ANALYSIS OF CONVECTIVE MASS-TRANSFER BY POTENTIAL RELAXATION .5. COPPER DEPOSITION IN THE PRESENCE OF ORGANIC PLATING ADDITIVES

Effective mass-transfer boundary-layer thicknesses at a rotating disk cathode during copper deposition from a CuSO4/H2SO4 electrolyte contai ning Cl- ions and a commercial plating additive, either Copper Gleam-P C or Selrex Cubath-100, have been measured experimentally using the po tential relaxation technique for i less-than-or-equal-to i(Lim) and di sk rotation speeds ranging from 30 to 400 rpm. Boundary-layer thicknes ses with Selrex Cubath additive were in agreement with the Levich equa tion for all current densities and disk rotation speeds. For Copper Gl eam-PC, boundary-layer thicknesses were smaller than those predicted b y the Levich equation for low disk rotation speeds (omega less-than-or -equal-to 100 rpm) and current densities less-than-or-equal-to 3 5 mA/ cm2. A theoretical convective mass-transfer model with hydrodynamic sl ip (a nonzero radial velocity) at the disk surface has been developed to explain the Gleam results and the slip velocity has been correlated with the fractional surface coverage of Gleam additive which adsorbs on the disk surface.