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.
Suppression of In surface segregation and growth of modulation‐doped N‐AlGaAs/InGaAs/GaAs structures with a high In composition by molecular‐beam epitaxy
A model is proposed for describing the origin of the growth mode transition from two to three dimensions during the molecular‐beam epitaxial growth of InGaAs on GaAs [H. Toyoshima, T. Niwa, J. Yamazaki, and A. Okamoto, Appl. Phys. Lett. 63, 821 (1993)]. In this model the amount of In atoms on the surface arising from surface segregation is crucial in determining the growth mode transition, which provides the upper limit of the In composition and/or the thickness of InGaAs for device applications. The increase of these limited values for a modulation‐doped structure with an InGaAs channel has been implemented on the basis of this model. A lower substrate temperature and a higher As4 pressure during the InGaAs growth greatly suppress the In segregation ratio leading to the decrease of the amount of In on the surface. These growth conditions enable the upper limit of the In composition and/or the critical thickness of the InGaAs channel to be increased, which further verifies the validity of the proposed mod...
Surface segregation of third-column atoms in group III-V arsenide compounds: Ternary alloys and heterostructures.
We report a systematic study of the segregation of third-column elements involved in group III-V arsenide structures to their (100) surface. The surface composition is obtained by in situ electron spectroscopies, on special structures built by molecular-beam epitaxy. In ternary alloys, an important surface enrichment in one of the third-column components is most often observed, leading to a near-binary surface. Heterojunctions between two given binary materials A and B are abrupt or not in composition, depending on the growth sequence (A grown on B or B grown on A): for one sequence, the top monolayer of the base material is gradually distributed in the growing overlayer. All these behaviors can be summarized by tendencies to surface segregation following IngGa\ensuremath{\ge}Al, and by segregation efficiencies that are either near zero or near unity depending on the way structures are built. The application of standard models to the segregation isotherms for ternary alloys yields segregation energies of 0.1\char21{}0.2 eV. The physical origin for the segregation process and its consequences on interface roughness along the growth axis are discussed.