TA AND TAN ADHESION TO HIGH-TEMPERATURE FLUORINATED POLYIMIDES - SURFACE AND INTERFACE CHEMISTRY

The practical adhesion of Cu/Ta to high-temperature fluorinated polyim ides (FPIs) was initially good but failed after the reliability test i nvolving treatment under the FPI curing condition five times (T-5). Bu t a thin layer (40 nm) of TaN greatly improved the reliability of the Cu/Ta-to-FPI adhesion. Both CF4 and in situ Ar plasma treatments of FP Is prior to metal deposition enhanced the metal-to-FPI adhesion streng th. CF4 plasma enriches the FPI surface with fluorine atoms and most o f fluorine is bound to carbon as CF3, CF2, and CE Ar plasma first dest roys CF3 and then C=O groups of the FPIs to yield a polar surface. The locus of failure by a 90 degrees peel test was found to be within the Ar-plasma-modified FPI layer but it moved toward the bulk of FPI, i.e . away from the metal-polymer interface, after the T-5 reliability tes t. The locus of failure in the case of weak adhesion where no plasma t reatment was done on FPI films was in the near-interface region within the FPI layer, and the failure seemed to occur in the weak boundary l ayers of FPI surfaces. Plasma treatment removes weak boundary layers a nd also increases FPI surface roughness. These two effects combined im proved the metal-to-FPI practical adhesion.