Researchers at Mitsubishi Electric said the material meets the dielectric constant, thermal robustness and mechanical strength criteria to be useful in chips at that process generation.

The company's polymer and advanced technology R&D center in Osaka, Japan, has developed a polyborazylene material with a k-value of 1.85 to 1.87, able to withstand a thermal process of 465°C and has the structural rigidity to survive grinding and polishing processes.

"We discovered this material with its high thermal stability and low-k by computer-aided molecular design and actually synthesized this proposed material," said Hideharu Nobutoki, head researcher at the R&D center. The k-value of 1.85 to 1.87 was verified as a bulk characteristic, Nobutoki told EE Times.

Mitsubishi was to have presented a paper on its development at the International Sematech Ultra Low-K Workshop on Tuesday (Sept. 18). That gathering was postponed following last week's terrorist attacks.

As researchers press forward with development of copper wiring with lower resistance, capacitance and attendant signal delays remain a major stumbling block for the 70-nm era, when speeds are expected to push past 3.5 GHz. Finding a substance that has a dielectric constant of about 1.9 to 2.0 is generally considered an essential element in combating this. Reaching this constant is one of the many critical targets defined by the National Technology Roadmap for Semiconductors for the 70-nm era.

Inorganic insulators are generally recognized as having high mechanical strength and heat resistance but inadequate dielectric constants. For example, SiOC film has thermal stability up to 550°C and a requisite mechanical robustness, but its dielectric constant of 2.7 to 3 is far too high, Mitsubishi researchers said.

Spun deposited porous inorganic insulators can hit a sub-2.0 dielectric constant and have sufficient thermal tolerance, but their porosity means they lack mechanical strength. Organic spun materials such as Silk from Dow Chemical Co. lack both the low constant and mechanical robustness, Mitsubishi said.

Polyborazylene potentially overcomes all these stumbling blocks, Nobutoki said.

While Mitsubishi has yet to integrate the material into experimental multilayer insulators, the substance is still undergoing feasibility studies and is a competitive "candidate" for 70-nm technologies, Nobutoki said.

"This material is still in the sphere of a feasibility study and true utilization is aimed at 2005 and afterwards," he said.

Nobutoki said it was unclear whether this low-k candidate would have utility down to the 60-nm process node. Mitsubishi has no plans to use the material in more imminent processes, such as its 100-nm technology, Nobutoki said.

Mitsubishi plans to have its 100-nm process ready in 2003, researchers said.