Effect of eutectic reaction between depositing atoms and substrate elements on morphological evolution of Sn–Bi–Sn multilayer deposition

• Published in: Materials chemistry and physics Vol. 250; p. 122960
• Main Authors: Tang, Y.K., Lin, E.J., Wang, J.Y., Lin, Y.X., Wu, C.Y., Chiu, C.Y., Lee, C.H., Wang, C.P., Liu, C.Y.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01-08-2020; Elsevier BV
• Subjects: Bismuth; Clusters; Coalescence; Copper; Deposition; Eutectic reactions; Evaporation; Evolution; Latent heat; Morphology; Multilayers; Sn–Bi solder layer; Substrates; Surface energy; Surface tension; Thin film growth process; Tin; Tin compounds; Thin film growth process; Evaporation; Sn–Bi solder layer; Coalescence; Morphology
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2020.122960

In this work, we studied the effect of the reaction between the depositing atoms and the substrate element on the morphological evolution of the each deposition of the Sn–Bi–Sn multilayer structure on the Cu substrate. For the deposition of the single Sn layer on the Cu substrate, the reaction between the depositing Sn atoms and the Cu substrate is very minimal. TEM study shows only a very thin interfacial Cu–Sn compound layer (17 nm) formed between the depositing Sn layer and the Cu substrate. Yet, the latent heat of the vaporized Sn (296.1 kJ/mol) melts the Sn deposition layer on the Cu layer. Owing to the surface tension of the molten Sn, the molten Sn could agglomerate as the Sn clusters for reducing the surface energy.
For the subsequent deposition of Bi and Sn layers, the eutectic reaction would occur between the depositing Bi atoms and the Sn clusters. The energy required for the eutectic reaction between the depositing atoms and the substrate elements is provided by the latent heat released from the vaporized Bi (or Sn) atoms arriving on the deposition surface. The eutectic liquid formed on the deposition surface serves as a medium to (1) receive and redistribute the depositing atoms and (2) dissolve and transport the substrate elements. The above process (1) and (2) explain the morphological evolution of the each deposition of the Sn–Bi–Sn multilayer structure and the mechanism of morphological evolution is proposed in this work.
•Reveal the morphological evolution of each deposition of the Sn–Bi–Sn multilayer on Cu.•Latent heat of the vaporized Sn melts the Sn deposition layer on Cu.•Surface tension of the molten Sn causes Sn clusters by reducing the surface energy.•Eutectic reaction results between the depositing Bi atoms and the Sn clusters.•The mechanism of morphological evolution of each deposition of the Sn–Bi–Sn multilayer is established.