Driving Moore’s law with CO2 lasers

Matthew Dale reports from the European Photonic Industry Consortium’s Executive Meeting on Industrial Lasers, where it was explained how CO­₂ lasers could be used to produce the next generation of computer processors

In response to the increasing use of solid state lasers in the machine tool industry, laser manufacturer Trumpf is now using its CO₂ lasers to develop EUV lithography systems for making the next generation of high-speed computer processors. These new processors will be crucial for addressing the high signal and data processing demands of the autonomous vehicles and mobile devices of the future.

This was one of the key messages delivered by the company at its headquarters in Ditzingen, Germany, at the start of June, where the European Photonics Industry Consortium (EPIC) held a meeting for executives of the laser processing industry.

In a keynote speech, Trumpf’s technology scout Dr Andeas Popp explained that this new application of CO­₂ lasers will be key for taking the next step in Moore’s law, which states that the number of transistors – and thus processing speed – of integrated circuits doubles approximately every 18 months. This is because the sizes of semiconductor structures on modern chips are gradually approaching atomic dimensions, a feat being made possible by complex exposure processes aided by lasers.

Up until now these exposure processes have been performed using UV radiation generated by 193nm excimer lasers. But, according to Popp, this wavelength range faces limitations when producing structures less than 10nm in size. With structures in the range of 5nm - believed by Trumpf to be a key requirement in the development of the next generation of powerful processors - exposure at shorter wavelengths in the extreme ultraviolet (EUV) range must be used to provide the resolution necessary for their fabrication.

Together with lithography technology manufacturer ASML, its subsidiary Cymer and optics giant Zeiss, Trumpf has been developing the CO2 laser technology for EUV lithography systems at 13.5nm.

In the collaboration's setup, a five-stage amplifier is used to ramp the output power of a CO₂ laser by a factor of approximately 10,000, from a few watts to approximately 30kW. The amplified pulses are then used to strike falling tin droplets in a vacuum chamber at a rate of 50,000 times per second, which ionises them to form an extremely hot plasma at 500,000 degrees kelvin. The plasma emits EUV radiation at a wavelength of 13.5nm in all directions, which is then collected by a mirror, and focused and directed through the lithography system to expose the silicon substrate.

^{Trumpf has partnered with ASML and Zeiss to develop a lithography system that generates extreme ultraviolet (EUV) radiation by striking tin droplets with an amplified CO2 laser pulse. (Image: Trumpf)}

The system is capable of processing more than 100 substrates an hour, enough to make it suitable for series production, according to Trumpf.

‘This is a real game-changer,’ Popp said. ‘We are very close to power levels that will enable very reasonable production and allow this technology to enter the mass market. This is how we now use CO­₂ lasers, because laser cutting solutions are now more oriented towards solid state lasers.’

Market share of solid state lasers in the machine tool sector has risen from 8 per cent in 2011, to 27 per cent in 2013, 56 per cent in 2015, and finally a 77 per cent share in 2017.

^{Trumpf uses a multi-stage amplifier process to generate the 30kW laser pulses required to ionize tin droplets and produce an intense plasma that emits EUV radiation. (Image: Trumpf)}

Berthold Schmidt, CEO and president of Trumpf Photonics, also discussed EUV lithography as an alternative application of ­CO₂ lasers in his presentation at the Stuttgart Laser Technology Forum, part of the Lasys show at the beginning of June. He said that Trumpf engineers are working to increase the power of the new lithography system, and have so far been able to achieve over 200W at the wafer processing level. ‘This is sufficient that this industry finally accepts this technology as a future standard,’ he said. ‘We see in our volume and our ramp-up numbers that this will be the future of silicon technology.'

Schmidt added that only these next-generation processors can empower safe autonomous driving, as one example of the need for fast processors. EUV lithography will therefore play an important role in realising future technologies that require large volumes of data to be processed, such as artificial intelligence or more powerful mobile devices.

The new EUV lithography technology driven by CO­₂ lasers ­has already generated interested for major semiconductor manufacturers, according to Trumpf, with such end users currently placing orders for the systems in order to ramp up their mass production throughout 2018 and 2019.