KRF-EXCIMER LASER-INDUCED NATIVE-OXIDE REMOVAL FROM SI(100) SURFACES STUDIED BY AUGER-ELECTRON SPECTROSCOPY

The mechanism of KrF-excimer-laser cleaning of Si(100) surfaces was st udied by Auger Electron Spectrescopy (AES) and Low-Energy Electron Dif fraction (LEED) spectroscopy. The dependence of the cleaning efficienc y on the laser fluence was investigated by using a mildly focused lase r beam and carefully measuring the energy density distribution of the laser spot impinging on the sample. These values were compared with th e AES spectra measured in different points of the irradiated area and with the morphology observed by optical microscopy. Samples as receive d from the manufacturer were first investigated. It was found that des orption of weakly bonded organic adsorbates occurs at energy densities as low as 0.3 J/cm(2), whereas significant oxide removal takes place only at an energy density above 0.8 J/cm(2), which produces damaged su rface morphologies. The experimental findings, in agreement with the t emperatures calculated for the laser-induced Si heating, indicated tha t a large fraction of the oxide film is dissolved in the molten silico n, leading to oxygen concentration below the AES detection limit only when the melted depth was of the order of several hundred nanometers. Atomically clean, damage-free Si(100) surfaces were obtained after irr adiation of samples pre-etched for 1 min in a HF: H2O (5%) solution, w hich had only a thin SiOx(x < 2) layer and F, C and O containing adsor bed species. Complete contaminant elimination was achieved in this cas e with 15 pulses at 0.8 J/cm(2) without any damaging of the surface.