A process of electrodepositing high purity copper in a via in a silicon substrate to form a through-silicon-via, comprising: providing a silicon substrate containing at least one via, wherein the via includes an inner surface having an internal width dimension in the range from 1.5 microns to 30 microns, a depth from 5 microns to 450 microns and a depth:width aspect ratio of at least 3:1; optionally, forming a dielectric layer on the inner surface of the via; forming a barrier layer over the inner surface of the via or over the dielectric layer when present, wherein the barrier layer inhibits diffusion of copper into the silicon substrate; forming over the barrier layer a basic metal layer of sufficient thickness and coverage of the inner surface of the via to obtain sufficient conductance for subsequent electrolytic deposition of copper; immersing the silicon substrate into an electrolytic bath in an electrolytic copper plating system with the basic metal layer connected as a cathode, the system further comprising an insoluble dimensionally stable anode and a source of copper metal, wherein the electrolytic bath comprises an acid, a source of copper ions, a source of ferrous and/or ferric ions, and at least one additive for controlling physical-mechanical properties of deposited copper; and applying an electrical voltage between the insoluble dimensionally stable anode and the basic metal layer, so that a current flows therebetween for a time sufficient to electrodeposit high purity copper to form a TSV, wherein a Fe +2 /Fe +3 redox system is established in the bath to provide additional copper ions to be electrodeposited by dissolving copper ions from the source of copper metal. providing a silicon substrate containing at least one via, wherein the via includes an inner surface having an internal width dimension in the range from 1.5 microns to 30 microns, a depth from 5 microns to 450 microns and a depth:width aspect ratio of at least 3:1; optionally, forming a dielectric layer on the inner surface of the via; forming a barrier layer over the inner surface of the via or over the dielectric layer when present, wherein the barrier layer inhibits diffusion of copper into the silicon substrate; forming over the barrier layer a basic metal layer of sufficient thickness and coverage of the inner surface of the via to obtain sufficient conductance for subsequent electrolytic deposition of copper; immersing the silicon substrate into an electrolytic bath in an electrolytic copper plating system with the basic metal layer connected as a cathode, the system further comprising an insoluble dimensionally stable anode and a source of copper metal, wherein the electrolytic bath comprises an acid, a source of copper ions, a source of ferrous and/or ferric ions, and at least one additive for controlling physical-mechanical properties of deposited copper; and applying an electrical voltage between the insoluble dimensionally stable anode and the basic metal layer, so that a current flows therebetween for a time sufficient to electrodeposit high purity copper to form a TSV, wherein a Fe +2 /Fe +3 redox system is established in the bath to provide additional copper ions to be electrodeposited by dissolving copper ions from the source of copper metal.