Characterization of process-induced lattice distortion in silicon by double-crystal x-ray topography using a curved collimator

Abstract

Instead of the conventional flat collimator a curved collimator was used in double-crystal x-ray topography. The curvature of the collimator was adjusted so that the Bragg condition for x-ray diffraction was uniformly satisfied over a wide area of the silicon wafer. The image area of the wafer was wide enough to characterize the local lattice distortion induced by test element groups of metal–oxide–semiconductor capacitors formed on the wafer. The lattice distortion was measured as variations in lattice plane spacing and in lattice plane orientation using local angular deviations from the Bragg condition. These angular deviations were determined by fitting the x-ray intensities measured at the same point on a series of topographs taken around the Bragg peak to the rocking curve of the sample. The lattice plane spacing changed abruptly by 10−6 at the boundary between the areas of gate oxide (11 nm thick) and the areas of field oxide (400 nm thick), and showed less variation within these areas. The lattice plane orientation changed monotonically in each area, with an inclination of the order of 10−5 rad within the largest gate oxide area (5×5 mm2).