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

Abstract

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 CuMn 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.