Laterally-diffused metal-oxide-semiconductor devices with a multiple-thickness buffer dielectric layer

A method of forming a structure for a laterally-diffused metal-oxide-semiconductor device, the method comprising:

• forming a drift well in a semiconductor substrate;
• forming a source region and a drain region in the semiconductor substrate;
• forming a gate dielectric layer on the semiconductor substrate;
• forming a buffer dielectric layer on the semiconductor substrate over the drift well;
• and
• forming a gate electrode laterally positioned between the source region and the drain region,
• wherein the buffer dielectric layer includes a first side edge adjacent to the drain region, a second side edge adjacent to the gate dielectric layer, a first section extending from the second side edge to the first side edge, and a plurality of second sections extending from the second side edge toward the first side edge, the first section has a first thickness, each of the second sections has a second thickness less than the first thickness, and the gate electrode includes a first portion that overlaps with the buffer dielectric layer and a second portion that overlaps with the gate dielectric layer, and
• wherein forming the buffer dielectric layer on the semiconductor substrate over the drift well comprises:
• forming a hardmask on the semiconductor substrate with an opening shaped to provide the first section and the second sections that are formed by a thermal oxidation process with the hardmask on the semiconductor substrate.