Reactive magnetron sputtering of molybdenum sulfide thin films: In situ synchrotron x-ray diffraction and transmission electron microscopy study

Abstract

The nucleation and growth of magnetron sputtered MoSx films has been investigated by in situ energy dispersive x-ray diffraction, electron microscopy, and elastic recoil detection analysis. The MoSx films (0.5⩽x⩽2) were prepared by reactive magnetron sputtering from a molybdenum target in an argon–hydrogen sulfide mixture at substrate temperatures up to 700 °C. Using time-resolved in situ x-ray diffraction it was found that the films start to grow with (001) orientation where the van der Waals planes are parallel to the substrate surface. Depending on the deposition conditions a crossover of texture to the (100) orientation occurs, which leads to very rough surfaces. This texture crossover occurs earlier at low substrate temperatures and/or high deposition rates and/or high energetic particle bombardment of the growing films. The MoSx films exhibit significant lattice strain (up to 4%) in the c direction, i.e., perpendicular to the van der Waals planes, which decreases at high substrate temperatures and/or low deposition rates. This lattice expansion is not caused by film stress. Instead, it seems to be connected with disturbed or turbostratic growth due to crystallographic defects induced by energetic bombardment of the films. Also, intercalation of hydrogen could be responsible for lattice expansion, since significant amounts of hydrogen were detected by elastic recoil detection analysis. The sulfur deficiency (up to 20%) found in films that were deposited at temperatures higher than 200 °C could have been initiated by the reducing effect of the atomic hydrogen in our Ar/H2S plasma.