This paper describes a procedure for preparing packaged GaN devices for photon emission microscopy from the backside, which has proven to be an effective method for isolating faults. The deprocessing technique was developed for GaN devices formed on thick p++ silicon substrates mounted in quad-flat no-lead (QFN) packages connected by gold wires. It consists of mechanical polishing, which removes backside metal and packaging material, and selective etching, which quickly etches the silicon while leaving the gold wires intact for electrical measurements. The authors describe each step of the process in detail and explain how emission spots are marked with a UV laser and analyzed in a FIB-SEM system to determine the underlying cause of failure.

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