Optical metrology of thickness and indium composition of epitaxial InxGa1−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 InxGa1-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 InxGa1-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 InxGa1-xAs layer thickness through post data processing using InxGa1-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 InxGa1-xAs layer is quantified by dispersion (n and k) values extracted from a specific wavelength. In this work, the n value of InxGa1-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.
Effect of growth conditions on surface roughening of relaxed InGaAs on GaAs
We report elastic light scattering measurements of the surface morphology of strained InxGa1–xAs on GaAs, grown by molecular beam epitaxy at different growth temperatures and In contents. During strain relaxation through formation of interfacial misfit dislocations, the surface of the film roughens in response to inhomogeneous surface strains produced by the interfacial misfit dislocations. The time dependence of this roughening is modeled by an Edwards–Wilkinson equation in which the deposition flux noise is neglected and the inhomogeneous surface stress is the only driving term.
Surface segregation in III-V alloys
Recent measurements which demonstrate the occurrence of surface segregation during the MBE growth of IIIaIIIb–V ternary semiconductor alloys and IIIa–V/IIIb–V heterostructures are reviewed. This preferential segregation drives to the surface one of the third-column elements involved, to the expense of the other, within their common sublattice. In ternary alloys, the surface is found to be nearly binary, and a short-scale interface roughness is detected in heterostructures. For arsenides, the direction and extent of the segregation process follow the In-Ga≥Al order. We discuss possible origins for the segregation process and the ability of standard segregation models to describe the results on ternary alloys and to predict composition profiles for any given heterostructure. These predictions are compared to recent measurements by high-resolution microscopy, ion scattering, photo-luminescence, or Raman scattering. Possible applications of the segregation process, and also remedies for avoiding it are finally discussed.