Polycrystalline Si1-xGex, has been recently shown as a favorable alternative to the poly-Si gate electrode for CMOS technology: the optical properties of this new material poly-Si1-xGex alloys layers are investigated here. Spectroscopic ellipsometry (SE) analysis on samples with different Ge contents up to 100%,, demonstrates both the composition dependency and the morphological change in the amorphous character of the material, while the x parameter increases. The technique is thus an easy and non-destructive method for layer composition as well as for material morphology control. These are important parameters for sub-micron(< 0.18 mu m) gate slacks material optimization. Layer morphology observation using XTEM and AFM are correlated here with SE, which in turn, would certainly be, in the near future, a routine control tool during the fabrication of the poly-SiGe gate structure.