Evaluation of Mask Quality Control Methods addressing Progressive Haze Issues

摘要

A traditional method of mask quality control in a fab has been wafer image qualification i.e., wafer inspection on printed monitor wafer or wafer inspection on production wafer. But recently many fabs that are using DUV lithography for low k1 process are experiencing the progressive defect growth challenge (such as crystal growth, haze, fungus, precipitate etc.) on their photomasks. The quality of some reticles will worsen over time due to this progressive defect problem on the mask. Hence it is important to detect such problems before they start impacting the device yield. An evaluation was constructed in a Japanese advanced logic fab to compare the performance between traditional image qualification methods and direct reticle inspection using TeraStar STARlight. The goal was to determine if the TeraStar STARlight inspection could provide the sensitivity required to give early warning of progressive defects before image qualification can detect these defects. Evaluation results show that TeraStar STASJight is the most effective method in a fab to provide early warning to a progressive defect growth on reticle that is likely to print later during mask life.