Photoresist Exposure And Development Effect And Its Application In Computational Lithography

This work describes the exposure and development effects of chemically amplified resists,and simulation experiments are performed in MATLAB.The lithography model includes optical imaging model and resist model.Compared with the imaging model,the analytic form of the resist model is not fully comprehensible to litho-engineers because of its physical and chemical complexity therefore not applicable in lithographic process.The constant threshold function is usually used for simple simulation[1].To this end,we develop in this thesis a more specific and reasonable resist model accounting for the physical and chemical reactions in the exposure and development process and justify the model with simulation results.First of all,this work briefly introduces the optical imaging model,or namely,the aerial image formation.On top of that,light propagation in the resist is further described.Upon principles of exposure in the conventional resist,the absorption of light by resist is introduced,and the exposure kinetics is described from a microscopic point of view.Subsequently,diffusion point spread function is applied to describe acid diffusion during post-exposure bake.Secondly,with the previous theoretical basis,we introduce the exposure process in chemically amplified resists.The exposure reaction converts the aerial image into an exposed acid latent image,the product of which acts as a catalyst to facilitate a second-step amplification reaction during post-exposure bake.Finally,the post-exposure bake converts the exposed acid latent image into an amplified latent image.As a result,the blocking group of the polymer in the resist is deblocked to generate soluble hydroxyl groups,changing the solubility of the resist.Then the development effect of resist is depicted.Development is a process in which a developer dissolves the resist.Its purpose is to dissolve the resist after the post-baking has changed its solubility,so that a binary resist image is finally formed:either the resist is dissolved,or remains intact on the wafer.In this thesis,the original kinetic model,the enhanced kinetic model and the notch model are simulated for after development image verification.These three models can simulate the vast majority of resist development behaviors.At last,we uses MATLAB to simulate the exposed and developed latent image.Here,the weighted average method is applied to reduce three-dimensional latent acid image to a twodimensional approximation.At the same time,considering the diffusion and reaction of the acid and base quenchers,the exposure latent image and the post-exposure bake latent image are computed.The feasibility of the model is verified by the intensity analysis of the sliced resist profile.All three development models are simulated to compute the resist profiles.