THE PHYSICS OF MACROPORE FORMATION IN LOW DOPED N-TYPE SILICON

Macropore formation in n-type silicon is a self-adjusting phenomenon characterized by a specific current density at the pore tip. At this specific current density, the dissolution reaction changes from the charge-transfer-limited to the mass-transfer-limited regime. The passivation of the pore walls in hydrofluoric acid is caused by a depletion of holes due to the n-type doping of the substrate. Equations based on these findings are presented and allow us to precalculate the dimensions of the pores. The validity of the model and its mathematical description is verified in experiments. Pores of a depth up to the water thickness and aspect ratios of 250 were etched using this method.