Plasma-etching technology with in situ etched-surface modification for highly reliable low-k/Cu dual damascene interconnects

The plasma-etching technology presented in this paper is for fabricating highly reliable Cu dual damascene interconnects (DDI) with organic low-k film through modification of the in situ etched surface during low-k etching. Nitrogen-based plasma with oxygen and high-molecular-weight fluorocarbon gas (C>2) chemically modifies the sidewall surface of the etched low-k film, changing it into the carbon nitride with fluorocarbon-polymer passivation from the etching gas. After wet cleaning, the fluorocarbon-polymer is removed selectively, leaving a carbon nitride modified layer (CNL) on the sidewall. The CNL has been found to suppress Cu diffusion into the low-k film. A stacked barrier structure of conventional barrier metal and CNL is expected to have high tolerance to Cu diffusion. Combining a dual-hard-mask etching sequence with the CNL modification, Cu DDIs with organic low-k film were fabricated with high yield.