Electronic Defect and Contamination Monitoring in Si Wafers Using Spectrally Integrated Photocarrier Radiometry

Abstract

The ability of spectrally integrated room-temperature photocarrier radiometry to image electronic defects and contamination in silicon wafers is presented. Amplitude and phase imaging contrast is a result of signal sensitivity to local variations in the recombination lifetime of photoexcited carriers. Experimental frequency scans are fitted to carrier density-wave theory to simultaneously obtain the recombination lifetime, diffusivity, and surface recombination velocities (front and back). Lifetime measurements are combined with lateral surface scans to produce quantitative lifetime imaging. Contaminated boron-doped silicon wafers with iron concentration ∼1011cm−3∼1011cm−3 on a baseline of ∼5×109cm−3∼5×109cm−3 have been successfully imaged and exhibit a much higher spatial resolution than surface photovoltage images. Recombination lifetime measurements before and after photodissociation of FeB pairs have been utilized for quantitative determination of iron concentration; however, lifetime accuracy limitations due to photodissociation by the excitation laser under medium-to-high optical injection levels required for photocarrier radiometric measurements compromise the accuracy of heavy ion (Fe) concentration measurements.