Ruthenium shows way to 2nm

October 09, 2020 //By Nick Flaherty
Researchers at imec in Belgium have shown that ruthenium (Ru) is a serious contender as a metal interconnect for 2nm chip-making process technology
Researchers at imec in Belgium have shown that ruthenium (Ru) is a serious contender as a metal interconnect for 2nm chip-making process technology

imec in Belgium has demonstrated metal interconnects built using ruthenium (Ru) that could be used for 2nm process nodes.

The electrically functional 2-metal-level interconnects were built with a ruthenium semi-damascene and airgap technology and shown for the first time at the 2020 International  Interconnect Technology Conference in XX this week.

The 2-metal-level semi-damascene module was built on 300mm wafers using Ru for the metallization with a 30nm pitch. These showed over 80 percent reproducibility with no evidence of shorting and a lifetime of more than 10 years. The mechanical stability of the Ru air-gapped structures was found to be comparable to today's dual-damascene copper interconnects. A metal pitch of 24nm is seen as necessary for a 2nm process technology.

An analysis of a 12-metal-layer analysis using a 64bit ARM processor core showed system-level benefits in terms of RC, power consumption and IR drop. Ru was also shown as a promising alternative for contact plugs in the middle-of-line of advanced nodes.

Alternative metallization materials such as Ru and alternative metallization approaches such as semi-damascene are a key area of research for back-end-of-line (BEOL) and middle-of-line (MOL) technologies for the 2nm technology node and beyond. For the BEOL, imec proposes a semi-damascene integration as an alternative to traditional dual-damascene integration. This needs metals other than copper or cobalt with a high bulk resistivity to be deposited without a diffusion barrier that can be patterned using a subtractive etch lithography. 

This allows for interconnect height increase which, in combination with using an airgap as a dielectric, promises to reduce the resistance-capacitance (RC) delay which is a major bottleneck for BEOL scaling.

"The results show that semi-damascene in combination with airgap technology not only outperforms dual-damascene in frequency and area, it also provides a scalable path for further enhancements," said Zsolt Tokei, program director nano-interconnects at imec. "Airgap shows the potential to improve performance by 10 percent while reducing the power consumption by more than 5 percent. The use of high-aspect-ratio wires can reduce the IR drop in the power network by 10 percent to improve reliability."

Next: 2nm semi-damascene mask 

Picture: 
A ruthenium semi-damascene process enables high-aspect-ratio wires (a-c) and high-density airgap (d) for a 2nm process

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