The influence of oxidizing agents on etching and passivation of silicon in KOH solution

Abstract

The effect of oxidizing agents (MnO 4 − and CrO 4 2−) on the electrochemistry, etching kinetics and etching morphology of p-type silicon in KOH solution has been studied. Electrochemical results show that reduction of MnO 4 − occurs via hole injection into the valence band of oxide-covered silicon, while the rate of cathodic reduction of CrO 4 2− is very low. The current density measured with MnO 4 − at negative potential drops to a low value when the surface oxide is removed and chemical etching starts. It is suggested that during etching, a surface intermediate is formed which can interact chemically with the oxidizing agents. This is confirmed by optical absorption measurements. At potentials positive with respect to the open circuit potential both oxidizing agents modify the formation of surface oxide. In addition, both oxidizing agents influence the surface morphology by ‘preventing’ pyramid formation. These results are discussed in terms of a model previously suggested for chemical etching of silicon in alkaline solutions.