High sensitivity repeater detection with broadband plasma optical wafer inspection for mask defect qualification

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As extreme ultra-violet (EUV) lithography moves into high volume manufacturing (HVM) for several critical layers for the N5 node, there is a need to develop a comprehensive strategy for mask re-qualification in the fab to mitigate contamination risks. The introduction of additional particle sources due to the scanner vacuum system and potential growth of film or particle deposition on the reticle, in combination with pellicle uncertainty, pose unique inspection challenges for EUV reticle defectivity compared to 193i reticles. EUV reticles are typically inspected with optical reticle inspection tools at outgoing quality control during their manufacture. Optical reticle inpsection tools are also traditionally used in the IC fab for incoming reticle qualification and periodic reticle re-qualification during production. However, to reduce material at risk in the IC fab there is a need for alternate inspection methodologies based on inspection of printed wafers. In addition, potential new defect mechanisms, such as those associated with the multi-layer mask of the EUV reticle, are driving fabs to re-qualify reticles in production using new methods that involve printed wafer inspection. The printed wafer inspection methodology is referred to as “reticle print check” or simply “print check”. In this paper we will describe the print check flow and show results from new developments in this methodology improving the capture of mask defects on wafer.