Carrier Recombination Lifetime Measurement in Silicon Epitaxial Layers Using Optically Excited MOS Capacitor Technique

Carrier recombination lifetime is a key semiconductor parameter that not only has a major role in how a variety of solid-state devices operate, but one that can also be used as a process cleanliness monitoring tool. Lifetime measurement on epitaxial wafers, where the epilayer thickness is smaller than the minority carrier´s diffusion length, has always been a challenging task. Although the pulsed MOS capacitor has been shown to be an eminently suitable technique for measuring the generation lifetime (τ_g) on these wafers, measuring the recombination lifetime (τ_r) yet has remained complicated and difficult to implement. In this paper, a new technique for accurate measurement of τ_r will be presented. Lifetime will be extracted from the capacitance transient (C-t) of an inverted MOS device while being excited by an optical pulse. In addition to its easy implementation, the recombination lifetime extracted this way is least affected by Si/SiO₂ surface and epi/substrate interface effects when compared with older techniques such as the photoconductance decay. TCAD simulations and experimental results will be presented to demonstrate the promising application of the optically excited MOS to the characterization of p/p⁺ silicon epitaxial layers.