Patent ID: 8637929

Claim:
A MOS transistor comprising: a semiconductor substrate formed with a first well of a first conductivity type; a second well formed in said first well in adjacent to said first well, said second well including a channel region of a second conductivity type adjacent to said first well; a source extension region of said first conductivity type formed in said second well at a first side of said channel region in contact with said channel region; a drain extension region of said first conductivity type formed in said first well at a second side opposite to said first side of said channel region with a separation from said channel region; and a gate electrode structure formed on said semiconductor substrate to cover said channel region and a part of said first well at said second side of said channel region, said gate electrode structure at least comprising: a first gate insulation film extending over said semiconductor substrate from a first side to a second side of said channel region, said first gate insulation film covering said channel region with a first film thickness, and a second gate insulation film adjacent to said first gate insulation film at said second side of said channel region, said second gate insulation film covering said part of said first well with a second film thickness larger than said first film thickness, said gate electrode structure further comprising a first gate electrode on said first gate insulation film, and a second gate electrode on said second gate insulation film, said first gate electrode and said second gate electrode being isolated from each other by an insulation film extending from said first gate insulation film, wherein said first gate electrode comprises a first conductive material, said first gate insulation film comprises a first insulating material, said second gate electrode comprises a second conductive material different from said first conductive material, and said second gate insulation film comprises a second insulating material different from said first insulating material.