The Ultimate surface photovoltage method of minority carrier diffusion length measurements reffered to as Ultimate SPV, replaces a sequential “one wavelength at a time” approach with simultaneous illumination with the entire set of wavelengths. In this multiwavelength beam, each monochromatic component is chopped with slightly different frequency. This enables simultaneous monitoring of all component SPV signals corresponding to different wavelengths using multi-frequency signal processing. The amplitude and phase of each component signals are then analyzed and used to calculate the diffusion length and surface lifetime. In-flight Ultimate SPV measurement, whereby the wafer continuously moves under SPV probe, is used for fast whole wafer mapping. In addition to speed advantages, Ultimate SPV offers a fundemental accuracy advantage due to elimination of differences in wafer condition during sequential illumination with individual wavelengths. High-speed measurements make it possible to add additional wafer treatments and perform multi-mapping required for separation of Fe and Cu in the silicon bulk. Wafer mapping in time of 2 minutes realized with Ultimate SPV is critical for monitoring of cobalt in silicon.
