The reaction of metallic alloys to H2Se/Ar is a promising technique to produce device quality CuInSe2 thin films. However, up to now the controllability of the film quality has been critically influenced by the segregation of secondary phases during growth. We indicate in this study that this phenomenon is strongly related to the selenization reaction temperature, and especially to the ramping procedure followed to the final selenization temperature. Metallic precursors which were slowly heated to temperatures around 400 degrees C are characterized by inhomogeneous film morphologies and X-ray fluorescence (XRF) measurements revealed a strong segregation of In towards the Mo back contact. In contrast, rapid heating of samples in H2Se/Ar to temperatures above 400 degrees C resulted in uniform and dense films with a high degree of compositional uniformity through the thickness of the samples. Transmission electron microscopy (TEM) indicated the presence of a low density of planar defects in these optimized films. Low temperature photoluminescence (PL) studies demonstrated that the optical properties of these polycrystalline thin Alms are very sensitive to post-growth treatment in Ar/H-2 and O-2.