A novel process to control the surface roughness and resistivity of electroplated Cu using thiourea

Thiourea is a well-known additive in the electroplating industry due to its excellent ability to reduce surface roughness. However, sulfur dissociated from the thiourea is often incorporated into the plated Cu film as the byproduct CuS, which then increases the film's resistivity. The two-step Cu electroplating method proposed here deposited a smoother Cu surface film and matched the resistivity (after annealing) attained using methods that employ a thiourea-free electroplating of the Cu film. The Cu film obtained through two-step plating contained a sulfur concentration that was below the detection limit of Auger electron spectroscopy (AES).