Universal approach for process optimization of chemically amplified photoresists in electron beam lithography

A critical factor in the fabrication of complex nano- and microstructures with high quality and reproducibility is the determination of a suitable working point. This applies particularly to lithography, which is the basis for transferring the desired patterns onto the substrate. For this reason, we present a generic process optimization methodology that has been successfully applied to four chemically amplified positive and negative tone electron beam lithography photoresists with different sensitivities. The method is iterative and designed for the best possible results with a minimum use of resources. This is accomplished by identifying the critical key factors in photoresist processing using contrast curves and determining their impact. Starting with the most influential bake parameter, the maximum effect is achieved. The method used is similar to the Bossung plot procedure and aims for a maximum process window. After the bake parameters, the fundamentals of development kinetics are discussed, and a method for determining an appropriate development time is presented. A mask making approach is then used to investigate the ideal exposure conditions. This includes the determination of an appropriate base dose in conjunction with proximity effect correction and sizing. The evaluation of this method is demonstrated by critical dimension linearity plots and scanning electron microscope cross sectional analysis of resist profiles. The results presented demonstrate the universality of the optimization approach.