A method, for forming a semiconductor device structure, includes: forming a conductive structure over a substrate, wherein the conductive structure includes twin boundaries. The forming the conductive structure includes: manipulating process conditions so as to promote formation of the twin boundaries and yet control a density of the twin boundaries to be outside a range for which a portion of a curve is an asymptote of a constant value, the curve representing values of an atomic migration ratio corresponding to values of the density of the twin boundaries.