Influence of Processing and Molecular Parameters on the Dissolution Rate of Poly‐(Methyl Methacrylate) Thin Films

The influence of processing and molecular parameters on the dissolution rate of poly‐(methyl methacrylate), PMMA, thin films (<1 μm) in methyl isobutyl ketone, MIBK, was studied in situ with a single‐element rotating‐polarizer ellipsometer (psi‐meter). Dissolution rates were highly sensitive to the molecular weight distribution, softbake cooling cycle, and dissolution temperature. The apparent activation energy for the dissolution of PMMA in MIBK varied from 25 to 43 kcal/mol depending upon softbake cooling rates and molecular weight distribution. The dissolution rate of air quenched, monodisperse PMMA samples was found to vary with the molecular weight to the −0.98 power. For slowly cooled samples this constant was 85% higher, suggesting improved contrast with slow cooling. Polydisperse samples dissolved about twice as fast as monodisperse ones of the same number average molecular weight. Samples slowly cooled after softbaking and aged for 100h at room temperature or at 60°C showed no change in the dissolution rate with aging. However, the dissolution rate of samples cooled rapidly after softbaking and aged at 60°C decreased by as much as 25%.