The influence of target history and deposition geometry on RF magnetron sputtered LiCoO 2 thin films

Abstract

Thin LiCoO 2 films, typically used as cathode layers in thin-film solid-state batteries were RF magnetron sputter-deposited using targets that were either freshly produced, or had seen over 100 h of sputter erosion. The substrates, as received (1 0 0) silicon wafers, were either held stationary or were rocked back and forth under the target. Film texturing, grain size, composition, and thickness were examined using X-ray diffraction (synchrotron light source), inductively coupled plasma-mass spectroscopy (ICP-MS), Rutherfords backscattering spectrometry (RBS) and stylus profilometry. Films that were sputtered from the heavily used target were, on average, lithium-deficient, while films deposited using the fresh target were slightly lithium-rich. Film thickness, composition, and type of crystallographic texture varied radially, in the plane of the film in the stationary substrate case, in a pattern that reflected the sputter target erosion ring. For films deposited with substrate motion, an ovular area was defined on the film in which composition, and texturing were essentially uniform. The Li/Co ratio in the target and subsequent films was found to decrease over many hours of sputtering. Possible causes for the compositional and orientational variations observed are discussed.