Abstract

Poly/metal stacked capacitors present challenges in terms of capacitor access and defect localization. As for defect localization, liquid crystal or thermal localization (also OBIRCH/TIVA) and passive voltage contrast (PVC) are used. PVC was found to be effective in terms of finding the bad stacked capacitor and a bad capacitor within the stack. This paper highlights brief process steps in 3-layer polysilicon/metal stacked capacitors. It discusses FA on stacked capacitors, providing information on fault isolation and capacitor access. It presents a case study on differentiating defective capacitors which failing due to vertical shorting. Internal probing between the capacitors within a stack allowed the differentiation between capacitor leakage and capacitor-capacitor shorting. For capacitor leakage, the defect can be identified by parallel lapping to remove the upper capacitor plate. For capacitor-capacitor short, if there is no visual defect seen, Pt chemical etch can be applied for PVC inspection.

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