Quantitative analysis of gettering mechanism of Si device by using imagig plate and convergentbeam electron diffraction

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Inmurity gettering is one of the important processes in Si device process. The extrinsic or intrinsic gettering technique has been used in the commercial process. The intrinsic gettering uses oxygen precipitates formed in Si wafers by heat-treatments. Lattice strains or lattice defects are considered to be gettering sinks for impurity elements. The quantitative analysis of the gettering sinks is very important to understand the gettering mechnaism and to improve gettering efficiency. In Particular it is of interest to analyze local lattice strains near the gettering sinks. Electron diffraction enables us to measure local lattice strains in high spatial resolution compared with X-ray diffraction or Ramann spectroscopy.Electron microscope images and convergent-beam electron diffraction (CBED) patterns are observed in Si wafer which is heattreated at 1000 ﾟC in oxygen atmosphere to produce oxygen precipitates. An oxygen precipitate is thin plate of several nm in thickness and several hundred nm in edge length. The plate is paralle to (100) plane of Si matrix, and the edge is parallel to (110). From the CBED patterns ovserved along [012] direction parallel to the plate of the precipitate, local lattice strains of Si matrix are measured as a function of the distance from a surface of the precipitate. Si lattices are distorted about 4% near the plate plane of the precipitate by the compressive stress, while they are distorted about 3% near the edge of the precipitate by the tensile stress. The lattice strains decrease with increase of a distance from the interface and disappear at about 1 mum.