The influence of oxidizing agents on etching and passivation of silicon inKOH solution

The effect of oxidizing agents (MnO4- and CrO42-) on the electrochemistry, etching kinetics and etching morphology of p-type silicon in KOH solution h as been studied. Electrochemical results show that reduction of MnO4- occur s via hole injection into the valence band of oxide-covered silicon, while the rate of cathodic reduction of CrO42- is very low. The current density m easured with MnO4- at negative potential drops to a low value when the surf ace oxide is removed and chemical etching starts. It is suggested that duri ng etching, a surface intermediate is formed which can interact chemically with the oxidizing agents. This is confirmed by optical absorption measurem ents. At potentials positive with respect to the open circuit potential bot h oxidizing agents modify the formation of sur face oxide. In addition, bot h oxidizing agents influence the surface morphology by 'preventing' pyramid formation. These results are discussed in terms of a model previously sugg ested for chemical etching of silicon in alkaline solutions. (C) 2000 Elsev ier Science Ltd. All rights reserved.