Identification of processing defects by focused ion beam (FIB)induced voltage contrast

摘要

Processing defects related to multiple stacked metal via and/orncontact structures were very difficult to verify to be a high resistancenopen issue or a bridge/leakage short issue. In this paper, FIB passivenvoltage contrast was very successfully implemented in 2 Mb SRAM debug tondifferentiate the two failure mechanisms, high via and/or contactnresistance versus substrate defect-induced junction leakage. It wasndemonstrated in four different cases that passive voltage contrast wasnused to reveal and locate the specific failure site and followed withnpinpoint diagnosis of the abnormality by TEM. It was also known thatnthese defects were invisible to optical microscopy and SEM. The 2Mb SRAMnprocess was a 0.25 μm, three-metal single-poly, 8-inch technology.nShallow trench isolation (STI), self-aligned TiSi₂ siliciden(salicide), and triple stacked W-plug processes were integrated in thenmanufacturing process. The failure mode and failure location werenfirstly identified by a MOSAID tester. Layer-by-layer deprocessing andntop-view SEM examination were used for structural inspection at thenfailure site prior to FIB imaging. As soon as the fault was isolated byna passive voltage contrast comparison study, precision TEM analyses werenutilized as the major tool for structural inspection in both plan-viewnand cross-section