The characterization of optical components using the Cary Deep UV spectrophotometer and ‘VW’ specular reflectance accessory

Significance of the Topic

Measurement of optical coating properties in the deep ultraviolet region (<175 nm) is critical for developing advanced optical components used in fields such as microlithography and semiconductor inspection. Extending the spectral range below the conventional 190 nm limit enables more accurate characterization of materials like magnesium fluoride coatings, ensuring high performance in demanding optical applications.

Aims and Overview

This study aimed to demonstrate the capabilities of the Cary Deep UV spectrophotometer combined with a VW absolute specular reflectance accessory for measuring deep UV reflectance spectra of magnesium fluoride coated optical components. Samples from different manufacturers were compared over the 140–250 nm range to evaluate coating differences.

Methodology and Instrumentation

A standard Cary spectrophotometer was modified for deep UV measurements by using magnesium fluoride coated optics, a solar-blind deuterium lamp and detector, and dual 1200 line/mm gratings blazed at 150 nm. All measurements were performed in a nitrogen-purged glovebox (<1 ppm O₂ and moisture) to allow reliable spectra down to 140 nm. Key instrumental parameters included:

• Spectral bandwidth: 5 nm
• Beam mode: Double
• Slit height: Reduced
• Light source: UV
• Zero SRA correction for baseline setting

Instrumentation Used:

• Cary Deep UV Spectrophotometer
• VW Absolute Specular Reflectance Accessory
• Cary 400/500 Extended Sample Compartment
• Nitrogen-purged glovebox

Main Results and Discussion

Absolute specular reflectance spectra revealed distinct differences among the three magnesium fluoride coated samples. One mirror exhibited high reflectance near 164 nm but low at 225 nm, while another showed the inverse behavior. A third sample displayed a smoother reflectance profile across the range. Duplicate scans for each component demonstrated excellent reproducibility, highlighting the accessory’s precision. The study confirmed the instrument’s ability to acquire high-quality spectra down to 140 nm.

Benefits and Practical Applications

• Enables quality control and process optimization for deep UV optical coatings.
• Supports development of microlithography and semiconductor inspection components.
• Offers a non-vacuum method for acquiring deep UV spectra, reducing complexity and cost.

Future Trends and Applications

Ongoing advancements may include integration of automated sample handling, extension of spectral capabilities below 140 nm, and application of the technique to novel coating materials. Such developments will further enhance performance evaluation of next-generation optical elements in semiconductor manufacturing and beyond.

Conclusion

The combination of the Cary Deep UV spectrophotometer, VW absolute specular reflectance accessory, and inert atmosphere setup provides a robust and precise method for characterizing magnesium fluoride coated optical components in the 140–250 nm range. This technique aids in distinguishing coating processes and ensures high-performance outcomes for critical optical applications.

References

1. Perkampus H-H. Encyclopedia of Spectroscopy. VCH; 1995.
2. Strong J. Procedures in Experimental Physics. 1st ed. Prentice-Hall; 1938:376.
3. Agilent Technologies. Part Numbers: Cary Deep UV Spectrophotometer (00 100783 00); VW Absolute Specular Reflectance Accessory (00 100438 00); Cary 400/500 Extended Sample Compartment (00 100466 00).
4. Cary WinUV Scan Software Help. Version 2.0.
5. Hind AR. R&D at the deep end. Chemistry in Australia. 2001;68(4):12.