Root cause analysis of gate shorts in semi-vertical GaN MOSFET devices

We present a failure analysis of semi-vertical trench GaN-MOSFETs after reliability testing to identify the root cause for failure. First, off-state step-wise electrical stress testing was performed until breakdown occurred. The defect sites were localized by EL microscopy and analyzed by high resolution TEM and EDX. At the sidewalls of the gate trench, steep steps were observed along the gate finger. A gate short close to one of the steep steps was identified at the defect position. The gate etch process was adapted to obtain smooth gate trenches and to improve the reliability of the device.