Relationship between Defect Risks and Effective Reaction Radius for Deprotection in Chemically Amplified Resist Process for Extreme Ultraviolet Lithography

The trade-off relationships between resolution, line edge roughness (LER), and sensitivity are a serious problem in the extreme ultraviolet (EUV) lithography. The increase of pattern formation efficiency is essentially required to simultaneously improve these three properties. The pattern formation efficiency is determined by the factors such as the absorption coefficient, W-value, the reduction potential of acid generator, the effective reaction radius for deprotection, and the efficiency of solubility switching. Among them, the increase of effective reaction radius requires particular attention, because the stochasticity of protected units also increases with the effective reaction radius. In this study, the relationship between defect risks and effective reaction radius for deprotection of chemically amplified resists was investigated using a Monte Carlo simulation under the condition of maximum chemical gradient. LER had a minimum value approximately at the effective reaction radius of 0.3 nm. The pinching and bridging risks decreased with the increase of effective reaction radius to 0.5 nm. However, its effect on the pinching and bridging risks differently depended on the initial standard deviation and the total sensitizer concentration.