With Alkaline Chemistry, Copper Could Be Forever

IBM shook the foundations of next-generation semiconductor-node planning when it asserted last month that copper would remain the interconnect of choice at 5 nanometers and below. Today (Dec. 12), Aveni (Massy, France) sought to drive a nail in the coffin of copper alternatives by demonstrating that replacing acid-based processing chemistries with an alkaline alternative can easily extend copper to the 3-nm node and quite possibly to the end of the road for complementary metal-oxide semiconductor (CMOS) technology.

Today’s copper dual-damascene interconnects are accompanied by a tantalum nitride (TaN) copper diffusion barrier and cobalt liner. As copper wires get thinner, acidic copper chemistries can etch through the liner, enabling the copper plating to interact with the underlying TaN film. The resultant formation of tantalum oxides can create random open circuits that reduce production yields. Semiconductor companies therefore have explored replacement options such as solid cobalt, ruthenium, graphene, and even carbon nanotubes.

Aveni claims its back-end-of-line alkaline electroplating chemistry makes a switch from copper unnecessary because it leaves the cobalt layer untouched. “One of the problems with acidic chemistries is that they often etch through to the underlying barrier layer. With alkaline chemistry, you do not have this underlay-etching problem,” Aveni CTO Frédéric Raynal told EE Times in an advance interview.

Raynal said acidic chemistry molecules are much larger than the molecules in the alkaline chemistry Aveni uses for its Sao-branded process. The large molecules inhibit acidic chemistries’ utility at or below the 40-nm pitches used for designs with aggressive design rules (10 nm and below). Whereas acidic chemistries are challenged to fill the advanced features of lower-level metal layers, such as Metal 1 through Metal 4, alkaline chemistries can be effectively employed for those layers, according to Aveni.

“To our knowledge, we are the only successful supplier of alkaline chemistries,” Raynal said. The company claims to be working with all of the semiconductor makers prototyping 5-nm chips except Intel, which it hopes to recruit.

Aveni promises to publish a paper fully explaining and quantifying its results in 2018.