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

Abstract

Three-dimensional modelling 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 TCAD simulations; resulting in the designer struggling to validate models and underappreciating the true behaviour 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 behaviours to be matched while limiting the computational effort for designers. The practical effects of birdsbeaking on device performance has 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.