Carrier recombination lifetime measurement of bonded SOI wafers by microwave photoconductivity decay method

Microwave photoconductivity decay (μPCD) method was used for the measurement of bulk carrier recombination lifetime of bonded silicon-on-insulator (SOI) wafers in order to evaluate the quality of the starting material from different vendors and to monitor the degradation of lifetime during processing of the wafers. The goal of the investigation was to determine a correlation between the carrier lifetime of the SOI layer of the starting material and the output of the devices fabricated on the same wafer. Bonded SOI wafers from three different vendors were evaluated by a KOBELCO LTA-1000EP semiconductor wafer lifetime measuring system in order to investigate the quality of device layer silicon for the fabrication of optoelectronic devices where carrier lifetime plays a dominant role. The salient feature of the measuring system is the availability of three lasers with different depth of penetration where one of the lasers penetrates only 1 μm which is suitable for lifetime measurement of SOI layer. The wavelength of the three lasers were 523 nm, 904 nm and 1047 mn with penetration depths of about 1 μm, 30 μm and 500 μm respectively. Measurements were conducted on both front and backside of the SOI wafers with three lasers to ensure the accuracy of the lifetime of the layer of interest. The repeatability of the measurement was excellent and was within 3%. Based on the measured carrier lifetime of the starting materials, SOI wafers from two vendors were selected for optoelectronic device fabrication. The lifetime map of each processed wafers was obtained and the measured short circuit current of the devices were found to correlate with the average carrier lifetime of the same wafers