Method of forming extrinsic base by diffusion from polysilicon/silicide source and emitter by lithography

A method of producing a semiconductor device comprising the following steps:

• (a') forming a silicon dioxide film on a surface of a semiconductor substrate, and then doping an impurity having a first conductivity type into a desired portion of the surface region of said semiconductor substrate to form a base;
• (b') forming a silicon nitride film on the entire surface, and laminating thereon a polycrystalline silicon film into which an impurity of said first conductivity type is doped and which has a hole on said base;
• (c') oxidizing the surface of said polycrystalline silicon film;
• (d') forming a polycrystalline silicon film, into which no impurity is substantially doped, on the entire surface, and then removing an undesired portion of said polycrystalline silicon film into which no impurity is substantially doped;
• (e') removing said silicon dioxide film formed by oxidation in said step (c');
• (f') removing the exposed portion of said silicon nitride film;
• (g') removing said polycrystalline silicon film, into which no impurity is substantially doped, and said silicon dioxide film exposed by said step (f');
• (h') forming at least a polycrystalline silicon film into which an impurity having said first conductivity type is doped, or forming a metal silicide film, on the entire surface, including on said silicon nitride film on at least said base;
• (i') forming a resist film on the entire surface of said polycrystalline silicon or metal silicide film, and selectively changing the solubility of a desired portion of said resist film;
• (j') removing the portion of said resist film having a high solubility by development, and removing the exposed portion of said polycrystalline silicon or metal silicide film, thereby exposing a portion of the silicon nitride film;
• (k') oxidizing the surface of said polycrystalline silicon or metal silicide film, leaving at least a remaining portion of the polycrystalline silicon film or metal silicide film as polycrystalline silicon or metal silicide, respectively;
• and
• (l') removing the exposed portion of said silicon nitride film to expose the silicon dioxide film, and removing the exposed silicon dioxide film to form a hole, and doping an impurity having a second conductivity type opposite to said first conductivity type into a desired portion of the surface region of said base to form an emitter.