Nyles Cody

Kinetics of Si incorporation into a Ge matrix for Si1−xGex layers grown by chemical vapor deposition

The growth rate and alloy composition of Si1−xGex layers grown in an industrial chemical vapor deposition (CVD) system have been analyzed as functions of the process parameters at a pressure enabling selective epitaxial growth. We systematically investigate the growth of Si1−xGex with 0.48<x<0.8, using GeH4∕SiCl2H2 partial pressure ratios up to 1.12, where the GeH4 flow was constant and the SiCl2H2 flow was varied. Epitaxial growth temperatures spanned from 350to600°C. The growth rate and alloy composition were limited by the surface reaction step with an activation energy of 1eV∕mol. A significant growth rate reduction is observed when increasing Si content. This feature is consistent with a passivation of the surface Si bonds with H and Cl atoms typical of chemical vapor deposition Si1−xGex layer growth. It is found empirically that x∕(1−x)∝pDCSΔn, Δn=0.32, where x is the Ge mole fraction and pDCS is the SiCl2H2 partial pressure. Then we tentatively develop a model to support the empirical laws found wi...

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 ε2 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 5Å for the strained-Si layer. Measurement precision for thickness was <1.5Å (3σ). for the strained-Si layer. Overall, the results show that a reliable and stable measurement of Strained-Si is possible using optical metrology.