Controlling macropore formation in patterned n-type silicon: Existence of a pitch-dependent etching current density lower bound

Experimental results on back-side illumination electrochemical etching of patterned (hole square-lattices with pitch p from 2 to 50 μm) n-type silicon substrates in HF-based electrolytes are reported. Experiments reveal the existence of a threshold current density Jpitch, which is strictly correlated to the pattern pitch, above which pore formation can be finely controlled beyond commonly accepted state-of-the-art rules. For instance, using the same silicon substrate, pore array with density D spanning over two orders of magnitude (from 0.0025 μm− 2 up to of 0.25 μm− 2) can be etched above a minimum porosity Pmin, and, in turn, a minimum pore diameter dmin, which depends on the pattern pitch. Etching current densities below such a critical value give rise to uncontrolled pore growth. The occurrence of the threshold current density Jpitch is interpreted in terms of current burst model.