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

超薄金属膜提供了电学、光学和等离子体特性的独特组合，这影响了广泛的应用，其中包括用于薄膜光电器件的透明电极。不幸的是，在宽范围的衬底上沉积薄金属膜导致纳米尺寸的岛状图案。因此，低于逾渗阈值，该层具有低电导率。一旦达到逾渗阈值，电导率增加数量级。通常，热蒸发或溅射的金属如Ag或Au的渗透阈值在10-15 nm的量级。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金属的轻微氧化。相反，通过原子层沉积（ALD）生长钴金属Ag或Cu仍处于起步阶段。有利地，ALD允许精确控制膜厚度、在大面积上的均匀生长以及在具有高纵横比的微米和纳米结构上的共形沉积。今天，ALD是一种成熟的技术来生长介电层，特别是用于许多应用的金属氧化物。等离子体辅助ALD（PA-ALD）能够生长非氧化物材料，例如氮化物和金属。为了克服传统的基于真空的ALD的限制，已经引入了大气压下的空间ALD，其甚至适合于卷对卷处理。该项目的主要目的是探索在大气压下沉积超薄金属膜的空间PA-ALD。我们打算收集这些金属层的成核和生长取决于衬底，空间APP-ALD的工艺参数（温度，等离子体和前体剂量等）的基本理解。和金属前体的类型。最终目标是APP-ALD的薄金属层具有高导电性和高透光率。因此，低温（< 120°C）空间APP-ALD的目标是需要以下研究任务：· 开发具有高蒸气压和在低温下对还原等离子体的高反应性的新型Ag和Cu前体，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金属层的透射率和电导率的极限。· 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膜。· 考虑大气压MLD以在金属的APP-ALD生长过程中包括痕量的有机分子，以抑制聚集，同时保持高电导率。

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.