A backside contact structure is created using the following sequence of steps: etching a deep trench from the front surface of the semiconductor wafer to the buried layer to be contacted; depositing an isolation layer into the trench which covers the surfaces of the trench; performing an ion beam anisotropic etch in order to selectively etch the isolation layer at the bottom of the trench; filling the trench with a conductive material in order to create an electrical connection to the backside layer. The process can either be performed at a front-end stage of wafer processing following the formation of shallow trench isolation structures, or at a back-end stage after device transistors are formed. The backside contact structure so fabricated is used to electrically isolate circuit structures constructed on the wafer's upper surface, so that the various components of an integrated circuit can operate at different reference voltages.