Chemical Probing of Water-Stable Methyl Species in Atomic Layer Deposition of Al₂O₃ from Trimethylaluminum and Water

Abstract

In atomic layer deposition (ALD) of Al 2 O 3 thin films using trimethylaluminum (TMA) and water, it is generally believed that the surface methyl species formed by chemical adsorption of TMA are sufficiently water-reactive to produce surface hydroxyls. However, recently, there have been several reports on the presence of persistent methyl species in the water exposure step during the Al 2 O 3 ALD process. Here, we performed in situ Fourier-transform infrared spectroscopic analysis to provide evidence that the surface methylated by TMA retains the water-stable methyl species on the surface after exposure to water. The C−H stretching mode of the waterstable methyl species appears at ∼2960 cm −1 with a higher wavenumber compared to that of the reactive methyl species (∼2940 cm −1 ). Furthermore, the water-stable (persistent) methyl species can be chemically probed with ozone (O 3 ) because ozone reacts with the persistent methyl species to form formate species. During the chemical probing by exposing the persistent methyl species to ozone, the C−H stretching mode of the persistent methyl species disappears at ∼2960 cm −1 and the asymmetric stretching mode of the formate species is observed at ∼1609 cm −1 . This reveals that the persistent methyl groups are consumed to form the formate species by the chemical probing with ozone. In addition, we propose a plausible reaction between the surface formate species and TMA, which may explain the observations made by the in situ FTIR investigation.

Accelerated Deep Learning Dynamics for Atomic Layer Deposition of Al(Me)3 and Water on OH/Si(111)

“…Perhaps, such diverse possibilities can produce a heterogeneous surface morphology. The consequences of this could be confirmed by experimental observation of water-stable methyl species or retention of hydroxyl groups as a source of hydrogen content …”

“…In addition to the operando spectroscopic analyses, , ab initio studies of the static structures and mathematical modeling of the reaction rates have paved a way for the fundamental understanding of the surface chemical reactions. However, the actual surface phenomena may differ from the static picture because the temperature-dependent reaction dynamics may follow reaction pathways that deviate from the adiabatic minimum energy paths.…”

“…23 Experimentally, gaseous HOAl-(CH 3 ) 2 was observed as a secondary reaction product during the water pulse, which was assigned to the desorption of the initial surface products during the ALD process. 24 T h i s c o n t e n t i s In addition to the operando spectroscopic analyses, 25,26 ab initio studies of the static structures and mathematical modeling of the reaction rates have paved a way for the fundamental understanding of the surface chemical reactions. However, the actual surface phenomena may differ from the static picture because the temperature-dependent reaction dynamics may follow reaction pathways that deviate from the adiabatic minimum energy paths.…”

Mechanistic Study on Molecular Layer Deposition of Titanicone from TiCl4 and Ethylene Glycol

“…The silica pellet was placed vertically by a stainless steel grid on the stage heater of the reactor. Silica pellets were prepared with fumed silica powder (S5505, Sigma-Aldrich) by following the procedure described elsewhere . The silica pellet temperature in the stainless-steel grid was controlled by adjusting the temperatures of the stage heater and reactor wall.…”

“…All FTIR spectra were obtained by averaging 400 scans. Unfortunately, the IR spectra in the low-frequency region below 1300 cm –1 are noisy because the silica pellet strongly absorbs IR below 1250 cm –1 (see the Supporting Information of ref ). Detailed experimental conditions for in situ FTIR experiments are listed in Table S1.…”