Study of Excimer Laser Enhanced Etching of Copper and Silicon with (Sub) Monolayer Coverages of Chlorine

Abstract

The chlorine gas assisted excimer laser etching of copper ans silicon is studied in the pressure range of 10^-6 to 10^-4 mbar. Time of flight distributions of the etch products are measured as a function of laser power density and gas pressure. The measured distributions can be simulated with Maxwell-Boltzmann distributions with temperatures between 800 and 6000K where the temperature increases with increasing chlorine pressure and laser power density. For Cu the etch rate and the temperature corresponding to the kinetic energy distributions increases with the number of laser shots till a steady state situation is reached. In this steady state the etch rate and temperature are uniquely related to the value of the laser power density, chlorine pressure and repetition rate. A RBS measurement shews that in such a steady state situation a chlorinated layer is formed with a thickness of the order of 1000 A with a chlorine concentration of the order of 10% in the first few hundred A. For silicon the chlorinated layer keeps a thickness of at most of the order of one monolayer. A possible etch mechanism is given.