Atomic Layer Deposition of MgO Using Bis(ethylcyclopentadienyl)magnesium and H₂O

Abstract

Magnesium oxide (MgO) atomic layer deposition (ALD) was performed using sequential exposures of bis(ethylcyclopentadienyl)magnesium (Mg(CpEt)2) and H2O. Quartz crystal microbalance (QCM) measurements monitored the mass deposition during MgO ALD and verified self-limiting reactions for each reactant. Extremely efficient reactions were observed that required reactant exposures of only ∼1 × 104 L (1 L = 1 × 10−6 Torr s). X-ray reflectivity (XRR) studies were used to confirm the QCM measurements and determine the film density and film thicknesses. The MgO ALD film density was 3.07 g/cm3. The largest MgO ALD growth per cycle was 1.42 Å/cycle at 150 °C and the growth per cycle decreased for temperatures >150 °C. Fourier transform infrared spectroscopy was used to study the CpEt* and OH* surface species during MgO ALD and also to monitor the bulk vibrational modes of the growing MgO films. Transmission electron microscopy of MgO ALD on ZrO2 nanoparticles revealed the conformality of the MgO films and confirmed the growth per cycle observed by the XRR studies. X-ray diffraction determined that the MgO ALD films were crystalline and consistent with the cubic phase. Rutherford backscattering determined that the Mg:O stoichiometry of the MgO ALD films was 0.95:1.05. The results allowed a growth mechanism to be established for MgO ALD using Mg(CpEt)2 and H2O. Only 30.8% of the Mg sites are observed to retain the CpEt* surface species after the Mg(CpEt)2 exposure. The efficient ALD of MgO using Mg(CpEt)2 and H2O should be useful for a variety of applications including the conformal coating of particles.