Crystal orientation and electrolyte dependence for macropore nucleation and stable growth on p-type Si

Macropore formation in moderately doped p-type Si was studied in mostly gal vanostatic experiments (2-10 mA cm(-2)) with various fluoride containing el ectrolytes and substrate orientations [(100), (511), (5 5 12), (111)] from the nucleation phase to the phase of stable pore growth. Macropores on p-ty pe Si always grow anisotropically in [100]- and [113]-directions. The most important parameter of the electrolyte is its ability to supply oxygen and hydrogen. Whereas oxygen is necessary for smoothing the pore tips. hydrogen is the decisive factor for the anisotropic growth and the passivation of m acropore side walls. Based on a better theoretical understanding of the ele ctrode processes in general pore formation in particular, etching condition s could be optimized for the generation of macropores in p-type Si with bet ter aspect ratios, better stability, and smaller diameters than those in n- type Si. (C) 2000 Elsevier Science S.A. All rights reserved.