Investigating the morphological evolution of ion-thinned Ag films via <i>in situ</i> ellipsometry

Abstract

Ion etching of Ag films following their deposition presents an alternative method to improve wetting and obtain conductive Ag films at low thicknesses. Moreover, this approach does not rely on conventional wetting mechanisms, allowing one to obtain qualitatively different Ag morphologies at a given thickness. To evaluate how the Ag morphology evolves during etching, established interference-enhanced in situ ellipsometry monitoring methods are supplemented with a complementary comparative modelling approach, allowing one to monitor both the formation of fully continuous films and conductive Ag networks throughout deposition, as well as the breakdown of these morphologies during etching. This reveals that breakdown behaviors of continuous and percolated film structures are driven by distinct mechanisms, contrary to their formation during Ag deposition. The critical film thicknesses obtained via etching are studied as a function of various deposition conditions in relation to the resulting Ag properties. This particularly highlights the methods to improve the performance of etched films through the control of growth conditions, while revealing far less dependence on film–substrate surface energy mismatch than during Ag deposition. The observed film breakdown behaviors are explained in terms of conventional solid-state dewetting mechanisms, i.e., grain boundary grooving and hole expansion mechanisms, adapted to the context of ion etching.