Low-Temperature Dopant-Assisted Crystallization of HfO2 Thin Films

We have studied the thermal atomic layer deposition (ALD) of HfO2 on native and chemical oxide GaAs(100) surfaces using the amide precursors tetrakis ethylmethyl amino hafnium and tetrakis dimethyl amino hafnium. Bright-field and high-resolution transmission electron microscopy data for the as-prepared HfO2 films deposited on both GaAs(100) oxide surfaces show that the films are polycrystalline and contain several large grains of the order of the film thickness and numerous smaller ones. X-ray diffraction confirms the presence of small crystallites that can be classified in forms other than monoclinic, while control films deposited on native oxide Si(100) surfaces are amorphous. Thermally treated films deposited on both Si and GaAs contain mainly monoclinic grains. Gallium and arsenic oxides are known to bubble through the growing HfO2 film so that at any point during the ALD process, there is mixing of the various III–V oxides in the film. These oxides seem to stabilize the various HfO2 polymorphs during low-temperature thermal ALD, allowing control of the film microstructure via the deposition process.