Electrochemical macroporous silicon etching with current compensation

The depth-dependent changes of macroporous etching in aqueous hydrofluoric (HF) solutions are addressed. Macroporous etching of n-type silicon in HF acid produces high aspect ratio structures. However, an irregular etch profile can emerge as the pore depth increases, in particular branched regions emerging from vertical pores. The root cause of this non-ideal etch profile is investigated, focusing on the dark current component of electrochemical etching. The dark current during etch progression was simulated, and it was found that increased dark current resulted from increasing the interfacial contact between the electrolyte and silicon surface. A software-mediated photocurrent compensation method is developed that periodically samples the dark current component of the etch and adjusts the overall etch current, achieving stable pore formation.