Modelling of silica film growth by chemical vapour deposition : Influence of the interface properties

Abstract
We have studied the main physical mechanisms involved in the growth of Chemical Vapor Deposition (CVD) systems. We have characterized W films by Scanning Tunneling Microscopy, and SiO₂ films by Atomic Force Microscopy (AFM) and Infrared and Raman spectroscopies. Tungsten CVD films display an unstable growth mode since the surface roughness increases continuously with deposition time. In order to assess the physical origin of the instability we have grown silica films in a low-pressure CVD reactor from SiH₄/O₂ mixtures at 0.3 nm/s at low (611 K) and high (723 K) temperatures. Silica films deposited at high temperature are rougher than those grown at low temperature. Moreover, they become asymptotically stable in contrast to those deposited at low temperature which are unstable. These different behaviors are explained within the framework of the dynamic scaling theory by the interplay for each growth condition between surface diffusion relaxation processes, shadowing effects, lateral growth, short-range memory effects and the relative concentration of active sites, mainly SiH and strained siloxane groups, and passive sites. A continuum growth equation taking into account these effects is proposed to explain the observed growth behavior for both sets of films. Computer simulations of this equation reproduce the experimental behavior.