Residual Stresses in Thin Films

The thermal and dynamic mechanical behaviors of triblock copolymers with a styrene/isoprene/styrene architecture were investigated in order to understand their adhesive properties. Both copolymer free films and films bonding together two titanium alloy plates were found to have thermal and mechanical response that was strongly dependent on joint preparation. Microphase separation in the melts of these triblock materials was felt to contribute to the observed phenomena namely, the presence of residual stresses in thin films which had been cooled while under high pressure. 

Lepienski, C.M., Pharr, G.M., Park, Y.J., Watkins, T.R., Misra, A., Zhang, X., 2004. Factors limiting the measurement of residual stresses in thin films by nanoindentation. Thin SoUd Films 447, 215-257. 

Another way to asses the residual stress in thin films is to utilize their critical thickness,... 

G. Guisbiers, O. Van Overschelde, M. Wautelet, Nanoparticulate origin of intrinsie residual stress in thin films. Acta Mater. 55(10), 3541-3546 (2007)... 

Figure 11.22 An example of the effeet of sputtering system pressure on residual stress in thin films. Redrawn with permission from D. W. Hoffman and John A. Thornton, Journal of Vaeuum Seienee Teehnology, 17, 380 (1980). Copyright 1980, AVS The Science Technology Society.

Film Adhesion. The adhesion of an inorganic thin film to a surface depends on the deformation and fracture modes associated with the failure (4). The strength of the adhesion depends on the mechanical properties of the substrate surface, fracture toughness of the interfacial material, and the appHed stress. Adhesion failure can occur owiag to mechanical stressing, corrosion, or diffusion of interfacial species away from the interface. The failure can be exacerbated by residual stresses in the film, a low fracture toughness of the interfacial material, or the chemical and thermal environment or species in the substrate, such as gases, that can diffuse to the interface. 

Fig. 4.43. A periodic array of cracks advancing steadily through a thin film, driven by residual stress in the film.

A bonding method using a sputtered Pyrex glass thin film as an intermediate layer has been studied [31]. A bend of the wafer sometimes observed after the sputtering deposition. It is originated in the residual stress in the Pyrex film. The residual stress in the film is related to the gas [Ar (90%) + 02 (10%)] pressure during the sputtering. A... 

Reiter G, Hamieh M, Damman P, Sclavons S, Gabriele S, Vilmin T, Raphael E. Residual stresses in thin polymer films cause rupture and dominate early stages of dewetting. Nat Mater 2005 4 754-758. 

Consequences of Transient Residual Stresses in Thin Polymer Films... 

Fig.1 Schematic representation of the elastic interaction between a thin film and substrate, generating residual stresses in the system, as described in the text.

Figure 9.40 shows another example of residual strain effects on the Raman spectrum. The Si stretching vibration changes its frequency when Si is in the form of a thin film on sapphire. We can compare the Raman band positions between the strain-free sample and strained sample to evaluate the bond length change, which can be converted to residual strain. The residual strain is commonly elastic in nature. Thus, the residual stress in materials can be determined with the linear elastic relationship between strain and stress. 

FIS 96] FISCHER K., OETTEL H., Analysis of residual stress gradient in thin films using Seemann-Bohlin x-ray diffraction . Mater. Sci. Forum, Trans Tech. Puh., Switzerland,... 

We anticipate that the entanglement density in the dry spin-coated films is lower than in an equilibrated bulk system. Such a departure fi om equilibrium most likely generates residual stresses. As one consequence, we tentatively attribute the observed hole nucleation, which initiated the dewetting process of holes, to the presence of such residual stresses within the film [165]. In this way, rupture can be related to the spin-coating process used to prepare thin polymer films. 

The presence of residual stresses in polymer thin films can thus be considered as an explanation for the rupture mechanism via heterogeneous nucleation. We have found that the probability for film rupture, defined as the maximum number of circular holes per unit area formed in a film of given thickness, also depended on ageing time, the time the film was stored at temperatures below Tg [17]. It should be noted that ageing of the films started at the time of the solvent quench during... 

Meanwhile, in domain-rich ferroelectric devices, besides the need for a direct visualization of internal residual stresses, a direct experimental assessment of domain texture and distribution is desirable, in order to control functional outputs. For example, a size effect on the ferroelectric phase transition in thin films may lead to a critical size of few tens of nanometers, below which the ferroelectric transition vanishes. 

Interface delamination and film fracture induced by residual stress in the thin film were the focus of discussion in the preceding chapter where models were developed within the framework of linear elastic fracture mechanics. Such analyses did not account for the actual separation of the film from its substrate. However, there are delamination processes for which transverse deflection of the film away from the substrate becomes an important consideration in a variety of practical applications. Examples include ... 

Chason, E., Sheldon, B. W., Freund, L. B., Floro, J. A. and Hearne, S. J. (2002), Origin of compressive residual stress in polycrystalline thin films. Physical... 

S. Ko, D. Lee, S. Jee, H. Park, K. Lee, W. Hwang, Mechanical properties and residual stress in porous anodic alumina structures. Thin Solid Films 515(4), 1932-1937 (2006)... 

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