Leveling compound control

A method of processing a plating solution, the method comprising:

• determining a suppressor concentration of a suppressor in the plating solution and a leveler concentration of a leveler in the plating solution, the determining including:
• comparing a rotating disk electrode (-RDE) potential measured from the plating solution at a predetermined time to reference data of RDE potential versus suppressor concentration or leveler concentration at the predetermined time, the predetermined time dependent on whether the suppressor concentration or leveler concentration is being determined;
• and
• determining the suppressor concentration and the leveler concentration based on a comparison of the measured RDE potential to the reference data of RDE potential versus suppressor concentration and leveler concentration, respectively;
• adjusting the plating solution after determining the suppressor concentration and the leveler concentration to form an adjusted plating solution;
• and
• plating a layer using the adjusted plating solution, wherein:
• determining the suppressor concentration comprises determining whether the suppressor concentration is less than a predetermined suppressor threshold, and
• determining whether the suppressor concentration is less than the predetermined suppressor threshold includes:
• comparing the measured RDE potential at a predetermined suppressor concentration time to reference suppressor data of RDE potential versus suppressor concentration in an absence of leveler at the predetermined suppressor time, and
• calculating the suppressor concentration of the plating solution based on a comparison of the measured RDE potential to the reference suppressor data.