Aluminum oxide from trimethylaluminum and water by atomic layer deposition: The temperature dependence of residual stress, elastic modulus, hardness and adhesion

Oili M.E. Ylivaara, Xuwen Liu, Lauri Kilpi, Jussi Lyytinen, Dieter Schneider, Mikko Laitinen, Jaakko Julin, Saima Ali, Sakari Sintonen, Maria Berdova, Eero Haimi, Timo Sajavaara, Helena Ronkainen, Harri Lipsanen, Jari Koskinen, Simo Pekka Hannula, Riikka L. Puurunen

    Research output: Contribution to journalArticleScientificpeer-review

    98 Citations (Scopus)

    Abstract

    Use of atomic layer deposition (ALD) in microelectromechanical systems (MEMS) has increased as ALD enables conformal growth on 3-dimensional structures at relatively low temperatures. For MEMS device design and fabrication, the understanding of stress and mechanical properties such as elastic modulus, hardness and adhesion of thin film is crucial. In this work a comprehensive characterization of the stress, elastic modulus, hardness and adhesion of ALD aluminum oxide (Al2O3) films grown at 110-300 C from trimethylaluminum and water is presented. Film stress was analyzed by wafer curvature measurements, elastic modulus by nanoindentation and surface-acoustic wave measurements, hardness by nanoindentation and adhesion by microscratch test and scanning nanowear. The films were also analyzed by ellipsometry, optical reflectometry, X-ray reflectivity and time-of-flight elastic recoil detection for refractive index, thickness, density and impurities. The ALD Al 2O3 films were under tensile stress in the scale of hundreds of MPa. The magnitude of the stress decreased strongly with increasing ALD temperature. The stress was stable during storage in air. Elastic modulus and hardness of ALD Al2O3 saturated to a fairly constant value for growth at 150 to 300 C, while ALD at 110 C gave softer films with lower modulus. ALD Al2O3 films adhered strongly on cleaned silicon with SiOx termination.

    Original languageEnglish
    Pages (from-to)124-135
    Number of pages12
    JournalThin Solid Films
    Volume552
    Early online date6 Dec 2013
    DOIs
    Publication statusPublished - 2014
    MoE publication typeA1 Journal article-refereed

    Keywords

    • Adhesion
    • Aluminum oxide
    • Atomic layer deposition
    • Elastic modulus
    • Hardness
    • Residual stress

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