A new gate oxide lifetime prediction method using cumulative damage law and its applications to plasma-damaged oxides

Abstract

A Model for Cumulative Damage LawThe Cumulative Damage Law to the electrical stress, which correlates charge-to-breakdown with constant current injection (Q,,) to time-to-breakdown with constantvoltage stress (t,,), is theoretically derived from the defect generation model. Based on this law, we propose a new gate oxide lifetime prediction method. Although in some cases, the degradation of gate oxide induced by the plasma and ion implantation processes can not be distinguished by tbd measurement, the new method allows an accurate and relevant evaluation of process-induced gate oxide degradation.The gate oxide wearout is related to the generation of the defects such as the electron trapping in the oxide and the interface states [4]. In general, the defect generation model includes the generation rate as a function of "the electron energy, E" in the oxide [4]. Since the electron energy relaxation length in SiO, films is about 5 nm [5], the energy distribution is assumed to be in equilibrium at the interface in the case of the oxide thicker than 5 nm. Therefore, instead of E, we introduce the new generation rate a(J) as a function of "the current density J" (or "the electrical field E,,") into the conventional rate equation as follows: Introduction dnldt = MJ) J l e ( N -n)(1) Process-induced degradation of gate oxide becomes a key issue in the development for highly reliable MOSFET devices. Charge-to-breakdown with constant current injection (Q,) has been proposed to evaluate the gate oxide degradation induced by the antenna effect [1],[21. However, the Q, method has little impact on the "lifetime" prediction (time-to-breakdown with constant-voltage stress ; tbd) of the gate oxide degradation. Also, the plasmainduced damage has not so far been characterized by t,, measurement. It is needed to clarify the relationship between Qbd and tbd and to evaluate the process-induced oxide lifetime degradation.The purpose of this paper is to present a new lifetime prediction method based on Cumulative Damage Law to the electrical stress. The Cumulative Damage Law [3], which explicates the relationship between Qbd and t, , is theoretically derived from a new defect generation model. It is also found that the gate oxide degradation induced by the plasma and ion implantation processes can not be characterized by the tbd testing. The present prediction method gives an excellent explanation for this phenomenon and clearly characterizes the plasma-induced and ion implantation-induced oxide lifetime degradation.where n is the defect density, e is the elemental charge, and N is the precursor defect sites. As shown in Fig.1, Qbd measurement introduces J-dependence of Q, and the defect generation rate MJ,J for (I). In the case of t, , measurement, J is a function of time in (1).We postulate that the oxide breaks down when n reaches a critical value No which is independent of the stress type. Then, the two equations can be integrated until n=No for both Qbd and tbd measurements, respectively. By assuming that a(J) in tbd testing is equa...

Impacts of plasma process-induced damage on ultra-thin gate oxide reliability

“…By using the electron trapping mode1[14] [20], the time dependence of Jleak is calculated as shown in Fig.6 for 4 nm-thick oxide with r=3986.4 under the gate injection. In this calculation, an electron capture cross-section of 1.0 X 10'scm2 and trap generation rate of 1.0X lo-* are used.…”