Simplified model for absorber feature transmissions on EUV masks

A new thin mask model for transmission through EUV absorber features is proposed, which, when linked to an EUV buried defect simulator, can rapidly assess a buried defect's impact on the printability of nearby features. The underlying physics of an absorber edge scattering is thoroughly investigated and simplified models for two of the key physical effects are shown to produce excellent results when compared to FDTD edge scattering. By simply adding calibrated line sources to the top comers of the absorber edges, as well as propagating the thin mask by about half the mask thickness, a greatly simplified model for feature transmissions is produced. The simplified model effectively converts the electrically thick nature of the absorber patterns (similar to 70nm or -5 lambda thick) into a thin mask model, while capturing all of the appropriate effects that are demonstrated in the far field image. Line and space example patterns for dense 32nm, 22nm, and 15nm features (on wafer) demonstrate the accuracy of the new thin mask model for even very tight pitches.