Abstract
Driven by the surging demand for ultra-low-loss, high-bandwidth, and high-power-threshold photonic integrated circuits (PICs) in artificial intelligence (AI) accelerators, data-center interconnects, and coherent optical communications, silicon nitride (SiNx) has solidified its position as a premier core waveguide material in silicon photonics. Although recent reviews have addressed key trends, device demonstrations, and broad prospects in SiNₓ PICs, systematic and detailed examinations dedicated to the fabrication technologies remain scarce, despite their critical role in enabling high-performance, scalable, and reliable PICs. In particular, limited attention has been paid to the essential process parameters and inherent trade-offs involved in achieving state-of-the-art low-loss waveguides and complex structures. A central challenge arises from the fundamental conflict between the high-temperature deposition requirements of high-performance SiNx films (e.g., LPCVD) and the thermal budget of complementary metal-oxide-semiconductor (CMOS) back-end-of-line (BEOL) processes. This paper systematically reviews the current state of the art, key trade-offs, and representative paradigms of silicon nitride (SiNx) micro- and nanofabrication technologies for PICs.. First, the physical mechanisms of optical loss and mechanical stress are quantitatively analyzed from the perspectives of chemical bond dynamics, interfacial scattering, and stress engineering. Subsequently, the process trade-offs among three major technological routes—hybrid integration, heterogeneous integration, and monolithic integration—in resolving the "thermal-stress-quality" trilemma are comparatively analyzed. The article highlights the comprehensive optimization process of modified plasma-enhanced chemical vapor deposition (PECVD), including dual-frequency stress tuning, chemical mechanical polishing (CMP) planarization, gas cluster ion beam trimming and rapid thermal annealing (RTA) for dehydrogenation. Finally, by surveying the process ecosystems of global mainstream photonic foundries, the physical limitations of current technologies are dissected. This review aims to provide theoretical support and process guidance for the fabrication of SiNx waveguides in next-generation large-scale, high-performance optoelectronic integrated chips.