Random telegraph signal: A sensitive and nondestructive tool for gate oxide single trap characterization

This paper presents the electrical characterization of thick and thin SiO₂ oxynitride performed by thermal and plasma nitridation processes. The impact of the nitridation technique is investigated using random telegraph signal (RTS) noise analysis. The variation of the gate oxide trap characteristics is determined with respect to the nitridation technique. Significant properties of traps are also pointed out. Main trap parameters, such as their depth with respect to the interface, nature, capture and emission times are extracted. These results illustrate the potential of RTS noise investigation for gate oxide characterizations.     

The effect of nitrogen plasma anneals on interface trap density and channel mobility for 4H-SiC MOS devices

We report results on the introduction of nitrogen at the SiC/SiO₂ interface using a plasma process, thus avoiding the detrimental effects of additional oxidation that accompany other standard nitridation processes, such as annealing in NO gas. The plasma process results in an ‘NO-like’ mobility for approximately 1/6 the interfacial nitrogen content injected via the gas anneal. Direct exposure of the oxide to the plasma is also shown to have a deleterious effect on the breakdown characteristics of the oxide.     

A Study on a Surface Preparation Method for Single-Crystal SiC Using an Fe Catalyst

In this study we investigated the possibility of removing and flattening a single-crystal silicon carbide (SiC) surface by a novel polishing method utilizing hydroxyl radicals (OH radicals) generated on an Fe catalyst surface. To demonstrate the feasibility of preparing a smooth SiC surface, an Fe catalyst and a SiC substrate were rubbed together in H₂O₂ solution, and then the area on the SiC surface that had come into contact with the Fe catalyst was observed in detail. The removal depth and surface microroughness were measured and evaluated using a phase-shift interference microscope and an atomic force microscope (AFM), respectively. Moreover, the removal of material from the SiC surface by utilizing an Fe catalyst rod was examined. The obtained results show that the hard SiC surface can be effectively polished and that the processed area on the SiC surface has atomic-level smoothness along the sliding direction. Moreover, it is shown that the removal characteristics of the SiC substrate depend on process parameters such as the process time, rotation speed, contact load, and concentration of H₂O₂ solution. These results provide useful information for preparing an atomically smooth SiC surface.     

Interfacial effects during GaN growth on 6H-SiC

GaN growth on 6H-SiC was investigated for heterojunction device applications. Dopant diffusion and surface reactions were discovered at the GaN/SiC heterojunction. A systematic study was therefore conducted focusing on: 1) SiC substrate preparation, 2) SiC nitridation; the effect of flowing ammonia (NH₃) at 1050°C on the SiC, and 3) the conductivity type and carrier concentration of the SiC substrate. Atomic force microscopy measurements revealed that the SiC substrates became smoother after the nitridation process possibly due to nitrogen chemisorption and etching. Current-voltage and capacitance-voltage measurements on Cr-Schottky diodes made on SiC revealed evidence for an increased potential barrier in the nitrided samples that can be explained by an interfacial monolayer ofSiN_x. Furthermore, we compared GaN/SiC heterojunction n-n and n-p diodes made from direct and selective GaN growth. Capacitancevoltage measurements on GaN/SiC n-p heterojunctions indicate that the effective doping in the junction increases as the growth temperature increases. Secondary ion mass spectrometry measurements exposed a tail of Al in the GaN due to acceptor out-diffusion from the p-SiC.     

SiC sedimentation and carbon migration in mc-Si by election beam melting with slow cooling pattern

The development of photovoltaic industry demands great amount of multicrystalline silicon. Carbon and SiC in silicon need to be contained in a limited amount since they can cause great adverse affect to solar cells. The behavior of carbon and its precipitation SiC in silicon by electron beam melting (EBM) with a slow cooling pattern was investigated in this study. SiC is found to sedimentate to ingot bottom after EBM. The presence of Si₃N₄ can be heterogeneous nucleation agent for SiC to nucleate continually and both of them precipitate to the ingot bottom. The comprehensive effect of slow solidification condition, temperature gradient and melt convection causes the sedimentation of SiC. It is also found that oxygen plays an important role on the migration of the dissolved carbon. The formation of carbon-oxygen complexes tend to migrate to ingot top since oxygen can transfer from silicon melt to vacuum environment during EBM.     

Observation and characterization of near-interface oxide traps in 3C-SiC MOS structures by quasi-static I-V method

The electrical properties of oxides grown on 3C-SiC by rapid thermal processing in various oxidizing and annealing atmospheres are investigated using a quasi-static method. According to the anomalous capacitance hump, the existence of two types of traps, interface and near interface oxide traps, is observed in quasi-static. By monitoring the sweep-rate measurement of the quasi-static current related to electron tunneling from interface traps to near-interface oxide traps, a profile of the traps in response time can be obtained. Based on the extracted parameters of the carrier traps, we demonstrate that the near SiO₂/3C-SiC interface is significantly improved when using 100% N₂O compared to 100% O₂ or even N₂-O₂ dilution as oxidizing gas. Also, we show that incorporating N₂ during the oxidation in O₂ is not favourable for the reduction of the near-interface oxide traps.     

Effect of N2O nitridation on the electrical properties of MOS gate oxides

Furnace annealing in N₂O is a convenient technique for improving the reliability of thermal oxides without significant modifications of the process flow. We investigate the impact of N₂O nitridation on MOSFET device performance, assessing the various factors contributing to the observed degradation of electron mobility. Estimates based on low-frequency C-V and charge pumping measurements show that nitridation causes a significant increase of the interface trap density in the vicinity of the conduction band. Interface traps contribute a parasitic component to the gate-channel capacitance, thus leading to an overestimate of the inversion charge. This effect accounts for a substantial fraction of the mobility degradation which is observed for the nitrided devices. The remaining degradation can be ascribed to an enhancement of Coulomb scattering, maybe due to differences in dopant segregation, and to a change of the surface roughness characteristics.     

Detailed analysis of charge pumping and IdVg hysteresis for profiling traps in SiO2/HfSiO(N)

By scanning 1/3 nm SiO₂/HfSiO(N) gate dielectrics with variable t_charge−t_discharge amplitude charge pumping technique (VT²ACP) and slow rate I_dV_g hysteresis, we study in detail the energy profile and estimate the spatial position (within SiO₂ or HKs layer) of pre-stress and stress-induced electron traps. Pre-stress traps are mainly at shallow energy levels while stress-induced traps are at deeper energy levels. We demonstrate that due to incomplete discharge of bulk traps, the commonly-used base level charge pumping (CP) sweep is not suited for trap energy profiling. Further, we show that in CP measurements, due to the non-negligible tail of the filling probability of traps, even at short charge times, a fraction of HK-bulk traps is scanned in addition to interfacial traps. When the trap density in the HK is significantly higher than in the IL, this fraction might dominate the CP signal and can cause misinterpretation of data. Finally, we point out the possible contribution of the initially-present traps in the formation of a percolation path causing the dielectric breakdown.     

Modification of 4H-SiC and 6H-SiC(0001)<Subscript>Si</Subscript> surfaces through the interaction with atomic hydrogen and nitrogen

The interaction of 4H-SiC(0001)_Si and 6H-SiC(0001)_Si surfaces with atomic hydrogen and atomic nitrogen produced by remote radio-frequency plasmas is investigated. The kinetics of the surface modifications is monitored in real time using ellipsometry, while chemical modifications of the surface are characterized using x-ray photoelectron spectroscopy (XPS). Film morphological properties are assessed with atomic force microscopy (AFM). A two-stage substrate preparation procedure is described that effectively removes oxygen from the SiC surface at low (200°C) temperature. In the first step, the SiC surface is etched with an HCl/HF acid solution as an alternative to the conventional HF(1%)-H₂O solution. The HCl/HF etch provides effective hydrogen passivation of the SiC surface. In the second step, the SiC surface is exposed to atomic hydrogen that selectively interacts with residual oxygen. In addition, the temperature dependence of the nitridation of SiC surfaces has also been investigated. It is found that interaction of SiC surfaces with atomic hydrogen at 200°C provides clean, smooth, and terraced surfaces suitable for epitaxial growth. In contrast, SiC surface exposure at high temperature (750°C) to atomic hydrogen and nitrogen results in very rough and disordered Si-rich surfaces. Finally, we find that the 4H-SiC surface is more reactive than the 6H-SiC surface to both species studied, independent of temperature. Surface geometry and electronic factors responsible for the observed reactivities are discussed.     

Traps in 4H-SiC Field-Effect Transistors Characterized by Capacitance- and Current-Mode Deep-Level Transient Spectroscopy

Traps in SiC long-gate metal–semiconductor field-effect transistors (FATFETs) at different wafer positions have been characterized by deep-level transient spectroscopy (DLTS) based on capacitance (C-DLTS) or current (I-DLTS). Two major electron traps, Z _1/2 and V _1/2, of energies 0.68 eV and 0.91 eV, respectively, are found mainly in the SiC buffer layer, and several hole-like traps appear in the surface or interface regions. In some regions of the wafer, an electron trap EH_6/7 of energy 1.77 eV is prominent. Trap EH_6/7 as well as the hole-like traps are not uniformly distributed on the wafer.     

On the RTS phenomenon and trap nature in Flash memory tunnel oxide

Aim of this work is the investigation of Random Telegraph Signal (RTS) in Flash memory cell. Current fluctuations have been performed also as a function of temperature in order to characterize the nature of traps responsible for noise in relatively thick tunnel oxide. Trap energy level and spatial localization from the Si/SiO₂ interface has been determined. The impact of stress has been also investigated showing no significant noise increase in single cell. This has been ascribed to the tunnel oxide technology whose heavy nitridation allows minimizing the degradation of the region responsible for RTS in Flash memory cell.     

Nitridation of silicon-dioxide films grown on 6H silicon carbide

This letter addresses the question of why it is possible to grow high-quality oxide films on N-type but not on P-type SiC. It provides results which indicate that the oxide/SiC interface would be inferior to the oxide/Si interface for both N-type and P-type SiC, if it were not for the beneficial effects of nitrogen incorporation. The letter presents, for the first time, results on nitridation of thermally grown oxides in NO and N₂O. The results demonstrate that the oxides grown on P-type can be improved by NO annealing, but not by N₂O annealing     

N-MOSFET oxide trap characterization induced by nitridation process using RTS noise analysis

This paper presents oxide trap characterization of nitrided and non-nitrided gate oxide N-MOSFETs using low frequency noise (LFN) measurements. The identification of defects generated by the gate oxide growth and the nitridation process is carried out using random telegraph signal noise analysis. Significant properties of traps induced by the nitridation process are pointed out. Main trap parameters, such as their nature, capture and emission times, cross-sections, energy levels, and position with respect to the Si/SiO₂ interface, are extracted. These results illustrate the potential of noise investigation for oxide characterizations.     

Lateral profiling of interface traps and oxide charge in MOSFETdevices: charge pumping versus DCIV

An improved oxide-charge and interface-trap lateral profiling charge pumping technique (iLPCP) is described. Erase-induced oxide charge and interface traps are investigated in flash EPROM devices. It is shown that the improved technique allows the extraction of profiles in cases where the previous method does not yield satisfactory results. A comparative study of iLPCP and of an existing direct current (DCIV) technique for lateral profiling of interface traps is conducted: both erase- and program-induced interface traps are investigated in flash EPROM devices. The results indicate that 1) iLPCP probes a much bigger portion of the gate region; 2) iLPCP probes a wider energy range; 3) DCIV is more sensitive deep in the channel and thus complements iLPCP     

Measurement of plasma etch damage by a new slow trap profilingtechnique

MOS capacitor structures with plasma damaged oxides have been used to demonstrate a new technique for profiling slow traps at the Si-SiO ₂ interface. The technique measures the density and trapping rate of slow traps by stepping the gate voltage in small increments and monitoring the resulting substrate current transients, thereby producing a profile of the traps in energy and response time. The response time is a function of the trap's energy position and distance from the interface. Some traps created by plasma etching are not obvious in quasistatic CV measurements, yet are clearly evident when the new technique is used. Results show an increase in slow trap densities and response times in the upper half of the silicon bandgap with long plasma overetch times. In comparison, wet etched control devices show only low densities of slow traps with shorter response times around the midgap     

Effects of temperature and pressure in oxynitridation kinetics on Si(100) with N2O gas

We have investigated oxynitridation of Si(100) surfaces with nitrous oxide (N₂O) gas in a wide range of substrate temperatures (600–1000 °C) and N₂O pressures (10⁻²–10² Pa). The growth rate and atomic composition of the oxynitride layer have been measured by in situ x-ray photoelectron spectroscopy. The surface morphology of the oxynitride layer has been also observed by scanning electron microscopy. The results show that in higher N₂O pressure (>1 Pa) regime, the nitridation reaction is suppressed by the oxide layer, which quickly forms on the surface. On the other hand, in lower pressure (<1 Pa) and higher substrate temperature (>900 °C) regime, the nitridation reaction strongly occurs because of the active oxidation (etching reaction), which causes the surface roughness. It is found by argon-ion-sputtering measurements that the nitride layer locally exists only near the surface at the reduced N₂O pressure. We discuss qualitatively the oxynitridation kinetics and the effective condition for growing the oxynitride layer.     

用于VLSI的SiO_xN_y薄膜的界面陷阱

采用雪崩热电子注入技术研究了用于VLSI的快速热氮化的SiO_xN_y薄膜界面陷阱。给出这种薄介质膜禁带中央界面陷阱密度随氮化时间的变化关系,观察到这种薄膜存在着不同类型的密度悬殊很大的电子陷阱。指出雪崩热电子注入过程中在Si/SiO_xN_y界面上产生两类性质不同的快界面态陷阱,并给出这两种陷阱在禁带中能级位置及密度大小关系;同时还给出禁带中央界面陷阱密度随雪崩注入剂量呈现弱“N”形变化关系,并对实验结果进行了讨论。     

离子注入氮化薄SiO_2栅介质的特性

研究了通过多晶硅栅注入氮离子氮化 10 nm薄栅 Si O2 的特性 .实验证明氮化后的薄 Si O2 栅具有明显的抗硼穿透能力 ,它在 FN应力下的氧化物陷阱电荷产生速率和正向 FN应力下的慢态产生速率比常规栅介质均有显著下降 ,氮化栅介质的击穿电荷 (Qbd)比常规栅介质提高了 2 0 % .栅介质性能改善的可能原因是由于离子注入工艺在栅 Si O2 中引进的 N+离子形成了更稳定的键所致     

Extraction of SiO2/SiC interface trap profile in 4H- and 6H-SiC metal-oxide semiconductor field-effect transistors from subthreshold characteristics at 25°C and 150°C

The profile of trap density at the SiO₂/SiC interface in SiC metal-oxide semiconductor field-effect transistors (MOSFETs) is critical to study the channel electron mobility and evaluate device performance under various processing and annealing conditions. In this work, we report on our results in determining the interface trap density in 4H- and 6H-SiC MOSFETs annealed in dry O₂, NO, and CO₂, respectively, based on the device transfer and currentvoltage characteristics in the subthreshold region at 25°C and 150°C. We also studied electron field-effect mobility, fixed oxide charge, and gate leakage in those devices.     

Nanostructured thin films based on TiO2 and/or SiC for use in photoelectrochemical cells: A review of the material characteristics,synthesis and recent applications

In solar energy harvesting research, there is growing interest in the study of photoelectrochemical (PEC) properties of the following classes of semiconductor materials: metal oxides and silicon-based compounds. The motivation is that such materials are being successfully used as photoelectrode in PEC cells. Special attention has been given to the wide band gap materials. This review discusses, from the material science perspective, the recent literature relating to two wide band gap semiconductor materials: one metal oxide, titanium dioxide (TiO₂), and one silicon-based compound, silicon carbide (SiC). Emphasis is placed on TiO₂ and SiC thin films for PEC applications. Materials characteristics, synthesis methods and recent photocatalytic applications are presented. Finally, the interesting effect of the efficiency increase of PEC devices developed from a hetero-junction of TiO₂ and SiC is discussed.