Effect of Wet Etched Thickness and Reoxidation on Reliability of Dual Gate Oxide for Sub-Quarter Micron Complementary Metal-Oxide-Semiconductor Devices

We investigated the effect of wet etched thickness and reoxidation on the reliability of dual gate oxide. The dual gate oxide was formed by a two-step thermal oxidation and wet etching process, where a photoresist was used to mask the thick gate oxide. The metal contamination caused by the photoresist was completely removed after the wet etching process. It was found that the wet etching significantly affected the gate oxide reliability and that the reoxidation was useful for forming a reliable oxide. The degradation of the thick gate oxide was due to an increase in oxide surface microroughness and thinning at the edges induced by a long wet etching time. The oxide reliability was significantly enhanced by improving the surface roughness when the oxide films were slightly etched during the wet etching process, and resulted in a deep subquarter-micron complementary metal-oxide-semiconductor (CMOS) transistor without thinning at the edges.