157nm Single-Layer and Bilayer Resists Based on α-Methylstyrene Polymers

Abstract

α-Methylstyrene derivatives such as 4-tert-butoxycarbonyloxy-α-methylstyrene (BOCMST), 4-tert-butoxy-α-methylstyrene (BUOMST), 4-(hexafluoro-2-hydroxyisopropyl)-α-methylstyrene (F₆PMST), 4-(hexafluoro-2-tert-butoxycarbonyloxyisopropyl)-α-methylstyrene (BOCF₆PMST) and 3, 5-difluoro-4-tert-butoxycarbonyloxy-α-methylstyrene (BOCF₂MST) were newly prepared. These monomers were radically copolymerized with methacrylonitrile (MAN) using 2, 2′-azobisisobutyronitrile. Ethoxyethyl, tetrahydropyranyl, and trimethylsilyl protected copolymers of MAN and 4-hydroxy-α-methylstyrene (HMST) were also prepared. The transmittance of these polymers (0.1μm thick) was 29-44% at 157nm. Dissolution properties of the polymers were studied. Trimethylsilyl protected MAN-HMST copolymer (MAN-SiMST) showed high etch resistance to oxygen plasma. Imaging was performed using MAN-SiMST as single-layer and bilayer resists.