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

Abstract

Complex logic chips are almost exclusively assembled in flip chip packaging. This type of assembly complicates traditional debug and circuit modification techniques. Development of new applications and new equipment now enable precise access to the circuitry of flip chip parts. One such application and the equipment developed are being introduced in this article. The technique makes use of optical beam induced current (OBIC) as a way to measure the amount of silicon that is left covering active areas of a flip chip circuit 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 enhancing 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 preserve the integrity of the part and allow access to the circuitry for probe point creation or circuit modification using FIB. OBIC offers a high level of resolution and accuracy in measuring thin layers of bulk silicon in flip 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.

Understanding image contrast to optimize procedures for focused ion beam contact level circuit editing

“…5,6 The development of techniques to increase the rate of bulk trenching, ultimately leading to the ability to perform full-thickness back side CE, furthered the art. The use of CAD overlay to allow for precise placement of local trenches facilitated success yields.…”