MOS transistor gates with thin lower metal silicide and methods for making the same

A method of fabricating transistor gate structures in a semiconductor device, the method comprising:

• forming a gate dielectric above a semiconductor body;
• forming a first silicon-containing material above the gate dielectric to a thickness of about 300 Å or less;
• forming a first metal over the first silicon-containing material;
• reacting the first metal with the first silicon-containing material to form a first metal silicide above the gate dielectric;
• forming a second silicon-containing material above the first metal silicide;
• selectively etching portions of the second silicon-containing material and the first metal silicide to form a patterned gate structure above the gate dielectric;
• forming a second metal over the second silicon-containing material;
• reacting the second metal with the second silicon-containing material to form a second metal silicide above the first metal silicide;
• forming an additional silicon-containing material above the first metal silicide;
• forming an additional metal over the first silicon containing material;
• and
• reacting the additional layer consisting essentially of metal with the additional silicon-containing material to form an additional metal silicide above the first metal silicide before forming the second silicon-containing material.