OXIDATION-ENHANCED ROUGHENING OF THIN CO FILMS DURING SPUTTERING BY O-2(+) IONS

Substantial variations in the erosion rate during low energy (5.5-10.5 keV) O-2(+) sputtering of polycrystalline Co thin films are demonstra ted by crater depth measurements as a function of sputtering time. At normal incidence the erosion rate is constant, while for oblique angle s (less than or equal to 55 degrees, with respect to surface normal) t he rate is between similar to 30% and 75% higher at the surface compar ed to that in the ''bulk.'' A clear relationship between the width of the preequilibrium region and the sputtering-induced roughness is show n, as revealed by surface stylus profilometry and atomic force microsc opy measurements. Sputtering by Ar+ ions, where no chemical compounds form, results in significantly smoother craters and the erosion rate i s constant. The development of the preequilibrium region during O-2(+) sputtering of Co is attributed to oxidation-induced roughening of Co. A model is proposed for the oxidation-enhanced roughening, which is f urther supported by results obtained from Rutherford backscattering sp ectrometry measurements of oxygen incorporation during O-2(+) bombardm ent and Ar+ sputtering combined with oxygen flooding. (C) 1996 America n Vacuum Society.