Abstract:
A method for manufacturing a susceptor includes: forming a concave pattern in a surface of a substrate to be processed; applying a SiC paste containing a SiC powder and a sintering agent to the surface of the substrate to be processed to fill the concave pattern to form a SiC coating layer; laminating a SiC substrate on the SiC coating layer; and firing the SiC coating layer to form a SiC layer having at least one convex section on the surface of the SiC substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-333544 filed on Dec. 26, 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 a method for manufacturing a susceptor that holds a semiconductor wafer, for example, used in performing film formation on the semiconductor wafer. 
     2. Description of the Related Art 
     Generally, a CVD (Chemical Vapor Deposition) apparatus is used in forming an epitaxial film or the like on a wafer in a semiconductor manufacturing process. In such a CVD apparatus, a wafer is placed on a susceptor made of SiC or the like and a uniform process gas is supplied to the wafer from above while the wafer is being heated and rotated to form an epitaxial film on the wafer, as described, for example, in Japanese Patent Application Laid-Open No. 11-67675. 
     In recent years, with developments for higher speed and higher withstand voltage in a power semiconductor device such as a power MOSFET or IGBT (insulated gate bipolar transistor), an epitaxial film formed on a wafer is required to grow as thick as tens to hundreds of micrometers. 
     However, when a wafer is heated and a process gas is supplied thereto from above as described above, a coating is also formed on members other than on the wafer, which causes the wafer to be stuck on a susceptor. Then, the wafer fractures and particles are produced therefrom, resulting in low yield and reliability. 
     Accordingly, for example, embossing a surface of the susceptor may be proposed to prevent a wafer from being stuck on the susceptor. However, it is difficult to prevent the wafer from being stuck on the susceptor by only the embossing work because rough surface portions will be completely buried due to thick film growth as thick as 100 μm. Accordingly, it will be required to form a highly rough surface; however, there is a problem that it is difficult to finely machine a surface of a rigid material such as SiC and further control the shape thereof to be spherical. 
     SUMMARY 
     A method for manufacturing a susceptor according to an aspect of the present invention includes: forming a concave pattern in a surface of a substrate to be processed; applying a SiC paste containing a SiC powder and a sintering agent onto the surface of the substrate to be processed to fill the concave pattern to form a SiC coating layer; laminating a SiC substrate on the SiC coating layer; and firing the SiC coating layer to form a SiC layer having convex sections on the surface of the SiC substrate. 
     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 drawing, 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 a susceptor according to an aspect of the present invention; 
         FIG. 2  is a top view of the susceptor according to an aspect of the present invention; 
         FIG. 3  is an enlarged view of a cross-sectional portion of the susceptor according to an aspect of the present invention; 
         FIG. 4  is a flowchart showing a manufacturing process of the susceptor according to an aspect of the present invention; 
         FIGS. 5 to 9  are illustrative views of a manufacturing process of the susceptor according to an aspect of the present invention; 
         FIG. 10  is an illustrative view of an epitaxial growth apparatus using the susceptor formed according to an aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     An embodiment according to the present invention will be described below with reference to the accompanying drawings. 
       FIG. 1  illustrates a sectional view of a susceptor formed according to the present embodiment and  FIG. 2  illustrates a top view thereof. As illustrated in the figures, convex sections  12  are formed on an entire top face (a wafer placement face) of a susceptor  11  made of SiC. As illustrated in an enlarged view of a cross-sectional portion of the susceptor of  FIG. 3 , a cross-sectional shape of each of the convex sections is semi-circular and a radius r thereof is, for example, 0.5 mm and an interval d between the convex sections is, for example, 1 mm. A SiC coating (not shown) is formed over the entire top face of the susceptor  11  including the convex sections. 
     Such a susceptor is formed as shown in a flowchart of  FIG. 4 . As illustrated in  FIG. 5 , a plurality of concave sections  15  having a predetermined diameter and depth are formed at predetermined intervals, for example, by mechanical grinding, in a surface of a carbon substrate  14  (Step  1 ). As illustrated in  FIG. 6 , a SiO 2  film  16  is formed in a thickness of about 0.5 μm over the entire surface of the substrate using, for example, a CVD method (Step  2 ). 
     A SiC paste in which a SiC powder, a carbon black and a boron carbide powder as a sintering agent and a binder such as acrylic-based resin or cellulose-based resin are dispersed in, for example, an organic amine-based solvent is prepared. Then, as illustrated in  FIG. 7 , the SiC paste is applied onto the carbon substrate  14  formed with the SiO 2  film  16  in a manner that fill the concave sections are filled (Step  3 ), thereby forming a SiC coating layer  17 . 
     After the SiC coating layer  17  is dried as needed, a SiC substrate  18  is laminated on the SiC coating layer  17  as illustrated in  FIG. 8  (Step  4 ). Subsequently, temporary firing is performed, for example, at 1,400 to 1,500° C. in an inert gas atmosphere or a vacuum to carbonize the binder in the SiC coating layer  17 , thereby forming a SiC layer  19  (Step  5 ). 
     A laminated body of the carbon substrate  14 , the SiO 2  film  15 , the SiC layer  19  and the SiC substrate  18  formed in this way is put into HF solution and the SiO 2  film  15  is selectively etched, thereby separating and removing the carbon substrate  14  from the SiC layer  19  and the SiC substrate  18  as illustrated in  FIG. 9  (Step  6 ). The SiC layer  19  and the SiC substrate  18  from which the carbon substrate  14  has been removed are fired in an inert gas atmosphere or a vacuum, for example, at 2,000° C. to sinter the SiC layer, thus forming a sintered SiC layer  20  (Step  7 ). 
     A SiC coating is applied on surfaces of the sintered SiC layer  20  and the SiC substrate  18  from which the carbon substrate has been removed by forming a dense CVD-SiC film, for example, using a CVD method (Step  8 ), thus obtaining the susceptor  11  as illustrated in  FIG. 1 . 
     The susceptor formed in this way is used for the epitaxial growth apparatus as illustrated in  FIG. 10 . A reaction chamber  21 , in which a wafer w of, for example, φ200 mm in diameter undergoes film formation, is provided with a gas supply port connected with a gas supply mechanism (not shown) for supplying a process gas including a source gas such as TCS and dichlorosilane onto the wafer w from above the reaction chamber  21 . At a bottom portion of the reaction chamber  21 , there are provided gas discharge ports  23  connected with a gas discharge mechanism (not shown) for discharging gas and controlling a pressure in the reaction chamber  21  to be constant (a normal pressure), which are provided, for example, at two positions. 
     At an upper portion of the reaction chamber  21 , there are disposed straightening vanes  24  for supplying a process gas supplied through the gas supply opening  22  onto the wafer w in a straightened state. 
     At the lower portion of the reaction chamber  21 , there are installed a motor (not shown), a rotating shaft (not shown), a rotation drive mechanism  25  for rotating a wafer w and including a ring  25   a , and the susceptor  11  connected with the rotation drive mechanism  25  and formed as described above. 
     Under the susceptor  11 , an in-heater  26   a  for heating a wafer w made of, for example, SiC is disposed. Between the susceptor  11  and the in-heater  26   a , an out-heater  26   b  for heating a peripheral edge portion of the wafer w made of, for example, SiC is installed. Under the in-heater  26   a , a disc-shaped reflector  27  for efficiently heating the wafer w is installed. There is further disposed a lifting pin  28 , penetrating through the in-heater  26   a  and the reflector  27 , for moving up and down a wafer w. 
     Using such a manufacturing apparatus for a semiconductor device, for example, a Si epitaxial film is formed on a wafer w. The wafer w is placed on the susceptor  11  formed with convex sections. At this time, the wafer w is held on respective tips of the convex sections. 
     Based on the temperature of the wafer w measured by a temperature measurement mechanism (not shown), a temperature control mechanism (not shown) appropriately controls temperatures of the in-heater  26   a  and the out-heater  26   b  within a range of, for example, 1,400 to 1,500° C. so that the temperature of the wafer w becomes, for example, 1,100° C. Further, the rotating mechanism  25  rotates the wafer w, for example, at a speed of 900 rpm. 
     Through the gas supply port  22 , a process gas containing, for example, 20 to 100 SLM of H 2  as a carrier gas, 50 sccm to 2 SLM of SiHCl 3  as a film-forming gas, trace amount of B 2 H 6  or PH 3  as a dopant gas, is introduced onto the straightening vanes  24  and supplied onto the wafer w in a straightened state. At this time, a pressure in a reaction chamber  21  is controlled to be, for example, 1,333 Pa (10 Torr) to normal pressure, by controlling valves of the gas supply ports  22  and the gas discharge ports  23 . In this way, various conditions are controlled and a Si epitaxial film of, for example, 100 μm in thickness is formed on the wafer w. 
     In this process, a Si film is also deposited on a peripheral edge portion of the wafer w and other portions of the susceptor  11 ; however, the wafer w is held on the tips of the convex sections, where a contact area is small and thus stress is suppressed. Further, even when thick-film growth of tens to hundreds of micrometers is performed, portions between the convex sections are not completely filled with the deposited Si film, thus preventing the wafer w from being stuck on the susceptor. 
     Hence, yield and reliability can be improved in forming semiconductor devices through an element formation process and an element separation process. The present embodiment is suitable for an epitaxial formation process for power semiconductor devices such as power MOSFETs or IGBTs (insulated gate bipolar transistor), in particular for those that require thick-film growth of tens to hundreds of micrometers in an N-type base region, a P-type base region or an insulation separation region. 
     In the present embodiment, a carbon substrate is used as a substrate to be processed to have concave sections; however, any substrate that is easy to process can be used other than a carbon substrate, such as a Si substrate. In addition, a SiO 2  film is formed on a surface of a substrate to be processed by the CVD method; however, the formation method is not particularly limited and thermal oxidation may be performed when a Si substrate is used. The formation of a SiO 2  film is not always required and any film that allows a sufficient selective ratio of a substrate to be processed to the SiC layer. In etching under such conditions that a sufficient selective ratio (a substrate to be processed&gt;a SiC layer) can be obtained between the substrate to be processed and the SiC layer, it is not necessary to interpose a film such as a SiO 2  film. 
     In the present embodiment, a SiC paste formed by dispersing a SiC powder, a carbon black and a boron carbide powder as a sintering agent, and a binder such as acrylic-based resin and cellulose-based resin in an organic amine-based solvent is used; however, the present invention is not limited thereto and a SiC paste (slurry) of a known composition may be used. 
     In the present embodiment, a carbon substrate was removed by etching after a SiC substrate had been laminated on a SiC paste and subjected to temporary firing; however, the present embodiment is not limited to this process. For example, the carbon substrate may be removed after a SiC substrate is laminated on a SiC paste and subjected to firing (sintering). 
     The shape of each of the convex sections on the susceptor formed according to the present embodiment is not limited to a semicircle in cross section, that is, a hemisphere. The convex sections may be of any shape that can hold a wafer placed thereon in a point-contact manner, such as a semiellipse-sphere, a shape having a hemisphere on a cylindrical column, a cone such as a circular cone. 
     In the present embodiment, a height of each of the convex sections is 0.5 mm; however, preferably, the height is larger than the film thickness of an epitaxial film to be formed. For example, in forming a film in a thickness of substantially 100 μm, a suitable height is 150 to 500 μm. In addition, the convex sections are formed over the whole susceptor surface at uniform intervals. 
     In order to suppress variations in temperature distribution caused by heat absorption or heat radiation in/from a holding portion, preferably, the convex sections are formed all over the whole susceptor surface as appropriate. The intervals may be uniform or may change depending upon locations. For example, when a temperature of a wafer outer peripheral portion is high, the convex sections may be arranged so that distribution thereof is sparse on the outer peripheral portion. 
     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 4  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.