Identification of optimal ALD process conditions of Nd2O3 on Si by spectroscopic ellipsometry

Variable angle spectroscopic ellipsometry (VASE) is used to investigate the thickness and optical properties of Nd2O3 films deposited by atomic layer deposition (ALD) at various process conditions. It is found that the films exhibit good thickness uniformity and an almost constant growth rate of 0.42 Ǻ/cycle in the temperature region of 290–330 °C. Further examination of the imaginary part of the dielectric functions of the selected samples demonstrates that all optically observable dielectric-related defects are located in the interface layer between the silicon substrate and the native oxide rather than in the bulk Nd2O3 layer. And, the defects within the band gap of the interface are found to be strongly affected by the deposition temperature. In the deposition temperature range of 300–320 °C, only one absorption peak of 3.53 eV besides the silicon substrate’s critical features is observed, indicating that the Si/SiO2/Nd2O3 stacks contain the fewest interfacial defects. Then the optimal ALD process condition for Nd2O3 is determined as Nd(thd)3 (thd = 2,2,6,6,-tetramethyl-3,5-heptanedionato) evaporation temperature: 185 °C, deposition temperature: 300–320 °C, saturation condition: Nd(thd)3 and pulse time longer than 0.5 s.