Coated Wafer Mapping Using UV-Vis Spectral Reflection and Transmission Measurements

Coated Wafer Mapping Using UV-Vis Spectral Reflection and Transmission Measurements

Importance of the Topic

Characterizing optical coatings and thin films across large substrates is essential for quality control and reliable device fabrication. Spatially resolved measurements reveal coating uniformity and material properties that influence performance in sensors and optoelectronic devices.

Study Objectives and Overview

This study demonstrates an automated mapping approach using the Agilent Cary 7000 Universal Measurement Spectrophotometer equipped with a Solids Autosampler to acquire spatially resolved reflection and transmission spectra on large coated wafers without repositioning or accessory changes. The method is applied to map the band gap across a graded zinc tin oxide layer deposited on a 4 inch sapphire wafer.

Instrumentation Used

The setup comprised:

• Agilent Cary 7000 UMS for multi-angle photometric spectroscopy over 250 to 2500 nm
• Agilent Solids Autosampler providing rotational and radial sample positioning

Methodology

The Solids Autosampler was mounted inside the Cary UMA measurement chamber, enabling two additional degrees of freedom radial and rotational motion. Transmission spectra were recorded from 200 to 700 nm with 4 nm spectral bandwidth and 0.1 s averaging time at 5 mm intervals from -40 to +45 mm along the wafer diameter. The 14 nm graded ZTO coating was produced by simultaneous HiPIMS of zinc and DCMS of tin, forming a composition gradient from Sn rich to Zn rich regions.

Main Results and Discussion

Transmission measurements revealed a systematic shift of the absorption edge towards lower energy at Zn rich positions. Band gap energies were extracted using a Tauc plot by plotting absorption squared versus photon energy and extrapolating to zero absorption. The mapped band gap ranged approximately from 3.3 to 3.7 eV across the diameter, highlighting composition dependent optical properties and enabling targeted sampling for device fabrication.

Benefits and Practical Applications

Automated spatial mapping reduces measurement variability, avoids accessory changes, and improves throughput for large substrates. The technique supports process development and quality assurance in industries relying on uniform optical coatings, including photovoltaics, displays, and sensors.

Future Trends and Potential Applications

Future enhancements may include integration with in situ process monitoring, extension to other materials and spectral regions, higher spatial resolution mapping, and advanced polarization studies to further enrich material characterization capabilities.

Conclusion

The Agilent Cary 7000 UMS with Solids Autosampler provides a robust automated platform for high resolution mapping of optical properties on large coated wafers. The demonstrated band gap mapping of graded ZTO on sapphire illustrates its value for materials research and industrial quality control.

References

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