Nano pyramid array on Si by concurrent growth of parallel and perpendicular spatial wave and local angle-dependent sputtering

Abstract

I report simultaneous growth of the Si nano-structures with wave vectors parallel and perpendicular to the projection of obliquely bombarding O2+ ions. At the initial stage of growth, finite length parallel and long length perpendicular nano-patterns are observed. Following the linear model of ion induced nanopatterning, the fast growth of amplitude of the developed structures as a function of ion fluence is observed. However, for further ion bombardment, change of local ion incidence angle leads to slope dependent nonlinear effects. At very high ion fluence when the amplitude is comparable to the wavelength of the structures, local angle-dependent sputtering and ion shadowing effect transforms the sinusoidal ripple to a triangular terraced structure. For further ion bombardment, the correlation length along ion beam direction increases faster than the parallel direction, which results in rotation of the initial nano-pattern and formation of the nano-pyramidal array structure. While nonlinear continuum Kuramoto-Sivashinsky equation predicts a disordered structure at such high fluence, we find pyramidal ordered structure formation by oxygen ion bombardment. Such nano-pyramidal structures could be used as a template for mask and resistless large area nano-dot lithography.