Non-lithographic method of forming ordered arrays of silicon pillars and macropores

Micrometre-scale Si pillars are formed by chemically enhanced laser ablation using nanosecond excimer laser irradiation of a Si single crystal in the presence of SF6. We demonstrate the importance of precursor holes in determining the positioning of the pillars and show that we can control the initiation of precursor holes by ruling a grating into the Si substrate prior to irradiation. A rule defines an edge from which the laser light diffracts. Near-field amplification of the laser intensity enhances the formation of the precursor holes and aligns them parallel to the rule. The pillars can be thinned and eventually removed by wet chemical etching in aqueous KOH, resulting first in ordered arrays of extremely high aspect ratio pillars (e.g. tens of micrometres in length, with similar to 10 nm tips) and then macropores. The shape of the macropore is determined by crystallography and the anisotropy of the wet etchant.