XeCl laser controlled chemical etching of aluminum in chlorine gas

The 308 nm XeCl laser assisted etching process of thin Al metal films on Si substrate in Cl₂ gas was investigated. Etch rates were measured versus the laser fluence on the sample, the laser repetition rate, the Cl₂ pressure and the sample temperature. Irradiation experiments under vacuum of films which were previously exposed to Cl₂, and laser assisted etching in rare gases, nitrogen and air mixtures with Cl₂ were also performed to elucidate the mechanism of the etching process. The surface morphology was investigated by scanning electron microscopy. The results show that a) Etch rates of up to about 1.5 m per pulse are obtained which are strongly dependent on the Cl₂ pressure and sample temperature. b) The etching mechanism is essentially a chemical chlorination of the Al in between the laser pulses which is followed by photo-ablation of the reaction products, c) AlCl₃ evaporation and redeposition processes can explain the observed results. d) The Al films can be etched fully and cleanly without damage to the smooth Si substrate. e) Etching through adjacent or imaged mask on the Al film yielded relatively smooth and well defined Al walls with structures of the order of 1 m.