New Materials Provide Innovation Yet Add Complexity

By Jeff Dorsch

If semiconductor materials had a personal Facebook page, its status would be: It’s Complicated.

The days of all silicon, all the time are starting to dwindle. Can any material or combination of materials be as simple and useful as Si?

Some say the semiconductor future belongs to carbon. Graphene, the carbon material that has many wondrous attributes, is not a good semiconducting material, however. IBM Research predicts that carbon nanotubes will take over from silicon at the 5-nanometer process node, when traditional scaling will no longer work. CNTs should be the basic semiconductor material of the 2020s, according to IBM.

For the latter half of this decade, however, there will still be silicon and other materials, including compound semiconductors and semiconductor alloys. Molybdenum disulfide is gaining fans among materials scientists.

“The channel is getting thinner and thinner,” says Aaron Thean, vice president of process technology and director of logic development at imec. With silicon germanium, “processing gets a lot more complicated,” he notes. “With III-V compounds, the key challenge there is the gate stack.”

The 10nm process node is “very tough,” Thean says, and that may be where SiGe really starts to shine. At the 7nm node, there is a “positive outlook for germanium,” he adds.

Thean is bullish on carbon nanotubes as a workhorse material of the future. CNTs possess “the upside of grapheme, but none of the downside,” he says. “The bandgap starts to open.

“A lot of people are working on this,” including IBM, Thean says, noting that there are several types of CNTs.

Gallium arsenide remains a popular material for specialty applications. Gallium nitride, gallium-nitride-on-silicon and silicon carbide are finding more uses these days. Research is going in strontium titanate and other oxide-based semiconductors.

For most providers of IC foundry services, plain old CMOS silicon answers most of their needs, according to Brian Trafas, chief marketing officer of KLA-Tencor. New architectures, such as FinFETs, are presenting challenges for foundries and other chipmakers, he says. A few years out, there may be a requirement for III-V FinFETs, Trafas adds. “That’s probably a 5-nanometer decision,” he says.

In addition to the new materials being used in logic devices, “there could be big changes in memory types” that will call for new and different materials, Trafas says. Magnetoresistive random-access memories (aka magnetic RAM), resistive RAM, and other cutting-edge memory chip technologies are bidding to replace DRAMs, SRAMs, and NAND/NOR flash memory devices, he notes.

With the adoption of new materials, collaboration between semiconductor manufacturing equipment vendors and their customers becomes “more important,” Trafas concludes.

Back for its second visit to SEMICON West this year is Element Six, the supplier of gallium-nitride-on-diamond wafers and synthetic diamond heat spreaders. In May, the company touted the use of its GaN-on-diamond wafers by Raytheon as an alternative to GaN-on-SiC as part of the Defense Advanced Research Project Agency’s Near Junction Thermal Transport program for improving power density and thermal management in GaN radio-frequency devices.

In addition to a TechXPOT session on materials for 3D NAND flash memories this week, Semiconductor Equipment and Materials International is planning its annual Strategic Materials Conference for September 30 and October 1 in Santa Clara, Calif. The 2014 theme for the SMC is “Materials Matter—Enabling the Future of IC Fabrication and Packaging.”

By the way, you can find “semiconductor materials” on Facebook – it’s a link to the Wikipedia article on semi materials.