FORMATION OF NODULAR DEFECTS AS REVEALED BY SIMULATION OF A MODIFIED BALLISTIC MODEL OF DEPOSITIONAL GROWTH

Nodular defects appear frequently in deposited films and coatings, esp ecially in those deposited under higher deposition rate and lower subs trate temperature. In order to understand the mechanism and to predict the effects of process parameters, a modified two-dimensional ballist ic model of deposition growth has been developed and programmed for co mputer simulation. In this model, both scattering of depositing partic les and surface diffusion of deposited particles are allowed. Simulate d experiments have been carried out with respect to the effects of dep osition rate, surface diffusivity of deposited particles, degree of sc attering of depositing particles and presence of substrate asperities. Morphological features of the nodular defects are reproduced by the s imulation. The results show that higher deposition rate, lower surface diffusivity of deposit and higher degree of scattering of depositing particles favour formation of nodular defects. Asperities on substrate are found usually responsible for formation of nodular defects; howev er, under favourable conditions, nodular defects can form without pres ence of any substrate asperity. (C) 1998 Chapman & Hall.