Low-voltage-point source microscope for interferometry
Low-voltage-point source microscope for interferometry
复制标题
用于干涉测量的低压点源显微镜
DOI：
10.1117/12.473498
复制
发表时间：
2002
期刊：
影响因子：
--
通讯作者：
A. Thesen
中科院分区：
文献类型：
--
作者：
B. Frost;D. Joy;A. Thesen
传统的扫描电子显微镜现在接近其性能的极限，如亚微米设计规则器件的计量。为了克服这些限制，我们已经设计，目前正在测试，一个低电压点源显微镜与nanotip场发射器，没有任何电子光学透镜。该显微镜被设计成可以在透射模式以及反射模式下操作。超尖场发射器在能量小于100 eV的情况下提供几纳安的发射电流。通过将样品放置在来自纳米尖端的发散电子束中并在离样品很远的距离处使用微通道板（MCP）观察物波来实现物波的放大。以这种方式获得的图像是失焦图像。由于没有透镜，因此开发了一种缩放放大倍率的特殊程序。由于来自点源的电子是高度相干的，样品的散焦图像是干涉图。在样品的边缘处衍射的电子在像平面中引起菲涅耳条纹。带电的多孔碳箔以与杨氏双缝实验相同的方式作用于电子，并产生由平行条纹组成的干涉图案。透射模式和反射模式之间的比较示出了关于放大率和干涉图案的极大相似性。透射模式所需的电子枪是两种操作模式之间最重要的区别。在45度反射下的实验结果与我们的模拟吻合得很好。在我们的模拟之后，90度的反射角对于最简单的图像解释是最有希望的。
Conventional scanning electron microscopes are now close to the limit of their performance for tasks such as the metrology of sub-micron design rule devices. In order to overcome these limits we have designed, and are presently testing, a low voltage point source microscope operated with a nanotip field emitter and without any electron optical lenses. The microscope is designed such that can be operated in the transmission mode as well as in a reflection mode. The ultra-sharp field emitter delivers emission currents of several nanoamps at energies less than 100 eV. The magnification of the object wave is achieved by placing the specimen in the divergent electron beam from the nanotip and observing the object wave using a microchannel plate (MCP) at a great distance from the sample. Images obtained that way are out of focus images. As no lenses are present a special procedure for scaling the magnification has been developed. Since electrons from a point source are highly coherent the out of focus images of the sample are interferograms. Electrons diffracted at an edge of the specimen cause Fresnel fringes in the image plane. An electrically charged holey carbon foil acts in the same way on the electrons as the Youngs double slit experiment and results in an interference pattern consisting of parallel fringes. A comparison between the transmission mode and the reflection mode shows great similarities with respect to the magnification and the interference pattern. An electron gun needed in the transmission mode is the most important difference between the two modes of operation. The experimental results at a reflection of 45 degrees are in good agreement with our simulation. Following our simulations a reflection angle of 90 degrees is most promising for easiest image interpretation.