Nondestructive measurement of free carrier lifetime and surface recombination velocity

An important factor influencing the generation and recombination in a semiconductor device is the fabrication process. A technique has been presented which enables one to measure the bulk lifetime and surface recombination velocity of a starting wafer as well as a partially or completely processed wafer. As a consequence, it is possible to study the influence of processing on the quality of devices and to develop an optimal fabrication procedure. This technique uses an infrared laser(probe beam) to monitor the carrier concentration via free carrier adsorption while periodically exciting free carriers by mean of a visible laser(exciter beam). The intensity of the exciter beam is sinusoidally modulated with an electro-optical modulator at frequencies of 100 Hz to 100 kHz. The free carriers generated by the exciter beam attenuate the probe beam and the resultant output is detected with a phase sensitive lock-in amplifier. The quantities measured are the amplitude and the phase of the detected beam relative to the exciter beam. The measured data is then fitted to theoretical expressions and the bulk lifetime and surface recombination velocities are determined. The amplitude and phase are independent quantities and the computed values from the two sets of data provide a self-consistency test