Hfo₂ Barrier Layers: Thickness-Dependent Corrosion Protection of Copper Thin Films for Potential Microelectronic Applications with Sweat Contact

Abstract

Copper conductive thin films or components in microelectronic devices face significant corrosion challenges that compromise long-term reliability. This study presents a comprehensive investigation of hafnium dioxide (HfO₂) as a protective barrier layer deposited by RF magnetron sputtering at varying thicknesses (150 and 300 nm) on copper substrates for possible microelectronic applications. Multi-technique characterization methods, including SEM-EDX, AFM, XRD, FTIR, UV–Vis spectroscopy, contact angle measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS), were employed to establish structure, property, and performance relationships. EDX results show that the addition of an HfO₂ layer significantly modified the surface morphology, especially on presence of 300 nm HfO₂ layer, so that the surface appears continuous and uniform. This is also supported by the FTIR analysis results, which indicate the presence of the strongest Hf-O and Hf-O-Hf vibrational bonds, thereby confirming the formation of an HfO₂ layer on the Cu surface. AFM results show an increase in surface topography roughness, caused by island-type growth (Volmer-Weber), as the thickness of the HfO₂ layer increases. The XRD results for un-coated sample shows sharp and clear diffraction peaks and indicates face-centered cubic (FCC) phase pattern of pure Cu nanoparticles. When the HfO2 layer added Cu layer, XRD pattern shows the formation of a broad hump in the range of 2θ ≈ 28°–35° and HfO2 layer formed is in the amorphous state. These results are correlated with the contact angle test results. UV–Vis results show that 300 nm HfO₂ coted films has the highest transmittance value across the entire wavelength range, as well as the lowest absorbance value. The 300 nm HfO₂ coating demonstrated optimal corrosion protection with 21.2 % reduction in corrosion current density (from 11.3 to 8.89 μA/cm2) and 29 % increase in polarization resistance (from 1.45 to 1.87 kΩ cm2) in artificial sweat environment. Finally, surface wettability studies revealed that increased hydrophobicity (contact angle:49.13° to 57.99°) was correlated with enhanced corrosion barrier performance. These findings establish RF-sputtered HfO₂ as a viable, scalable solution for copper protection in next-generation microelectronic and wearable biosensor applications.