Kiyohiko Sakakibara

A quantitative analysis of time-decay reproducible stress-induced leakage current in SiO/sub 2/ films

In the cases of both Fowler-Nordheim (FN) stress and substrate hot-hole stress, three reproducible stress-induced leakage current (SILC) components have been found for the repeated unipolar gate-voltage scans in 9.2 nm wet oxides. To clarify the mechanisms of these current components, a quantitative analysis has been developed. By precisely modeling the phonon assisted tunneling process, it has been shown that the E-J and t-J characteristics of the reproducible current components can be completely simulated as electron tunneling processes into the neutral traps, each with a single trap level. From this analysis, the physical parameters of the traps have been estimated with a reasonable degree of accuracy. Furthermore, the increase in distribution of the neutral trap density toward both the SiO/sub 2/ interfaces has also been estimated.

A quantitative analysis of stress induced excess current (SIEC) in SiO/sub 2/ films

The low-level stress induced excess current (SIEC) characteristics of 92 /spl Aring/ wet oxide are investigated in detail. As a result of the systematic investigations of the low-level E-J characteristics and the corresponding changes of net oxide charge, we have found that SIEC can be interpreted as electron tunneling processes into five kinds of different traps. As for the reproducible SIEC components, a quantitative analysis has been developed. By precisely modeling the trap assisted tunneling process, it has been shown that the E-J and t-J characteristics of the pretunneling region can be completely simulated as an electron tunneling process into the neutral trap. Using this analysis, it has been found that the local neutral trap density in bulk SiO/sub 2/ remains constant under the same hole fluence Qhole, regardless of the electric field strength during V/sub g/>0 FN stresses. In consequence, it has been concluded that the neutral trap has been created by holes injected into the oxide during the stresses.

Identification of stress-induced leakage current components and the corresponding trap models in SiO/sub 2/ films

Time-decay stress-induced leakage current (SILC) has been systematically investigated for the cases of both Fowler-Nordheim (FN) stress and substrate hot-hole stress. From the three viewpoints of the reproducibility of the-current component for the gate voltage scan, the change of oxide charge during the gate voltage scan, and the resistance of the current component to thermal annealing, it has been found that time-decay stress-induced leakage current is composed of five current components, regardless of stress type. Trap models corresponding to each current component have been proposed. In addition, it has also been proven that holes generate the electron traps related to one of those current components.

Influence of holes on neutral trap generation

Using a newly proposed method for estimating the neutral trap density, generation characteristics of the neutral trap during various stress types have been investigated. From the analysis of the trap-generation kinetics, two types of trap generation closely related to holes have been identified. At the first stage of stress application, holes interact with the pre-existing structural origins of the neutral traps, then the neutral traps are generated. Influence of hole energy on this type of trap generation is also identified. After that, as holes pass, they also create the structural origins of the traps. The holes interact with these structural origins and the neutral traps are generated as a secondary effect. Thus, the increase in the neutral trap density shows up clearly with increase in the hole fluence. The stress-strength dependence of the increase in the neutral trap density can also be interpreted in terms of the influence of hole energy on the trap generation.

Identification of stress-induced leakage current components and the corresponding trap models in SiO/sub 2/ films [MOS transistors]

Time-decay stress-induced leakage current (SILC) has been systematically investigated for the cases of both Fowler-Nordheim (FN) stress and substrate hot-hole stress. From the three viewpoints of the reproducibility of the current component for the gate voltage scan, the change of oxide charge during the gate voltage scan, and the resistance of the current component to thermal annealing, it has been found that time-decay stress-induced leakage current is composed of five current components, regardless of stress type. Trap models corresponding to each current component have been proposed. In addition, it has also been proven that holes generate the electron traps related to one of those current components.

A 1" format 1.5 M pixel IT-CCD image sensor for an HDTV camera system

A 1-in. format 1.5-million pixel IT (interline transfer) CCD (charge coupled device) image sensor has been developed for an HDTV (high-definition television) camera system. To achieve a low smear ratio while maintaining a high level of sensitivity, the authors have developed a new impurity profile of a buried P/sup +/-layer and an on chip microlens array whose material is a deep-UV resist. Using this sensor, a high-fidelity picture with a horizontal resolution of 820 TV lines has been obtained. The IT-CCD sensor has achieved a smear ratio of less than -90 dB, a sensitivity level of 80 nA/Lx, and a maximum charge handling capacity of 1.2*10/sup 5/ electrons. >

On a universal parameter of intrinsic oxide breakdown based on analysis of trap-generation characteristics

It is found, even at room temperature, that hole fluence to breakdown Q/sub p/ of wet oxides is not a constant value for different oxide fields, but has a strong stress-electric-field dependence. Based on the neutral trap-generation characteristics related to SILC, this oxide-breakdown behavior dependent on the stress-electric field is analyzed. A novel model is proposed in which oxide breakdown is triggered when the current level of steady-state SILC via electron tunneling between traps reaches a critical value. From the spatial distribution of traps, we have concentrated on the critical trap pair whose electron-tunneling probability has the smallest value in the middle of the SiO/sub 2/ films. To verify this model, the convoluted trap density which is related to the electron-tunneling probability between the critical trap pair is investigated. As a result, it is found that this convoluted trap density remains constant regardless of stress-electric field and oxide thickness. This means that this convoluted trap density is a universal parameter for oxide breakdown.

2-dimensional simulation of FN current suppression including phonon assisted tunneling model in silicon dioxide

Two-dimensional effect of trapped electrons on device characteristics are calculated using a two-dimensional device simulator including a trap-filling current model. As the result of simulation, FN current is suppressed when the neutral trap density is over 10/sup 19/ cm/sup -3/. The results correspond to the endurance characteristics of flash memories.

A 1 inch Format 1.5M Pixel IT-CCD Image Sensor for an HDTV Camera System.

A one-inch format 1.5 M pixel Interline Transfer (IT) CCD image sensor has been developed for an HDTV camera system. We focused on two areas to achieve a low smear ratio while maintaining high sensitivity. One is the VCCD device structure. By using the device simulator, we have developed a new impurity profile for the buried P+-layer under the VCCD. The other focus area is the optical structure. Considering the incident angle, we simulated the optical path. This simulation helped us determine the size of an optical shield and an onchip microlens made of a deep-UV resist. We have achieved a sensivity of 80 nA/lx, a maximum charge handling capacity of 1.2×105 electrons, and a smear ratio less than-110 dB. A high-fidelity picture with a horizontal resolution of 820 TV lines has been obtained.