Extreme ultraviolet lithography is one of the key technologies enabling the continued miniaturization of semiconductor devices. At the heart of an EUV lithography machine is a light source that must generate intense, stable radiation at 13.5 nanometers. To do this, a powerful laser strikes tiny molten tin droplets, creating a hot plasma that emits EUV light.
Although this process sounds simple, the physics behind it is highly complex. In a new review article, researchers examine the flow physics and modeling challenges that govern laser-produced plasma EUV sources. They show that EUV generation is not only a plasma or optics problem, but also a multiscale fluid dynamics problem involving laser-droplet interaction, droplet deformation, radiation transport, phase change, debris transport, etc.
One major challenge highlighted by the authors is the enormous range of scales involved. The process begins with ultrafast laser-plasma interaction and droplet deformation, but eventually extends to debris transport and deposition over much longer times and larger distances. This makes direct simulation difficult and creates a need for models that can connect plasma physics, radiation hydrodynamics, multiphase flow, rarefied gas dynamics, and particle transport.
The review also emphasizes the importance of debris control. Even if a source produces strong EUV radiation, tin debris can contaminate collector mirrors and reduce system lifetime. Understanding how debris forms, moves, and can be redirected is therefore essential for improving the reliability of future EUV light sources.
By bringing together insights from simulations, experiments, and theoretical analysis, the authors aim to provide a common framework for both the laser-plasma community and the fluid mechanics community. The review suggests that future advances in EUV source performance will depend not only on stronger lasers or better optical systems, but also on a deeper understanding of the flow physics inside the source chamber.
The authors conclude that fluid dynamics will play an increasingly important role in the design of high-efficiency, stable, and debris-resistant EUV light sources. Such understanding may also support the development of future lithography technologies beyond today’s EUV systems.
Authors: Kai Leong Chong, Bo-Fu Wang, Feng Wang, Rui Yan, Hang Ding, Chao Sun, and Quan Zhou.
Corresponding authors: Hang Ding, Chao Sun, and Quan Zhou.
Institutions involved include: Shanghai University, Tsinghua University, and University of Science and Technology of China.
National Science Review
Systematic review