Laser activation and metallisation of insulators

An analysis is made of two-stage metallisation of insulator surfaces. Laser ablation of the surfaces of a number of insulators (activation stage) creates, on the irradiated surface, catalytic centres capable of reducing metals (deposition stage) in special solutions. Autocatalytic deposition spreads a metal over the whole ablated surface. A review is given of the experimental data on laser activation of Al₂O₃, SiC, diamond, ZrO₂, and other insulators. Surface activation is observed in a wide range of laser radiation wavelengths and is retained for a long time, which makes it possible to deposit a number of metals (Cu, Ni, Pt, Pd, etc.) with a spatial resolution of the order of several microns. A model of the process is considered: according to this model, laser activation is the result of modification of a band gap of an insulator by ablation and appearance of a nonzero density of the electron states with energies close to the reduction potential of a metal. This in turn may be related to the formation of point defects (for example, F centres in Al₂O₃ and ZrO₂) in an insulator or to band bending in the field of mechanical stresses that remain in the treated material after ablation. Data on the activation of insulators by mechanical indentation are in qualitative agreement with the proposed model.