Anomalous Stress Effects of Trench Isolation

This paper highlights some of the anomalous stress effects of trench isolation on bipolar transistor parameters and yield. The deep trench isolation module forms part of a 1¿m BiCMOS process. By directly comparing side by side trenched and non-trenched bipolar transistors, the influence of the trench process on both current gain and parasitic capacitance is demonstrated. In addition, arrays of bipolars were used to determine the factors influencing the bipolar transistor defect density, their interactions and the process modifications required to maximize bipolar yield.