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Quantitative, high resolution two-and-three dimensional dopant mapping in the Scanning Electron Microscope by Secondary Electron Spectro-Micro

通过二次电子能谱显微镜在扫描电子显微镜中进行定量、高分辨率二维和三维掺杂剂测绘

基本信息

批准号：
EP/E029892/1
负责人：
Colin Humphreys
金额：
$ 5.82万
依托单位：
University of Cambridge
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2007
资助国家：
英国
起止时间：
2007 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FE029892%2F1
关键词：
Quantitative resolution two three dimensional

项目摘要

Mobile phones and modern electronic devices in general are becoming increasingly smaller, faster and more powerful. This is possible because electronic circuits required for their operation become smaller and smaller allowing the devices to shrink or to add more circuits in the same volume. These circuits are based on the principle that the conductivity in certain well specified areas changes when a voltage is applied. This is achieved by putting a few atoms with fewer or more electrons, called dopant atoms, into a semiconductor material such as silicon. It is crucial that exactly the correct number of atoms are put into exactly the right place. This is challenging in itself but in addition we have to make sure that we can confirm that we have achieved the right number of dopant atoms in the right place, because otherwise the device will not work to its specification. This is called dopant mapping because it links the number of dopant atoms to spatial coordinates in one (1D), two (2D) or three(3D) dimensions. For future devices we need to know how the number of dopants changes within three nanometers in 3D. The main aim of the work proposed here is to provide a solution to the above challenge. Because it is such a difficult problem to tackle many techniques have been developed so far but all have short comings. One such technique is to use a scanning electron microscope (SEM), where electrons of certain energy impinge on a surface causing other electrons, called secondary electrons (SE)s, to leave that surface. The number of SEs depends on the number of dopant atoms in the irradiated region but in a complex way and accurate quantification is therefore difficult. Also this approach does not have the potential to give us the information we need from regions as small as 3nm in diameter because, even when our impinging electron beam is that small, SEs in silicon can come from atoms12 times further below the surface. To solve this problem we propose to exploit another property of the SEs and this is their energy. SEs have a range of energies (energy spectrum) depending on how deep below the surface they were generated. We anticipate that we will be able to locate dopant atoms with a few nanometer resolutions by using high energy SEs only. We hope to obtain an accurate quantification by measuring the shift of the energy spectra of differently doped regions. To extend the 2D technique to 3D we need to remove thin layers of material in a controlled way and apply the 2D technique for each layer. Focused ion beam (FIB) instruments are made for this purpose and operate by firing Ga+ ions of a certain energy (normally 30kV) at the target surface, which leads to the removal of target surface atoms. A side effect of this technique is the incorporation of Ga in the surface. We have found that this effect is so pronounced at 30kV that a quantification of dopants is not possible. Therefore we propose to add a special low energy module to our existing FIB that allows us to reduce the Ga ion energy by up to 120 times, thus reducing the incorporation of Ga and other damage in the target surface. The proposed work addresses all the issues which currently hamper accurate, high resolution (3D) dopant mapping in the SEM. It therefore has the potential to bring us all one step closer to smaller, better and more powerful semiconductor devices in the future.

移动的电话和现代电子设备总体上正变得越来越小、更快和更强大。这是可能的，因为其操作所需的电子电路变得越来越小，允许设备缩小或在相同体积中添加更多电路。这些电路是基于这样的原理，即当施加电压时，某些特定区域的电导率会发生变化。这是通过将具有更少或更多电子的原子（称为掺杂剂原子）放入半导体材料（如硅）中来实现的。关键是要把正确数量的原子放在正确的位置。这本身就具有挑战性，但除此之外，我们必须确保我们能够确认我们在正确的位置获得了正确数量的掺杂剂原子，因为否则器件将无法按照其规格工作。这被称为掺杂剂映射，因为它将掺杂剂原子的数量与一维（1D）、二维（2D）或三维（3D）空间坐标联系起来。对于未来的器件，我们需要知道掺杂剂的数量如何在3D中在3纳米内变化。这里提出的工作的主要目的是为上述挑战提供一个解决方案。由于这是一个很难解决的问题，迄今为止已经开发了许多技术，但都是短期的。一种这样的技术是使用扫描电子显微镜（SEM），其中具有一定能量的电子撞击表面，导致称为二次电子（SE）的其他电子离开该表面。SE的数量取决于辐照区域中的掺杂剂原子的数量，但以复杂的方式，因此难以精确量化。此外，这种方法没有潜力从直径小至3nm的区域中为我们提供所需的信息，因为即使我们的撞击电子束很小，硅中的SE也可能来自表面以下12倍的原子。为了解决这个问题，我们建议利用SE的另一个属性，这是它们的能量。SE具有一定的能量范围（能谱），这取决于它们在地表以下产生的深度。我们预计，我们将能够定位掺杂剂原子的几个纳米的分辨率，仅使用高能量SE。我们希望通过测量不同掺杂区域的能谱的移动来获得准确的定量。为了将2D技术扩展到3D，我们需要以受控的方式去除材料的薄层，并对每一层应用2D技术。聚焦离子束（FIB）仪器是为此目的而制造的，并且通过在靶表面发射一定能量（通常为30kV）的Ga+离子来操作，这导致靶表面原子的去除。这种技术的副作用是Ga在表面中的结合。我们已经发现，这种效应在30kV下是如此明显，以至于掺杂剂的量化是不可能的。因此，我们建议在现有的FIB中添加一个特殊的低能量模块，使我们能够将Ga离子能量降低高达120倍，从而减少Ga的掺入和靶表面的其他损伤。所提出的工作解决了目前妨碍在SEM中进行准确的高分辨率（3D）掺杂剂映射的所有问题。因此，它有可能使我们所有人在未来更小，更好，更强大的半导体器件。