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 HfO₂ film as prepared by the conventional vapor deposition method. On the other hand, a similar HfO₂ 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.