Lithography and Chemical Modeling of Acid Amplifiers for Use in EUV Photoresists

Abstract

We postulate that the best way to simultaneously improve resolution, line edge roughness (LER), and sensitivity all in EUV resists is to increase the number of acid molecules generated per absorbed photon. In previous work, we showed that acid amplifiers (AAs) decompose auto-catalytically to effectively increase the amount of acid generated from each EUV photon.
In this paper, we show that AAs can simultaneously give better sensitivity and lower LER to improve Z-Parameter up to 3X compared to resists without AA. Acid amplifiers must be thermally stable to prevent the creation of acid in unexposed regions of the resist film. We use thermally-programmed spectroscopic ellipsometry to measure the decomposition of AAs in resist films and to identify structural features that influence the stability of AAs.
We also present the construction and utilization of a mathematical model that describes acid diffusion and acid amplifier decomposition in resist films. Using this model, we explored how the acid gradient between exposed and unexposed regions of a resist film is altered as a function of several variables; resist quantum yield, acid and base diffusion, AA and base loading, and AA decomposition kinetics. Out of the variables that were investigated, the model results are in general agreement with experimental results and demonstrate the potential for AAs to simultaneously improve resolution, LER and sensitivity.