Strained-silicon metrology using a multi-technology optical system

A selection of thin Si layers grown epitaxially upon thick relaxed SiGe films were measured using the combination of optical metrology techniques available on the Opti-Probe 7341 system. The techniques used included in particular (i) angle resolved laser Beam Profile Reflectometry (BPR) with S and P polarization, (ii) Broad-band visible-DUV spectrophotometry (BB), and (iii) spectroscopic ellipsometry (SE). The measured parameters included the Ge-content of the relaxed SiGe layer, the thickness and optical dispersion of the thin Si layer, and the thickness of the native oxide layer on the strained Si. Strain in the Si layer can be recognized by a significant downwards shift in the energy of the E1 peak and in the magnitude of the E2 peak in the e 2 dispersion curve, which is consistent with theoretical predictions when the strain in the layer is tensile. The thickness measurements of the Si layer made by the Opti-Probe were found to be in agreement with subsequent SIMS analysis to within 5a for the strained-Si layer. Measurement precision for thickness was <1.5a (3σ). for the strained-Si layer. Overall, the results show that a reliable and stable measurement of Strained-Si is possible using optical metrology.