Roughening in Plasma Etch Fronts of Si(100)

A novel etch front roughening phenomenon has been observed in the plasma etching of Si(100). The morphology exhibits a network structure with holes which coarsen with etech time, and a wavelength selection with a characteristic spatial frequency decreasing with time. The average local slope is invariant while the vertical roughness grows as w~t^β, with β0ex0ex=0ex0ex0.91±0.03. We suggest a nonlocal Langevin equation based on the redistribution of the reactant gas flux by local morphological features. Numerical calculations give results consistent with our experiments.