Thermal stability of nanoscale silver metallization in Ag/W/Co/Si(1 0 0) multilayer O. Akhavan a , A. Azarm a , A.Z. Moshfegh a, * , M.A. Bahrevar b a Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran, Iran b Materials and Energy Research Center, P.O. Box 14155-4777, Tehran, Iran Available online 18 January 2006 Abstract In this work, we have studied thermal stability of nanoscale Ag metallization and its contact with CoSi 2 in heat-treated Ag(50 nm)/W(10 nm)/ Co(10 nm)/Si(1 0 0) multilayer fabricated by sputtering method. To evaluate thermal stability of the systems, heat-treatment was performed from 300 to 900 8C in an N 2 ambient for 30 min. All the samples were analyzed by four-point-probe sheet resistance measurement (R s ), Rutherford backscattering spectrometry (RBS), X-ray diffractometry (XRD), and atomic force microscopy (AFM). Based on our data analysis, no interdiffiusion, phase formation, and R s variation was observed up to 500 8C in which the Ag layer showed a (1 1 1) preferred crystallographic orientation with a smooth surface and R s of about 1 V/&. At 600 8C, a sharp increase of R s value was occurred due to initiation of surface agglomeration, WSi 2 formation, and interdiffusion between the layers. Using XRD spectra, CoSi 2 formed at the Co/Si interface preventing W silicide formation at 750 and 800 8C. Meantime, RBS analysis showed that in this temperature range, the W acts as a cap layer, so that we have obtained a W encapsulated Ag/CoSi 2 contact with a smooth surface. At 900 8C, the CoSi 2 layer decomposed and the layers totally mixed. Therefore, we have shown that in Ag/W/Co/Si(1 0 0) multilayer, the Ag nano-layer is thermally stable up to 500 8C, and formation of W-capped Ag/CoSi 2 contact with R s of 2 V/& has been occurred at 750–800 8C. # 2005 Elsevier B.V. All rights reserved. PACS: 68.60.Dv; 68.37.Ps; 68.55.Jk Keywords: Silver; Nano-metallization; Co silicide; W interlayer 1. Introduction By the year 2010, typical dimensions of wires and contacts in ultralarge-scale integration (ULSI) are predicted to shrink down to values less than 50 nm [1]. Since current densities and clock frequencies will dramatically increase, future demands on advanced metallization are a serious challenge, and Ag next to Cu is one of the most promising materials for novel metallization schemes. Ag posses the lowest resistivity among all metals and its high oxidation resistance differentiates it from Al and Cu. On the issue of electromigration, Ag provides an electromigration resistance better than Al. In addition, it was measured that sputtered Ag can reach the same electromigra- tion resistance as Cu grown by chemical vapor deposition [2]. These properties of Ag make it one of the promising high- conductivity candidates to be considered as a possible interconnect material for future ULSI technology. However, Ag has some disadvantages such as weak adhesion to SiO 2 [3], high diffusivity in SiO 2 [4], agglomeration upon annealing [5], and corrosion in sulfur and chlorine ambient [6]. Thus, thin film structures of only pure Ag are not suitable for ICs interconnects. To overcome these stability problems, similar to Cu metallization [7–10], a buffer layer should be applied between Ag layer and Si substrate, which may also result in a self- encapsulation process to enhance further the reliability of Ag metallization. Concerning this, some various buffer layers such as SiO 2 [11], Ti, TiN and Ti(O)N [12,13], TaN [12,14], TiW and also some dielectric materials [12], Al [15,16] and Cu [17] have been used. In addition, a valuable review about the encapsulated Ag metallization can be found in [18]. It is worthy to note that, the mainstream of Ag metallization will be in contact with silicides including TiSi 2 , CoSi 2 , and NiSi [19,20]. Although these silicides can act as a buffer layer resulting www.elsevier.com/locate/apsusc Applied Surface Science 252 (2006) 5335–5338 * Corresponding author. Fax: +98 21 6601 2983. E-mail address: moshfegh@sharif.edu (A.Z. Moshfegh). 0169-4332/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2005.12.070