Atomic layer deposition of tantalum oxide and tantalum silicate from TaCl5, SiCl4, and O3: growth behaviour and film characteristics

Abstract

Tantalum oxide (Ta₂O₅) and tantalum silicate (TaSiO_x) films were grown by atomic layer deposition from TaCl₅, SiCl₄, and O₃. Saturation of absorption was observed for TaCl₅ at short TaCl₅ pulses. However, long TaCl₅ exposure resulted in a reduced growth per cycle of Ta₂O₅ and TaSiO_x films due to concomitant etching. The saturated growth per cycle of Ta₂O₅ was ∼0.77 Å per cycle at a deposition temperature of 300 °C and ∼1 Å per cycle at 250 °C. Quadrupole mass spectrometry revealed that TaCl₅ chemisorbed on the surface with negligible ligand removal. Subsequently, the reaction with O₃ led to the formation of both chlorine oxides (Cl_xO_y) and chlorine (Cl_x) as by-products. Si incorporation was found to be feasible using supercycles including SiCl₄/O₃ cycles although no SiO₂ deposition was observed for SiCl₄/O₃ cycles only. At a deposition temperature of 300 °C, self-limiting growth was observed as a function of SiCl₄ and O₃ pulse time. This suggests that the adsorption of SiCl₄ on Ta-terminated surfaces is more favorable than on Si-terminated ones, similar to the case of the equivalent H₂O-based ALD process. The Cl impurity levels in Ta₂O₅ films from TaCl₅ and O₃ were found to be lower than those in films from TaCl₅ and H₂O. The Ta₂O₅ and TaSiO_x films were amorphous as deposited. Ta₂O₅ crystallized into orthorhombic β-Ta₂O₅ at a temperature of 740 °C while TaSiO_x showed no signs of crystallization up to 900 °C. Amorphous Ta₂O₅ and Ta_0.6Si_0.4O_x films showed dielectric constants of 31 and 24, respectively, and exhibited lower leakage current densities than those deposited from TaCl₅, SiCl₄, and H₂O.