Ultraviolet laser-induced oxidation of silicon: The effect of oxygen photodissociation upon oxide growth kinetics

Abstract

New results on ultraviolet laser-induced formation of high-quality patterned silicon dioxide (SiO2) layers on silicon substrates at room temperature are presented. Comparison studies of oxide growth using pulsed excimer lasers at wavelengths of 193 nm (ArF) and 248 nm (KrF) show a dramatic rate enhancement at 193 nm which is attributed to the greater reactivity of O atoms produced by the photodissociation of O2. This growth enhancement depends exponentially upon laser pulse intensity over the range 0.05–0.40 J/cm2. The initial oxide growth rate at 193 nm varies linearly with laser exposure and sublinearly with oxygen pressure indicating that the observed rate is primarily the reaction of Si with O atoms at the Si-SiO2 interface. Growth kinetics and oxide stoichiometry are determined by careful analysis of the laser exposed regions following each laser shot using angle-resolved x-ray photoelectron spectroscopy with 150-μm spatial resolution. After one laser shot, a SiOx interface layer is clearly visible. Subsequent laser shots show the oxide peak shifting to higher energy as the oxide thickness increases until the characteristic ∼4.5-eV chemical shift for SiO2 (relative to the bulk Si 2p peak) is realized at a thickness of ∼2 nm. The nonstoichiometric SiOx layer is still present at this oxide thickness but is confined to the interface region (<1 nm) as observed in thermally grown oxides. Fourier transform infrared spectra show a frequency of 1070 cm−1 for the Si-O stretching mode and a bandwidth of 99 cm−1 implying that these laser-grown stoichiometric oxides are under compressive stress with a broader SiOSi bond angle distribution than thermal oxides.