Residual stress in thin films made by atomic layer deposition

High residual stress in thin films cause problem for wafer processing and measurements which assume planar wafers. Residual stress in thin film, in part, is caused by thermal mismatch between the substrate and the film, while intrinsic thin film stress accounts for another part. Residual stress of films made by atomic layer deposition (ALD) has been occasionally reported, but so far, there have been little systematic studies. We have in a large collaborative project called MECHALD grown and characterized a wide series of thin films made by ALD for residual stress, including Al₂O₃, TiO₂, SiO₂, TiN, AlN and NbN. Some stress results have been published earlier [1], while most have so far remained unpublished. Most films were made by "regular" ALD, while some employed energy-enhanced methods such as the use of ozone as a reactant or plasma enhanced ALD (PEALD). Most of the films were under tensile stress, while a few had close to zero stress, or were slightly on the negative (compressive) side. All films with zero or compressive stress, originated from process where growth was somehow in the "energy-enhanced" side, namely, ozone or plasma was used as reactant, or reactant decomposition was likely to occur. Acknowledgements: MECHALD Tekes project and the Finnish Centre of Excellence on Atomic Layer Deposition are thanked for funding this work. References: [1] 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, Aluminum oxide from trimethylaluminum and water by atomic layer deposition: The temperature dependence of residual stress, elastic modulus, hardness and adhesion, Thin Solid Films 552 (2014) 124-135.