Initial Growth Study of Atomic-Layer Deposition of Al₂O₃ by Vibrational Sum-Frequency Generation

Abstract

The initial growth during the atomic-layer deposition (ALD) of Al 2 O 3 using trimethylaluminum (TMA) and water was studied on two starting surfaces: SiO 2 and −H-terminated Si(111) [H/Si(111)]. In situ spectroscopy ellipsometry (SE) showed virtually immediate growth of Al 2 O 3 on both surfaces, although for H/Si(111) a reduced growth-per-cycle was observed in the initial 20 cycles. The underlying surface chemistry during the initial cycles of ALD was monitored with in situ broadband sum-frequency generation (BB-SFG) spectroscopy. For the SiO 2 surface, the −CH 3 surface groups were followed revealing that only the first TMA half-cycle deviates from the steady-growth regime. The reaction cross section of the initial TMA half-cycle (σ TMA = 2.0 ± 0.2 × 10 –18 cm 2 ) was a factor of 3 lower than the cross section of the TMA half-cycle during the steady-growth regime of ALD (σ TMA = 6.5 ± 0.6 × 10 –18 cm 2 ). All H 2 O half-cycles, including the first, showed steady-growth behavior with a corresponding reaction cross section (σ H 2 O = 4.0 ± 0.4 × 10 –20 cm 2 ). Therefore, only the first ALD cycle was affected by initial growth effects on the SiO 2 starting surface, in line with the SE data. For the H/Si(111) surface, the Si–H groups were monitored with BB-SFG spectroscopy, revealing a reaction cross section of σ TMA = 3.1 ± 0.3 × 10 –18 cm 2 for the first TMA half-cycle on H/Si(111); a factor two lower than that during the steady regime of Al 2 O 3 . These results demonstrate that the chemistry during the initial growth regime of Al 2 O 3 ALD on SiO 2 and H/Si(111) shows subtle but measurable differences compared to the steady-growth regime.

Reaction and Growth Mechanisms in Al2O3 deposited via Atomic Layer Deposition: Elucidating the Hydrogen Source

“…One mechanism may be due to a low reactivity of the (heavy) water with surface −CH 3 ligands, which has been proposed to be one of the main limiting factors in the GPC at low temperatures. 41 Vandalon et al have shown there is a persistent amount of −CH 3 surface groups after the H 2 O pulse, which significantly decrease by increasing the deposition temperature higher than 250 °C. 41 Shirazi et al have also shown through DFT calculations the persistency of methyl ligands after a water pulse.…”

AlN PEALD with TMA and forming gas: study of plasma reaction mechanisms

“…In the literature, it is very popular to use the exponential function to represent the ALD reactions. [36][37][38] However, for the exponential function, the slope (absolute value) monotonously decreases to zero. Some ALD reactions experience an initial growth delay due to the surface effect.…”

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

“… 29 With BB-SFG spectroscopy, the functional groups present on the surface during ALD can be identified and the (relative) density of surface groups can be followed in situ , as is illustrated by our earlier work monitoring the density of CH 3 , OH, and Si–H groups during ALD of Al 2 O 3 . 30 − 32 Identification of the hydrocarbon species on the surface of the precursor is of particular interest for the Pt ALD process and, therefore, the CH stretch region of the IR spectrum was probed with BB-SFG spectroscopy. Apart from identifying surface groups, the reaction kinetics during the precursor half-cycle and the influence of temperature on the surface chemistry were also studied.…”