Estimating resist parameters in optical lithography using the extended Nijboer-Zernike theory

This study presents an experimental method to determine the resist parameters at the origin of a general blurring of a projected aerial image. The resist model includes the effects of diffusion in the horizontal plane and image blur that originates from a stochastic variation of the focus parameter. We restrict ourselves to the important case of linear models, where the effects of resist processing and focus noise are described by a convolution operation. These types of models are also known as diffused aerial image models. The used mathematical framework is the so-called extended Nijboer-Zernike (ENZ) theory, which allows us to obtain analytical results. The experimental procedure to extract the model parameters is demonstrated for several 193-nm resists under various conditions of postexposure baking temperatures and baking times. The advantage of our approach is a clear separation between the optical parameters, such as feature size, projection lens aberrations, and the illuminator setting on one hand, and process parameters introducing blur on the other