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

The feasibility of using a surface acoustic wave (SAW) sensor as a nov el, nondestructive evaluation (NDE) technique for studying the relativ e adhesion of thin polyimide (PI) films on quartz (SiO2) has been exam ined. PI films are of interest because of their widespread use in micr oelectronics, where there is a continuing need for improved film prope rties 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 i nterface. The results show clear differences in the comparative SAW hu midity response for films applied with and without an adhesion promote r and with and without a chromium intermediate layer. Temperature and humidity ageing was observed to have a greater effect on the SAW humid ity response for films without adhesion-improving treatments. A theore tical analysis identified changes in the PI film properties as the phy sical mechanism responsible for the primary SAW sensor response. The p roperties of the PI film that change as a function of humidity are den sity, elastic constants, and stress. The more dominant of these factor s appear to be density and elastic constant changes.