A study is undertaken to determine the effect of low (10 g/L) and high (100 g/L) acid conditions on superconformal copper electroplating. The suppressor used is the surfactant P-104 at 200 ppm, with the accelerator bis(3-sulfopropyl)-disulfide (SPS) at a concentration of 5-35 ppm. High acid open circuit potential and polarization curves are shifted approximately -30 mV from low acid, both with and without P-104; Tafel slopes are the same at similar to 100 mV/decade. P-104 displays the same suppression strength in both electrolytes. Patterned 100 nm trenches show that the rate of high and low acid filling is essentially the same at low SPS concentration (5 ppm). As SPS increases, high acid filling is improved; the effect in low acid is inverse, albeit not as strong. As suppression strength is the same in high and low acids, the dependence on SPS during filling is attributed to acceleration, which involves an interaction between suppressor and accelerator molecules. (C) 2009 American Vacuum Society. [DOI:10.1116/1.3212933]