Patent ID: 8809950

Claim:
A semiconductor structure, comprising: a first type substrate; a first type body doped region on the first type substrate; a first type heavily-doped region on the first type body doped region; a second type well region on the first type substrate; a diffused second type well region between the second type well region and first type body doped region and adjoined to the second type well region, wherein a second type impurity concentration of the diffused second type well region is lower than a second type impurity concentration of the second type well region; a second type heavily-doped region on the second type well region; an isolation structure on the diffused second type well region, wherein a doped depth of the diffused second type well region is substantially equal to that of the second type well region, and wherein the isolation structure directly adjoins the second type heavily-doped region and the diffused second type well region; and a gate structure on the first type substrate between the first type heavily-doped region and isolation structure, wherein the second type well region extends laterally beneath the second type heavily-doped region, and the diffused second type well region extends laterally beginning from the second type well region beneath the isolation structure without passing beneath the first type heavily-doped region, arranged such that a difference in the second type impurity concentration between the second type well region and the diffused second type well region obtains a field buffering effect.