Correlation method based mask to mask overlay metrology for 32nm node and beyond

The new photomask registration and overlay metrology system PROVE (TM) at Carl Zeiss has been developed and already delivered to customers to meet the increased industry requirements for pattern registration tools in terms of resolution and in-die measurement capability. Main drivers of the tool performance specifications are double exposure and double patterning approaches which will help to extend the 193nm lithography platforms while keeping the semiconductor industry conform to ITRS roadmap requirements. To guarantee the demanding tool performance, PROVE (TM) features highly stable hardware components for the stage and environmental control. Moreover, sophisticated image analysis algorithms as for instance correlation methods have been developed to overcome limitations of standard approaches. In this paper we focus on mask-to-mask overlay metrology as one of the critical components of modern lithography. To achieve the challenging requirements with the PROVE (TM) tool, an overlay reproducibility budget is prepared that takes into account stage, image analysis and global effects like mask loading and environmental control. The corresponding parts of the budget are quantified by means of PROVE (TM) overlay measurements, performed on typical box-in-frame structures. This allows the identification of critical error contributions and the corresponding improvement strategies. In particular, it will be shown, that the new developed correlation methods of PROVE (TM) will significantly reduce image analysis and camera noise contributions.