CuIn1-xGaxSe2 thin films were obtained from a combination of Cu-Se electrodeposited and In and/or Ga evaporated precursors, by heating in selenium vapor atmosphere. The compound formation processes were studied as a function of three variables : (1) the precursors deposition sequence, (2) the x = Ga/(In + Ga) film ratio, and (3) the annealing temperature. X-ray diffraction analysis have shown that after 500 degrees C annealing, single-composition alloy thin films were obtained from the different precursor sequences. For sample temperatures below 500 degrees C, structural data have established that different reaction pathways have led to the final quaternary compound formation, depending on the deposition sequence. Alloying processes are enhanced in those arrangements that favor binary selenide formation. Atomic force microscopy images have shown that grain size and surface roughness decrease as the Ga/(ln + Ga) ratio increases in the single-composition alloy thin films.