Sol−Gel Fabrication of Dielectric HfO₂ Nano-Films; Formation of Uniform, Void-Free Layers and Their Superior Electrical Properties

Solution-based fabrication of a high-quality metal oxide nano-film (∼10-nm thickness) by the surface sol−gel process and postannealing is reported. Hafnium(IV) n -butoxide in toluene−ethanol was chemisorbed onto hydroxylated Si wafer to give a uniform gel layer, of which alkoxide group was then hydrolyzed and subjected to a second cycle of chemisorption/hydrolysis. Annealing of a 10-cycle film at 500 °C produced uniform, void-free HfO 2 layer of 5.7-nm thickness. Its electrical properties, dielectric constant, leakage current, and dielectric breakdown were comparable to the HfO 2 film as prepared by the conventional vapor deposition method. On the other hand, a similar HfO 2 nano-film prepared by spin-coating provided a less homogeneous layer in a high-resolution TEM image. The electrical properties of the latter film were much inferior to those of the surface sol−gel film. We concluded that the solution-based method is suitable for fabrication of dielectric nanofilms of metal oxide.