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P H O T O N I C S

A giant bid to etch tiny circuitsIntel invests US$1 billion into extreme-ultraviolet light technology that will quarter thesize of transistors.

B Y K A T H E R I N E B O U R Z A C

Consumers take it for granted thattheir mobile phones and laptopswill get faster and more powerful

with each generation. After all, the semi-conductor industry has always made it so, bydoubling the number of transistors it can fitonto a microchip every couple of years. Butcurrent techniques are reaching their limit.

Now, the industry is racing to develop aneconomically viable way to etch even smaller

features onto microchips. The solution couldbe a technique called extreme-ultraviolet(EUV) lithography, which uses very-short-wavelength light to create features thatare four times finer than those on currentmicrochips. But overcoming the chemistry,physics and engineering challenges involvedis costing the industry billions of dollars.

On 9 July, Intel the worlds largest manu-facturer of microchips announced that itwould invest 3.3 billion (US$4.1 billion) inASML in Veldhoven, the Netherlands, the lead-ing supplier of lithography equipment to thesemiconductor industry. One-quarter of thatis earmarked for research and development(R&D) of EUV equipment. The situationhas changed from, Can we make it work? toWe have to make it work, says Stefan Wurm,director of lithography at Sematech, a semicon-ductor R&D consortium in Albany, New York.

The integrated circuit pattern on a microchipis made by shining light through a mask onto asilicon wafer that is coated with light-sensitivematerial called a photoresist. Where light hitsthe photoresist, it cures a pattern onto the sur-face of the chip that is then etched in chemi-cally. The smallest features on todays chipsare 22 nanometres across, and are imprintedusing deep ultraviolet light, typically with a

wavelength of around 193 nm. Even that is astruggle, requiring tricks such as immersing thelens in water and using two exposure steps. Its

already been optimized to the extreme, saysLuc Van den hove, chief executive of Imec, ananoelectronics research company in Leuven,Belgium, that works with the semiconductorindustry to test EUV lithography equipment.

DOWN, DOWN, DOWN

The only way to pattern smaller features is toshorten the wavelength used. Lowering it to13.5 nm should allow microchip factories toproduce features of 5 nm or smaller. But sucha dramatic shortening will require a rethink ofthe optics, photoresists, masks and light sourcebehind lithography systems. Most parts of theprocess are ready for prime time, but the lightsource still presents problems.

Almost all materials even air absorblight with wavelengths as short as 13.5 nm, sothe process needs to be take place in a vacuum.And because the light cannot be guided withconventional mirrors and lenses, optics maker

Carl Zeiss, headquartered in Oberkochen,Germany, has had to come up with alternativedesigns. The good news is, Zeiss knows how

to make these mirrors, says Jos Benschop,senior vice-president for technology atASML. The bad news, he adds, is that eventhese specialized mirrors made from80 alternating layers of atomically smoothsilicon and molybdenum absorb a lot ofEUV light, so the light must be very bright.

The dimmer the light, the longer it takes tocure the photoresist, and because lithographyis the slowest step in microchip manufacture,the strength of the EUV source is the key tokeeping costs down. The first generation of

EUV sources offered only about 10 watts oflight, enough to pattern just 10 silicon wafersan hour. Benschop says that commercialsystems must reach 200 watts and patternat least 100 wafers an hour. To reach thesegoals, ASML is working with two compa-nies: Cymer in San Diego, California; andXTREME Technologies, in Aachen, Ger-

many, a subsidiary of Tokyo-based Ushio.Cymer, for instance, is fine-tuning a systemthat uses a 20-kilowatt laser to blast dropletsof tin into a 500,000-degree plasma that emitsEUV light.

ASML has just a few years to reach its goal.Intel says that it can use the current technologyfor two more generations of microchips, butonly by adding expensive patterning steps andbuying more lithography machines. Benschopadmits that EUV technology should have beenready yesterday.

While it rushes to get the first EUVlithography systems ready for production,ASML faces another challenge from Intel. Cir-cuits are typically etched on to 300-mm-widesilicon wafers, but the chip giant wants to moveto 450-mm-wide wafers for EUV lithography.The shift could double the number of circuitsthat can be patterned at once but it wouldalso require ASML to develop new manufactur-

ing equipment, which Intel wants by 2016. TheR&D challenges ASML is facing are enormous,says Van den hove.

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ASML devices make EUV light by turning tin into plasma.

A S M L

HARVARD

UNIV./

CALTECH

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