DC and pulse plating of copper in acidic sulphate solutions containing benzotriazole (BTA) has been studied. When BTA is the only additive present, it generally has a stronger effect than the plating mode and significantly enhances deposit morphology and surface brightness over that produced in additive-free solutions. XPS and voltammetry analyses indicate that BTA is present at the surface of the deposit, but not through the entire coating, and does not become depleted within the solution over the course of plating. This may help explain why the initial surface smoothness and brightness is maintained as the coating grows beyond 5 mu m thick. Plating mode does have a strong effect on deposit morphology under specific conditions. Pulse current plating at low frequency (50 Hz) and low duty cycle (20%) produces deposits with poorer quality than that obtained by DC plating. Pulse reverse plating yields very coarse and dull coatings when the frequency is low enough for metal dissolution to occur during the reverse time. Regardless of the plating mode, the addition of Cl- eliminates most of the beneficial effects of BTA and leads to very rough and dull deposits. The observed effects are discussed in light of previous research on the electrodeposition and corrosion of the Cu-BTA and Cu-BTA-Cl systems.