A study of n-induced residue defect on gate oxide after lithography rework

Abstract

In order to improve the semiconductor device performance, decoupled plasma nitridation (DPN) process was used to form the ultra-thin gate oxide film. But we recently found serious residue defect on gate oxide film if we did lithography rework with chemical method. This defect was like a circular-pattern about several-micron in diameter and hard to be removed. The results also showed that the thickness decrease and photoresist (PR) footing phenomenon would become worse after rework. After performing some experiments, we found that the N element doped in the gate oxide film could be one possible origin for this defect. And a model was proposed to explain the generation mechanism of this residue defect based on above analysis. Finally, an optimized lithography rework method was used to avoid the generation of the defect successfully.