Process considerations, chemically amplified

The chemically amplified resists reported here for deep-UV applications require a post-exposure thermal treatment process step to effect the deprotection reaction. This step has proven to be critical, and in order to understand the processing considerations it is instructive to discuss, qualitatively, the various primary and secondary reactions that occur with these systems during both exposure and PEB, ie ... 

The process control of the post-exposure bake that is required for chemically amplified resist systems deserves special attention. Several considerations are apparent from the previous fundamental discussion. In addition for the need to understand the chemical reactions and kinetics of each step, it is important to account for the diffusion of the acid. Not only is the reaction rate of the acid-induced deprotection controlled by temperature but so is the diffusion distance and rate of diffusion of acid. An understanding of the chemistry and chemical kinetics leads one to predict that several process parameters associated with the PEB will need to be optimized if these materials are to be used in a submicron lithographic process. Specific important process parameters include ... 

Distillation with chemical reaction is a process of great complexity. Not only does it impose simultaneous consideration of the rate equations of mass transfer and chemical change but also amplifies their interaction through the presence of heat of reaction. Further, it poses questions regarding equilibrium data and questions the validity of such concepts as plate efficiency. 

To cause an appreciable change in the dimensions (cross section) of the solid object, a considerable amount of the liquid medium is necessary. Since this type of interaction process is volume based, it is characterized by a rather low rate of proliferation of the chemical reaction between the solid and the medium into the bulk of a solid phase. Second, the degrading action of the medium is amplified with an increase in temperature. 

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