Modeling of Thin Film Single and Multilayer Nanosecond Pulsed Laser Processing

Abstract

A complete model of nanosecond pulsed laser scribing of arbitrary thin multilayer structures is presented. The chain of events is separated according to timescale; an initial simulation considers material response during the pulse; another combines this result with the much slower effects of heat flow away from the laser axis. The former considers heating, vaporization and phase explosion of metals in the course of a single pulse, accounting for variations in thermal conductivity and optical absorption as the material becomes superheated and approaches its critical temperature. The latter calculates the bidimensional heat flow in a complete multilayer structure over the course of a scribing operation, combining material properties and considering removal by both shortpulse ablation and longterm heating of the work piece. Simulation results for the single pulse ablation of an aluminum target align well with published experimental data both in terms of phaseexplosion threshold and ablation depth as a function of fluence. Bidimensional heat flow simulations of a polypropylene–aluminum–polypropylene triplex structure reveal the progression of events toward steady state behavior; aluminum ejected due to shortpulse ablation and plastic removed due to conduction.