Asian Scientist (Aug. 2, 2013) – Researchers have developed ultra-thin saws made of carbon nanotubes and diamond that can cut through silicon wafers with minimum kerf loss.
You can’t saw without producing sawdust – and that can be expensive if, for example, the “dust” comes from wafer manufacturing in the photovoltaic and semiconductor industries, where relatively high kerf loss has been accepted as an unavoidable, if highly regrettable, fact of life.
But now, scientists from Australia and Germany have teamed up to develop a saw wire that is set to effect dramatic reductions in kerf loss. In place of diamond-impregnated steel wires, the researchers use ultra-thin and extremely stable threads made of carbon nanotubes coated with diamond.
The potential of coated carbon nanotubes has long been understood: possible applications include its use as a hard and tough composite material or as a component of highly sensitive sensors and thermoelectric generators.
However, the new material is extremely difficult to synthesize. Diamonds only grow under extreme conditions – at temperatures of around 900 degrees Celsius in an atmosphere containing hydrocarbons.
Furthermore, growing diamonds on nanotubes is a tricky proposition, because carbon tends to form graphite. In order to catalyze the formation of the diamond phase, it’s necessary to use reactive hydrogen to prohibit the deposition of graphite. However, this process also damages the carbon nanotubes.
During their experiments, the researchers chanced upon a solution for protecting the fine carbon nanotubes from the reactive hydrogen used to catalyze diamond growth.
“During our first experiments, fused silica from the reaction chamber accidentally came into contact with the coating plasma. It settled on the substrate and protected it against the aggressive hydrogen,” said researcher Manuel Mee.
And to his surprise, diamonds actually grew on this layer. Tests with a transmission electron microscope further revealed that the nanotubes were undamaged under their protective layer.
“The new saw wires held out the promise of being far superior to traditional steel wires. Because of their high tensile strength, they can be manufactured much thinner than steel wires – and that means significantly less kerf loss,” said Mee.
A joint patent application has been filed for the method and corresponding products while the researchers are currently carrying out sawing tests.
“To be able to show our partners in industry the potential the technology holds, we have to demonstrate how it can help solar companies to save material when processing wafers,” said Mee.
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Source: Fraunhofer IWM.
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