Laser-assisted chemical etching of copper

Abstract

Copper films several microns thick can be rapidly etched (0.1-0.5 μm/s) in a chlorine atmosphere using 308 nm pulsed excimer laser radiation. Etch rates exhibit a practical threshold of ∼0.1 J/cm2 and saturate above 0.3 J/cm2. The etching mechanism involves reaction of copper and chlorine in the time between the laser pulses to form a nonstoichiometric chloride which is thermally ablated by the laser. Photochemical effects appear to be unimportant. The etch rate increases roughly as the square root of the laser pulse rate, suggesting that reactive diffusion is a limiting factor. As the substrate temperature increases, the etch rate rises, then falls, indicating the competition of processes such as adsorption, desorption, and reaction of chlorine molecules on copper chloride surfaces. A simple model based on chemical kinetics suggests that the copper-chlorine reaction at pressures above 0.1 Torr is controlled by a physisorbed intermediate state.