Excimer laser machining and metallization of vias in aluminium nitride

Aluminium nitride (AlN) is a high thermal conductivity, high electrical resistivity, low dielectric constant ceramic with a small thermal coefficient of expansion mismatch to silicon. Machining and metallization processes for fired AlN are needed for prototype and small scale fabrication of power hybrid substrates and multichip module packages. Ablation has been investigated with a KrF (248 nm) laser to determine the dependence of ablation rate on ambient pressure, fluence and hole depth. Ablation rate is constant with increasing depth, and increases with increasing fluence and decreasing pressure. Depth control of less than 0.2 μm pulse−1 can be achieved and vias can be metallized by ablating a metal sheet attached to the substrate. The attached sheet also prevents fracture of the substrate by absorbing shock waves generated during ablation.