Column-growth mechanisms during KrF laser micromachining of Al₂O₃–TiC ceramics

Abstract

This paper aims to contribute to the understanding of column-formation mechanisms in Al₂O₃–TiC ceramic composites due to processing with excimer laser radiation. The mechanisms proposed in the literature to explain the formation of such columns can be grouped into four categories: hydrodynamic mechanisms, vapour phase deposition mechanisms, spatial modulation of absorbed energy mechanisms, and shadowing mechanisms. In the case of Al₂O₃–TiC ceramics, the first two types of mechanisms can be excluded because experimental results show that the column core is composed of material in a pristine condition. A theoretical simulation of the spatial modulation of absorbed energy due to radiation reflected from pre-existing topographic artefacts reveals that this mechanism does not explain the fact that columns only grow during the first 100–200 laser pulses and can, therefore, be ruled out. By contrast, predictions of the shadowing mechanism with TiC globules formed during the first laser pulses shielding the substrate and favouring column growth are in semiquantitative agreement with experimental observations.