Vias of at least approx. 1:1 aspect ratio in substrates are filled with material which exhibits a thermally driven amorphous/crystalline phase change. This is performed within a vacuum process chamber. During a first timespan the material is sputter-deposited by DC sputtering from a material target. In a subsequent timespan a void, which may remain in the via as material covered by the addressed sputtering, is opened by etching performed with the help of an inductively coupled plasma generated by an Rf driven electric coil and applying to the substrate with the via an Rf bias.