EUV on the home stretch

ASML’s decade-long, dogged pursuit of EUV as the next-generation lithography technology was vindicated in early 2017, when ASML reported customers had placed big batches of orders for EUV systems.

Billions of euros worth of orders for EUV systems silenced the skeptics who for years had claimed EUV would never be used to manufacture chips.

For ASML, this meant that its responsibility to the semiconductor industry had only increased further. As major chip makers were planning their next wave of products, they were counting on ASML’s engineering teams to jump the remaining technical hurdles, and then manufacture, ship and support a larger number of EUV systems.

EUV had to graduate from the R&D lab to the manufacturing fab.

In the months that followed, ASML’s thousands of engineers were able to tick off a number of milestones.

First, they showed that full-size pellicles could be manufactured without defects that influence the imaging. These thin protective covers for the photomask — a thousand times thinner than household plastic wrap — had long been considered both crucial for the introduction of EUV and impossible to make. Later in the year, the team put the pellicle through a series of tests and demonstrated that it could withstand the heat as well as the mechanical stress of high-volume chip production.

The next milestone, reached mid-year, was achieving the target throughput of 125 wafers per hour on a complete system in ASML’s Veldhoven factory. Since higher throughput means that one system can produce more chips, this was a closely-watched metric of the economic value of EUV.

Hans Meiling, Vice President EUV Service- and Product Marketing and with the EUV program since its early days, noted that the very first EUV prototype system needed more than 21 hours to expose a full wafer. At 125 wafers per hour, today’s EUV systems run more than 2,600 times faster.

The higher throughput was achieved with a brighter EUV light source, which delivers the energy needed for exposure to the wafer faster, the culmination of years of work at ASML’s San Diego site.

“We didn’t get here the way we thought we would,” says Alex Schafgans, principal scientist. “We thought we would have to build more powerful lasers. Instead, we learned how to convert plasma into EUV light more efficiently.”

Other technical advances included even better optics, a new illumination system and new sensors. It all resulted in the NXE:3400B, the most advanced EUV system yet. The first was shipped to a logic customer in the first half of 2017.

This latest EUV machine offers improved matched-machine performance for EUV and immersion systems — another 2017 milestone. Since chip makers plan to use EUV and immersion systems in conjunction for the most challenging layers on a chip, the image placement of one system must very closely match the other, so that a layer imaged with one system can be placed accurately on top of one imaged by the other system. The newest systems, the NXE:3400B and the NXT:2000i, achieved an overlay accuracy of 1.9 nanometers.

In the meantime, ASML’s customer support and manufacturing teams were boosting their ability to build, ship, install and service a growing number of EUV systems. In 2017, ASML shipped 10 EUV systems, each the size of a city bus, and the company is planning to boost its output to 22 in 2018.

For ASML’s customer support organization, which maintains an office close to every major fab of the company’s customers, getting ready for the introduction of EUV has meant training hundreds of engineers in how to service the new technology.

Now, at the start of 2018, EUV is on the home stretch to volume introduction.