Simulation study on image contrast and spatial resolution in helium ion microscope

We performed Monte Carlo simulation of helium (He) ion induced secondary electron (SE) emission in order to compare the secondary electron image characteristics between He and gallium (Ga) scanning ion microscopes (SIM) and scanning electron microscope (SEM). For 10-50 keV He ion bombardment SE yield increases gradually with increasing the atomic number, Z2, of the target, as well as for the electron bombardment. However, for 30 keV Ga ion bombardment, SE yield shows an opposite Z2 dependence. The calculated SE yield is much larger than that for both electron and Ga ion bombardment. The incident angle dependence of the SE yield approximately obeys the inverse cosine law even at high angles of 85 degrees and more. On the other hand, for electron bombardment, the incident angle dependences are much weaker for low energy and high Z2. These indicate that the image contrast on He-SIM is clearer than those of SEM. Among the electron excitations by incident He ions, recoiled target atoms and excited electrons, the first one having narrow excitation volume dominates the SE yield, so that the spatial image resolution in SIM using zero-diameter He beams with the energies of 10-50 keV is prospected to be smaller or better (<0.1 nm) than for 30 keV Ga ion and 1 keV electron beams.     

Monte Carlo simulation of topographic contrast in scanning ion microscope

Topographic contrast of secondary-electron (SE) images in a scanning ion microscope (SIM) using a focused gallium (Ga) ion beam is investigated by Monte Carlo simulation. The SE yield of heavy materials, in particular, due to the impact of 30 keV Ga ions increases much faster than for the impact of electrons at < or =10 keV as a function of the angle of incidence of the primary beam. This indicates the topographic contrast for heavy materials is clearer in a SIM image than in a scanning electron microscope (SEM) image; for light materials both contrasts are similar to each other. Semicircular rods with different radii and steps with large heights and a small wall angle, made of Si and Au, are modeled for comparison with SE images in SEM. Line profiles of the SE intensity and pseudo-images constructed from the profiles reveal some differences of the topographic contrast between SIM and SEM. We discuss not only the incident-angle effect on the contrast, but also the effects of re-entrances of primary particles and SEs to the neighboring surface, the effect of a sharp edge on the sample surface, and the effects of pattern size and beam size.     

Origins of material contrast in scanning ion microscope images

A Monte Carlo simulation of ion-induced kinetic electron emission (KE) was carried out to study the material contrast in scanning ion microscope (SIM) images, i.e. secondary electron (SE) yields decreasing with atomic number Z2 of the target, which is opposite to that for scanning electron microscope (SEM) images. The simulations show that SE yields decrease with increasing Z2 for the targets of Al (Z2 = 13), Cu (Z2 = 29) and Au (Z2 = 79) bombarded by 10 approximately 40 keV gallium (Ga) ions. Details of the SE yield according to the collision partners (i.e. Ga ion, recoiled target-atom and excited electron) clarify the origins of material (or Z2) contrast in the Ga-SIM images. Cause and effect on the material contrast are as follows: the heavier (or slower) collision partner transfers less energy to the excited electrons and leads to a poorer multiplication of other excited electrons in the cascade process. The simulation also predicts that the Ga-SIM images are more sensitive to the outermost target surface than the SEM images. material contrast, atomic number contrast, secondary electrons, secondary electron yield, scanning ion microscope, scanning electron microscope     

Response function and optimum configuration of semiconductor backscattered-electron detectors for scanning electron microscopes

A new highly efficient design for semiconductor detectors of intermediate-energy electrons (1?C50 keV) for application in scanning electron microscopes is proposed. Calculations of the response function of advanced detectors and control experiments show that the efficiency of the developed devices increases on average twofold, which is a significant positive factor in the operation of modern electron microscopes in the mode of low currents and at low primary electron energies.     

A virtual scanning electron microscope. 3. A semiempirical model of the SEM signal generation

Experiments are analyzed on scanning electron microscopes (SEMs) with test objects having a trapezoidal profile and large tilt angles of the side walls. Based on the analysis, a semiempirical generation model of images in a SEM, operating in the low-voltage mode and high-voltage mode during recording back-scattered and secondary slow electrons (SSEs), is proposed. The model is intended for application in a virtual SEM (VSEM).     

Time of flight spectrometer for scanning electron microscope

Experimental results which show the feasibility of use a time-of-flight spectrometer to obtain energy information of emitted electrons in a scanning electron microscope (SEM) are presented. The method is able to simultaneously display the energy distribution of emitted electrons over their entire energy range, from elastic backscattered electrons down to the low energy secondary electrons, and is thus predicted to have major signal-to-noise benefits for topographic, material, and voltage contrast in an SEM.<>     

Scanning electron mirror microscopy and scanning electron microscopy of integrated circuits

The recently developed scanning electron mirror microscope (SEMM) is compared with other types of electron microscopes, such as the electron mirror microscope (EMM) and the scanning electron microscope (SEM), for examining integrated circuits. Potential advantages of the SEMM include high resolution, elimination of electron bombardment damage, and high sensitivity of voltage gradients, magnetic fields, and topography. Preliminary observations of integrated, circuits obtained with the feasibility SEMM at various specimen potentials are discussed.     

Energy dependence and depth distribution of electron beam-induced damage in GaAs/AIGaAs heterostructures

We have investigated the effects of electron beam (EB) irradiation on the optical and electrical properties of GaAs/AIGaAs heterostructures in the energy range between 5 and 25 keV and at electron doses of 1 x 10¹⁶~1 x 10²¹ electrons/cm². The most pronounced effects were observed for 10 keV EB irradiation. The photoluminescence (PL) intensity from quantum wells and the two-dimensional-electron-gas (2DEG) mobility were reduced at doses greater than 1 x 10¹⁹ electrons/cm² and 5 x 10²⁰ electrons/cm², respectively. On the other hand, for 5 and 25 keV, those degradations were not observed. For various EB energies, the depth distribution of EB-induced damage was determined by both PL and 2DEG mobility measurements. Using a Monte-Carlo simulation, the damage distribution was shown to be correlated with the energy-loss distribution of incident electrons. Namely, the penetration of 5 keV electrons is too shallow to cause any damage in the active region at around 100 nm depth. On the other hand, since the energy-loss distribution of 25 keV electrons is too broad and deep due to the reduced cross section of collisions between the electrons and target, it has little effect on the photoluminescence (PL) and the 2DEG mobility. Consequently, 10 keV electrons lose most of their energy in the active region (100 nm depth), being consistent with the observed degradation of the PL and 2DEG mobility.     

Noise in secondary electron emission: the low yield case

Studies concerning assessment of the image quality in scanning electron microscopes and studies evaluating the detective efficiency of the secondary electron (SE) detectors in these microscopes must be based on statistics of SE emission. The vast majority of previous studies have applied Poisson statistics, although their prerequisites have not been satisfied in most cases. This paper is concerned with the limits to the applicability of Poisson statistics to SE emission. Adequate definition of a non-Poisson factor in the variance of the number of SEs emitted is discussed, and a simple formula for this factor is derived for the low yield case in which both the primary and the backscattered electron are assumed not to release more than one SE. These conditions are met with conductive specimens composed of light elements at primary electron (PE) energies of tens of keV. For the lightest specimens, such as carbon, the non-Poisson factor can even be neglected for PEs >10 keV.     

A virtual scanning electron microscope. 4. Simulator-based implementation

A virtual scanning electron microscope (VSEM), which is based on a simulator of information, obtained on a real scanning electron microscope (SEM), is described. A semiempirical generation model of images in a SEM, operating in the low-voltage mode and high-voltage mode during recording backscattered and secondary slow electrons, forms the basis of a virtual SEM. A method of comparing real and virtual images is proposed. Examples of operation of the virtual SEM are given for elements of structures which are located both far from the edges of the structure and near these edges.     

Detection of glycoconjugates by lectin gold labelling, silver enhancement, and scanning electron microscopy

A method for detecting glycoconjugates on cell surfaces in scanning electron microscopy is described. Terminal saccharides were specifically recognized by a lectin conjugated to biotin, and, after incubation with an anti-biotin antibody conjugated to colloidal gold, silver enhancement was used to produce deposits large enough to be detected in standard scanning electron microscopes. Secondary electron images revealed the ultrastructure of the tissue investigated, while backscattered electron images showed the distribution of lectin binding sites. Using digital recording and processing, the two channels were combined in colour-encoded images. The new method brings together lectin histochemistry and scanning electron microscopy and thus allows the three-dimensional distribution of glycoconjugates to be analysed at an ultrastructural level.     

我国电子显微镜的研制与生产

本文记述了我国研制与生产的各种电子显微镜，主要是透射电子显微镜，扫描电子显微镜和电子探针X射线微区分析仪。1958－1959年中国科学院长春光学精密机械研究所制成了我国第一台电子显微镜，又率先自行设计研制完成100kV大型电子显微镜。根据1996－1997年国家科委组织的一项调查，当时我国拥有2021台电子显微镜，包括透射电子显微镜756台，扫描电子显微镜1165台，合计1921台。其中，进口915台，占47．6％；我国生产了100台，占52．4％，但大多为中、低档产品。中国科学院北京科学仪器研制中心KYKY，上海电子光学技术研究所和南京光学仪器厂生产的占国产1006台中的95％以上。云南大学，北京仪器厂，上海第三分析仪器厂和国营4503厂也分别研制或生产了几种透射电子显微镜和扫描电子显微镜。     

Regrowth of heavy-ion implantation damage by electron beams

Electron transparent Si, Ge and GaP samples were implanted with 50 keV Xe⁺ ions to a dose around 10¹¹ ions/cm². At this implantation condition, each heavy ion created a small, spatially isolated amorphous zone. Following the ion implantation, the samples were irradiated with electrons having energies from 25 to 300 keV at temperatures 90 and 300 K. At each electron energy, transmission electron microscopy (TEM) images of a selected sample area were taken in regular time intervals to record the evolution of the implant damage. At all electron irradiation conditions it was observed that the amorphous zones shrunk with increasing electron dose and some of them eventually disappeared. The most interesting result is the observation that regrowth occurs below the displacement threshold and, moreover, regrowth rate increases when decreasing electron energy below ∼100, ∼125 and ∼200 keV, for Si, GaP and Ge, respectively. These results are discussed in terms of possible mechanisms stimulating regrowth.     

低能电子束对抗蚀剂曝光的Monte Carlo模拟

考虑二次电子的产生和散射，利用Monte Carlo方法模拟了具有高斯分布特征的低能入射电子束斑在抗蚀剂中的散射过程，分别得到了电子束在抗蚀剂中的穿透深度和能量沉积的分布图。发现在能量小于2．5keV范围内的模拟结果与实验结果相吻合，这比用传统的不考虑二次电子的Bethe公式得到的模拟结果更加符合实际的电子散射过程，精度更高。另外还发现电子束能量越低，曝光的分辨率和效率越高，这一结果也与实验相吻合。结果表明，二次电子的产生和散射对电子束曝光起了重要的作用，需考虑它们的影响。     

Determination of the ion angular distribution for electron cyclotron resonance,plasma-etched HgCdTe trenches

Ion angular distribution (IAD) affects the width and aspect ratio in electron cyclotron resonance (ECR)-etched HgCdTe trenches. The IAD was determined by etching studies together with scanning electron microscopy (SEM) analysis. The results confirm that low-energy, large-angle ions contribute to the etching of the photoresist, while higher-energy, low-angle ions are responsible for HgCdTe etching. The HgCdTe ECR etching was further elucidated by sputter-bombardment theory. This model correctly predicts the nature and depth of the damage region in ECR-etched HgCdTe as well as the distribution and composition of the ejected material.     

Operation of an electronic lithograph in the mode of a scanning electron microscope

The operation of the Raith-150 electronic lithograph in the mode of a scanning electron microscope is examined. Sizes of the pixel and effective diameter of an electron probe are determined along both scanning directions. The parameters of a system for scanning and forming the lithograph??s electron probe compare well with those of the best scanning electron microscopes.     

High Purity and Large-scale Preparation of β-Ga2O3 Nanowires and Nanosheets by CVD and Their Raman and Photoluminescence Characteristics

Ga2O3 nano-structures,nanowires and nanosheets are produced on Au pre-coated(111) silicon substrates with chemical vapor deposition(CVD) technique.By evaporating pure Ga powder in the H2O atmosphere under ambient pressure the large-scale preparation of β-Ga2O3 with monoclinic crystalline structure is achieved.The crystalline structures and morphologies of produced Ga2O3 nano-structures are characterized by means of scanning electron microscope(SEM),X-ray diffraction(XRD),selected area electron diffraction(SAED) and transmission electron microscope(TEM).Raman spectrum reveals the typical vibration modes of Ga2O3.The vibration mode shifts corresponding to Ga2O3 nano-structures are not found.Two distinguish photoluminescence(PL) emissions are found at about 399 nm and 469 nm owing to the VO-VGa excitation and VO-VGa-O excitation,respectively.The growth mechanisms of Ga2O3 nanowires and nanosheets are discussed with vapor-liquid-solid(VLS) and vapor-solid(VS) mechanisms.     

Sr3Ga2O5Cl2:Sm3+荧光粉的制备及发光特性

采用传统的高温固相法成功合成了Sr3-xGa2O5Cl2:Sm3+系列橙红色荧光粉。使用X射线衍射仪（XRD）测试了样品的晶体结构,样品的形貌和颗粒尺寸由扫描电子显微镜（SEM）表征,使用荧光光谱仪测试了样品的光致发光光谱和衰减寿命。Sr3Ga2O5Cl2晶相为单斜结构,掺杂的Sm3+离子取代Sr2+的格位成为荧光粉的发光中心。样品的激发光谱由O2-→Sm3+的电荷迁移带和Sm3+离子4f内层电子的特征激发峰组成,位于230 nm、404 nm的激发峰较强。发射光谱的峰值位于565、601、650 nm处,分别对应于Sm3+的4G5/2→6H5/2、4G5/2→6H7/2、4G5/2→6H9/2特征跃迁。样品的发光强度随着Sm3+浓度的增加先增大后减小,最佳掺杂浓度为3.0% mol。根据实验数据对浓度淬灭的原因进行了探讨,浓度淬灭机理为电偶极-电偶极相互作用。     

Experimental evaluation of depth-dependent lateral standarddeviation for various ions in a-Si from one-dimensional tiltedimplantation profiles

This paper presents an experimental evaluation of the lateral standard deviation for various ions implanted in amorphous silicon (a-Si) with a simple extraction method using no complicated structures. First, we derive a model for the tilted implantation profile as a function of both tilt angle and lateral standard deviation, assuming a Gaussian lateral distribution function. This model is based on the assumption that two-dimensional (2-D) ion implantation profiles can be constructed from lateral and vertical distribution functions which are independent of each other, and it enables us to extract lateral standard deviation by only evaluating one-dimensional (1-D) (vertical) impurity profiles. Next, we systematically measure the ion implantation depth profiles at various tilts (0-60°) with high resolution using secondary ion mass spectrometry (SIMS) and apply our proposed model for arsenic (As), phosphorus (P), antimony (Sb), and boron (B) ion implantations in a-Si over a wide energy range (20-160 keV) with a fixed dose of 1×10¹⁴ cm^-2. We successfully estimated not only average lateral standard deviation but also its depth dependence. Despite the simplicity of the model, the extracted depth-dependent lateral standard deviation shows good agreement over a wide energy range with the reported data calculated by theory or simulations. It is also shown that the lateral standard deviation has a linear depth dependence, and the lateral spread increases with the increase of depth for As, P, and Sb; on the other hand, it decreases for B, which reflects the difference of atomic mass between the incident ions and the target atoms     

扫描电镜中的算法进展

在过去的二十年中,同透射电镜一样,在扫描电镜上也取得了许多硬件的进展,如浸没式物镜、减速模式和新型探测器技术.测试技术的进步包括硬件和软件两方面内涵.伴随硬件的进步,借助信息科学(包括人工智能(AI)和其他统计数学方法),人们在成像和光谱学方面也有了新的机遇.硬件与软件结合,可以实现更高精度、更高通量的表征,也使得如今...