Mixed wire structure and method of making the same

A method for connecting metal layers in a mixed wire structure for a semiconductor substrate, the method comprising:

• forming a lower metal layer and a via in the mixed wired structure in a dielectric structure on the semiconductor substrate, wherein a layer of a barrier metal is absent between the lower metal layer and the via;
• forming a trench in the dielectric structure for an upper metal layer that contacts the via;
• forming a barrier metal layer on the via and in the trench;
• forming the upper metal layer after forming the barrier metal layer, wherein the barrier metal layer is located between the via and the upper metal layer;
• depositing a sacrificial layer on a layer of a first metal in the dielectric structure for the mixed wire structure, wherein the layer of the first metal is for the lower metal layer and the via in the mixed wired structure;
• removing a portion of the sacrificial layer such that the layer of the first metal for the lower metal layer is exposed and a remaining portion of the sacrificial layer on the layer of the first metal defines the via for the mixed wire structure;
• etching the layer of the first metal, wherein a thickness of the layer of the first metal is reduced to form the lower metal layer and the via;
• depositing additional dielectric material on the dielectric structure such that the lower metal layer is covered by the dielectric structure;
• and
• planarizing the dielectric structure with the additional dielectric material such that the remaining portion of the sacrificial layer defining the via is exposed,
• wherein, forming a trench in the dielectric structure for the upper metal layer that contacts the via comprises:
• etching the dielectric structure after planarizing the dielectric structure to define a pattern in the dielectric structure for the upper metal layer in the metal layers.