Ultra-thin metal layers by plasma-assisted spatial atomic layer deposition at atmospheric pressure

超薄金属薄膜提供了电学、光学和等离子体特性的独特组合，影响了广泛的应用，其中包括薄膜光电器件的半透明电极。不幸的是，在广泛的衬底上沉积金属薄膜会导致纳米尺寸的岛状图案。因此，在渗透阈值以下，该层具有低电导率。一旦达到渗透阈值，电导率就会增加几个数量级。通常，热蒸发或溅射的银或金等金属的渗透阈值约为10-15纳米。为了改善金属层的润湿性，人们考虑了几种方法，如表面功能化、使用合金和在沉积过程中轻微氧化金属。超薄金属层的大量研究要么采用溅射沉积，要么采用热蒸发。相反，原子层沉积法（ALD）生长铸造金属Ag或Cu还处于起步阶段。有利的是，ALD可以精确控制薄膜厚度，在大面积上均匀生长，并在高纵横比的微纳米结构上进行保形沉积。今天，ALD是一种成熟的技术，用于生长介电层，特别是金属氧化物，用于许多应用。等离子体辅助ALD （PA-ALD）使非氧化物材料，如氮化物和金属的生长。为了克服传统真空ALD的局限性，在大气压下引入了空间ALD，它甚至适用于卷对卷加工。该项目的中心目标是探索空间PA-ALD在大气压下沉积超薄金属薄膜。我们打算根据基底、空间APP-ALD的加工参数（温度、等离子体和前驱体剂量等）和金属前驱体的类型，对这些金属层的成核和生长有一个基本的了解。最终目标是具有高导电性和高透光率的薄金属层的APP-ALD。因此，针对低温（< 120°C）空间APP-ALD，需要完成以下研究任务：•开发具有高蒸汽压和高反应性的新型Ag和Cu前体，以在低温下还原等离子体，并具有足够的热稳定性。•研究成核和成膜的初始阶段。•确定APP-ALD金属层的透光率和导电性极限。•探索表面功能化的可能性，例如通过有机官能团或非氧化物无机薄膜。•考虑大气压MLD，在金属的APP-ALD生长过程中加入微量有机分子，以抑制聚类，同时保持高导电性。

Ultra-thin metal films provide a unique combination of electrical, optical and plasmonic properties, which impact a wide range of applications, among them semitransparent electrodes for thin-film optoelectronic devices. Unfortunately, the deposition of thin metal films on a wide range of substrates results in nanometer sized island-like patterns. Thus, below the percolation threshold, the layer has a low conductivity. The conductivity increases by orders of magnitude once the percolation threshold is reached. Typically, the threshold for percolation of metals like Ag or Au which are thermally evaporated or sputtered is on the order of 10-15 nm. To improve wetting of the metal layer several approaches such as surface functionalization, the use of alloys, and slight oxidation of the metal during deposition have been considered.The vast amount of studies on ultra-thin metal layers employed either sputter deposition or thermal evaporation. On the contrary, the growth of coinage metals Ag or Cu by atomic layer deposition (ALD) is still in its infancy. Advantageously, ALD allows for a precise control of film thickness, homogeneous growth over large areas and a conformal deposition on micro- and nanostructures with high aspect ratios. Today, ALD is a well-established technique to grow dielectric layers, especially metal-oxides for a number of applications. Plasma-assisted ALD (PA-ALD) enables the growth of non-oxide materials, such as nitrides and metals. To overcome the limits of conventional vacuum based ALD, spatial ALD at atmospheric pressure has been introduced, which is even suitable for roll-to-roll processing. The central aim of this project is to explore spatial PA-ALD at atmospheric pressure for the deposition of ultra-thin metal films. We intend to gather a fundamental understanding of the nucleation and growth of these metal layers depending on the substrate, the processing parameters of the spatial APP-ALD (temperature, plasma and precursor dose, etc.) and the type of metal precursor. The ultimate goal is the APP-ALD of thin metal layers with a high conductivity and high optical transmittance. Therefore, low temperature (< 120°C) spatial APP-ALD of is targeted which requires the following research tasks:• To develop novel Ag and Cu precursors with high vapor pressure and high reactivity towards reducing plasma at low temperatures, with sufficient thermal stability. • To study the initial stages of nucleation and film formation. • To identify the limits of transmittance and conductivity of the APP-ALD metal layers. • To explore the possibility of surface functionalization, e.g. by organic functional groups or by non-oxide inorganic films. • Consider atmospheric pressure MLD to include trace amounts of organic molecules in the APP-ALD growth process of the metal to suppress clustering while at the same time retain high electrical conductivity.