Method of electroless plating and electroless plating apparatus

A method of electroless plating for processing a plating surface to form a barrier layer on a substrate, comprising a step of

• feeding a processing solution used in at least one of the pre-processing steps of the electroless plating and the electroless plating step to the plating surface for puddling treatment, wherein the processing solution includes a first metallic material supplying a main ingredient of said barrier layer, a first complexing agent of an amphoteric ion type, a second complexing agent adapted to promote a plating reaction, a pH adjusting agent;
• said processing solution is prepared divided into a first solution and a second solution, wherein the second solution includes a reducing agent;
• the first and second solutions are mixed to obtain said processing solution before feeding to said plating surface;
• wherein said puddling treatment comprises:
• placing the processing solution on the substrate while the substrate is substantially rotationally fixed;
• allowing the processing solution to remain on the substrate a predetermined amount of time;
• and
• rotating the substrate to remove excess processing solution.