DIRECTIONALITY OF SPUTTERED CU ATOMS IN A HOLLOW-CATHODE ENHANCED PLANAR MAGNETRON

Angular distributions of sputtered Cu atoms in a planar magnetron discharge have been measured using a directional quartz microbalance. The discharge, in both Ar and Kr gases, was enhanced at low pressures, e.g., 0.07 Pa, using a hollow cathode electron source. Several means of improving the directionality, i.e., decreasing the angular spread of the sputtered atoms, were investigated. Increasing the discharge voltage to 770 V and increasing the gas pressure to not more than 1 Pa (for a throw distance of 50 mm) marginally improved the directionality of the angular distribution. Significant directionality was achieved using filter collimators which consisted of an array of collimating tubes. Our measurements show that in the absence of gas scattering collisions the collimating effect can be described by geometric shadowing. A Cu cathode with an array of collimating holes machined into the surface was shown to have a collimating effect at high discharge voltages and low current densities. We develop a simple model of the trajectories of ions approaching the cathode to explain the dependence of the angular distribution on the discharge conditions and radial position.