High-reflectance La/B-based multilayer mirror for 6.x  nm wavelength

Area of Science:

• Materials Science
• Optics
• Thin-Film Deposition

Background:

• Multilayer optics are crucial for applications operating at specific wavelengths, including extreme ultraviolet (EUV) lithography and plasma diagnostics.
• Lanthanum (La) and Boron (B) based multilayers are promising for soft X-ray applications, but their reflectivity is often limited by interfacial reactions.
• Achieving high reflectivity at 6.7-nm wavelength requires precise control over layer interfaces to prevent the formation of optically detrimental compounds.

Purpose of the Study:

• To develop and report a novel hybrid thin-film deposition procedure to significantly enhance the reflectivity of La/B-based multilayer structures.
• To investigate methods for preventing the formation of undesirable LaBx and BN compounds at the interfaces of La/B multilayers.
• To assess the potential of the developed deposition technique for multilayer optics operating at 6.7-nm wavelength and beyond.

Main Methods:

• A hybrid thin-film deposition procedure was employed for fabricating La/B multilayer structures.
• A special scheme of La passivation, involving nitridation, was implemented to control interfacial reactions.
• Time-dosed nitridation was applied at the initial stage of deposition to prevent BN formation at the La-on-B interface.

Main Results:

• The developed procedure significantly enhanced the reflectivity of La/B-based multilayer structures.
• A peak reflectance of 64.1% at 6.65 nm was achieved for the multilayer structure, measured at 1.5-degrees off-normal incidence.
• The nitridation process successfully prevented the formation of the optically unfavorable LaBx compound at the B-on-La interface and undesired BN at the La-on-B interface.

Conclusions:

• The hybrid thin-film deposition procedure with controlled La passivation is effective in enhancing the reflectivity of La/B multilayer optics.
• The method demonstrates a viable approach to mitigate interfacial compound formation, crucial for high-performance multilayer mirrors.
• This research shows good potential for further increasing the reflectivity of multilayer structures at the critical 6.7-nm wavelength.