Large-scale curvilinear photonic patterns metrology: exploring a new method based on CD-SEM images contour stitching

Background: Silicon photonics technologies require a high design-to-pattern fidelity in order to ensure the desired component functionality. Dimensional metrology is currently carried out by optical measurement on dedicated structure. Aim: Numerous studies report on dedicated optical monitoring structures for controlling waveguide morphology, but none address the CD-SEM imaging method directly after the lithography-etch process. Approach: We propose here a smart algorithmic method based on CD-SEM imaging and contour extraction, enabling the actual reconstruction of the wafer pattern. This method involves a number of challenges linked to imaging tools with restricted fields of view, compared to the large-scale, curved aspects of waveguides. Results: The methodology developed comprises 3 main phases: data preparation prior to imaging, the imaging phase and post-processing for contour extraction and reconstruction. This method was first developed using synthetic CD-SEM images, then applied to a photonic structure on a 300 mm silicon wafer. Conclusion: Whereas the CD-SEM structures conventionally used in dimensional pattern control allows local information in a single orientation, our approach enables integral analysis of photonic structures, opening the door to process assessment directly after the patterning stage.