Ar1000 cluster ion beam was used to fabricate irregular structures of a micrometer scale on the surface of pressed Si powder of 60 nm nanoparticles (NPs). The average density of the target material played an important role in the surface features formation. The samples with lower average density, i.e. with larger distance between adjacent NPs demonstrated more developed surface morphology, which implied an importance of the degree of freedom of NP and its beam induced mobility in formation of the surface features. At higher average density a process of particle erosion was accompanied by the debris formation, which filled the gaps between the NPs, blocked the particle mobility, and, eventually, resulted in conventional smoothing effect.