Elemental characterisation of sub 20 nm structures in devices using new SEM-EDS technology

The continuing decrease in structure and defect size in devices has driven many applications away from SEM towards thin sample preparation and TEM investigation. The latest FIB/SEM technology has the capability to image structures down to less than 5 nm on a bulk or thin specimen but cannot provide supporting chemical information from EDS. Here we investigate a new more sensitive EDS detector, which for the first time provides chemical information at these high spatial resolutions in the SEM. We outline operating conditions that are suitable to chemically resolve semiconductor structures below 20 nm. Based on these results we propose workflows to speed up failure analysis by obtaining the analysis result directly in the FIB/SEM without the need for TEM analysis.     

聚焦离子束技术制备与样品表面平行的TEM样品

制备目标材料的高质量TEM样品对TEM测试表征和结果分析具有决定性作用.聚焦离子束（FIB）技术由于其微观定位选区制样的优势在TEM样品制备上已有一定应用.本文介绍了FIB/SEM双束系统制备与样品表面平行的TEM样品的方法（“V-cut”）,并与传统的FIB制备TEM样品的方法（“U-cut”）进行比较,分析了该方法对实现某些特殊研究目的的独特性和适用性.     

2D-mapping of dopant distribution in deep sub micron CMOS devices by electron holography using adapted FIB-preparation

Transmission electron microscopy (TEM) is a widely used tool for analysis of very large scale integrated (VLSI) semiconductor devices. As a special TEM-feature, off-axis electron holography obtains information about the electrical characteristics of a specimen, which are connected to the dopant concentration in the bulk material. Compared with conventional TEM, application of electron holography for dopant profiling demands a higher quality of specimen preparation, e.g. in terms of thickness homogeneity. Since preparation by means of focused ion beam (FIB) has become an industrial standard for TEM-investigations, its facilities are investigated for meeting the high holographic demands. It turned out that, besides many advantages like precision and speed, the use of FIB for preparation introduces new specific problems, e.g. it is hardly possible to visualize doped areas of semiconductors on a classical, thin FIB specimen. Additionally, some artifacts of FIB-preparation have no great importance for normal TEM analysis, but do significantly influence the results of holographic analysis. In order to satisfy the higher demands of preparation for holography, a special procedure for FIB-preparation has been newly developed.     

聚焦离子束制备透射电子显微镜样品的两种厚度判断方法

透射电镜样品的厚度是透射电镜(TEM)表征中一个重要参数,快速准确地判断样品厚度是制备高质量样品的前提.本文通过使用聚焦离子束(FIB)制备了带有厚度梯度的透射电镜样品(Si、SrTiO3和LaAlO3),并提出两种制样过程中快速判断厚度的方法.第一种通过扫描电子显微镜(SEM)的衬度变化经验地判断样品的厚度;第二种是用FIB在样品边缘切一个斜边,通过SEM测量斜边侧面的宽度用几何方法推断样品的厚度.这两种方法都通过会聚束电子衍射(CBED)和电子能量损失谱(EELS)测量的厚度作为检验标准.对比认为,样品较薄时用SEM衬度测厚比较合适;样品比较厚时用几何方法测量比较直接.     

The use of the focused ion beam in failure analysis

Since the introduction of the Focused Ion Beam (FIB), many applications have been developed. This article deals with a stand alone FIB in a failure analysis laboratory where it is used for material characterisation and sample preparation. In this paper examples will be given of FIB applications as used for failure analysis and process monitoring of semiconductor devices.     

一种GaAs PHEMT器件的失效分析

随着Ga As PHEMT(赝配高电子迁移率晶体管)器件的广泛应用,器件的可靠性及失效分析方法越来越受到人们的重视。该文采用半导体参数分析仪、聚焦离子束(FIB)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、能谱仪(EDX)等分析方法对一种PHEMT器件进行失效分析,为实际生产和加工过程中的失效分析提供了参考。     

Reducing focused ion beam damage to transmission electron microscopy samples

One of the most important applications of focused ion beam (FIB) systems is sample preparation for transmission electron microscopy (TEM). However, the use of the FIB inherently involves changing and damaging the sample, and thereby degrades the TEM resolution. This paper addresses the beam-induced damage and artifacts, particularly in applications involving silicon semiconductors. The damage appears in the form of amorphization on the surface of the TEM foil. The characteristics of this amorphous damage were studied by making TEM observations of cross sections of the affected foil. The damage is typically 20 to 30 nm thick for a 30 keV FIB, which is generally overly thick for modern silicon devices with feature sizes less than 250 nm. This paper reviews the reported damage depths of FIB-prepared samples, which are determined by experiments and calculations. Several damage reduction techniques, such as the use of gas-assisted etching, low energy FIB, cleaning the FIBfabricated cross section by wet or dry etching and cleaning by broad ion beam (BIB) milling have also been reviewed, with emphasis on applicability to silicon devices. We conclude that the use of low energy FIB and cleaning by argon BIB are particularly efficient techniques.     

A study of the damage on FIB-prepared TEM samples of AlxGa1-xAs

The damage produced by focused ion beam (FIB) milling on a TEM sample of AlGaAs crystals has been studied. The damage observed on the sidewall of an AlGaAs transmission electron microscopy (TEM) sample was an amorphous layer. The thickness of the amorphous layer linearly increased with an increase in FIB accelerating voltage from 5 to 30 kV. The thickness of the amorphous layer of Al(x)Ga(1-x)As was constant at 3 nm and was independent of the Al concentration x when the accelerating voltage was below 5 kV. The thickness of the amorphous layer of Al(x)Ga(1-x)As decreased with an increase in Al concentration x when the accelerating voltage was above 5 kV. FIB milling at 5 kV effectively minimizes the thickness of the amorphous layer and also provides flat sidewalls on multilayer samples of Al(x)Ga(1-x)As that are prepared for TEM and scanning electron microscopy (SEM).     

Application of Fast Laser Deprocessing Techniques on large cross-sectional view area sample with FIB-SEM dual beam system

Cross-sectional analysis is one of the important areas for physical failure analysis. Focus Ion Beam (FIB) and mechanical polish sample preparation are commonly used and necessary techniques in the semiconductor industry and Failure Analysis (FA) Company (Wills and Perungulam, 2007). However, each technique has its own limitation. Mechanical polishing technique easily induces artifact by mechanical force, especially on advance technology node. FIB can eliminate mechanically damaged artifact, but have the limitation on cross-sectional view area. Another potential technique will be plasma FIB, it used very high milling current and fast milling speed (Hrnčíř et al., 2013). However, it comes with a very high cost and having the contamination issue. The contamination issue greatly affects the low kV Scanning Electron Microscopy (SEM) imaging quality. In recent semiconductor industry FA, low kV SEM imaging is preferable, because high kV imaging will introduce delamination artifacts especially on organic material from packaged sample. In this paper, Fast Laser Deprocessing Techniques (FLDT) application is further enhanced on large area cross-sectional FA with fast cycle time and low-cost equipment. This is to prevent from mechanical damage. In short, the proposed FLDT is a cost-effective and quick way to deprocess a sample for defect identification in cross-sectional FA.     

Advanced FIB sample preparation techniques for high resolution TEM investigations of HEMT structures

In this paper advanced sample preparation techniques based on focused ion beam (FIB) optimized for TEM investigation of high electron mobility transistor (HEMT) structures are presented. It is shown that the usage of an innovative in-situ lift-out method combined with X2 window and backside milling techniques as well as live thickness control and end point detection can significantly improve the quality of electron transparent samples required for high resolution TEM investigations. This advanced preparation flow is evaluated and demonstrated at GaN HEMT structures for atomic resolution TEM investigation.     

Evaluation of scanning capacitance microscopy sample preparation by focused ion beam

Due to the continuous reduction of the critical dimensions of semiconductor devices, it becomes very important to know the two dimensional (2D) doping profile for electrical performance of devices. Scanning Capacitance Microscopy (SCM) is a powerful technique for qualitative analysis of 2D doping species distribution, measuring small capacitance variations with high spatial resolution. For 2D carrier profiling, the region of interest must be accessible to the profiling instrument. SCM samples require cross-sectioning to expose the inner sample at a visible surface. In some analysis, the failure is localized at a very accurate address up to hundreds of nanometers. With the traditional polishing method of sample preparation it is very difficult to reach the exact location. For this reason we are investigating a new way to prepare SCM sample with Focused Ion Beam (FIB) and plasma etch in order to accurately choose the scanning zone. This paper presents a method to obtain SCM scans after a sample preparation by FIB and the influence of the FIB and the Plasma etcher on cross-sectioned SCM samples.     

Physical failure analysis in semiconductor industry—challenges of the copper interconnect process

Since the copper interconnect dimensions shrunk continuously, physical failure analysis becomes increasingly important for process optimization. Failure localization and defect analysis in interconnect structures as well as analysis of barrier/seed step coverage are challenges of the copper inlaid technology. Failure localization in via chain test structures using voltage contrast analysis with SEM/FIB tools and OBIRCH and subsequent destructive failure analysis using FIB/SEM and TEM are described. The inspections of voids in copper interconnects and of buried residuals in vias are typical tasks for process monitoring, which make the application of leading-edge analytical techniques necessary. Barrier/seed step coverage analysis at via chains challenges both TEM sample preparation and analysis. 3D object reconstruction by electron tomography is a promising future method for this task.     

Thermal approach of defects generation on copper/organic dielectric interface due to SEM inspections

Scanning electron microscopy (SEM) sometimes induce defects on samples during imaging. We study in this article the thermal effects of SEM views on the Cu/BCB interface, in focused ion beam (FIB) cross sections. Electrons can lead to local thermal power dissipation due to their deceleration and create delamination. A TEM lamella sample preparation method was also found to avoid this kind of delamination. In this case, the thermal dissipated power could be reduced due to the fact that a big part of the incoming electrons could go through the sample without interactions. Several thermal simulations (2D/3D) were carried out to estimate the field of temperatures under electron beam and to explain the Cu/BCB interface delamination.     

FIB参数对低介电常数介质TEM样品制备的影响

研究了使用聚焦离子束(FIB)方法制备低k介质的TEM样品时离子束参数对介质微观形貌的影响,发现低k介质的微观形貌与离子束参数具有较强的相关性。传统大离子束流、高加速电压的FIB参数将导致低k介质多孔性增加、致密度下降;且k值越低,离子束参数影响越大。对于亚65nm工艺中使用的k值为2.7的介质,当离子束流减小到50pA、加速电压降低到5kV时,FIB制样方法对介质致密度的影响基本可忽略,样品微观形貌得到了显著改善;而对于65nm工艺中使用的k值为3.0的介质,其微观形貌受离子束参数的影响则相对较小。     

聚焦离子束技术制备超薄TEM样品-X2样品台的应用

聚焦离子束技术在制备TEM样品方面得到了广泛的应用。普通传统的制样减薄方法存在远端薄区极易弯曲和薄区厚度不均匀的问题。针对存在的这些问题本文使用Zeiss公司的X2样品台采取交叉减薄的方法制备一个具有均匀的极薄的TEM样品。本文主要介绍X2样品台的工作原理和交叉减薄的实验过程,并分析了该方法在制备TEM样品时存在的优缺点以及其独特的适用性。     

Noncontacting measurement of thickness of thin titanium silicidefilms using spectroscopic ellipsometer

Spectroscopic ellipsometry has gained increasing attention in semiconductor process control because the technique is nondestructive and noncontacting. This paper demonstrates the capability of spectroscopic ellipsometer to measure the thickness of conducting thin films of titanium silicide. Unlike cross section TEM measurement, this technique does not involve elaborate process of sample preparation. This technique does not require calibration and is used to determine thickness of silicide films from few tens of angstrom up to tens of nanometer. The thickness of titanium silicide film measured at a single point, using spectroscopic ellipsometer and TEM analysis differs by only 4%     

Cross-sectional nanoprobing sample preparation on sub-micron device with fast laser grooving technique

Cross-sectional sample preparation is one of the most important failure analysis (FA) techniques in the semiconductor industry. It was commonly used for film stack critical dimension measurement, defect identification, electrical fault isolation and etc. However, cross-sectional sample preparation to a specific target location on a sub-micron device is very challenging and time-consuming. This is because of mechanical polishing easily caused metal smear, delamination, film peel-off, micro-cracked and etc. This paper focused on cross-sectional nanoprobing (XNP) sample preparation improvement in quality and quantity. A laser blast to deprocess or create a groove at near to target location before conventional mechanical polishing and focus ion beam (FIB) fine milling. The proposed technique not only reduces the sample preparation time to the sub-micron target location but also prevent mechanical damages that caused by mechanical polishing technique.     

A review of focused ion beam technology and its applications in transmission electron microscopy

The role of focused ion beam (FIB) fabrication in the development of sample preparation techniques for transmission electron microscopy (TEM) has been described in this paper. Since the repeatability of FIB sampling and TEM observations has become important, the microsampling and in situ lift-out methods are currently in wide use. Furthermore, artifacts induced during FIB milling and the consequent difficulties with energy dispersive X-ray spectroscopy are detailed. The remarkably increased capability of scanning ion microscopy and its applications are also discussed.     

晶圆制造、运输、封装过程中Al焊垫污染源的研究

半导体芯片上Al键合焊垫在集成电路器件良率测试和封装中是非常重要的。研究焊垫污染来源对晶圆制造和金线键合工艺的改进将会有极大的帮助。结合案例采用扫描电子显微镜(SEM)、能量弥散X射线探测器(EDX)、透射电子显微镜(TEM)、聚焦离子束显微镜(FIB)等分析研究了焊垫污染的来源。结果表明,键合焊垫上的F沾污的来源可能与顶层金属蚀刻或焊垫打开过程中的蚀刻气体或者运输相关;异常焊垫上较高的C和O可能是在晶背减薄过程中引入的;运输过程中的包装纸导致了异常焊垫上O和K沾污;异常焊垫上的Si尘埃形成于晶粒切割过程中;焊垫腐蚀区域的Cl则来源于焊垫蚀刻气体。     

适用于深沟槽结构观测的TEM样品制备技术

对于深沟槽DRAM电容这类纵向深度深(超过5μm)但是平面尺寸又很小(小于0.2μm×0.2μm)的结构来说,传统的TEM制样方法,无法满足其细微结构全面观测的需求,此外传统的方法制样也比较费时,成功率也比较低。介绍了一种FIB横向切割技术,适用于对这类结构的观测。它与传统FIB制样方法的主要区别在于,切割方向由纵向切割改为横向切割。用这种方法制备的TEM样品,可以完整地观测同一个深沟槽DRAM电容结构的所有细微结构。制样过程比较简单、速度快、成功率高。以一个实例分析、比较了传统制样方法和新的制样方法,突显了FIB横向切割技术的优点。