In this study we examined the influence of the illumination intensity and the presence of poly(ethylene oxide) (PEO) as an additive for the process of copper electrodeposition onto p-Si(100). The study was carried out by means of cyclic voltammetry (CV) and the potential step method from which the corresponding nucleation and growth mechanism (NGM) were determined. Both methods were performed under illumination for the electron's photogeneration. Likewise, a morphologic analysis of the deposits obtained at different potential values by means of atomic force microscopy (AFM) was carried out. In the first stage, Mott-Schottky measurements were taken to characterize the energetic of the semiconductor/electrolyte interface. The CV results indicated that the presence of PEO inhibits the electrochemical reaction of oxide formation on the surface of the semiconductor, This allows a decrease in the overpotential associated with the electrodeposition . process. The analysis of the jlt transients shows that in the absence of additive the NGM corresponds to progressive 3D diffusional controlled (PN3DDIFF), while in the presence of PEO the NGM corresponds to instantaneous 3D diffusional controlled (IN3DIDT). In both cases analysis by the AFM technique was performed and confirmed these mechanisms, The morphologic analysis by this technique led us to the conclusion that the deposits made in the presence of additive are more homogeneous.