Extended Data Fig. 3: Pathway of Cu diffusion into Si3N4 waveguides during device fabrication.
From: Deterministic soliton microcombs in Cu-free photonic integrated circuits
a, Schematic of the photonic Damascene process for low-loss Si3N4 waveguide fabrication, including preform etching, reflow, LPCVD Si3N4 and SiO2 deposition, planarization, and annealing. b-e, Depth-resolved Cu concentration profiles: b, after preform etching and reflow; c, post Si3N4 deposition and planarization; d, after Si3N4 annealing (1200 °C, 11 hours), showing Cu incorporation into the Si3N4 waveguide; e, post SiO2 cladding deposition and annealing, revealing Cu localization exclusively within the Si3N4 waveguide core.
