Conference Agenda

The rapid evolution of information technology—driven by artificial intelligence, cloud computing, search engines, e-commerce, and Big Data—has spurred increasing demand for new application areas. Photonics remains central to expanding global communication networks, yet there is growing pressure to develop highly integrated solutions rather than rely on separate components. While traditional microelectronics-photonics hybrid integration methods, such as mass-reflow and thermo-compression bonding, do mitigate thermally induced warpage through uniform pressure, these approaches are often difficult to implement effectively in silicon photonics. Consequently, the field now demands more advanced techniques that ensure precise alignment of photonic devices, faster assembly, and consistent reproducibility on high-volume production scales.

In this context, Laser-Assisted Bonding (LAB) has emerged as a promising alternative to existing bonding methods, offering higher speed and improved energy efficiency. Its primary advantage lies in the localized application of heat, which minimizes thermal stress and reduces warpage—an especially critical consideration in photonic integration, where even slight structural changes may cause optical axis misalignment, elevated insertion or signal losses, and potential component damage.

To achieve the level of alignment required, we implement a through-silicon imaging method with bottom illumination. This arrangement makes it possible to visualize the waveguides simultaneously on both the semiconductor chip and the silicon substrate, thereby enabling advanced image recognition-based alignment strategies for optimal results.

In a practical demonstration, we employed LAB to mount a 1×1 mm III–V multichannel chip onto a silicon photonic circuit. Through localized heating, we quickly raised the photonic circuit’s temperature above the solder’s melting point and formed bonds meeting the shear bond force specifications outlined in MIL-STD-883H. Crucially, this bonding process decreases thermally induced stress and curtails warpage on the bonded surfaces. Validating LAB’s functionality in this setting also underscores its potential to enhance overall yield in photonic integration.

Notably, LAB enables both rapid bonding and waveguide alignment through bottom illumination/irradiation and real-time through-silicon imaging—an essential requirement for effective photonic integration. Taken together, these findings represent a significant step forward in photonic integration technologies, highlighting LAB’s capability to address the expanding and increasingly stringent needs of this rapidly developing sector.

This work was supported by Business Finland under project SmartFab (Advanced Automated Manufacturing Tools for Fabrication of Photonics Components and Systems, Joint action identifier 5100/31/2022) and Academy of Finland through Photonics Flagship program PREIN (Photonics REsearch and INnovation) #320168.

The constantly shifting landscape of information technology—spurred by advancements in artificial intelligence, cloud computing, search engines, e-commerce, and Big Data—has intensified the demand for new application spaces. Although photonics is instrumental in broadening worldwide information networks, contemporary requirements favor tightly integrated solutions over standalone components. This shift necessitates advanced methodologies capable of delivering stringent alignment tolerances for photonic devices, rapid assembly, and consistent reproducibility at volume. Precise alignment is paramount, since even minor deviations can significantly decrease optical coupling efficiency, device performance, and productivity in high-throughput manufacturing.

A key strategy for addressing these challenges lies in Short Wavelength Infrared (SWIR) imaging, which exploits silicon’s transparency at wavelengths above 1 µm to enable real-time observation of bonding interfaces through the silicon substrate—using a bottom-illumination architecture. As silicon photonics gains traction, achieving waveguide-to-waveguide alignment before and controlling it after assembly to submicrometer accuracy becomes increasingly critical, preventing unacceptably high coupling loss. In this work, we showcase the development of a Through-Silicon Microscopy (TSM) System that unites an infrared imaging channel with a laser-irradiation channel for efficient and energy-effective Laser-Assisted Bonding (LAB) assembly process. By combining classical optical system design principles with cutting-edge imaging approaches—such as computational reconstruction algorithms and phase microscopy—we established optimal system parameters through finite element and ray-tracing simulations, while experimental validations confirmed robustness under diverse operating conditions. The result is a powerful platform for next-generation photonic integration, delivering precise, high-throughput characterization and alignment with minimal thermal-induced warpage.

Central to this design is a cost-effective TSM setup featuring bottom illumination/irradiation architecture and a dedicated laser channel for LAB. This configuration supports a rapid, energy-efficient, and flexible bonding procedures, simultaneously ensuring sub-µm alignment for heterogeneous photonic integration. Overall, our findings underline the versatility and scalability of this approach, positioning it as a compelling solution for contemporary photonics challenges.

This work was supported by the Academy of Finland (project no. 336357, PROFI 6 - TAU Imaging Research Platform)