Gravity-related transport process in off-axis sputtering deposition

In the reactive off-axis sputtering deposition of ZnO films, three transpor t regimes from a ballistic motion to a diffusive drift of the ejected speci es were observed when the growth pressures were varied from 5 to 150 mTorr, The distribution of the film thickness at different substrate locations wa s measured, When the substrate surface was parallel to the gravity vector, a film thickness variation along the direction of gravity was detected in t he region of diffusive transport deposition. This phenomenon depends strong ly on the growth pressures while only slightly on the growth temperatures. Based on experimental results, a gravity-related motion of the sputtered sp ecies is proposed in film growth under relative low growth pressures. (C) 2 001 Elsevier Science B.V. All rights reserved.