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Abstract

A new method of using a NO or N.sub.2 O treatment on a first area on a wafer in order to form a thinner oxide film in the first area and a thicker oxide film in a second area on a wafer using a single oxidation step is achieved. A semiconductor substrate of a silicon wafer is provided wherein a first area is separated from a second area by an isolation region. The silicon substrate in the second area is treated with NO or N.sub.2 O whereby a high-nitrogen silicon oxide layer is formed on the surface of semiconductor substrate in the second area. A tunnel window is defined in the first area and the oxide layer within the tunnel window is removed. The silicon wafer is oxidized whereby a tunnel oxide layer forms within the tunnel window and whereby a gate oxide layer is formed overlying the high-nitrogen silicon oxide layer in the second area. The tunnel oxide layer has a greater thickness than the combined thickness of the gate oxide layer and the high-nitrogen silicon oxide layer. A conducting layer is deposited and patterned overlying the tunnel oxide layer and the gate oxide layer and fabrication of the integrated circuit device is completed.

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First Claim