FEATURE LITHOGRAPHY
The future of EUV lithography
Extreme ultraviolet lithography holds the potential for transforming semiconductor manufacturing. Gemma Church finds that commercial systems could be put into production within the next two years
T
he commercial deployment of Extreme Ultraviolet (EUV) lithography systems has been hit by years of delays and has met
scepticism along the way. But the technical need for EUV lithography has continued to push for the development of production-ready machines – could we be on the brink of a breakthrough? The answer, perhaps unsurprisingly, seems to be a resounding ‘yes’ from the companies developing the machines to make EUV lithography a mainstream technology. But such optimism is not misplaced, as there have been a number of interesting developments in the EUV lithography arena in terms of the optical processes and technologies being used. The primary application area for EUV lithography is within the semiconductor industry, where Moore’s Law – an observation that the number of transistors in an integrated circuit of a given size, and at an acceptable cost, doubles roughly every two years – drives manufacturers to cram as many transistors as possible onto increasingly tiny
chips. This means the transistors must shrink in size too; so, semiconductor lithography machines must be able to print finer features with every new generation of chips. The functional elements of a microchip are transferred from a mask to a silicon wafer by means of complex optical systems. Winfried Kaiser, senior vice president of product
36 ELECTRO OPTICS l FEBRUARY 2016
EUV technology is the future of lithography optics for Carl Zeiss SMT. This technology uses EUV light at 13.5nm
strategy for the semiconductor manufacturing technology business group of Zeiss, said: ‘The uniformity and flexibility of the illumination system and the resolving power of the projection optics play the crucial part in determining how small the structures on a microchip can be.’
The past few
years have seen a renewed vigour within the EUV lithography market
Shortening the wavelength of the light means higher resolution and smaller features – so, EUV lithography is, theoretically, perfectly positioned to meet these demands. Kaiser added: ‘EUV radiation has an approximately 15 times shorter wavelength than the UV light
sources currently used in optical lithography.’ Producing an operational EUV lithography system is easier said than done. The real- world technological challenges that need to be overcome for EUV lithography to become a reality are enormous. ‘The biggest challenge is the fact that EUV light, with a wavelength of 13.5nm, is absorbed by all known materials,
even by air itself. This makes it necessary to develop a completely new concept for lithography optics,’ Kaiser explained. ‘Zeiss utilises all of its competence to develop the necessary technological expertise and skills to enable this cutting-edge technology.’ EUV photons are also difficult to produce. Many EUV systems use a laser-produced plasma (LPP) source, a high-energy laser that is fired onto a microscopic droplet of molten liquid, usually tin, around 40,000 times a second. This droplet turns it into plasma, emitting EUV light, which is then focused into a beam.
The glass of a lens would absorb the EUV photons immediately, so the machine has to use mirrors instead. Herein lies another challenge, as the mirrors must be polished with extreme precision. To put this into perspective, if one of the mirrors were to be blown up to the size of Germany, the biggest bump would need to be less than one tenth of a millimetre high. These mirrors are coated with around
@electrooptics |
www.electrooptics.com
Zeiss
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56