Low-Temperature Atomic Layer Deposition of α-Al₂O₃ Thin Films

Abstract

The atomic layer deposition of Al 2 O 3 films on Si(100) and α-Cr 2 O 3 was studied. The films were grown via AlCl 3 -H 2 O, AlCl 3 -O 3 , Al(CH 3 ) 3 -H 2 O, and Al(CH 3 ) 3 -O 3 processes at 300−750 °C. The films deposited from AlCl 3 and H 2 O at temperatures ≥ 400 °C on α-Cr 2 O 3 contained the corundum phase of alumina (α-Al 2 O 3 ). The densities and refractive indices of the α-Al 2 O 3 films were close to the corresponding values of single-crystal α-Al 2 O 3 and exceeded markedly those of amorphous Al 2 O 3 . The α-Al 2 O 3 phase was also obtained in the films deposited at 450 °C on α-Cr 2 O 3 from AlCl 3 and O 3 and from Al(CH 3 ) 3 and H 2 O. However, the crystallinity, densities, and refractive indices of the latter films were lower than those of the films deposited at 450 °C on α-Cr 2 O 3 from AlCl 3 and H 2 O. Etching in hot (110 °C) 80% H 2 SO 4 was used to characterize the chemical resistance of the films in aggressive environments. The etching rate of α-Al 2 O 3 deposited at 450−750 °C was more than 1000 times lower than that of predominantly amorphous Al 2 O 3 , and also lower than those of the films that were grown on Si(100) at 750 °C and contained γ-Al 2 O 3 , δ-Al 2 O 3 , and/or θ-Al 2 O 3 .

Influence of Substrates on Structure Development and Concentration of Residual Impurities in Hafnium–Titanium-Oxide Films Grown by Atomic Layer Deposition

“…Even larger differences in the concentrations of residual chlorine have been observed when the compositions of Al 2 O 3 films grown from AlCl 3 and H 2 O on crystalline α-Cr 2 O 3 seed layers and pristine Si substrates have been characterized. In the crystalline α-Al 2 O 3 films deposited on α-Cr 2 O 3 at 450–500 °C, the concentration of residual chlorine was by an order of magnitude lower than that in the amorphous films grown on Si substrates at the same process parameters …”

“…Atomic layer deposition (ALD) is a method that has extensively been studied and applied for producing thin and ultrathin films for a number of applications, particularly for those where the deposition of films on substrates with complex shapes is needed. − The ALD method is based on self-limited surface reactions that are expected to lead to the formation of a film with the required thickness and composition. However, in real ALD processes, films with considerable concentrations of impurities, related to the incomplete removal of precursor ligands, are usually obtained. ,− These ligands obviously have a detrimental effect on the crystallization of films . This conclusion is based on a result that crystal growth has been observed at growth temperatures ( T G ) that enable the deposition of films with a sufficiently low concentration of impurities. ,− …”

“…However, in real ALD processes, films with considerable concentrations of impurities, related to the incomplete removal of precursor ligands, are usually obtained. ,− These ligands obviously have a detrimental effect on the crystallization of films . This conclusion is based on a result that crystal growth has been observed at growth temperatures ( T G ) that enable the deposition of films with a sufficiently low concentration of impurities. ,− …”

“…On the other hand, recent studies have revealed that the concentration of residual impurities may markedly depend on the crystal structure of films formed in the ALD processes. , For instance, the rutile-phase TiO 2 films grown from TiCl 4 and O 3 on RuO 2 seed layers have contained lower amounts of chlorine residues than the anatase-phase TiO 2 films simultaneously grown on silicon substrates in the same ALD process at the same T G . Even larger differences in the concentrations of residual chlorine have been observed when the compositions of Al 2 O 3 films grown from AlCl 3 and H 2 O on crystalline α-Cr 2 O 3 seed layers and pristine Si substrates have been characterized.…”

Atomic-Layer-Deposited Aluminum Oxide Thin Films Probed with X-ray Scattering and Compared to Molecular Dynamics and Density Functional Theory Models

“…12 High substrate temperatures can be employed using the AlCl 3 and water process due to the high thermal stability of the chloride precursor, in which case crystalline films can be obtained. 13 However, the vast majority of ALD alumina films are grown using TMA coupled with an oxygen precursor (water, ozone, or oxygen plasma) under conditions that result in amorphous films, with the upper limit of the deposition temperature dictated by the decomposition temperature of TMA. Postdeposition annealing of amorphous alumina films at or above 900−1050 °C results in crystallization.…”