A process and structure for enabling the creation of reliable electrical through-via connections in a semiconductor substrate and a process for filling vias. Problems associated with under etch, over etch and flaring of deep Si RIE etched through-vias are mitigated, thereby vastly improving the integrity of the insulation and metallization layers used to convert the through-vias into highly conductive pathways across the Si wafer thickness. By using an insulating collar structure in the substrate in one case and by filling the via in accordance with the invention in another case, whole wafer yield of electrically conductive through vias is greatly enhanced.