X-ray topography studies of the defect depth profile in processed silicon wafers

Intrinsic gettering and other defect control techniques now form an integral part of most silicon device processes. For these methods to be effective in enhancing device performance, the nature and extent of defect introduction must be carefully monitored. X-ray topography provides the only nondestructive means of achieving this. Oxygen precipitation during intrinsic gettering treatment of silicon has been examined by both section topography and double-crystal reflection topography, using laboratory and synchrotron X-ray sources. In the case of double-crystal reflection topography, the depth sensitivity was varied by an appropriate choice of diffraction conditions, thereby enabling defect depth profiling through the wafer. Care must be taken, however, in the interpretation of such images, since the effective penetration depth is different for sigma and pi polarizations and harmonic components may be present, each of which has a different depth penetration. In addition, process-induced curvature gives rise to a variation in the diffraction conditions across the wafer.