Modeling of Large Area Trench IGBTs: The Effect of Birds-Beak

Three-dimensional (3-D) modeling is becoming an increasingly prevalent technique to model more complex device structures. However, this alone is insufficient to accurately model large area devices. This study images the birds-beak in a commercial insulated gate bipolar transistor (IGBT) and highlights how this processing uncertainty, which impacts the channel properties, has a strong effect on the accuracy of technology computer-aided design (TCAD) simulations; resulting in the designer struggling to validate models and underappreciating the true behavior of the device. It has been demonstrated that the birds-beak effect can be accounted for by a simple two-device model which allows for small-scale and large-scale device behaviors to be matched while limiting the computational effort for designers. The practical effects of birds-beaking on device performance have also been considered, and it has been shown that the variation in threshold voltage across the chip area results in a 32% reduction in short-circuit endurance time for the device. To overcome this, an alternative n+ emitter implantation is proposed, using a combination of arsenic and phosphorus, so that the device threshold is unaffected by the presence of birds-beaking and its variation during processing.