Patent ID: 7563726

Claim:
A method for fabricating a semiconductor device, comprising the steps of: forming a silicon oxide layer on a silicon substrate divided into a cell region where NMOS transistors are formed and a peripheral region where NMOS and PMOS transistors are formed by performing a first oxidation process; selectively removing the silicon oxide layer in the peripheral region; performing a plasma nitridation process on an exposed surface of the silicon substrate in the peripheral region and a surface of the silicon oxide layer in the cell region, thereby forming silicon-nitrogen bonds on the surface of the silicon substrate in the peripheral region and silicon-oxygen-nitrogen bonds on the surface of the silicon oxide layer remaining in the cell region; and performing a second oxidation process to form an oxynitride layer on the surface of the silicon substrate with the silicon-nitrogen bonds and transform the remaining silicon oxide layer with the silicon-oxygen-nitrogen bonds into a targeted silicon oxide layer, thereby forming the oxynitride layer on the silicon substrate in the peripheral region and the targeted silicon oxide layer on the silicon substrate in the cell region, wherein the targeted silicon oxide layer is formed by diffusing nitrogen out of the silicon-oxygen-nitrogen bonds during the second oxidation process.