Method Of Fabricating Isolated Semiconductor Devices In Epi-Less Substrate

A process of fabricating a semiconductor device 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, said first opening having a first lateral dimension;
• implanting a dopant of a second conductivity type through the first opening to form a first deep layer;
• forming a second mask on the surface of the substrate, said second mask having a second opening, said second opening having a second lateral dimension, said second lateral dimension being entirely enclosed within said first lateral dimension;
• and
• implanting dopant of the first conductivity type through the second opening to form a second deep layer, said second deep layer being laterally constrained within said first deep layer, said second deep layer overlapping said first deep layer and having an upper boundary above said first deep layer;
• and
• implanting additional dopant of the first conductivity type through the second opening to form a third deep layer, said third deep layer being laterally constrained within said first deep layer, said third deep layer overlapping said first deep layer and having an lower boundary below said first deep layer.