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

Significance of the Topic

Spectral reflection and transmission measurements are essential for understanding the optical behavior of coatings and semiconductor films. Mapping these properties across large substrates helps evaluate uniformity, enables targeted selection of material regions with specific band gap energies, and supports the development of alternative transparent conducting oxides to replace costly ITO.

Objectives and Study Overview

This study demonstrates an automated mapping approach using the Agilent Cary 7000 Universal Measurement Spectrophotometer (UMS) equipped with a Solids Autosampler. A graded zinc tin oxide (ZTO) film deposited on a 4 in sapphire wafer was characterized to resolve spatial variations in optical band gap energy at 2 mm × 2 mm resolution across a 100 mm diameter.

Methodology and Instrumentation Used

Measurements were carried out in transmission mode over 200–700 nm (7.8–1.7 eV) with 4 nm spectral bandwidth and 0.1 s signal averaging. The Cary 7000 UMS performs multi-angle photometric spectroscopy from 5° to 85° incidence, combining reflection and transmission without moving the sample. The Solids Autosampler adds radial (z) and rotational (Φ) positioning, enabling unattended mapping of large wafers at user-defined intervals.

Key Results and Discussion

Transmission spectra collected at 5 mm increments from –40 mm to +45 mm across the wafer reveal a systematic shift of the absorption edge. A Tauc plot method ((Absorption)² vs. energy) was used to extract band gap energies. Results range from approximately 3.35 eV at the tin-rich bottom to 3.70 eV at the zinc-rich top. This profile highlights the compositional gradient imparted by simultaneous HiPIMS (Zn) and DCMS (Sn) sputtering.

Benefits and Practical Applications of the Method

• Automated, high-throughput mapping of large substrates without accessory changes.
• Elimination of spectral inconsistencies due to sample repositioning.
• Ability to select regions with precise band gap values for device fabrication.

Future Trends and Opportunities

The integration of advanced positioning with multi-angle measurements paves the way for detailed studies of diffuse reflectance in textured coatings and polarization-dependent properties. Future work may extend to in situ monitoring during film deposition, incorporation of additional spectroscopic modalities, and mapping of complex multilayer optical stacks.

Conclusion

The Agilent Cary 7000 UMS coupled with the Solids Autosampler delivers robust, high-resolution mapping of optical properties on large wafers. The technique provides reliable band gap profiling of graded ZTO films, offering a powerful tool for material optimization and quality control in research and industrial applications.

References

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