Inline Mapping of Amorphous Silicon Layer Thickness of Heterojunction Precursors Using Multispectral Imaging
In this paper, we present an inline characterization technique to determine spatially resolved thickness maps of ultra-thin layers on textured silicon substrates. The technique is based on multispectral imaging and optical modelling of discrete spectral reflectance data using rigorous polarization...
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TIB Open Publishing
2025-01-01
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| Series: | SiliconPV Conference Proceedings |
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| Online Access: | https://www.tib-op.org/ojs/index.php/siliconpv/article/view/1324 |
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| author | Saravana Kumar Christian Diestel Saed Al-Hajjawi Jurriaan Schmitz Marc Hemsendorf Jonas Haunschild Stefan J. Rupitsch Stefan Rein |
| author_facet | Saravana Kumar Christian Diestel Saed Al-Hajjawi Jurriaan Schmitz Marc Hemsendorf Jonas Haunschild Stefan J. Rupitsch Stefan Rein |
| author_sort | Saravana Kumar |
| collection | DOAJ |
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In this paper, we present an inline characterization technique to determine spatially resolved thickness maps of ultra-thin layers on textured silicon substrates. The technique is based on multispectral imaging and optical modelling of discrete spectral reflectance data using rigorous polarization ray tracing and the transfer matrix method. The study demonstrates that quantitative inspection of ultra-thin amorphous silicon (a-Si) layers on textured silicon substrates requires an extension of the standard RGB illumination by two additional LED wavelengths in the near-UV. As the required five images are measured in less than a second, the tool is a suitable candidate for inline applications. The optical modelling requires reflectance-calibrated images which are obtained via linear calibration functions and allows the a-Si thickness to be determined at each pixel. The thin-film thickness can be determined either by a direct modelling of the measured reflectance spectra or by a differential approach using the reflectance spectra before and after coating to eliminate effects from non-idealities due to scattering as well as instrumental errors. The a-Si thickness extracted from the reflection data at the five chosen LED wavelengths shows good quantitative agreement with reference values from spectrally-resolved differential reflectance data. Evaluating a test sample with an intentional a-Si thickness variation, we compared the results from the multispectral thickness map and reference values from spectroscopic ellipsometry. We found good quantitative agreement for a-Si thicknesses above 10 nm and a slight overestimation of about 1.5 nm for thinner layers. Overall, the multispectral approach based on only five different channels proves to allow quantitative thickness maps with reasonable accuracy at inline speed.
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| format | Article |
| id | doaj-art-c793a151c7064d56b6ead5ffd1982dab |
| institution | Kabale University |
| issn | 2940-2123 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | TIB Open Publishing |
| record_format | Article |
| series | SiliconPV Conference Proceedings |
| spelling | doaj-art-c793a151c7064d56b6ead5ffd1982dab2025-01-04T09:48:20ZengTIB Open PublishingSiliconPV Conference Proceedings2940-21232025-01-01210.52825/siliconpv.v2i.1324Inline Mapping of Amorphous Silicon Layer Thickness of Heterojunction Precursors Using Multispectral ImagingSaravana Kumar0https://orcid.org/0000-0001-9818-0203Christian Diestel1Saed Al-Hajjawi2https://orcid.org/0000-0003-0767-9012Jurriaan Schmitz3https://orcid.org/0000-0002-9677-825XMarc Hemsendorf4https://orcid.org/0009-0006-7211-8536Jonas Haunschild5Stefan J. Rupitsch6Stefan Rein7Fraunhofer Institute for Solar Energy Systems Fraunhofer Institute for Solar Energy SystemsFraunhofer Institute for Solar Energy Systems University of Twente Isra Vision (Germany)Fraunhofer Institute for Solar Energy SystemsUniversity of FreiburgFraunhofer Institute for Solar Energy Systems In this paper, we present an inline characterization technique to determine spatially resolved thickness maps of ultra-thin layers on textured silicon substrates. The technique is based on multispectral imaging and optical modelling of discrete spectral reflectance data using rigorous polarization ray tracing and the transfer matrix method. The study demonstrates that quantitative inspection of ultra-thin amorphous silicon (a-Si) layers on textured silicon substrates requires an extension of the standard RGB illumination by two additional LED wavelengths in the near-UV. As the required five images are measured in less than a second, the tool is a suitable candidate for inline applications. The optical modelling requires reflectance-calibrated images which are obtained via linear calibration functions and allows the a-Si thickness to be determined at each pixel. The thin-film thickness can be determined either by a direct modelling of the measured reflectance spectra or by a differential approach using the reflectance spectra before and after coating to eliminate effects from non-idealities due to scattering as well as instrumental errors. The a-Si thickness extracted from the reflection data at the five chosen LED wavelengths shows good quantitative agreement with reference values from spectrally-resolved differential reflectance data. Evaluating a test sample with an intentional a-Si thickness variation, we compared the results from the multispectral thickness map and reference values from spectroscopic ellipsometry. We found good quantitative agreement for a-Si thicknesses above 10 nm and a slight overestimation of about 1.5 nm for thinner layers. Overall, the multispectral approach based on only five different channels proves to allow quantitative thickness maps with reasonable accuracy at inline speed. https://www.tib-op.org/ojs/index.php/siliconpv/article/view/1324Amorphous SiliconInline CharacterizationSilicon Heterojunction Solar CellsThickness MapsMultispectral Imaging |
| spellingShingle | Saravana Kumar Christian Diestel Saed Al-Hajjawi Jurriaan Schmitz Marc Hemsendorf Jonas Haunschild Stefan J. Rupitsch Stefan Rein Inline Mapping of Amorphous Silicon Layer Thickness of Heterojunction Precursors Using Multispectral Imaging SiliconPV Conference Proceedings Amorphous Silicon Inline Characterization Silicon Heterojunction Solar Cells Thickness Maps Multispectral Imaging |
| title | Inline Mapping of Amorphous Silicon Layer Thickness of Heterojunction Precursors Using Multispectral Imaging |
| title_full | Inline Mapping of Amorphous Silicon Layer Thickness of Heterojunction Precursors Using Multispectral Imaging |
| title_fullStr | Inline Mapping of Amorphous Silicon Layer Thickness of Heterojunction Precursors Using Multispectral Imaging |
| title_full_unstemmed | Inline Mapping of Amorphous Silicon Layer Thickness of Heterojunction Precursors Using Multispectral Imaging |
| title_short | Inline Mapping of Amorphous Silicon Layer Thickness of Heterojunction Precursors Using Multispectral Imaging |
| title_sort | inline mapping of amorphous silicon layer thickness of heterojunction precursors using multispectral imaging |
| topic | Amorphous Silicon Inline Characterization Silicon Heterojunction Solar Cells Thickness Maps Multispectral Imaging |
| url | https://www.tib-op.org/ojs/index.php/siliconpv/article/view/1324 |
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