Al2O3 Atomic Layer Deposition with Trimethylaluminum and Ozone Studied by in Situ Transmission FTIR Spectroscopy and Quadrupole Mass Spectrometry

The atomic layer deposition (ALD) of Al 2 O 3 using sequential exposures of Al(CH 3 ) 3 and O 3 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 Al 2 O 3 ALD were performed on ZrO 2 particles for temperatures from 363 to 650 K. The FTIR spectra after Al(CH 3 ) 3 and ozone exposures showed that the ozone exposure removes surface AlCH 3 * species. The AlCH 3 * species were converted to AlOCH 3 * (methoxy), Al(OCHO)* (formate), Al(OCOOH)* (carbonate), and AlOH* (hydroxyl) species. The TMA exposure then removes these species and reestablishes the AlCH 3 * species. Repeating the TMA and O 3 exposures in a sequential reaction sequence progressively deposited the Al 2 O 3 ALD film as monitored by the increase in absorbance for bulk Al 2 O 3 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 ≥650 K. QMS analysis of the gas phase species revealed that the TMA reaction produced CH 4 . The ozone reaction produced mainly CH 4 with small amounts of C 2 H 4 (ethylene), CO, and CO 2 . Transmission electron microscopy (TEM) was also used to examine the Al 2 O 3 ALD films deposited on the ZrO 2 particles. These TEM images observed conformal Al 2 O 3 ALD films with thicknesses that were consistent with an Al 2 O 3 ALD growth rate of 1.1 Å/cycle. The surface species after the O 3 exposures and the mass spectrometry results lead to a very different mechanism for Al 2 O 3 ALD growth using TMA and O 3 compared with Al 2 O 3 ALD using TMA and H 2 O.