Pulsed Plasma with Synchronous Boundary Voltage for Rapid Atomic Layer Etching

提案标题：用于快速原子层蚀刻的具有同步边界电压的脉冲等离子体主要研究员：Economou，Demetre J.研究所：休斯顿大学提案编号：CBET-0903426该提案将进行研究，以开发一种实用方法的原理和技术，通过脉冲蚀刻设备的电子设备来一次一个原子单层地蚀刻表面。创造这样一种方法是推进纳米科学和纳米技术的迫切需要。新的，有希望的中心想法是脉冲等离子体和离子轰击，而不是反应气体。目前的等离子刻蚀技术不具备对小于20 nm的精细结构进行图案化所需的控制水平或无损伤特性。与用于脉冲气体注射的快速作用机械阀门相比，控制电等离子喷涂器应该容易得多。此外，传统的原子层刻蚀(Alet)非常慢，因为它通过长时间的反应物吸附和净化步骤来脉冲引入刻蚀气体，但新型的Alet应该具有快得多的刻蚀速率(X30)，因为电脉冲可以比机械脉冲进行得快得多。基本知识将出现在脉冲等离子体，等离子体-表面相互作用，以及等离子体辅助形成纳米结构的新方法。后者将对纳米技术的各个领域产生广泛的影响，允许制造新兴技术，包括用于光电子学、量子器件和纳米结构的突变异质结构界面和极薄的层。在该奖项下开展的研究中，将为快速ALET开发具有同步边界电压的新型脉冲等离子体方法。将使用静电屏蔽的电感耦合等离子体(ICP)，其中主要包含稀有气体和微量(例如，1%Cl2)反应气体。因为等离子体电势将低于化学溅射？在阈值下，应该可以在约1 S处形成饱和产物(例如，用于硅刻蚀的SiClx)层，而不需要刻蚀。这一层将通过近单能离子轰击来去除，该离子轰击是在快速脉冲的电感耦合等离子体功率(例如，50？ON/100？OFF)的短时间段(~0.5GV)内产生的，结合在大部分余辉(电感耦合等离子体断电)期间施加到边界电极(边界电压)的正直流偏置电压的同步脉冲。在此期间，离子能量将被精确控制为高于化学溅射的阈值，但低于衬底的物理溅射阈值，从而导致自限蚀刻。边界电压的同步脉冲也将使离子角分布(IAD)变得更尖锐，约为±3°。窄的iAD对于具有垂直侧壁的高度各向异性的刻蚀是必不可少的，尤其是对于刻蚀纳米孔。为了了解脉冲等离子体与同步边界电压之间的复杂相互作用，将进行等离子体实验和模拟，包括测量时间分辨的离子轰击能量和角分布。这些实验将与刻蚀实验相结合，包括惰性气体离子质量、反应物(氯、溴、碘)质量和电负性对亚表面晶格损伤和Alet单层精度的影响。现场和非现场诊断将被用来测量作为化学吸附层表面复盖率和衬底损伤的函数的产品去除率。这项研究将涉及两名博士生、两名本科生和几项外展活动，包括与等离子体科学联盟的合作，以提高公众对等离子体社会效益的认识。本科生(超过50%的休斯顿大学学生是少数族裔)以及一名教师将通过该大学的本科生研究经验(REU)和教师研究经验(RET)计划进行招聘。

Proposal Title: Pulsed Plasma with Synchronous Boundary Voltage for Rapid Atomic Layer EtchingPrincipal Investigator: Economou, Demetre J. Institution: University of HoustonProposal No: CBET-0903426 This proposal will conduct research to develop the principles and techniques for a practical method of etching surfaces away, one atomic monolayer at a time, by pulsing the electronics of an etching device. Creating such a method is a critical need for advancing nanoscience and nanotechnology. The novel, promising central idea is to pulse the plasma and ion bombardment rather than the reactive gases. Current plasma etching techniques do not have the level of control or damage-free nature that is needed for patterning delicate structures smaller than 20 nm. It should be far easier to control electrical plasma applicators as compared to fast acting mechanical valves used to pulse gas injection. Furthermore, conventional Atomic Layer Etching (ALET) is very slow because it pulses the introduction of etching gases with long reactant adsorption and purging steps, but the new type of ALET should have a much faster etching rate (x30) because electrical pulsing can be performed much faster than mechanical pulsing. Basic knowledge will emerge on pulsed plasmas, plasma-surface interactions, and new methods for plasma-aided formation of nanostructures. The latter will have broad impact on diverse areas of nanotechnology, permitting the fabrication of emerging technologies including abrupt heterostructure interfaces and extremely thin layers for optoelectronics, quantum devices, and nanostructuresIn the research carried out under this award, novel pulsed plasma methods with synchronous boundary voltage will be developed for rapid ALET. An electrostatically shielded, inductively coupled plasma (ICP) will be employed, containing mostly rare gas with a trace (e.g., 1% Cl2) of reactive gas. Because the plasma potential will lie below the ?chemical sputtering? threshold, it should be possible to form a saturated product (e.g., SiClx for Si etching) layer in about 1 s, without etching. This layer will then be removed by nearly monoenergetic ion bombardment, created in a short period (~0.5 s) of rapidly pulsed ICP power (e.g., 50ì ON / 100ì OFF), combined with synchronous pulses of a positive DC bias voltage applied to a boundary electrode (boundary voltage) during most of the afterglow (ICP power OFF). During this period, the ion energy will be precisely controlled to lie above the threshold for chemical sputtering but below the threshold for physical sputtering of the substrate, resulting in self-limiting etching. Synchronous pulsing of the boundary voltage will also sharpen the ion angular distribution (IAD) to about ±3°. Narrow IADs are essential for highly anisotropic etching with vertical sidewalls, especially for etching nanoholes. Plasma experiments and simulations will be performed to understand the complex interactions between the pulsed ICP and the synchronous boundary voltage, including measurements of time-resolved ion bombardment energy and angular distributions. These will be coupled with etching experiments including the effect of noble gas ion mass, and reactant (Cl, Br, I) mass and electronegativity on sub-surface lattice damage and ALET monolayer accuracy. In-situ and ex-situ diagnostics will be employed to measure product removal rate as a function of chemisorbed layer surface coverage and substrate damage. Silicon and GaN ALET will be investigated, but the method will be applicable to a variety of substrates.Educationally, the research will involve two PhD students, two undergraduates, and several outreach activities, including a collaboration with the Coalition for Plasma Science to increase public awareness for societal benefits of plasmas. Undergraduate students (more than 50% of the University of Houston students are minorities) as well as a teacher will be recruited with the help of the Research Experience for Undergraduates (REU) and Research Experience for Teachers (RET) programs of the university.