Technological Advancements and Future Directions of EUV Lithography and Masks

Introduction

As the semiconductor industry continues to push the limits of manufacturing capabilities, EUV lithography has emerged as a core technology for advanced semiconductor fabrication. With the continuous shrinkage of device feature sizes and increasing device density, this technology faces both exciting opportunities and significant challenges, demanding innovative solutions [1].

EUV Lithography and Mask Defects

EUV lithography has become the leading technology in advanced semiconductor manufacturing. One notable advancement is the maturation of EUV mask pellicle technology. As a protective thin film, the pellicle safeguards the mask from contaminants and defects during the lithography process. After years of development, EUV pellicles are now widely adopted across the industry and play a critical role in maintaining mask integrity and ensuring high yield in semiconductor production.

High-NA EUV Technology and Challenges

High Numerical Aperture (High-NA) EUV lithography represents a new phase in semiconductor manufacturing. This technology enables the printing of smaller features but also introduces unique challenges. A key limitation is that the exposure field of high-NA systems is only half the size of that in traditional EUV and optical lithography tools. For large chips, two separate masks must be used to expose the entire die, requiring precise stitching at the exposure boundary.

An alternative approach under exploration is the use of large-format masks. Interest in this solution is evident from the increased attendance at the recent large-format mask symposium, where participants grew from 70 last year to 150 this year. However, the industry has yet to reach a definitive decision on this path.

Multi-Beam Mask Writers and Advanced Features

Multi-beam mask writers have become a key technology for producing masks with ultra-small features, excellent line width control, and minimal line edge roughness. These capabilities are essential for future process nodes that require sub-resolution assist features. Recent developments include upgraded models with enhanced performance compared to previous generations.

An innovative strategy in mask writing is the selective application of high exposure doses to feature edges to enhance edge sharpness. A particularly efficient implementation of this method is pixel-level dose correction, which enables real-time dose adjustments during the mask writing process, eliminating the need for additional data preparation time.

Curvilinear Features and Infrastructure Development

The industry is increasingly adopting curvilinear features on masks, driven by technologies such as source-mask optimization and inverse lithography. These approaches allow for a larger process window and higher density. While multi-beam mask writers have addressed the practical challenges of fabricating curvilinear features, the supporting infrastructure is still evolving. Ongoing progress in this area indicates that curvilinear features will become more prevalent in future mask designs.

Innovation in EUV Photoresist Technology

EUV photoresist technology continues to evolve, with a focus on understanding and optimizing electron behavior. Unlike optical lithography, chemical reactions in EUV photoresists are driven by photoelectrons and secondary electrons rather than direct photon absorption. Recent research has improved our understanding of how secondary electrons move within photoresist materials, which is critical for achieving better resolution at smaller process nodes.

One promising innovation in this area is vertically aligned photoresists, where the resist molecules are oriented perpendicularly to the substrate. This emerging approach may offer benefits such as reduced line edge roughness and improved etch selectivity at lower exposure doses, although it remains under development.

Sustainable Manufacturing Practices

Sustainability is gaining increasing attention in the semiconductor industry, particularly in the area of photoresist materials. A significant development is the introduction of PFAS-free electron beam resists, which address environmental concerns while maintaining high performance. This marks a meaningful step toward more sustainable semiconductor manufacturing.

Conclusion

The field of EUV lithography and mask technology continues to evolve rapidly, driven by the demand for ever-smaller semiconductor process nodes. From innovations in High-NA systems and multi-beam mask writers to advancements in photoresist technology and sustainable practices, the industry is actively addressing current challenges while preparing for future needs. As these technologies mature, they will enable the manufacturing of next-generation semiconductor devices, while maintaining a commitment to environmental responsibility.

Reference

[1] H. Levinson, "Takeaways From The 2024 SPIE Photomask Technology + EUV Conference," Dec. 4, 2024.