Surface to surface electrical isolation of integrated circuits has been achieved by forming N type moats that penetrate the silicon as deeply as required, including across the full thickness of a wafer. The process for creating the moats is based on transmutation doping in which naturally occurring isotopes present in the silicon are converted to phosphorus. Several methods for bringing about the transmutation doping are available including neutron, proton, and deuteron bombardment. By using suitable masking, the bombardment effects can be confined to specific areas which then become the isolation moats. Four different embodiments of the invention are described together with processes for manufacturing them.
