Adsorption of Oxygen in Laser-Induced Amorphous Silicon

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Gibbons, Hess, and Sigmon, eds. Laser andElectron-Bean Solid Interactions and :-:aterials Processing

117

ADSORPTION OF OXYGEN IN LASER-INDUCED AMORPHOUS SILICON

YUNG S. LIU, S. W. CHIANG AND F. BACON General Electric Research and Development Center Schenectady, New York 12301 USA

ABSTRACT Amorphous silicon has been produced on a single crystalline silicon surface by intense UV laser radiation at 266 nm followed by rapid quenching. In addition, formation of oxide of several tens of nanometers has been observed when irradiation takes place in air or in 02 ambient. Various experimental techniques including Transmission Electron Microscopy (TEM), sputtered Auger Electron Spectroscopy (AES), and differential Fourier-transform IR spectroscopy (FT-IR) have been employed to study adsorption of oxygen during rapid melting and resolidification process. The present results suggest a new processing technique for forming thin oxide film, namely, "Laser-induced oxidation." INTRODUCTION In most laser annealing experiments, it has been shown that the ambient condition has little or no effect on the formation of the crystalline structure. On the other hand, in a recent report on the formation of noncrystalline phase 1 aluminum induced by a pulsed Ruby laser, it has been shown that the existence of small grains of hexagonal Al-N phase of the size on the order of 100A embedded in an amorphous Al film induced by laser irradiation followed by rapid quenching. These experiments were performed in air at room temperature. A possible mechanism of the formation of Al-N compound was attributed to surface adsorption of nitrogen during laser irradiation. Previously, formation of 2 3 amorphous silicon using pulsed lasers has been discussed. , There was, however, no discussion of adsorption of any impurities in the amorphous silicon layer formed in these experiments. In this work, we report an observation of the formation of Si0 2 in the amorphous silicon layer formed by pulsed UV laser irradiation. The amorphous silicon was studied by electron channeling technique and Transmission Electron Microscopy (TEM). The oxide profile was analyzed using Auger Electron Spectroscopy (AES) combined with ion sputtering. Formation of oxide was further confirmed using differential Fourier-transform IR (FT-IR) spectroscopy. The oxide thickness was found to increase from about 60A to about 300A as the UV laser energy density is increased. These oxide thicknesses shall be compared with the native oxide thickness of about 10A for an un-irradiated sample. The formation of oxide is attributed to adsorption of oxygen during the period of meltJ'>-; followed by rapid resolidification. The adsorbed oxygen impurity is believed to inhibit the regrowth rate and thus facilitate amorphous silicon forration. The present study suggests a new and rapid process for forming thin oxide layer, namely, "Laser-induced Oxidation." EXPERIMENTAL In the experiments, floating-zone grown (FZ) silicon (p-type, 4Q-cm) wafers of (100) and (111) orientations were used. The UV laser p

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