Excimer Laser Induced Oxidation of Silicon: Characterization of the Oxide Stoichiometry in the Interface Region

Abstract

AbstractNew results on the ultrafast laser-induced formation of high-quality patterned silicon dioxide (SiO2) layers on silicon substrates at room temperature are presented. Using a pulsed ArF excimer laser (λ = 193 nm) operating at pulse energies near the melting threshold of silicon, SiO2 layers can be grown at a rate of 3–4 Å/pulse with an oxygen pressure of 500 torr. This growth rate exceeds by a factor of 5 the rate found using a XeCI excimer laser (λ = 308 nm) indicating that oxygen atoms produced by the direct photodissociation of oxygen by the ArF excimer laser play a role in achieving this extremely fast oxidation rate. Careful analysis of the laser exposed regions following each laser shot was performed using angle-resolved XPS with 150 micron spatial resolution. After one laser shot, a nonstoichiometric SiOx interface layer (<5Å) 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 ∼20Å. The nonstoichiometric SiOx layer is still present at this oxide thickness but is confined to the interface region (<10Å) as observed in thermally grown oxides. Oxide thicknesses obtained by angle-resolved XPS were confirmed using sputter depth-profiling. XPS measurements on samples irradiated at low oxygen pressure (5 torr) show evidence for oxidation of the silicon substrate outside the focused laser beam (2X). At this pressure the recombination time for oxygen atoms is long enough to allow diffusion and apparent reaction with the silicon substrate at reduced temperatures.