Process of producing thin film transistor

A method of producing a thin film transistor, comprising the steps of:

• forming an insulation film and a conductive film, on a semiconductor layer having a first semiconductor region and a second semiconductor region;
• forming a resist mask covering said first semiconductor region and having a first pattern over said second semiconductor region;
• patterning said conductive film into said first pattern;
• performing first implantation of a P-type impurities into said second semiconductor region, with the conductive film of said first pattern as a mask;
• removing the resist mask of said first pattern;
• forming a resist mask covering said second semiconductor region and having a second pattern over said first semiconductor region;
• patterning said conductive film into said second pattern;
• forming a resist mask of a third pattern, by removing an outer peripheral portion of the resist mask of said second pattern;
• performing second implantation of an N-type impurities into said first semiconductor region, with the conductive film of said second pattern as a mask;
• patterning said conductive film into said third pattern;
• removing the resist mask of said third pattern from said first semiconductor region;
• and
• performing third implantation of N-type impurities into said first semiconductor region, with the conductive film of said third pattern as a mask.