Patterning optimization for single exposure BLP and SNLP DRAM layers with 0.33NA and 0.55NA EUV lithography

The superior resolution of High Numerical Aperture (HNA) Extreme Ultraviolet (EUV) lithography opens an era of single patterning techniques for sub-10 nm chips, including Dynamic Random-Access Memory (DRAM). In this report, we present the impact of HNA EUV on improving the performance of DRAM patterning, concentrating on the development of a single mask solution with 0.33 NA EUV lithography for two important layers, bit-line-periphery (BLP) and storage-node-landing-pad (SNLP), i.e. Hex-Pillars. A 20% exposure dose reduction in a comparison with our previous report [V. T. Pham et al SPIE 2024] is gained, when all experiments were conducted in 0.33 NA EUV on pitch 34 nm DRAM. And about 30 to 50% dose reduction gains for the exposure on pitch 28 to 32 nm in comparison to the best performance resulted for pitch 34nm with 0.33 NA EUV exposure, thanks to the superior resolution of HNA EUV. Absolute value of dose-to-size is 40 mJ cm^-2 with HNA exposure. Even though it is expected smaller than one at 0,33NA, significant Depth of Focus (DoF) value at HNA has been obtained for the overlapping process window of SNLP-BLP. Both numerical and experimental results on pitch 28nm HEX-pillar show DoF of about 80 nm, which are promising starting points for optimization in HNA lithography. All the results are after etch inspection (hard mask or metallic layer) In the end, our simulation results pave the route to enhance the DoF for the aggressive pitch DRAM (toward pitch 24nm) by optimizing the illumination sources for the next experiments.