Abstract

Silicon nitride films with the best optical quality can be realized with low pressure chemical vapor deposition (LPCVD) [1]. However, high mechanical stress within the LPCVD silicon nitride films leads to formation of cracks and prevents thick films (> 400 nm) with high optical quality. A number of clever processes have been developed in order to prevent cracks, such as patterning of crack barriers, multi-step deposition and a Damascene process that deposits silicon nitride into trenches. In addition, to reduce material losses and achieve ultralow propagation losses (~1 dB/m), long-time high temperature annealing (1200 °C for 3 hours) is needed, which can cause dopant diffusion and damage of prefabricated temperature-sensitive devices. Hence, LPCVD Si₃N₄ is very challenging for applications in back-end-of-line processes and foundry compatible processes. In recent years, low-temperature deposited Si₃N₄ thin films have attracted increasing interest for 3D hybrid integration of Si₃N₄ with other materials. Here we report the fabrication of ultralow-loss Si₃N₄ photonics film by reactive sputtering at room temperature [2]. Directly after room-temperature sputtering, the Si₃N₄ film loss is 32 dB/m without thermal annealing and the intrinsic optical quality factor (Q) of the fabricated microresonators is 1.1 million in the L-band. This propagation loss is already lower than that of annealing-free LPCVD Si₃N₄ film deposited at 780 °C [3].

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