Process for producing semiconductor integrated circuit device and semiconductor integrated circuit device

A process for producing a semiconductor integrated circuit device having a dual gate CMOS, comprising the steps of:

• (a) forming a silicon-containing electrode film over a gate insulating film containing a silicon oxide film formed over a silicon surface representing a major surface of a semiconductor wafer;
• (b) forming a refractory metal film over said silicon-containing electrode film via a barrier layer;
• (c) forming a gate electrode by patterning said silicon-containing electrode film, said barrier layer and said refractory metal film;
• and
• (d) after said step (c), subjecting said silicon-containing electrode film to a thermal oxidation treatment in a mixed gas atmosphere containing a hydrogen gas and steam and having a moisture concentration in a range of from 5% to a maximum concentration such that said refractory metal film is substantially not oxidized, wherein said steam is synthesized from hydrogen and oxygen in the presence of a catalyst, and said mixed gas atmosphere is produced by diluting said steam using hydrogen such that said moisture is provided in said range.