ANODIC SILICON DISSOLUTION IN ACIDIC FLUORIDE ELECTROLYTE - A PROBE BEAM DEFLECTION INVESTIGATION

Si anodic dissolution in acidic fluoride medium has been investigated in different regimes (porous silicon formation, electropolishing under stationary and oscillating current) by probe beam deflection (PBD) or the ''mirage'' technique. Evolution of deflection signal allows monit oring of dissolution processes both under polarization and at open cir cuit, providing for example an estimate of the oxide etch-back times d uring open circuit corrosion. The time evolution of deflection signal during current oscillations reveals components resulting from electroc hemical film formation and chemical dissolution. The PBD technique sho ws larger etching rates for the less passivating film (low potential) and smaller etching rates for the better passivating film (high potent ial). Our observations are compared with those obtained from spectrosc opic investigations of the oxide layer and their relevance for models of oxide formation, and dissolution is here discussed.