Applications of fs lasers to nonlinear spectroscopy and process control of Si(001) interfaces

Abstract

Si(001) interfaces are among the most technologically important for nonlinear optical analysis, yet their exceptionally weak interfacial second harmonic susceptibility χ(2)s has strongly inhibited quantitative interface-specific second harmonic (SH) spectroscopy and related nonlinear optical process control applications. The advent of widely tunable, unamplified femtosecond (fs) solid-state lasers has overcome this barrier by enabling unprecedented SH generation efficiency (~ 106 photons/s) with minimal interface heating (<20 K).1 We have exploited these capabilities to characterize technologically important characteristics of buried SiO2/Si(001) interfaces, including microroughness,2 band-bending,3 strain,4 and interface oxidation stoichiometry5 by SH spectroscopy with a single unamplified Ti: sapphire fs laser beam. Here, as an example, we highlight an interface-specific SH electro-modulation spectroscopy3 study of a Cr/SiO2/Si(001) MOS structure, and its extension to a fs-time-resolved SH pump-probe study of carrier dynamics in the space-charge region (SCR). In addition we illustrate real-time (< 0.1 s kinetic resolution) SH monitoring of hydrogen (H) coverage of Si1-xGex(001) epitaxial growth surfaces during UHV chemical vapor deposition.