Patent Publication Number: US-2009239362-A1

Title: Apparatus for manufacturing semiconductor device and method for manufacturing semiconductor device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-075956 filed on Mar. 24, 2008, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for manufacturing a semiconductor device and a method for manufacturing a semiconductor device, which, for example, supplies process gas onto a semiconductor wafer while heating the wafer and forms a film on the wafer while performing high-speed rotation. 
     2. Description of the Related Art 
     In recent years, with requirements for further price reduction and higher performance of semiconductor devices, there have been requested higher productivity in a film formation process as well as improvement in uniformity of film thickness and dust reduction. 
     As a method used to satisfy such requests, Japanese Patent Application Laid-Open No. 11-67675 discloses a method for film formation by heating while performing high-speed rotation, using a single-wafer type epitaxial film formation apparatus. In addition, there has been an expectation for higher productivity by use of a large-diameter wafer of, for example, φ300 mm and highly efficient use of inexpensive Cl source gas such as trichlorosilane (hereinafter referred to as “TCS”) and dichlorosilane. 
     However, in forming a thick epitaxial film having a film thickness in excess of 150 μm to be used for, for example, an IGBT (insulated gate bipolar transistor), there is a problem that high productivity is difficult to ensure. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an apparatus for manufacturing a semiconductor device and a method for manufacturing a semiconductor device, with higher film formation speed and utilization efficiency of source gas and thus capable of attaining high productivity. 
     According to an aspect of the present invention, there is provided an apparatus for manufacturing a semiconductor device including: a reaction chamber in which a wafer is introduced and is subjected to film formation; a rotor provided with a holding member holding the introduced wafer at an upper portion thereof and a heater heating the wafer therein; a rotation drive mechanism connected with the rotor and rotating the wafer; a gas supply mechanism supplying a predetermined flow rate of process gas to the reaction chamber; a gas exhaust mechanism exhausting gas from the reaction chamber and controlling the pressure in the reaction chamber to be a predetermined pressure; and a rectifying plate rectifying the process gas and supplying the gas onto the wafer hold on the holding member. The apparatus further includes: an annular rectifying fin mounted on a lower portion of the rectifying plate, having a larger lower end inside diameter than an upper end inside diameter thereof and downward rectifying gas exhausted in an outer circumferential direction from above the wafer; and a distance control mechanism for controlling a vertical distance between the rectifying plate and the wafer and a vertical distance between the rectifying fin and the rotor top face to be predetermined distances, respectively. 
     According to another aspect of the present invention, there is provided a method for manufacturing a semiconductor device, including: holding a wafer in a reaction chamber; controlling the pressure in the reaction chamber to be a predetermined pressure; rectifying process gas and supplying the process gas onto the wafer from above while heating and rotating the wafer; and discharging surplus process gas and exhaust gas above the wafer containing reaction by-product generated by the process gas in an outer circumferential direction from above the wafer by the rotation of the wafer. The method further includes: controlling at least a height of a space above the periphery of the wafer so that a backflow rate, flowing onto the wafer, of the exhaust gas discharged in the outer circumferential direction is a predetermined value; and rectifying the exhaust gas at a predetermined gradient above the periphery of the wafer and discharging the exhaust gas downward. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a sectional view of an apparatus for manufacturing a semiconductor device according to an aspect of the present invention; 
         FIG. 2A  illustrates a conventional gas flow; 
         FIG. 2B  is illustrates a gas flow according to an aspect of the present invention; 
         FIGS. 3 to 5  are sectional views of an apparatus for manufacturing a semiconductor device according to an aspect of the present invention, respectively; 
         FIG. 6  is a structural sectional view of a rectifying fin according to an aspect of the present invention; and 
         FIG. 7  is a sectional view of a super junction structure according to an aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments according to the present invention will be described with reference to the drawings. 
     First Embodiment 
       FIG. 1  is a sectional view of an apparatus for manufacturing a semiconductor device according to the present embodiment. In a reaction chamber  11  which a wafer w is loaded and subjected to film formation, a rotor  12  is installed. At the upper portion of the rotor  12 , a holding member  13  for holding a loaded wafer is loaded, below which a ring  14  for supporting the holding member  13  is provided. Inside the ring  14 , there are disposed an in-heater  15   a  and an out-heater  15   b  for heating a wafer w, and the like. 
     Around an outer periphery of the rotor  12 , there is disposed a reflection board  16  for increasing thermal efficiency by reflecting radiated heat. The rotor  12  is connected to a rotation drive mechanism  17  for rotating the wafer w through an opening at a lower portion of the reaction chamber  11 . 
     At the top of the reaction chamber  11 , there is disposed a gas supply port  18  which configures a gas supply mechanism, connected with a mechanism for controlling the types of gas and the flow rate thereof (not illustrated), supplies a predetermined flow of process gas. At the bottom of the reaction chamber  11 , there is disposed a gas exhaust port  19  which configures a gas supply mechanism connected with a pressure gauge (not illustrated), a pump (not illustrated) and the like, exhausts gas from the reaction chamber  11  and controls a pressure in the reaction chamber  11  to be a predetermined pressure. 
     Above the rotor  12 , there is provided a rectifying plate  20  which rectifies supplied process gas and supplies the rectified gas onto the wafer. The rectifying plate  20  is integrated with a liner  21  covering a wall surface of the reaction chamber  11 . On the underside of the rectifying plate  20 , there is fixed an annular rectifying fin  22  which has a larger lower end inside diameter than an upper end inside diameter thereof, is made of, for example, quartz and downward rectifies gas exhausted in an outer circumferential direction from above the wafer w. 
     The liner  21  integrated with the rectifying plate  20  and the rectifying fin  22  is connected with a lifting mechanism  23  mounted outside the reaction chamber  11  and moves the liner  21  up and down to control a vertical distance between the rectifying plate  20  and the wafer w which is a height of the space above the wafer and a vertical distance between the rectifying fin  22  and a top face of the rotor  12  which is a height of the space above a periphery of the wafer to be predetermined distances, respectively. 
     Using such an apparatus for manufacturing a semiconductor device, for example, a Si epitaxial film is formed on a Si wafer. A wafer w of, for example, φ200 mm is introduced into the reaction chamber  11  and placed on the holding member  13 . The downward movement of the liner  21  brings the rectifying plate  20  and the wafer w, and the rectifying fin  22  and the top face of the rotor  12  closer to each other by the same variation, respectively, thus the distances are controlled to be the respective predetermined distances. The in-heater  15   a  and the out-heater  15   b  control a temperature of the wafer w to be 1100° C. The rotation drive mechanism  17  rotates the wafer w, for example, at a speed of 900 rpm. 
     The process gas prepared to have a TCS concentration of, for example, 2.5% is introduced at, for example, 50 SLM from the gas supply port  18 . The process gas is supplied onto the wafer w in a rectifyd state through the rectifying plate  20  to grow a Si epitaxial film on the wafer w. 
       FIGS. 2A  schematically illustrates a gas flow, respectively. Exhaust gas, such as surplus process gas containing TCS and dilution gas supplied onto the wafer W, and HCl which is a reaction by-product, is exhausted in the outer circumferential direction by rotation of the wafer w, as indicated by an arrow. However, at this time, a part of gas is flowed back onto the wafer w by convection or the like. 
     In epitaxial growth using Cl source gas, if, for example, TCS is used, the following expression (1) is obtained when TCS and H 2  are supplied: 
       SiHCl 3 +H 2 →Si+3HCl   (1). 
     As the reaction of the above (1) proceeds to the right, a Si epitaxial film is formed, but HCl is also produced together with Si. The reaction shown by the above (1) is an equilibrium reaction formed of a plurality of reactions and therefore HCl to be exhausted flows back and, if gas is not displaced, a HCl mole ratio on the wafer w becomes higher and equilibrium shifts to the left. It is regarded that this restrains the advance of a Si generation reaction, thus lowering an epitaxial growth rate. 
     Hence, it is expected that control of a backflow of gas restrain the epitaxial growth rate from lowering. As illustrated in  FIG. 23  by attaching the rectifying fin  22  to rectify and to exhaust the gas downward above the periphery of the wafer, the backflow of the gas can be prevented to some degree. A viscous flow is generated when a mean free path λ of molecules in the process gas inversely proportional to a pressure is sufficiently smaller than a size L of the reaction chamber  11 . When the inside of the reaction furnace  11  is controlled to be above, for example, approximately 1333 Pa (10 Torr) or more, a viscous flow is generated inside the reaction furnace  11 . 
     When the viscous flow is generated, the viscous resistance increases as a clearance relative to the holding member  13  becomes narrower due to the rectifying fin  22 . An increase in the viscous resistance restrains a flow in the outer circumferential direction. Since a difference between a flow rate in the outer circumferential direction and a backflow rate is constant and almost the same as a supply rate of process gas, the backflow rate can be reduced by restraining the flow in the outer circumferential direction. 
     In a case where such a rectifying fin  22  is provided, the backflow rate depends upon a vertical distance between the rectifying plate  20  and the wafer w and a vertical distance between the rectifying fin  22  and the top face of the rotor  12 . By reducing the vertical distance, not the horizontal distance, viscous resistance increases, and thus generation of a backflow can be restrained. 
     For example, reduction in the vertical distance between the rectifying plate  20  and the wafer w to approximately 40% allows the backflow rate to be reduced to approximately 40%. Reduction in the vertical distance between the rectifying fin  22  and the top face of the rotor  12  to approximately 1/14 allows the backflow rate to be restrained to ⅓ or less. 
     To load and place the wafer w on the holding member  13 , a lower end of the rectifying fin  22  is required to be mounted above the top face of the wafer w to some degree. If the rectifying fin  22  is fixed, there is a structural limit in reducing the vertical distance. Therefore, by lowering the rectifying plate  20  and the rectifying fin  22  after the wafer w is placed on the holding member  13 , the vertical distance can be reduced. 
     By mounting the rectifying fin  22  with a reduced vertical distance, a backflow can be restrained to approximately 40% as compared to a case where the rectifying fin  22  is not mounted, which allows an epitaxial growth rate to increase by approximately 4%. 
     Deposits accumulate on the rectifying fin  22  due to the process gas flow. Restraining the backflow allows dust caused by deposits generated at the rectifying fin  22  to be restrained from adhering to the wafer w. Further, restraining an influence of the backflow upon a flow of process gas onto the wafer w improves uniformity in a film thickness within a wafer surface by approximately 2%. 
     On the other hand, the backflow rate of gas depends upon a rotational speed and has a tendency of increasing with the rotational speed increase. This is caused by the fact that high-speed rotation generates a centrifugal force and hence a flow rate in the outer circumferential direction increases. When the rotational speed is increased by a process, the backflow rate increases, thus the film forming rate and the like fluctuate, causing the problem that a process window (margin) is difficult to ensure. 
     In such a case, in increasing a rotational speed with a constant gas supply volume according to process recipe, the rectifying plate  20  and the rectifying fin  22  are lowered. On the other hand, in decreasing the rotational speed, the rectifying plate  20  and the rectifying fin  22  are raised. By controlling a vertical distance according to a rotational speed in this way, a backflow rate can be kept constant and a process window can be ensured. 
     In the present embodiment, the reflection board  16  for increasing thermal efficiency by reflecting radiated heat is disposed around the outer periphery of the rotor  12 . The backflow rate also depends upon a distance between the reflection board  16  and the rectifying fin  22 . Therefore, to restrain the backflow rate, it is also effective to reduce the distance between the reflection board  16  and the rectifying fin  22 . When the upper end of the reflection board  16  projects higher than the top face of the rotor  12  such as the holding member  13 , convection occurs between the reflection board  16  and the top face of the rotor  12 . Therefore, preferably, the upper end of the reflection board  16  is attached so as not to project higher than the top face of the rotor  12 . 
     Second Embodiment 
       FIG. 3  illustrates a sectional view of an apparatus for manufacturing a semiconductor device according to the present embodiment. The structure of the reaction chamber  11  is almost the same as that of the first embodiment, but is different in that a lifting mechanism  33  is connected with a rotor  32 , instead of a liner  21 . 
     By using such an apparatus for manufacturing a semiconductor device, for example, a Si epitaxial film can be formed on a Si wafer in the same way as in the first embodiment and the same effects as in the first embodiment can be achieved. 
     Preferably, the in-heater  15   a,  the out-heater  15   b  and the like disposed in the rotor  32  are also moved up and down together with the rotor  32  in order to restrain variation in heating conditions. The reflection board  16  is also preferably moved up and down together with the rotor  32  in terms of the restraint of variation in heat reflection efficiency and of the backflow. 
     Third Embodiment 
       FIG. 4  illustrates a sectional view of an apparatus for manufacturing a semiconductor device according to the present embodiment. The structure of the reaction chamber  11  is almost the same as that of the first embodiment, but is different in that a lifting mechanism  43  is not connected with a liner  41  but is separated from the liner  41  and connected with a rectifying plate  40  integrated with a rectifying fin  42 . The lifting mechanism  43  is connected with the rectifying plate  40  through a plurality of (e.g. three) shafts  43   a  connected via bellows piping or the like and is structured to move up and down. 
     By using such an apparatus for manufacturing a semiconductor device, for example, a Si epitaxial film can be formed on a Si wafer in the same way as in the first embodiment and the same effects as in the first embodiment can be achieved. 
     Fourth Embodiment 
       FIG. 5  illustrates a sectional view of an apparatus for manufacturing a semiconductor device according to the present embodiment. The structure of the reaction chamber  11  is almost the same as that of the first embodiment, but is different in that a lifting mechanism  53  is not connected with a liner  51  but is connected with a rectifying fin  52  separated from a rectifying plate  50 . Therefore, the rectifying plate  50  cannot be moved up and down, but a distance between the rectifying fin  52  and a top face of the rotor  12 , which most contributes to restraint of a backflow rate, can be controlled, thus achieving advantageous effects with a simple structure. The lifting mechanism  53  is connected with the rectifying plate  50  through a plurality of (e.g. three) shafts  53   a  connected via bellows piping or the like and is structured to move up and down. 
     By using such an apparatus for manufacturing a semiconductor device, for example, a Si epitaxial film can be formed on a Si wafer in the same way as in the first embodiment and the same effects as in the first embodiment can be achieved. 
     In these embodiments, the rectifying fin is of an annular body having an approximately rectangular cross section, but a gap between the fin and the liner may be filled, as illustrated in  FIG. 6 . Further, the rectifying fin may have a bulk shape integrated with a filler. In the case of a structure without a liner, a gap between the fin and the reaction chamber is filled. By applying a filler having high thermal conductivity in this way, the rectifying fin is cooled down, for example, to approximately 600° C., thus making it difficult to form deposits on a surface of the rectifying fin. 
     In addition, by using SiC or a material having carbon covered with SiC for the rectifying fin, the rectifying fin can be provided with a function as a reflection plate for reflecting heat radiation from a heater, thus increasing heating efficiency by the heater. Further, by induction heating thereof, the rectifying fin can be provided with a function as a heater, thus effectively restraining heat radiation of a wafer peripheral edge. 
     According to the embodiments described above, film formation rate and utilization efficiency of source gas are increased and hence a film such as an epitaxial film can be formed on a semiconductor wafer w with high productivity. In addition, higher yield of semiconductor devices formed through an element formation process and an element separation process and stability of element characteristics as well as higher wafer yield can be achieved. 
     In particular, excellent element characteristics can be obtained by application of the embodiments to an epitaxial formation process for a power semiconductor device such as a power MOSFET and an IGBT, which requires film thickness growth of 100 μm or more in a n-type base region, p-type base region, an insulation separation region or the like. 
     Further, in these power semiconductor devices, the embodiments can be favorably used, particularly, in forming a super junction structure as illustrated in  FIG. 7 . In forming such a super junction structure, after a p-type epitaxial film is formed, a fine groove is formed using a photolithography method and an n-type epitaxial film is formed in the groove. Since an epitaxial film can be smoothly formed in an ideal rectifying state even in the fine groove by restraining the backflow, an excellent super junction structure can be formed. 
     While the epitaxial film is formed on an Si substrate in this embodiment, it can be applied to forming of a polysilicon layer and it can be applied also to other compound semiconductors, for example, a GaAs layer, a GaAlAs layer, and an InGaAs layer. It can also be applied to forming of a SiO 2  film and a Si 3 N; film, and in the case of SiO 2  film, monosilane (SiH 4 ) and gases of N 2 , O 2 , and Ar are fed, and in the case of Si 3 N 4  film, monosilane (SiH 4 ) and gases of NH 3 , N 2 , O 2 , and Ar are fed. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.