Optical metrology of thickness and indium composition of epitaxial In _xGa _1-xAs layers on Si substrates

An optical metrology solution using a Spectroscopic Ellipsometer (SE) tool has been demonstrated to monitor the thickness and indium composition of In _xGa _1-xAs layers on Si substrates for III-V compound semiconductor channel devices. Fundamentally, the SE tool is based on light interference and phase shift effects corresponding to individual material properties. A wide range of wavelengths (190 ∼ 840nm) of the SE spectra is used to collect elliptically polarized light and for dispersion model characterization to float n and k values at each wavelength. The SE data for In _xGa _1-xAs and indium composition is quantified using TEM (Transmission Electron Microscopy) and RBS (Rutherford Backscattering Spectrometry) showing excellent correlation. In the range of 190nm to 840nm wavelengths SE is able to provide In _xGa _1-xAs layer thickness through post data processing using In _xGa _1-xAs/GaAs layer thickness with surface roughness consideration. Reducing the surface roughness is expected to enable more accurate and higher intensity of elliptically polarized light from films so that the best film model can be applied to float n and k values. Indium composition of the In _xGa _1-xAs layer is quantified by dispersion (n and k) values extracted from a specific wavelength. In this work, the n value of In _xGa _1-xAs/GaAs film stack at 219nm shows excellent proportional relationship with RBS data on three different indium compositions, while k value at 248nm shows excellent inverse relationship. This is a promising solution to evaluate critical growth parameters such as indium composition and to offer detailed and immediate feedback on the deposition process. This solution can be extended to other compound materials - characterizing thickness and composition by correlating n and k values for each wavelength.