Cross-sectional atomic force microscopy of focused ion beam milled devices

We have developed and demonstrated new techniques for failure analysis based on focused ion beam (FIB) cross-sectioning and inspection by atomic force microscopy (AFM). Normally, inspection after FIB cross-sectioning is done by scanning electron microscopy (SEM). As features of interest shrink below limits detectable by SEM, often the next method chosen is transmission electron microscopy (TEM). However, sample preparation for site-specific TEM is difficult and time-consuming, even using newer methods based on FIB milling. AFM offers higher resolution imaging than SEM, and relaxes many of the sample preparation constraints of TEM. The AFM/FIB technique has been demonstrated on GaAs-AlGaAs and GaAs-InGaP heterojunction bipolar transistors (HBTs), including devices which have been electrically stressed to failure.