N-Si(100)在氯化膽鹼有機溶液中之電化學蝕刻行為

Abstract

The aim of this work was to prepare porous silicon (PS) by electrochemical etching of ntype silicon (100) in a choline chloride/ethylene glycol and dimethyl sulfoxide ionic liquid system containing NH4F without the aid of illumination. DC potentiodynamic polarization analyses were conducted, and the anodic polarization curves were analyzed in search of optimal potentials for preparing PS potentiostatically. It was found that the etching rate of the n-type silicon increased to 1.2 μm/h with increasing potential, and the depth of the pores could reach 29 μm. The optimal bias to obtain PS with a uniform distribution of pores that had the greatest depth was 9 V. The flat-band voltage of the system could be evaluated with the Mott-Schottky model. The flat-band voltage was found to be more positive in the choline chloride/ethylene glycol system than that in the aqueous solution. A higher flat-band voltage led to a greater bending in interfacial energy bands between the silicon and the electrolyte. The greater bending in the energy bands might have created a higher extent of charge separation, driven the electron holes to the silicon surface, and increased the thickness of the space charge. As a result, the etching rate of the n-type Si(100) was higher in the ionic liquid system than that in the aqueous system, as ammonium fluoride was used as the etchant instead of hydrogen fluoride.