Trends in sputter yield data in the film deposition regime

Abstract

Knowing the fundamental trends of sputter yield in the sputtering regime used for film deposition is crucial for understanding the mechanisms of sputter deposition, interpreting yield data, and predicting the results of experiments. One source of experimental yield data is the comprehensive compilation [N. Matsunami, Y. Yamamura, Y. Itikawa, N. Itoh, Y. Kazomata, S. Miyagawa, K. Morita, R. Shimizu, and H. Tawara, At. Data Nucl. Data Tables 31, 1 (1984)]. They published graphical yield-energy curves based on empirical parameters which were best fits to nearly all the projectile-target combinations available in 1983. We interpret this experimental data using theoretical results from a ``simplified collisional model'' of sputtering. For 1-keV noble gas projectiles, several trends show forth (some old and some new): First, there is a repeating pattern in the dependence of yield on target atomic number, with the period being each row of the Periodic Table. Second, surface binding energy is the single most important target parameter; the yield varies roughly as ${1/U}_{\mathrm{sb}}^{1.3}$ for the empirical data, but as ${1/U}_{\mathrm{sb}}^{0.5}$ for the pure linear cascade sputtering mechanism. Third, while the principal mechanism is the linear cascade, the nonlinear cascade makes a detectable contribution to the experimental yield for yield values above \ensuremath{\sim}1. Fourth, for target atomic numbers above \ensuremath{\sim}35, the yield increases monotonically with projectile mass; for lighter targets the yield exhibits a maximum at an intermediate projectile mass. Fifth, the energy dependence of yield for a given projectile-target combination from \ensuremath{\sim}0.5 to 2 keV is, to a good approximation, $Y(E)\ensuremath{\propto}{E}^{0.5}.$ Scatter due to experimental error is evident in the data: Matsunami et al.'s approach of combining the results of different experiments, resulting in their empirical yield curves, is useful for compensating for this.