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 <theta(i)< 85 degrees. Threshold energies for sputtering E-th are also predicted and shown to vary with theta(i). We show that for energies below what is experimentally considered as threshold for physical sputtering (E(th(expt))similar to 60 eV) a yield between 0.01 and 0.1 Cu/ion is observed for some off-normal angles of incidence [C. Steinbruchel, Appl. Phys. Lett. 55, 1960 (1989)]. We show that Y proportional to E-i-E-th below E-th(expt) when Y is a maximum with respect to theta(i) (at theta(i)=45 degrees). We find that Y proportional to E-i(1/2)-E-th(1/2) at other angles of incidence. We show that S is sensitive to E-i and theta(i) in this regime. In particular, when theta(i)=85 degrees, we see that ln S similar to 1/E-i for E(i)greater than or equal to 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. (C) 1999 American Institute of Physics. [S0021-8979(99)06516-0].