Monitoring Conformality in ALD Manufacturing: Comparing Lateral and Vertical High Aspect Ratio Test Structures

Mikko Utriainen, Feng Gao, Riikka L. Puurunen, Stefan Riedel, Alireza M. Kia

    Research output: Contribution to conferenceConference AbstractScientificpeer-review


    Atomic Layer Deposition (ALD) technology enables manufacturing of
    conformal thin films into such deep microscopic trenches and cavities that
    the film characterization becomes a true challenge. In ALD applications
    these 3D microstructured substrates are typically vertically oriented high
    aspect ratio (HAR) structures. Monitoring and control of conformality relies
    predominantly on cross-sectional sample preparation and SEM/TEM
    characterization. This approach has several challenges, e.g. need to break
    the wafer, seeing only thin slice, cleavage plane inaccuracy, multiple
    repeated samples to get reliable data and long response times.
    A potential approach to circumvent the challenges is a MEMS-based allsilicon lateral high aspect ratio (LHAR) test structure, PillarHall® developed
    at VTT [1-2]. The LHAR test chip is IC cleanliness proven and thus
    potentially compatible to any cleanroom environment. This study focuses
    to research questions: How reliable and accurate is LHAR test in 300 mm
    wafer manufacturing environment and, especially, how does it compare to
    vertical HAR structures.
    The LHAR Test Chip (LHAR3 -series, AR range 2:1 - 10000:1, 500nm gap
    height) was employed for the first time on the carrier wafer in 300 mm
    wafer ALD process (Jusung Eureka 3000) in Fraunhofer IPMS. The ALD
    process was foundry’s default ZrO2/Al2O3 laminate process, 22 nm, carried
    out in two process variation runs (A=optimized for 3D, B=planar) at same
    temperature and cycle numbers. In the same run was employed LHAR and
    vertical trench test structures (AR 20:1). Conformality of both structures
    were analyzed by SEM cross-sections, with appropriate sample
    Findings show that conformality in LHAR is comparable to vertical HAR
    within accuracy limits of step coverage metrology within the comparable
    AR range. Furthermore, in this study, higher aspect ratios in LHAR test chip
    shows significant differences between the process variations while in VHAR
    they are small. Therefore, even optical microscope metrics from LHAR
    provides fast relative insight to the process variations and can be utilized in
    monitoring. LHAR enables also access to gain more detailed compositional
    information on the trench wall e.g. by ToF-SIMS, which is under
    examination and a topic of further studies.
    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


    Conference18th International Conference on Atomic Layer Deposition, ALD/ALE 2018
    Abbreviated titleALD/ALE 2018
    Country/TerritoryKorea, Republic of
    Internet address


    • PillarHall
    • LHAR
    • ALD
    • conformality
    • Characterization


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