Design and implementation of a S-parameter wafer defect scanner

We describe the design and implementation of a real-time automated scanning system that gives an S-parameter image of a semiconductor wafer, thus allowing the density of vacancy type defects to be shown as a function of position on the wafer. A conventional 22Na positron source of 0.5 mm diameter rasters across 5 x 5 cm2 region of two times per hour in rectilinear motion. Gamma ray energies Eγ are processed using a standard HP Ge spectroscopy system and a 14 bit nuclear ADC. Over a period of 1-2 days a high resolution 128 x 128 pixel image with 256 colours (scaled to the S-parameter range) can be formed as a wafer defect map. The system is reliable, interactive and user-friendly (patent pending 2003). (orig.)