Patent ID: 8329525

Claim:
A method, comprising: forming, above a first part, a second part and a third part of a semiconductor substrate, a first oxide layer having a first thickness; etching, above the second part of the semiconductor substrate, the first oxide layer; forming, above the second part of the semiconductor substrate, a second oxide layer having a second thickness smaller than the first thickness; etching, above the third part of the semiconductor substrate, the first oxide layer; forming, above the third part of the substrate, a third oxide layer having a third thickness smaller than the second thickness; nitriding the second oxide layer and the third oxide layer, without nitriding the first oxide layer above the first part, so as to form a first oxy-nitride layer above the second part of the semiconductor substrate and a second oxy-nitride layer above the third part of the semiconductor substrate; forming a first gate structure over the first oxide layer for a first metal-oxide semiconductor transistor which uses the first oxide layer as a gate oxide layer; forming a second gate structure over the first oxy-nitride layer for a second metal-oxide semiconductor transistor which uses the first oxy-nitride layer as a gate oxide layer; and forming a third gate structure over the second oxy-nitride layer for a third metal-oxide semiconductor transistor which uses the second oxy-nitride layer as a gate oxide layer.