In this work it is presented a study on the structural, compositional and electrical properties of HfO₂, HfO₂/SiO₂ and HfO₂/Al₂O₃ dielectric layers deposited by sputtering without any intentional substrate heating. The films were deposited from 2 inches ceramic targets of HfO₂, SiO₂ and Al₂O₃ using argon (Ar) and oxygen (O₂). The incorporation of SiO₂ and Al₂O₃ was obtained by co-sputtering and it was controlled by adjusting the r.f. power ratio on the targets.
The HfO_x films present a microcrystalline structure even when deposited at room temperature. The average grain size determined by the Scherrer formula may overcome 100 nm depending on the processing conditions. The crystallinity decreases with the oxygen flow due to a reduction on the energy of the species reaching the substrate, associated with the decrease on the deposition rate. However, the lowest leakage current in crystalline silicon MIS structures (below 10⁹ Acm^-2 at 10V on films with a thickness around 180 nm) was obtained for a ratio Ar/O₂ of 14/1 sccm, indicating higher oxygen flow does not lead to further improvement on the electrical characteristics.
The co-deposition of SiO₂ has a strong influence on the structure since the films become amorphous. Also the roughness is decreased where the values determined by spectroscopic ellipsometry are less than an half of those obtained for HfO_x films. The refractive index stays between the values for pure HfO₂ and SiO₂ and the gap increases more than 0.4 eV, confirming the incorporation of silicon oxide. The leakage in MIS structures is reduced by a factor of 2. Only the dielectric constant is negatively affected due to the lower value for the SiO₂. The same structural effect is observed when using Al₂O₃ instead of SiO₂.  Again, the refractive index and the band gap confirm that HfO_x films are incorporating aluminum oxide. The reduction on the dielectric constant may be minimized since the value for pure Al₂O₃ is around 9.  

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