1. Background
Wafer bonding is a key process in advanced packaging, MEMS fabrication, and silicon-on-insulator (SOI) manufacturing, where the integrity of the bonding interface directly influences device reliability and long-term performance. Surface preparation plays a critical role in determining bond quality, and even small deviations can lead to the formation of voids [1]. Particles, surface contamination, and insufficient surface smoothness can create bonding voids, i.e., localized air gaps trapped between the wafers.
These voids can reduce thermal conductivity, weaken mechanical stability, and, in severe cases, lead to delamination or device failure during thermal cycling or subsequent processing steps [1,2]. Early detection of voids is therefore essential for process control and yield optimization in wafer bonding applications.
Because silicon is opaque in the visible spectrum but highly transparent in the near-infrared (NIR) range, infrared transmission imaging has become a standard non-destructive method for inspecting bonded silicon wafers. This technique enables visualization of subsurface features at the bonding interface without sample preparation, and macroscopic IR inspection systems are widely used to assess bonding quality across full wafers [3]. Such systems enable rapid identification of large voids, particles, and non-uniform bonding regions.
However, many existing macroscopic IR inspection systems rely on complex illumination schemes or offer limited spatial resolution, which can restrict image clarity and reduce sensitivity to smaller defects during full-wafer inspection. Recent studies have highlighted the need for improved NIR imaging configurations and higher-resolution detectors to enhance void detectability and reduce inspection uncertainty [4]. These limitations motivate the development of imaging approaches that provide higher resolution, simpler optical configurations, and improved defect sensitivity.
2. Objective
The objective of this application note is to evaluate the capability of the Jay Photonics MacroIR Inspection System to detect bonding voids in bonded silicon wafers using full-wafer infrared transmission imaging.
In particular, this study demonstrates the ability of the system to perform one-shot imaging of entire wafers with high spatial resolution, enabling the visualization of bonding defects such as voids and interface irregularities. The system performance is assessed through imaging experiments on bonded wafer samples and compared with results obtained using an existing macroscopic infrared inspection system available at C2MI, the largest electronic systems research and development Centre in Canada.
3. Methodology
Sample: Several bonded silicon wafer samples were inspected during the evaluation, including:
- Collective bonding (die-on-wafer) samples
- Silicon–silicon bonded wafers containing particles that induce bonding voids
These samples enable the visualization of bonding defects and provide representative examples of void formation at bonded wafer interfaces.
System under test: The evaluation was performed using the Jay Photonics MacroIR Inspection System, a macroscopic infrared imaging platform designed for full-wafer inspection of bonded silicon wafers. The system combines uniform infrared illumination with a high-resolution imaging sensor to enable single-acquisition imaging of entire wafers.
Reference system: For benchmarking purposes, images obtained with the Jay Photonics MacroIR system were compared with images acquired using an existing macroscopic infrared inspection system available at C2MI.
The reference system uses halogen-based illumination optimized for near-infrared transmission, combined with a high-sensitivity monitoring camera capable of operating at very low illumination levels. This system is routinely used for macroscopic inspection of bonded silicon wafers.
4. Observations and Analysis
4.1. Full-Wafer Bonding Inspection
Figure 1: Single shot of collective bonding – die on wafer using Jay Photonics system (Fig. 1B) and C2MI (Fig. 1A) revealing the bonding voids and interface features across full wafer.
As shown in Fig. 1B, images acquired using the Jay Photonics MacroIR system clearly reveal bonding voids and interface features across the full wafer. Comparable images from the reference system (1A) confirm similar macroscopic features, thereby validating the inspection principle.
It is worth noting that the images were acquired several months apart. Changes in the appearance of Newton rings, including their partial or complete disappearance, can be attributed to the temporal evolution of the bonding interface rather than differences between the inspection systems.
4.2. Impact of High Pixel Count
Figure 2: Digital zoom of bonded structures in images obtained with the Jay Photonics system (2B) and the C2MI system (2A). The comparison highlights the higher resolution of the Jay Photonics system, with bonding void features clearly visible.
Figure 2 demonstrates that the high pixel density of the Jay Photonics camera enables effective digital zoom. Fine structures and small bonding voids that are difficult to distinguish with lower-resolution systems become clearly visible, demonstrating the benefit of combining full-wafer imaging with high spatial resolution.
4.3. Silicon–Silicon Bonding Test
Fig 3: Silicon–silicon bonded wafer imaged using the Jay Photonics system (3B) and the C2MI system (3A). The Jay Photonics prototype demonstrates higher image resolution and improved defect visibility.
A dedicated silicon–silicon bonded wafer containing a small number of particles was used to demonstrate bonding void detection. The resulting air gaps are clearly visible using the Jay Photonics MacroIR system (Fig. 3B). Compared with the reference system, the Jay Photonics prototype provides higher image resolution and improved defect visibility.
5. Conclusion
The Jay Photonics MacroIR Inspection System demonstrates full-wafer infrared inspection capability for the detection of bonding voids in silicon wafers. The system is based on a proprietary infrared camera and LED-based illumination source featuring a uniquely engineered spectrum, which together enable single-shot imaging with exceptional spatial resolution, surpassing conventional macroscopic IR inspection systems.
These results validate the system’s high performance for bonding inspection applications and demonstrate its scalability across a range of wafer sizes.
6. Curious to See the Difference?
Side-by-side comparisons between the Jay Photonics MacroIR system and the reference macroscopic IR inspection system clearly demonstrate the advantages of higher resolution, improved image clarity, and full-wafer, one-shot acquisition.
If you are interested in evaluating your own bonded wafers or exploring additional inspection capabilities Contact us to schedule a demonstration.
Stay tuned for upcoming application notes and demonstrations from Jay Photonics.
Acknowledgement
Special thanks to C2MI for providing the sample and conducting the comparative tests.
References:
[1] Tong, Q.-Y., & Gösele, U. Semiconductor Wafer Bonding: Science and Technology. Wiley, 1999.
[2] Niklaus, F., Stemme, G., Lu, J.-Q., & Gutmann, R. Adhesive wafer bonding. Journal of Applied Physics, 99, 031101 (2006).
[3] Du, M., Li, D., & Liu, Y. Investigation of plasma activated Si–Si bonded interface by infrared image analysis. Micromachines, 10(7), 445 (2019).
[4] Chen, Cong, et al. Detection of bonding voids for 3D integration. Metrology, Inspection, and Process Control XXXVII. Vol. 12496. SPIE, 2023.