US Patent 8003525 Semiconductor device and method of manufacturing the same

A GaN layer and an n-type AlGaN layer are formed over an insulating substrate, and thereafter, a gate electrode, a source electrode and a drain electrode are formed on them. Next, an opening reaching at least a surface of the insulating substrate is formed in the source electrode, the GaN layer and the n-type AlGaN layer. Then, a nickel (Ni) layer is formed in the opening. Thereafter, by conducting dry etching from the back side while making the nickel (Ni) layer serve as an etching stopper, a via hole reaching the nickel (Ni) layer is formed in the insulating substrate. Then, a via wiring is formed extending from an inside the via hole to the back surface of the insulating substrate.