Plasma-Surface Interactions During In-Situ Photo-Assisted Etching

反应离子蚀刻（或等离子体蚀刻）是集成电路（或“芯片”）制造中的关键操作，以产生纳米（十亿分之一米）尺度的极其精确的特征。没有这个过程，我们就不会有便携式手机，笔记本电脑和所有其他我们认为理所当然的现代奇迹。更小的特征尺寸将允许更多的晶体管被封装到芯片上，从而增加信息存储和更快的计算机。在过去的50年里，芯片速度和功能的这种演变一直在稳步发展，遵循摩尔定律，该定律指出芯片上的晶体管数量大约每18个月翻一番。最近，在研究硅的反应离子蚀刻时，有一个相当惊人的发现：即使在没有反应离子存在的情况下，硅也会被蚀刻。仔细的实验表明，这种蚀刻是由于光子，起源于等离子体。这种等离子体光辅助蚀刻产生的蚀刻特征形状对于集成电路来说不是最佳的，因此可能被证明是新兴的原子精度蚀刻领域中的一个亮点。本计画将结合联合收割机实验与模拟，以了解电浆光辅助蚀刻的机制，并找出抑制此现象的条件。这项研究将产生在等离子体-半导体界面的光物理和化学的基本理解，并将在微电子工业以及纳米技术领域产生重大影响，具有明显的社会效益。实验和模拟的结合将解决这样的问题：（a）光子和i）正离子，ii）电子，iii）负离子，iv）卤素原子的协同效应是什么？(b)鞘层电势是否影响光辅助蚀刻速率，如果是，是如何影响的，原因是什么？(c)在用亚波长特征图案化的样品的情况下，表面等离子体激元（等离子体激元）的效果是什么？将采用一种新型的双等离子体反应器，以提供受控的离子，UV-VUV光子和自由基轰击基板的通量。在差分泵浦分析室中，通过衬底保持器上的针孔测量撞击衬底的UV-VUV光强度、离子通量和离子能量。电场分布和物种（电子，空穴，正离子）在等离子体中以及在固体通量的自洽模拟，以及表面等离子体传播和吸收的电磁计算将被执行。模拟与实验相结合，将提供不同的衬底偏置（在半导体鞘的电位），光子通量和能量，掺杂剂浓度，以及纳米特征的大小和纵横比的光辅助蚀刻的机制的见解。最后，将尝试利用硅的光辅助蚀刻来产生具有尺寸（例如，3 nm直径）比通过常规反应离子蚀刻产生的那些小得多。

Reactive ion etching (or plasma etching) is a critical operation in the manufacturing of integrated circuits (or 'chips') to produce extremely precise features, at the nanometer (a billionth of a meter) scale. Without this process we would have no portable cell phones, laptop computers and all the other modern marvels we take for granted. Ever smaller feature dimensions will allow more transistors to be packed onto chips, resulting in increased information storage and faster computers. This evolution in chip speed and function has progressed steadily over the past 50 years, following Moore's Law, which states that the number of transistors on a chip doubles about every 18 months. Recently, while studying reactive ion etching of silicon, a rather startling discovery was made: silicon was etched, even when no reactive ions were present. Careful experiments revealed that this etching was due to photons, originating in the plasma. This in-plasma photo-assisted etching produced etched feature shapes that are not optimum for integrated circuits and thus may prove to be a show-stopper in the burgeoning field of etching with atomic precision. This project will combine experiments and simulations to understand the mechanism of in-plasma photo-assisted etching, and identify conditions to suppress this phenomenon. The study will produce a fundamental understanding of the photo-physics and chemistry at the plasma-semiconductor interface and will have a significant impact in the microelectronics industry as well as the field of nanotechnology, with clear societal benefits.This systematic investigation of plasma-surface interactions will focus on in-situ photon-plasma synergism, and its effect on etching of semiconductor materials in halogen-containing plasmas. A combination of experiments and simulations will address questions such as: (a) What are the synergistic effects of photons and i) positive ions, ii) electrons, iii) negative ions, iv) halogen atoms? (b) does the sheath potential affect photo-assisted etching rates and if so, how and what is the cause? (c) what is the effect of surface plasmons (plasmonics) in the case of samples patterned with sub-wavelength features? A novel dual plasma reactor will be employed, to provide controlled fluxes of ions, UV-VUV photons, and radicals bombarding the substrate. The UV-VUV light intensity, ion flux and ion energy striking the substrate will be measured through a pinhole on the substrate holder, in a differentially pumped analysis chamber. Self-consistent simulations of the electric field distribution and species (electrons, holes, positive ions) fluxes in the plasma as well as in the solid, and electromagnetic calculations of surface plasmon propagation and absorption will be performed. Simulations coupled with experiments will provide insights in the mechanism of photo-assisted etching for varying substrate bias (potential of the sheath over the semiconductor), photon flux and energy, dopant concentration, as well as nanofeature size and aspect ratio. Finally, attempts will be made to exploit photo-assisted etching of silicon to create nanoholes with dimensions (e.g., 3 nm dia.) much smaller than those produced by conventional reactive ion etching.