Semiconductor device having triple well structure

Claim 1

A semiconductor device comprising: a semiconductor substrate doped by a first-type impurity; a plurality of isolation films for defining a first active region, a second active region, and a third active region in a unit cell of the semiconductor substrate; a buried-impurity layer doped with a second-type impurity, the buried-impurity layer being formed in the semiconductor substrate at a predetermined depth from a surface of the first active region wherein the surface includes portions of the isolation films which are positioned at both sides of the first active region; a first well region of the first-type impurity formed beneath the second active region, the second active region being adjacent to the first active region; a second well region of the first-type impurity formed in the semiconductor substrate to a predetermined depth from the surface of the first active region and the second well region of the first-type impurity is also separated at a predetermined distance from the buried-impurity layer; a first well region of the second-type impurity is formed beneath the third active region; a second well region of the second-type impurity is formed beneath a selected portion of the isolation films defining the first active region and the second active region; and a first doping region of the first-type impurity and a second doping region of the first-type impurity formed respectively right beneath the surface of said first active region and right beneath a surface of said second active region, said first doping region having a dopant concentration lower than a dopant concentration of said second doping region.