Atomic Layer Deposition of Al₂O₃Using Trimethylaluminum and H₂O: The Kinetics of the H₂O Half-Cycle

Abstract

Atomic layer deposition (ALD) of Al 2 O 3 using trimethylaluminum and H 2 O is known to proceed through sequential surface reactions that leave the surface alternately terminated with AlCH 3 and OH groups. Using in situ reflection− absorption infrared spectroscopy in a flow reactor, we monitor the consumption of AlCH 3 groups by brief pulses of H 2 O at temperatures between 105 and 300 °C. At low temperatures, the surface reactions occur by what appears to be two stages that can be fit to a biexponential decay. Rate laws based on species of AlCH 3 groups that also predict a biexponential decay are found to depend on unrealistic activation energies for their constituent reactions when applied to the data. However, a model in which the effective activation energy changes linearly with AlCH 3 coverage does adequately fit the data. This model produces the apparent biexponential decay at low temperatures, and it confirms prior suggestions of a coverage dependence in the rate constant. The decrease in the effective activation energy with increasing coverage can be interpreted in terms of a cooperative effect between adjacent AlCH 3 groups. These findings may provide a framework for further studies, and both the kinetic model and parametric fits to the data may be useful in the construction of models of this important ALD process.

Surface Chemistry during Atomic Layer Deposition of Pt Studied with Vibrational Sum-Frequency Generation

“…The BB-SFG signal is proportional to the coverage and not to the change in coverage as is the case for, e.g ., FTIR difference spectra, which rules out any persistent CH 3 species after the O 2 exposure as having been seen for other ALD processes. 31 , 45 , 46 Not all CH 3 groups undergo complete dehydrogenation in the precursor half-cycle since Figures 4 and 8 show clear evidence of CH 3 on the surface at the end of the precursor half-cycle. The temperature has a strong impact on the relative amounts of the surface species at the end of the precursor half-cycle: Figure 8 shows that the amount of C=C is fairly constant, while the CH 3 coverage decreases with temperature.…”

A review of surface roughness impact on dielectric film properties

“…The thickness of the as-deposited thin film can be adjusted precisely at the atomic scale by the total number of ALD cycles. [110,111] Hyde et al [112] and Waldman et al [113] utilised the ALD of alumina to introduce surface hydrophilicity to the initially hydrophobic polypropylene (PP) membranes. Nikkola et al [114] utilised a similar procedure for enhancing hydrophilicity and therefore the anti-fouling capacity of thin film composite (TFC) polyamide (PA) reverse osmosis (RO) membranes.…”

A Secondary Reaction Pathway for the Alumina Atomic Layer Deposition Process with Trimethylaluminum and Water, Revealed by Full-Range, Time-Resolved In Situ Mass Spectrometry

“…The latter argument was given as well by Sperling et al, explaining the double exponential decay of surface CH 3 groups observed by in situ infrared spectroscopy during the water pulse. 8 This was solved tentatively by introducing a coverage-dependent activation energy. It seems that, after all, the TMA-water process is not as ideal as generally believed.…”