EUV (Extreme Ultraviolet) lithography is a core technology that has supported scaling from the 7nm generation onward. To achieve even higher resolution, the industry is introducing High NA EUV (numerical aperture NA = 0.55).

Compared with conventional EUV (NA = 0.33), it is expected to deliver major improvements, including:

● Higher resolution (approx. 1.7x)

● Fewer patterning steps

● Reduced line edge roughness at the 2nm generation and beyond

High NA EUV is a next-generation lithography technology also known as “EUV 2.0.”

The biggest challenges in scaling are as follows:

● Line widths beyond a certain point physically cannot be printed

● Line edge roughness (LER) makes device characteristics unstable

● Multi-patterning increases the number of process steps and costs

● Optical limits (resolution = λ / (2 NA))

Because the EUV wavelength is fixed at 13.5nm, the only way to improve resolution is to “raise the NA.”

(1) Higher Resolution

Moving from the conventional NA = 0.33 to High NA = 0.55 delivers approximately 1.7x higher resolution.

This makes it more likely that the line widths required for the 2nm / 1.4nm generations can be printed in a single exposure.

(2) Less Multi-patterning

With conventional EUV, two or three EUV exposures were sometimes required. High NA EUV expands the range of patterns that can be printed in a single exposure, which leads directly to:

・Fewer process steps (lower cost and shorter time)

・Fewer masks

・Improved yield

(3) Anamorphic Optics

Because of the constraints of its large-aperture optical system, High NA EUV adopts:

・“Anamorphic imaging,” in which the magnification differs between the vertical and horizontal directions

This results in the following characteristics:

・Resolution is maximized

・The exposure field becomes vertically elongated

・New rules are required for mask design

While High NA improves performance, it also brings the following technical challenges.

(1) Mask Blur

As resolution improves, pattern blurring (blur) caused by factors such as:

・Absorption in the mask layer

・Spread of multilayer reflection

・Scattered light

becomes more pronounced. Because this particularly affects the stability of fine patterns, improvements in mask materials are needed.

(2) Lower Throughput (Productivity)

Although resolution increases, the exposure field becomes smaller, so:

・The area that can be printed in one shot is narrower

・Scan speed is constrained

→ The number of wafers processed per tool decreases.

To compensate, ASML is pursuing measures such as:

・Higher laser output

・Light source stabilization

・Faster scanners

(3) Even Stricter Requirements for Resists

To suppress line edge roughness (LER), new resists are needed that satisfy requirements such as:

・Sensitivity

・Toxicity

・Low volatility

・Pattern stability

Particularly at the 2nm generation, “stochastic defects” can no longer be ignored and have become the biggest challenge for the EUV process.

Intel

Planned to be the world’s first to introduce High NA EUV, around 2025. Full-scale adoption from Intel 18A onward.

TSMC

Cautious about early adoption. The N2 generation relies mainly on conventional EUV, with possible partial adoption at N2P.

Samsung

Actively pursuing the combination of GAA × High NA. However, its schedule for introduction into volume production has not been announced.

The likely order of adoption speed is expected to be:

Intel > Samsung > TSMC

・Secures productivity for the 2nm / 1.4nm generations and beyond

・Reduces costs by cutting multi-patterning

・Stabilizes electrical characteristics through more precise patterns

・Provides the optical foundation for the transition from FinFET to GAA

In short, it can be called the core lithography technology of the post-FinFET era.

・High NA EUV is a next-generation lithography technology with NA = 0.55

・It greatly improves resolution and is essential for continued scaling

・It reduces the number of exposures, cutting process steps, masks, and costs

・However, it also faces many challenges, including mask blur, throughput, and resists

1.Why is High NA EUV needed?

2.Explain the characteristics of anamorphic optics.

3.Name two challenges specific to High NA EUV.

 

Column Supervisor: Koji Kakumoto (President, OTIS Co., Ltd.)

After studying abroad and working in planning and development at a trading company, he joined OTIS Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as President, working to drive business growth and strengthen the organization.

 

This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.