X-ray diffraction microscopy: A new approach to the study of failure mechanism in semiconductor devices

The conventional view of the influence of crystal imperfections on device performance is based on the fact that devices made with dislocation-free silicon are not better than devices made with less perfect silicon. This view, however, has overlooked the fact that in making a device, defects will be introduced by the fabrication steps. Thus in practice one cannot avoid lattice defects. The questions then arise as to what are the harmful defects; can the number of these defects be reduced; by what processing steps are they introduced; can they be avoided, and if not can they be utilized to advantage? In order to answer these questions, it is necessary to have a non-destructive technique which (a) allows an inspection of the silicon slice after each processing step, and (b) is capable of detecting the existence of structural defects and the segregation of impurities at these defects. Such a technique is x-ray diffraction microscopy. The application of this new technique to the study of harmful defects in the semiconductor substrate, in the epitaxial layer, after thermal oxidation, after the opening of windows in the oxide and after the diffusion process will be discussed. In addition, the technique has been applied to silicon slices containing large numbers of diode or transistor structures. Correlation between defects and breakdown phenomena has been established.