Effect of energy above laser-induced damage thresholds in the micromachining of silicon by femtosecond pulse laser

A 400 nm second harmonic Ti:sapphire femtosecond laser was applied to struc ture silicon base on a direct-write process in air. A series of lines were ablated with pulses of 300-fs duration at varying power densities ranging f rom 50 to 100 nJ of energy on 2 " silicon (1 1 1) wafers. In this event, we investigate and report extensive laser induced thermal damage and redeposi tion encompassing the ablated lines at high energy levels above the damage threshold of the silicon. In addition. the effect of polarisation on the di rection of micromachining is also observed and discussed. The resolution an d quality of these lines were also found to hold a linear relationship to t he laser energy up to its thermal threshold limit. (C) 2001 Published by El sevier Science Ltd.