A novel run-time MEEF-driven defect disposition extending high resolution contamination inspection to next generation photomask

The advent of device miniaturization necessitates sub-half-micron features delineated on reticles where photomask quality, more so than ever, exerts remarkable yield impact on 65 nm node and below. The introduction of advanced reticles considerably augments the mask error enhancement factor (MEEF) in the non-linear regime ensuing aggressive OPC features. The increased MEEF leads to tightened defect capture criteria, in which many of the previously insignificant defects become of interest and may have substantial yield impact. To provide desired sensitivity, a high resolution inspection is a must; it also effectively monitors mask reliability. However, the productivity of such inspection greatly depends on defect disposition efficacy in sorting out critical defects from the large population detected on contaminated masks [1-3]. Anchoring high resolution reticle inspection, wafer fabs are in a relentless pursuit of optimal defect disposition method to meet the throughput demand. In particular, progressive defects or haze, induced by repeated laser exposure, continue to be a source of reticle degradation threatening device yield. Early detection of these defects to circumvent the printability impact becomes vitally important yet challenging. In addition to its size, the defect criticality also largely depends upon defect optical transmittance, residing surface, its proximity to a printing pattern as well as lithography parameters such as NA and sigma [4-6]. A MEEF-driven lithographic detector named "Litho3" has been designed that can be used run-time during mask inspection to effectively group the critical defects into a single bin based on their potential yield impact. The coordinates of these critical defects, identified by the above Litho3 detector, can then be transferred from reticle to wafer and subsequently subject to printability validation, upon which defective sites can be analyzed thoroughly on reticle or wafer review tools. Such capability reduces inspection cycle time by improving defect disposition efficacy, also assists in determining lithography process window and a further comprehension of defect progression mechanism.