New techniques in SIMS analysis of HgCdTe materials

This paper presents two new approaches used in the secondary ion mass spectrometry (SIMS) for high sensitivity dopant and impurity analysis in HgCdTe materials, namely, the high mass resolution with dynamic transfer and the MCs⁺ technique. It is shown that better detection limits for As and Cu can be obtained at a level of 2–5e14 at/cm³. The MCs⁺ technique has added advantages of better measurement precision, monitoring Cd composition in the same profile, and small device area analysis capability. Advantages and trade-offs of each technique are discussed and compared. An updated detection limit table for all elements measured in HgCdTe materials using SIMS is also presented.     

二次离子质谱技术在砷化镓工艺中的应用

砷化镓工艺过程中出现的问题往往与杂质的分布有关 ,二次离子质谱技术是研究各种成分的三维分布的主要测试方法之一 ,由于其自身的特点使其成为分析器件失效原因的最有效的检测手段。利用 SIMS技术对砷化镓材料、离子注入、外延生长、光刻、欧姆接触形成、肖特基势垒形成及钝化等工艺中出现的典型问题进行了研究分析 ,找出了失效原因 ,为改进工艺提供了依据。     

Dopant,composition and carrier profiling for 3D structures

With the transition from planar to three-dimensional device architectures, devices such as FinFETs, TFETs and nanowires etc. become omnipresent. This requires the dopant atom positioning relative to the gate edges and contacts with controlled 3D distribution, adequate conformality, appropriate concentrations and activation, all of which are important challenges which need to be resolved since they determine the device performance. Developing an appropriate doping technology for the next technology generation requires a concurrent effort in establishing adequate metrology such that appropriate feedback on process steps and the underlying physics can be generated in a timely manner and with sufficient resolution and accuracy. When assessing performance of such metrology tools and concepts for 3D devices and structures, one needs to address not only the ability to achieve 3D spatial resolution, but also the physical property which is probed, i.e. dopants versus carriers, as well as the complexity of the method used because this impacts on success rate, turn-around time, throughput, automation etc. An evaluation in terms of time to data is as important as the technical capabilities.Although techniques with inherently good 3D resolution (e.g. atom probe tomography) might appear to offer the ideal solution for these applications, routine application is still hampered by localization problems during sample preparation, reconstruction artefacts due to inhomogeneous evaporation and differential laser light absorption, limited sensitivity due to the reduced counting statistics, poor tip yield, small throughput, etc. Hence, complementary analysis using 1D methods like secondary ion mass spectrometry (SIMS) are being explored to provide dopant or composition analysis in 3D structures given its high degree of reproducibility, ease of application and industrial acceptance. Targeting carrier profiling in 3D structures and confined volumes as a complement to atom probe (or SIMS) dopant profiles, has led to the extension of scanning probe microscopy (SPM) methods (which are inherently 2D) toward 3D metrology by exploiting either dedicated test structures or through novel approaches such as Scalpel SPM.The application of these SPM methods for 3D structures and confined volumes has demonstrated that the changing surface/volume ratio in confined devices leads to various phenomena (e.g. dopant deactivation, enhanced diffusion,..) which are not observed in blanket sample experiments. More emphasis should therefore be placed on the analysis of devices and structures with the relevant dimensions relative to the exploration of blanket experiments. Thus, the metrology concepts addressed in this paper may be very useful for such investigations.     

Secondary Ion Mass Spectrometry and Time-of-Flight Secondary Ion Mass Spectrometry Study of Impurity Measurements in HgCdTe

In this study, time-of-flight (TOF) secondary ion mass spectrometry (SIMS) was compared against dynamic SIMS to determine detection limits and background levels for nine impurities: Li, Na, K, Al, Ni, As, In, Fe, and Cu. Statistics were gathered by measuring six material test structure samples from six different liquid phase epitaxy (LPE) HgCdTe double layer heterojunction (DLHJ) wafers. Also included is a comparison between dynamic SIMS and TOF-SIMS capabilities.     

Surface analytical techniques

This review briefly describes some of the techniques available for analysing surfaces and illustrates their usefulness with a few examples. In particular, Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), sputter neutral mass spectroscopy (SNMS) and laser Raman spectroscopy are all described. In analysing a surface, AES and XPS would normally be considered first, with AES being applied where high spatial resolution is required and XPS where chemical state information is needed. SIMS and SNMS can be performed together and can detect smaller surface concentrations. Laser Raman spectroscopy is useful for determining molecular bonding. Techniques which give topographic information, such as scanning tunnelling microscopy (STM) and atomic force microscopy (AFM), have not been considered.     

SIMS在碲镉汞红外焦平面探测器工艺中的应用

文章介绍了二次离子质谱仪的结构及其基本工作原理,并通过对典型应用的分析,介绍了二次离子质谱分析技术在高灵敏度碲镉汞红外焦平面探测器材料和器件制备工艺中的作用,特别是在结探监测和微量杂质监控方面所发挥的重要作用。     

Microcrystalline silicon solar cells: effect of substrate temperature on cracks and their role in post‐oxidation

Microcrystalline silicon (µc‐Si:H) cells can reach efficiencies up to typically 10% and are usually incorporated in tandem micromorph devices. When cells are grown on rough substrates, “cracks” can appear in the µc‐Si:H layers. Previous works have demonstrated that these cracks have mainly detrimental effects on the fill factor and open‐circuit voltage, and act as bad diodes with a high reverse saturation current. In this paper, we clarify the nature of the cracks, their role in post‐oxidation processes, and indicate how their density can be reduced. Regular secondary ion mass spectrometry (SIMS) and local nano‐SIMS measurements show that these cracks are prone to local post‐oxidation and lead to apparent high oxygen content in the layer. Usually the number of cracks can be decreased with an appropriate modification of the substrate surface morphology, but then, the required light scattering effect is reduced due to a lower roughness. This study presents an alternative/complementary way to decrease the crack density by increasing the substrate temperature during deposition. These results, also obtained when performing numerical simulation of the growth process, are attributed to the enhanced surface diffusion of the adatoms at higher deposition temperature. We evaluate the cracks density by introducing a fast method to count cracks with good statistics over approximately 4000 µm of sample cross‐section. This method is proven to be useful to quickly visualize the impact of substrate morphology on the density of cracks in microcrystalline and in micromorph devices, which is an important issue in the manufacturing process of modules. Copyright © 2010 John Wiley & Sons, Ltd.     

基于强散射点径向积累的高分辨极化目标检测研究

研究了宽带高分辨雷达杂波环境中的目标检测问题,提出了基于强散射点径向积累的高分辨极化目标检测方法,利用宽带波形固有的径向高分辨力对目标进行一维距离成像,结合目标的极化特性,估计出回波中强散射点的数量和分布,通过对不同径向分辨单元内的强散射点进行积累,可有效地提高信杂比,实验仿真结果表明本文方法能够有效改善雷达的检测性能.     

硅中磷杂质的SIMS定量检测

利用SIMS(二次离子质谱仪)测试了国产重掺砷硅单晶中的痕量杂质磷,通过样品前期处理和精密的仪器调试,使检测时间缩短,并使硅中磷的检测限达到5×10¹³ cm^-3。实验结果表明,样品的前期处理工艺会对检测结果产生影响。不同处理工艺得到的样品,在表面粗糙度方面产生区别。不同的表面粗糙度,影响到样品的测试时间和测试精度。同时,通过仪器调试,仪器的真空度达到1×10^-10 torr,使测试背底和检测限降低。     

Applying secondary ion mass spectrometry to the analysis of elements in goblet cells of conjunctiva

We investigated the location of elements in the goblet cells of rat conjunctiva by analyzing ion images produced by secondary ion mass spectrometry (SIMS) and comparing them with those produced by energy dispersive X-ray analyser (EDX). Conjunctivas of normal Spraque-Dawley rats were quenched in propane prechilled liquid nitrogen. Semi-thin sections were made with a cryo-ultramicrotome, freeze-dried, carbon-coated and observed under a light microscope, SIMS and scanning electron microscope (SEM). In the element analysis by SIMS, images of positive ions were examined with an O2+ primary ion source and images of negative ions with a Ga+ ion source. The same sections were observed and analysed with SEM-EDX. Morphological features and images of elements with SIMS and EDX were compared. Na, Mg, K, and Ca were detected as positive ions and OH, CN, P, S, and Cl as negative ions with SIMS, but C, N, O, Na, Mg, P, S, Cl, K, and Ca were detected with EDX. The spatial resolution of SIMS in element location was higher than that of EDX. Many elements were clearly located in the goblet cells on ion images by SIMS. Element ion images were demonstrated more densely in goblet cells than in other parts within conjunctiva and by SIMS compared to EDX. SIMS is a useful method for the detection of elements and their locations in ocular tissues and cells.     

Analysis of V/III incorporation in nonstoichiometric GaAs and InP films using SIMS

Using secondary ion mass spectrometry (SIMS), we have investigated the excess group V content in GaAs and InP films grown by molecular beam epitaxy at low temperature. Using the inherent depth profiling capability of SIMS, we investigated the V/III ratio in films grown at nominally constant temperatures and also in films grown with stepped temperature profiles. Thickness profiles of the V/III ratio show the effects of intentional temperature changes and of an unintentional drift in the actual substrate temperature during growth. The ability to measure as little as 0.1% excess As and about 0.2% excess P indicates excellent measurement resolution. SIMS analysis is also used to identify a narrow growth temperature range over which InP can be grown with appreciable nonstoichiometry yet remain monocrystalline.     

Secondary Ion Mass Spectrometry (SIMS) for Chemical Characterization of Metal Halide Perovskites

Metal halide perovskite (MHP) solar cells have attracted much attention due to the rapidly growing power conversion efficiency that has reached 25.2% in a decade, comparable to established commercial photovoltaic modules. Compositional engineering is one of the most effective methods to boost the performance of MHP solar cells. Further improving the efficiency and the stability of MHP solar cells necessitates good understanding of the chemical–efficiency correlation and the chemical evolution during the degradation of MHP solar cells. In this regard, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) is a powerful tool to investigate the chemical aspect of MHPs and has played an important role in advancing the development of MHP optoelectronics. However, up to date, a review that can guide future utilization of ToF‐SIMS in the MHP development is missing. Herein, the capabilities of ToF‐SIMS in MHP investigations are summarized and analyzed from simple material synthesis and chemical distribution to more complicated device operation mechanism and stability. The strength of ToF‐SIMS in resolving important issues in this field, such as interface composition, ion migration, and degradation in MHP is highlighted. Finally, an outlook with an emphasis on making the utmost of ToF‐SIMS in developing MHP devices is provided.     

基于AlN和GaN形核层的AlGaN/GaN HEMT外延材料和器件对比

使用金属有机物化学气相淀积(MOCVD)方法在蓝宝石衬底上分别采用AlN和GaN作为形核层生长了AlGaN/GaN高电子迁移率晶体管(HEMT)外延材料,并进行了器件制备和性能分析.通过原子力显微镜(AFM)、高分辨率X射线双晶衍射仪(HR-XRD)和二次离子质谱仪(SIMS)等仪器对两种样品进行了对比分析,结果表明采用AlN形核层的GaN外延材料具有更低的位错密度,且缓冲层中氧元素的拖尾现象得到有效地抑制.器件直流特性显示,与基于GaN形核层的器件相比,基于AlN形核层的器件泄漏电流低3个数量级.脉冲Ⅰ-Ⅴ测试发现基于GaN形核层的HEMT器件受缓冲层陷阱影响较大,而基于AlN形核层的HEMT器件缓冲层陷阱作用不明显.     

Formation of a buried collector layer in RF-bipolar devices by ion implantation

High-dose implantation of arsenic (As) buried collector layer formation for bipolar/BiCMOS processes has been studied. Wafers with and without screen oxide were subjected to high-dose implants with different energies. Some wafers were given a low-temperature anneal before XTEM and SIMS analyses. Defects observed after As implants of 6E15 cm⁻² through screen oxide after low-temperature anneal were annihilated at the subsequent high-temperature steps, but the direct implant of As into the silicon is preferred since fewer defects are generated and there is no knock-on of oxygen into the material. Fabricated devices showed excellent electrical performance. However, the upper limit (dose and/or energy) at which perfect recrystallization does no longer occur has not been defined and the process limit is consequently not established.     

Imaging Surface Immobilization Chemistry: Correlation with Cell Patterning on Non‐Adhesive Hydrogel Thin Films

High‐fidelity surface functional group (e.g., N‐hydroxysuccinimide (NHS) reactive ester) patterning is readily and reliably achieved on commercial poly(ethylene glycol) (PEG)‐based polymer films already known to exhibit high performance non‐fouling properties in full serum and in cell culture conditions. NHS coupling chemistry co‐patterned with methoxy‐capped PEG using photolithographic methods is directly spatially imaged using imaging time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and principal components statistical analysis. Patterned NHS surface reactive zones are clearly resolved at high sensitivity despite the complexity of the polymer matrix chemistry. ToF‐SIMS imaging also reveals the presence of photo‐resist residue remaining from typical photolithography processing methods. High cross‐correlation between various ion‐derived ToF‐SIMS images is observed, providing sensitive chemical corroboration of pattern chemistry and biological reactivity in complex milieu. Surface‐specific protein coupling is observed first by site‐selective reaction of streptavidin with NHS patterns, followed by identical patterns of biotinylated Alexa‐labeled albumin coupling. This suggests that streptavidin immobilized on the patterns remains bioactive. Fluorescently labeled full serum is shown to react selectively with NHS‐reactive regions, with minimal signal from methoxy‐capped regions. Insufficient serum is adsorbed under any conditions to these surfaces to support cell attachment in serum‐containing media. This reflects the high intrinsic non‐adsorptive nature of this chemistry. Fibroblasts attach and proliferate in serum culture only when a cell adhesion peptide (RGD) is first grafted to NHS regions on the PEG‐based surfaces. Longer‐term serum‐based cell culture retains high cell‐pattern fidelity that correlates with chemical imaging of both the NHS and RGD patterns and also lack of cell adhesion to methoxy‐capped regions. Cell staining shows orientation of adherent cells within the narrow patterned areas. Cell patterns are consistently retained beyond 15 days in serum media.     

金掺杂HgCdTe气相外延生长及二次离子质谱研究

通过气相外延技术生长了Au掺杂的Hg1-xCdxTe薄膜材料。利用傅里叶光谱仪和金相显微镜对外延材料进行了表征。通过二次离子质谱(Secondary Ion Mass Spectroscopy, SIMS)技术分析了Au在Hg1-xCdxTe外延层以及CdZnTe衬底中的纵向分布趋势。利用SIMS技术还分析了I、II族和VI、VII族杂质在Hg1-xCdxTe外延层以及CdZnTe衬底中的纵向分布趋势,发现衬底和外延层的过渡区具有吸杂作用。研究结果对提高探测器的性能具有指导意义。     

The application of radioanalytical methods in semiconductor technology

For about 25 years the radioanalytical activation analysis, autoradiography and radiotracer technique have been widely used in the development of semiconductor technology. The advantages of these techniques are its high detection sensitivity by simultaneous determination of a broad spectrum of elements in a wide range of materials, making visible impurity inhomogenities and element distributions with a resolution down to a few micrometers.The latest results from analyses of semiconductor material development, device fabrication and of auxiliary materials used in this process are presented.     

半绝缘SiC单晶电阻率均匀性研究

采用非接触电阻率面分布(COREMA)方法对本实验室生长得到的2英寸(50 mm)4H和6H晶型半绝缘SiC单晶片进行电阻率测试,结果发现数据的离散性大,低者低于测试系统下限105Ω.cm,高者高于其上限1012Ω.cm,甚至在同一晶片内会出现小于105Ω.cm,105~1012Ω.cm和大于1012Ω.cm的不同区域,而有的晶片则电阻率的均匀性较好。将SiC电阻率测试结果与二次离子质谱(SIMS)对晶体内主要杂质V,B和N含量测试结果相结合,初步探讨得到引起掺钒SiC单晶电阻率的高低及均匀性的变化由补偿方式决定,在深受主补偿浅施主模式下,V的浓度控制在2×1016~3×1017cm-3,N的浓度控制在1×1016cm-3左右,深受主钒充分补偿浅施主氮,制备得到的SiC单晶具有半绝缘性,且电阻率均匀性好。     

Vapor growth of InP for MESFET’S

Epitaxial layers of InP have been grown by the conventional In/PCl₃/H{ion2} technique. With the aim of fabricating FET’s structures, we have studied the growth of low doped buffer layers and the doping by H₂S. It has been shown, that the purity of the layers increases from experiment to experiment and that low doped layers, in the 10¹³ – 10¹⁴ cm^-3 range, are obtained after growth of about 10 layers. Evidence for the purity of these layers have been obtained from Hall, photoluminescence and SIMS measurements. Cr and Fe outdiffusion from the substrate has been studied by SIMS. Fe is found to diffuse from the substrates, even in the case of substrates which are not intentionally doped with Fe. Some FET’s have been fabricated on epitaxial structures with and without buffer layers: the static characteristics of the transistors are encouraging (I_Dss = 24 mA, g_m = 19 mS for a gate of 2 μm and 200 μm in length and width, respectively); the pinch-off is better in devices fabricated from structures with buffer layers.     

环境气氛对二维超薄ZnO纳米片紫外探测器性能的影响

二维宽带隙半导体材料独特的纳米结构是高性能紫外光电探测器的潜在理想材料,但是在实际应用过程中,各种环境气氛可显著影响紫外光探测器件的性能。文中采用化学气相沉积方法制备超薄二维ZnO纳米片,并利用该纳米片制作了紫外光探测器件。将探测器件置于密闭系统中进行测试,排除了不同应用环境对测试结果的影响,同时重点研究了不同极性分子对二维超薄ZnO纳米片紫外探测器性能的影响。研究结果表明,在极性分子存在的条件下,ZnO纳米紫外光探测器的暗电流降低1.5~2倍,灵敏性和响应率提高了约1.5倍。