Zirconia thin films by atomic layer epitaxy.: A comparative study on the use of novel precursors with ozone

Zirconium oxide thin films have been deposited by atomic layer epitaxy (ALE) using Zr(thd)(4),Cp2Zr(CH3)(2) and Cp2ZrCl2 (thd = 3,3,5,5-tetramethylheptane-3,5-dionate, Cp cyclopentadienyl) as zirconium precursors and ozone as the oxygen source. A plateau of constant growth rate (ALE window) was observed for the Zr(thd)(4)/O-3 process at 375-400 degreesC, for Cp2Zr(CH3)(2)/O-3 at 310-365 degreesC and for Cp2ZrCl2/O-3 at 275-350 degreesC. Within these temperature ranges constant deposition rates of 0.24, 0.55 and 0.53 Angstrom (cycle)(-1) were obtained, respectively. Deposited films were characterised by XRD and AFM for crystallinity and surface morphology, while TOF-ERDA was used to analyse the ZrO2 film stoichiometry and possible impurities. Films deposited by optimised parameters from Cp2Zr(CH3)(2)/O-3 and Cp2ZrCl2/O-3 were crystalline showing the preferred (-111) orientation of monoclinic ZrO2. In all films, the orthorhombic zirconia phase was also present, although at higher temperatures its relative amount decreased. Zr(thd)(4)/O-3 process produced films with lowest crystallinity consisting of both orthorhombic and monoclinic phases. According to TOF-ERDA, films were nearly stoichiometric with less than 0.5 atom% hydrogen and carbon. Outside the ALE window, a small chlorine contamination (0.1-0.3 wt%) was observed by XRF when the ZrO2 films were deposited from Cp2ZrCl2/O-3 at 200-275 degreesC.