Investigation of the throw distance of sputtered atoms under consideration of gas rarefaction

The throw distance (TD) of sputtered atoms of a variety of elements was measured via the pressure-dependent atomic deposition rate. For each element the pressure-dependent rate was determined at a low- and a high sputtering power with typical nominal power-densities of 0.3 and 4 W/cm2, respectively. The Keller–Simmons formula, which contains the TD as an explicit fit parameter, well describes the functional dependence of rate on pressure. For low-mass targets (Al, Si, V), the TD was found to be independent of sputtering power over the range investigated. At increased atomic mass—first observed for Cr—increasing sputtering power causes an increase of the TD, what is related to the stronger gas rarefaction for these elements. It is estimated that a gas density reduction by less than 20% is uncritical for an accurate determination of the TD. The TDs of the elements (measured at negligible gas rarefaction) are found to depend linearly on the product of velocity persistence in argon and surface binding energy. The velocity persistence is fairly proportional to the logarithm of the atomic mass for elements heavier than 20 amu.