Effect of thermal curing on thermomechanical properties of polyimide films having rodlike molecular skeleton formed on a silicon substrate

Stresses in polyimide films coated on silicon wafers were measured in situ during the curing and cooling cycles. The films had a single rodlike molecular skeleton. Stress measurements were performed on films of uniform thickness under several different heating rates during the curing cycle. After the stress measurements, the cured polyimide films were examined by thermal mechanical analysis. The stress after the curing cycle increased with increasing heating rate during the curing cycle. Similarly, the thermal coefficient of expansion of the cured polyimide film increased with increasing heating rate. This phenomenom was thought to be caused by the decrease in the degree of in-plane orientation of the polyimide molecular chain with increased heating rate. The in-plane orientation was presumed to be influenced by the evaporation rate of the residual solvent.