Electron Beam Inspection in Physical Mode: Overpolish Monitoring of RMG CMP

For a recent replacement metal gate (RMG) FINFET technology using an SOI substrate, an inhomogeneous polish post Tungsten fill of the RMG was discovered. For particular wide-gate structures, the Tungsten polish within the reticle field and across the wafer varied widely despite being in control using the established kerf metrology structure. This was discovered after the technology had been ramped to production. An in-line monitor was needed but could not be dependent on kerf structures to monitor within-reticle variation, since these monitored only narrow-gate within-wafer and wafer-to-wafer variation. So, a within reticle inspection using Electron Beam Inspection (EBI) was used to characterize the within-reticle and within-wafer variation of the wide-gate structures.