METHOD OF FABRICATING SEMICONDUCTOR DEVICE

摘要

PURPOSE:To prevent change of the threshold value of the metal insulator semiconductor (MIS) in it second gate by so doping an impurity in the vicinity of the surface of a polysilicon layer as to reduce the impurity concentration lower than the deeper portion to thereby decrease its automatic doping phenomenon. CONSTITUTION:A P-type semiconductor substrate 1 is selectively oxidized to thereby form a field oxidation film 2 and a first gate insulation film 3 having a thinner active region thereon. Then a first polysilicon layer 4 is formed on the entire surface of the substrate 1. Phosphorus is ion implanted on the layer 4 so that its concentration may become peak in the deeper portion therein. Then, the layer 4 and part of the film 3 are removed by an etching process to thereby partially expose the substrate 1 and to then form an interlayer insulation film 6 on the surface of the layer 4 and a gate insulation film 5 on the surface of the substrate 1 by an oxidation process. Then, a second polysilicon layer 7 is formed thereon to remove unnecessary portion thereof. Then, phosphorus (P), arsenic (As) or stibium (Sb) is diffused on the surface of the exposed substrate 1 to thereby form an N<+>-type diffused layer 8 thereon so as to complete a two-layer polysilicon type MIS semiconductor element.