Subwavelength single layer absorption resonance antireflection coatings.

Area of Science:

• Optics and Photonics
• Materials Science
• Nanotechnology

Background:

• Molybdenum-silicon multilayer mirrors (Mo/Si MLM) are crucial for extreme ultraviolet (EUV) lithography.
• Achieving near-zero reflectance is essential for enhancing the performance of Mo/Si MLMs.

Purpose of the Study:

• To derive theoretical design rules for an effective absorbing resonance antireflection coating.
• To apply and validate these rules for coatings on Mo/Si MLMs in the 100-400 nm spectral range.

Main Methods:

• Theoretical derivation of design rules based on coating thickness and optical constants.
• Deposition of SixCyNz thin films using electron beam co-deposition with N+ ion implantation.
• Characterization of optical constants via variable angle spectroscopic ellipsometry.

Main Results:

• Design rules show strong dependence on coating thickness and optical constants.
• Below 230 nm, absorbing films provide additional phase shift for suppression below quarter-wave limit.
• Above 230 nm, minimal absorption (k < 0.2) is required, with increasing thickness towards quarter-wave limit.
• Demonstrated reflectance reduction from 58% to 0.3% at 285 nm using a 20 nm Si0.52C0.16N0.29 film.

Conclusions:

• The derived design rules are effective for creating high-performance antireflection coatings.
• Absorbing thin films offer a viable strategy for reflectance suppression in EUV lithography.
• The developed SixCyNz films show promise for advanced optical coating applications.