Thermal processing method and apparatus therefor

Abstract

An Si.sub.3 N.sub.4 layer is formed on a surface of a wafer, which is an object to be processed, at a high temperature of, for example, 780.degree. C., using a vertical thermal processing apparatus having a reaction tube of a double-wall structure comprising an inner tube and an outer tube in which a predetermined reduced-pressure status is maintained within the reaction tube while a reaction gas comprising, for example, SiH.sub.2 Cl.sub.2 and NH.sub.3 is made to flow from an inner side to an outer side of the inner tube by the action of a first gas supply pipe and first exhaust pipe provided in the thermal processing apparatus. Next, the temperature in the interior of the reaction tube is raised to, for example, 1000.degree. C., a reaction gas comprising, for example, H.sub.2 O vapor and HCl is made to flow from the outer side to the inner side of the inner tube by the action of a second gas supply pipe and second exhaust pipe, and an SiO.sub.2 layer is formed by the oxidation of the surface of the Si.sub.3 N.sub.4 layer formed on the surface of the wafer, under normal-pressure conditions. The use of a combined chamber enables the implementation of film formation and either oxidation or diffusion processing without having to remove the object to be processed from the reaction tube, and thus prevents the intrusion of a natural oxide layer or the incorporation of particles into a thin film structure of, for example, SiO.sub.2 and Si.sub.3 N.sub.4 layers used as a multi-layer insulating film for devices such as DRAMs.