Description
Fluorocarbon (FC) layer formation controls profile integrity in high aspect ratio etching. Low substrate temperature enhances polymer accumulation and modifies surface reaction balance. This study investigates the effect of H₂O addition on FC layer formation and etching behavior of SiO₂ and Si₃N₄ films in CₓFᵧ plasmas. An inductively coupled plasma chamber generates CF₄ and C₄F₈ plasmas under self-bias and 40 W bias conditions. Substrate temperature ranges from 20 °C to −60 °C. Ellipsometry measures etch rates, and XPS and VSEM analyze surface composition and bonding structure. CF₄ self-bias plasmas exhibit non-monotonic temperature dependence. The etch rate decreases from 20 °C to −40 °C due to enhanced FC passivation and increases again at −60 °C. H₂O addition shifts this transition behavior and modifies the balance between fluorination and carbon-rich layer formation. C₄F₈ self-bias plasmas increase FC layer thickness as substrate temperature decreases. XPS confirms an increased C–C bonding fraction at low temperature. H₂O addition produces the thickest FC layer, and O₂ addition reduces carbon accumulation through CO formation. Bias-assisted etching reveals a minimum etch rate near −20 °C in both CF₄ and C₄F₈ plasmas with H₂O addition. This temperature defines a common critical point in CₓFᵧ-based low-temperature etching. Substrate temperature and H₂O addition govern FC layer chemistry and etching kinetics. These results provide a controlled pathway for mechanism understanding and profile optimization in advanced plasma processing.