A Comparison of Thin Silver Films Grown Onto Zinc Oxide via Conventional Magnetron Sputtering and HiPIMS Deposition

Silver coatings are commonly deposited via dc magnetron sputtering for use in a variety of applications that require high transparency to visible light and good electrical conductivity, including, for example, low-emissivity coatings. The films need to be fully dense in order to achieve the correct optical and electrical properties, although the typical growth mechanism for silver films is by the nucleation and coalescence of islandlike structures that can result in the generation of voids within the coating and uneven surface topography. As a consequence, in order to achieve acceptable electrical properties, the optical transparency of the silver coating is often compromised due to the excessive film thicknesses required for continuous electrically conductive layers. Conventional methods used to enhance the adatom mobility, hence increasing the density of the coatings, include the application of an electrical bias to the substrate or substrate heating, both of which can be problematic for large-area dielectric substrates such as float glass or polymer web. One alternative is the production of a coating using a deposition flux with a high fraction of ionization. This can be achieved via high-power impulse magnetron sputtering (HiPIMS), leading to an enhanced delivery of energy to the adatoms via recombination at the substrate surface. Thin films of silver were deposited onto zinc oxide-coated glass substrates via continuous dc and pulsed-dc magnetron sputtering and also via HiPIMS at the same time-averaged power in order to compare the structure and growth mechanisms via techniques, including AFM, XRD, and Hall-effect measurements for the electrical characterization.