A method of manufacturing an interconnect substrate by electroless plating, including: (a) forming a catalyst layer with a specific pattern on a substrate; (b) immersing the substrate in a first electroless plating solution including a first metal to deposit the first metal on the catalyst layer to form a first metal layer; and (c) immersing the substrate in a second electroless plating solution including a second metal to deposit the second metal on the first metal layer to form a second metal layer, an ionization tendency of the first metal being higher than an ionization tendency of the second metal.