A magnetic null-based debris mitigation system for protecting optics in laser-produced plasma EUV lithography

Background

Extreme ultraviolet (EUV) lithography is a critical technology in the semiconductor industry, enabling the fabrication of ever-smaller and more complex integrated circuits. EUV systems generate light at a wavelength of 13.5 nm using laser-produced plasma (LPP) sources, typically by firing high-energy lasers at molten tin droplets. This process creates intense bursts of EUV light but also produces significant debris, including fast and slow tin ions and neutral atoms. The debris poses a severe threat to the delicate multilayer mirrors used to collect and focus EUV light, as even minor contamination or damage can drastically reduce system efficiency and increase maintenance costs. As the demand for higher throughput and smaller feature sizes continues to grow, the need for effective debris mitigation solutions becomes increasingly urgent to ensure the reliability and longevity of EUV lithography equipment.

Current approaches to debris mitigation primarily rely on introducing hydrogen buffer gas into the EUV chamber. The hydrogen serves two purposes: it slows down energetic tin ions and chemically reacts with tin deposits to form volatile stannane (SnH₄), which can be pumped away. However, this method has significant drawbacks. High hydrogen pressures are required to effectively stop fast ions, but these pressures can lead to mirror damage through ion implantation and blistering, ultimately shortening mirror lifespan. Additionally, increased gas density absorbs EUV light, reducing overall collection efficiency and throughput. Magnetic field-based methods have also been explored, but conventional perpendicular field configurations tend to trap ions through magnetic mirroring, causing some ions to remain confined and eventually neutralize on sensitive surfaces. These limitations highlight the pressing need for new debris mitigation strategies that can protect critical optics without compromising EUV generation or system performance.

Technology

The described technology is a sophisticated debris mitigation system for laser-produced plasma (LPP) extreme ultraviolet (EUV) lithography sources, which are critical for advanced semiconductor manufacturing. This system employs three-dimensional magnetic nulls—specific points in space where the magnetic field is zero, characterized by a spine line and a fan plane—to channel ionized tin debris away from sensitive collection mirrors. The magnetic nulls are generated by strategically arranged electromagnetic coils or permanent magnets positioned outside the EUV light cone, ensuring no interference with the EUV beam. The system includes a droplet source to position molten tin droplets at the null, a collection mirror with a central hole for the laser beam, and dynamically controlled magnetic field generators. By adjusting coil currents, the system can fine-tune the shape and position of the magnetic null, optimizing the routing of debris along the fan plane or spine line and guiding it safely through a hole in the mirror or toward less sensitive areas.

This technology is differentiated by its exploitation of the unique topology of magnetic nulls, which fundamentally alters ion trajectories compared to traditional perpendicular magnetic field methods. Unlike prior approaches that trap ions—leading to eventual neutralization and mirror damage—this system ensures that ions experience unstable, erratic paths near the null, causing them to escape predictably along designated routes. This eliminates the need for high-pressure buffer gases, which can cause mirror blistering and reduce EUV collection efficiency. The magnetic null’s zero-field region preserves the delicate laser-plasma interaction, while its tunable geometry allows for real-time adaptation to changing debris patterns. Simulation results confirm that this method significantly reduces ion flux to mirrors and distributes debris over a larger area, thereby extending mirror lifetime, reducing maintenance, and enhancing the overall efficiency and reliability of EUV lithography systems.

Benefits

• Effectively channels ionized debris away from sensitive EUV collection mirrors, reducing mirror damage.
• Eliminates ion trapping by exploiting the unique topology of three-dimensional magnetic nulls, allowing ions to escape predictably.
• Reduces the need for high-pressure buffer gases, minimizing mirror blistering and EUV absorption by background gas.
• Preserves laser-plasma interactions by maintaining zero magnetic field at the plasma location.
• Enables dynamic control of magnetic null shape and position via adjustable coil currents for optimized debris mitigation.
• Increases EUV system lifetime and reliability by minimizing debris accumulation and maintenance requirements.
• Spreads ion impacts over a larger area, preventing concentrated damage and improving system efficiency.
• Integrates seamlessly with existing EUV system geometries without interfering with the EUV light path.

Applications

• EUV lithography system debris mitigation
• Semiconductor manufacturing mirror protection
• High-precision optics contamination control

Additional info

A system mitigates debris in laser-produced plasma EUV sources by generating three-dimensional magnetic nulls. These nulls, created by external electromagnetic coils, channel ionized tin droplets along their fan plane or spine line, guiding them away from sensitive collection mirrors. This method avoids ion trapping, reduces buffer gas reliance, and preserves laser-plasma interactions, enhancing system reliability and mirror lifetime.