MICRO-EFFECTS OF RESPUTTERING DUE TO NEGATIVE-ION BOMBARDMENT OF GROWING THIN-FILMS

Negative ion bombardment of an evolving thin film can cause changes in the film's surface due to resputtering of the already deposited mater ial. Through the study of rf-sputtered perovskite (BaTiO3) thin films, we have found that surface micro-effects, i.e., changes in the surfac e morphology of the films at the mum-scale level, are dependent on the deposition conditions. Ripples, cones, ridges, and etch pits of vario us shapes and sizes were all observed on growing films. A transformati on of the morphology of the top surface of the film as a function of b oth deposition time and location on the substrate has been observed. T he type of surface morphology found at any point was found to be depen dent on a number of factors, including deposition rates, flux and ener gy of bombarding ions, and the average angle of incidence of the bomba rding ions. We have developed a qualitative model for the formation of these surface features, based on the resputtering yield as a function of the average angle of incidence of the bombarding ions. The model s uggests that surface nonuniformities, often ripples, initiate the deve lopment of etch pits. Other mechanisms of the surface morphology devel opment (such as clustering) are used to explain the formation of surfa ce features other than etch pits.