Aveni keeps copper in play for future chip nodes

Aveni keeps copper in play for future chip nodes

Technology News |
By Peter Clarke

Aveni said that recent research with partners had shown that its SAO copper electroplating chemistry does not impact a cobalt liner in damascene processes and that it that its process enables the continued use of copper at and beyond the 5nm node.

For most of the foundries the 10nm node or N10 means a 48nm minimum metal pitch and metal lines and spaces of about 24nm, said Frédéric Raynal, chief technical officer at Aveni. At that level conventional copper deposition via an acidic electroplating bath is just about ok but it takes longer to fill at those dimensions, said Raynal.

Frédéric Raynal, chief technical officer at Aveni

However, for Intel N10 is more aggressive with 36nm metal pitch. “This why Intel has transitioned to bulk cobalt,” said Raynal. “The drawback is resistance which is four times the value of copper.” Increased resistance impacts both the attainable performance and power consumption.

There are other more exotic possibilities such as replacing copper with ruthenium, graphene or carbon nanotubes, but these are as yet more or less untried in commercial manufacturing process flows.

Advanced dual-damascene structures employ an atomic layer deposition tantalum nitride (TaN) copper diffusion barrier, a thin chemical vapor deposition (CVD) cobalt liner, and the electroplated copper fill layer, which makes up most of the wiring. Earlier generations (before the 7nm node) also use physical vapor deposition (PVD) of a copper seed layer between the cobalt and copper fill, but advanced devices are phasing out this film due to marginal seed coverage and integration hurdles.

Next: Recent study

In a recent study, aveni compared its SAO alkaline-based copper electroplating chemistry performance with a conventional, commercially available acidic copper plating chemistry. The samples to be plated were 3nm CVD cobalt over TaN. The study results showed that the acidic copper chemistry attacked the cobalt liner, causing the plating chemistry to react with the underlying TaN film and form tantalum oxide (TaOx). TaOx formation is another failure mode of devices, because it creates an effective open circuit that prevents current flow.

Aveni’s SAO chemistry is based on an alkali bath which preserves the bottom-up copper fill and extends it to smaller dimensions with improved electrical performance in terms of both yield and electromigration of copper. The method supports direct plating on liner such as a cobalt liner on a 42nm pitch, the company said. With Aveni’s SAO chemistry, the cobalt remained intact and TaOx was not formed, which enables the extension of copper interconnects to process nodes at 5nm and below.

Raynal commented: “We were extremely excited about these results, because they substantiate our position that SAO alkaline-based chemistry for copper electroplating is superior to acidic chemistries, especially with the thinner cobalt liners used in advanced nodes.”

Aveni plans to publish complete findings on its alkaline copper plating in a report in early 2018.

Related links and articles:

News articles:

Globalfoundries launches 7nm ASIC platform

Samsung Foundry begins production of second 10nm process

Using copper pillars to increase analog IC power dissipation

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