British researchers have found a way to use ultraviolet (UV) light instead of furnaces to create the silicon dioxide insulation layer on computer chips, a breakthrough that could lead to big energy savings for chip makers and lower prices for customers.
Creating a film of silicon dioxide on the surface of silicon wafers is an important stage in chip manufacturing. It serves as the insulating layer into which electrical circuits are later etched using photolithography, and also as the "active gate layer" that helps switch the transistors.
The dioxide builds up naturally when silicon is exposed to air, a bit like iron oxidises into rust, but the process is very slow at room temperature. Chip makers today bake silicon wafers in furnaces at up to 1,000 degrees centigrade to accelerate the process.
The engineers at University College London have found a way to speed up the dioxide creation at room temperature using UV lamps, said Ian Boyd, chair of electronic materials at the university's Department of Electronic and Electrical Engineering, who leads the project. They can create a suitable layer of dioxide in about the same amount of time it takes to blast the silicon in a furnace, he said.
A lot of testing remains and it could be several years before the technology is ready for commercial use, Boyd said. But the payoffs could be significant. The technique uses much less energy than a blast furnace, which could save millions of dollars for chip makers and allow them to reduce the prices of chips. It could also make chip manufacturing more efficient, since when furnaces are used, components added to the chips earlier in the manufacturing process can become diffused in the high temperatures.
The researchers have been contacted about their work by big chip equipment makers, and some chip manufacturers have also expressed interest, according to Boyd. He declined to name the companies.
Key to the research was identifying the right type of UV light. The engineers experimented for years with UV light at wavelengths of 122 nanometers and 172 nms, but that still required heating the silicon to 400 degrees, Boyd said. They recently reduced the wavelength to 126 nms - creating what Boyd called "very deep UV" - and found they could create the dioxide at room temperature.
"When you break oxygen molecules into two oxygen atoms using UV radiation at 200 nanometers or so, the atoms are not very aggressive oxidizers. But with this very deep UV we've developed, one of the atoms becomes an extremely aggressive oxidiser, and that's the secret," he said.
The scientists have grown dioxide films 10 nms to 15 nms thick -- more than sufficient for CMOS chip manufacture. A nm is a billionth of a metre, or about the length of three atoms side by side. The lamps resemble the florescent light tubes used in offices and can be made relatively cheaply, Boyd said. "They could be mass produced very easily. They'd need a bit of development, like the early light bulbs."
The next step for the scientists is to test the properties of the silicon dioxide in a clean room at the new London Center for Nanotechnology, to see if it's suitable for commercial use. They have to figure out things like how much voltage and current the dioxide can withstand before it breaks down, and how often the current can be passed back and forth before they become defective.
"Chip manufacturers tend to be very conservative and reluctant to change the way they do things," Boyd said. "You have to prove beyond all doubt that what you're doing will improve what they already have."
The researchers have yet to publish a paper on their discovery, although Boyd has presented it at conferences.
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