Using a ruthenium-based layer as a barrier layer over copper can improve performance in dense metal-insulator-metal (MIM) capacitors used in RF and analogue applications, according to recent research.

Usually tantalum (Ta) and tantalum nitride (TaN) are used as a barrier layer, but a team of researchers from IBM has found that by matching the orientations of the ruthenium and copper grain structures, there is less electron scattering and hence resistance is reduced.

Ruthenium offers the advantage that it enables copper to be directly electroplated on to the metal and minimises the problem of filling high aspect-ration structures with them in physical-vapour-deposition which is found when Ta and TaN are used.

IBM's work follows that undertaken by researchers from NEC Corp, which has employed ruthenium barrier layers to copper lines with a consequent 12.4 per cent reduction in resistance levels.

The team from IBM are currently showcasing the fruits of their research at the International Interconnect Technology Conference in San Francisco, which runs until June 6th.

Sources:
ST, others report progress on novel interconnects
04/06/07
http://www.eetimes.com/news/semi/showArticle.jhtml?articleID=199900786

IITC Preview: New Materials Reduce RC Delays
04/06/07
http://www.reed-electronics.com/semiconductor/article/CA6428441

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