DEVELOPMENT, PRELIMINARY TESTING AND FUTURE APPLICATIONS OF A RATIONAL CORRELATION FOR THE GRAIN DENSITIES OF VAPOR-DEPOSITED MATERIALS

It is conjectured and found in this work that the grain densities (sui tably normalized) of vapour-deposited solid materials depend principal ly on competition between the successful arrival rate of their reagent molecules and the surface diffusion rate of admolecules on their grow ing surfaces. The ratio of these two rates defines an important dimens ionless Damkohler number, called here the ''burial'' parameter, beta. Available grain density data for seven vapour deposited materials [sil icon (Si), gallium arsenide (GaAs), silicon carbide (SiC), silicon nit ride (Si3N4), titanium oxide (TiO2), boron nitride (BN) and graphite ( C)] are used to establish and test the ''universality'' of the propose d normalized grain density versus burial parameter correlation. As ant icipated, these data show that the normalized grain densities of these materials increase with their corresponding burial parameters. Moreov er, for estimated burial parameters much less than unity, the deposits formed are indeed reported to be amorphous, while the deposits are ob served to be crystalline under conditions for which beta much greater than 1 is estimated. As the burial parameter decreases, the reported g rain densities of turbostratic, ''layered'', materials are found to de crease more gradually than for materials with no turbostratic structur e. While the present implementation of this basic hypothesis cannot be regarded as ''complete'', it is argued that a rationally-based, reaso nably ''universal'' vapour deposit density correlation of this general form can be quite useful in making rational predictions of deposit qu ality. Moreover, it appears that this path to such mechanistically pla usible correlations, which, using available experimental data, can be implemented/tested even in the absence of a ''complete'' theory, can b e broadened to include other important deposit characteristics via the introduced of additional characteristic time ratios.