The invention discloses an interconnection structure and a formation method thereof. The formation method comprises steps: a substrate is provided; a dielectric layer is formed on the substrate; a conductive structure is formed in the dielectric layer; a cap layer is formed on the conductive structure and the dielectric layer, wherein the cap layer is a Si-doped cap layer; and annealing treatmentis carried out on the conductive structure and the cap layer. In the technical scheme of the invention, the cap layer is the Si-doped cap layer, Si atoms in the cap layer can react with a material ofthe conductive structure to form bonds, the connection strength between the cap layer and the conductive structure is thus improved, electro migration of the formed interconnection structure can be suppressed, and the reliability of the formed interconnection structure can be improved.