Charge-up Phenomenon Research Articles

Li Distribution in a LiNi1/3Mn1/3Co1/3O2 Positive Electrode Analyzed Using Reflection Electron Energy-Loss Spectroscopy

Li-ion batteries are commonly used as energy-storage devices, where it is important to examine the spatial distribution and chemical state of Li with high spatial resolution to understand various phenomena pertaining to their use. To this end, analytical techniques using electron beam sources are advantageous due to their high spatial resolution. Observations of the Li distribution on the nanometer scale can be successfully obtained using electron energy-loss spectroscopy (EELS) with transmission electron microscopy (TEM) or scanning TEM (STEM) [1, 2]. However, TEM/STEM have inherent requirements in terms of sample preparation such as size or thickness, which limits its application range. Scanning electron microscopy (SEM) is much more commonly used and has a high spatial resolution on the nanometer scale, and it can observe larger particles or multiple samples in one sample holder. Ishida et al. reported the Li distribution of carbon and Li metal by using scanning auger electron spectroscopy (AES) [3]. Lithium-transition metal oxides with low electron conductivity are frequently used as electrode materials. However, the Li KLL signal in AES often overlaps with AES signals from other transition metal elements. The charge-up phenomena of a sample can cause problems during AES analysis, which complicates the discussions around chemical shifts. Despite this, the technique is applicable in analyzing light elements in materials with high spatial resolution. We performed Li analysis by reflection EELS (REELS) with SEM, and found that this technique is effective in obtaining the K-edge core-loss spectrum of Li. We identified the differences in chemical state in Li K-edge spectra for each sample, where the features of these REELS spectra were similar to those observed by TEM-EELS. As such, we proposed REELS as a method for lithium analysis in Li-metal oxides, and reported the successful detection of different chemical states of Li in various Li compounds. Using a single crystal Li4Ti5O12 substrate, elemental Li mapping was successfully carried out before and after electrochemical Li insertion and extraction [4]. In the present study, we expand the application of REELS to the analysis of positive electrode materials. The positive electrode material in Li-ion batteries is typically a Li-transition metal oxide of micron particle size. We applied REELS to determine the Li distribution in a LiNi1/3Mn1/3Co1/3O2 positive electrode after a charging/discharging cycle. Combined with scanning spreading resistance microscopy (SSRM), the changes in electrical conductivity of the Li-poor particles inside the electrode were visualized. [1] J. Kikkawa, T. Akita, M. Tabuchi, M. Shikano, K. Tatsumi, and M. Kohyama, Electrochem. Solid-State Lett. 11 183 (2008).[2] N. Taguchi, T. Akita, H. Sakaebe, K. Tatsumi, and Z. Ogumi, J. Electrochem. Soc. 160 2293 (2013).[3] N. Ishida, D. Fujita, J. Electron Spectrosc. Relat. Phenom. 186 39 (2013).[4] N. Taguchi, M. Kitta, H. Sakaebe and T. Akita, J. Electron Spectrosc. Relat. Phenom. 203 40 (2015).

Evaluation of Electrostatic Charging Properties of Insulating Materials Used for Spacecrafts by Means of Electron Beam Irradiation

Many kinds of insulating materials are used not only outside but also inside the body of a spacecraft. It is well-known that these materials charge up as the result of the interaction with space plasma and/or high-energy charged particles. The charge-up phenomenon is possible to induce electrostatic discharge (ESD) on the surface or in the bulk of the material and to cause malfunctions or damages of the spacecraft systems. Therefore it is necessary to evaluate the charging properties of the materials used for spacecrafts as ground testing. From this viewpoint, the properties of several materials by means of electron beam irradiation simulating the hot plasma in space were investigated. The surface potential and the bulk current through the material were measured during the beam irradiation. The decay of the surface potential after stopping the beam irradiation was also measured to evaluate the volume resistivity.

Charge neutralization using secondary electron shower for shave-off depth profiling by focused ion beam secondary ion mass spectrometry

It is very important problem for microbeam analyses to neutralize charge-up phenomenon. In our previous study, the charge-up phenomenon occurred during the shave-off depth profiling in the case of insulated samples. We developed a new neutralization method to improve the accuracy of the shave-off depth profile by FIB-SIMS. By using new method, ripples on secondary ion signals were suppressed and the shave-off depth profile reflected the precise layered shape of insulator samples without charge-up problems.

Evaluation of annular pupil for scanning transmission electron microscope formed by focused ion beam technique

Annular pupils for electron optics were developed using a focused ion beam (FIB) technique to realize an increase in the depth of focus, aberration-free imaging and separation of amplitude and phase images under scanning transmission electron microscopy (STEM). A tantalum plate 30 μm thick was used as the annular pupil material in the present experiment. The annular pupils were designed with various outer diameters from ϕ120 μm to ϕ40 μm. The inner diameter was designed at 60 to 80% of the outer diameter. The fabricated annular pupils were inspected by scanning ion beam microscopy and scanning electron microscopy. Annular pupils were successfully obtained at the designed size, although the slits of the pupils were slightly tapered by the ion beam etching process. These annular pupils were loaded on a STEM and confirmed to display no charge-up phenomenon by observation of the projection image on a scintillator using a CCD camera. We confirmed the image taken by annular pupil with narrow width was able to suppress the influence of the normal illumination.

集束イオンビームを用いた電子光学系輪帯瞳用アパーチャの作製

Micro-apertures for annular pupil on electron optics have been developed using a focused ion beam technique to realize an increase in the depth of focus, aberration-free imaging and separation of amplitude and phase images under scanning transmission electron microscopy (STEM). A tantalum plate 30 μm thick was used as the annular pupil material in the present experiment. The apertures were designed with various outer diameters from φ120 μm to φ60 μm and at inner diameter of 80% outer diameter. Fabricated apertures were characterized by a scanning ion-beam microscope and a scanning electron microscope. Apertures were successfully obtained at the designed size, although the slits of the pupils were slightly tapered by the ion-beam etching process. These annular pupils were loaded on a STEM and confirmed to display no charge-up phenomenon by observation of the projection image on a scintillator using a CCD camera.

Effects of plasma chamber pressure on the etching of micro structures in SiO/sub 2/ with the charging effects

Many problems in ion-enhanced etching are caused by the charge-up effect as the aspect ratio increases with the decrease of a semiconductor device size. The energy and angle distribution of particles are important factors in the etching process which can be controlled by the pressure of a plasma chamber. In the present paper, we varied the pressure of plasma and studied the charge-up phenomenon for the aspect ratios 5 and 10. In the low pressure RF-capacitively coupled plasma (CCP) chamber, ions with higher energy and small angle distribution have been detected. On the other hand, in the high-pressure RF-CCP chamber, ions with low-energy and high-angle distribution are observed. At a high-aspect ratio, the charge-up potential is reduced when the pressure of a plasma chamber is high. At a high pressure, more vertical etching feature is expected.

イオンマイクロビームによる高分子材料の超微細加工

The physical phenomena which occur during ion micro beam processing of polymers are basically different from those of metals. The electrical and thermal conductivity of polymers are extremely low. The first one induces charge-up phenomenon and the second may cause the evaporation of the materials owing to localized heating around the beam irradiated area. The purpose of this study was to investigate the thermal effects and evaporation of the materials which influence the removal rate of the surface material together with sputtering. Sputtering and thermal evaporation are responsible for removal of the material during the microprocessing of polymers using a highly focused ion beam. Investigations were done for the case of nylon-6 which are widely used as biomaterials. The highly focused, ion beam of Ga, with a diameter of 0.2 μm and energy of 30 keV, was used with different irradiating time, ranging from 10 to 70 s. The widths and depths of fabricated lines were measured using AFM. The machinability of nylon-6 was evaluated by estimating the removal rate.

Surface quality and laser-damage behaviour of chemo-mechanically polished CaF2 single crystals characterized by scanning electron microscopy

A significant increase in the ultraviolet laser-damage threshold of CaF2 (1 1 1) single-crystal surfaces after surface finishing by chemomechanical polishing (CMP) with colloidal silica has been demonstrated as compared to conventional mechanical-abrasive polishing (MAP). It was shown that CMP yields an up to 12-fold increase of the damage threshold fluence up to Fth = 30 J cm−2 for 1-on-1 nanosecond pulses of 248 and 193 nm excimer laser irradiation. Even after 5-on-1 irradiations, the damage threshold remains as high as Fth = 15 J cm−2 in the case of CMP. For both polishing procedures, the change in dielectric surface properties has been characterized by means of scanning electron microscopy (SEM) using electron beam-induced charge-up phenomena. These were mainly detected by the variation of emitted secondary electron (SE) yield δSE depending on the primary electron (PE) energy. Two kinds f charge-up phenomena were employed: (i) the onset or vanishing of statistically fluctuating SE yield bursts during slow-scan imaging (“stripe pattern” method), and (ii) the temporal decay of the electron beam-induced charge-up inside an electrically conducting mask (charge decay method). Both these phenomena disappeared after CMP. It is concluded that this disappearance results from removing the subsurface damage layer which is typical of MAP.

Charge-up Phenomena of Insulated Metals in X-Ray Photoelectron Spectroscopy

The X-ray power dependence of the charge-up shift of a photoelectron line was examined for metal films insulated from a spectrometer. As the X-ray power increased, the observed line position shifted to a higher binding energy, and approached an asymptotic value. This charge-up behavior was treated based on the balance between the photoelectron emission from the sample surface and electron injection from an aluminum window of the X-ray source and from other electron sources. It was concluded that, for insulated metals, the vacuum level of the sample is aligned to that of the spectrometer when the X-ray power is extrapolated to zero, i.e., the magnitude of the charge-up is equal to zero. The work function of the spectrometer was successfully determined with samples having a known work function. A new method to obtain the binding energy relative to the vacuum level for insulators is proposed.

Deterioration of insulating films on silicon wafer due to surface charging during ion implantation

Charge-up phenomena during ion implantation were studied using the wafers (1) covered with the 1 μm thick photoresist and (2) fabricated with the MOS capacitor devices. The wafers were implanted with 35 keV As+ at the beam currents of 1 mA to 10 mA. The surface potential was measured by a capacitive probe set in the chamber. The ion distribution was also measured by a beam profile monitor placed behind the rotating disc. Surface charging on the photoresist wafers in some cases led to the puncture of the resist layer. Probe measurement showed that the charge-up phenomena were to a large extent governed by the behavior of the secondary electrons generated at ion implantation. The wafers with the MOS devices hardly failed by the charge build-up because of the bulk conduction through the thin oxide. However, the C-V measurement indicated that the deterioration of the oxide were influenced by the beam distribution.

イオン注入中のウェハ帯電現象の解析

Charge-up phenomena during ion implantation were studied using the wafers (1) covered with the 1μm thick photoresist and (2) fabricated with the MOS capacitor devices. The wafers were implanted with 35keV As+ at the beam currents of 1mA to 10mA. The surface potential was measured by a capacitive probe set in the chamber. The ion distribution was also measured by a beam profile monitor placed behind the rotating disc. Surface charging on the photoresist wafers in some cases led to the puncture of the resist layer. Probe measurement showed that the charge-up phenomena were to a large extent governed by the behavior of the secondary electrons generated at ion implantation. The wafers with the MOS devices hardly failed by the charge build-up because of the bulk conduction through the thin oxide. However, the C-V measurement indicated that the deterioration of the oxide are influenced by the beam distribution.

High speed flat guide ceramic stage for electron-beam lithography system

A high speed precision ceramic x–y stage has been developed for a high throughput submicron e-beam lithography system. This stage gives beam exposure during high speed continuous stage movement and shortens the step-and-repeat overhead time. In this exposure method the eddy current on the stage surface caused by high speed stage movement in a magnetic leakage field from the objective lens deteriorates the patterning accuracy. To reduce the eddy current, the stage has no metal bulk parts and the major components are made of a fine ceramic material which is of light weight and low thermal expansion. In order to prevent charge-up phenomenon, electric conductivity of the ceramic has been controlled by adding a small amount of nonmagnetic metal and the nonconductive parts are coated with a thin metal layer. A plate structure with flat guide is used to lighten the stage for achieving both constant velocity movement and high speed step-and-repeat performance. A unique separation mechanism between stage and drive bar with piezoelectric elements has been developed for x–y independent movements avoiding vibration from the driving mechanism. The major stage components and specimen chamber are designed by using dynamic vibration simulation. The stage drive mechanism, which is comprised of roller screws and dc motors, operates with a velocity and position controller. The maximum velocity of 160 mm/s, positioning time of 150 ms/10 mm, and yawing accuracy of ±3 μrad, is achieved. This stage has a direct wafer holding mechanism, operating with an automated wafer loader system which can handle 100 wafers/h.

Fabrication of ECL gate arrays on quick turn-around line

A quick turn-around line (QTL) technology, including a high-speed on-line data system, electron-beam direct writing, and dry process technologies are described in this paper. Electron-beam pattern data is converted by a VAX 11/780 and transmitted to the electron-beam exposure system (EBES) through a communication controller at the speeds of 1 Mbits/s. After various data manipulations, patterns are quickly written directly on wafers. The first metal layer using an Al-Si-Cu alloy is etched in a reactive ion beam etcher with carbon tetrachloride (CCl 4 ). In order to avoid the charge-up phenomenon of the electron beam, the surface of the silicon nitride (SiN) interlevel insulation layer is coated with a thin conductive layer of TiW. TiW/SiN layers are successively etched by the reactive ion etching (RIE) with CF 4 + O 2 (2%). The damage induced by electron-beam irradiation on the device is perfectly annealed out with a 450°C anneal. Bias-temperature tests have been performed on various logic circuits used in a main frame computer.