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Article Dans Une Revue Applied Surface Science Année : 2021

TiO2-SiO2 mixed oxide deposited by low pressure PECVD: Insights on optical and nanoscale electrical properties

Résumé

TixSi1-xO2 thin films appear as promising materials to replace SiO2 for DRAM devices. For theeffective down scaling, these mixed oxides should combine the best properties from SiO2 (lowleakage current) and TiO2 (high dielectric constant). In this study, TixSi1-xO2 thin films weredeposited by low pressure PECVD. Varying the Titanium Tetra-Isopropoxide (TTIP) andHexamethyldisiloxane (HMDSO) precursors flow rate allows us to obtain nanostructured filmswith tunable properties. Their surface chemical composition was assessed by X-rayPhotoelectron Spectroscopy (XPS). Atomic Force Microscopy (AFM) revealed that the surfaceroughness increases with the Ti content. Spectroscopic Ellipsometry (SE) showed that a smallamount of Ti is enough to induce a decrease of the energy gap and an increase of the refractiveindex, while preserving a low surface roughness. Since these mixed oxide films exhibitnanodomains with three different environments with randomly distributed Si-O-Ti bonds, SiO2-like and TiO2-like bonds, electrical properties are investigated at nanoscale in terms of dielectricpermittivity, charge injection, trapping and transport via electrical modes derived from AFM asElectrostatic Force Microscopy (EFM), Kelvin Force Probe Microscopy (KPFM) andConductive AFM (C-AFM). Despite a chemical composition evolving at the nanoscale, thiswork highlights that the electrical behavior can be considered as homogeneous (at the AFMresolution scale). A small amount of Ti induces a decrease in the amount of trapped electronsdue to charge transport increase and a strong decrease of trapped holes. Moreover, afterinjection, the rate of charge decay increases with the Ti content. These features were interpretedon the basis of the energy diagrams deduced from the Valence Band measurement highlightingthe n-type semiconducting character of the Ti-rich films. As a conclusion, TixSi1-xO2 films withx=0.33 allows the best compromise in terms of dielectric permittivity improvement, chargeinjection and transport behavior.
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Dates et versions

hal-03449033 , version 1 (25-11-2021)

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Maria Mitronika, C Villeneuve-Faure, F Massol, Laurent Boudou, W Ravisy, et al.. TiO2-SiO2 mixed oxide deposited by low pressure PECVD: Insights on optical and nanoscale electrical properties. Applied Surface Science, 2021, 541, ⟨10.1016/j.apsusc.2020.148510⟩. ⟨hal-03449033⟩
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