Vertical Bipolar Transistor Test Structure for Measuring Minority Carrier Lifetime in IGBTs

Vertical PNP bipolar transistor test structures were fabricated, which can be integrated on the same wafer with functional IGBTs. Common-base current gain was measured by applying zero voltage to the leaky back side junction, from which minority carrier lifetime in the base region was extracted. The structure makes it possible to measure the lifetime after a real IGBT fabrication process flow, and to correlate it with the characteristics of IGBTs on the same wafer.