(113d) Atomic Layer Deposition of HfO2, TiO2 and HfxTi1-xO2 Nano-Scale Films by Using Metal Precursors and H2O
Tetrakis (diethylamino) hafnium, tetrakis (diethylamino) titanium and H2O were used for the atomic layer deposition of HfO2, TiO2 and HfxTi1-xO2 films on silicon substrates. The addition of Ti was investigated as a means to increase the scalability of HfO2 by increasing the dielectric constant (κ) value of the stack while maintaining the favorable properties of HfO2 such as thermal stability and low leakage current. The atomic layer deposition (ALD) growth rates were 1.2 Å/cycle for HfO2 and 0.6 Å/cycle for TiO2. The ALD temperature windows were found to be between 175 and 250 °C for HfO2, and between 150 and 200 °C for TiO2 with an overlapping region between 175 and 200 °C. The overlap of these ALD windows is critical to ensure ALD growth kinetics for composite HfxTi1-xO2 films. The variable compositions of HfxTi1-xO2 were prepared by varying the HfO2/TiO2 ALD cycle ratios, and excellent tunability of film composition was confirmed by x-ray photoelectron spectroscopy (XPS). Both as-deposited films and films annealed at 600, 800 and 1000 °C were analyzed by XPS, Phase Shift Interferometry (PSI) and Grazing Incidence X-ray Diffraction (GIXRD). XPS results of the as-deposited and post-deposition annealed HfO2 and TiO2 films revealed different interfacial reactions occurring during deposition and post-annealing processes. From XPS analysis, both HfO2 and TiO2 films were found to be carbon free. Based on PSI and GIXRD results, as-deposited HfO2 and TiO2 films were found to be amorphous but began to crystallize after annealing at 600 °C with HfO2 into a monoclinic structure and TiO2 into an anatase structure. The HfxTi1-xO2 films remain amorphous up to 800 °C and after annealing at 1000 °C the HfxTi1-xO2 films with various Ti compositions crystallized into monoclinic and orthorhombic phases.