Mechanical and optical properties of as-grown and thermally annealed titanium dioxide from titanium tetrachloride and water by atomic layer deposition

Oili M.E. Ylivaara*, Andreas Langner, Xuwen Liu, Dieter Schneider, Jaakko Julin, Kai Arstila, Sakari Sintonen, Saima Ali, Harri Lipsanen, Timo Sajavaara, Simo-Pekka Hannula, Riikka L. Puurunen

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

19 Citations (Scopus)
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The use of thin-films made by atomic layer deposition (ALD) is increasing in the field of optical sensing. ALD TiO2 has been widely characterized for its physical and optical properties, but systematic information about the influence of thermal history to optical and mechanical properties of the film is lacking. Optical applications require planar surface and tunability of the refractive index and residual stress. In addition, mechanical properties such as elastic modulus and film hardness influence the performance of the layer, especially, when optics is integrated with microelectromechanical systems. In this work, optical properties, density, elemental analysis, residual stress, elastic modulus and hardness of as-grown ALD TiO2 thin films on silicon were studied at temperature range from 80 to 350 °C and influence of post-ALD thermal annealing was studied on films annealed up to 900 °C. ALD TiO2 films were under tensile stress in the scale of hundreds of MPa. The stress depended both on the ALD temperature and film thickness in a complex way, and onset of crystallization increased the residual stress. Films grown at 110 and 300 °C were able to withstand post-ALD annealing at 420 °C without major change in residual stress, refractive index or extinction coefficient. Elastic modulus and hardness increased upon crystallization with increasing ALD temperature. The results presented here help to improve the design of the optical devices by choosing films with desired optical properties, and further help to design the post-ALD thermal budget so that films maintain their desired features.

Original languageEnglish
Article number138758
Number of pages11
JournalThin Solid Films
Early online date26 May 2021
Publication statusPublished - 31 Aug 2021
MoE publication typeA1 Journal article-refereed


  • ALD
  • Atomic Layer Deposition
  • elastic modulus
  • hardness
  • optical properties
  • residual stress
  • TiO


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