Long-term changes in Al thin-film extreme ultraviolet filters

Area of Science:

• Materials Science
• Optical Engineering
• Thin-Film Technology

Background:

• Thin-film aluminum (Al) filters are widely used for their high transmittance in the 17-67 nm range and low transmittance in visible and near-UV regions.
• Oxidation of Al filters forms amorphous aluminum oxide (Al2O3) layers, which possess significantly lower transmittance than bulk Al, thus affecting overall filter performance.
• Understanding the long-term stability and transmittance degradation of Al filters in uncontrolled environments is critical for their reliable application.

Purpose of the Study:

• To quantify the transmittance of aged thin-film Al filters.
• To monitor and map the development of transmittance changes in Al filters over a two-year period.
• To assess the impact of environmental exposure on Al filter performance.

Main Methods:

• Characterization of transmittance for aged thin-film Al filters.
• Longitudinal monitoring of Al filter transmittance over two years (2016 onwards).
• Exposure of filters to an uncontrolled atmosphere to simulate real-world conditions.

Main Results:

• The study provides transmittance data for very old Al filters.
• A detailed map of transmittance evolution over two years was generated.
• Significant transmittance reduction was observed due to oxidation and Al2O3 layer formation.

Conclusions:

• Oxidation is a primary factor limiting the long-term performance of thin-film Al filters.
• The amorphous Al2O3 layer significantly reduces filter transmittance.
• Transmittance degradation is a continuous process that must be considered in applications relying on Al filters.