Influence of the initial electrochemical potential on the growth mechanism and properties of anodic oxides on (100) Si

The effect of electrode area and anodic growth mode on the thickness and properties of anodic oxides on (100) Si were investigated. The oxide thickness depends strongly on the electrode area for the growth mode where the electrode was in contact with the electrolyte before the anodic potential was applied as a step to 8 V-SCE, reaching a maximum for microelectrodes of similar to 10(-3) cm(2) area. In contrast, if the potential was deliberately ramped at 100 mV/s from the open-circuit potential to the final growth potential, the oxide thickness was independent of sample size. Thinner oxides with superior electrical response (as evaluated by ac impedance spectroscopy) were obtained using a ramped mode of growth. In order to fabricate macroelectrodes with the properties of microelectrodes, the potentiostat was stepped to the desired potential and then the sample was gradually manually lowered into the electrolyte. It was concluded that the mechanism by which the first few layers of oxide on (100) Si are formed is of crucial importance in establishing the mechanism of oxide growth for the entire oxide film.