AXIALLY-RESOLVED STUDY OF HIGHLY IONIZED PHYSICAL VAPOR-DEPOSITION

The evolution of the ionization of sputtered aluminum is examined in a n inductively coupled plasma. The experimental configuration consists of a conventional magnetron with an immersed, rf induction coil positi oned between the target and the downstream substrate. Measurement of t he number of aluminum atoms and ions as a function of distance from a magnetron target reveals a decreasing neutral density and a nearly con stant ion density. The neutral metal density is well described by a si mple diffusion model with a source term near the target while the meta l ion density is approximately that of a diffusion-dominated, volume-g enerated plasma. These two spatial distributions result in a monotonic ally increasing ionization fraction versus distance from the target. E vidence suggests that the ionized physical vapor deposition method req uires that sputtered species be nearly thermalized before ionization i s probable. (C) 1997 American Vacuum Society.