Method for making integrated circuit transistors with isolation and substrate connected collectors utilizing simultaneous outdiffusion to convert an epitaxial layer

A semiconductor integrated circuit process comprising the steps:

• providing a semiconductor substrate wafer having one conductivity type;
• ion implanting a first impurity of said one conductivity type into a first group of selected regions of the surface of said substrate wafer;
• ion implanting a second impurity into said surface of said substrate wafer, said second impurity being of material capable of doping said semiconductor to a conductivity type opposite to said one conductivity type and in a concentration substantially lower than that of said first impurity said first and second impurities having a higher diffusion coefficient than the substrate impurity;
• growing a first substantially intrinsic epitaxial layer of semiconductor on said substrate wafer;
• depositing a third impurity into the surface of said first epitaxial layer in a second group of selected regions, said third impurity being capable of imparting said one conductivity type to said semiconductor, said second group of selected regions including regions in registry with said first group of selected regions;
• growing a second epitaxial layer of semiconductor on said first epitaxial layer, said second epitaxial layer having said one conductivity type;
• and
• forming isolation diffusions in said second epitaxial layer using an impurity that is capable of imparting said second conductivity type to said semiconductor and extending completely through said second epitaxial layer, whereby said diffusion causes said second impurity to dope said first epitaxial layer and causes said first and third impurities to dope said first epitaxial layer so that said first and third impurities span said first epitaxial layer in said first group of selected regions.