Simulation of the SiConi preclean process to predict uniform oxide removal on Si wafers

Semiconductor wafers are essential in modern-day electronics, typically used for photovoltaics or ICs, and go through multiple processing stages before final deployment. The SiConi preclean is one such remote plasma-assisted dry surface preparation process that involves simultaneous exposure of the wafer substrate with a SiO₂ film to NF₃, and NH₃ reactive plasma. As a result, fluorosilicate salts are generated via a reaction of the NH₄F reactive species with the SiO₂ film followed by an annealing process where volatile salts are sublimated to SiF₄ and NH₃. The combined process allows for a damage-free removal of surface oxide, resulting in decreased contact resistance and enhanced reliability of middle-of-the-line (MOL) interconnects. While SiConi is one of the more commonly used dry preclean processes, the role of various physical parameters during the process remains to be determined. This study focuses on carrying out numerical simulations of the SiConi etch process to determine conditions for uniform center-to-edge oxide removal. A 300mm Si wafer is set up under a showerhead that delivers reactants from a remote plasma and the final thickness of the oxide layer is measured. We evaluate the influence of temperature and predict oxide removal for blanket and patterned wafers.