Imec has demonstrated that precise control of gas compositions during post-exposure EUV lithography steps can help in minimizing the required exposure dose, thereby unlocking higher wafer throughput.

In particular, improved dose response of metal-oxide photoresists (MORs) has been achieved when the EUV post-exposure bake step is performed under elevated oxygen concentrations.

Gas control speeds EUV wafer throughput

Metal-oxide resists (MORs) have emerged as leading candidates for advanced EUV lithography applications, offering superior resolution, reduced line-edge roughness, and good EUV dose-to-size performance compared to chemically amplified resists (CARs).

Their better pattern transfer capability for small features and thin resist films makes them particularly attractive for the highest resolution metal layers, exposed using High NA EUV lithography.

Imec now demonstrates that the dose response of MORs can be further improved by raising the oxygen concentration above atmospheric levels during the EUV lithography post-exposure bake step – a critical heat treatment step after EUV resist exposure and before resist development.

Pollentier, “the trend is observed for both model MOR and commercial MOR materials. This finding shows for the first time that carefully controlling the gas composition during key lithography steps can significantly cut the required EUV exposure dose, directly boosting the throughput of the EUV scanner and reducing process costs. This is just a first result from the BEFORCE tool: the controlled gas composition provides an additional knob to study the origins of environmental effects on the lithographic variability of MOR materials. Equipment manufacturers can use these insights as a guideline to adapt their tools for improved EUV lithography throughput and stability.”

The results were achieved using BEFORCE, a unique research tool developed by imec to investigate the role of the ambient environment on critical dimension (CD) stability and performance of MORs.

“In commercial EUV clusters, resist-coated wafers are exposed in vacuum and then transferred to the post-exposure bake unit, where they are heated under atmospheric conditions,” says Imec’s Kevin Dorney, “our BEFORCE tool mimics these operations, but the wafer transfer and post-exposure bake are isolated from the cleanroom atmosphere and can be performed in precisely controlled environments allowed by gas injection and mixing systems. This unique ability, in combination with an integrated photo-speed measurement, was key to revealing the role of oxygen in boosting MOR’s dose response.”

Gas control speeds EUV wafer throughput 2

To optimally exploit the positive impact of gas compositions on the MOR performance, a more fundamental understanding of the chemical mechanism at play during the resist’s post-exposure bake is essential.

Experiments are ongoing to correlate MOR performance to observations of chemical changes during bake – captured by an integrated Fourier transform infrared spectrometer – under varying environmental conditions.

The planned expansion of the BEFORCE tool with advanced metrology capabilities will enable imec to drive even more impactful results.

BEFORCE can be used more broadly to study both MOR and CAR resists and is accessible to imec’s partners for resist evaluation.

The presented achievements and preliminary fundamental insights are shared in two papers at the 2026 SPIE Advanced Lithography + Patterning Conference:

* Paper 13983-36 – ‘Unraveling a new dose reduction strategy for metal oxide resist by the atmospheric environment of the post exposure bake,’ I. Pollentier et al.

* Paper 13983-50 – ‘Chemical origins of environmental modifications to the lithographic chemistry of MOR resists,’ K. Dorney et al.

By: DocMemory
Copyright © 2023 CST, Inc. All Rights Reserved