Optical Probing of VLSI ICs from the Silicon Backside

With the advent of C4 packaging technology, Intel has developed, in conjunction with a technology partner, an integrated, laser-based optical backside probing system. This article begins with a description of the basic system operation. This is followed by a discussion on the electro-optic effect in CMOS, which is used for the signal acquisition. The question of invasiveness of the photo-injected carriers is then discussed. Information on the entire probing environment is also provided. The article also discusses results and presents a comparison with other waveform acquisition techniques. It ends with a brief discussion on the developments needed to scale the technique to future processes.