After ten years of research and development, ASML officially delivered the first batch of modules of the first HighNA (high numerical aperture) EUV lithography system-TWINSCANEXE:5000 to Intel in December 2023, representing an important step forward in cutting-edge chip manufacturing.
Recently, ASML published a popular science article titled "5 Things You Should Know About High Numerical Aperture EUV Lithography", which further introduced the High-NA lithography system.
The following is Xinzhixun’s translation of the article:
At present, chip manufacturers still rely on transistor shrinkage to promote the advancement of microchip technology. Although, this is not the only way to improve the chip, for example, novel architecture, advanced packaging, etc. can also improve performance. But there's a reason Moore's Law is essentially a universal law: For more than 50 years, transistor "scaling" has been behind the exponential growth in computing power.
For years, we have been pushing deep ultraviolet (DUV) lithography technology to its limits. In order to reduce the size of the smallest feature that can be photolithographed (called the critical dimension (CD)), we can adjust two main parameters: the wavelength of light λ and the numerical aperture NA.
However, there is not much room left in our DUV systems to adjust these parameters.
According to the Rayleigh formula, it can be seen that the lithography resolution (R) is mainly determined by three factors, namely the wavelength of light (λ), the sine value (sinθ) of the maximum angle that light can pass through the lens (lens aperture angle half angle θ), the refractive index (n) and the coefficient k1. In addition to lithography resolution, the depth of focus (DOF) is also crucial. A large depth of focus can increase the clear range of etching and improve the quality of lithography. The depth of focus can also be improved by increasing the refractive index (n) of the system.
EUV lithography allows us to make significant adjustments to the wavelength parameters, it uses 13.5nm light, while the highest resolution DUV systems use 193nm light. When our first pre-production EUV lithography platform, the NXE, first shipped in 2010, its CD dropped from over 30nm for DUV to 13nm for EUV.
1. What is high numerical aperture EUV lithography?
High numerical aperture EUV is the next step in our ongoing pursuit of scaling. Like the NXE system, it uses EUV light to print tiny features on silicon wafers.
By adjusting the NA parameter we can provide better resolution:The new platform, called EXE, can provide chipmakers with 8-nanometer CDs. This means they can print transistors that are 1.7 times smaller than the NXE system, resulting in a 2.9 times increase in transistor density.
How do we get higher resolution in high numerical aperture EUV systems? Why do chipmakers invest in new technologies? What does this mean to you?
1. Larger anamorphic optical devices, clearer imaging
The major advancement in high numerical aperture EUV lithography is new optics. "NA" refers to numerical aperture - a measure of an optical system's ability to collect and focus light.
It's called HighNAEUV because we increased the NA from 0.33 in the NXE system to 0.55 in the EXE system. The higher the NA, the higher the resolution of the system.
Achieving an increase in numerical aperture means using larger mirrors. But a larger mirror will increase the angle at which light hits the engraved lines, where the pattern is to be printed. At larger angles, the reticle loses reflectivity, so the pattern cannot be transferred to the wafer.
The problem could have been solved by shrinking the pattern by a factor of 8 instead of the 4x used in the NXE system, but this would have required the chipmaker to switch to a larger reticle.
Instead, EXE uses an ingenious design: anamorphic optics.
Instead of shrinking the pattern being printed evenly, the system's mirrors shrink it 4x in one direction and 8x in the other.
This solution reduces the angle at which light hits the reticle and avoids reflection problems. What's important is that
It also allows chipmakers to continue using traditional-sized reticles, minimizing the impact of new technologies on the semiconductor ecosystem.
△ZEISS’s high numerical aperture EUV mirror test (Picture source: ZEISSSMT)
2. Faster workbench, higher productivity
Thanks to anamorphic optics, the EXE system's exposure field size is half that of its predecessor, the NXE system. Therefore, patterning a single wafer requires twice the number of exposures.
Twice the number of exposures could mean doubling the time for wafer lithography. So how to solve this problem? Faster wafer and reticle stage movement speeds.
The wafer stage acceleration in the EXE system reaches 8g, which is twice the speed of the NXE wafer stage.
The acceleration of EXE's crosshair stage is four times that of NXE, that is, 32g, which is equivalent to a racing car accelerating from 0 to 100 km/h in 0.09 seconds.
With the new platform, the TWINSCANEXE:5000 can etch more than 185 wafers per hour, an increase over NXE systems already used in high-volume manufacturing.
We have developed a roadmap to increase production capacity to 220 wafers per hour by 2025. This productivity is critical to ensuring that integrating high numerical aperture into chip fabs is economically viable for chip manufacturers.
△Open, fully assembled TWINSCANEXE:5000
3. Easier manufacturing to improve cost efficiency
High numerical aperture EUV lithography will enable chipmakers to print the smallest features on state-of-the-art microchips. But in the meantime, chipmakers aren't just sitting on the sidelines. They found other ways to work around the resolution limitations of lithography systems by using more complex production processes.
These solutions come at a cost. They increase production time and provide additional opportunities to introduce defects that can affect chip performance.
The EXE:5000's CD is 8nm, allowing chipmakers to streamline their manufacturing processes. The result is more cost-effective production of advanced microchips.
4. Versatility and modularity enable better performance
EXE:5000 represents an evolution of EUV lithography technology, not a revolution. We reused as much existing EUV technology as possible and only changed aspects necessary to provide system resolution and productivity enhancements.
And, like our NXEEUV system, the EXE system is composed of modules that can be tested independently before being integrated into a complete system.
Why are we prioritizing versatility and modularity across our entire EUV lithography system? Because in this way all our systems will benefit from the lessons learned from more than 20 years of EUV development. Using tried and tested techniques reduces the risk of problems.
These modules simplify system installation and integration into customer fabs. This means systems will start producing chips sooner - our customers will start R&D in 2024-2025 and enter high-volume production in 2025-2026.
The faster timeline is good news for everyone: The sooner these systems can start printing state-of-the-art chips, the sooner the cutting-edge technology they support will be available.
△Assemble TWINSCANEXE:5000
5. Improved chip functionality, performance and energy efficiency
The EXE:5000's 8nm resolution means chipmakers can pack more transistors into a single chip. Smaller transistors are more energy efficient - meaning the chip will be able to do more with fewer resources.
As a result, the tiny features printed by the EXE:5000 will form the basis of state-of-the-art microchips. And, because of the productivity of the system, chipmakers can manufacture these chips in large quantities.
Impact of high numerical aperture EUV lithography
Chip innovation is becoming increasingly important in today's digital world. Consumers expect new and next-generation electronic devices to be smaller, more functional, better, and faster. With high numerical aperture EUV lithography, chipmakers can meet these consumer demands.
The first chips manufactured using EXE:5000 will be 2nm node logic chips. Memory chips with similar transistor density will follow. These chips will combine the tiniest functionality with leading-edge architecture to power the technologies of the future: robotics, artificial intelligence, the Internet of Things, and more.