Metal Trench Critical Dimension and Overlay Minor Variation Monitoring Method with Voltage Contrast Inspection

Abstract

The investigation aims at the metal trench critical dimension (CD) and overlay variation monitoring methodology with voltage-contrast (VC) inspection. The VC inspection with negative charging mode was performed to detect metal trench CD and overlay variation issue, at NDC film deposition layer post second metal layer chemical and mechanical polish. Dark VC (DVC) defects were found at extreme wafer edge, which would cause end of line (EOL) yield loss by data retention soft bin failure. DVC defects were identified by inline SEM review results with high voltage and PFA analysis results. It was demonstrated that the defects were induced by metal trench CD and overlay variation. Furthermore, the defects impacted factors, including uniformity of thin film deposition and chemical and mechanical polish (CMP), the etching rate performance of all in one etch process, and even the e-chuck accumulated contamination of lithography, were also investigated. By increasing the relative process tools' offline monitor frequency and optimizing the prevent maintenance method of lithography tool, defects were fixed and trend low. The study here extended the usage of VC inspection to detect CD and overlay minor variation.