Synchrotron X-ray topography is a well established characterization tool for analyzing defect structures and strain in single crystal materials. We have further extended this method to quantitatively measure the residual strain and stress in any single crystal material. This is achieved by the modified technique of synchrotron X-ray topography, where a grid made out of X-ray absorbing material is placed in the path of incident or diffracted beam. By applying the principal of ray tracing to the recorded topographs, all the six components of strain and stress tensor has been calculated and mapped over the entire area of the crystal. This novel non-destructive method of stress measurement can prove to be an invaluable tool for both single crystal manufacturers and users.
Single crystal substrates are subjected to a series of processes including cutting, polishing, thermal treatment, brazing, soldering and finally encapsulation in a package during device fabrication. These processes introduce internal or residual strain/stress in the crystal which are not only detrimental to the performance of the device but also can ultimately lead to device failure. Synchrotron X-ray topography method is a powerful non destructive characterization tool for imaging 1-D, 2-D or 3-D defects in nearly perfect single crystals. In our current research we have attempted to measure residual strain and stress in single crystal silicon or in general any single crystal material and mapped it over the entire crystal surface area. For this purpose we used the principle of X-ray reticulography along with the ray tracing technique. In the experimental setup, single crystal material is placed on a goniometer and is aligned such that the surface of the crystal is perpendicular to the incident X-ray beam. A fine grid made out of X-ray absorbing material is placed in the path of incoming X-ray beam, which effectively splits the beam into multiple micro-beams. Diffraction pattern of the entire crystal is recorded at a specific specimen film distance. Each of the microbeam after interacting with the particular region in the crystal is diffracted by a specific plane(s). Combination of all the diffracted microbeams constitute a topograph called reticulograph. Distortion recorded on the reticulographs represents strain or the distortion in the crystal lattice plane. A non-destructive method to calculate residual stress level within the crystal is an invaluable tool for single crystal device manufacturers. We have devised a non-destructive, non-invasive method using X-ray diffraction imaging technique, Stress Mapping Analysis by Ray Tracing (SMART), to fully determine the state of stress and strain within the crystal. Strain and stress maps generated from different single crystals will be presented and discussed.