Stresses in ALD films: Aiming for zero stress thin films

Riina Ritasalo, Oili Ylivaara, Tero Pilvi, Tommi Suni

    Research output: Contribution to conferenceConference AbstractScientificpeer-review

    Abstract

    When grown films by atomic layer deposition (ALD) both intrinsic and thermal stresses are formed into the film; latter due to the mismatch in the thermal expansion coefficient of the substrate and the grown film. Films under high residual stress may cause problems for further processing, and for device performance and reliability. High residual stress can induce film delamination or buckling; bend released structures or the materials where the films are attached. Especially in microelectromechanical system (MEMS) manufacturing, zero or well-controlled residual stress is desired, as the stress effect is more prominent on released structures. Here, the residual stress measured from most common metal oxides deposited by thermal ALD processes on silicon substrates are presented. The thermal processes have an advantage that those can be scaled up to batch processing to achieve through-put and cost efficiency required for volume production. By varying the process parameters (e.g. temperature, chemicals) we aim for zero stress films or film stacks as well as for comprehensive stress data set to help for example MEMS designers and process integrators choosing proper thin film material, and ALD process chemistry and process conditions.
    All films were grown in Picosun™ R-200 advanced reactors using thermal ALD processes. Deposited materials were HfO2, TiO2, SiO2, Al2O3 and Ta2O5 and combinations of these. The ALD temperature was varied between 150°C and 300°C. The substrates used were 150 mm diameter double side polished silicon wafers, which have been pre-measured for stresses before the ALD. For stress measurement we used TOHO FLX-2320-S wafer curvature measurement tool and the measurements were carried out at room temperature. Deposited film thicknesses were measured with Semilab SE-2000 ellipsometer.
    Residual stress data from most common metal oxides are presented. For some of the films there is also comparison for the same film material made with different precursors. In Figure 1 the residual stress data for the HfO2 film grown at varying temperature is presented. The stress changes from compressive to tensile as the ALD temperature was increased from 150°C to 200°C.
    Original languageEnglish
    Pages49
    Publication statusPublished - 29 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

    Keywords

    • ALD
    • Atomic Layer Deposition
    • residual stress
    • OtaNano

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