《电镜材料检测方法》ppt课件

1、扫描电子显微术扫描电子显微术Scanning Electron Microscopy电子显微的一个粗略年表电子显微的一个粗略年表1930年末：第一台透射电子显微镜年末：第一台透射电子显微镜1935年：德国的年：德国的Knoll提出了扫描电提出了扫描电镜的概念镜的概念(STEM的概念的概念, 100mm 分分辩率辩率)1938年：年：Von Ardenne开场进展实验开场进展实验室研讨，室研讨，SEM-50 mm分辨率分辨率1942：Zworykin. Hillier, 制成了第制成了第一台实验室用的扫描电镜一台实验室用的扫描电镜 - 今天扫描电镜的全部根本原理今天扫描电镜的全部根本原理 - 5

2、0 nm 分辨率分辨率 - 问题问题: 贵贵, 照相曝光时间长照相曝光时间长,电子干扰噪声电子干扰噪声 结论结论: SEM 不适用不适用!1948：C.W. Oatley, 剑桥大学剑桥大学SEM 的历史的历史19381938年年ArdenneArdenne用一个透射电镜用一个透射电镜(TEM)(TEM)的光栅电子束第一次推的光栅电子束第一次推断了断了 SEM SEM 19421942年年, Zworkin, Zworkin等人第一次为块状样品开展了等人第一次为块状样品开展了SEM .SEM .19651965年，第一台商品年，第一台商品SEM.SEM.SEMSEM的分辨率被不断地提高从的分辨

3、率被不断地提高从1942 1942 年的年的50nm50nm到今天的到今天的0.5nm.0.5nm.SEM SEM 检测信号用于检测信号用于 确定成分信息确定成分信息, , 如如 特征特征X-X-射线射线, , 背散射背散射电子电子, ,阴极发光阴极发光, , 俄歇电子和样品电流等。俄歇电子和样品电流等。第一个扫描电镜安装第一个扫描电镜安装剑桥大学，剑桥大学，1951年年第一台商用扫描电镜第一台商用扫描电镜 High Resolution Field Emission SEMSEM images have a natural 3D lookAnd now a look inside the S

4、EM.SEM-Scanning Electron Microscope (or microscopy)TEM- Transmission Electron MicroscopeAEM- Analytical Electron MicroscopeSTEM- Scanning Transmission Electron MicroscopeEPMA-Electron Probe MicroAnalyzerSPM-Scanned Probe Microscope (STM, AFM)To see a VIRTUAL SEM, go to the following link:micro.magne

5、/primer/java/electronmicroscopy/magnify1/index.htmlSEM 的构造的构造气动保险阀扫描线圈扫描线圈Signals available from SEMSignalsSEM的主要性能：的主要性能：1，分辨率，分辨率二次电子和俄歇电子的分辨二次电子和俄歇电子的分辨率高，特征率高，特征X射线调制成显射线调制成显微图像的分辨率最低。微图像的分辨率最低。电子束进入轻元素样品电子束进入轻元素样品 滴状作用体积滴状作用体积电子束进入重元素样品电子束进入重元素样品 半球状作用体积半球状作用体积SEM的分辨率即二次电子相的分辨率即二次电子相的分

6、辨率的分辨率电子束进入重元素样品后，电子束进入重元素样品后，立刻向横向扩展，因此在分立刻向横向扩展，因此在分析重元素时，即使电子束的析重元素时，即使电子束的束斑很细小，也不能到达较束斑很细小，也不能到达较高的分辨率，此时二次电子高的分辨率，此时二次电子和背散射电子之间的分辨率和背散射电子之间的分辨率的差距明显变小。的差距明显变小。影响影响SEM分辨率的三大要素：电子束的束斑大小，检测信号的分辨率的三大要素：电子束的束斑大小，检测信号的类型以及检测部位的原子序数类型以及检测部位的原子序数SEM分辨率的测定方法：分辨率的测定方法：在知的放大倍数普通在知的放大倍数普通在在10万倍的条件下，万倍的条件

7、下，把在图像上测到的最小把在图像上测到的最小间距除以放大倍数所得间距除以放大倍数所得数值就是分辨率。数值就是分辨率。When theoretically considering the electron probe diameter alone, the higher the accelerating voltage, the smaller is the electron probe. However, there are some unnegligible demerits in increasing the accelerating voltage. They are mainly as

8、 follows:1) Lack of detailed structures of specimen surfaces. 2) Remarkable edge effect. 3) Higher possibility of charge-up. 4) Higher possibility of specimen damage.In SEM, finer surface structure images can generally be obtained with lower accelerating voltages. At higher accelerating voltages, th

9、e beam penetration and diffusion area become larger, resulting in unnecessary signals (e.g., backscattered electrons) being generated from within the specimen. And these signals reduce the image contrast and veils fine surface structures. It is especially desirable to use low accelerating voltage fo

10、r observation of low-concentration substances.加速电压对 SEM 像的影响 Always consider Interaction Volume扫描电子显微术：例子The effect of Accelerating Voltage on SEM Images 30 kV10 kV 5 kV 3 kVSpecimen: Toner 墨粉When high accelerating voltage is used as at (a), itis hard to obtain the contrast of the specimen surfacest

11、ructure. Besides, the specimen surface is easilycharged up. The surface microstructures are easilyseen at (b).(a) 30 kV x 2,500(b) 5 kV x 2,500Specimen: Evaporated Au particles.The image sharpness and resolution are betterat the higher accelerating voltage, 25 kV.(a) 5 kV x 36,000(b) 25 kV x 36,000S

12、pecimen: Filter paper.At 5 kV, the microstructures of the specimensurface are clearly seen as the penetration anddiffusion area of incident electrons is shallow.(a) 5 kV x 1,400(b) 25 kV x 1,400Fig. 6 Specimen: Sintered powder.At low accelerating voltage, while surface microstructurescan be observed

13、, it is difficult to obtain sharp micrographsat high magnifications. (a) 5 kV x7,200(b) 25 kV x7,200Specimen: Paint coat.When a high accelerating voltage is used, more scatteredelectrons are produced from the constituent substanceswithin the specimen. This not only eliminates the contrastof surface

14、microstructures, but produces a differentcontrast due to backscattered electrons from thesubstances within the specimen.(a) 5 kV x2,200(b) 25 kV x2,200SE (secondary electron) imagingHigh resolution (better than 5nm) is obtainable with most SEMsBetter than 2 nm resolution is possible in some cases10

15、nm resolution is very routine (unless the sample limits the resolution, as is often the case)二次电子： 在入射电子作用下被轰击出来并分开样品外表的样品原子 的核外电子。这也是一种真空自在电子 。 由于原子核和外层价电子间的结合能很小，因此，外层的电子较容易和原子脱离，使原子电离。用IS表示二次电子流。 一个能量很高的入射电子射入样品时，可以产生许多自在电子。其中90%来自于外层价电子。 特 征： 1)二次电子能量较低。普通不超越50 ev，大部分几ev；2)来自表层510nm深度范围；3)对样品外表化

16、形状非常敏感，因此能有效地反映样品外表的形貌；4)其产额与原子序数间没有明显的依赖关系。因此，不能进展成分分析。 成像原理二次电子产额对微区外表的几何外形非常敏感，如下图，随入射束与试样外表法线夹角增大，二次电子产额增大。 由于电子束穿入样品激发二次电子的有效深度添加了，使外表5-10 nm作用体积内逸出外表的二次电子数量增多。 根据上述原理画出二次电子形貌衬度的表示图 对于实践样品，外表形貌要比上面衬度的情况复杂得多，但构成二次电子衬度的原理是一样的。 实践样品中二次电子的激发过程表示图 1)凸出的尖棱，小粒子以及比较陡的斜面处SE产额较多，在荧光屏上这部分的亮度较大 2)平面上的SE产额较

17、小，亮度较低。 3)在深的凹槽底部虽然能产生较多二次电子，使其不易被控制到，因此相应衬度也较暗。 Edge effect (secondary electron emission differing with surface condition).Influence of edge effect on image qualityAmong the contrast factors for secondary electrons, the tilt effect and edge effect are both due to the specimen surface morphology. Se

18、condary electron emission from the specimen surface depends largely on the probes incident angle on the specimen surface, and the higher the angle, the larger emission is caused. The objects of the SEM generally have uneven surfaces.There are many slants all over them, which contribute most to the c

19、ontrast of secondary electron images. On the other hand, large quantities of secondary electrons are generated from the protrusions and the circumferences of objects on the specimen surface, causing them to appear brighter than even portions.Specimen IC chip.The higher the accelerating voltage, the

20、greater is theedge effect, making the edges brighter.Influence of edge effect on image qualityThe degree of the edge effect depends on the accelerating voltage. Namely, the lower the accelerating voltage, the smaller the penetration depth of incident electrons into the specimen. This reduces bright

21、edge portions, thus resulting in the microstructures present in them being seen more clearly.Normally, secondary electron images contain some backscattered electron signals. Therefore, if the tilt direction of the specimen surface and the position of the secondary electron detector are geometrically

22、 in agreement with each other, more backscattered electrons from the tilted portions are mixed, causing them to be seen more brightly due to synergism.(a) 5 kV x720 Tilt Angle: 50(b) 25 kV x720 Tilt Angle: 50Specimen: IC chip.5 kV x1,100The sides of patterns are viewed by tilting the specimen.The am

23、ount of signals is increased.Use of specimen tilt：a) Dependence of image quality on tilt angle1) Improving the quality of secondary electron images; 2) Obtaining information different form that obtained when the specimen is not tilted, that is, observing topographic features and observing specimen s

24、ides. 3) Obtaining stereo micrographs.Fig. 13 shows a photo taken at a tilt angle of 0 (a) and a photo taken at 45 (b). Their comparison shows that the latter is of smooth quality and stereoscopic as compared with the former. When the specimen is tilted, however lengths observed are different from t

25、heir actual values. When measuring pattern widths, etc., therefore, it is necessary to measure without specimen tilting or to correct values obtained form a tilted state.(a) Tilt angle: 0(b) Tilt angle: 45Specimen: Back sides of oleaster leaves. Moreinformation is obtained from stereo-pair photos.Us

26、e of specimen tilt：b) Stereo micrographsWith SEM images it is sometimes difficult to correctly judge their topographical features. In such a case observation of stereo SEM images makes it easy to understand the structure of the specimen. Besides, stereo observation allows unexpected information to b

27、e obtained even from specimens of simple structure. In stereo observation, after a field of interest is photographed, the same field is photographed again with the specimen tilted from 5 to 15. Viewing these two photos using stereo glasses with the tilting axis held vertically provides a stereo imag

28、e.Use of specimen tilt：c) Detector position and specimen directionThe amount of secondary electrons produced when the specimen is illuminated with an electron beam, depends on the angle of incidence theoretically. However, there arises a difference in the image brightness depending on whether the ti

29、lted side of the specimen is directed to the secondary electron detector or the opposite side.With a long specimen, for example, the brightness differs between the side facing the detector and the opposite side.In such a case, directing the longitudinal axis of the specimen to the detector makes the

30、 brightness uniform.Fig. 16 Specimen: FiberDetector position and specimen direction.Specimen: Fiber7kV x2,200Directing the longitudinal axis of the specimen to the secondary electron detector makes the right and left sides equally bright.(An SRT unit is used to direct the image longitudinally.)Use o

31、f specimen tilt：c) Detector position and specimen direction(a) Specimen directed as at 1(b) Specimen directed as at 2(c) Specimen directed as at 3Backscattered electrons vary in their amount and direction with the composition, surface topography, crystallinity and magnetism of the specimen. The cont

32、rast of a backscattered electron image depends on (1) the backscattered electron generation rate that depends on the mean atomic number of the specimen, (2) angle dependence of backscattered electrons at the specimen surface, and (3) the change in the backscattered electron intensity when the electr

33、on probes incident angle upon a crystalline specimen is changed.Use of backscattered electron signals背散射电子：背散射电子是指被固体样品中的原子核或核外电子反弹回来的一部分入射电子。用Ib示背散射电子流。 弹性背散射电子：普通样品外表原子核反弹回来可达数千至数万ev。 非弹性背散射电子：电子在固体中经过一系列散射后最终由原子核反弹的或由核外电子产生的，不仅方向改动，能量也有不同程度的损失。其能量分布范围很宽，数十ev至数千ev。 特征： 1)弹性背散射电子远比非弹性背散射电子所占的份额多 ；2

34、)能量高，例如弹性背散射，能量达数千至数万ev ；3)背散射电子束来自样品外表几百nm深度范围 ；4)其产额随原子序数增大而增多 ；5)用作形貌分析、成分分析原子序数衬度以及构造分析通道花样。Retractable BSE detector in chamberObjectivelensSecondary detector (ETD)BSE paths and detector locationsObjectivelensBSE from adjacent regions on flat sampleSEM Compositional imageBackscattered SEM image

35、of an PbSn alloy showing contrast based on the atomic number. The brighter areas are Pb-rich.1 背散射电子的衬度原理及运用 背散射电子用于：1形貌分析来自样品表层几百nm范围2成分分析产额与原子序数有关3晶体构造分析基于通道花样衬度1BE形貌衬度特点1用BE进展形貌分析时，其分辨率远比SE像低。2图象衬度很强，衬度太大会失去细节的层次。以下图是检测器接纳BE和SE的情况BE能量高，以直线轨迹逸出样品外表，对于背向检测器的样品外表，因检测器无法搜集到BE而变成一片阴影，因此，其图象衬度很强，衬度太大会失

36、去细节的层次，不利于分析。因此，BE形貌分析效果远不及SE，故普通不用BE信号2BE原子序数衬度原理 原子序数Z与背散射电子产额的关系如图。E40，对E非常敏感。进展分析时，样品上原子序数较高的区域中由于搜集到的背散射电子数量较多，故在荧光屏上的图象较亮。因此，利用原子序数呵斥的衬度变化可以对各种金属和合金进展定性的成分分析。需留意以下二点： 1用BE进展成分分析时，为防止形貌衬度对原子序数衬度的干扰，被分析的样品只进展抛光，而不用腐蚀。2既进展成分分析又要进展形貌分析时，可采用对称分布的检测器搜集信号同一部位的BE，然后计算机处置分别得到形貌信号和成分信号。如下图。a成分有差别，形貌无差别b

37、形貌有差别，成分无差别c成分形貌都有差别 相加为成分像相减为形貌相The backscattered electron image contains two types of information:one on specimen composition and the other on specimentopography. To separate these two types of information, a paired semiconductor detector is provided symmetrically with respect to the optical axis.

38、 Addition of them gives a composition image while subtraction gives a topography image. And with composition images of crystalline specimens, the difference in crystal orientation can be obtained as the so-called “channeling contrast, by utilizing the advantage that the backscattered electron intens

39、ity changes largely before and after Braggs condition.Use of backscattered electron signalsPrinciples of composition image and topography imageSE versu BSE images of alloyObjectivelensCu/Zn Alloy, SE (left), BSE (right).0.1 Atomic Number Difference.6.2 吸收电子成像的衬度原理及运用 如前所述，吸收电子产生的电流 当样品很厚，It = 0，那么：

40、所以，吸收电子象的衬度是与背散射电子和二次电子像的衬度是互补的。 实践上，SE信号与原子序数没有明显关系，因此，可以以为，背散射电子像和吸收电子像衬度正好相反。The generation region of backscattered electrons is larger than that of secondary electrons, namely, several tens of nm. Therefore, backscattered electrons give poorer spatial resolution than secondary electrons. But bec

41、ause they have a larger energy than secondary electrons, they are less influenced by charge-up and specimen contamination.Use of backscattered electron signalsTOPOX-ray (Si)X-ray (Al)BEISEICOMPOSpecimen: Slug20kV x1,100The backscattered electron image is important also as a supplementary means for x

42、-ray analysis.Influence of charge-up on image quality Specimen: Resist.Charge-up can be prevented by properly selecting the accelerating voltage.(a) 1.0 kV x3,200(a) 4 kV(b) 10 kV(b) 1.3 kV x3,200Specimen: Foreleg of vinegar fly.Charge-up can be reduced by using low accelerating voltage.Specimen dam

43、age by electron beamSpecimen: Compound eye of fly. 5 kV x1,00When a specimen area is irradiated with an electron probe for a long time at high magnification, it may be damaged as shown in (b).(b)(a)ContaminationWhen the electron probe is irradiated on a specimen portion fora long time, its image may

44、 lose sharpness and become dark. Thisis caused by the residual gas in the vicinity of the specimen beingstruck by the electron probe. This phenomenon is called specimencontamination.The conceivable residual gases in the specimen chamber, whichcause contamination are:1) Gas caused from the instrument

45、 itself.2) Gas that specimens bring into the instrument3) Gas that the specimen itself gives off.Specimen: ITO.A x18,000 photo taken after a long-time electron probe scanning at x36,000. As compared with the clear image of peripheral region, the middle region shows reduced contrast and lacks image s

46、harpness.5 kV x18,000电子探针显微分析X-ray Microanalysis Comparison of Energy Dispersive Spectroscopy EDS能谱仪能谱仪 and Wavelength Dispersive Spectroscopy spectra WDS波谱仪波谱仪能谱仪成分分析的特点能谱仪成分分析的特点:优点优点:1, 探测探测X射线的效率高，射线的效率高，( 探头与样品近探头与样品近,不用不用经过分光晶体衍射经过分光晶体衍射)能谱仪的灵敏度比波谱仪能谱仪的灵敏度比波谱仪高一个数量级。高一个数量级。2, 可在同一时间内对分析点内一切元素可

47、在同一时间内对分析点内一切元素x射线射线光子的能量进展测定和计数，几分钟内可得光子的能量进展测定和计数，几分钟内可得到定性分析结果到定性分析结果,而波谱仪只能逐个逐个丈量而波谱仪只能逐个逐个丈量每种元素的特征波长。每种元素的特征波长。3, 构造简单，没有机械传动部分，因此稳定性构造简单，没有机械传动部分，因此稳定性和反复性都很好。和反复性都很好。4, 不用聚焦，对样品外表没有特殊要求，适宜不用聚焦，对样品外表没有特殊要求，适宜于粗糙外表的分析任务。于粗糙外表的分析任务。缺陷缺陷:1，分辨率低于波谱仪。，分辨率低于波谱仪。 EDS: 160eV WDS:510eV2，只能测试，只能测试Z大于大于

48、11的元素的元素,而波谱仪可测而波谱仪可测Z从从4到到92间的一切元素。间的一切元素。 EDS里里Si(Li)探测器的铍窗口限制探测器的铍窗口限制3， Si(Li)探测器必需求液氮冷却。探测器必需求液氮冷却。 电子探针的主要功能就是进展微区成分分析。它是在电子光学和X射线光谱学原理的根底上开展起来的一种高效率分析仪器。 其原理是：用细聚焦电子束入射样品外表，激发出样品元素的特征X射线，分析特征X射线的波长或能量可知元素种类；分析特征X射线的强度可知元素的含量。其镜筒部分构造和SEM一样，检测部分运用X射线谱仪，用来检测X射线的特征波长波谱仪和特征能量能谱仪，以此对微区进展化学成分分析。 EPM

49、A的构造和任务原理：的构造和任务原理：电子探针的信号检测电子探针的信号检测系统是系统是X射线谱仪射线谱仪6.2.2 能量分散谱仪能谱仪能量分散谱仪能谱仪EDS 1. 任务原理任务原理 利用不同元素利用不同元素X射线光子特征能量不同特点进展成分分析射线光子特征能量不同特点进展成分分析 锂漂移硅能谱仪锂漂移硅能谱仪Si(Li)框图框图 X-ray Microanalysis Overview of EDS system 电子绝缘体场效应晶体管能谱仪成分分析的特点能谱仪成分分析的特点:优点优点:1, 探测探测X射线的效率高，射线的效率高，( 探头与样品近探头与样品近,不用不用经过分光晶体衍射经过分光晶体衍射)能谱仪的灵敏度比波谱仪能谱仪的灵敏度比波谱仪高一个数量级。高一个数量级。2, 可在同一时间内