Current thinking

Carbon nanotubes could replace aluminium and copper on micro-electric interconnectors thanks to a technique developed in the UK. Siobhan Wagner explains.

The semiconductor industry typically uses aluminum or copper for on-chip interconnectors. Now researchers from UK company Surrey Nanosystems believe they have developed a machine, the NanoGrowth 1000n, that will effectively replace those materials with carbon nanotubes.

These have long been an attractive material for semiconductor applications because of their extraordinary mechanical and unique electronic properties, including exceptional current carrying capacity, which would lead to faster microprocessors.

The material has not been used in chips until now because no-one has developed a system that can grow nanotubes in an environment that is compatible with microchip production.

Microchips and transistors, such as the Pentium processor, are manufactured using what is known as the complementary metal oxide semiconductor (CMOS) process. This must happen at a relatively low temperature window, between 200ºC and 380ºC, or the microchip could be destroyed. The tricky thing about integrating carbon nanotubes into the chips is that, traditionally, they have been grown under much higher temperatures.

The machine developed by the Surrey researchers is the first to achieve carbon nanotube growth at both low and higher temperatures up to 1,000ºC.

Ben Jensen, one of the developers of the device, said a key feature is the ability to repeat similar results again and again. This differs to the way laboratories currently fabricate nanomaterials with ‘bespoke equipment’ that have difficulty achieving repeatable results, he said.

Jensen compared the design of the NanoGrowth 1000n module to a ‘miniature chemical factory’ that contains a processing vacuum chamber and a PC control system running the data acquisition.

In the last four years the researchers have developed a flexible closed-loop control system that allows users to define target tolerances to achieve repeatability.

Also, as the process runs, the system analyses all the process parameters in real-time and logs the data so that users have a statistical report of the performance.

The versatility of the system is a key feature, he said. The tool is designed for a variety of nanomaterial fabrication and comes with both chemical vapour deposition and plasma-enhanced CVD processing capability.

The module can also handle processing techniques such as inductively coupled plasma, and also features dual sputter sources for catalyst deposition, which includes a module for delivery of vapour-phase catalysts such as ferrocene, and modules to add process stages for automated pilot production or high throughput.

The system also comes with ready-to-use fabrication programs that provide nanomaterial growth recipes in the form of software templates that users can adapt for their own applications.

‘Many of our customers want to take the materials, grow them on a substrate and integrate them into a sensor, a MEMS device or into a microchip. They don’t want to spend years and years learning how to grow the materials.’ said Jensen.

‘We take the technology and the processes developed at Surrey, translate those and put them into the nanogrowth tool. That enables customers to literally load their recipe, press the button, put their wafer in and get the material they require.’