Shape modifications of self-organised colloidal silica nanomasks on silicon

Regular stencil-type nanomasks with mask openings in the 60 nm range were fabricated on Si(1 0 0) by self-assembly from a colloidal suspension of silica spheres in water. Masks were irradiated with high doses of keV C+ ions at different implantation conditions. SEM and cross-sectional TEM investigations show strong changes of the mask geometry due to both a collective motion of spheres and the formation of pronounced menisci at the contact points of spheres. Results are interpreted in terms of sputter surface erosion superimposed with ion beam induced viscous flow, acting towards a surface minimisation