Photo-carrier radiometry of semiconductors: A novel powerful optoelectronic diffusion-wave technique for silicon process non-destructive evaluation

Laser-induced infrared photo-carrier radiometry (PCR) is introduced as an emerging semiconductor NDT technology, both theoretically and experimentally through deep sub-surface scanning imaging and signal frequency dependencies from Si wafers. PCR completely obliterates the thermal infrared emission band (8–12 μm), unlike the known photothermal signal types, which invariably contain combinations of carrier-wave and thermal-wave infrared emissions due to the concurrent lattice absorption of the incident beam and non-radiative heating. The PCR theory is presented as infrared depth integrals of carrier-wave (CW) density profiles. Experimental aspects of this new methodology are given, including the determination of photo-carrier transport parameters (surface recombination velocities, carrier diffusion coefficients, recombination lifetimes and carrier mobilities) through modulation frequency scans. CW scanning imaging is also introduced. High-frequency, deep-defect PCR images thus obtained prove that very-near-surface (where optoelectronic device fabrication takes place) photo-carrier generation can be detrimentally affected not only by local electronic defects as is commonly assumed, but also by defects in remote wafer regions much deeper than the extent of the electronically active thin surface layer.