Abstract

The majority of work in the theory of thin film growth has been directed at studying two extreme regimes of the problem. On the one hand, there have been numerous investigations of heteroepitaxial growth of thin films under near-equilibrium conditions. At the other extreme, there has been interest in the morphology of films grown under highly nonequilibrium conditions where the surface mobility of the adatoms is severely limited, resulting in strong shadowing effects and nonlinear columnar growth modes. It has been found, however, that the best conditions for producing x-ray multilayer structures correspond to an intermediate regime, that being far from equilibrium but under sufficiently energetic conditions to promote layer formation. Although of considerable technical importance, there has been little theoretical attention paid to this intermediate regime. Experimentally, this growth regime is realized by bombarding the surface during deposition with a primary or secondary flux of energetic particles, such as is achieved in ion-assisted evaporation or sputtering at low pressures. Under these conditions the deposited layers are usually amorphous or nanocrystalline and the root-mean-square (rms) roughness of the interfaces can be maintained to < 5 Å throughout the multilayer, a condition required for good x-ray optical performance. In this paper we present a simple linearized, stochastic model for the growth of multilayer structures in this moderately energetic regime.

© 1994 Optical Society of America