Macropore formation on p-type Si in fluoride containing organic electrolytes

Electrochemical oxidation of p-silicon of different crystal orientation and doping density has been investigated in fluoride containing nonaqueous sol ution of acetonitrile and dimethylformamide. The formation of a macroporous layer with macropore diameter and length in the micron range in acetonitri le is observed only if the resistivity of the silicon exceeds similar to 10 Ohm.cm for both (100) and (111) crystal orientations, whereas in dimethylf ormamide the macroporous layer can be formed on similar to 1 Ohm.cm substra tes. The influence of water concentration in the electrolyte on the morphol ogy of the macropores has also been studied. The resistivity of the used el ectrolyte solutions was measured and compared to that of silicon. Formation of a macroporous layer is explained by the effective collection of holes a t the tip of the growing macropores. (C) 1998 The Electrochemical Society, Inc. S1099-0062(98)01-066-9.