With the news that Nippon Telegraph & Telephone Corp claims to have perfected a synchrotron for generating X-rays for use in etching – it was actually built for the Japanese phone giant by a joint venture consortium – and intends using it to fabricate 64M bit memory chips (CI No 880), the race to see who will capture the international market for the next generation of chips is hotting up – and Oxford-based Oxford Instruments Plc is right there in the thick of it. Soft X-rays Scientists are striving to use X-rays to make chips that are faster and more powerful. X-ray lithography, as the process is known, uses a giant particle accelerator, a synchrotron, to gouge out circuits to sub-micron design rules on Silicon or Gallium Arsenide. The synchrotron accelerates electrons with giant magnets to the point where violent collisions occur, thereby creating emissions, which include X-rays that are unobtainable in any other way. Using the X-rays the manufacturer is be able to cram far more components on to the chip. Light has traditionally been the key to chip-making. In optical lithography large drawings are made of patterns for tiny circuits. These drawings are then reduced in size and transferred onto a mask. Finally a bright light shining through the mask etches circuits on Silicon wafers coated with photo-sensitive chemicals. As circuits have got smaller it has been necessary to use light with ever-shorter wavelengths. Chip-makers use ultraviolet light, but even so the production of circuits of 0.5 microns is seen as the limit, as diffraction makes accurate focussing impossible. X-rays however only start to cause trouble at a thousandth of a micron, which is far finer than any design rules conceived for use in electronic circuitry. But the kinds of X-rays used by doctors and dentists are too hard for etching chips – instead of carving out the features they tend to bore right through. Soft X-rays, close to the ultra-violet spectrum are the ideal and this is where the synchrotron comes in. But the development and operation of synchrotron technology looks set to be an extremely expensive business. It is estimated that the capital cost of a synchrotron chip factory will be in the region of $500m. Another problem is their size, the synchrotron at the centre for European Research into Nucleoniucs in Switzerland is fifty miles long, and actually crosses the border into France. Chip-makers therefore have striven to make a machine that is small enough and cheap enough to be used in factories for X-ray lithography. IBM, which is dedicated to remaining self sufficient in all but the most routine semiconductor components, has been working on a $40m synchrotron about 50 feet in diameter at the US Brookhaven National Laboratory near Upton, New York. It has also contracted to have 20-foot diameter prototype machine built at its chip factory in East Fishkill, New York – by Oxford Instruments Plc. Manufacturers in West Germany and Japan have already embarked on table-top synchrotrons about six feet in diameter. But shrinking the things creates other problems: where a full-size synchrotron can use giant magnets that operate at room temperature, to generate the necessary magnetic intensity to create collisions that will emit X-rays in a desk-top synchrotron, the power of those giant magnets has to be generated from something much smaller. And the only way that anyone can presently see of doing it without drawing unacceptable currents is to use the phenomenon of superconductivity. And until two years ago, that was believed to happen only at temperatures within a degree or two of Absolute Zero. That in turn requires super-cooling with expensive liquid Helium – and that is the approach that is being used in the first generation of desk-top synchrotrons. The observation, at IBM’s Zurich resaerch laboratory in Switzerland, of superconductivity at relatively high temperatures in new ceramic materials, promises to make it possible to make superconducting magnets that need to be cooled to only about minus 170oC, which can be achieved with much ch
eaper liquid Nitrogen cooling – but those are at least four or five years away. There is also a difficulty with the masks: the X-ray radiation is so strong that it can easily cause damage. And while it is possible to direct the X-rays generated by the synchrotron out of a series of ports – perhaps six or eight on a desk-top synchrotron – directing them is well-nigh impossible, so that the mountain must be brought to Mahomet – that is to say the wafer must be manipulated in front of the stationary beam of X rays, making infinitesimally fine movements. Three-year lead The research and development is so costly that it is believed that no single corporation has the resources to achieve the X-ray goal. It is not surprising therefore that Japan’s Ministry of International Trade and Industry reportedly plans to invest $700m this year in the design and development of a working X-ray lithographic system. In the US the Federal Government has earmarked a mere $25m for research, with the Pentagon, worried about the military implications, devoting $15m to the problem. Indeed, reports the New York Times, there is a strong body of opinion in the US that keeping up in the synchrotron race is essential to it staying ahead in the technologies that are critical for military power and industrial development. Here in the UK, Oxford Instruments is pushing ahead with research and development. It claims to have a three-year lead over its rivals and is preparing to go into volume production. The company has invested large sums of money in the last two years, and received a major boost in June of last year when it won that contract from IBM to develop an electron storage ring synchrotron (CI No 705). Rodney Griffiths, marketing manager, reckons there will be a market for up to 200 table-top synchrotrons costing about $10m each, 95% of which are expected to be sold to chip manufacturers in the US and Japan.
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