Ultra-Narrowband Induced Transmission Filter for EUV Lithography

This invention introduces a transmission-based induced filter operating in the extreme ultraviolet (EUV) regime. The purpose of the invention is to create high transmittance and ultranarrow band filters for EUV lithography even with losses. The filter is composed of EUV-compatible mirrors and a lossy medium. At the resonance frequency, there is minimal attenuation, despite the absorptive material in the cavity, because the induced transmission resonance enables constructive interference in transmission and reflective suppression.  

Background: 
High-numerical-aperture EUV lithography systems play an important role in semiconductor manufacturing, enabling the printing of extremely small features on integrated circuits. These systems demand narrow spectral bandwidths, and transmission filters play a vital role in achieving this precision. They ensure narrow spectral bandwidths that are essential for minimizing chromatic aberration, enhancing imaging fidelity, protecting optics, and maintaining throughput. As chipmakers continue to demand smaller and smaller feature sizes, the performance and precision of these filters will be a critical enabler of next-generation lithography.

Applications: 

• EUV lithography
• Spectral purity filters for laser-produced plasma sources
• Narrowband imaging filters in EUV metrology 
• Free-space EUV beamlines or source diagnostics
• Free-space EUV beamlines or source diagnostics
• On-chip EUV filtering for integrated optics

Advantages: 

• Minimizes chromatic aberration and maintains a high resolution in high numerical aperture imaging
• High transmission efficiency 
• Transmission-based filtering allows for compact optical paths, on-axis filtering architectures, and oblique angle filtering
• Mechanical stability 
• Angle-dependent tunability enables spectral shaping and use of off-axis collectors