What Impact Does Radio Frequency Power Have on the Growth Process and Optical Properties of Silicon Nitride Thin Films Made by RF Sputtering at Room Temperature?

Silicon nitride (SiN_X) is widely known for its exceptional hardness, making it a highly sought-after ceramic material. Its remarkable electrical and optical properties make it an excellent candidate for integration into microelectronics and photonics applications. Conventionally, SiN_X thin films are obtained through chemical vapor deposition (CVD) techniques, which necessitate high temperatures, thereby limiting the range of compatible substrates [1]. Despite ongoing efforts to optimize CVD processes and lower the required temperatures, their inherent high temperatures still pose challenges, particularly when working with temperature-sensitive materials [2].<br/><br/>In contrast, sputtering techniques offer a host of advantages over CVD techniques, including the ability to deposit SiN_X thin films at low temperatures without introducing hydrogen contamination [3]. However, achieving SiN_X thin films with desirable properties at room temperature remains a complicated task. Various parameters such as pressure, gas flow, bias voltage, and electrical power have been extensively investigated to comprehend their influence on the optical, electrical, and mechanical characteristics of SiN_X thin films [4]. Surprisingly, the impact of radiofrequency power (RF-P) on the structural and microstructural properties of these films, using a Si₃N₄ target at room temperature and in the absence of chemically active gases, has received limited attention.<br/><br/>This research delved into exploring the effects of RF-P on the growth of SiN_X thin films through non-reactive magnetron sputtering conducted at room temperature. Our findings revealed that when applying RF-P ≤ 50 W and limiting the deposition time to ≤ 120 minutes, the films exhibited polycrystalline silicon nitride particles in their α phase. By increasing either of these parameters, the formation of polycrystalline conglomerates of α-Si₃N₄ was facilitated, leading to improved film continuity and surface uniformity. Additionally, we observed a noteworthy increase in optical absorbance and a shift of the absorption edge toward the near-infrared (NIR) region when RF-P ≥ 50 W. Based on our results, we conclude that it is indeed feasible to grow thin SiN_X films at room temperature using our self-designed magnetron sputtering. These films demonstrate promising properties suitable for applications in electronic and optoelectronic devices.<br/><br/><b>References</b><br/>[1] Kaloyeros AE, Pan Y, Goff J, Arkles B. Review—Silicon Nitride and Silicon Nitride-Rich Thin Film Technologies: State-of-the-Art Processing Technologies, Properties, and Applications. ECS J Solid State Sci Technol 2020;9:063006. https://doi.org/10.1149/2162-8777/aba447.<br/><br/>[2] Kaloyeros AE, Jové FA, Goff J, Arkles B. Review—Silicon Nitride and Silicon Nitride-Rich Thin Film Technologies: Trends in Deposition Techniques and Related Applications. ECS J Solid State Sci Technol 2017;6:P691–714. https://doi.org/10.1149/2.0011710jss.<br/><br/>[3] Rodríguez-López R, Soto-Valle G, Sanginés R, Abundiz-Cisneros N, Águila-Muñoz J, Cruz J, et al. Study of deposition parameters of reactive-sputtered Si3N4 thin films by optical emission spectroscopy. Thin Solid Films 2022;754:139313. https://doi.org/10.1016/j.tsf.2022.139313.<br/><br/>[4] Dergez D, Schneider M, Bittner A, Pawlak N, Schmid U. Mechanical and electrical properties of RF magnetron sputter deposited amorphous silicon-rich silicon nitride thin films. Thin Solid Films 2016;606:7–12. https://doi.org/10.1016/j.tsf.2016.03.029.