MOLECULAR-DYNAMICS SIMULATIONS OF AR- DISTRIBUTIONS OF REFLECTED ENERGIES AND ANGLES( AND CL+ IMPACTS ONTO SILICON SURFACES )

Previous profile evolution studies of plasma-assisted etch processes h ave shown that ions scattered from sidewalls can lead to microtrench f ormation on the bottom of an etched feature [see, for example, Dalton ct al., J. Electrochem. Sec. 140, 2395 (1993)]. In these studies, the ions impacting feature surfaces with incident angles above a critical value were assumed to reflect specularly from the surfaces. In the pre sent article, we describe the energy and angle distributions of reflec ted atoms obtained from molecular dynamics (MD) simulations. We simula ted Ar+ and Cl+ ions impacting model silicon surfaces. The ion inciden t energies Ei were 20, 50, and 100 eV. We varied the ion incident angl es theta(i) from 0 degrees to 85 degrees from the;surface normal. The model silicon surfaces had chlorine coverages of 0 monolayers (ML) of Cl, 1 ML Cl, and 2.3 ML Cl. We determined the Ar and Cl reflection pro babilities, i.e., the fraction of Ar and Cl atoms scattered from the s urfaces during the 1-2 ps MD trajectories. For theta(i) greater than o r equal to 75 degrees, we found that the reflection probabilities were greater than 90% in most cases. For these large incident angles, we d escribe the distributions of energies E-r and angles (polar theta(r) a nd azimuthal phi(r)) for the Ar and Cl atoms reflected from the surfac es. The results of the MD simulations are compared with the assumption of specular scattering. In addition, we compare the average energies of the reflected atoms with the predictions of two simple models based on the binary collision approximation. We discuss the effects of inci dent ion species, E-i, theta(i), chlorine surface coverage, and surfac e roughness on these results. (C) 1998 American Vacuum Society. [S0734 -2101(98)04506-0].