Comparative study of line width roughness (LWR) in next-generation lithography (NGL) processes

Abstract

In this paper, we conduct a comprehensive comparative study of next-generation lithography (NGL) processes in terms of their line width roughness (LWR) performance. We investigate mainstream lithography options such as double patterning lithography (DPL), self-aligned double patterning (SADP), and extreme ultra-violet (EUV), as well as alternatives such as directed self-assembly (DSA) and nano-imprint lithography (NIL). Given the distinctly different processing steps, LWR arises from different sources for these patterning methods, and a unified, universally applicable set of metrics must be chosen for useful comparisons. For each NGL, we evaluate the LWR performance in terms of three descriptors, namely, the variation in RMS amplitude (σ), correlation length (see manuscript) and the roughness exponent (α). The correlation length (which indicates the distance along the edge beyond which any two linewidth measurements can be considered independent) for NGL processes is found to range from 8 to 24 nm. It has been observed that LWR decreases when transferred from resist into the final substrate and all NGL technology options produce < 5% final LWR. We also compare our results with 2008 ITRS roadmap. Additionally, for the first time, spatial frequency transfer characteristics for DSA and SADP are being reported. Based on our study, the roughness exponent (which corresponds to local smoothness) is found to range from ~0.75-0.98; it is close to being ideal (α = 1) for DSA. Lastly using EUV as an example, we show the importance of process optimization as these technologies mature.