Scaling behavior and mechanism of formation of Si O2 thin films grown by plasma-enhanced chemical vapor deposition

Abstract

This paper reports a study of the kinetic roughening of Si O2 thin films prepared by plasma-enhanced chemical vapor deposition (PECVD). Tetramethylsilane has been used as a precursor, and the synthesis has been carried out under remote and in-plasma configurations. The analysis of surface topography of the films by atomic force microscopy shows an anomalous scaling behavior that cannot be represented by the Family-Vicsec scaling relation of dynamic scaling theory. The application of different methods for obtaining the roughness exponent α yields different values of this exponent (α=0.7 for the height-height correlation function and α=1.3 for the power spectral density function for long deposition times) in all experimental conditions. Moreover, a strong variation of the α exponent with deposition time has been determined for the samples grown in remote mode. This correlates with the presence of a crossover region of the growth exponent β, which varies from a first value of 1.3 for low deposition times to another of 0.3 for longer deposition times. Such a variation is not found for the samples grown in the plasma, characterized by a β value of 0.28. The results obtained can be explained by the combined effect in the growth process of a low diffusivity of the physisorbed species along with the existence of nonlocal interactions due to shadowing effects. These two assumptions are in agreement with the empirical knowledge existing about the kinetics of the growth of Si O2 thin films by PECVD and establish a link between the scaling properties of the films with the surface chemistry during the film growth.