Wafer-Level Optical Characterization: Improving Chip Selection Through Yield Analysis
As photonic integrated circuits (PICs) continue to grow in complexity, wafer-level optical characterization is becoming increasingly important for verifying chip performance before dicing. For customers, knowing which chips are functional at this stage can make a significant difference in how efficiently they are selected for further processing.
At LioniX International, we are developing optical characterization solutions that bring testing from the individual chip level to the wafer level. By measuring chips across a wafer, we can gather the data needed for yield analysis and support automated chip selection, reducing the need to characterize each chip individually after dicing.
Schematic Optical Characterization Machine Setup
Why Wafer-Level Characterization?
Traditionally, our process control with optical characterization has been performed on one or two chips after they have been diced from the wafer. Since dicing is a destructive and expensive process, wafer-level rework is no longer possible, and resources are wasted. This approach provides only limited information about the performance of the remaining chips.
Wafer-level optical characterization allows us to measure not only test chips but also functional chips before dicing and assess their optical performance against predefined specifications. This provides a more complete picture of wafer-level yield and helps identify which chips meet the required criteria.
Designing for Testability
Wafer-level characterization does not start when a wafer reaches the test bench. It starts during the design phase.
To enable optical characterization at wafer level, photonic integrated circuits need to be designed with testing in mind. Depending on the application, this may involve incorporating grating couplers into functional chips or including dedicated test structures that allow key optical parameters to be measured before dicing.
This Design for Test approach is becoming increasingly important as the photonics industry moves towards higher-volume manufacturing. Considering testability early in the design process helps provide the optical access required for wafer-level characterization.
Wafer-Level Characterization in Practice: Lab on Chip
An example of our progress in wafer-level optical characterization is the NXTGEN | Lab on Chip project, in which we developed and demonstrated an optical characterization setup capable of measuring all chips across a wafer.
The setup combines optical measurements with chip-to-chip alignment, achieving an interval of 11 seconds between consecutive chips, including alignment and full spectral characterization of all functional channels, including Free Spectral Range and Extinction Ratio extraction. In this complete measurement run, 106 chips were characterized in 30 minutes, providing detailed information about the optical performance of the characterized chips.
Wafer Map: OSROM FSR Map
Spectra
Tailored Characterization Solutions
Every photonic application has its own measurement requirements. Together with our partner Surfix, we developed a dedicated optical characterization process for assessing the quality of their specialized photonic biosensor chips. The functionality of these sensors comes alive only in liquid environments, and in this collaboration, Surfix has developed a coating mimicking the water environment while simultaneously being compatible with the characterization equipment.
For customers with different characterization requirements, we can explore the development of customized solutions tailored to their applications.
Camera view
Camera view: Coupled light
Let’s Explore the Possibilities Together
Wafer-level optical characterization offers a way to evaluate chip performance before dicing, making it easier to determine which chips meet the required specifications.
Whether you’re interested in wafer-level yield analysis or have a specific optical characterization challenge, we’d be happy to discuss your requirements and explore what is possible for your application.
Contact us to learn more about our optical characterization capabilities.
Dr. Philip P.J. Schrinner started his scientific career at the (RWTH) Aachen University, where he received his B.Sc and M.Sc in the field of quantum/nano technology. To further deepen his background and to research in the field of integrated optics, he proceeded with his PhD at the University of Münster (WWU). After designing, fabricating and characterizing hybrid quantum light sources in photonic integrated circuits in the university cleanroom and labs, he joined Lionix International in 2021. In addition to developing new hybrid photonic assemblies, he is now the project leader for several commercial, national and EU projects.
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