Unraveling Dose Reduction in Metal Oxide Resists via Post-Exposure Bake Environment

Key Takeaways

• Higher O₂ (50%) cuts dose-to-gel 25‑30%.
• Humidity boosts photo‑speed only under low O₂.
• PEB atmosphere controls resist condensation more than PED.
• Vacuum PEB raises D2G, air PEB lowers it.
• BEFORCE enables precise gas‑mix control for MOR optimization.

Summary

Researchers at imec introduced the BEFORCE platform to study how post‑exposure bake (PEB) environments affect metal‑oxide EUV resists. By precisely mixing oxygen, humidity, and other gases, they demonstrated that raising O₂ to 50 % and adjusting relative humidity can lower the dose‑to‑gel (D2G) by 25‑30 %. Experiments showed that the PEB atmosphere, not the post‑exposure delay, dominates condensation and photo‑speed. The findings point to a practical route for dose reduction without compromising resist stability.

Pulse Analysis

Extreme ultraviolet (EUV) lithography is the bottleneck for sub‑5 nm semiconductor production, and metal‑oxide resists (MORs) have emerged as a promising high‑resolution alternative. Yet MORs are highly sensitive to ambient gases after exposure, making dose efficiency a critical challenge. Understanding the chemistry that occurs during the post‑exposure bake (PEB) can unlock significant performance gains, but conventional tools lack the ability to isolate individual atmospheric variables. The BEFORCE platform fills this gap by integrating a bake chamber, EUV source, and real‑time FTIR monitoring, allowing researchers to simulate clean‑room conditions with exact oxygen, humidity, and temperature settings.

Data from imec’s experiments reveal a non‑linear relationship between oxygen concentration and photo‑speed. Raising O₂ from the standard 21 % to 50 % consistently reduces the dose‑to‑gel metric by up to 30 %, indicating that the photochemical cross‑linking reactions are far from saturated at ambient levels. Humidity plays a complementary role: under low‑oxygen conditions, higher relative humidity accelerates condensation, further lowering D2G, whereas in oxygen‑rich environments the benefit plateaus. Crucially, the study isolates the PEB step as the dominant factor—air‑filled PEB promotes film‑thickness changes and faster gelation, while vacuum PEB suppresses these effects regardless of the preceding delay atmosphere.

For chip manufacturers, these insights translate into tangible economic advantages. A 25‑30 % dose reduction directly improves EUV tool throughput, reduces power consumption, and eases the strain on photo‑mask defectivity. Moreover, the ability to fine‑tune bake atmospheres without altering resist chemistry offers a low‑cost pathway for existing fab lines to adopt MORs at scale. As the industry moves toward higher volume production under the EU’s Chips Joint Undertaking, integrating BEFORCE‑derived process windows could become a standard best practice, accelerating the transition to next‑generation lithography while maintaining yield and reliability.