Ion Implantation and Synthesis of Materials - Studium

12.8 Computer Simulation 175orientation, impurities in the material, ion species, and angles used for sputtering.An extremely rough surface can reduce the sputtering yield.Gas bubble formation and blistering effects have been widely observed in highdoseimplantations of inert-gas ions. Backscattering measurements of depthdistributions often show very low concentrations of implanted species in the nearsurfaceregion. This indicates that the inert-gas atoms can escape from the materialeven without sputtering. In these cases, the simple model described in the previoussections does not apply.12.8 Computer SimulationSputtering has been modeled using both Monte Carlo and molecular dynamiccomputer simulations. A review of the simulation literature is given in Eckstein(1991).The SRIM program, a binary collision Monte Carlo approach, has been used topredict sputtering yields (Fig. 12.2). The incident ions and the recoil atoms are10NiXeArSputtering Yield, Y10 –1 110 –210 –3xxx++xx x++ +xxxx x x xx xx x++ + ++ + + + + ++ +Ion calc. meas.H + +D x x4 HeNeArXeFig. 12.11. Comparison of SRIM calculations with experimental measurement of thesputtering yield, Y, versus incident energy for gas ions incident on a Ni target (from Ziegleret al. 1985)x+++xD+H10 2 10 3 10 4 10 5Incident Energy, E 0 (eV)Ne4 He