Cu(In1−x,Gax)Se2 (CIGS) thin films can be deposited with a high versatility of composition by a hybrid one-step co-sputtering/evaporation process. In this paper, plasma analysis is performed with an optical emission spectroscopy non-contact tool, following light emissions from different plasma species: sputtered copper, gallium, indium but also evaporated selenium. The variations of plasma characteristics are correlated with target self-bias voltage. Hence, the selenium flow threshold avoiding target poisoning and the main parameter controlling the CIGS composition are determined. This study allows us to set up a process calibration method by means of correlation between the selenium evaporation temperature and the elemental composition of the deposited thin film.