The deep ultraviolet spectroscopic properties of a next-generation photoresist

Importance of the Topic

Deep ultraviolet (DUV) spectroscopy is essential for the development and evaluation of advanced photoresist materials aimed at next-generation optical lithography. As lithographic wavelengths shorten toward 157 nm, conventional resist formulations exhibit excessive absorption, driving the search for new polymer chemistries and reliable analytical methods to assess film transparency and uniformity at these wavelengths.

Objectives and Study Overview

This study aimed to characterize the deep UV specular reflectance properties of a novel photoresist using a Cary Deep UV spectrophotometer configured with a VW absolute specular reflectance accessory within a nitrogen-purged glovebox. Key goals included:

• Assessing the reproducibility of reflectance measurements without sample repositioning.
• Evaluating coating homogeneity via reflectance scans at multiple wafer locations.
• Demonstrating the capability of the DUV system to yield high-quality spectra between 150 nm and 250 nm.

Methodology and Instrumentation

Measurements were performed under inert atmosphere to eliminate air absorption below 190 nm. The instrumentation and protocol included:

• Cary Deep UV Spectrophotometer with nitrogen purging (permits operation down to ~140 nm).
• VW Absolute Specular Reflectance Accessory for absolute and comparative mirror-based calibration.
• Extended sample compartment and rear beam attenuator to optimize signal levels.
• Spin-coated photoresist film on a 10 cm silicon wafer, scanned from 150 nm to 250 nm at 3 nm bandwidth and 600 nm/min.
• Zero and 100 % reflectance baseline corrections applied prior to sample scans.

Main Results and Discussion

Reflectance spectra demonstrated excellent reproducibility and uniformity:

• Five consecutive scans at a fixed position showed negligible variation, confirming instrument stability.
• Reflectance profiles acquired at five different wafer locations overlapped closely, indicating a highly homogeneous coating.

Although film thickness was unspecified—precluding absolute performance claims at 157 nm—the observed low reflectance and consistency suggest promising transparency for deep UV lithography.

Benefits and Practical Applications

The combined use of DUV spectroscopy and VW accessory under nitrogen purging offers:

• Non-vacuum operation down to ~140 nm, simplifying deep UV measurements.
• Accurate absolute specular reflectance without matched reference mirrors.
• Rapid assessment of resist coating uniformity critical for quality control in microfabrication.

Future Trends and Potential Uses

As lithography advances to 157 nm and beyond, future efforts will focus on:

• Developing fluorocarbon and silicon-based polymers (siloxanes, silsesquioxanes) with minimal deep UV absorption.
• Integrating spectroscopic tools into in-line process monitoring for real-time film diagnostics.
• Expanding instrumentation capabilities for sub-140 nm measurements without vacuum systems.

Conclusion

This work demonstrates that a Cary Deep UV spectrophotometer equipped with a VW absolute specular reflectance accessory and inert atmosphere enables reliable, high-quality DUV reflectance measurements of photoresist films. The approach confirms coating homogeneity and provides a robust platform for evaluating next-generation lithographic materials.

Reference

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8. Agilent Technologies. Part numbers: Cary Deep UV Spectrophotometer 00 100783 00; VW Specular Reflectance Accessory 00 100438 00; Cary 400/500 Rear Beam Attenuator 00 100441 00; Cary Extended Sample Compartment 00 100466 00.
9. Agilent Cary WinUV Scan Software Help, Version 2.0.