Atomic layer deposition of ZnO thin films using a liquid cyclopentadienyl-based precursor

Abstract

A new compound, bis(n-propyltetramethylcyclopentadienyl)zinc [Zn(Cppm)2], was synthesized as a Zn precursor for atomic layer deposition (ALD) of ZnO films. The compound is a liquid at room temperature and is thermally stable below ∼230 °C. Although the vapor pressure of this precursor is low (1 Torr at 99 °C), it is sufficient for the material to be used in ALD. ZnO thin films were deposited on p-type Si(100) wafers at 200 °C by ALD using the precursor. Three types of ZnO films were grown using different oxidants: (a) O2 plasma, (b) H2O, and (c) H2O followed by O2 plasma. The growth rates expressed in the growth per cycle were (a) 0.13 nm/cycle, (b) 0.07 nm/cycle, and (c) 0.10 nm/cycle, respectively, and all of the resultant films had a hexagonal wurtzite structure. Cross-sectional transmission electron microscopy revealed that, although all of the ZnO films were crystalline. X-ray diffraction analysis determined that the (002) orientation was dominant when the oxidant was H2O, and that the (103) orientation was observed when O2 plasma was used. All of the obtained films were nearly stoichiometric. Using H2O as an oxidant, very small amounts of impurities remain in the film. However, high-purity ZnO films can be deposited using H2O followed by O2 plasma as oxidants.