Microstructure control of magnetron sputtered nanocomposite films: from dynamic roughening to dynamic smoothening: Invited talk

Dynamic roughening is a common phenomenon observed in plasma processing of materials, including both film deposition and plasma etching. That is to say, the roughness of a growing/etching interface becomes higher and higher with the processing time or the film thickness/etching depth. In film growth, the competition between interface roughening and smoothening essentially determines the nano-/microstructure and consequently the properties of a deposited film. This lecture presents several new findings on the breakdown of dynamic roughening in thin film growth. With increasing energy flux of concurrent ion impingement during pulsed DC magnetron (reactively) sputtering, a transition from dynamic roughening to dynamic smoothening is observed in the growth behavior of TiC/a-C(:H) nanocomposite films. The nanocomposite films show a negative growth exponent and ultra-smoothness (RMS roughness ~0.2 nm at film thickness of 1.5 µm). Based on high resolution cross-sectional transmission electron microscopy observations, an amorphous front layer ~2 nm thick covers the nanocomposite film during growth and suppresses the influence of nanocrystallites on the roughness evolution of the nanocomposite films, which is a solid experimental proof of the impact-induced downhill flow model [1] and subplantation model [2]. We were able to predict the evolution of surface roughness based on a linear equation of surface growth which contains two diffusivity parameters that control the atomic mobility along the growing outer surface. The model is in good agreement with atomic force microscopy measurements of roughness evolution [3-6]. The result indicates a general solution of microstructure control in the deposition of thin films with (reactively) sputtering.