Molecular Weight and Polydispersity Effects on Electron Beam Lithography Performance of RAFT-Mediated PMMA

The performance of electron beam lithography (EBL) is highly dependent on the resist material, and the behavior of main-chain scission (MCS) resists such as PMMA is strongly influenced by the molecular weight and polydispersity index (PDI). To systematically investigate these factors, a series of PMMA resists with precisely controlled molecular weight and PDI were synthesized via RAFT polymerization, and broad-distribution samples were obtained through blending. Results show that soft-bake temperature significantly affects pattern fidelity and line-edge roughness (LER), with PMMA-200 k exhibiting optimal performance at 140 °C soft-bake, achieving L/S patterns with line critical dimensions (CDs) of 25 nm and an LER of 2.24 nm. Low number-average molar mass (Mn) PMMA (13 k, PDI <1.1) displayed high roughness or line breakage at 25–40 nm feature sizes, whereas high-Mn samples (68 k, 133 k, 200 k, PDI <1.1; 128 k, PDI = 1.35) all showed LER <3 nm, indicating that increasing Mn and reducing PDI can improve performance; however, for high-Mn samples without low-Mn chains, this enhancement is relatively limited. In contrast, commercial PMMA with higher Mn but broader distributions exhibited lower resolution and higher LER, suggesting that low-Mn chains (∼12,670 g/mol) in broad-distribution samples are the main limiting factor. PMMA-200 k also achieved L/3S EBL patterns with a line CD of 22 nm, complex EBL patterns, and L/S patterns with a line CD of 30 nm and LER of 2.51 nm under EUV exposure. Importantly, low-Mn components existing in the samples greatly limit the lithographic performance greatly. These findings provide guidance for the optimization and development of MCS-type resists.