193 nm single layer resist strategies, concepts, and recent results

Abstract

Matrix resins used in conventional resists are not suitable for use at 193 nm due to their opacity. Hence new materials that are functionally similar to but structurally different from novolac and poly(hydroxy styrene) are required for 193 nm lithography. We report on the use of alternating copolymers of cycloolefins with maleic anhydride as effective 193 nm matrix resins, with or without dissolution inhibitors based on polyfunctional cholates, for 193 nm lithography. Due to their structural diversity, the required high transparency and etch stability, compatibility with industry standard 0.262 N tetramethyl ammonium hydroxide (TMAH) can be built into the polymer by conventional free redical polymerization techniques. A correlation between the molecular properties of the resist components (matrix resin, dissolution inhibitor, photoacid generator, and base additive) and resist lithographic performance parameters is illustrated. The formulations containing dissolution inhibitors currently show 0.13 μm line/space (L/S) pair and 0.11 μm isolated line resolution at 20–30 mJ/cm2 photospeeds with good process latitude, etch resistance, and environmental stability. These materials are completely compatible with 0.262 N TMAH development, show poly and oxide etch rates comparable to that of deep-ultraviolet resists used in manufacturing today, and exhibit postexposure delay stabilities of greater than 2 h for 0.16 μm features at 13 ppb concentrations of ammonia or N-methyl pyrrolidone. The importance of reflectivity control at the 193 nm imaging wavelength and how it can be handled by a multilayer dielectric antireflective coating (ARC) has been elucidated. An optimized resist and ARC system shows 0.14 μm l/s pair resolution over 100 nm poly topography and exhibits a resolution of 60 nm isolated lines and 80 nm with >0.8 μm depth of focus using a Levenson phase shift mask. The design and utility of photoacid generators that serve both the photoacid generation and amine additive functions in low activation energy resist systems and the base additive function in high activation energy system are also described. The use of these photodecomposable bases (PDBs) has been shown to dramatically alleviate the outgassing during exposure in low activation energy chemically amplified (CA) resists. In high activation energy CA resists, use of a PDB that is basic but generates an acid upon exposure to light or radiation provides some relief in designing 193 nm resists that are fast, yet stable, to environmental and substrate contamination effects.