Regression analysis of photodecomposable quencher concentration effects on chemical gradient in chemically amplified extreme ultraviolet resist processes

Abstract

Chemically amplified resists have been used in the state-of-the-art extreme ultraviolet (EUV) lithography. A basic additive has been added to the resist formula as a quencher to control acid diffusion. In this study, the effects of photodecomposable quencher (PDQ) concentration on the chemical gradient (an indicator of line edge roughness) in chemically amplified EUV resist processes were investigated. The chemical gradient was calculated on the basis of the sensitization and reaction mechanisms for different half-pitches, sensitivities, photoacid generator (PAG) concentrations, PDQ concentrations, and effective reaction radii for deprotection. The obtained 130 000 data were analyzed by least squares, lasso, ridge, and elastic net regressions. Regarding the contribution to the chemical gradient, PDQ concentration was apparently symmetric to PAG concentration. Optimum PDQ concentrations were well predicted (accuracy of approximately 10%) within the examined variable ranges even with 495 training data using the fitted parameters obtained by lasso, ridge, and elastic net regressions.