Stress evolution during growth of 1-D island arrays: Kinetics and length scaling

Abstract

To explore the mechanisms controlling residual stress in thin films, we have measured the stress evolution during electrodeposition of Ni on lithographically patterned substrates with different pattern spacings and growth rates. Studying films with a controlled island geometry allows us to relate the stress (measured using wafer curvature) to the evolution of the morphology. We analyze the measurements with a model that focuses on the stress that develops where adjacent islands grow together to form new elements of grain boundary. Residual stress in polycrystalline thin films is a persistent problem, since it can significantly reduce film performance or lead to failure [1]. A deeper understanding would enable it to be predicted and controlled. Numerous studies have shown how the stress evolution depends on the material, processing conditions and evolving microstructure (many studies are reviewed in [2,3,4]). Films with low atomic mobility tend to grow in a state of tensile stress while films with higher mobility are compressive. Similarly, raising the growth temperature [5] or decreasing the growth rate [6] can change the stress from tensile to compressive. During growth, the stress goes through multiple states that correspond with the evolving microstructure, i.e., from isolated nuclei (low or compressive stress) through island coalescence (tensile stress) to a continuous film (steady-state stress that depends on growth rate) [7]. Various mechanisms have been proposed to explain different aspects of the stress evolution. Compressive stress in the nucleation stage has been attributed to lattice compression induced by the surface stress [8]. Hoffman [9] proposed that the tensile stress arises due to attractive forces between islands when the grain boundary forms, similar to the reason for cracks closing [10]. The origin of the post-coalescence compressive stress is more controversial, with various groups attributing it to: adatoms on

Ultralow Stress, Thermally Stable Cross-Linked Polymer Films of Polydivinylbenzene (PDVB)

“…For example, a low surface mobility during deposition promotes film growth under tensile stress whereas high mobilities lead to films in compressive stress. 39 The evolution of film stress in our PDVB coatings exhibit a behavior qualitatively similar to the one observed in the growth of amorphous Ge (a-Ge) and Si films 23,40 after isolated islands coalesce into a continuous film at about ∼4 nm. At this stage, the a-Ge film reaches a maximum tensile stress value that rapidly becomes more compressive with thickness alike to asdeposited PDVB films depicted in Figure 7.…”

“…In such systems, early deposition occurs through growth of independent islands that induce tensile stress upon island coalescence; as the film grows thicker, the additional incremental stress on the film becomes less tensile. , Atomic mobility of the material during deposition, growth temperature, and growth rate are factors known to contribute to film stress in either a tensile or compressive way. For example, a low surface mobility during deposition promotes film growth under tensile stress whereas high mobilities lead to films in compressive stress …”

Origins of residual stress in thin films: Interaction between microstructure and growth kinetics

“…To provide a framework for understanding stress evolution, we have proposed a kinetic model (4,5) that predicts the stress evolution as a function of the growth conditions (temperature (T), diffusivity (D), and growth rate (R)) as well as the microstructure (grain size (L)). The model has been shown to be consistent with several studies of stress versus thickness for uniform and patterned (6,7) films and stress versus growth rate (5,8). However, the validity and limits of the model need to be explored by comparing its predictions with a wider range of experimental results.…”

Sonochemical Coating of Textiles with Zinc Oxide: Robust, Silver-Seeded Growth on Cotton for Effective UV Shielding

“…Estimates of microstrain along the c -axis in the films were obtained using the equation from Daniel et al It is likely that ZnO coatings were under slight tensile stress, probably originating from one or a combination of; (1) the mismatch in the thermal expansion coefficient of the ZnO and the cotton substrate, or; (2) the relaxation of intermolecular stresses in the ZnO . Tensile stress generation is near-universally observed for Volmer–Weber type (i.e., island coalescence-based) thin film growth, especially in lattice-mismatched materials . In brief, isolated but growing islands, which mainly generate compressive stresses, eventually impinge, coalesce (where energetically favorable), and competitively grow, thus forming predominantly tensile stresses, to then eventually form a continuous, polycrystalline thin film under a steady-state stress; with increasing strain energy generated when isolated islands meet .…”