A Reticle Quality Management Strategy in Wafer Fabs Addressing Progressive Mask Defect Growth Problem at low k1 Lithography

摘要

DUV lithography has introduced a progressive mask defect growth problem widely known as crystal growth or haze. Even if the incoming mask quality is good, there is no guarantee that the mask will remain clean during its production usage in the wafer fab. These progressive defects must be caught in advance during production in the fabs. The ideal reticle quality control goal should be to detect any nascent progressive defects before they become yield limiting. So a high- resolution mask inspection is absolutely needed, but then the big question is: "how often the fabs need to re-inspect their masks"? A previous work towards finding a cost effective mask re-qualification frequency was done by Vince Samek et al. of IBM and Dadi Gudmundsson et al. of KLA-Tencor in 1999, but this work was prior to the above mentioned progressive defect problem that industry started to see at a much higher rate during just the last few years. In this present paper a realistic mask re-qualification frequency model has been developed based on the data from an advanced DRAM fab environment that is using low k1 lithography. Statistical methods are used to analyze mask inspection and product data, which are combined in a stochastic model.