Thermal Annealing Effects on the Atomic Layer Deposited LaAlO[sub 3] Thin Films on Si Substrate

Abstract

The changes in film structure of amorphous atomic layer deposited LaAlO 3 thin films after thermal annealing were examined by medium-energy ion-scattering measurements and angle-resolved X-ray photoelectron spectroscopy. Thermal annealing induces Si-rich LaSiO and Al-deficient LaAl x Si y O z layers on a few monolayers of SiO 2 . Al atoms do not participate in silicate formation during annealing. Instead, they migrate toward the film surface, which induces nonhomogeneity in the films along the vertical direction. The concentrations of Al and La on the film surface increase and decrease, respectively, as a result of Si diffusion from the substrate and silicate formation.LaAlO 3 is a promising gate dielectric material in future complementary metal-oxide-semiconductor devices on account of its larger bandgap ͑ϳ6.2 eV͒ and comparable dielectric constant ͑24-27͒ compared with HfO 2 . 1,2 It is also thermodynamically stable on Si substrates. 3,4 It was reported that as-deposited amorphous LaAlO 3 films on Si by molecular-beam deposition do not exhibit any SiO 2 or silicate interface layer. 4 Moreover, epitaxial Si films maintain an abrupt interface with LaAlO 3 substrates even after annealing at 900°C. 3 However, the interfacial stability of LaAlO 3 /Si varies according to the types of deposition techniques used for LaAlO 3 growth. In many cases, inevitable interface layer formation between the amorphous LaAlO 3 thin films and Si substrate during film deposition and postdeposition annealing ͑PDA͒ have been reported. 1,2,5-9 Interface layer formation normally has an adverse effect on the device performance. In this study, the equivalent oxide thickness of a LaAlO 3 film increased from 2.23 to 2.46 nm after PDA at 800°C. However, the mechanisms for the interfacial reaction between the LaAlO 3 thin films and Si substrate during film deposition and PDA are not completely understood. Previous studies using angleresolved X-ray photoelectron spectroscopy ͑ARXPS͒ 1 and secondary ion mass spectroscopy 2 reported that Al-deficient interfacial La x Al y O z Si layers are formed during film growth. The authors also reported a loss of interfacial Al atoms, which had been interposed between the La 2 O 3 layer and Si substrate. 10 Moreover, an Al-rich surface layer was obtained from the La 2 O 3 /Al͑O,N͒/Si structure after thermal annealing at 800°C. 10 It was suggested that the migration of Al atoms to the surface is related to interface layer formation. In order to adopt LaAlO 3 films as a gate oxide, studies on changes in film/substrate structure and the stoichiometry of LaAlO 3 films at high temperatures are essential.In this study, 5-6 nm thick LaAlO 3 thin films were deposited on Si substrates by the sequential deposition of La 2 O 3 and Al 2 O 3 submonolayers in an atomic layer deposition ͑ALD͒ manner. The LaAlO 3 films were annealed by rapid thermal annealing ͑RTA͒ and the structural variations were investigated.An alternating layer of La 2 O 3 and Al 2 O 3 thin films were deposited on a p-type Si͑100͒ wafer to form a LaAlO 3...

Atomic Layer Deposition of Gadolinium Aluminate using Gd(iPrCp)3, TMA, and O3 or H2O

“…For La [12,13] A related material is LaAlSiO x , which can be formed by thin film reaction of LaAlO 3 with SiO 2 during high-temperature annealing, similar to other rare-earthcontaining oxides. [14,15] Interestingly, this high-temperature silicate is reported to have an even higher band gap ($7.0 eV) in combination with k $ 18. [16] Gd x Al 2-x O 3 has also been reported for NVM applications, but in this case as a charge-trapping layer, in which the charge is stored in a similar manner to the floating gate described above.…”

(Invited) Rare Earth Materials for Semiconductor Applications

“…In addition, because of their tendency to form silicates, they can react with the standard SiO 2 interfacial layer in CMOS logic gate stacks, increasing the total permittivity and facilitating EOT-scaling (11,12,13,14). For this purpose, binary rare earth oxides are preferred as ternary oxides have been observed to demonstrate silicate induced phase separation (6,15). Rare earth oxides are studied to stabilize the highly sensitive interfaces for high-mobility substrates and improve the electrical properties (16,17).…”

Effects of Rapid Thermal Annealing and Different Oxidants on the Properties of LaxAlyO Nanolaminate Films Deposited by Atomic Layer Deposition

“…Moreover, the change of values of thickness of four La x Al y O films before and after annealing is negligible. This can be explained by the densification of the films after thermal annealing [25].

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