Investigation of stagnation point flow in an inductively coupled plasma for improved deposition processes

Plasma-enhanced atomic layer deposition (PEALD) enables precise thickness control and uniformity in thin-film processes [1]. In PEALD reactors operating at Torr-level pressures, plasma spatial uniformity has a significant impact on deposition quality [2]. A fluid-plasma model was used to study how RF power, gas pressure, and flow rate affect plasma in an inductively coupled plasma (ICP) reactor. A PEALD reactor was designed with two distinct internal regions—the ICP source region and the diffuser region—and both Ar plasma and N₂/Ar plasma were considered. For Ar plasma, detailed reaction chemistry was considered, and simulation results showed good agreement with Langmuir probe measurements. Increasing RF power led to higher electron density and temperature, thereby enhancing ionization rate. Higher gas pressure increased collision frequency, promoting energy transfer but limiting plasma diffusion. An increased gas flow rate improved plasma transport to the substrate region. Geometric modifications of the diffuser mitigated central ion flux concentration and significantly improved plasma uniformity. The distribution of N(⁴S) in N₂/Ar plasma, which is important for silicon nitride (SiN) deposition, was also examined. The model accounted for the actual showerhead open ratio, and the results closely matched measured SiN thickness profiles. These findings demonstrate that optimizing process parameters and reactor geometry enhances PEALD spatial uniformity for uniform thin films.