Cutting EUV Dose via Underlayer Engineering

The Core Challenge of EUV lithography Scaling

Extreme-ultraviolet lithography powers leading-edge semiconductor manufacturing. But as nodes shrink, materials become the bottleneck. Photoresists must balance four competing goals: high resolution, low dose, low line-edge/linewidth roughness, and near-zero defects. Lowering the EUV dose increases scanner throughput. It also increases randomness, because fewer photons form each feature. A SPIE 2026 paper by Achintya Kundu and colleagues tests a different lever: the layer under the resist.

What Is an Underlayer, and How Does It Impact EUV Performance?

An underlayer is a thin film between the wafer and the EUV lithography resist. It does not print patterns by itself. But it affects adhesion, electron generation, energy transfer, development behavior, and pattern stability. Conventional underlayers are usually spin-coated. In contrast, dry deposited underlayer films offer tighter control of thickness and composition. They also avoid solvent-related issues and reduce coating variability. This matters more for ultra-thin stacks in next-generation high-NA EUV.

Testing Dry Underlayers With Metal-Oxide Resists

The team paired a dry-deposited organic underlayer with a metal-oxide resist. Metal-oxide resists absorb EUV strongly and etch well. However, they often need higher doses. They can also suffer defects, edge roughness, and pattern collapse. Here, the underlayer was designed to tune the resist–substrate interface. The goal was to use exposure energy more efficiently.

33% Dose Cut Delivers Major Semiconductor Manufacturing Benefits

The key result was a large reduction in the dose needed to print target dimensions. Follow-on reporting suggests about a 33% dose cut with a metal-oxide resist. That is a meaningful EUV dose reduction for fabs. Dose directly limits scanner throughput. If the same critical dimension is reached with less energy, more wafers can be processed per hour. That lowers cost per patterned layer.

Dose Reduction Without Compromising Pattern Roughness

Lower dose is only useful if pattern quality holds. With fewer photons, stochastic variation can increase edge roughness. The team compared sensitivity and roughness together. Roughness stayed about the same while dose dropped. So the gain was not a “blurrier” print threshold. It reflects a better stack-level response with controlled pattern fidelity.

Minimal Defects and a Wide Usable Process Window

Defects can kill yield at advanced nodes. EUV can produce missing features, bridges, breaks, and microbridges. Even tiny defect rates matter when chips contain billions of features. The team measured defects across the usable dose range, not just average CD. The dry underlayer reduced observed defects and preserved a practical process window. Higher sensitivity did not require worse defectivity.

What Drives This Improved Performance?

Multiple mechanisms likely contribute. The underlayer changes how secondary electrons are generated and transported. Those electrons drive the chemistry that controls dissolution during development. The underlayer also affects interfacial energy, adhesion, and development kinetics. A uniform dry-deposited surface can reduce local variability at the resist bottom interface. That helps thin resists print more consistently.

Key Implications for Future Chip Production

The work argues for optimizing the full materials stack, not only the resist. A well-engineered dry deposited underlayer can cut dose, maintain roughness, and reduce defects. Those are three requirements for production viability. The approach is especially relevant for high-NA EUV, where films are thinner and tolerances are tighter. Underlayer engineering may be a practical path to faster, cheaper, and more reliable scaling.