REACTION VESSEL

PROBLEM TO BE SOLVED: To manufacture a high pressure resistant, lightweight and inexpensive reaction vessel by forming the section of an inner surface crossing a shaft in the longitudinal direction into the square shape, and forming an outer wall to be thicker gradually from the ends of respective planes constituting the inner face toward the central direction of the planes. SOLUTION: A heating means 2 such as an infrared ray lamp and an induction heating source, a gas source and reaction gas or the like, an exhaust means and the like are provided on the periphery of a reaction vessel 1, and a wafer 3 is loaded in the reaction vessel 1 to form a membrane. The gas in the reaction vessel 1 is removed to reduce the atmospheric pressure in the vessel and form the vacuum state therein. The section of the inner surface of the reaction vessel 1 is oblong, and the inside of the reaction vessel 1 is of the rectangular parallelopiped shape. An outer wall of the reaction vessel 1 is formed thicker gradually from the ends of respective planes forming the rectangular parallelopiped toward the central sections of respective planes. The pressure resistance of the reaction vessel 1 can be uniformized by forming the central sections of respective planes of low pressure resistance into the thick wall as above-mentioned.