Surface diffusion is one mechanism by which surfaces roughen during high temperature processing of semiconductor materials. Here, the free energy of an elastic crystal is assumed to be the sum of the elastic strain energy and the surface energy, and these two quantities determine the chemical potential for mass transport by surface diffusion. A gradient in chemical potential along the surface provides the driving force for diffusive mass transport which tends to lower the overall free energy of the system. These concepts are applied in considering the transient evolution of waviness of a nearly flat surface in a highly strained elastic solid. In particular, the three-dimensional problem of growth or decay of an initial slight depression in a nominally flat surface is studied by solving the mass transport equation. The process can be described in considerable detail by adhering to an assumption that the amplitude of surface fluctuations is small. [References: 19]
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