Differential sputtering yields of refractory metals by ion bombardment at normal and oblique incidences

Abstract

Currently, the problems of sputter erosion and spacecraft contamination due to deposition of sputtered material are generally handled by numerical computer codes. These codes rely on sputtering data as “inputs” which are needed to compute the magnitude and trajectory of the sputtered particles. The basic sputtering data available for these codes tend to be incomplete. Often only total sputter yields, with units of sputtered atoms per ion, have been measured. The total sputter yields characterize the total amount of material sputtered, but without directional trajectory information of the sputtered particles. Thus, without such directional information, computer codes make assumptions on the angular sputtering profile, which are often not in agreement with the actual profiles. The angular description of the sputtering is treated by differential sputter yields (y()), with units of sputtered atoms per ion per steradian, which quantifies sputtering as a function of angular direction ( is the polar angle relative to the surface normal). Differential sputter yields are reported for Molybdenum, Tantalum, and Tungsten after exposure to Xenon, Krypton, and Argon ion bombardment at multiple angles of incidence (0 - 60°) and ion energies (150 - 1500 eV). Differential yields were measured by sweeping a Quartz Crystal Microbalance in a semicircular arc over a target in the plane defined by the target normal and ion beam axis. Differential yields were integrated to obtain total sputter yields. The dependence of total yield on angle of incidence was also investigated. The total yields were found to be largest for angles of incidence between 45° and 60°. The effects of the bombarding ion energy and the ion mass-to-target atom mass ratio on the differential yield distributions are discussed. In addition, measurements of differential sputter yields as a function of both polar and azimuthal angles are presented.