
               
               
                   
               
             
          
         
       
     
     With respect to the heating apparatus of the invention, its cylindrical body made of glass-like carbon is in cylindrical shape, and the heating apparatus is of course usefully applicable to heat treatment on cylindrical objects to be heated, such as cylindrical substrates of photoconductor drums. 
     The foregoing invention has been described in terms of preferred embodiments. However, those skilled, in the art will recognize that many variations of such embodiments exist. Such variations are intended to be within the scope of the present invention and the appended claims.