Particle Generation During Photoresist Dissolution
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A lattice-type Monte Carlo based mesoscale model and simulation of the lithography process has been described previously . The model includes the spin coating, post apply bake, exposure, post exposure bake and development steps. This simulation has been adapted to study the insoluble particle generation that arises from statistically improbable events. These events occur when there is a connected pathway of soluble material that envelops a volume of insoluble material due to fluctuations in the deprotection profile that occur during the post exposure bake . Development erodes the insoluble material into the developer stream as an insoluble particle. This process may produce a cavity on the line edge that can be far larger than a single polymer molecule. The insoluble particles generated may coalesce in developer to form large aggregates of insoluble material that ultimately deposit on the wafer surface and the tooling. The recent modifications made in mesoscale models for the PEB and dissolution steps, which have enabled this study are briefly described. An algorithm that was used for particle detection in the current study is also discussed. The effect of the resist formulation and the different lithographic steps, namely, exposure, post exposure bake and development, on the extent of particle generation is analyzed. These simulations can be used to set process variables to minimize the extent of particle generation.