Focused ion beam (FIB) systems use a gallium liquid metal ion source as the source of the ions, providing a typical beam current range of 1 pA to 20-60 nA. Using a reactive gas in addition to the FIB usually enhances the etch rate from 1 to 15 times, but with the combination of xenon difluoride gas and a silicon substrate the enhancement can be over 1000 times. Such an enhancement makes the removal of large volumes of Si more practical, even with the typical upper end of FIB currents of 20-60 nA. This paper discusses the application of full-thickness silicon trenching to the process development of WtW bonding. With the increase in 3DIC, it is expected that fresh process characterization and failure analysis techniques will be required. The work presented shows the feasibility of extending FIB techniques to the process development of wafer-to-wafer bonded samples even on full-thickness wafers.