Investigations on Microstructure, Surface Topography, and Growth Process of Sputtered Molybdenum Showing Texture Turnover

The microstructure and surface topography of molybdenum films prepared by magnetron sputtering at a low rate of about 1 Å/s was investigated by electron microscopy (SEM and TEM) and atomic force microscopy (AFM). Films of 3 μm thickness exhibit a columnar microstructure visible by TEM and SEM. Low pressure deposited films consist of densely packed columns, whereas high pressure films consist of free standing columns with inter-columnar spacing of the order of 100 Å. In the early state of growth (23 nm film thickness) the development of dome-like structures on the surface of the dense films is observed by AFM. These structures, whose number (and to a lesser extent size) increases with film thickness, form the top of the microcolumns. No evidence for a relationship between microstructure and the evolution of a special kind of texture has been found. An estimate is given for the energy flux from the target and for the energy loss of the sputter-ejected Mo and reflected Ar atoms in dependence on the traveled distance–pressure product. Reflected argon neutrals give the far superior contribution (80 to 90%) to the energy impinging the growing film. These calculations explain the strong influence of the argon pressure on the density and microstructure of the films. The pressure-dependent deposition rate is well described by an existing model. A different meaning of the so-called “thermalization distance” being a key parameter of the model is suggested. The appearance of the texture turnover in the Mo films is explained by the minimization on the film surface energy under particle bombardment.