Phase Variation Mapping, a Dynamic Laser Stimulation Technique with Picosecond Timing Resolution

Timing issues in modern CMOS technology can be very difficult to localize, especially when circuits are sensitive to timing variation in the picosecond range. Very powerful time resolved emission (TRE) tools are limited to bandwidths of sim;52 ps and can be SNR limited. Dynamic laser stimulation (DLS) identifies circuit´s marginal regions by slightly perturbing local timing. It has the unique ability to induce timing perturbations proportional to the laser beam power. Therefore, timing perturbation can be made sufficiently small (i.e. in the picosecond range or less) not to modify the overall device behavior. Laser induced timing perturbation can speed-up or slow down transitions either from 1 to 0 (VDD to VSS) or from 0 to 1 (VSS to VDD). Knowledge of the physics behind those effects will help the designer or failure analyst to resolve timing issues. Unfortunately, timing perturbation measurements are often difficult to perform with suitable accuracy. This paper presents a new technique, phase variation mapping (PVM), which overcomes measurement accuracy issues. The measurement is based on a phase sensitive detector which provides an analog output representation of the laser induced timing variation. PVM belongs to a broader class of variation mappings techniques (which we refer to as `xVM´) aimed at solving a variety of marginality-related IC issues