Highly conformal film growth by chemical vapor deposition. I. A conformal zone diagram based on kinetics

Abstract

The authors present a unified description of conformal film growth in recessed features by low pressure chemical vapor deposition. Experimental data on step coverage and growth rate are interpreted in terms of a kinetic model for the elementary surface processes. This model is combined with the continuity equation for gas transport and consumption to predict the values of the precursor pressure and substrate temperature (p,T) that are necessary for conformal coverage to occur for a given precursor. They introduce a conformal zone diagram that considers the gas phase limitations (maximum precursor pressure and onset of secondary reactions), the surface limitations (minimum reaction temperature, precursor adsorption and desorption rates, and film growth rate), and the aspect ratio of the feature to be coated; the allowed intersection between the resulting boundaries defines the (p,T) zone for conformal growth. Sufficient precursor pressure is identified as a major requirement for conformal film growth, one that is not met by many commercially available molecules. Finally, they derive an approximate analytical solution to the inverse problem: what are the experimental conditions necessary to afford a desired degree of step coverage on a given aspect ratio feature at a desired growth rate. The solution depends on a set of rate constants in the kinetic model that can be extracted from measurements of the film growth rate as a function of precursor pressure and substrate temperature on trench or planar substrates.