Heat treatment system and method

When an oxidation process for semiconductor wafers is carried out by a batch type furnace, the uniformity of the thickness of a film is intended to be improved so as to be capable of carrying out a low temperature process. In a system for feeding a mixed gas of hydrogen gas and water vapor into a reaction vessel to carry out a so-called wet oxidation, a ventilation resistance material is provided in an outside passage of a double-pipe passage for heating gas in an external combustion system, and a mixed gas of hydrogen gas and hydrogen chloride gas is passed through the ventilation resistance material to be heated to a process temperature or higher by means of the heater of the combustion system to previously produce a very small amount of water vapor to carry out a dry oxidation. When dinitrogen oxide gas is used for producing a nitrogen containing silicon oxide film, dinitrogen oxide gas is passed through the outside passage to be previously activated. In addition, a process gas is preheated by a heating part, which is provided outside of a process chamber, to lower a process temperature while ensuring the uniformity of a process. N2O gas and SiH2Cl2 gas are fed into a reaction tube 102, which has been pressure-reduced to a predetermined degree of vacuum, to deposit a thin film on the surface of a wafer at a predetermined process temperature. At this time, a heating chamber 151 provided in a N2O gas feed passage is heated by a heater element 153, and N2O gas is passed through the heating chamber 151 to be preheated to be fed into the reaction tube 102. In addition, an orifice 106 is formed in the N2O gas feed passage between the heating chamber 151 and the reaction tube 102. Thus, even in a low pressure process, the pressure in the heating chamber 151 is higher than the pressure in the reaction tube 102 due to pressure loss at the orifice 106, so that it is possible to efficiently preheat the process gas in the heating chamber 151 to lower the process temperature.