Analysis of Selectively Grown Epitaxial Si[sub 1−x]Ge[sub x] by Spectroscopic Ellipsometry and Comparison with Other Established Techniques

The increased interest in epitaxial Si 1-x Ge x /Si heterostructures for device applications requires very good control of layer thickness and composition. Unfortunately, most of the well-developed characterization methods, such as Rutherford backscattering spectroscopy (RBS), secondary ion mass spectroscopy, and photoluminescence measurements are unsuitable as production measurement tools. On the other hand, spectroscopic ellipsometry (SE) allows a fast, in-line, and nondestructive analysis, including wafer mapping capabilities. This paper demonstrates the suitability of SE for the determination of both Ge content and layer thickness of epitaxial Si 1-x Ge x for Ge contents between 1 and 35%. By describing the optical dispersion by means of the harmonic oscillator model, we obtained a clear correlation between the Ge content and E n (1), the resonant energy of the first oscillator, and n max , the peak value of the real part of the refractive index. The small spot (30 × 30 μm) size allows one to characterize Si 1-x Ge x layers selectively grown in an isolation structure. The small window size prevents RBS measurements. SE allowed the fine tuning of a selective epitaxial growth process with regard to growth rate, Ge incorporation, and wafer uniformity.