Spectrophotometric Spatial Profiling of Coated Optical Wafers

Significance of the topic

Optical thin film coatings require accurate, cost-effective spectroscopic characterization to optimize performance and quality control. Automated multi-angle spectroscopic mapping of large substrates enhances productivity, reduces per-sample cost, and supports robust quality assurance in research and manufacturing of optical coatings.

Objectives and Overview of the Study

This study demonstrates an automated workflow to map coating uniformity across a 200 mm diameter wafer. Using the Agilent Cary 7000 UMS spectrophotometer with the Solids Autosampler and Universal Measurement Accessory, the aim was to acquire angular-resolved UV-Vis-NIR reflection data at defined surface points without manual intervention.

Methodology and Instrumentation

• Instrumentation:
  • Agilent Cary 7000 UMS UV-Vis-NIR spectrophotometer (250–2500 nm)
  • Universal Measurement Accessory (UMA) for multi-angle photometric spectroscopy (5°–85° incidence)
  • Agilent Solids Autosampler supporting samples up to 200 mm diameter with radial (z) and rotational (Φ) positioning
  • S-polarization measurements using an automated nanowire grid polarizer
• Sample Mounting: 8” wafer secured with minimal-edge contact clamps to protect coatings
• Mapping Profile: Eight diametrical chords at 22.5° intervals; 27 spatial points per chord (5 mm step) plus edge points at 92 mm and 93 mm
• Measurement Conditions:
  • Angle of incidence: 7° near-normal
  • Beam aperture: 3° horizontal × 1° vertical
  • Spectral bandwidth: 4 nm
  • Data intervals: 1 nm (UV-Vis), 4 nm (NIR)
  • Signal averaging: 0.5–1 s per scan
• Determined radial measurement limit at 94 mm radius to avoid beam clipping

Main Results and Discussion

• Central reflectance spectrum showed >99% reflection between 950 nm and 1150 nm, peaking at 1064 nm
• Spatial mapping at 1064 nm revealed a gradual decrease in reflectance from center to edge in both s- and p-polarizations, indicating slight coating nonuniformity near the wafer periphery
• Reproducibility at the center was better than 0.1% over a 6.5-hour run, highlighting system stability
• Outliers corresponded to surface contamination identified through visual inspection

Benefits and Practical Applications

• Automated, unattended mapping reduces analysis time and labor
• High spatial resolution (≈2 mm × 2 mm) supports detailed uniformity assessment
• System flexibility allows integration into R&D and production QA/QC workflows
• Enhances yield optimization by identifying coating process variability across large substrates

Future Trends and Opportunities

As automated multi-angle spectroscopic mapping matures, integration with real-time process control and machine learning-driven data analysis will enable predictive adjustment of deposition parameters. Expansion to other coating materials and integration with in-line metrology could further accelerate industrial adoption.

Conclusion

The Agilent Cary 7000 UMS with Solids Autosampler delivers reliable, high-resolution mapping of optical coating uniformity on large wafers. Its automation capability and precise multi-angle measurements make it a valuable tool for both development and quality control of thin film coatings in research and manufacturing environments.

References

• Burt T., Zieschang F. Optical Coating Uniformity of 200 mm (8”) Diameter Precut Wafers. OSA Meeting 2016
• Burt T., Haq F. High volume optical component testing using Agilent Cary 7000 UMS with Solids Autosampler, Agilent publication 5991-4071EN, 2005
• Burt T., Haq F. Coated wafer mapping using Agilent Cary 7000 UMS with Solids Autosampler, Agilent publication 5991-4072EN, 2014
• Death D.L. et al. The UMA: A new tool for Multi-angle Photometric Spectroscopy. OIC OSA Meeting, 2013
• Tikhonravov A.V. et al. Optical characterization and reverse engineering based on multiangle spectroscopy, Appl. Opt. 2012, 51, 245-254
• Amotchkina T.V. et al. Oscillations in the spectral behavior of total losses in dielectric films, Opt. Exp. 2012, 20, 16129-16144