PROCESS FOR FABRICATING AN ISOLATED FIELD EFFECT TRANSISTOR IN AN EPI-LESS SUBSTRATE

摘要

A process of fabricating a semiconductor device is disclosed comprising providing a semiconductor substrate of a first conductivity type, the substrate not containing an epitaxial layer; forming a first mask on a surface of the substrate, said first mask having a first opening defining a location of a first deep layer in a lateral dimension; implanting a dopant of a second conductivity type through the first opening to form the first deep layer; forming a second mask on the surface of the substrate, said second mask having a second opening defining a location of a second deep layer in the lateral dimension, a width of the second opening being less that a width of the first opening; and implanting dopant of the first conductivity type through the second opening to form the second deep layer. The projected range of the implant of dopant of the first conductivity type is less than the projected range of the implant of dopant of the second conductivity type such that the second deep layer overlaps and extends above the first deep layer. Alternatively, the projected range of the implant of dopant of the first conductivity type is greater than the projected range of the implant of dopant of the second conductivity type such that the second deep layer overlaps and extends below the first deep layer.