Application of Photoemission Microscopy and Focused Ion Beam Microsurgery to an Investigation of Latchup

Radiation-induced latchup sites in a high-performance commercial application-specific integrated circuit (ASIC) manufactured in a bipolar gate array have been identified using a photoemission (PE) microscope before and after isolating individual circuit elements with a focused ion beam (FIB) system. Latchup sites were determined to be associated with grounded unused resistors and transistors in an emitter-coupled logic (ECL) input buffer. Simulation of the oxide isolation scheme confirmed the presence of pnpn structures at the likely latchup sites. A corrective action to redesign the layouts to disconnect unused resistors and transistors resulted in successful elimination of latchup in the ECL buffers.