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.

This paper presents a method that allows top view SEM inspection on GaN devices previously subjected to PEM analysis from the backside and the associated sample preparation procedures. By filling the backside cavity with glob-top resin and epoxying the device to a piece of silicon, it is possible to remove all covering layers with a sequence of wet etches. A dried Ag liquid strap eliminates SEM charging problems and backside laser marks are made visible from the front side using an IR wavelength. The paper describes each step of the process in detail along with the results of the frontside SEM inspection.