Minority carrier diffusion length measurements of semiconductors using a multiwavelength laser SQUID microscope

We evaluated single crystal silicon wafers with a p-n junction structure using a laser superconducting quantum interference device (SQUID) microscope. A high temperature superconductor SQUID magnetometer was used to detect photogenerated magnetic signals with an amplitude of several pico-tesla. The relationship between the photogenerated magnetic fields and the wavelengths of the excitation light was investigated. The minority carrier diffusion length was obtained by using a multiwavelength (680 to 850 nm) laser SQUID microscope. The results were found to be in good agreement with those obtained using the probe contacting method. The laser SQUID microscope can enable a truly noncontacting and contamination-free test of equipment with a high spatial resolution, and can enable testers to make quantitative evaluations. While surface pretreatment is necessary in traditional destructive measurements, the laser SQUID method can be used to take immediate measurements without any required pretreatment. These features make this method highly advantageous for monitoring the semiconductor process.