A model for the thermal degeneration of a positive optical photoresist

Positive optical photoresists have been used extensively in the semiconductor industry and in the manufacture of thin-film disk- and tape-drive heads. Mathematical models for the exposure and development phases of the lithography process have been well defined, but scant information on modeling of the pre-bake phase is available. A pre-bake model which describes the deterioration of the photoactive component in a positive optical resist is derived. A mass balance and the kinetics of the situation are used to describe the change in the Dill exposure model parameters. Experimental verification of the model is shown with three photoresists whose parameters are calculated for different wavelengths of light. The effect of the resist solvent on the exposure model parameters is discussed