INTERPRETATION OF THE DIFFUSE-SCATTERING CLOSE TO BRAGG PEAKS BY X-RAY TOPOGRAPHY

Perturbations from crystal perfection will result in diffuse X-ray sca ttering, which can be imaged by topography to yield defect information without the swamping contribution of perfect-crystal scattering. This paper illustrates the importance of the probe shape for obtaining top ographic images in this diffuse region not only to aid interpretation but to isolate the contributors to this scattering. The diffuse scatte ring in the vicinity of the Bragg peaks of GaAs, Si and Ge substrate c rystals has been mapped to very high resolution and the diffuse scatte ring has been imaged by topography. It was found that the majority of the scattering emanates from surface damage and dislocations and not p oint defects or thermal diffuse scattering (TDS). These latter two com ponents are found to be second-order effects in general and are only j ust discernable as a very weak background intensity in highly perfect crystals. This topography method is very sensitive to surface damage. This is because the associated diffuse scattering close to a Bragg pea k can be used to form an image. Therefore, this relatively intense sca ttering provides a topograph within a few hours for assessing substrat e-surface quality. The sensitivity of the method is illustrated with i mages of surface defects and dislocations in very perfect semiconducto rs. A procedure for measuring the diffuse scattering emanating from mi crodefects is also presented.