Area-Selective Chemical Vapor Deposition of Thin Films: Suppression of Nucleation on Oxides by Amine Adsorption

先进的微电子芯片，无论是民用还是军用，都应该更快，执行更多的数据操作，消耗更少的电力。为了实现这些目标，未来设备的尺寸将会缩小，例如，晶体管的有效宽度将小于10纳米(0.4百万分之一英寸)。传统的芯片制造工艺涉及多个步骤，其中在整个区域上沉积一层薄薄的材料，例如金属，然后在该层上形成与器件相对应的图案，并通过化学蚀刻去除不需要的材料。然而，在如此小的尺寸下，图案化步骤变得非常困难和昂贵，因为图案必须与其下面的部分制造的器件精确对准。作为回应，该项目开发了一种方法，消除了许多图案化和蚀刻步骤的需要：开发了一种化学气相沉积路线，使一层材料选择性地沉积在已有的图案特征之上，但不会沉积在不需要的表面上。它还可以制造新的三维晶体管结构和微电子学以外的其他类型的纳米器件结构。因此，该项目的成果提高了美国高科技产业的制造能力和经济竞争力，这对国家繁荣至关重要，也是我们国防系统所需的。科学和技术成果在主要的专业会议、同行评议的文献和主要微电子行业的研讨会上得到报告。该项目还通过培训研究生研究助理来支持美国多样化劳动力的发展，研究生研究助理将这项研究作为其论文的中心重点。当将合适的胺分子(如氨)添加到前体原料(如金属羰基分子)中时，通过化学气相沉积的方法实现了金属薄膜的区域选择性沉积。在生长所需厚度的金属薄膜所需的时间内，金属薄膜(如钴或Ru)沉积在导电衬底上，而不是沉积在二氧化硅、二氧化钛、氧化铝或氧化镁等氧化物表面上。胺的作用是抑制氧化物表面的金属成核，特别是那些带有酸性羟基的氧化物表面，否则金属岛就会在氧化物表面形成。该项目测试了有关胺与氧化物表面和吸附前驱体相互作用的机理假设，包括位阻挡作用和表面从酸性向碱性转化的作用。实验变量包括不同氧化物表面的修饰、不同前体-胺组合的使用、生长温度和分压。分析方法有原位傅里叶变换红外光谱检测吸附物的同一性，椭圆偏振光谱检测成核的开始，非原位微观结构探针法检测吸附物的成键和数量。对潜在机制的科学确定将使这种方法能够可靠地用于先进的器件制造，并将其扩展到其他前体、胺和表面。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Advanced microelectronic chips, for both civilian and military applications, should be faster, perform more data operations, and consume less electrical power. To meet these goals, the size of future devices will be reduced, e.g., the active width of a transistor will be less than 10 nanometers (0.4 millionths of an inch). Conventional chip fabrication processes involve multiple steps in which a thin layer of material, such as metal, is deposited over the entire area, then a pattern corresponding to the devices is formed over that layer, and unwanted material is removed by chemical etching. However, at such small size the patterning step becomes significantly difficult and costly because the pattern must align precisely with the partially fabricated device below it. In response, this project develops an approach that obviates the need for many of the patterning and etching steps: a chemical vapor deposition route is developed such that a layer of material deposits selectively on top of already-existing pattern features, but does not deposit on surfaces where it is not wanted. It can also enable the fabrication of new, three-dimensional transistor structures and other types of nanoscale device structures beyond microelectronics. Thus, the results of the project boost the manufacturing capabilities and economic competitiveness of the U.S. high technology industry critical to national prosperity and needed for our national defense systems. The scientific and technical results are reported at major professional conferences, in the peer-reviewed literature, and by seminars at major microelectronic industries. The project also supports the development of a diverse U.S. workforce through training of graduate student research assistants, who perform this research as the central focus of their dissertation. Area-selective deposition of thin metal films by chemical vapor deposition occurs when a suitable amine molecule, such as ammonia, is added to the precursor feedstock, such as a metal carbonyl molecule. The metal film, such as cobalt or ruthenium, then deposits on conductive substrate features but not on oxide surfaces such as silica, titania, alumina, or magnesia during the time required to grow the desired thickness of metal film. The role of the amine is to suppress metal nucleation on oxide surfaces, especially those with acidic hydroxyl groups, on which metal islands would otherwise form. This project tests mechanistic hypotheses concerning the interaction of the amine with the oxide surface and with adsorbed precursor, including the roles of site-blocking and conversion of the surface from acidic to basic character. Experimental variables include modification of different oxide surfaces, the use of different precursor-amine combinations, growth temperature, and partial pressures. Analytical methods are in-situ Fourier transform IR spectroscopy to detect the identity of adsorbates, and spectroscopic ellipsometry to detect the onset of nucleation, and ex-situ microstructural probes of adsorbate bonding and quantity. The scientific determination of underlying mechanisms will enable the reliable use of this approach for advanced device fabrication, as well as its extension to other precursors, amines and surfaces.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.