Patent ID: 7023069

Claim:
A method of manufacturing a semiconductor device comprising: providing a semiconductor substrate having first and second main surfaces opposite to each other, the semiconductor substrate having a heavily doped region of a first or a second conductivity type proximate the second main surface and having a lightly doped region of the first conductivity type proximate the first main surface; forming in the semiconductor substrate one or more trenches, first mesas and second mesas, each trench being disposed between adjacent mesas and each trench having an approximate equal width along its entire length, the first mesas having a width substantially less than a width of the second mesas; oxidizing sidewalls and bottoms of each trench; depositing a doped oxide into each trench and on the tops of the first and second mesas; and thermally oxidizing the semiconductor substrate at a temperature sufficient enough to cause the deposited oxide to flow so that the silicon in each of the first mesas is completely converted to silicon dioxide while the silicon in each of the second mesas is only partially converted to silicon dioxide and so that each of the trenches is filled with oxide.