Diffusion barrier properties of AlMoNbSiTaTiVZr high-entropy alloy layer between copper and silicon Ming-Hung Tsai ⁎ , Jien-Wei Yeh, Jon-Yiew Gan Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 300, Taiwan Available online 14 July 2007 Abstract The application of an AlMoNbSiTaTiVZr high-entropy alloy film as diffusion barrier for copper metallization has been investigated. The AlMoNbSiTaTiVZr and copper layers are deposited sequentially, without breaking vacuum, onto silicon substrates by DC magnetron sputtering. The AlMoNbSiTaTiVZr films are found to possess a stable amorphous structure due to their high-entropy and limited diffusion kinetics. The AlMoNbSiTaTiVZr high entropy alloy film is determined to prevent copper–silicide formation up to 700 °C for 30 min. Thus, HEAs appear to have potential use as effective diffusion barriers for copper metallization. © 2007 Elsevier B.V. All rights reserved. Keywords: High-entropy alloy; Diffusion barriers; Amorphous structure; Thermal stability 1. Introduction With the ever-increasing demand for higher circuit density and reduced RC time delay in microelectronics, there has been a drive towards the replacement of aluminum by copper for the interconnection material, due to the improved resistance to electromigration and lower resistivity of the latter. Unfortunately, the high diffusivity of Cu into Si or SiO 2 at elevated temperatures is a serious issue for device reliability. This facilitates the use of a diffusion barrier layer between copper and Si or SiO 2 , which, due to the continual scaling down of the interconnections, must be as thin as possible. These diffusion barrier layers are therefore required to have excellent high-temperature chemical and struc- tural stability. Furthermore, due to grain boundaries of crystalline materials offering fast diffusion paths for copper, the barrier layer is required to have an amorphous structure [1]. In recent efforts to produce efficient diffusion barrier layers for Cu metallization, a variety of methods have been explored. Some research has focused on modifying conventionally used systems, such as the addition of a thin Al interlayer to improve the performance of TiN diffusion barrier layers [2]. Another approach is to alloy copper with a strong oxide former, such as Al, Mg or Mn [3,4]. The use of alternative process techniques, such as atomic layer deposition (ALD) [5], has also been examined. The most recently explored diffusion barrier layers appears to be the ultrathin organic layers produced by the self-assembled mono- layer (SAM) technique [6,7], however the low working tempera- ture is a drawback of these barrier layers. An alternative candidate material, known as “high-entropy alloy” (HEA), is considered in the present work for its potential use in diffusion barrier applications. HEAs are defined as alloys that are composed of at least five principal metal elements, with the concentration of each principal element ranging from 5 to 35 at.% [8]. It has been found that HEAs exhibit a wide range of novel properties, such as the tendency to form multiprincipal element solid solutions instead of numerous complex compounds [9], the development of nanoscale or even amorphous structures without the need for special process treatments [8,10], have wide ranging mechan- ical properties [8], exhibit good corrosion properties [11,12], show limited diffusion kinetics [8,13] and have high thermal stability [8]. The high thermal stability, amorphous forming capability and limited diffusion kinetics suggest HEAs to have great potential to be used as diffusion barrier materials. In the present work, the diffusion barrier capabilities of an equimolar AlMoNbSiTaTiVZr HEA shall be examined. A standard Cu/HEA/Si test structure, with the barrier thickness set at 100 nm, shall therefore be produced in order to test the Available online at www.sciencedirect.com Thin Solid Films 516 (2008) 5527 – 5530 www.elsevier.com/locate/tsf ⁎ Corresponding author. Department of Materials Science and Engineering, National Tsing Hua University, 101, Sec. 2, Kuang Fu Road, Hsinchu 300, Taiwan. Tel.: +886 3 5742621; fax: +886 3 5722366. E-mail address: d927526@oz.nthu.edu.tw (M.-H. Tsai). 0040-6090/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.07.109