Line edge roughness of sub-100 nm dense and isolated features: Experimental study

Abstract

The nanoscale roughness in patterned images has become a crucial problem in advanced lithography. We have designed and implemented an experiment to study the line edge roughness (LER) for both dense line and space (DEN) and isolated (ISO) lines. The resist selected is UV-6 (a positive tone chemically amplified resist (CAR) from Shipley), and as a comparison, non-CAR such as poly(methylmethacrylate) (PMMA) is also measured. After development, the resist is analyzed using high resolution scanning electron microscopy (SEM) (LEO 1550 VP). An in-house made software is used for LER estimations. Our results indicate that DEN lines appear to be rougher than ISO lines given the same dose and nominal modulation. This is fully accounted by the lower modulation of DEN patterns caused by proximity effects. In addition, CAR resists like UV-6 are much rougher than non-CARs such as PMMA. A simple percolation model based on stochastic modeling predicts the observed trends.