EUV dose reduction for pitch 28 nm line-space

Abstract

Lithography accounts for the highest total CO2 equivalent emissions for imec N3 technology node and the second highest emissions for imec N5 technology node. Additionally, the resolution-line edge roughness (LER)-sensitivity i.e., the RLS trade-off will push the EUV dose higher to improve lithographic performance. All these factors combined will result in increased costs and increased CO2 emissions as the industry shifts toward advanced technology nodes. Reducing the EUV exposures dose while maintaining LER and defectivity with respect to the reference process can be one of the most impactful ways to achieve cost reduction, throughput improvement and CO2 emission reduction. In this paper, we experimentally tested various ways to reduce EUV dose for CAR and MOR to print pitch 28 nm line-space structures while minimizing the impact on LER and defectivity. The impact of several tuning knobs for dose reduction was explored: resist formulation, post-exposure pattern rectification, underlayer, post-exposure bake (PEB), development, mask CD bias and mask material type. Using only material and post-exposure process optimizations, up to 26% EUV dose reduction was observed with comparable performance in terms of line roughness and defectivity. Similarly, by optimizing the mask CD bias and mask material type, we can expect about 12% EUV dose reduction while also improving the peak normalized image log slope (NILS), as confirmed by simulation results. Finally, we will demonstrate that the 'low dose process' that we obtained, can be transferred from printing pitch 28 nm line-space structures to printing regular tip-to-tip structures with similar reduction in EUV dose at comparable tip-to-tip LCDU performance with respect to the reference process. It is critical that we consider the impact of these changes on the climate, so these process changes will also be evaluated relative to the baseline with respect to changes in equivalent CO2 emissions.