Pseudo-binary (HfO₂)_x(SiO₂)_1-x has attracted much attention due to the interesting possibility of combining the high breakdown field of SiO₂ (E_g = 9 eV) and high dielectric constant (22~25) of HfO₂ in a complex material to keep a relatively high dielectric constant and a low leakage current.[1,2] In this work, HfO₂)_x(SiO₂)_1-x composite films were deposited from hafnium tetra-tert-butoxides (HTB) and tetraethylorthosilicate (TEOS) precursors by using an plasma-enhanced atomic layer deposition (PEALD) process. The film thickness increased almost linearly with increasing number of precursor-oxygen plasma cycles. An optimal control over the final composition was achieved by setting the deposition cycles of HfO₂ and SiO₂. Fourier Transform Infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) analysis showed that the composite films were fully oxidized. The Si-O-Hf bonds were formed in the PEALD deposited composite films and more Hf-O-Hf component than Hf-O-Si and Hf-O-H were formed in the Hf rich films. The band gap determined from the XPS O 1s plasmon loss spectrum increased from 5.6 to 5.98 eV with increasing the Si content in the as-deposited films, and it increased slightly after the composite films were annealed at 600 and 900^oC, respectively. Time-of-flight static secondary ion mass spectrometry (TOF-SSIMS) depth profiles showed that Hf is almost uniformly distributed throughout the films, and Hf and O exhibited a sharp decay at the Si interfacial substrate. Some Hf presence at the interface with Si could be attributed to ion beam-induced mixing of Hf into the interfacial layer. The low carbon content in these films, which is confirmed by XPS, resulted from the ambient surface contamination. The as-deposited and annealed films at 900^oC were determined to be amorphous by x-ray diffraction (XRD), suggesting that the introduction of SiO₂ into HfO₂ matrix prevented crystallization and kept the film amorphous at high temperatures. The as-deposited HfO₂)_x(SiO₂)_1-x composite films showed superior electrical properties, including dielectric constants from 5.3 to 11.5 and leakage current density several orders of magnitude lower than that of SiO₂ at the same equivalent oxide thickness.

[1] R. M. Wallace and G. Wilk, MRS Bulletin, 192, 27 (2002). [2] R. Puthenkovilakam, M. Sawkar, and J. P. Chang, Appl. Phys. Lett., 202902, 86 (2005).