Paul van Gerven
19 March

Lots of high-NA EUV technology was never meant to be used exclusively in high-NA tools. The first low-NA tool equipped with ‘high-NA’ technology has now been shipped.

ASML has started the installation of the first low-NA EUV tool that’s been fitted with technology originally developed for high-NA systems. Thanks to more powerful ‘high-NA’ wafer stages, along with a more efficient light source, the NXE:3800E is capable of processing over 220 wafers per hour (wph) at a dose of 30 mJ/cm2, up from 160 wph at the same dose sported by its predecessor, the NXE:3600D. Additionally, the latest model features a (machine-matched) overlay of 0.9 nm, compared to 1.1 nm for the 3600D.

The stages of high-NA tools had to be seriously beefed up to compensate for the throughput-hurting characteristics of high-NA optics. By definition, a higher NA involves ‘fatter’ light cones, hitting EUV mirrors at a wider range of angles. Unmitigated, this would result in light loss and therefore a hit in throughput, since the reflectance of EUV mirrors is angle-dependent. To avoid losing a significant portion of light, ASML increased the magnification, which shifts the angles of incidence back into optimal territory.

ASML NXE3800
ASML employees seeing off the first NXE:3800E system. Credit: ASML/X

A higher magnification, however, causes throughput issues of its own. Doubling magnification would have shrunk the exposure field by a factor of 4 if mask size was to remain the same, requiring four times as many exposure steps to fill up a wafer. Limiting the damage, ASML opted for anamorphic optics, which doubles the magnification to 8x in one direction and maintains 4x in the other, thus only halving the exposure field (again, at the same mask size). By also halving the time needed for an exposure step, throughput would be maintained – hence the need for faster stages.

These beefed-up stages were never meant to be used in high-NA systems exclusively, however. ASML’s engineers were instructed to develop stages that are fully backward compatible with 0.33-NA systems. This principle of commonality applies to many more high-NA components, including the source and the wafer handling unit. Ultimately, this helps bring down the cost of chip manufacturing.

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Boon

The new stages don’t actually move faster. Stage speed during exposure is dictated by source power and transmission of the optics. The 3800E has the same set of optics on board as the 3600D but is fitted with a more efficient source, increasing EUV output without increasing energy input, an ASML spokesperson confirmed to Bits&Chips. This partially explains the throughput improvement.

The contribution of the stages to the throughput boost, then, is to speed up all stage movements in between exposures. The stages accelerate twice as fast to scanning speed compared to existing low-NA stages. Similarly, deceleration is doubled as well. The stepping motion, in which the stage is repositioned for the next exposure, even involves acceleration and deceleration four times as high. Overall, this roughly halves the time needed for an exposure step, from which now both high-NA and low-NA scanners benefit.

Incidentally, the 3800E tool currently being installed, as well as an unknown number of additional tools, have a throughput of 195 wph. They’ll get an upgrade to ≥ 220 wph later. Shipment of tools featuring the high throughput from the get-go will start later this year, the spokesperson said, adding that some customers preferred to receive 3800E systems as soon as they become available.

An additional boon of the 3800E is reduced energy consumption. By using not much more power while boosting throughput, less energy is needed to expose a wafer. “The energy savings are 20-25 percent per wafer,” the spokesperson told Bits&Chips. ASML is a member of the Semiconductor Climate Consortium (SCC), which aims for the global semiconductor ecosystem to reach net zero emissions by 2050.

First light

ASML announced the installation of the first 3800E in a post on X, stating that “chipmakers have a need for speed! With its new wafer stages, the NXE:3800E will deliver leading-edge productivity for printing advanced chips. We’re pushing lithography to new limits.”

Shipment of the first high-NA tool, the EXE:5000, commenced in December. Another EXE:5000 system assembled in ASML’s and Imec’s joint High-NA Lab recently reached the ‘first light’ milestone and will soon be made available to chipmakers.

For an in-depth look at ASML’s high-NA system design, please refer to the 2023 ASML special edition of Bits&Chips.