Ultrashort-laser-pulse machining characteristics of aluminum nitride and aluminum oxide

This paper analytically investigates the ablation characteristics of aluminum nitride and aluminum oxide irradiated by an ultrashort pulse laser. Aluminum oxide or aluminum nitride has been one of the main ceramic packaging materials used for microelectronics packaging. However, a more extensive use of these ceramics has been limited due to their high inherent hardness and brittleness. An ultrashort pulsed laser micromachining could be a viable technology for these ceramics. The hyperbolic thermal model instead of heat transfer equation based on Fourier’s law is employed to study the ablation rate of an ultrashort laser pulse machining for aluminum nitride and aluminum oxide. The ablation depth per pulse predicted by this study agrees with the available experimental data. The delay of temperature rise is presented for the case of laser pulse duration shorter than thermal diffusion relaxation time. This study also demonstrates the reasons why high temperature is obtained for an ultrashort laser pulse machining of materials. The distinctions of properties such as thermal diffusivity, optical penetration depth, thermal expansion coefficient and reflectivity result in the differences of the ablated depth per pulse between aluminum nitride and aluminum oxide.