Process for forming gate oxides possessing different thicknesses on a semiconductor substrate

A process for fabricating an integrated circuit comprising the steps of:

• (a) growing a semiconductor layer on a substrate;
• (b) forming an oxide layer upon the semiconductor layer;
• (c) amorphizing a selected area of the semiconductor layer to form an amorphized underlayer;
• (d) removing the oxide layer to expose the semiconductor layer having both amorphized and non-amorphized regions;
• (e) simultaneously growing gate oxide on the amorphized and non-amorphized regions of the semiconductor layer, including growing gate oxide on the amorphized underlayer, wherein the amorphized underlayer causes a differential in thickness in the gate oxide for forming the gate oxide of a first thickness on the non-amorphized region and of a second thickness greater than the first thickness on the amorphized region of the semiconductor layer to provide regions of the semiconductor layer adapted for different operating voltages.