Yoshiki Yonamoto

Detection of nitrogen related traps in nitrided/reoxidized silicon dioxide films with thermally stimulated current and maximum entropy method

We constructed the new method to analyze thermally stimulated current (TSC) using maximum entropy method. This method allows us to extract trap density depending on trap energy level [Nt(Et)] from a TSC curve. Using this to analyze TSC of as-deposited, nitrided, and reoxidized thin silicon dioxide films, we were able to determine Nt(Et) of hole traps with very highly energy resolution and to observe the generation of nitrogen related hole traps.

Enhanced carrier transport by defect passivation in Si/SiO2 nanostructure-based solar cells

We investigate the relationship between the defect states and the carrier transport property of Si nanostructure-based solar cells. The solar cell consists of a Schottky junction including Si/SiO2 multiple quantum wells. The carrier transport is significantly enhanced by forming gas annealing of Si/SiO2 multiple quantum wells, which is well correlated with the decrease in the Pb and E′ center densities evaluated by electron spin resonance. In particular, we find that high temperature (>600 °C) annealing is necessary to passivate E′ center. Our results demonstrate the significance of defect passivation for the realization of high efficiency Si nanostructure-based solar cells.

Interface traps responsible for negative bias temperature instability in a nitrided submicron metal-oxide-semiconductor field effect transistor

Traps responsible for negative bias temperature instability (NBTI) in a nitrided submicron n-type metal-oxide-semiconductor field effect transistor (nMOSFET) were investigated in an atomic scale. By spin dependent transport, we could observe interfacial Pb-centers distinguishably and show that NBTI occurs mainly through an increase in Pb1-center rather than Pb0-center. This can be explained in terms of the atomic bonding configuration between silicon, nitrogen, and hydrogen atoms.

Application of Maximum Entropy Method to Semiconductor Engineering

The maximum entropy method (MEM) is widely used in research fields such as linguistics, meteorology, physics, and chemistry. Recently, MEM application has become a subject of interest in the semiconductor engineering field, in which devices utilize very thin films composed of many materials. For thin film fabrication, it is essential to thoroughly understand atomic-scale structures, internal fixed charges, and bulk/interface traps, and many experimental techniques have been developed for evaluating these. However, the difficulty in interpreting the data they provide prevents the improvement of device fabrication processes. As a candidate for a very practical data analyzing technique, MEM is a promising approach to solve this problem. In this paper, we review the application of MEM to thin films used in semiconductor engineering. The method provides interesting and important information that cannot be obtained with conventional methods. This paper explains its theoretical background, important points for practical use, and application results.

Similarity and difference in temperature dependent recovery of HCS and NBTI

We investigated the temperature dependence of recovery behavior in p-channel MOSFETs after subjected to hot carrier stress (HCS) and negative bias temperature stress (NBTS) from the recovery activation energy distributions of threshold voltage shifts (E_r^V) and of interface states (E_r^D). Both E_r^V and E_r^D are composed of the two elements, so-called recoverable- and permanent components (R and P). We found that the temperature dependent recovery after HCS and NBTS can be interpreted by R and P. In addition, the degradation mechanism, i.e., origins of R and P, was discussed. This study sheds light on the high temperature degradation mechanism.

Recovery behavior in negative bias temperature instability

We have studied the recovery behavior observed in negative bias temperature instability (NBTI) from the aspect of bulk hole traps. Using the maximum entropy method to analyze isochronal annealing data, we evaluated the contributions of bulk hole traps with energy level Et to the initial threshold voltage shifts just after NBT stresses, ΔVOTi(Et). Their shapes are Gaussian-like depending on the NBT stress temperatures, and ΔVOTi(Et) can explain NBTI recovery behaviors as well as the universality. The validity of a previously proposed empirical function describing NBTI recovery curves was confirmed, and the physical meanings of that function were examined. This study proves the importance of hole detrapping events and sheds light on the NBTI recovery mechanism.

Compositional dependence of trap density and origin in thin silicon oxynitride film investigated using spin dependent Poole–Frenkel current

The compositional dependence of trap density and origin in thin silicon oxynitride (SiOxNy) films deposited by the low pressure chemical vapor deposition method was investigated using spin dependent Poole–Frenkel (SDPF) current technique. SDPF detected two kinds of traps, K-center (N3Si⋅, where means a dangling bond) and K′-center (N2OSi⋅). With increasing oxygen concentration, the amount of K-center decreases. On the other hand, K′-center increases up to O/O+N=0.25 and then it decreases. We propose the model that the change in the film strain by oxygen atoms induces these phenomena.

Study on individual traps in metal–oxide–semiconductor field-effect transistors by means of thermally stimulated threshold voltage shift

A novel method, thermally stimulated threshold voltage shift (TSTVS), was introduced to investigate individual trap properties in the gate SiO2 oxide film of submicron p-type metal–oxide–semiconductor field-effect transistors (pMOSFETs). TSTVS measures temperature-dependent threshold voltage shift (∆Vth(T)). First, electrical stresses are imposed on a pMOSFET to fill traps with carriers, resulting in ∆Vth. Second, the sample temperature is raised at a constant rate. The captured carriers are thermally emitted and ∆Vth decreases. The trap properties can be revealed from ∆Vth(T). Although TSTVS is similar to the conventional thermally stimulated current (TSC) method, there are several advantages, e.g., higher sensitivity and discrimination ability of carrier polarity. TSTVS was applied to a pMOSFET subjected to electrical stress. The TSTVS signal exhibited several abrupt steps corresponding to individual carrier detrappings, meaning that TSTVS could detect even a single trap. In addition, the carrier polarity was determined by the sign of the steps (upsteps or downsteps). We also revealed the trap energy level through repetitive TSTVS measurements. The presence of two traps in the pMOSFET, i.e., hole and amphoteric traps, was confirmed from these features. We also compared the results with the conventional TSC and found that they could be interpreted by using the proposed atomic structures of traps.

Recovery and universality in NBTI

Abstract The fast recovery behavior in negative bias temperature instability (NBTI) in SiON gate p-type metal–oxide–silicon field effect transistors was investigated. The fast recovery is due to the hole detrapping from the K -center ( N 3 Si , where denotes a dangling bond). The Gaussian function-like hole trap energy level distribution explains the universality in the fast recovery. The results shed light on the NBTI mechanism.

Direct trap observation in stressed SiO2 with electrically detected magnetic resonance

We investigated traps in unstressed/stressed SiO2 thin films with electrically detected magnetic resonance. In the unstressed SiO2, only Eγ′-centers (O3≡Si⋅, ⋅ denotes a dangling bond) were observed. After imposing stresses, SiO2 exhibited soft-breakdown (SBD) or hard-breakdown (HBD) phenomena. The digital noise called random telegraph noise induced by a single trap was seen in the SBD-SiO2. We found that it is a single Eγ′-center. Also, we revealed that analog noises seen in the HBD-SiO2 originate from Si3≡Si⋅ traps. Our observations clearly show a close relationship between breakdown phenomena and traps.