Actual measurement data obtained on new 65nm generation mask metrology tool set

For 65nm photo mask lithography, metrology becomes significantly more important. Especially the requirements of the photo mask users versus critical dimension (CD) control, CD homogeneity and CD mean to target, give strong head-aches to lithography and process control engineers. Despite the fact that optical CD metrology has limitations versus resolution it still provides valuable information since measurement takes place in transmission similar to the application of the mask during printing to the wafer. The optical resolution should at least support to measure minimum features of 250nm on the masks in the linear regime. In order to qualify structure fidelity and width of assist structures and small contact holes as well as certain OPC pattern which are usually smaller than the limits of optical measurement capability, actually CD SEM systems are recognized as the tool of choice to qualify the reticles. No matter which kind of CD metrology tool is used, long-term repeatability over several days must be below 1nm (3 sigma). This paper will show measurement performance data on two types of reticle CD measurement systems targeting the 65nm node reticles. Another issue of high importance is pattern placement or registration metrology on reticles. Roadmaps of leading edge mask users request a maximum placement error of less than 13nm for the 65nm technology node. This strong require-ment challenges the control of the mask lithography tool and the long-term repeatability of the registration metrology system must not exceed 2.5nm. This paper summarizes the actual performance of Leica's mask metrology tool set and the improvements on the individ-ual systems leading to the respective performance.