Agglomeration of Pt thin films on dielectric substrates

Abstract

The agglomeration of metal thin films on dielectric materials is a topic of high technological importance. In this contribution, a coupled morphology-agglomeration approach has been chosen to reveal the basic mechanism of rupture, mass transport, and the substrate dependence of agglomeration. The morphological evolution of Pt thin films has been investigated by means of scanning electron microscopy, atomic force microscopy, and focused ion-beam (FIB) etching techniques. Pt thin films were deposited on amorphous ${\text{Si}}_{3}{\text{N}}_{4}$ and polycrystalline yttria stabilized ${\text{ZrO}}_{2}$ substrates and subjected to heat treatments up to 1193 K for 2 h. Three main observations have been made: (i) the early stage of rupture can be described via basic thermodynamics as an order-disorder transition. The dominating mechanism of initial film rupture is a defect associated barrierless nucleation of holes in the spinodal regime of the Pt thin film as shown by means of Minkowski measures. (ii) Up to 1073 K the hole growth is found to be a surface-diffusion limited process, and in first approximation it is in agreement with Brandon and Bradshaw's theory for the morphological evolution of thin metal films at elevated temperatures. Values for mass transport have been derived. (iii) It is shown that two in general independent physical processes control the morphological evolution and kinetics of thin-film agglomeration: one attributes to the film-ambient interface and the other to the film-substrate interface. Void formation at the film-substrate interface is enhanced by a factor of 9 in the case of the amorphous-crystalline interface due to a lower adhesion energy of the film. The corresponding adhesion energies have been determined experimentally using FIB techniques and the Wulff-Kaishew theorem for equilibrium crystal shapes.