Methods for forming hafnium oxide within a three-dimensional structure, such as in a high aspect ratio hole, are provided. The methods may include depositing a first hafnium-containing material, such as hafnium nitride or hafnium carbide, in a three-dimensional structure and subsequently converting the first hafnium-containing material to a second hafnium-containing material comprising hafnium oxide by exposing the first hafnium-containing material to an oxygen reactant. The volume of the second hafnium-containing material may be greater than that of the first hafnium-containing material. Voids or seams formed during the deposition of the first hafnium-containing material in the three-dimensional structure may be filled by the expanded material after exposing the first hafnium-containing material to the oxygen reactant. Thus, the three-dimensional structure, such as a high aspect ratio hole, can be filled with hafnium oxide substantially free of voids or seams.