Semiconductor structure including high voltage device

A high voltage device comprising:

• a substrate with a device region defined thereon;
• a first isolation structure in the substrate, the first isolation structure comprising first and second opposing sidewalls and a bottom portion connecting the first and second sidewalls;
• a gate stack disposed on the substrate in the device region, the gate stack having first and second opposing sides, the first side being adjacent to the first isolation structure;
• a channel region located in the substrate beneath the gate stack;
• a first diffusion region located in the substrate, the first isolation region is separated from the channel by the first isolation structure;
• and
• a first drift region in the substrate coupling the channel to the first diffusion region, wherein the first drift region comprising a non-uniform depth profile conforming to the profile of the bottom portion and the first sidewall, and at least a portion of the profile of the second sidewall of the first isolation structure.