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 (TaSiOx) 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 TaSiOx 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 (ClxOy) and chlorine (Clx) 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 TaSiOx films were amorphous as deposited. Ta2O5 crystallized into orthorhombic β-Ta2O5 at a temperature of 740 °C while TaSiOx showed no signs of crystallization up to 900 °C. Amorphous Ta2O5 and Ta0.6Si0.4Ox films showed dielectric constants of 31 and 24, respectively, and exhibited lower leakage current densities than those deposited from TaCl5, SiCl4, and H2O.