Fluorination of Al2O3 blocking layer for improving the performance of metal‐oxide‐nitride‐oxide‐silicon flash memory

The characteristics of Al₂O₃ film grown by atomic‐layer deposition as blocking layer with and without fluorine plasma treatment were investigated based on a capacitor structure of Al/Al₂O₃/TaON/SiO₂/Si. The physical structure was studied by transmission electron microscopy, and the chemical composition of the blocking layer was analyzed by X‐ray photoelectron spectroscopy and secondary ion mass spectroscopy. Moreover, the surface roughness of the blocking layer was investigated by atomic force microscopy. Compared with a capacitor with Al₂O₃ blocking layer, the one with fluorinated Al₂O₃ displayed higher programming/erasing speeds, better endurance property and better charge retention characteristic because the fluorination could reduce excess oxygen and traps in the blocking layer, thus forming a larger barrier height at the interface between the charge‐trapping layer and the blocking layer. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of interface characteristics of Al2O3/Si under various O2 plasma exposure times during the deposition of Al2O3 by PA-ALD

Plasma-assisted atomic layer deposition (PA-ALD) is more suitable than thermal atomic layer deposition (ALD) for mass production because of its faster growth rate. However, controlling surface damage caused by plasma during the PA-ALD process is a key issue. In this study, the passivation characteristics of Al₂O₃ layers deposited by PA-ALD were investigated with various O₂ plasma exposure times. The growth per cycle (GPC) during Al₂O₃ deposition was saturated at approximately 1.4?Å/cycle after an O₂ plasma exposure time of 1.5?s, and a refractive index of Al₂O₃ in the range of 1.65–1.67 was obtained. As the O₂ plasma exposure time increased in the Al₂O₃ deposition process, the passivation properties tended to deteriorate, and as the radio frequency (RF) power increased, the passivation uniformity and the thermal stability of the Al₂O₃ layer deteriorated. To study the Al₂O₃/Si interface characteristics, the capacitance-voltage (C-V) and the conductance-voltage (G-V) were measured using a mercury probe, and the fixed charge density (Q_f) and the interface trap density (D_it) were then extracted. The Q_f of the Al₂O₃ layer deposited on a Si wafer by PA-ALD was almost unaffected, but the D_it increased with O₂ plasma exposure time. In conclusion, as the O₂ plasma exposure time increased during Al₂O₃ layer deposition by PA-ALD, the Al₂O₃/Si interface characteristics deteriorated because of plasma surface damage.     

Effect of thermal annealing sequence on the crystal phase of HfO2 and charge trap property of Al2O3/HfO2/SiO2 stacks

In this study, we investigated the effect of a post annealing sequence on the HfO₂ crystal phase and the memory window of charge trap devices with TiN-Al₂O₃-HfO₂-SiO₂-Si stacks. The charge trap dielectrics of HfO₂ were deposited by atomic layer deposition and were annealed in an oxygen environment with or without Al₂O₃ blocking oxides. X-ray diffraction analysis showed that, after thermal annealing, the predominant crystal phase of HfO₂ is divided into tetragonal and monoclinic phase depending on the presence or absence of Al₂O₃ blocking oxide. In addition, deconvolution of X-ray diffraction spectra showed that, with increasing annealing temperature, the fraction of the tetragonal phase in the HfO₂ film was enhanced with the Al₂O₃ blocking oxide, while it was reduced without the Al₂O₃ blocking oxide. Finally, measurements of program/erase and increase-step-pulse programming showed that the charge trap efficiency and the memory window of the charge trap devices increased with decreasing fraction of tetragonal HfO₂.     

Interfacial reactions and oxidation behavior of Al2O3 and Al2O3/Al coatings on an orthorhombic Ti2AlNb alloy

The uniform and dense Al₂O₃ and Al₂O₃/Al coatings were deposited on an orthorhombic Ti₂AlNb alloy by filtered arc ion plating. The interfacial reactions of the Al₂O₃/Ti₂AlNb and Al₂O₃/Al/Ti₂AlNb specimens after vacuum annealing at 750 °C were studied. In the Al₂O₃/Ti₂AlNb specimens, the Al₂O₃ coating decomposed significantly due to reaction between the Al₂O₃ coating and the O-Ti₂AlNb substrate. In the Al₂O₃/Al/Ti₂AlNb specimens, a γ-TiAl layer and an Nb-rich zone came into being by interdiffusion between the Al layer and the O-Ti₂AlNb substrate. The γ-TiAl layer is chemically compatible with Al₂O₃, with no decomposition of Al₂O₃ being detected. No internal oxidation or oxygen and nitrogen dissolution zone was observed in the O-Ti₂AlNb alloy. The Al₂O₃/Al/Ti₂AlNb specimens exhibited excellent oxidation resistance at 750 °C.     

Al2O3钝化及其在晶硅太阳电池中的应用

介绍了Al₂O₃的材料性质及其原子层沉积制备方法, 详细阐述了该材料的钝化机制(化学钝化和场效应钝化), 并从薄膜厚度、热稳定性及叠层钝化等角度阐释其优化方案. 概述了Al₂O₃钝化在晶体硅太阳电池中的应用, 主要包括钝化发射极及背面局部扩散电池和钝化发射极及背表面电池. 最后, 对Al₂O₃钝化工艺的未来研究方向和大规模的工业应用进行了展望.     

The electrical properties of dielectric stacks of SiO2 and Al2O3 prepared by atomic layer deposition method

We produced dielectric stacks composed of ALD SiO₂ and ALD Al₂O₃, such as SiO₂/Al₂O₃, Al₂O₃/SiO₂, and SiO₂/Al₂O₃/SiO₂, and measured the leakage currents through the stacks in comparison with those of the single oxide layers. SiO₂/Al₂O₃ shows lowest leakage current for negative bias region below 6.4 V, and Al₂O₃/SiO₂ showed highest current under negative biases below 4.5 V. Two distinct electron conduction regimes are observed for Al₂O₃ and SiO₂/Al₂O₃. Poole-Frenkel emission is dominant at the high-voltage regime for both dielectrics, whereas the direct tunneling through the dielectric is dominant at the low-voltage regime. The calculated transition voltage between two regimes for SiO₂ (6.5 nm)/Al₂O₃ (12.6 nm) is −6.4 V, which agrees well with the experimental observation (−6.1 V). For the same EOT of entire dielectric stack, the transition voltage between two regimes decreases with thinner SiO₂ layer.     

Stacked and nanolaminated Al2O3/TiO2 for surface passivation and encapsulation of silicon

Silicon solar cells passivated with Al₂O₃ require a capping layer that protects the passivation layer from humidity because of sensitivity of Al₂O₃ to moisture. Al₂O₃/TiO₂ stacks obtained by atomic layer deposition have been known to provide a high level of passivation layers because of their excellent field‐effect passivation. In this work, degradation of this Al₂O₃/TiO₂ stack, when exposed to humidity, is examined, and an attempt is made for a humidity‐resistant encapsulation layer by adding Al₂O₃/TiO₂ nanolaminates that can be deposited in‐situ without breaking vacuum. Placing the nanolaminate on top of the TiO₂ and Al₂O₃ stack is found to lead to almost no degradation even after 10 days of humidity exposure. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

TiN/Al2O3纳米多层膜的共格外延生长及超硬效应

采用多靶磁控溅射法制备了一系列具有不同Al₂O₃调制层厚度的TiN/Al₂O₃纳米多层膜. 利用X射线能量色散谱、X射线衍射、扫描电子显微镜、高分辨透射电子显微镜和微力学探针表征了多层膜的成分、微结构和力学性能. 研究结果表明，在TiN/Al₂O₃纳米多层膜中，单层膜时以非晶态存在的Al₂O₃层在厚度小于1.5 nm时因TiN晶体层的模板效应而晶化，并与TiN层形成共格外延生长，相应地，多层膜产生硬度明显升高的超硬效应，最高硬度可达37.9 GPa. 进一步增加多层膜中Al₂O₃调制层的层厚度，Al₂O₃层逐渐形成非晶结构并破坏了多层膜的共格外延生长，使得多层膜的硬度逐步降低. 关键词： 2O₃纳米多层膜')" href="#">TiN/Al₂O₃纳米多层膜 外延生长 非晶晶化 超硬效应     

Al2O3增强的Co2-C98/Al2O3/Si异质结的光伏效应

随着能源危机的加剧,太阳能电池作为开发和利用太阳能的一种普遍形式, 日益受到世界各国的重视.随着太阳能电池向着高效率、薄膜化、无毒性和原材料丰富的方向发展, 单纯的硅系太阳能电池已经无法达到这样的要求,因此新的材料和工艺的开发利用迫在眉睫. 本文研究了碳材料在硅异质节上实现光伏效应的改善及其可能在太阳能电池上的应用. 采用脉冲激光沉积方法制备的Co₂-C₉₈/Al₂O₃/Si异质结构在标准日光照射 (AM1.5, 100 mW/cm²)条件下,可获得0.447 V的开路电压和18.75 mA/cm²的电流密度, 转换效率可达3.27%.通过电容电压特性和暗条件下的电输运性能测量, 证明了氧化铝层的引入不但对单晶硅的表面起到了物理钝化作用,减小了反向漏电流, 使异质结界面缺陷、界面能级和复合中心减少,还起到了场效应钝化作用, 增加了异质结界面的势垒高度,增加了开路电压,使异质结的光伏效应显著增强.     

Physical studies on composites Ag7I4VO4-Al2O3

The electrical properties of the solid electrolytes Ag₇I₄VO₄-Al₂O₃ (0-40 mol% Al₂O₃) are investigated. The electrical conductivity, dielectric constant and dielectric loss are increased by increasing the concentration of Al₂O₃; showing a maximum at 30 mol% Al₂O₃. The conductivity is found to be increased by decreasing the particle size of Al₂O₃. The results are explained using the random resistor network model (RRN). This is due to the formation of a highly conducting interface layer along the matrix-particle interface. This layer is destroyed at concentrations higher than 30 mol% Al₂O₃.     

The improvement of Al2O3/AlGaN/GaN MISHEMT performance by N2 plasma pretreatment

This paper discusses the effect of N 2 plasma treatment before dielectric deposition on the electrical performance of a Al2O3 /AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor(MISHEMT),with Al2O3 deposited by atomic layer deposition.The results indicated that the gate leakage was decreased two orders of magnitude after the Al2O3 /AlGaN interface was pretreated by N 2 plasma.Furthermore,effects of N 2 plasma pretreatment on the electrical properties of the AlGaN/Al2O3 interface were investigated by x-ray photoelectron spectroscopy measurements and the interface quality between Al2O3 and AlGaN film was improved.     

The structure and optical characters of the ZnO film grown on GaAs/Al2O3 substrate

In this paper ZnO films are grown on GaAs/Al₂O₃ substrates at different temperature by metal-organic chemical vapor deposition (MOCVD). The GaAs/Al₂O₃ substrates are formed by depositing GaAs layer (∼35 nm) on the Al₂O₃ substrate. The results of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) demonstrate that most of the Ga and As atoms form Ga-As bond and the GaAs layer does not present any orientation. The characters of the ZnO films grown on GaAs/Al₂O₃ substrates are investigated by XRD, photoluminescence (PL), atomic force microscopy (AFM) and Raman scattering. Compared with ZnO film grown on Al₂O₃ substrate, ZnO film prepared by our fabrication scheme has good crystal and optical quality. Meanwhile its grain size becomes bigger according to the AFM image. Raman analysis indicates that the intrinsic defects and the in-plane tensile stress are obviously reduced in ZnO/GaAs/Al₂O₃ samples.     

Investigation of 4H—SiC metal—insulation—semiconductor structure with Al2O3/SiO2 stacked dielectric

Atomic layer deposited (ALD) Al₂O₃/dry-oxidized ultrathin SiO₂ films as high-k gate dielectric grown on the 8° off-axis 4H-SiC (0001) epitaxial wafers are investigated in this paper. The metal-insulation-semiconductor (MIS) capacitors, respectively with different gate dielectric stacks (Al₂O₃/SiO₂, Al₂O₃, and SiO₂) are fabricated and compared with each other. The I-V measurements show that the Al₂O₃/SiO₂ stack has a high breakdown field ( ≥ 12 MV/cm) comparable to SiO₂, and a relatively low gate leakage current of 1× 10^-7 A/cm² at electric field of 4 MV/cm comparable to Al₂O₃. The 1-MHz high frequency C-V measurements exhibit that the Al₂O₃/SiO₂ stack has a smaller positive flat-band voltage shift and hysteresis voltage, indicating less effective charge and slow-trap density near the interface.     

磁性隧道结Ni80Fe20/Al2O3/Co的研究

用等离子体氧化形成中间绝缘层的方法可重复制备出具有隧道磁电阻（TMR)效应的Ni₈₀Fe₂₀/Al₂O₃/Co磁性隧道结.光透射谱等实验结果表明等离子体氧化能可控制地制备较致密的Al₂O₃绝缘层.样品的TMR比值在室温下最高可达6.0％,反转场可低于800A/m,相应的平台宽度约为2400A/m.结电阻R_j的变化范围从百欧到几百千欧,并且TMR比值随零磁场结偏压增大单调减小. 关键词：     

A study of GaN MOSFETs with atomic-layer-deposited Al2O3 as the gate dielectric

Accumulation-type GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) with atomic-layer-deposited Al₂O₃ gate dielectrics are fabricated. The device, with atomic-layer-deposited Al₂O₃ as the gate dielectric, presents a drain current of 260 mA/mm and a broad maximum transconductance of 34 mS/mm, which are better than those reported previously with Al₂O₃ as the gate dielectric. Furthermore, the device shows negligible current collapse in a wide range of bias voltages, owing to the effective passivation of the GaN surface by the Al₂O₃ film. The gate drain breakdown voltage is found to be about 59.5 V, and in addition the channel mobility of the n-GaN layer is about 380 cm²/Vs, which is consistent with the Hall result, and it is not degraded by atomic-layer-deposition Al₂O₃ growth and device fabrication.     

Enhanced water vapor barrier properties for biopolymer films by polyelectrolyte multilayer and atomic layer deposited Al2O3 double-coating

Commercial polylactide (PLA) films are coated with a thin (20 nm) non-toxic polyelectrolyte multilayer (PEM) film made from sodium alginate and chitosan and additionally with a 25-nm thick atomic layer deposited (ALD) Al₂O₃ layer. The double-coating of PEM + Al₂O₃ is found to significantly enhance the water vapor barrier properties of the PLA film. The improvement is essentially larger compared with the case the PLA film being just coated with an ALD-grown Al₂O₃ layer. The enhanced water vapor barrier characteristics of the PEM + Al₂O₃ double-coated PLA films are attributed to the increased hydrophobicity of the surface of these films.     

Electrical characteristics of polycrystalline Si layers embedded into high-k Al2O3 gate layers

The electrical characteristics of polycrystalline Si (poly Si) layers embedded into high-k Al₂O₃ (alumina) gate layers are investigated in this work. The capacitance versus voltage (C-V) curves obtained from the metal-alumina-polysilicon-alumina-silicon (MASAS) capacitors exhibit significant threshold voltage shifts, and the width of their hysteresis window is dependent on the range of the voltage sweep. The counterclockwise hysteresis observed in the C-V curves indicates that electrons originating from the p-type Si substrate in the inversion condition are trapped in the floating gate layer consisting of the poly Si layer present between the top and bottom Al₂O₃ layers in the MASAS capacitor. Also, current versus voltage (I-V) measurements are performed to examine the electrical characteristics of the fabricated capacitors. The I-V measurements reveal that our MASAS capacitors show a very low leakage current density, compared to the previously reported results.     

The diffusion of silicon atoms in stack structures of La2O3 and Al2O3

The interfacial reactions and electrical characteristics of stack structures of La₂O₃ and Al₂O₃ were investigated as a function of the annealing temperature. In the case of Al₂O₃/La₂O₃/Si (ALO structure), the La₂O₃ in contact with the Si substrate was readily transformed into La-silicate by the diffusion of Si atoms, while in the case of La₂O₃/Al₂O₃/Si (LAO structure), interfacial reactions between the Al₂O₃ layer and the Si substrate were suppressed. After an annealing treatment at 700 °C, the Al₂O₃ in the ALO structure can play an effective role in blocking the hydration of La₂O₃, resulting in an unchanged interfacial layer. However, the Al₂O₃ layer in the LAO structure was unable to suppress the diffusion of Si atoms into the La₂O₃ film. When the annealing temperature reached 900 °C, both structures showed a similar depth distribution with a high content of Si atoms diffused into the films. The change in the elemental distributions via the diffusion and reaction of Si atoms affected the electrical characteristics at the interface between ALO/LAO structure and Si substrate, specifically the trap charge density (D_it) and band gap (E_g) values.     

Al2O3/SiO2 films prepared by electron-beam evaporation as UV antireflection coatings on 4H-SiC

Al₂O₃/SiO₂ films have been deposited as UV antireflection coatings on 4H-SiC by electron-beam evaporation and characterized by reflection spectrum, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The reflectance of the Al₂O₃/SiO₂ films is 0.33% and 10 times lower than that of a thermally grown SiO₂ single layer at 276 nm. The films are amorphous in microstructure and characterize good adhesion to 4H-SiC substrate. XPS results indicate an abrupt interface between evaporated SiO₂ and 4H-SiC substrate free of Si-suboxides. These results make the possibility for 4H-SiC based high performance UV optoelectronic devices with Al₂O₃/SiO₂ films as antireflection coatings.     

Corrosion behaviour of sintered NdFeB coated with Al/Al2O3 multilayers by magnetron sputtering

Al/Al₂O₃ multilayers were deposited on sintered NdFeB magnets to improve the corrosion resistance. The amorphous Al₂O₃ films were used to periodically interrupt the columnar growth of the Al layers. The structure of the multilayers was investigated by Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HRTEM). It was found that the columnar structure was effectively inhibited in the multilayers. Subsequent corrosion testing by potentiodynamic polarization in 3.5 wt.% NaCl and neutral salt spray test (NSS) revealed that the Al/Al₂O₃ multilayers had much better corrosion resistance than the Al single layer. Furthermore, for multilayers with similar thickness, the corrosion resistance was improved as the period decreased.