Research on Electron Emission from Dielectric Materials by a Monte Carlo Method

The charge accumulation in an insulating material under an electron beam bombardment exerts a significant influence to scanning electron microscopic imaging. This work investigates the charging formation process by a self-consistent Monte Carlo simulation of charge production and transportation based on a charge dynamics model. The charging effect in a semi-infinite SiO₂ bulk and SiO₂ trapezoidal lines on a SiO₂ or Si substrate has been studied. We used two methods to calculate the spatial distributions of electric potential and electric field for two different systems respectively: the image charge method was used to deal with a semi-infinite bulk, and, random walk method to solve the Poisson equation for a complex geometric structure. The dynamic charging behavior depending on irradiation time has been investigated for SiO₂. The simulated CD-SEM images of SiO₂ trapezoidal lines with charging effect included were compared well with experimental results, showing the contrast change of SEM image along with scanning frames due to charging.     

Low field DC investigation of hot carrier trapping in silicon dioxide films

The experimental method used in this work is based upon the idea of nonavalanche injection of carriers heated by direct electric field. The structure consisted of an n-channel MOS transistor and two p-n junctions. The process of charge injection in this structure was investigated by studying the dependence of gate current on heating voltage. The trapping properties of the SiO₂ film were studied by monitoring the charging of the film during injection of electrons. The capture cross-sections, the trap centre concentrations and the dependence of the capture cross section on the electric field for fields between 1 MV/cm and 2.5 MV/cm were determined.     

Experimental analysis of the stability of electrostatic bits for assisted nano-assembly

Scanning probe microscopy(SPM)-based nanolithography with injected charges into layered electrets, such as silicon dioxide (SiO₂) and silicon nitride, is a promising tool with far-reaching applications, such as controlled nano-assembly of macro-molecules and data storage. Despite its potential, some practical limitations exist. This paper describes an experimental investigation of the process of charging and charge dissipation in SiO₂ using an AFM probe tip and surface potential (Kelvin probe) microscopy. The stability of charge bits on hexamethyl disilazane(HMDS)-treated SiO₂ under low dielectric constant liquids, fluorocarbon, and benzene has been demonstrated. Results from a numerical simulation of a theoretical charging model, in which the charge traps are assumed to be localized on the silicon/SiO₂ interface, are also presented. The charge transport mechanism considered is modified Fowler–Nordheim tunneling.     

Image contrast enhancement in field-emission scanning electron microscopy of single-walled carbon nanotubes

The image contrast enhancement in scanning electron microscopy of single-walled carbon nanotubes (SWNTs) on SiO₂ surfaces was experimentally investigated using a field-emission scanning electron microscope (FESEM) using a wide range of primary electron (PE) voltages. SWNT images of different contrasts were obtained at different PE voltages. Image contrast enhancement of SWNTs was investigated by charging SiO₂ surfaces at different PE voltages. The phenomena are ascribed to the surface potential difference and charge injection between SWNTs and SiO₂ substrates induced by the electron-beam irradiation.     

Self-consistent charge-up simulation for the microscopic feature of SiO2 layer in rf capacitive discharge

The charge-up simulation of the microscopic feature with SiO₂ layer was investigated in various conditions of rf capacitive discharge by using the three-dimensional (3-D) particle-in-cell (PIC) charge-up simulation coupled with the one-dimensional (1-D) particle-in-cell Monte Carlo collision (PIC-MCC) simulation of rf capacitive argon discharge. The result showed that the charge-up effect on the micro-trench was greatly influenced by the conditions of the gas pressure and the discharge voltage in rf capacitive discharge. Based on the analysis of the distributions of electrons and ions arriving at the substrate in various plasma conditions, the charge-up effect and its reduction mechanisms on the micro-trench of capacitive discharge were discussed. This article is expected to provide qualitative and quantitative insight for the understanding of charging and its reduction mechanism on many plasma processes performed by the rf capacitive discharge.     

Analysis of charged device model (CDM) ESD in MEMS

The effect of charge injection due to CDM ESD in capacitive MEMS structures is analyzed. The results show that as feature size is reduced, ESD injected charge produces a change for the stiction effect which is inversely proportional to the square of the plate area and a change in the dielectric layer breakdown which is inversely proportional to the plate area. An electric field model is developed to examine charge and voltage modes in MEMS. A charge injection test method is proposed to determine the susceptibility of MEMS to CDM ESD.     

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.     

Analysis of charge injection processes including ESD in MEMS

The effect of charge injection due to human body model (HBM) electrostatic discharge (ESD), charged device model (CDM) ESD and triboelectrification in capacitive microelectromechanical systems' (MEMS) structures is analyzed. The results show that as feature size is reduced, the effect remains constant for charging by triboelectrification. However, HBM ESD injected charge produces a change which is inversely proportional to the square of the gap separation and CDM ESD injected charge produces a change which is inversely proportional to the square of the plate area.     

The effect of Si surface nitridation on the interfacial structure and electrical properties of (La2O3)0.5(SiO2)0.5 high-k gate dielectric films

Thermal stability, interfacial structures and electrical properties of amorphous (La₂O₃)_0.5(SiO₂)_0.5 (LSO) films deposited by using pulsed laser deposition (PLD) on Si (1 0 0) and NH₃ nitrided Si (1 0 0) substrates were comparatively investigated. The LSO films keep the amorphous state up to a high annealing temperature of 900 °C. HRTEM observations and XPS analyses showed that the surface nitridation of silicon wafer using NH₃ can result in the formation of the passivation layer, which effectively suppresses the excessive growth of the interfacial layer between LSO film and silicon wafer after high-temperature annealing process. The Pt/LSO/nitrided Si capacitors annealed at high temperature exhibit smaller CET and EOT, a less flatband voltage shift, a negligible hysteresis loop, a smaller equivalent dielectric charge density, and a much lower gate leakage current density as compared with that of the Pt/LSO/Si capacitors without Si surface nitridation.     

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.     

SiO2的赝晶化及AlN/SiO2纳米多层膜的超硬效应

采用反应磁控溅射法制备了一系列不同SiO₂层厚度的AlN/SiO₂纳米多层膜，利用X射线衍射仪、高分辨透射电子显微镜和微力学探针表征了多层膜的微结构和力学性能，研究了SiO₂层在多层膜中的晶化现象及其对多层膜生长方式及力学性能的影响. 结果表明，由于受AlN六方晶体结构的模板作用，溅射条件下以非晶态存在的SiO₂层在其厚度小于0.6 nm时被强制晶化为与AlN相同的六方结构赝晶体并与AlN形成共格外延生长. 由于不同模量的两调制层存在晶格错配度，多层膜中产生了拉、压交变的应力场，使得多层膜产生硬度升高的超硬效应. SiO₂随层厚的进一步增加又转变为以非晶态生长，多层膜的外延生长结构受到破坏，其硬度也随之降低. 关键词： 2纳米多层膜')" href="#">AlN/SiO₂纳米多层膜 赝晶化 应力场 超硬效应     

First-principles study of the segregation of boron dopants near the interface between crystalline Si and amorphous SiO2

We investigate the stability of boron dopants near the interface between crystalline Si and amorphous SiO₂ through first-principles density functional calculations. An interstitial B is found to be more stable in amorphous SiO₂ than in Si, so that B dopants tend to segregate to the interface. When defects exist in amorphous SiO₂, the stability of B is greatly enhanced, especially around Si floating bond defects, while it is not significantly affected near Si–Si dimers, which are formed by O-vacancy defects.     

A comprehensive study of MEMS behavior under EOS/ESD events: Breakdown characterization,dielectric charging,and realistic cures

The breakdown characterization of both out- and in-plane electrostatically actuated RF–MEMS switches with air-gaps from 1.0 to 6.7 μm was studied. The emitted electromagnetic field during the testing was analyzed, in order to have an indication of the air-breakdown occurrence. Furthermore, we studied the effect of TLP and HBM events on the dielectric charging of tested MEMS, furnishing the experimental evidence that ESD events should not be responsible of this important reliability problem for MEMS, and that ESD tester parasitic elements can influence the MEMS electromechanical behavior characterization. Finally, a simple, but effective, varistor based protection structure was explored.     

反应溅射VN/SiO2纳米多层膜的微结构与力学性能

采用V和SiO₂靶通过反应溅射方法制备了一系列具有不同SiO₂和VN调制层厚的VN/SiO₂纳米多层膜. 利用X射线衍射、X射线能量色散谱、高分辨电子显微镜和微力学探针表征了多层膜的微结构和力学性能. 结果表明：在Ar，N₂混和气体中，射频反应溅射的SiO₂薄膜不会渗氮. 单层膜时以非晶态存在的SiO₂，当其厚度小于1nm时，在多层膜中因VN晶体层的模板效应被强制晶化，并与VN层形成共格外延生长. 相应地，多层膜的硬度得到明显提高，最高硬度达34GPa. 随SiO₂层厚度的进一步增加，SiO₂层逐渐转变为非晶态，破坏了与VN层的共格外延生长结构，多层膜硬度也随之降低. VN调制层的改变对多层膜的生长结构和力学性能也有影响，但并不明显. 关键词： 2纳米多层膜')" href="#">VN/SiO₂纳米多层膜 共格外延生长 非晶晶化 超硬效应     

Dry etching characteristics of GaN using Cl2/BCl3 inductively coupled plasmas

ICP power/RF power, operating pressure, and Cl₂/BCl₃ gas mixing ratio are altered to investigate the effect of input process parameters on the etch characteristics of GaN films. The etch selectivity of GaN over SiO₂ and photoresist is studied. Although higher ICP/RF power can obtain higher GaN/photoresist etch selectivity, it can result in faceting of sidewall and weird sidewall profile due to photoresist mask erosion. Etch rates of GaN and SiO₂ decrease with the increase of operating pressure, and etch selectivity of GaN over SiO₂ increases with the increasing operating pressure at fixed ICP/RF power and mixture component. The highest etch selectivity of GaN over SiO₂ is 7.92, and an almost vertical etch profile having an etch rate of GaN close to 845.3 nm/min can be achieved. The surface morphology and root-mean-square roughness of the etched GaN under different etching conditions are evaluated by atomic force microscopy. The plasma-induced damage of GaN is analyzed using photoluminescence (PL) measurements. The optimized etching process, used for mesa formation during the LED fabrication, is presented. The periodic pattern can be transferred into GaN using a combination of Cl₂/BCl₃ plasma chemistry and hard mask SiO₂. Patterning of the sapphire substrate for fabricating LED with improved extraction efficiency is also possible using the same plasma chemistry.     

Eu(TTFA)3掺杂SiO2杂化胶体球的合成及特性

采用改进的碱催化法和种子法分别制得了稀土配合物Eu(TTFA)₃掺杂的SiO₂杂化胶体球,并用透射电子显微镜和荧光分光光度计对其显微形貌和荧光光谱特性进行了详细地研究.结果表明,两种方法都可以获得单分散性的、稀土配合物掺杂SiO₂杂化胶体球,且都具有Eu³⁺离子典型的荧光光谱特性.Eu(TTFA)₃掺杂入SiO₂胶体球中后,有机配体TTFA在短波长处的吸收明显增强了,最大的吸收峰位也向短波长方向移动大约20～30 nm,Eu³⁺离子5D0→7F2发射跃迁仍然具有良好的窄线发光特征,同时荧光峰值的形态和位置受SiO₂基体的影响发生轻微的变化.     

Large-scale potential fluctuations caused by SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> compositional inhomogeneity

The short-range order in amorphous SiO _x (0 ≤ x ≤ 2) films has been studied by high-resolution X-ray photoelectron spectroscopy. Both the random bonding and random mixture models do not describe experimental photoelectron spectra of SiO _x (x ≤ 2). An intermediate model of the SiO _x structure has been proposed. The measured photoelectron spectra of the SiO _x (x ≤ 2) valence band indicate the presence of the silicon phase and silicon oxide.     

Radiation damage effects on power VDMOS devices with composite SiO2–Si3N4 films

Total dose effects and single event effects on radiation-hardened power vertical double-diffusion metal oxide semiconductor (VDMOS) devices with composite SiO₂-–Si₃N₄ film gate are investigated. The relationships among the important electrical parameters of the samples with different thickness SiO₂-–Si₃N₄ films, such as threshold voltage, breakdown voltage, and on-state resistance in accumulated dose, are discussed. The total dose experiment results show that the breakdown voltage and the on-state resistance barely change with the accumulated dose. However, the relationships between the threshold voltages of the samples and the accumulated dose are more complex, not only positive drift, but also negative drift. At the end of the total dose experiment, we select the group of samples which have the smaller threshold voltage shift to carry out the single event effect studies. We find that the samples with appropriate thickness ratio SiO₂-–Si₃N₄ films have a good radiation-hardening ability. This method may be useful in solving both the SEGR and the total dose problems with the composite SiO₂-–Si₃N₄ films.     

Dielectric properties of thin-film ZrO<Subscript>2</Subscript> up to 50 GHz for RF MEMS switches

The dielectric properties of zirconium dioxide (ZrO₂) ceramic thin films were characterized up to 50 GHz using coplanar waveguides (CPWs) and metal–insulator–metal (MIM) capacitors with top circular electrodes. The ZrO₂ films were deposited using a chemical solution onto high-resistivity Si wafers and metal layers. The real part of the dielectric constant of approximately 22 and 26 was extracted at 50 GHz for CPW and MIM structures, respectively, and the loss tangent was approximately 0.09 at 50 GHz. C–V and I–V measurements were carried out to determine low-frequency and DC dielectric properties. The measurement results indicate that ZrO₂ is a promising material to be used as a dielectric layer for radio-frequency (RF) microelectromechanical systems (MEMS) capacitive switches.     

Electron-beam charging of dielectrics preirradiated with moderate-energy ions and electrons

The effects of charging of dielectric targets irradiated with moderate-energy electrons in a scanning electron microscope are examined. Considerable differences in the kinetics of charging of the reference samples and the samples preirradiated with ions and electrons are reported. These differences are attributed to the processes of radiation-induced defect formation in Al₂O₃ (sapphire) and SiO₂ that are, however, dissimilar in nature. The contributions of surface structure modification and changes in the electrophysical parameters of the surface (specifically, the charge spreading effect) are revealed. Critical doses of irradiation with Ar⁺ ions and electrons inducing active defect formation in dielectric targets and critical values of internal charge fields producing a significant contribution to the temporal parameters of Al₂O₃ and SiO₂ charging are determined.