The Reliability Of The Nitrogen Ion Implantation On Gate Oxide Tddb Effect

With the development of technology, gate dielectric in CMOS has to be scaled down continually and aggressively (from 20-30nm to several nanometer) to achieve higher device performance. However, the device operation voltage, which is currently about 1.0V reaching the bottleneck, can not be reduced as much as the thickness of gate oxide. Therefore, the electric field of gate oxide becomes higher and higher. The slowing of voltage scaling has become a significant new challenge for meeting gate dielectric reliability requirements. Poor gate oxide dielectric property will result in instablility of MOSFET, such as threthod voltage shift, degration of Gm, increasing of leakage, etc., and even breakdown of oxide, thus inducing failure of MOSFET, and the whole IC. Hence, breakdown of gate oxide, including TDDB (Time Dependence Dielectric Breakdown) and TZDB (Time Zero Dielectric Breakdown), is always one of the hot topics in ULSI reliability field, and one of the most important root causes which limits process intergration.Nitrogen implant is one of the choices to reduce ultra-thin gate leakage and increase K value. However, there is few reseach on the nitrogen implantation effect on TDDB. This paper presents the nitrogen implant effects on ultra-thin gate oxide time dependent dielectric breakdown. In literature, the dielectric breakdown is explained by anode hydrogen release (AHR) [2] or the anode hole injection (AHI)[3] models. The test methodology/method and lifetime calculation model will be detailed in this study.It is found that the nitrogen implant can improve TDDB reliability on NMOS while the corresponding gate leakage during TDDB stressing is much reduced. A deeper implantation with higher implant energy has a larger impact. In this study, the experimental observation is mainly attributed to the nitrogen penetration into the gate dielectric, which then enhances the capability of electron negative trap. Detailed study shows that the nitrogen-assisted interface traps increase with nitrogen implant energy, leading to a reduced leakage current during TDDB stressing and longer time to breakdown (Thd).