Temperature and fluence effects on the evolution of regular surface morphologies on ion-sputtered Si(111)

Abstract

Results of a survey of the morphological evolution of the surface of Si(111) are presented for conditions in which regular patterned morphologies are spontaneously created during low energy $(250--1200\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$, oblique incidence (60\ifmmode^\circ\else\textdegree\fi{} from normal), ${\mathrm{Ar}}^{+}$ ion beam etching at elevated temperature $(500--750\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$. The morphological evolution was found to vary with sputtering time (fluence), ion flux, ion energy, and sample temperature. Experimental regimes in which it is appropriate to analyze ripple evolution in terms of the linear Bradley-Harper theory are identified, through which we find that the activation energy for surface mass transport on ion-bombarded Si(111) is $1.7\ifmmode\pm\else\textpm\fi{}0.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, in general agreement with measurements made in other manners. At higher fluence, nonlinear pattern forming effects are observed, including the observation of the formation of three distinct regular morphologies: two types of one-dimensional ripple arrays that differed both in orientation and regularity, and a two-dimensional array consisting of dots, all of which appear in different fluence regimes. All patterns possessed submicron periodicity and nanometer scale amplitudes. In addition, the wavelengths of one-dimensional ripples were often observed to coarsen with fluence, an effect potentially attributable to step-edge dynamics.