Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Amorphous to polycrystalline phase transition in La2 O3 ﬁlms grown
on a silicon substrate forming Si-doped La2 O3 ﬁlms†
S. R. Lee,∗1 A. Kim,∗2,∗3 S. Choi,∗2,∗3 T. Ikeda,∗4 T. Kobayashi,∗5 T. Isoshima,∗6 S. Cho,∗7 and Y. Kim∗1,∗8
Currently, the semiconducting industry is heavily reliant on Si-based electronic devices. SiO2 has beenused as a principal dielectric in Si-based industry owing
to its good ﬁlm properties and stability in the complementary metal-oxide-semiconductor (CMOS) process.
However, its low dielectric constant has raised issuesof low performance of device and large leakage current with decreasing gate thickness, channel length,etc. Consequently, extensive eﬀorts have been made toﬁnd alternative dielectrics with high-permittivity (κ)
on Si as a replacement for SiO2 . One of importantconditions for high-κ dielectric is that the dielectric
layer should not result in the formation of silicide or
SiO2 interfacial layer between silicon wafer and dielectric layer. Intriguingly, it has been shown that upon
the deposition of La2 O3 is deposited on Si, La silicate
is formed rather than a SiO2 interfacial layer.1)
In this study, we used a pulsed laser deposition(PLD) method to obtain a high-quality La2 O3 ﬁlm ona Si substrate. Using a high-resolution transmission
electron microscope (HRTEM) it was observed thatapproximately 10 nm thick amorphous La2 O3 layer
was initially formed on Si. Subsequently, and thena polycrystalline La2 O3 layer was formed on top of
the amorphous La2 O3 layer, as Fig. 1(a), which is attributed to Ostwald’s step rule, this is a metastablestate formation prior to the formation of a stable stateof a material. HRTEM images also suggested thatno interfacial oxide layer was formed between La2 O3and Si. Furthermore, through an in-depth study using Rutherford backscattering (RBS), performed at theRIKEN Pelletron accelerator facility, it was further
conﬁrmed that La-Silicate interfacial layer is extremelyreduced, as Fig. 1(b). Rather, the results of X-ray photoelectron spectroscopy atomic depth proﬁle analysis,using Ar+ ion beam sputtering, indicated the presenceof La-silicate present over the entire La2 O3 ﬁlm, asFig. 1(c). This suggests that Si diﬀuses through whole
thick La2 O3 ﬁlms, thereby forming Si-doped La2 O3ﬁlms. Our study suggests that employment of ad†
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8

Condensed from the article in Phys. Status Solidi A 219,2200318 (2022)
Surface and Interface Science Laboratory, RIKENInterdisciplinery Materials Measurement Institute, Korea
Research Institute of Standards and Science
Department of Nano Science, University of Science andTechnology
RIKEN Nishina Center
Neutron Beam Technology Team, RIKEN
RIKEN Cluster for Pioneering Research
Division of Physical Metrology, Korea Research Institute ofStandards and Science
Department of Applied Chemistry, University of Tokyo- S28 -Fig. 1. (a) Transmission electron microscope image ofpolycrystalline/amorphous La2 O3 ﬁlms, (b) Rutherford backscattering, and (c) X-ray photoelectron spectroscopy atomic depth proﬁle of La2 O3 /Si.

vanced growth technique may improve the status ofhigh-κ gate oxide of La2 O3 gate oxide in CMOS industry.
Reference1) T. Kawanago et al., Proc. 41st European Solid State
Device Research Conf., Helsinki, Finland, 2011-4, p. 67.