Porous silicon nanocolumn formation is the result of the merging of nearest-neighbor nanopores. In this paper we describe isolated submicrometer filaments formed by silicon anodization in HF solutions. The merging of nearest-neighbor pores may result in the formation of isolated submicrometer silicon filaments. The filament formation is explained by a model which takes into account filament wall layer passivation by hydrogen atoms. The formation of one isolated wire structure is a consequence of the pore diameter enlargement resulting from the available area decrease with etching time.