Dry plasma-enhanced adhesion of Ti/Cu seed layers to ABF substrates for fine-pitch packaging reliability

Abstract

In advanced 3D packaging, strong adhesion between Ajinomoto Build-up Film (ABF) substrates and sputtered Ti/Cu seed layers is essential for mechanical reliability and high-density integration. However, weak adhesion between titanium and the epoxy–silica composite ABF remains a major challenge. This study investigates the effects of dry plasma surface treatment and Ti seed layer thickness on the adhesion performance of sputtered Ti/Cu layers on ABF substrates. Surface characteristics were evaluated using water contact angle and roughness measurements, while titanium grain size and crystallographic orientation were analyzed by X-ray diffraction. Adhesion strength was quantified by 90° peel tests. The results indicate that Ar plasma treatment for 60 s combined with a 50 nm Ti seed layer improved adhesion strength by ∼10% (0.749 kgf/cm) compared with conventional wet desmear treatment (0.671 kgf/cm). This enhancement is attributed to reduced Ti grain size and the formation of a preferential (002) orientation. The failure mode shifted from interfacial delamination to cohesive failure within the ABF substrate, indicating strengthened interfacial bonding. In addition, dry plasma-treated surfaces exhibited lower roughness and higher electrical conductivity (50.17 × 10⁶ S/m) than wet-treated samples (18.15 × 10⁶ S/m). These findings provide practical interfacial engineering strategies for reliable seed layer deposition on ABF substrates.