Ni-Ion-Implantation-Assisted Ultrathin Interlayer for Cu/PI Metallization in Low-Power Electronics

Reliable Cu/polyimide (PI) metallization requires strong interfacial adhesion while minimizing the thickness of the metallic adhesion layer. In this study, Ni ion implantation was combined with physical vapor deposition to construct an ultrathin Ni interlayer on a 25 μm-thick PI substrate. Three metallization schemes were compared: 20 nm Ni/2 μm Cu, 10 nm Ni/2 μm Cu, and Ni-ion-implanted PI/5 nm Ni/2 μm Cu. Ni ions were implanted at an energy of 5 keV and a fluence of 1 × 1014 ions cm−2. The implantation treatment decreased the water contact angle of PI from 75° to 64° and increased its surface free energy from 36.41 to 42.99 mJ m−2, primarily through an increase in the polar component. Surface observations showed uniformly distributed implantation-associated micro/nanostructures with characteristic dimensions of approximately 50–300 nm, which may provide additional nucleation and anchoring sites for the subsequently deposited Ni layer. Cross-sectional transmission electron microscopy showed an undulating, locally embedded Ni/PI interface, while elemental profiles were consistent with a gradual transition across the modified interfacial region. The Ni-ion-implanted sample with a 5 nm Ni interlayer exhibited an average 180° peel strength of 1.13 N mm−1, compared with 0.62 and 0.30 N mm−1 for the 20 and 10 nm Ni interlayers, respectively. It also showed the lowest measured sheet resistance of 3.25 mΩ sq−1. Taken together, these results suggest that, under the conditions examined, Ni ion implantation can support a reduction in deposited Ni thickness while maintaining or improving the adhesion and electrical performance of Cu/PI metallization.