Variable roughness development in statically deposited SiO2 thin films: a spatially resolved surface morphology analysis

For the first time a systematic analysis of the growth front evolution of statically deposited silica films in an atmospheric pressure-plasma enhanced chemical vapour deposition (AP-PECVD) reactor was carried out. The growth front evolution was studied as a function of time and position in the reactor. Focussed beam spectroscopic ellipsometry was used to assess the local film growth rate and atomic force microscopy (AFM) to analyse the surface roughness development. Spatially resolved AFM analysis showed a strong dependence of the rms roughness on the position, and consequently on the thickness and local deposition rate (LDR), in the reactor. Time resolved surface morphology analysis at two specific positions at high and low LDR indicated different growth exponents beta = 0.33 and beta = 0.11, respectively. From the analysis of the static roughness development in the AP-PECVD reactor certain limitations on the deposition time and the maximum LDR for dynamic or web rolled deposition conditions have been elucidated. Moreover, the system is characterized by a set of roughness exponents alpha(loc) = 0.9, alpha(s) = 1.6 and global roughness exponent alpha = 2.3. The different values of alpha indicate an anomalous scaling behaviour of the system whereas different growth exponents beta suggest a breakdown of the anti-shadowing mechanism.