1 Department of Management Engineering, Technical University of Denmark2 Department of Manufacturing Engineering, Technical University of Denmark
The relationships between growth-conditions, topography and microstructure, and physical properties of electrochemically deposited copper, nickel and zinc-iron alloys were studied. Growth was investigated while systematically varying process parameters such as electrolyte chemistry, type and concentration of additives, current density, and mass transport. The grown films were analysed by a variety of characterisation techniques - including optical light microscopy, electron microscopy, atomic force microscopy, X-ray diffraction, thin film tensile testing, and nano-indentation. Studies of anomalous Zn-Fe alloy electrodeposition from a chloride-based electrolyte, suggest that a zinc-chloro-hydroxy-precipitate layer forms close to the cathode during deposition. Deposition current density, as well as the chloride-content of the electrolyte, controls the stability of the corresponding boundary layer at the cathode and hereby the composition of the deposited Zn-Fe alloy. Alloys with Fe-contents ranging from 5-80 wt-% were deposited from the same electrolyte, characterised by a sharp change in deposit-composition with electrochemical current density, which made the deposition of well-defined Zn-Fe compositionally modulated alloys (CMA) possible. Ni membranes were deposited from a Watts type electrolyte with or without the sulphur-containing additive sodium-saccharin. This additive caused a strong levelling as well as a grain refining effect on Ni-deposits. However, additional microstructural defects were introduced in the deposits with the use of sodium-saccharin, which led to embrittlement of the deposits. By using ultrasonic streaming near the cathode during electrodeposition in the Watts type electrolyte, improved material distribution in machined 3-dimensional groove geometries was observed. Electrochemical deposition of buried contacts for high efficiency silicon photovoltaic cells led to the development of a patented process for superconformal Cu-filling of high aspect ratio vias, while further studies on electrochemical Cu-deposition from acidic electrolytes led to the formulation of a 3-dimensional zone-structure diagram for electrodeposited Cu.