Ellipsometric and microwave reflectivity studies of current oscillations during anodic dissolution of p-Si in fluoride solutions

Periodic current oscillations during anodic dissolution of monocrystalline p-Si(100) in buffered ammonium fluoride solutions (0.1 mol dm(-3) fluoride, pH 4.5) were investigated using a flow cell in order to eliminate mass tra nsport limitations. The flow cell was designed to permit simultaneous in-si tu ellipsometry, impedance and potential modulated microwave reflectivity m easurements. Analysis of the ellipsometric response showed that the current oscillations are accompanied by a synchronous variation of the overall oxi de thickness with an amplitude of 4.5 +/- 0.1 nn. Analysis of the relations hip between the total oxide thickness and the current during the oscillatio n cycle shows that to a first approximation the rate of chemical dissolutio n of anodic oxide remains constant. Oscillations of the electrode admittanc e and potential modulated microwave reflectivity were also measured. The im aginary component of the admittance is related to the oscillation in thickn ess of a narrow inner region of 'dry' oxide and to changes in the accumulat ion capacitance. The oscillation in the potential modulated microwave refle ctivity is interpreted in terms of the changes in the density of holes accu mulated at the p-Si \ SiO2 interface. (C) 2001 Elsevier Science B.V. All ri ghts reserved.