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<E_i<175 eV, and incident angles 0<θ_i<85°. Threshold energies for sputtering E_th are also predicted and shown to vary with θ_i. We show that for energies below what is experimentally considered as threshold for physical sputtering (E_th(expt)∼60eV) 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∝E_i - E_th below E_th(expt) when Y is a maximum with respect to θ_i (at θ_i=45°). We find that Y∝E^1/2_i - E^1/2_th at other angles of incidence. We show that S is sensitive to E_i and θ_i in this regime. In particular, when θ_i=85°, we see that 1nS∼1/E_i for E_i≥20eV. 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.