Enhanced flexible mask specifications

A new methodology for a mask quality, flexible mask specifications, is proposed. This methodology consists of two major concepts. One is a flexibly selected pattern to guarantee a mask quality for each device and each level of a device. This pattern, hot spot pattern, is selected using a full chip level lithography simulation. The other is flexibly changeable combination of each tolerance of each error component (e.g. CD mean to target, CD uniformity). A mask quality is judged by not each error component, but a total lithography margin. In this methodology, following two points are important. A hot spot pattern should be correctly selected in terms of having large impact on critical dimension (CD) on wafers. An amount of lithography margin reduction due to mask manufacturing error should be correctly estimated. We have improved this methodology in those two points. Firstly, a hot spot pattern is selected in terms of difference of Dose-MEF factor in addition to a pattern having small lithography margin. A Dose-MEF factor defines as ratio of target exposure shift to mask CD error. A difference of Dose-MEF reduces a common lithography margin with patterns having CD errors. Secondary, we measure all kinds of hot spot patterns directly. A common lithography margin is obtained from Exposure-defocus tree (ED-tree) based on actual measurement data. Applying these improved methodologies to memory device mask with 130nm node, we can obtain a lithography margin precisely in comparison with the previous method.