Grazing-Incidence La/B-Based Multilayer Mirrors for 6.x nm Wavelength

Area of Science:

• Materials Science
• Optics
• Thin Film Technology

Background:

• Grazing incidence multilayer mirrors are crucial for manipulating soft X-ray radiation.
• Lanthanum nitride/boron (LaN/B) multilayers show promise for 6.x nm applications but suffer from oxidation issues.
• Surface degradation limits the long-term stability and performance of these optical devices.

Purpose of the Study:

• To investigate the fabrication and stability of LaN/B multilayer mirrors for 6.x nm radiation at a large angle of incidence (77° off-normal).
• To identify the cause of surface deterioration in LaN/B multilayers when exposed to air.
• To develop a passivation strategy to enhance the environmental stability of these mirrors.

Main Methods:

• Fabrication of LaN/B multilayers with varying periodicity and layer thicknesses.
• Surface analysis and characterization of multilayer mirrors after exposure to ambient air.
• Optimization of passivation layer (LaN) thickness to prevent oxidation of underlying layers.

Main Results:

• Initial LaN/B multilayers showed significant surface deterioration due to LaN oxidation, even with a boron cap.
• The protective effectiveness of the boron layer was found to be dependent on the thickness of the underlying LaN layer.
• A modified 15 nm LaN/La/B multilayer with a 0.4 nm LaN passivation layer demonstrated excellent stability for six months.
• An initial reflectivity of 74.5% at ~6.66 nm and 77° AOI was achieved, with only a 0.5% decrease over six months due to surface contamination.

Conclusions:

• A thin lanthanum nitride passivation layer significantly enhances the oxidation resistance of LaN/B multilayer mirrors.
• The optimized multilayer structure provides a stable and high-performance solution for 6.x nm radiation applications.
• These findings pave the way for more durable multilayer optics in extreme ultraviolet lithography and microscopy.