Thermomechanical properties of aluminum oxide thin films made by atomic layer deposition

Oili M.E. Ylivaara (Corresponding Author), Andreas Langner, Satu Ek, Jari Malm, Jaakko Julin, Mikko Laitinen, Saima Ali, Sakari Sintonen, Harri Lipsanen, Timo Sajavaara, Riikka L. Puurunen

Research output: Contribution to journalArticleScientificpeer-review

Abstract

In microelectromechanical system devices, thin films experience thermal processing at temperatures some cases exceeding the growth or deposition temperature of the film. In the case of the thin film grown by atomic layer deposition (ALD) at relatively low temperatures, post-ALD thermal processing or high device operation temperature might cause performance issues at device level or even device failure. In this work, residual stress and the role of intrinsic stress in ALD Al2O3 films grown from Me3Al and H2O, O3, or O2 (plasma ALD) were studied via post-ALD thermal processing. Thermal expansion coefficient was determined using thermal cycling and the double substrate method. For some samples, post-ALD thermal annealing was done in nitrogen at 300, 450, 700, or 900 °C. Selected samples were also studied for crystallinity, composition, and optical properties. Samples that were thermally annealed at 900 °C had increased residual stress value (1400-1600 MPa) upon formation of denser Al2O3 phase. The thermal expansion coefficient varied somewhat between Al2O3 made using different oxygen precursors. For thermal-Al2O3, intrinsic stress decreased with increasing growth temperature. ALD Al2O3 grown with plasma process had the lowest intrinsic stress. The results show that ALD Al2O3 grown at 200 and 300 °C is suitable for applications, where films are exposed to post-ALD thermal processing even at temperature of 700 °C without a major change in optical properties or residual stress.

Original languageEnglish
Article number062414
JournalJournal of Vacuum Science and Technology A: Vacuum, Surfaces and Films
Volume40
Issue number6
DOIs
Publication statusPublished - 1 Dec 2022
MoE publication typeA1 Journal article-refereed

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