Control of localized access to circuitry through the backside using focused ion beam technology

Complex logic chips are almost exclusively assembled in flip chip packaging . This type of assembly complicates traditional debug and circuit modificat ion techniques. Development of new applications and new equipment now enabl e precise access to the circuitry of flip chip parts. One such application and the equipment developed are being introduced in this article. The techn ique makes use of optical beam induced current (OBIC) as a way to measure t he amount of silicon that is left covering active areas of a flip chip circ uit after a trench has been milled in the bulk silicon using a focused ion beam (FIB) system. The apparatus is all contained in one system thus enhanc ing the throughput of such work. When accessing the circuitry of flip chip parts, it is crucial to be able to locally remove silicon from the backside to within a few microns of the circuitry. This is necessary in order to pr eserve the integrity of the part and allow access to the circuitry for prob e point creation or circuit modification using FIB. OBIC offers a high leve l of resolution and accuracy in measuring thin layers of bulk silicon in hi p chips. In this article we describe the apparatus used, the details of the application, data collected, and a theoretical model developed to confirm the experimental findings. (C) 1999 American Vacuum Society. [S0734-211X(99 )08406-1].