Structural, Electrical and Dielectric Properties of Sputtered TiO_2 Films for Al/TiO_2/Si Capacitors

摘要

Metal-oxide semiconductor capacitors based on titanium dioxide (TiO_2) gate dielectrics were prepared by RF magnetron sputtering technique. The deposited films were post-annealed at temperatures in the range 773-1173 K in air for 1 hour. The effect of annealing temperature on the structural properties of TiO_2 films was investigated by X-ray diffraction and Raman spectroscopy, the surface morphology was studied by atomic force microscopy (AFM) and the electrical properties of Al/TiO_2/ρ-Si structure were measured recording capacitance-voltage and current-voltage characteristics. The as-deposited films and the films annealed at temperatures lower than 773 K formed in the anatase phase, while those annealed at temperatures higher than 973 K were made of mixtures of the rutile and anatase phases. FTIR analysis revealed that, in the case of films annealed at 1173 K, an interfacial layer had formed, thereby reducing the dielectric constant. The dielectric constant of the as-deposited films was 14 and increased from 25 to 50 with increases in the annealing temperature from 773 to 973 K. The leakage current density of as-deposited films was 1.7 × 10~(-5) and decreased from 4.7 × 10~(-6) to 3.5 × 10~(-9) A/cm~2 with increases in the annealing temperature from 773 to 1173 K. The electrical conduction in the Al/TiO_2/ρ-Si structures was studied on the basis of the plots of Schottky emission, Poole-Frenkel emission and Fowler-Nordheim tunnelling. The effect of structural changes on the current-voltage and capacitance-voltage characteristics of Al/TiO_2/ρ-Si capacitors was also discussed.