Depth spectroscopy analysis of La-doped HfO2 ALD thin films in 3D structures by HAXPES and ToF-SIMS

Alireza, M. Kia, Clemens Mart, Nora Haufe, Mikko Utriainen, Riikka L. Puurunen, Wenke Weinreich

    Research output: Contribution to conferenceConference AbstractScientificpeer-review


    Doped-HfO2 based ferroelectrics have been widely studied for the application in advanced CMOS technologies such as ferroelectric random-access memory (FeRAM) or ferroelectric field effect transistor (FeFET). Studies show that there is a strong link between the ferroelectric properties with the highest remanent polarization value of the doped-HfO2 and the structural properties of the film. In ultrathin ferroelectric films, the concentration of La dopant directly affects the stabilization of the polar orthorhombic phase (Pca2I) which impact spontaneous polarization of ferroelectric films[1]. In this research, we characterized La concentration in HfO2 on 3D structures to show the uniformity of dopant distribution inside the hafnia from top to bottom of a high aspect ratio (HAR) structure. We use atomic layer deposition (ALD) for excellent step coverage in HAR structures. ALD provides precise controlling of the dopant distribution within a layer. However, regulating the dopant concentration in a thin film requires a platform which could be easily characterized and measured.

    In this study, we used lateral high aspect ratio (LHAR) test structures (PillarHall™ developed at VTT [2-3]) as a new platform to perform precise measurements of hafnia doped thin film along the deposition gap in LHAR structure. On this purpose, we combined time-of-flight secondary ion mass spectrometry (ToF-SIMS) with X-ray photoelectron spectroscopy (XPS) and highly novel hard-XPS (HAXPES) to make a comparative study on deposited La-doped HfO2 thin films with ALD. We compare La stoichiometry in planar structures with LHAR structures. By then with ToF-SIMS capability of data imaging and integrating data points from the region of interest, doping profiles can be quantified together with understanding the trench wall in-depth penetration. Furthermore, we compared generated quantitative information from depth analysis of different La concentrations in LHAR structures with the help of both traditional XPS measurements using an Al Kα X-ray source and extended depth of analysis experiments using a Cr Kα (hard) X-ray source (the Cr X-ray source provides depths analysis about 3 times higher than standard Al Kα source).
    [1] Mart et al., Appl. Phys. Lett., 114, no. 10, 2019.
    [2] Gao et al., Vac. Sci. Technol. A, 33, 2015.
    [3] Puurunen et al., AF-SuA15, ALD 2017.
    Original languageEnglish
    Publication statusPublished - 2019
    MoE publication typeNot Eligible
    Event18th European Conference on Applications of Surface and Interface Analysis (ECASIA) - Dresden, Germany
    Duration: 15 Sept 201920 Sept 2019


    Conference18th European Conference on Applications of Surface and Interface Analysis (ECASIA)
    Internet address


    • La-doped HfO2
    • ALD
    • ToF-SIMS
    • high aspect ratio structures
    • hard-XPS
    • OtaNano


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