Laser infrared photothermal radiometry of semiconductors: Principles and applications to solid state electronics

The photothermal origins and physical principles of the novel diagnostic technique of laser infrared photothermal radiometry of semiconductors are presented. Following super-bandgap optical excitation, it is shown that the signal consists of two contributions, one from the de-exciting carrier density (plasma wave) and another from direct absorption and heating of the lattice (thermal wave). The advantage of this technique over other photothermal methods in the field of diagnostics in solid-state electronics lies with the domination of the signal by the plasma wave component over a broad high-frequency range, quite accessible by today's electronic instrumentation. As a result, the primary photoinjected carrier parameters can be easily and reliably measured: lifetime, tau, electronic and thermal diffusivities, D and alpha, respectively, and surface recombination velocities, s(j), on both semiconductor wafer surfaces. The theoretical section is complemented with key applications chosen from a rapidly increasing set of case studies, including Si wafer substrate transport property diagnostics, contamination control of chemically cleaned process wafers, MOS capacitor structures, carrier lifetime depth profiles in ion-implanted wafers, and bulk crystalline and thin-film photoconductors. (C) 1998 Elsevier Science Ltd. All rights reserved.