Binary halftone chromeless PSM technology for λ/4 optical lithography

Binary halftone chromeless PSM (CLM) can be described as a 100% transmission attenuated PSM (attPSM). The term "binary halftone" refers to a novel OPC application to achieve the necessary CD control across the full feature-pitch range. We find that CLM is very complimentary -with high numerical aperture (NA) and with off-axis illumination (OAI). In our wafer-printing experiment, we have achieved 70nm through-pitch printing performance, using a KrF resist process. This was done in combination with a rule-based SB-OPC approach. At least 0,4 mum overlapped DOF with more than 6% exposure latitude has been attained for sub-100nm printed features. For 2D complex patterns, we have observed a very strong optical proximity effect. CLM appears to be more sensitive to proximity effects, but less sensitive to lens aberration effects. Further experimentation and verification is required. Current mask-making processes appear to be capable of manufacturing CLM. We conclude that CLM has great potential to achieving production-worthy lambda/4 (or 0.2k(1)) lithography. The technology risk is neither in mask making nor in application software, but may be in reticle inspection and repair.