An atomistic mechanism for the production of two- and three-dimensional etch hillocks on Si(111) surfaces

The formation of stable and unstable two-dimensional etch hillocks during the NH4F etching of Si(111) surfaces was observed by scanning tunneling microscopy and explained using atomistic, kinetic Monte Carlo simulations. These hillocks are kinetic, self-propagating features on the etching steps. The hillocks have a characteristic shape and size which is governed by the relative rates of site-specific etching. In simulations of highly miscut surfaces, step-step collisions lead to the coalescence and self-organization of 2D (two dimensional) hillocks into 3D (three-dimensional) hillocks. This coalescence was driven by step-step collisions which promote a "step broaching" behavior. As a result, the terrace width distribution of the 3D hillocked surfaces is exponential in form. The formation of 2D and 3D hillocks is controlled by the reactivity of a single minority species on the etching surface. Unlike previous models of hillock formation, chemical heterogeneities, such as contamination or reactant depletion, are not required for hillock formation. (C) 1999 American Institute of Physics. [S0021-9606(99)71439-X].