SOI LIGBT devices with a dual P-well implant for improved latching characteristics

The authors explore the inherent tradeoff between latching current density and threshold voltage in a typical lateral insulated-gate bipolar transistor (LIGBT), which uses a shallow implant and long drive-in to form its P-well. The latching performance of LIGBTs in silicon-on-insulator (SOI) substrates is compared to that of equivalent devices in bulk silicon. Two techniques are proposed for improving the latchup/threshold tradeoff in these SOI devices. Retrograde P-well implants are shown to yield significant improvements while adding little complexity to the fabrication process. Dual P-well implants are shown to effectively decouple the latching current from the threshold voltage, yielding LIGBTs with latching current densities over 1300 A/cm²