Application note
1. Background
Infrared imaging is commonly assumed to be incompatible with metal-coated silicon wafers due to the high reflectivity and opacity of metals like gold, chrome and titanium. However, during a live demonstration at Photonics North 2025, Jay Photonics had the opportunity to test a real-world sample brought by a graduate student working on gold-hyperdoped silicon.
Despite the presence of a rear metallic contact, the microscope provided clear images of the internal structure, challenging the assumption that gold layers always block IR imaging.
2. Objective
Although not originally planned as a formal test, this demonstration became an opportunity to explore the feasibility of infrared transmission imaging through a metalized wafer and more specifically, to evaluate the effect of localized gold hyperdoping on image contrast.
Could Jay Photonics’ IR system provide usable imaging through this type of material stack?
3. Sample & Setup
Sample details:
- Substrate: Silicon with localized gold hyperdoping
- Rear contact: 50 nm gold + 10 nm titanium coated on the entire wafer
- Silicon Wwafer thickness: 500 µm
- Special feature: Gold hyperdoped patterns for absorbing IR light
Imaging setup:
- Instrument: Si-Through-HR infrared microscope (standard configuration)
- Orientation: Gold-side down
- Illumination: Infrared transmission
- Imaging conditions: real-time acquisition with no lag or post-processing
- Environment: Trade show floor (no prep or stabilization)
4. Observations
The system successfully produced clear images of the wafer’s internal structure localized between the 500-µm thick silicon wafer and the two metal layers. In particular, dark zones were visible in areas corresponding to gold-hyperdoped regions, suggesting the success of the project in making silicon more sensitive to infrared light.
The thin gold/titanium stack did not prevent imaging, and no sample preparation was required.
6. Conclusion
This unexpected result demonstrates that Jay Photonics’ IR imaging system can deliver clear, high-contrast results even in complex material stacks involving rear metal layers and highly doped silicon.
It expands the scope of compatible materials and encourages new use cases in doped wafer inspection, IR material research, and early-stage prototyping of advanced silicon devices.
Acknowledgment
Special thanks to Derrick Wu, graduate student at the University of Ottawa and member of the SUNLAB, for providing the sample and sharing context from his master’s research on gold-hyperdoped silicon.
This project was conducted under the supervision of Dr. Karin Hinzer and Dr. Jacob Krich.
To learn more about his work, you can follow updates from SUNLAB or connect with Derrick directly via Linkedin or academic networks.