ADHESION STUDIES OF POLYIMIDE FILMS USING A SURFACE-ACOUSTIC-WAVE SENSOR

The feasibility of using a surface acoustic wave (SAW) sensor as a novel, nondestructive evaluation (NDE) technique for studying the relative adhesion of thin polyimide (PI) films on quartz (SiO2) has been examined. PI films are of interest because of their widespread use in microelectronics, where there is a continuing need for improved film properties such as the dielectric constant and adhesion. A dual delay line SAW sensor was used to study the effect of humidity on the PI-quartz interface. The results show clear differences in the comparative SAW humidity response for films applied with and without an adhesion promoter and with and without a chromium intermediate layer. Temperature and humidity ageing was observed to have a greater effect on the SAW humidity response for films without adhesion-improving treatments. A theoretical analysis identified changes in the PI film properties as the physical mechanism responsible for the primary SAW sensor response. The properties of the PI film that change as a function of humidity are density, elastic constants, and stress. The more dominant of these factors appear to be density and elastic constant changes.