Repair of thin thermally grown silicon dioxide by anodic oxidation

Anodic oxidation in 0.1 M HCl followed by a post-rapid thermal annealing process has been used to repair defects existing in thin thermally grown oxide layers (3 and 6 nm) on a p-type silicon substrate. The improved quality of the insulator layer is particularly useful for applications that require large gate areas in Metal-Insulator-Semiconductor (MIS) or Electrolyte-Insulator-Semiconductor (EIS) devices such as Light-Addressable Potentiometric Sensors (LAPS) and Scanning Photo-induced Impedance Microscopy (SPIM). Different methods have been used to characterize the oxide. High-frequency capacitance-voltage curves and ac impedance spectra showed that there was no significant change of the oxide thickness after repair, and the number of the interface states of the oxide was increased for both types of samples. Ramped voltage stress (RVS) measurements of Metal-Oxide-Semiconductor (MOS) structures with gate electrodes 2 mm in diameter showed leakage currents of 0.75 nA cm⁻² for the repaired and annealed 3 nm thick oxide and 1.31 nA cm⁻² for the repaired and annealed 6 nm thick oxide at accumulation voltage. XPS measurements confirmed that there was no change of the oxide thickness and no contamination with other ionic species after repair. AFM results showed a good agreement with the other characterization methods.