Decay length of the pressure dependent deposition rate for magnetron sputtering

Abstract

The pressure dependence of the deposition rate for magnetron sputter deposition of various elemental semiconductors and metals was investigated by x-ray measurements on sputtered films and quartz monitor measurements. It was found that for all elements investigated the dependence of the rate Φ on pressure-distance (pd) is well described by Φ=Φ0(1−e−cpd)/cpd. The value of c equals the inverse characteristic pressure-distance product (pd)0, which is the characteristics of the exponential decay of rate with pressure for low pressures. The experimental data of (pd)0 vary from 4.6 Pa cm for aluminum to 120 Pa cm for tungsten. It is shown that (pd)0 depend on both material specific properties and process parameters. The material specific properties are mainly the atomic mass and diameter, and the surface binding energy. The process parameters target voltage and power density act via the increase of the mean free path and the reduction of gas density, respectively, on (pd)0. As a first approximation, the characteristic pressure-distance product for argon as sputtering gas is proportional to the product of target atomic mass, average atomic energy and thermal mean free path.