Abstract: The emission microscopy (EMMI) test is proposed as an effective method to control the polysilicon over-etching time of advanced CMOS processing combined with a novel test structure,named a poly-edge structure.From the values of the breakdown voltage (Vbd) of MOS capacitors (poly-edge structure),it was observed that,with for the initial polysilicon etching-time,almost all capacitors in one wafer failed under the initial failure model.With the increase of polysilicon over-etching time,the number of the initial failure capacitors decreased.Finally,no initial failure capacitors were observed after the polysilicon over-etching time was increased by 30s.The breakdown samples with the initial failure model and intrinsic failure model underwent EMMI tests.The EMMI test results show that the initial failure of capacitors with poly-edge structures was due to the bridging effect between the silicon substrate and the polysilicon gate caused by the residual polysilicon in the ditch between the shallow-trench isolation region and the active area,which will short the polysilicon gate with silicon substrate after the silicide process.

Key words: polysilicon over-etching, gate oxide reliability, emission microscopy