Diffusion layers in metal interconnects

A plating method comprising:

• contacting a patterned substrate with a plating bath in a plating chamber, wherein the pattern substrate comprises at least one metal interconnect with a contact surface that is exposed to the plating bath, and wherein the metal interconnect is made of a first metal characterized by a first reduction potential;
• and
• plating a diffusion layer on the contact surface of the metal interconnect, wherein the diffusion layer is made of a second metal characterized by a second reduction potential that is larger than the first reduction potential of the first metal in the at least one metal interconnect,
• wherein the plating bath comprises one or more ions of the second metal and a grain refining compound that reduces the formation of pinhole defects in the diffusion layer, the grain refining compound is characterized by a concentration in the plating bath of less than or about 0.05 M, and wherein the diffusion layer is plated on the contact surface of the metal interconnect at a rate of less than or about 5 nm/min.