Molecular Spectroscopy Application eHandbook

Significance of the Topic

Optical performance and uniformity of backlighting films and thin-film coatings are critical for modern LED and LCD displays. Highly reflective reflector films enable light-guide panels to achieve the required luminous efficiency. Small variations in multi-layer polymeric or dielectric coatings—in thickness, spectral response, or polarization behavior—can directly impact display brightness, contrast and viewing uniformity.

Study Objectives and Overview

• Map specular reflectance uniformity of an 8-inch coated wafer at 1,064 nm in s- and p-polarization.
• Demonstrate fully automated, unattended multi-angle spectrophotometric measurements on large samples.
• Identify defects or contamination via spatial profiling across the wafer radius.

Methodology and Instrumentation

• Instrument: Agilent Cary 7000 Universal Measurement Spectrophotometer (UMS) with Universal Measurement Accessory (UMA) and Solids Autosampler for 200 mm samples.
• Measurement geometry: near-normal incidence (7°), s- and p-polarization; beam apodized to 3° × 1° (vert. × horiz.).
• Optical settings: spectral range 250–2 500 nm, data intervals 1 nm (UV/Vis) and 4 nm (NIR), bandwidth 4 nm, averaging time 0.5 s.
• Spatial mapping: eight diametric scan chords, 27 points per chord at 5 mm radial steps plus two 1 mm steps near the edge; total of 216 measurement positions.
• Sample mounting: 200 mm diameter coated wafer held by an 8-inch round sample tray in the autosampler, minimizing edge contact.

Main Results and Discussion

• Center-wavelength reflectance spectrum at 7° incidence shows > 99 % reflection in 950–1 150 nm band.
• Spatial profiles at 1 064 nm exhibit a gradual R_s and R_p decrease from ≥ 99.2 % at center to ≥ 98.0 % near the 94 mm radius, indicating excellent centrosymmetry.
• Measurement reproducibility at the center point is better than 0.1 % over the 6.5-hour run, far exceeding the observed radial variation.
• A few outliers correspond to localized surface contamination, detectable by spectral anomalies.

Advantages and Practical Applications

• Fully automated, unattended profiling reduces per-sample measurement time and operator labor.
• High angular and spatial resolution reveals coating non-uniformities, enabling process optimization.
• Capable of mapping large substrates and multiple samples for QA/QC in manufacturing environments.
• Supports polarization-sensitive, multi-angle reflectance and transmission analyses in a single run.

Future Trends and Potential Uses

• Integration into real-time production monitoring for thin-film deposition and optical component fabrication.
• Extension to gradient materials or bandgap mapping for photovoltaic or semiconductor research.
• Development of advanced data-analysis algorithms for defect localization and automated process feedback.
• Application to novel nanostructured coatings with bespoke polarization and angular responses.

Conclusion

The Cary 7000 UMS with Solids Autosampler provides versatile, high-throughput UV-Vis-NIR spectral mapping of large optical substrates. Automated multi-angle s- and p-polarized reflectance profiling across an 8-inch coated wafer reveals sub-percent uniformity variations, with < 0.1 % measurement repeatability over several hours. This capability empowers manufacturers and researchers to detect coating non-uniformities and surface defects early, optimize deposition processes, and ensure consistent performance of optical display components.

References

1. Burt T., Zieschang F. “Optical Coating Uniformity of 200 mm Precut Wafers”, OSA OIC (2016).
2. Burt T., Haq F. “High-volume optical component testing using Cary 7000 UMS with Solids Autosampler”, Agilent App Note 5991-4071EN (2014).
3. Burt T., Haq F. “Coated wafer mapping using Cary 7000 UMS with Solids Autosampler”, Agilent App Note 5991-4072EN (2014).
4. Death D.L. et al. “The UMA: New tool for Multi-angle Photometric Spectroscopy”, OSA Topical Meeting (2013).
5. Tikhonravov A.V. et al. “Optical characterization and reverse engineering based on multiangle spectroscopy”, Appl. Opt. 51, 245–254 (2012).