The influence of asymmetric spectrum of DUV light on imaging performance in advanced technology nodes

Abstract

In the manufacturing of advanced integrated circuits, ArF immersion lithography remains the primary tool for the patterning process. With the increasing requirements for critical dimension uniformity (CDU) in advanced technology nodes, every nanometer of CD variation becomes crucial. Over the past decades, scanner manufacturers have continuously adopted many technologies to improve the performance of DUV light sources, aiming to reduce CD variation caused by bandwidth, central wavelength, and other factors as much as possible. Previous investigations into the impacts of source bandwidth on imaging performance have provided the foundation for this work. In previous simulations of limited light bandwidth, Gaussian and Lorentzian symmetric line shapes were often used to represent the laser spectrum. However, the emitted beam from excimer lasers always exhibits some level of asymmetry in reality. This study focuses on the impact of spectral asymmetry on imaging performance. We conducted researches on the effects of various laser bandwidth shapes on the imaging of the critical patterns such as line space and other 2D patterns. We introduced an asymmetry parameter Δn to characterize the spectrum change. In the modeling part of this study, backward propagation (BP) neural network was established to predict the effects of a certain range of asymmetric spectra. We conclude that although the laser bandwidth in modern scanners is relatively low, the asymmetry of the laser spectrum does have certain impacts on CD variations depending on the mask pattern.