Method of fabricating semiconductor

A method of fabricating a semiconductor device, comprising:

• providing a semiconductor substrate having a first type well and a second type well, and a field oxide layer formed therebetween;
• performing a first photolithography process, including forming and patterning a first photo-resist layer over the substrate to cover the first type well and a first predetermined gate region on the second type well;
• implanting a second type impurity into the exposed second type well to form a first source/drain region;
• forming a first silicon oxide layer on the first source/drain region;
• removing the first photo-resist layer to form a first opening on the first predetermined gate region;
• performing a second photolithography process, including forming and patterning a second photo-resist layer over the semiconductor substrate to cover the second type well and a second determined gate region on the first well;
• implanting a first type impurity into the exposed first type well to form a second source/drain region;
• forming a silicon oxide layer on the exposed first type well;
• removing the second photo-resist layer to form a second opening on the second predetermined gate region;
• forming a gate oxide layer and a conductive layer in the first opening and the second opening;
• and
• etching the conductive layer until exposing the first oxide layer and the second oxide layer;
• wherein the conductive layer is a gate.