Modeling of Thermodynamic and Transport Phenomena in CVD Processes for Nano-Scale Applications

Abstract

To illustrate the concept of the inter-dependence between multi-component chemical reactions and transport phenomena, a theoretical investigation of a halogen-cycle tungsten filament incandescent lamp was undertaken based on local thermochemical equilibrium (LTCE) coupled with Fickian and thermal (Soret) transport of species. Deposition of tungsten on the bulb wall leads to 'bulb blackening', resulting in reduction in the luminous efficiency of the lamp, a problem typically combated by addition of small amounts of halogen and oxygen. Utilizing temperature-dependent Soret diffusion factors, elemental fluxes were analyzed. Zero element flux (ZEF) maps were generated based on temperature-dependent Soret diffusion factors. The element solubilities and the filament-to-wall element segregation were found to be strongly dependent on the bulb wall temperature, oxygen fill pressure and Soret diffusion factors. Transport-affected shifts in element solubilities from pure LTCE condition were studied. Implications of this study for the modelling of commercial CVD processes are highlighted.