Fabrication of differential gate oxide thicknesses on a single integrated circuit chip

Techniques for fabricating integrated circuits having devices with gate oxides having different thicknesses and a high nitrogen content include forming the gate oxides at pressures at least as high as 2.0 atmospheres in an ambient of a nitrogen-containing gas. In one implementation, a substrate includes a first region for forming a first device having a gate oxide of a first thickness and a second region for forming a second device having a gate oxide of a second different thickness. A first oxynitride layer is formed on the first and second regions in an ambient comprising a nitrogen-containing gas at a pressure in a range of about 10 to about 15 atmospheres. A portion of the first oxynitride layer is removed to expose a surface of the substrate on the second region. Subsequently, a second oxynitride is formed over the first and second regions in an ambient comprising a nitrogen-containing gas at a pressure in a range of about 10 to about 15 atmospheres to form the first and second gate oxides. Respective gate electrodes are formed over the first and second gate oxides. The oxynitride gates can have a nitrogen content in a range of about 0.2 to about 2.0 percent which can prevent the diffusion of boron ions from the gate electrodes into the oxynitride gates, thereby improving device characteristics. The oxynitride gates of different thicknesses are suitable for high and low voltage devices on the same integrated circuit.