Sensors to analyse layer structures already during epitaxial growth provide valuable information for developing device structures and for ensuring the reproducibility of run-to-run conditions. Most analytical online tools are applicable to all major growth techniques. Today a variety of probes is routinely integrated into growth systems for monitoring in situ sample temperature, growth rate, layer thickness, composition, strain, and other parameters of the growth process. Sensors measure either the ambient in the vicinity of the growing sample or the sample surface. Ambient analysis comprises mass spectrometry and optical probes; they provide information about the mass transport, the kind and density of species, their temperature, and potential mutual reactions. Surface probes include diffraction techniques and various optical tools. Surface sensitivity for diffraction is achieved by applying grazing-incidence angles, and the diffracted electron and X-ray beams disclose the surface morphology and reconstructions. Optical probes are widely applied in gaseous growth ambient. The selectivity for the surface may strongly be enhanced by taking advantages of symmetry-related surface properties, and several optical probes can resolve the growth of single monolayers. The chapter describes prominent techniques for in situ analysis of epitaxy. After discussing ambient analysis using mass spectrometry and optical spectroscopy, surface probes are considered. Structural analysis by reflection high-energy electron diffraction and by X-ray diffraction is outlined, and optical probes by pyrometry and deflectometry yielding data on temperature and strain are presented. The text then focuses on reflectometry, ellipsometry, and reflectance-difference spectroscopy (reflectance-anisotropy spectroscopy); these techniques provide both chemical and structural information.
Surface and Ambient ProbingSemiconductor devices consist of many epitaxial layers with different composition. The demand to control the perfection of growth in situ, i.e., already during epitaxy, led to the development of various analytical tools. Some of these sensors are today routinely integrated into commercial growth systems and allow for online monitoring
