Reliability Analysis on TiN Gated NMOS Transistors

Abstract

Compared to poly Si gate, metal gate has no gate depletions and experiences inversion capacitance gain, which makes an advantage for devices scaling. In this paper, we investigated the gate oxide leakage current and Time Dependent Dielectric Breakdown (TDDB) characteristics of TiN and poly Si electrodes with a 3.5 to 5 nm SiO2 dielectric thickness range. According to the Transmission Electron Microscope (TEM) analysis there is difference in oxide thickness. The SiO2 thickness of TiN gate electrode has been reduced by ~0.25 nm, considerably because of a scavenging effect. We normalized the reduced SiO2 thickness with an electrical oxide field, and there were no differences between the two electrodes in gate leakage current, accumulation breakdown voltage (BV), and accumulation TDDB lifetime. Therefore, we found the scavenging effect of TiN electrodes seems to affect little the leakage current and TDDB reliability of SiO2 dielectric. On the other hand, the BV and TDDB lifetime of TiN electrode in the inversion region are little bit better than that of the poly electrode. We think this differences are originated from the difference between TiN/SiO2 and poly Si/SiO2 interfaces.