High-performance copper-seed-layer deposition using 60-MHz high-frequency–direct current superimposed magnetron sputtering

This study aims to demonstrate the deposition of high-performance Cu-seed layers using a very high frequency–direct current (VHF–DC) superimposed magnetron sputtering system for sub-20-nm dual-damascene interconnects. Plasma diagnostics revealed substantial improvements in plasma properties with electron densities measured at n_e ≈ 1.71 × 10¹⁶ m⁻³ for direct current magnetron sputtering (DCMS), n_e ≈ 3.08 × 10¹⁶ m⁻³ for 40.68 MHz VHF–DC, and n_e ≈ 1.63 × 10¹⁷ m⁻³ for 60 MHz VHF–DC. These enhancements enabled superior step coverage and thin-film uniformity, particularly in high-aspect-ratio structures, achieving a bottom-to-top coverage ratio exceeding 100 % at an RF bias of 200 W. Comparative analysis using X-ray diffraction and X-ray photoelectron spectroscopy showed that Cu[sbnd]Mn films deposited via VHF–DC superimposed sputtering exhibited improved Cu (111) crystallinity, reduced void formation, and enhanced adhesion compared to conventional DCMS. These findings reveal VHF–DC superimposed sputtering as a critical technological advancement, offering enhanced process reliability and scalability for next-generation semiconductor devices.