Diffusivity measurements in polymers: II. Residual casting solvent measurement by liquid scintillation counting

Simulation of the microlithographic process plays an increasingly important role in the manufacturing of integrated circuitry. Unfortunately, most lithography simulations still lack fundamental relationships that link the resist chemistry and the final resist image. This study is directed towards generating the data necessary to quantify one of these relationships, the effect of residual casting solvent on the resist image. The amount of casting solvent was measured as a function of the post apply bake temperature and time for several casting solvents directly by using liquid scintillation counting. These measurements were carried out on four identical diazonaphthoquinone-novolac resist formulations cast with different radio-labeled casting solvents (ethyl cellosolve acetate, PGMEA, diglyme, and ethyl lactate). From these data we have estimated the diffusion coefficients for the solvents and the dependence of these coefficients on temperature. These data are then convolved with dissolution parameters and Dill parameters to isolate and establish the relationships between these parameters and the post apply bake process that controls the amount of residual casting solvent.