Mask qualification of a shifted gate contact issue by physical e-beam inspection and high landing energy SEM review : DI: Defect Inspection and Reduction

Photomask issues can result in shifted pattern defects printed on the wafer. In the case of sub-1x nm nodes, these pattern defects of interest (DOI) can be difficult for conventional optical inspections to detect. In this paper we present a case study of a new mask qualification for a MOL gate open (GO) contact mask layer. The new mask was introduced to compensate for a known open between trench silicide (TS) contact and GO. During qualification, a shift in the GO overlay was seen on one section of the wafer and suspected to be the cause of a TS-gate short. A Design of Experiments (DOE) was created to investigate if the issue was solely mask related or if it could be mitigated during processing (litho/etch). Physical mode e-beam inspection was used to monitor the DOE wafers, however the resolution of the e-beam inspection tool was not sufficient to conclusively classify the defects observed. A high resolution, high landing energy SEM defect review was introduced post e-beam inspection to better monitor the splits running as part of the DOE.