FIB Chip Repair: Improving Success by Controlling Beam-Induced Damage and Thermal/Mechanical Stress

Abstract

Focused Ion Beam (FIB) success has become more difficult as microchip process technology advances, requiring new techniques for damage control both during the microsurgery procedure and before the finished product can be electrically tested. Ultra thin gate dielectrics, shallower junctions, less ‘white space,’ and new materials surrounding active devices all create additional challenges for imaging, targeting, controlling instantaneous charge damage, and the removal of residual implanted charge. On the macro level, global thinning of bulk silicon housed in hybrid packages is causing new problems with thermal management and mechanical stress. Techniques and procedures used to control electrostatic discharge type damage become ever more critical when working on poorly buffered or isolated device elements, especially from the backside. Implanted gallium and residual charge perturb electrical characteristics, and must be dispersed prior to power-up thru carefully controlled bake steps. Left in place, these FIB-induced perturbations are likely to cause poor functionality or even latchup. The mechanical rigidity and thermal dissipation properties of newer, complex package types must also be restored post-FIB, otherwise cracked silicon or a thermal overload event might be the outcome. In this paper, we will attempt to address some of the common causes of FIB-induced failure on newer silicon and package technologies, and how they might be overcome. FIB techniques and preparatory processes must continue to evolve in order to deal effectively with the problems of direct beam damage, residual charge elimination, and sample stress management.