Tantalum, tantalum nitride, and chromium adhesion to polyimide: effect of annealing ambient on adhesion

The adhesion of Ta, TaN (cubic), TaNx (mixture of cubic and amorphous phases), and Cr to 3,3',4,4'-biphenylene tetracarboxylic acid dianhydride-p-phenylenediamine-derived polyimide (BPDA-PDA PI) has been characterized. The PI surface was subjected to CF4-reactive ion etching (RIE) and Ar-sputtering prior to interface preparation. The peel adhesion at T-0 (initial) shows the following order: TaNx∼ TaN < Ta∼ Cr, with all samples failing in apparently virgin PI. After ten thermal cycles to 400°C in forming gas the peel adhesion showed the following trend: TaNx < TaN∼ Ta ∼ Cr, whereas if the annealing was done in N2 the order changed to TaNx∼ TaN « Ta < Cr. The peel locus of failure was always in the apparently virgin PI in the Cr/PI samples, while the Ta/PI samples failed in the modified PI, and the TaN/PI and TaNx/PI samples failed between the Ta-nitride and the Cu peel backing film after thermal cycling.