NASA’s Langley Research Center has developed a method of using x-ray diffraction (XRD) to detect defects in cubic semiconductor (100) wafers. The technology allows non-destructive evaluation of wafer quality in a simple, fast, inexpensive process that can be easily incorporated into an existing fab line. The invention adds value throughout the semiconductor industry, but is especially relevant in high-end, high-speed electronics where wafer quality has a more significant effect on yields.
Developed to enhance NASA’s capabilities in fabricating chips for aeronautics applications, the method supplants existing methods that not only destroy the wafer in question, but can take as long as a day to determine the quality of a single wafer. This new approach can be applied to any cubic (100)-oriented semiconductor crystal, including silicon, SiGe, and GaAs, which is at least 90% of commercial wafers. It can also be used to evaluate the quality of epi layers deposited on wafer substrates, and of ingots before they are sliced into wafers.
By detecting significant wafer defect problems before circuits are fabricated, yields can be increased considerably and cost issues avoided. The required equipment can be purchased relatively inexpensively, and training for instrument operators can be accomplished in two weeks.