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

We have studied the main physical mechanisms involved in the growth of Chem ical Vapor Deposition (CVD) systems. We have characterized W films by Scann ing Tunneling Microscopy, and SiO2 films by Atomic Force Microscopy (AFM) a nd Infrared and Raman spectroscopies. Tungsten CVD films display an unstabl e growth mode since the surface roughness increases continuously with depos ition time. In order to assess the physical origin of the instability we ha ve grown silica films in a low-pressure CVD reactor from SiH4/O-2 mixtures at 0.3 nm/s at low (611 K) and high (723 K) temperatures. Silica films depo sited 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 explai ned within the framework of the dynamic scaling theory by the interplay for each growth condition between surface diffusion relaxation processes, shad owing 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 effec ts is proposed to explain the observed growth behavior for both sets of fil ms. Computer simulations of this equation reproduce the experimental behavi or.