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| March 2009 |
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Laser surveys defects in computer microchips
The manufacturers of microchips for, among others, computers could benefit from research done by Stellenbosch University laser physicist Dr Pieter Neethling on the defects regularly experienced in the production process of microchips. Neethling was awarded his doctorate in physics by Stellenbosch University (SU) in December. His dissertation, completed under the supervision of Prof Erich Rohwer of the Department of Physics, is entitled “Electric field-induced second-harmonic (EFISH) measurements of highly boron-doped p+-type Si/SiO2”. It might sound like quite a mouthful, but the research he has done at the Laser Research Institute at Stellenbosch University could have practical implications for the computer industry. According to Dr Neethling, silicon semiconductors – in the form of transistors – are the basis of all modern electronic apparatus. Transistors are among others used to strengthen electronic signals or to switch them on and off. “They’re used in computers and cell phones – even in washing machines,” Dr Neethling says. Silicon is the most commonly occurring metallic chemical element and is generally used in the manufacturing sector. Silicon is ideal for the manufacture of transistors because it forms silicon dioxide, a naturally insulating oxide. This means that silicon – when exposed to air – is always protected by an insulating layer of silicon dioxide. This is a very important characteristic when it comes to manufacturing transistors. Due to improved technology, however, transistors are becoming more and more dense and examples used in computer microchip transformers are becoming smaller and smaller. “Small concentrations of defects occurring naturally between silicon and silicon dioxide are now suddenly playing a huge role in the functioning of the transistor,” Dr Neethling explains. Dr Neethling’s research concentrated specifically on the behaviour of these defects and why they occur. Among other things, he irradiated oxidised silicon with an ultra-short pulse laser light – known as a near-infrared femtosecond laser – to trace defects, specifically after their electronic behaviour. A femtosecond laser emits extremely short light impulses: one femtosecond equals one billionth of one millionth of a second. (One femtosecond is to one second what one second is proportionally – time wise – to 32 million years.) The laser also monitors defects by means of a technique called second-harmonic generation. “We hope that manufacturers of silicon transistors will shortly be able to use this information to manufacture more reliable microchips,” says Neethling. More information:
or Engela Duvenage, Media: Faculty of Science, Stellenbosch University
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Pieter Neethling +27 (21) 808 3609/3380