Development of low-temperature deposition processes by atomic layer epitaxy for binary and ternary oxide thin films

Abstract

Atomic layer epitaxy (ALE) method was employed for the study of growth of binary and ternary metal oxide thin films. As background for the study, the basic principles of the ALE method are presented together with a review of existing ALE deposition processes and precursors for oxide thin films.

The suitability of β-diketonate type precursors (M(thd)3 M=Sc,Y,La; thd = 2,2,6,6-tetramethylheptanedione) and ozone were studied for ALE depositions of Group 3 oxides, namely Sc2O3, Y2O3 and La2O3. All three oxides could be deposited by a self-limiting ALE process once a suitable deposition temperature was identified. The optimal deposition temperature was found to depend on the position of the self-limiting deposition region, but also on the impurity content, which increases at low deposition temperatures. Deposition rate of Sc2O3 was considerably higher from organometallic precursor, (C5H5)3Sc, than from β-diketonate precursor (0.75 Å(cycle)-1 vs. (0.125 Å(cycle)-1).

In a second set of experiments, the suitability of the ALE processes developed was tested for the deposition of ternary thin films, namely yttria-stabilised zirconia (YSZ) and lanthanum aluminate. Before these processes were applied, study was made of the deposition of ZrO2 from β-diketonate and organometallic precursors at 200-500 °C. Furthermore, ALE deposited MgO films were tested for their suitability as buffer layers between silicon substrate and LaAlO3 film. Crystalline YSZ films were obtained regardless of the yttrium to zirconium ratio, whereas the LaAlO3 films were crystalline only after annealing at 900 °C.