Patent ID: 7682926

Claim:
A method of forming a semiconductor substrate, the method comprising: performing an ion implanting process over a semiconductor substrate in a cell/core region to form an ion implanted region in the cell/core region; selectively etching a portion of the semiconductor substrate located at a portion of a boundary of the ion implanted region to form a first recess exposing the ion implanted region; removing the ion implanted region using the first recess to form an under-cut space in the substrate; forming a first insulating film to fill the under-cut space and the first recess; selectively etching a portion of the semiconductor substrate at a portion of a boundary of the first insulating film to form a second recess exposing the first insulating film, wherein the first recess and the second recess are formed in different locations of the semiconductor substrate; and forming a second insulating film to form a SOI structure in the substrate of the cell/core region, the second insulating film filling the second recess, wherein the first insulating film and the second insulating film form a barrier layer that electrically separates a floating body of the SOI structure in the cell/core region from a bulk body in a peripheral region of the semiconductor substrate.