The optimization of deep trench isolation structure for high voltage devices on SOI substrate

In this paper, the process and layout optimizations for improving the isolation performance of deep trench structures on SOI substrate are proposed. In the view of process flow, the reasons for forming weak points (located at the trench bottom) in deep trench structure are analyzed. In order to solve this problem of the weak points, a method of etching partial buried oxide after etching silicon is put forward, which can increase the thickness of isolation oxide at trench bottom by 10–20%. In aspect of layout structure, a voltage drop model of double trench structures is presented and verified by the experimental results, which indicates that breakdown voltage of double trench is a function of trench spacing. It is noted that the minimum trench spacing allowed by the process design rule can ensure superior isolation capability for double trench structure. Both methods for improving the performance of the device have also been verified in 0.5 μm HV SOI technology.

► The causes of forming weak points in deep trench structure are analyzed.
► Two methods for improving the isolation performance of deep trench structure are proposed.
► A voltage drop model of double trench structures is presented.
► The model is verified by experiment results.