Etch chemistry effect study for poly stringer defect on high topology PIP process

This paper shows the study of the effect of etch chemistry towards poly stringer defect found in Polysilicon-Insulator-Polysilicon (PIP) processes. This defect was detected after Poly2 etching process and further enhanced after Sidewall (SW) etching process. The formation of stringer defect was caused by the topology of the double poly PIP capacitor structure and insufficient process recipe margin. Therefore, the challenge was to eliminate the defect by developing an optimal Poly2 etching recipe. The weakness of the existing process had been identified and a design of experiment (DOE) was carried out to identify the optimal condition for defect removal as well as to maintain a good polysilicon gate profile. Through the full factorial DOE, it was found that the gas combination of HBr and Cl₂ in an optimum pressure condition was a major factor and a concern in this case. The poly stringer defect was then eliminated completely with the new Poly2 etching recipe.