The method comprises affixing a thin sheet of crystal (8) onto metal (6) of same type as the sheet but amorphous or of small grain size, deposited in trenches of a substrate (1) to form interconnect lines for example. Annealing progressively imposes the crystalline structure of the sheet onto the lines. When the crystal (8) is removed, highly conductive crystalline lines are obtained since the grains thereof have been greatly enlarged.