Cap metal forming method

A method for forming a cap metal on a processing surface of a substrate provided with two or more regions having different water-repellent properties, the method comprising:

• holding the substrate horizontally by a rotatable holding mechanism installed in an inner chamber covered by an outer chamber;
• supplying a nonreactive gas which has a temperature equal to or higher than a preset plating process temperature into the outer chamber via a gas supply hole provided in a top surface of the outer chamber;
• forming a pressure gradient between the inner chamber and the outer chamber;
• and supplying a plating solution to a preset position on the processing surface of the substrate so as to form the cap metal on at least one of the regions,
• wherein the nonreactive gas is supplied onto the processing surface of the substrate and flows on the processing surface of the substrate, and transfers heat to the substrate, thereby suppressing the temperature decrease of the plating solution flowing on the processing surface of the substrate, and
• in the pressure gradient forming step, the nonreactive gas is uniformly introduced from the outer chamber into the inner chamber through a plurality of gas inlet openings provided at a sidewall of the inner chamber and spaced apart at equal distances, and is uniformly injected onto the processing surface of the substrate through a rectifying plate disposed above the processing surface of the substrate and below the plurality of gas inlet openings inside the inner chamber.