Workarounds for EUV mask pellicles that are outside the optical wavelengths used for reticle inspection tools.
As the Extreme Ultraviolet (EUV) lithography ecosystem is being actively mapped out to enable sub-7nm design rule devices, there is an immediate and imperative need to identify the EUV reticle (mask) inspection methodologies. The introduction of additional particle sources due to the vacuum system and potential growth of haze defects or other film or particle depositions on the reticle, in combination with pellicle uncertainty pose unique inspection challenges when compared to 193i reticles.
EUV reticles are typically inspected with optical reticle-inspection tools. However, if there is a pellicle on the EUV mask which is non-transmissive to the optical wavelengths used in the reticle inspection tools, then there is a need for alternative inspection methodologies based on inspection of printed wafers. In addition, due to the potential new defect mechanisms associated with the EUV reticles, fabs are looking for additional methods to re-qualify reticles in production using printed wafer inspections. The printed wafer inspection methodology is referred to as “Reticle Print Verification” or “Reticle Print Check.” This paper discusses these alternative inspection methodologies that are being developed in collaboration with imec using an advanced broadband plasma (BBP) patterned wafer optical inspection (KLA-Tencor 3905) and e-beam review systems (KLA-Tencor eDR7280).
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