AVS 50th International Symposium
    Surface Science Thursday Sessions
       Session SS1-ThM

Paper SS1-ThM5
Effects of Diffusion and Chemical Reactivity on Step Bunching: The Formation of Macrosteps During Etching

Thursday, November 6, 2003, 9:40 am, Room 310

Session: Patterned Growth and Etching of Semiconductors
Presenter: S.P. Garcia, Cornell University
Authors: S.P. Garcia, Cornell University
H. Bao, Cornell University
M.A. Hines, Cornell University
Correspondent: Click to Email
The chemical production of macroscopic features on etched silicon surfaces was investigated using scanning tunneling microscopy and atomistic, kinetic Monte Carlo simulations. Macroscopic features arise when atomic steps bunch together into enormous macrosteps with heights on the order of microns. In aqueous silicon etching, step bunching is driven by spatial inhomogeneities in the etchant, as demonstrated by experiments in which diffusive transport is controlled. Under conditions of step-flow etching, inhomogeneities can be enhanced when random fluctuations bring some steps close together. The inhomogeneities can influence the etch rate locally. For example, etchant depletion can lead to local deceleration of step etching, whereas heat released by the etching reaction can lead to local acceleration. This coupling of chemical reactivity to diffusion-controlled processes may cause closely spaced steps to speed up or slow down. To understand how atomic-scale chemical processes and mesocale diffusion produce step bunching, we have developed a simulation that combines an atomically realistic, two-dimensional model of etching with a continuum model of diffusion. Simulations generated by this technique show that step bunching can give rise to a variety of etch morphologies, all of which are strongly affected by the site specificity of etching and by the effect of diffusion on local reactivity.