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 urrent density, the dissolution reaction changes from the charge-transfer-limited o the mass-transfer-limited r gime. 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 wafer thickness and aspect ratios f 250 were etched using this method. Pore formation is a well-known feature of many metal and semiconductor electrodes under anodic conditions in different electrolytes. Common products, for example alu-minum capacitors, have been manufactured for decades using electrochemical pore formation to enhance the per-formance of the devices. Nevertheless in most cases the physics of pore formation is poorly understood. The formation of porous layers on silicon electrodes an