Multi-Axial Elastic Averaging for Sub-Micron Passive Alignment of Photonic Components

In recent years, heterogeneous integration (HI) has become a game-changing technology for the construction of complex photonic integrated circuits. Comparing to monolithic integration (MI) technique, chips are stacked or add-on during HI. These components are attached to the substrate using an active or passive alignment scheme. As the passive alignment system does not actively search for the optical axis, it allows more die to be bonded per unit time as compared to active alignment. The main challenge is then to obtain consistent sub-micron alignment accuracy during chip manufacturing process to ensure good device performance. To achieve sub-micron alignment accuracy, slide-stop structures with multi-axial elastic averaging coupling designs are implemented. In this work, optical dies are bonded to silicon interposers with two geometrically different slide-stop designs: triangle and rectangle in designs, respectively. Due to an additional surface contact and smaller internal angle for the former, the triangle slide-stop design improves the translational-axes and rotational-axis post-bond alignment accuracy, from (Reference) −0.27 µm ± 2.54 µm @ 3sigma to (slide-stop) −0.09 µm ± 1.37 µm @ 3sigma, (Reference) 1.00 µm ± 3.19 µm @ 3sigma to (slide-stop) 0.39 µm ± 1.29 µm @ 3sigma, and (Reference) 0.06° ± 0.34° @ 3sigma to (slide-stop) 0.0002° ± 0.15° @ 3sigma respectively. Finally, narrower optical power output distribution of P-down bonded lasers with triangle slide-stop over lasers with rectangle slide-stop is demonstrated.