1.  Field of the Invention
The present invention relates to a thermal processing apparatus for performing a processing accompanied with heating on a substrate and a method therefor. 
2.  Description of the Background Art
Conventionally, in various stages of a process for manufacturing a semiconductor substrate or the like (hereinafter, referred to simply as “a substrate”), a thermal processing is performed on the substrate, and a rapid thermal process (hereinafter, referred to as “RTP”) is used as a method of thermal processing.  In the RTP, by heating the substrate in a chamber with halogen lamps or the like to raise the temperature thereof up to a predetermined temperature in a short time, it is possible to perform processings which have been hard to execute by a conventional long thermal processing with an electric furnace, such as thinning of an insulating film such as an oxide film, suppressing of rediffusion of impurities (or dopants) implanted by ion implantation in an activation process, or the like.  In recent proposed is a technique for heating a substrate in a shorter time with flash lamps as a heating source for a substrate. 
A thermal processing apparatus for performing a thermal processing, not only the RTP, on a substrate has necessity to keep a thermal processing chamber clean so as to avoid deterioration in quality caused by deposition of unnecessary particles on a surface of the substrate, and various techniques to prevent contamination in the thermal processing chamber with the unnecessary particles or the like.  For example, Japanese Patent Application Laid Open Gazette No.  7-78863 discloses a technique to prevent evaporation of unnecessary substances on a back surface of a susceptor for supporting the substrate and avoid emergence of particles due to removal of the unnecessary substances by providing an edge portion of the susceptor and an edge portion of a preheating ring in a complementary step-like form. 
Further, Japanese Patent Application Laid Open Gazette No.  4-334018 discloses a technique to perform a thermal processing with excellent uniformity by accommodating a substrate in a holder which is made of the same material as the substrate is made of and has almost the same infrared absorptivity, thermal conductivity and the like as the substrate has. 
The contamination in a thermal processing chamber is caused by not only the above-discussed particles which emerge when evaporated unnecessary substances are removed but also pieces of a substrate broken in a processing.  In a thermal processing using flash lamps, particularly, a substrate is sometimes broken in pieces by quick thermal expansion of its surface since the surface temperature of the substrate rises in an extremely short time. 
In a conventional apparatus, since the pieces of the broken substrate are scattered widely in the thermal processing chamber and penetrate into gaps of a complicated structure, in order to remove the contaminants and recover the function of the apparatus, it is necessary to open (sometimes disassemble) the thermal processing chamber for cleaning of the inside thereof and this needs a lot of time and labor.  Enlarging the susceptor which holds the substrate is a possible method to suppress the scatter of the substrate pieces near the susceptor, but this method is not a realistic one since it leads to upsizing of a whole thermal processing apparatus.