1.  Field of the Invention
The present invention relates to a heat treatment apparatus capable of reducing generation (deposition) of a sublimate during a heat treatment process. 
2.  Description of the Related Art
The manufacturing process of semiconductor devices or liquid crystal panels has various kinds of processes such as a cleaning process, a coating process, an exposure process, a drying process and the like with respect to a substrate to be processed.  In intermediate steps of the manufacturing process there are provided a pre-baking process and a post-baking process, and the substrate is disposed and heat-treated within a heat treatment apparatus so as to be transferred to the next process. 
Herein, there is already known such a structure as shown in patent reference 1 as the heat treatment apparatus which dries a liquid applied to the surface of the substrate.  In such a structure, although there have been studied devices for ensuring a uniform temperature distribution of a heating means arranged on a mounting table and for making a solvent-rich atmosphere by lessening a space over the substrate with a top plate provided above the mounting table, it is impossible to prevent the sublimate from being generated, for example. 
Further, patent reference 2 discloses that an N2 gas which is heated up to substantially the same temperature as a heating temperature of a heating means is supplied into and at the same time exhausted out of a heat treatment apparatus so that the gas within the heat treatment apparatus is changed in a brief period of time.  With this structure, however, it is difficult to remove the sublimate generated.     Patent reference 1: Japanese Patent No.  3,324,902.     Patent reference 2: Japanese Patent Application publication No.  H10-12522. 
It became clear from the results of various experiments and analyses with respect to the heat treatment made by the inventor that, in the case of lessening the space over the substrate as mentioned above, not only does the solvent evaporate from an applied membrane of the solvent formed on the surface of the substrate during the treatment, but sublimate substances such as low molecular resins, dyestuffs, etc.  contained in the applied liquid also evaporate.  Because the sublimate substances (namely, sublimates) are deposited on a low temperature region within a processing chamber, they are prone to be deposited especially on the upper region (the surface of an upper wall) within the processing chamber (housing).  When being deposited on the upper region like this, there is a possibility of being accumulated on the substrate. 
As mentioned hereinabove, when ensuring the uniform temperature distribution on the substrate within the processing chamber, it is impossible to avoid the problem of the sublimate. 
Further, there is another problem that partial unevenness in drying of the applied liquid, etc.  is developed because the entire substrate is not able to be heated evenly when the substrate becomes large in size.  Furthermore, in addition to the above, as the heating means itself for the substrate becomes large in size, it is expected that the transport of the apparatus itself will become difficult.