The influence of target composition and thermal treatment on sputtered Al thin films on Si and SiO 2 substrates D. Resnik a,b,⇑ , J. Kovacˇ c , M. Godec d , D. Vrtacˇnik a,b , M. Mozˇek a,b , S. Amon a,b a Laboratory of Microsensor Structures and Electronics, Faculty of Electrical Engineering, University of Ljubljana, Trzˇaška 25, Ljubljana 1000, Slovenia b Centre of Excellence Namaste, Jamova 39, 1000 Ljubljana, Slovenia c Jozef Stefan Institute, Jamova 36, Ljubljana 1000, Slovenia d Institute of Metals and Technology, Lepi pot 11, Ljubljana 1000, Slovenia article info Article history: Received 18 August 2011 Received in revised form 17 February 2012 Accepted 28 February 2012 Available online 20 March 2012 Keywords: DC sputtering Thermal annealing Al hillocks Al grains Al texture abstract Al thin films deposited by DC magnetron sputtering from two different target compositions Al–1%Si and Al–1%Si–0.5%Cu on n-type Si (1 0 0) and on SiO 2 substrates were investigated. Surface morphology was studied as a function of deposition temperature and thermal annealing of deposited Al thin films by opti- cal microscopy, SEM and AFM analyses. Hillock formation in the Al layer was found to be strongly depen- dent on the deposition temperature in the range of 373–573 K and less on the annealing temperature in the range of 573–773 K. Hillock size and density were significantly increased when Al was sputtered on SiO 2 substrate compared to Si substrates. Al grain size was increased when sputtered from Al–Si target composition compared to Al–Si–Cu and was not influenced significantly by the annealing process. Depo- sition of Al films from Al–Si–Cu target composition resulted in lower hillock density and orthogonally packed fine grain structure when deposited on (1 0 0) Si substrate. Strong (1 1 1) texture of Al films on SiO 2 substrate for both target composition and (1 0 1) texture when deposited on Si substrate were deter- mined by EBSD method. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Sputter deposition of metal thin films is widely used in the fab- rication of various microelectronic and microelectromechanical devices. Al is a common metal in microelectronics for interconnec- tions and ohmic contacts to the external periphery of devices and adheres well to silicon and dielectric layers. To suppress Al/Si inter- diffusion, which can cause spiking, 1% of Si is commonly added to pure Al. In addition to that, copper is added to avoid electromigra- tion phenomenon when conducting high current densities. Often, roughness of such thin films is increased by the appear- ance of hillocks. Hillocks are considered as local out-of-surface pro- trusions of polycrystalline Al thin films. It has been established that hillocks grow in response to the relaxation processes of compres- sive stress in Al film which occurs mainly due to thermal mismatch of deposited Al film and substrate in particular when films are sub- dued to the annealing heat treatment [1–5]. The relative softness of the aluminum easily results in plastic deformation of thin films [1]. Hillock growth is also observed in the deposition process of amor- phous materials such as thick plasma enhanced chemical vapor deposited (PECVD) amorphous silicon and can be successfully sup- pressed by tailoring the residual stress [6]. During the annealing treatment step, the processes such as grain growth and dislocation motion cause additional favorable conditions for hillock growth. The resulting Al grain size also affects the 1/f noise in RF applications [7]. Hillocks usually result in a film that is milky and exhibits reduced optical reflectivity. Hillocks can also cause short circuits between the conducting lay- ers which are separated by thin dielectric layer when their height is in the order of dielectric layer thickness in multilevel metalliza- tion schemes. Capping layers deposited on the top of Al layer were found to suppress the hillock growth [8], however in many cases this approach can not be realized due to process restrictions. To provide more accurate information on hillock formation and their suppression, our investigation was focused on thermal condi- tions that potentially influence the hillock growth and can be ap- plied during or after the metallization process step. The first thermal process investigated was the preheat step of the substrates in vacuum chamber just prior to Al sputtering sequence, defining the deposition temperature, and the second thermal process was the annealing step after the Al film was deposited on Si or SiO 2 sub- strate. A comparative study between two target compositions Al–Si and Al–Si–Cu has been carried out to reveal the influence and to determine optimal conditions for preparing the fine grained Al films with low hillock density. 0167-9317/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.mee.2012.02.048 ⇑ Corresponding author at: Laboratory of Microsensor Structures and Electronics, Faculty of Electrical Engineering, University of Ljubljana, Trzˇaška 25, Ljubljana 1000, Slovenia E-mail address: drago.resnik@fe.uni-lj.si (D. Resnik). Microelectronic Engineering 96 (2012) 29–35 Contents lists available at SciVerse ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee