A novel strategy of lithography-error-budget optimization for the 65-nm node: mask specifications for hyper-NA imaging

摘要

This paper presents the first results on mask critical-dimension (CD) specifications for the hyper-numerical aperture (hyper-NA) lithography. The mask CD specifications have been derived from experimental results applying the immersion lithography with NA being 0.85. The experiment has been performed for a hole pattern corresponding to the 65-nm node with NA = 0.75 or 0.85. From this experiment, it was found that the higher-NA condition (NA = 0.85) makes the mask CD tolerance being more than doubled as compared to that under the lower-NA condition of NA = 0.75 while retaining the depth-of-focus (DOF) margin. This relaxation in the CD tolerance is attributable to the enlargement of DOF in the immersion lithography where the DOF becomes more than n times larger than that with the dry lithography under the same resolution limit (n: refractive index of immersion fluid). Analyses of the mask CD tolerance have been performed by applying a newly-developed method, that enables a quantitative analysis of mask CD error and DOF margin. In addition, the mask CD error margin for the 45-nm node have also been estimated by performing a lithography simulation under conditions with NA = 1.07 and 1.20. From this simulation, it was predicted that for the case when NA = 1.07, the mask CD error margin requires specifications on mask that are almost unachievable if one concerns the status of current mask manufacture processes together with the forecast, on the processes given in the ITRS 2004 roadmap. On the other hand, the simulation predicted that the higher-NA condition (NA = 1.20) with the immersion imaging realizes a relaxation in the mask CD tolerance, leading to realistic specifications on mask. Therefore, this strategy realizes a breakthrough to avoid the "mask crises".