Method for manufacturing a thin oxide for use in semiconductor integrated circuits

A method for forming a semiconductor device, the method comprising the steps of:

• providing a substrate having a surface;
• growing a sacrificial oxide on the surface of the substrate at a temperature of 950.degree. C.-1050.degree. C., the sacrificial oxide having a first portion and a second portion different from the first portion;
• masking the second portion of the sacrificial oxide with a photoresist layer;
• etching the sacrificial oxide from the first portion using a plasma etch process where the plasma contains both fluorine and carbon and where the second portion of the sacrificial oxide is protected from substantial etching by the photoresist layer, the etching depositing carbon into the surface of the substrate under the first portion to form a carbon-containing region;
• removing the photoresist layer;
• etching the sacrificial oxide from the second portion using a wet etch process comprising fluorine;
• growing a gate oxide over the first and second portions after the step of etching, the carbon-containing region retarding oxide growth so that a thickness of the gate oxide over the first portion of the substrate is less than a thickness of the gate oxide over the second portion of the substrate;
• forming a first MOS transistor using the gate oxide over the first portion of the substrate;
• and
• forming a second MOS transistor using the gate oxide over the second portion of the substrate.