Roles of Primary Hot Hole and FN Electron Fluences in Gate Oxide Breakdown
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ABSTRACT In this work, we report the link between the primary hot hole and Fowler Nordheim (FN) electron injections in oxide breakdown mechanism. A simple breakdown model is established. The experimental method is carefully designed to measure the primary hot hole fluence and FN electron fluence separately and accurately. The calculation based on our model is in very good agreement with our experiments. Oxide breakdown is stimulated by a combined effect when the sum of the trap density DPr activated by primary hot hole injection and the trap density D" activated by FN electron injection reaches a critical value D,,i. The hole is two orders of magnitude more effective than FN electron in causing breakdown. Since primary hot hole injection may occurs under many realistic device operation in the circuit, existing oxide lifetime projected from conventional TDDB measurement by only applying FN stress is overestimated in many cases. The model demonstrated in this work lays the groundwork in approaching a more appropriate way for predicting the oxide reliability and lifetime.
INTRODUCTION
Gate oxide breakdown is one of the most serious bottle-necks in scaling metal-oxidesemiconductor field-effect transistors (MOSFETs). Numerous breakdown models have been proposed including some conflicting ones. For example, early work on breakdown was attributed to electron injection and electron trapping [1], while subsequent works [2,3] concluded that breakdown was due to FN electron-induced hole trapping. In this work, we call the electron induced hole the "secondary hole"[4]. Although this secondary hole trapping model has been widely accepted, there aie disagreements [5-8]. Weinberg et al. claimed that hole trapping was not the main cause for breakdown [5]. H. Satake et al. proposed a two step model that coexistence of electrons and holes was necessary for oxide breakdown [6]. K. Kamakura et al investigated oxide breakdown using substrate hot hole (we name it "primary hole") injection [8]. They found that the critical hole fluence leading to oxide breakdown was much larger than that normally observed in the case of FN stressing [3]. This finding led them to believe that another defect generation process due to electron injection played an important role. The works in [7] and [8] actually overestimated the primary hole fluence as will be explained in the following section. Therefore the conclusions derived from those works are doubtful. The objective of this work is 'to develop a reliable experimental method to separate the FN electron and hot hole fluences accurately and establish a simple quantitative model to link the effect of electron and hole injections in gate oxide breakdown. 99 Mat. Res. Soc. Symp. Proc. Vol. 592 © 2000 Materials Research Society
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Fig. 1. The energy band diagram of pMOSFET during FN electron and primary hole injections. The inset shows pMOSFET test structure. Vinj switches on and off periodically with an adjusted duty cycle. 10* S U
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