Dependence of surface smoothing, sputtering and etching phenomena on cluster ion dosage

Abstract

The dependence of surface smoothing and sputtering phenomena of Si ( 1 0 0) solid surfaces irradiated by CO(2) cluster ions on cluster-ion dosage was investigated using an atomic force microscope. The flux and total ion dosage of impinging cluster ions at the acceleration voltage of 50 kV were fixed at 10(0) ions/cm(2)s and were scanned from 5 x 10(10) to 5 x 10(13) ions/cm(2), respectively. The density of hillocks induced by cluster ion impact was gradually increased with the dosage up to 5 x 10(11) ions/cm(2), which caused that the irradiated surface became rough from 0,4 to 1.24 nm in root-mean-square roughness (sigma(rms)). At the boundary of the ion dosage of 10(12) ions/cm(2), the density of the induced hillocks was decreased and sigma(rms) was about 1.21 nm, not being deteriorated further. At the dosage of 5 x 10(13) ions/cm(2), the induced hillocks completely disappeared and the surface became very flat as much as sigma(rms) = 0.7 rim. In addition, the irradiated region was sputtered as deep as 5.4 nm. From the experiment of isolated Cluster ion impact oil the Si surfaces, it was observed that the induced hillocks nm high had the surfaces embossed at the lower ion dosages, The surface roughness was slightly increased with the hillock density and the ion dosage, At higher than a critical ion dosage, the induced hillocks were sputtered and the sputtered particles migrated from the side of the hillock to the valleys among the hillocks in order to fill. After prolonged irradiation of cluster ion, it was observed that the irradiated region was very flat and etched. A simple phenomenological model in terms of dosage-dependent aequential surface embossment. sputtering, smoothing and etching processes was suggested to explain these cluster-ion impact interactions with the Si surfaces at various dosages. (C) 2002 Elsevier Science B.V. All rights reserved.