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Atomic Layer Deposition with Trimethylaluminum and Ozone Studied by in Situ Transmission FTIR Spectroscopy and Quadrupole Mass Spectrometry

The atomic layer deposition (ALD) of Al2O3 using sequential exposures of Al(CH3)3 and O3 was studied by in situ transmission Fourier transform infrared (FTIR) spectroscopy and quadrupole mass spectrometry (QMS). The FTIR spectroscopy investigations of the surface reactions occurring during Al2O3 ALD were performed on ZrO2 particles for temperatures from 363 to 650 K. The FTIR spectra after Al(CH3)3 and ozone exposures showed that the ozone exposure removes surface AlCH3* species. The AlCH3* species were converted to AlOCH3* (methoxy), Al(OCHO)* (formate), Al(OCOOH)* (carbonate), and AlOH* (hydroxyl) species. The TMA exposure then removes these species and reestablishes the AlCH3* species. Repeating the TMA and O3 exposures in a sequential reaction sequence progressively deposited the Al2O3 ALD film as monitored by the increase in absorbance for bulk Al2O3 infrared features. The identification of formate species was confirmed by separate formaldehyde adsorption experiments. The formate species were temperature dependent and were nearly absent at temperatures g650 K. QMS analysis of the gas phase species revealed that the TMA reaction produced CH4. The ozone reaction produced mainly CH4 with small amounts of C2H4 (ethylene), CO, and CO2. Transmission electron microscopy (TEM) was also used to examine the Al2O3 ALD films deposited on the ZrO2 particles. These TEM images observed conformal Al2O3 ALD films with thicknesses that were consistent with an Al2O3 ALD growth rate of 1.1 Å/cycle. The surface species after the O3 exposures and the mass spectrometry results lead to a very different mechanism for Al2O3 ALD growth using TMA and O3 compared with Al2O3 ALD using TMA and H2O.