Mechanisms limiting conformality in thermal and plasma-assisted ALD investigated by Lateral High Aspect Ratio structures

Mikko Utriainen, Feng Gao, Riikka L. Puurunen, Karsten Arts (Corresponding author), Vincent Vandalon, Erwin Kessels, Harm Knoops

    Research output: Contribution to conferenceConference AbstractScientificpeer-review

    Abstract

    This work investigates the processes governing conformality achieved by
    ALD, using Lateral High Aspect Ratio (LHAR) test structures supplied by
    VTT.1
    We show that these structures are well suitable for investigating the
    underlying ALD chemistry, as the shape of the thickness profile and the
    penetration depth are indicative for the growth regime and provide insight
    into parameters such as sticking probabilities.
    In the new PillarHall™ LHAR3 structures the reacting species diffuse
    underneath a removable membrane which is supported by pillars giving a
    500 nm spacing. This configuration offers new possibilities compared to
    traditional vertical structures. Among others, top-view diagnostics can be
    applied to straightforwardly determine the thickness profile and material
    properties. A range of diagnostics is validated in this work for this top-view
    analysis. Moreover, the structure has features with aspect ratios up to
    10000. Therefore a non-fully saturated profile is acquired for even the most
    conformal processes, which provides information on the limiting
    mechanisms.
    Two cases are discussed to exemplify these possibilities. Firstly, in the case
    of thermal ALD of Al2O3 using TMA and water it is known from recent work
    that at low temperatures the growth is limited by the reduced reactivity of
    H2O towards –CH3 groups.2
    We examine how this reactivity affects the
    conformality, by measuring and simulating Al2O3 thickness profiles for
    different substrate temperatures. For example, at 200°C table temperature
    a sloping profile is observed with a half-thickness-penetration-depth
    (HTPD) of ~400 μm (AR=800). This profile seems to be consistent with the
    low sticking probability of water at these temperatures (s~3·10-5).2
    That is,
    from Monte Carlo simulations a growth regime in between reaction-limited
    and diffusion-limited growth is expected for this sticking probability and
    penetration depth, yielding such a sloping profile.
    Secondly, in the case of plasma-assisted ALD of Al2O3 recombinationlimited growth is observed, as the HTPD is reduced to ~30 µm (AR=60)
    through recombination of the reactive O radicals. As even these short
    profiles can be resolved using top-view diagnostics, the LHAR3 structures
    can be employed to investigate recombination probabilities in plasmaassisted ALD as well. On the basis of the aforementioned studies, these and
    other insights into ALD chemistry relevant to conformal growth will be
    provided.
    Original languageEnglish
    Number of pages1
    Publication statusPublished - 30 Jul 2018
    MoE publication typeNot Eligible
    Event18th International Conference on Atomic Layer Deposition, ALD/ALE 2018: Featuring the 5th International Atomic Layer Etching Workshop - Songdo Convensia in Incheon, Incheon, Korea, Republic of
    Duration: 29 Jul 20181 Aug 2018
    https://ald2018.avs.org/

    Conference

    Conference18th International Conference on Atomic Layer Deposition, ALD/ALE 2018
    Abbreviated titleALD/ALE 2018
    CountryKorea, Republic of
    CityIncheon
    Period29/07/181/08/18
    Internet address

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