56 holes 58 define the contour of the vias which will be formed in interconnection layer n i 1 holes 58 may be obtained by means of an adapted mask by a physico chemical etching performed in the presence of argon and of c 4 f 8 further a hydrofluoric acid hf cleaning step is carried out after the etching during the etching and the cleaning contaminating products for example fluorine penetrate into the pores of porous dielectric material 50 as illustrated in fig3 d by arrows 60 at the step illustrated in fig3 e an etching of the portion of oxide layer 52 and of layer 50 of porous dielectric material which are not protected by titanium nitride layer 54 has been performed as an example this etching may again be a physico chemical etching in the presence of argon and of c 4 f 8 followed by a cleaning with hydrofluoric acid this etch step enables forming the contour of the conductive tracks and of the vias of interconnection level n i 1 it is performed so that holes 58 cross thin sicn layer 46 and that they reach conductive tracks 40 of interconnection level n i in the same way as in the previous etch.