Ultra-thin gate oxides prepared by alternating current anodization of silicon followed by rapid thermal anneal

An advanced method to prepare ultra-thin (<30 Å) anodic oxides is proposed. The voltage polarity applied to the silicon wafer is switched between a positive and a negative value periodically during anodic oxidation. It is belived that the more effective negative charges causing a barrier height for electron tunneling are generated in the oxide when a negative bias is applied to the wafer. In addition, the compensation effect of anion redistribution during voltage polarity switching contributes to eliminating the number of leakage paths in the oxide. Therefore, oxides prepared by this technique and followed by rapid thermal anneal exhibit lower leakage current and higher breakdown endurance than the conventional constant-voltage anodic oxides and the rapid thermal oxides do. In addition, various switching conditions are investigated to examine the effects of negative bias and the switching frequency upon the characteristics of oxides so that a better growth condition can be found to grow high-qua lity gate oxides. © 2001 Elsevier Science Ltd. All rights reserved.