Improvement of LWR/LER in ArFi lithography by optimization of resist formulation and laser E95

The reduction of Line Width Roughness (LWR) and Line Edge Roughness (LER) is crucial for improving edge placement error (EPE) in ArF immersion lithography. This is especially important for patterns with a pitch of 80nm or less, where low image contrast exacerbates LWR and LER. Among the many factors that can affect the LWR/LER, we believe that the contributions of photoresist and laser speckle are important, and therefore we focused on these two factors in this study. For the photoresist, we have tested 5 combinations of two types of platforms and three different Monomer Deprotection Efficiencies (MDE) in order to figure out the effect of LWR/LER reduction. Notably, one of the 5 combinations is a photoresist for mass production using a conventional platform and is used as a benchmark for the experiments. The speckle is known to be caused by coherence, which consists of spatial coherence and temporal coherence, of the lasers. In this experiment, we controlled the coherence by adjusting the temporal coherence and investigated the effect of speckle on LWR and LER. Furthermore, since the temporal coherence is inversely proportional to the laser bandwidth, e.g., E95, we controlled the temporal coherence by setting E95 to 0.20pm, 0.30pm and 0.45pm in the experiment. As a result, it was confirmed that the new platform resist has a better LER than the conventional platform resist, and that the LWR/LER tends to improve significantly when the MDE is above a certain value. It was also confirmed that the wider the E95, the better the LWR/LER.