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.