Tunneling leakage current in ultrathin (<4 nm) nitride/oxide stack dielectrics

Abstract

The leakage current in high-quality ultrathin silicon nitride/oxide (N/O) stack dielectric is calculated based on a model of one-step electron tunneling through both the nitride and the oxide layers. The results show that the tunneling leakage current in the N/O stack is substantially lower than that in the oxide layer of the same equivalent oxide thickness (EOT). The theoretical leakage current in N/O stack has been found to be a strong function of the nitride/oxide EOT ratio: in the direct tunneling regime, the leakage current decreases monotonically as the N/O ratio increases, while in the Fowler-Nordheim regime the lowest leakage current is realized with a N/O EOT ratio of 1 : 1. Due to the asymmetry of the N/O barrier shape, the leakage current under substrate injection is higher than that under gate injection, although such a difference becomes smaller in the lower voltage regime. Experimental data obtained from high quality ultrathin N/O stack dielectrics agree well with calculated results.

Failure physics of ultra-thin SiO2gate oxides near their scaling limit

“…In this latter regard, it is worth mentioning that both thermal [10,83] and deposited [84] oxynitrides can be more reliable than pure oxide films. Moreover, high quality silicon nitride and nitride/oxide stacked dielectrics are also expected to play a role for films with equivalent oxide thickness of about 1 nm because of reduced leakage [85].…”

Physical limits of silicon transistors and circuits

“…The results depend on how the mixture is processed. One method places a layer of silicon nitride above a thin SiO 2 layer as the gate insulator (Shi et al 1998). The valued qualities of the contact of SiO 2 on silicon are preserved.…”

Local Thinning Induced Less Oxide Breakdown in MOS Structures Due to Lateral Non-Uniformity Effect

“…The downscaling of gate oxide thickness leads to increasing importance of issues on oxide degradation characteristics due to larger operating oxide field and direct tunneling current [1][2][3][4][5][6][7] . For gate oxide thinner than 4.0 nm, the direct tunneling becomes dominant mechanism for carrier transport in MOS structures 8,9 . In this thickness regime, the voltage drop and the electric field in oxide layer can be significantly altered by the magnitude of direct tunneling current, and the oxide field does not increase monotonically with decreasing oxide thickness.…”