Insulated gate bipolar transistor structure having low substrate leakage

A high voltage semiconductor transistor, comprising:

• a semiconductor substrate;
• a first well region over the semiconductor substrate;
• a second well region in the first well region;
• an insulating structure over and partially embedded in the first well region, the insulating structure isolated from contact with the second well region;
• a gate structure near the insulating structure over the first well region;
• a drain region in the first well region across the insulating structure from the gate structure, wherein the drain region comprises a first drain portion adjacent to the insulating structure and a second drain portion farther away from the insulating structure;
• a source region in the second well region disposed on a side of the gate structure opposite the drain region;
• and
• a trench isolation feature in the first well region, the trench isolation feature being proximate to an implanted oxygen layer,
• wherein the first drain portion is separated from the second drain portion by a portion of the trench isolation feature, and
• wherein the trench isolation feature surrounds one or more of the second well region, the insulating structure, the gate structure, the source region, and the first drain portion.

A high voltage semiconductor transistor, comprising:

• a semiconductor substrate;
• a first well region over the semiconductor substrate;
• a second well region in the first well region;
• an insulating structure over and partially embedded in the first well region, the insulating structure isolated from contact with the second well region;
• a gate structure partly on the insulating structure over the first well region;
• a drain region in the first well region across the insulating structure from the gate structure, wherein the drain region comprises a first drain portion adjacent to the insulating structure and a second drain portion farther away from the insulating structure;
• a source region in the second well region disposed on a side of the gate structure opposite the drain region;
• and
• a trench isolation feature in the first well region, the trench isolation feature being proximate to an implanted oxygen layer,
• wherein the first drain portion is separated from the second drain portion by a portion of the trench isolation feature, and
• wherein the trench isolation feature and the implanted oxygen layer together surround one or more of the second well region, the insulating structure, the gate structure, the source region, and the first drain portion.