Method of producing semiconductor having two-layer polycrystalline silicon structure

Abstract

In a semiconductor manufacturing process for a semiconductor device having two layers of polycrystalline silicon and a Double Diffused Drain (DDD) type transistor, the number of heat treatment processes is minimized to avoid degrading the quality of a gate oxide film, such as a tunnel oxide film in an EEPROM. After forming a gate electrode of a DDD transistor and a lower electrode of a capacitor, for example, of a first polycrystalline silicon film, a DDD impurity diffusion region is formed by a heat treatment process combined with a thermal oxide growth process for producing an oxide dielectric for the capacitor and a gate oxide of a peripheral transistor. A second polycrystalline silicon film is then formed as a gate electrode of the peripheral transistor and an upper electrode of the capacitor, thereby reducing the number of process steps and improving the quality of the gate oxide film and a tunnel oxide film by reducing the length of the heat treatment processes.