Microstructure and surface proﬁling study on the inﬂuence of substrate type on sputtered aluminum thin ﬁlms F.M. Mwema a,b,⇑ , E.T. Akinlabi a , O.P. Oladijo a,c a Department of Mechanical Engineering Science, University of Johannesburg, Auckland Park Kingsway, South Africa b Department of Mechanical Engineering, Dedan Kimathi University of Technology, Nyeri, Kenya c Department of Chemical, Metallurgy & Materials Engineering, Botswana International University of Science & Technology, Palapye, Botswana article info Article history: Received 26 September 2019 Received in revised form 22 October 2019 Accepted 14 February 2020 Available online 2 March 2020 Keywords: Aluminum thin ﬁlms Microstructure Sputtering Substrate Surface roughness abstract In this article, the inﬂuence of the type of substrates on properties of aluminum thin ﬁlms prepared through sputtering technology is presented. The deposition was undertaken at constant substrate tem- perature of 90 °C and RF power of 350 W for 2 h on glass and steel substrates. Microstructural properties were analyzed using ﬁeld emission scanning electron microscopy (FESEM). The optical non-contact sur- face proﬁler (OSP) was used to study the topology and roughness characteristics of the ﬁlms on different substrates. The results show that ﬁlms grown on mild and stainless-steel substrates exhibited different morphologies and surface topology from those grown on glass substrates, indicating the inﬂuence of the substrate type on the deposition, nucleation, growth and ﬁlm formation of Al thin ﬁlms. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientiﬁc committee of the 10th International Con- ference of Materials Processing and Characterization. 1. Introduction Aluminum thin ﬁlm is extensively used as an interconnection material in large scale integrated circuits (IC). They are also used as thin ﬁlm materials for liquid crystal display (LCD) systems. These applications are necessitated by their attractive attributes such as low resistivity of 2.65–2.82 Â 10–8 XÁm (in fact it is the fourth lowest resistive material after silver, copper and gold), high adhesion to various substrates and generally affordable and avail- able [1]. Aluminum is also a stable material and therefore attrac- tive for electronic applications. Aluminum thin ﬁlms are also used in optical devices such as front-surface or reﬂective surfaces of MEMS mirrors, interferometry, solar concentrators and cookers due to good reﬂectance properties (for instance, 90% solar reﬂec- tance) [2–6]. Aluminum is preferred (to silver) for optical reﬂec- tance in concentrated solar plants (CSP) since it less prone to tarnishing, higher mechanical strength and it naturally forms alu- mina on its surface which makes it environmentally stable [2,7]. In electronic applications, Al thin ﬁlms are mostly deposited on silicon and silicon (IV) oxide (SiO 2 ) substrates. The deposition of these ﬁlms on such substrates is associated with some challenges such as formation of hillocks and reaction between the substrate and the ﬁlms. Hillocks usually form at temperatures above 300 °C, (although on glass they can form at lower temperatures during sputtering [8]) and can be prevented in two ways: (i) by addition of second phase metals into the Al matrix during deposi- tion such as Cu [3] and (ii) sandwiching Al ﬁlms onto two metallic layers such as titanium [9–11]. To enhance interface adhesion and strength between Al and Si/SiO 2 , annealing must be undertaken. The best annealing temperature for electrical conductivity is 450 °C; however, at this temperature, the two materials tend to dissolve into each other to eutectic point. This forms an alloy which interferes with the electrical conductivity of the ﬁlms. This prob- lem is avoided by introducing a barrier layer of metal between the Al and Si substrate. In this way, the metal barrier becomes the substrate for the deposition process. As such, there are mostly three substrates for preparation of Al thin ﬁlms namely, Si/SiO 2 , metals and glass. Although several studies have reported on properties of Al thin ﬁlms sputtered on different substrates, there are very few of them discussing a direct relationship on the inﬂuence of the substrate type. One of the few studies comparing the properties of Al thin ﬁlms sputtered on glass, silicon wafer and steel substrates is that by Khachatryan et al. in 2018 [9]. The study revealed important results on the inﬂuence of the substrate type on the growth of Al thin ﬁlms: (i) The growth rate of the grains for Al thin ﬁlms https://doi.org/10.1016/j.matpr.2020.02.309 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientiﬁc committee of the 10th International Conference of Materials Processing and Characterization. ⇑ Corresponding author. E-mail address: fredrick.mwema@dkut.ac.ke (F.M. Mwema). Materials Today: Proceedings 26 (2020) 1496–1499 Contents lists available at ScienceDirect Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr