Formation of ultra-thin continuous Pt and Al films by RF sputtering

Abstract Platinum and Al films deposited on a glass substrate by radio frequency (RF) sputtering are investigated for transitions in film continuity, from discontinuous to continuous, through the characterization of the electrical properties and microstructure of films with thicknesses of 0.4–600 nm. In order to clarify the influence of sputtering conditions on the process of deposition, the following conditions are varied: target-substrate distance; substrate temperature and RF power. Using a criterion of the negative temperature coefficient of resistance (TCR), which is an electrical property of discontinuous films, the minimum thickness required for the film continuity is determined for each sputtering condition. In the case of Pt film deposition, the minimum thickness for the continuity is restricted to within a range of 0.4–1.0 nm, irrespective of sputtering conditions. This may be related to the nature of the Pt film, which tends to grow in a relatively two-dimensional mode. In contrast, the minimum thickness of the Al film is greater than that of the Pt film and ranges from 1 to 9 nm depending on the sputtering conditions. From the results of atomic force microscopy (AFM) observations, the grain-size of the Al film deposited at 100°C is found to be larger than that for a film deposited at room temperature. The difference between the minimum thicknesses for Pt and Al film, continuity, and the effect of sputtering conditions are discussed based on the interaction between the metal atoms and the glass substrate and on the melting points of the materials.