The Joy of SOI: As Viewed from a Backside FIB Perspective

For most advanced semiconductor products, the preferred methodology for achieving Focused Ion Beam (FIB) circuit modification and node access is through the backside of the chip. The high density of interconnect wiring and the presence of C4 solder bumping has made complex edits virtually impossible with conventional frontside techniques. IBM has developed a set of procedures for performing backside edit on circuits built using the Silicon-On-Insulator (SOI) process. While the basic approach and techniques parallel many of the established practices developed for handling transistors built in conventional bulk silicon, there are a number of key and critical differences. In this paper, we will address the basic instruction set developed for successful FIB work on SOI product. This will include backside silicon surface preparation, charge control, endpointing during high volume silicon removal, global and local coordinate lock techniques, floor voltage contrast phenomena, floor preparation and preservation, fill pattern issues and advantages, and finally the target structure alignment, access, connection and/or removal. Post process bake and handling will also be discussed.