Stress in polyimide films having a rodlike molecular skeleton formed on a silicon substrate

Stress measurements of polyimide films deposited on silicon wafers were performed in situ during the curing and cooling cycles. The films were constructed from a single polyimide having a rodlike molecular skeleton. The stress in the film varied with film thickness. The stress before curing decreased with increasing film thickness. On the other hand, the stress after the thermal cycle increased with increasing film thickness, resulting from the increasing thermal coefficient of expansion. This phenomenon was thought to be caused by the decrease in the degree of the in-plane orientation of the polyimide molecular chain with decreasing stress before the curing process.