Abstract

Thin films prepared by vapor deposition methods have a range of applications which demand control over the microstructural, electronic, and/or optical properties. Empirical classification schemes for the morphology of vapor-deposited thin films have been developed over the years in attempts to provide physical insights into the relationships between preparation parameters and resulting film properties.^1-3 A variety of computational techniques have also been applied to model film growth and to elucidate the physical principles that account for the observed morphological development. These include continuum,⁴ molecular dynamics,⁵ Monte Carlo,⁶ and ballistic aggregation⁷ techniques. In continuum models of film growth, many authors have studied the stability of one-dimensional surface profiles in response to sinusoidal perturbations of wavelength, λ_r.^4,8-10 Effects of finite atomic size⁴ and shadowing by asperities⁸ have been proposed to enhance the perturbations, whereas adatom surface diffusion damps them. A smooth profile can be regained for λ_r<λ_o, where λ_o is the adatom diffusion length. When λ_r>λ_o a modulated profile develops that appears analogous to experimentally-observable columnar morphology. In the experimental situation, clustering associated with initial nucleation is the dominant surface perturbation for thin film deposition on dissimilar substrates. It is technologically important to determine and control the evolution of surface morphology with subsequent film growth. Of direct importance here is the ability to fabricate multilayered structures with atomically smooth interfaces.

© 1992 Optical Society of America