DETERMINATION OF THICKNESS AND GE CONTENT OF STRAINED SI1-XGEX LAYERS ON SI SUBSTRATE BY 2-WAVELENGTH ELLIPSOMETRY

Fixed-wavelength ellipsometry at two wavelengths, lambda = 632.8 and 785 nm, is used for the determination of thickness and composition of thin epitaxial Si1-xGex films on silicon substrates. The results are compared to those obtained by X-ray double crystal diffractometry (DCD). The real part of the refractive index at 785 nm of these strained thin Si1-xGex layers is determined for the Ge content range of 0.10 < x < 0.22. A linear dependence of the real part of the refractive index on the Ge content is found. For fitting experimental and calculated curves it is necessary to adjust the thickness of a native oxide on top of the Si1-xGex layer. To obtain the best agreement in thickness measurements from both techniques, ellipsometry and DCD, it is necessary to modify the imaginary part of the refractive index.