Cu sputtering and deposition by off-normal, near-threshold Cu+ bombardment: Molecular dynamics simulations

Sputter yields Y and sticking coefficients S are essential inputs for feature profile evolution studies. Molecular dynamics simulations are used to compute sputter yields and sticking coefficients for Cu+ ions impinging on a Cu surface at various incident energies 15<Ei<175 eV, and incident angles 0<θi<85°. Threshold energies for sputtering Eth are also predicted and shown to vary with θi. We show that for energies below what is experimentally considered as threshold for physical sputtering (Eth(expt)∼60 eV) a yield between 0.01 and 0.1 Cu/ion is observed for some off-normal angles of incidence [C. Steinbrüchel, Appl. Phys. Lett. 55, 1960 (1989)]. We show that Y∝Ei−Eth below Eth(expt) when Y is a maximum with respect to θi (at θi=45°). We find that Y∝Ei1/2−Eth1/2 at other angles of incidence. We show that S is sensitive to Ei and θi in this regime. In particular, when θi=85°, we see that ln S∼1/Ei for Ei⩾20 eV. We discuss some assumptions commonly used in profile simulation studies which may now be relaxed, with an eye toward improving the predictive power of those simulations.