Reliability of silicon nitride gate dielectric in vertical thin-film transistors

This paper presents results of a systematic investigation of the impact of film thickness on leakage current and electrical breakdown of plasma enhanced chemical vapor deposited (PECVD) silicon nitride (SiNx). We consider SiNx films of various thicknesses, in the range 50 to 300 nm, deposited on both planar and vertical sidewalls in resemblance to the structural topology of the vertical thin film transistor (VTFT). The electrical breakdown strength for 150-300 nm thick films was approximately 7 MV/cm, while the value dropped to similar to 3 MV/cm for 50 nm thick films deposited under the same process conditions. In all cases, failure is inevitably accompanied by an increase in pinhole density. The results show that the reliability and leakage current of the gate dielectric in vertical thin film transistors depends on the step coverage of the SiNx on the vertical sidewall.