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March 1998


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New Virginia Tech technique for polymers
Can lead to improved VLSI performance

A new copolymerization technique developed at Virginia Tech could lead to improved integrated VLSI chip performance by replacing oxide components with polymer materials.

The new technique allows the creation of low-dielectric-constant materials for interconnects in integrated circuits that produce less crosstalk, less power dissipation, and fewer delays than conventional oxide-based components.

"The industry continues to miniaturize VLSI chips in an effort to increase the density and speed of the devices- and one of the key limitations is the interconnection technology," explained Professor Seshu Desu, director of the Thin Films Laboratory where the new technique was developed.

"The current standard for interconnects materials are a conductive metal such as aluminum, and silicon oxide (SiO2) for the dielectric- to separate the conductors and minimize intercommunication, or crosstalk. Developers are currently working on switching from aluminum to copper, which will increase the speed by 30 percent," he continued.

"However, with the metal/SiO2 configuration, the increased speed and capacity will introduce more crosstalk between the lines, which can degrade a chip's performance. Moreover, there is power dissipation at the transistor device level that is proportional to capacitance. Switching to copper does not improve power loss. It's the dielectric constant of silicon oxide that is the stumbling block.

"Instead, we developed a method to produce a polymeric material with a low dielectric constant that reduces delays (thus increasing speed), while at the same time reduces crosstalk and power dissipation," Desu said. "With our technique, polymer materials can be made that can serve as interlevel dielectrics, thus protect against crosstalk and power dissipation."

The difficulty of producing such materials in the past has been that polymers typically cannot withstand the high temperatures involved in manufacturing miniature components. "That is one of the advantages of silicon oxide," Desu said. "It can withstand, say, 800° C, where most polymers could only take up to 350-400°."

Desu's team's technique enables polymers to be deposited by chemical vapor deposition, a preferred method for producing the miniaturized devices, which can withstand temperatures as high as 500°C. "We can now make the necessary nanocomposites and hybrids," he said.

"Now we can dial in any dielectric constant and thermal decomposition/stability temperature and start screening the new materials for optimum properties."

A patent on the process is pending.

The Bradley Department of Electrical and Computer Engineering
Virginia Tech

Last Updated, April 29, 1998
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