Atomic layer deposition of high-quality Al2O3 and Al-doped TiO2 thin films from hydrogen-free precursors

Abstract

Possibilities for atomic layer deposition of Al2O3 films from chloride and ozone were studied in order to avoid application of precursors that could leave hydrogen impurities in the films. Growth of Al2O3 was obtained at substrate temperatures of 300–450°C. At these temperatures, the growth rate was close to the values reported for corresponding H2O-based processes. Studies of thin-film composition revealed that reactivity of O3 was sufficient to ensure deposition of films with chlorine concentration below 0.05at.% at 350–450°C. Application of the AlCl3–O3 atomic layer deposition process for in situ Al-doping of TiO2 thin films demonstrated that the amount of Al incorporated into the films during a single deposition cycle depended on the doping level. A reason for this effect was the influence of Al-doping on the phase composition of the film material. Al-doping of the TiO2 films significantly reduced the surface roughness allowing deposition of high-density films with very flat surfaces. In capacitor structures with capacitance equivalent oxide thicknesses below 0.4nm, the Al-doped TiO2 films deposited from TiCl4, AlCl3 and O3 demonstrated markedly lower leakage current densities than the films with similar capacitance densities grown from TiCl4, Al(CH3)3 and H2O and from TiCl4, Al(CH3)3 and O3 did.