Experimental and Computer Simulation Study of the Variation with Depth of the X-raySection Topograph Images of a Dislocation

International audienceA systematic study of the variations of the contrast of a dislocation in silicon on section topographs with thedepth of the line was performed both experimentally and with computer simulations. Mo Kalpha1 radiationand 33-3 and -3-33 symmetric reflections were used. The crystal thickness was 440 microns so that the value of mu*twas 0.64. The influence of the orientation of the dislocation was studied for values of the angle betweenthe line and its Burgers vector ranging between 60 and 90 ° in the glide plane. It was observed that when thedislocation lies close to the entrance surface, whatever its orientation, its image is centred around the traceof the plane of incidence passing through the intersection of the dislocation with the direct beam whilewhen the dislocation lies close to the exit surface its image is centred around the projection of the disloca-tion on the section pattern. The variation of the orientation of the image for intermediate depths of thedislocation is interpreted by means of the geometrical construction of the dynamical image. The values of theorientation of the image calculated according to this simple model are in good agreement with thosemeasured on both experimental and simulated topographs. The same geometrical model enables thedifference in the relative positions of the direct and dynamic images of stereo pairs to be explained. A newfeature was observed in the simulated images and several of the experimental ones, namely a con-centration of intensity along the projection of the dislocation in the reflected direction. Slit width wastaken into account in the simulations for a better fit with experimental topographs but not polarization,which was taken to be normal to the plane of incidence. Because of the small value of the crystalthickness and of mu*t, the variation of the contrast with the Burgers vector is very small, making itsdetermination very difficult