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

Macropore formation in n-type silicon is a self-adjusting phenomenon c haracterized by a specific current density at the pore tip. At this sp ecific current density, the dissolution reaction changes from the char ge-transfer-limited to the mass-transfer-limited regime. The passivati on 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 th ese findings are presented and allow us to precalculate the dimensions of the pores. The validity of the model and its mathematical descript ion is verified in experiments. Pores of a depth up to the water thick ness and aspect ratios of 250 were etched using this method.