Surface damage of thin AlN films with increased oxygen content by nanosecond and femtosecond laser pulses
2009
AlN films deposited on sapphire substrates were damaged by single UV nanosecond (at 248 nm) and IR femtosecond
(at 775 nm) laser pulses in air at normal pressure. The films had high (27-35 atomic %) concentration of oxygen
introduced into thin surface layer (5-10 nm thickness). We measured damage threshold and studied morphology of the
damage sites with atomic force and Nomarski optical microscopes with the objective to determine a correlation between
damage processes and oxygen content. The damage produced by nanosecond pulses was accompanied by significant
thermal effects with evident signatures of melting, chemical modification of the film surface, and specific redistribution
of micro-defect rings around the damage spots. The nanosecond-damage threshold exhibited pronounced increase with
increase of the oxygen content. In contrast to that, the femtosecond pulses produced damage without any signs of
thermal, thermo-mechanical or chemical effects. No correlation between femtosecond-damage threshold and oxygen
content as well as presence of defects within the laser-damage spot was found. We discuss the influence of the oxygen
contamination on film properties and related mechanisms responsible for the specific damage effects and morphology of
the damage sites observed in the experiments.
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