Void-free trench isolation based on a new trench design

In this paper, in order to avoid the voids during deep trench isolation, an inverted trapezium shaped trench is proposed which is beneficial to polysilicon refill since the top opening size is larger than that of the bottom. An optimized micromachining process is used and an inverted trapezium shaped trench is achieved by isotropic etching. On the other hand, for the filling effect, the completely smooth transition curve type trench is better than the trench with sharp corners. Compared with the linear trench, the completely smooth transition curve type trench can improve the strength of mechanical connection. Through combining the novel trench design with the optimization of trench design, a deep trench without voids can be guaranteed. A void-free deep isolation trench is finally realized which enables the electrical isolation between two movable microstructures or between a movable and a fixed microstructure.