Methodology for determining critical dimension scanning electron microscope measurement condition of sub-20 nm resist patterns for 0.33 NA extreme ultraviolet lithography
A methodology to determine the optimum measurement condition of extreme ultraviolet (EUV) resist patterns in a critical dimension scanning electron microscope has been established. Along with many parameters that need to be optimized simultaneously, there are conflicting requirements of small resist shrinkage and high measurement precision. To overcome these difficulties, we have developed a methodology for ArF resist patterns from shrinkages and precisions predicted by the Taguchi method. In this study, we examined the extendibility of the methodology to sub-20 nm EUV resist patterns. The predicted shrinkage by the Taguchi method for an 18 nm EUV resist pattern showed a large prediction error due to its different dependence on acceleration voltage from ArF, so we used the shrinkage curve to predict shrinkage instead of the Taguchi method, as shrinkage depends only on irradiated electron dose. In contrast, precision can be predicted well by the Taguchi method as with ArF. We propose a methodology that consists of separate prediction procedures for shrinkage and precision using the shrinkage curve and Taguchi method, respectively. The proposed method was applied to an 18-nm EUV resist pattern. The optimum measurement condition with shrinkage of 1.5 nm and precision of 0.12 nm was determined.