Optimization of anti-reflective coatings for lithography applications

We present a new multilayer anti-reflective coating (ARC) optimization method. We have developed a software which allows the optimization of ARC consisting of up to 20 layers on any substrate with incident light integration over the aperture of lithography objectives and diffraction effects. The optimization includes not only the determination of optimal layer parameters (i.e. optical constants n and k, and thickness d) for minimized back-to-resist reflection (RID of exposing light but also the determination of appropriate intervals of parameters corresponding to values smaller then desired values of R-12. By this way the calculation of the process window of technological parameters is essentially improved. The optimization procedure delivers the process parameter for the deposition process determining the characteristics for the ARC layer, namely flow ratio of the source gases, for different ARC layers using optical constants obtained by spectroscopic ellipsometry and reflection spectroscopy. Based on these results the optical constants, thickness and corresponding compositions of low pressure (LP) chemical vapor deposition (CVD) silicon-nich nitride (SiNx), plasma-enhanced (PE) CVD silicon-rich nitride (SiNx), and silicon-nich oxynitride (SiNxOy) were obtained. The optimized films fulfill the anti-reflective requirements for ArF (lambda=193 nm), KrF (lambda=248 mn) laser and i-line (lambda=365 nm) lithography. X-ray photoelectron spectroscopy was applied for determination of the film composition. As an example, results of single layer ARC optimization for gate film stack and multi layer ARC optimizations for emitter window and metallization film stack are presented.