Effect of molecular weight on the EUV-printability of main chain scission type polymers

Abstract

Unclear light-matter interactions in the Extreme UV lithography (EUVL) process cause the sub-optimal performance of the current photoresist platforms. Furthermore, adopting conventional chemically amplified resist (CAR) is problematic in EUVL because of the exacerbated stochastic effects. Therefore, alternative platforms with simpler chemistry, such as the main chain scission (MCS)-type photoresist, can pave the way for efficient printability at higher resolutions. In this work, fundamental analysis of a simple MCS-type photoresist – polymethyl methacrylate (PMMA), is studied and correlated with the parameters of EUV-patterning (called litho-parameters). Contrast curve analysis with different solvents shows MIBK–IPA (1 : 3) mixture as the best developer for EUV-patterning of PMMA. Higher M_w (950k) shows the best EUV-printability compared to the lower M_w (15k, 120k, and 600k) PMMA for 50 nm dense line–space (L/S). To understand the effect of polymer properties on printability, desorption and Gel Permeation chromatography (GPC) studies are conducted, which show that the higher M_w PMMA provides better litho-parameters (higher MCS – to – side-chain scission (SCS) ratio, higher GPC peak shift, and lower GPC peak overlap after EUV-exposure) compared to the lower M_w PMMA. Additionally, it is found that the PMMA chains require minimum energy of 9 eV to induce chemical reactions in the film. The main hypothesis obtained from this study is that for MCS-type EUV resists, higher M_w material provides better printability than the lower M_w material. This is further validated on an engineered MCS-copolymer system. Finally, it is observed that the inhomogeneous dose-deposition during EUV-exposures might hamper the printability of the MCS-type resist.