Atomic Layer Deposition of Y2O3 Using Tris(butylcyclopentadienyl)yttrium and Water

Abstract

In this work, atomic-layer deposition (ALD) of yttrium oxide (Y2O3) was demonstrated using tris(butylcyclopentadienyl)yttrium (Y(CpBut)3) and H2O . Yttrium precursor showed thermal stability and a high reactivity in surface reactions with H2O. In situ monitoring of the deposition process by quartz crystal microbalance (QCM) showed that the growth of oxide is accompanied by the absorption of water into the bulk of the film, which can lead to chemical vapor deposition (CVD) type processes. Reducing amount of dosed water as well as purge time extension during ALD cycling allow to mitigate the CVD effects. The Y2O3 film growth rate 230°C varied depending on the number of cycles and had maximum value of 1.7 A/cycle. The films obtained at 230°C had a cubic polycrystalline structure with an average density of 96% of the Y2O3 bulk density. The X-ray photoelectron spectroscopy (XPS) measurements showed a carbon impurity level below the detections limit (~0.2 at %). The O/Y atomic concentration ratio estimated by Rutherford backscattering spectroscopy (RBS) was ~1.58. As deposited Y2O3 films had a refractive index of 1.85 (at 632.8 nm), whereas with protective ALD Al2O3 film, the refractive index was 1.73.