Laser sputtering. Part II. The mechanism of the sputtering of Al₂O₃

Abstract

In an attempt to establish the mechanisms by which crystalline Al2O3is sputtered in vacuum by intense photon pulses, detailed scanning-electron-microscope studies have been made. Micrographs of specimens bombarded by pulses at 532 nm, produced by second harmonic generation from a Nd: YAG laser, suggest sputtering due to thermal-stress-induced exfoliation. Micrographs of specimens bombarded by pulses at the fourth harmonic, 266 nm, as well as excimer-laser pulses at 248 or 193 nm, are characterized by an anomalous absence of thermal or exfoliational features. Thus, at these wavelengths, in regions of uniform illumination there was no evidence of obvious melting, frozen-in capillary waves, thermal-stress-induced fracture, or exfoliation. Only in regions of extreme intensity variation were any of these found, namely melting and exfoliation. It is therefore suggested that there may be a competing electronic sputtering mechanism. The sputtering was in all cases accompanied by intense emission from excited neutral Al atoms which served as a sensitive criterion for the sputtering threshold. © 1984.