Patent ID: 6933196

Claim:
A method for making a semiconductor substrate, comprising: forming first and second trenches on a semiconductor on insulator (SOI) substrate, wherein said forming of the first and second trenches comprises forming a pad oxide film on the SOI substrate, forming a mask layer on the pad oxide film, partially exposing an upper surface of the SOI substrate by removing parts of the pad oxide film and the mask layer corresponding to the first and second trenches, and applying an anisotropic etching process to the SOI substrate using the remaining mask layer as an etching mask; forming a first insulating film on the first and second trenches; forming first conductive type patterns over the SOI substrate, including the first and second trenches filling in the first and second trenches; and forming a second insulating film by oxidizing an exposed part of the SOI substrate between the first and second trenches without a mask, wherein said forming first conductive type pattern in said second trench comprises forming a low voltage device and said forming first conductive type pattern in said first trench comprises forming a high voltage device.