Electron microscopy of geometrically confined copper thin films after rapid lateral solidification A. Kulovits ⁎, R. Zhong, J.M.K. Wiezorek, J.P. Leonard Department of Mechanical Engineering and Materials Science, University of Pittsburgh, 648 Benedum Hall, 3700 O' Hara Street, Pittsburgh, PA 1526, USA abstract article info Article history: Received 10 March 2008 Received in revised form 29 October 2008 Accepted 13 November 2008 Available online xxxx Keywords: Laser processing Rapid solidification Texture Copper Solidification microstructure We have used transmission electron microscopy and scanning electron microscopy to study the microstructure in polycrystalline 200 nm thick copper thin films that are geometrically confined between transparent amorphous silicon oxide layers after single pulse laser melting and rapid lateral solidification (RLS). The microstructure consisted predominantly of directionally solidified grains with an in-plane columnar structure and dimensions of up to 22 μm long and about 1 μm wide. A b100N preferred orientation in the vicinity of the average growth direction in the thin film plane has been identified for these high aspect ratio columnar grains produced by RLS in this Cu thin film12. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Polycrystalline metal thin films are used in a variety of device applications, where combinations of their electromagnetic, thermal, mechanical, and surface-chemical properties are critical [1,2]. These properties frequently depend sensitively on the thin film microstructure, including morphology, scale and orientations of grains. A detailed understanding of the microstructural evolution during processing of metal and alloy thin films is therefore important for optimization of properties for performance in a given device application. We have recently used single-pulse excimer laser-induced rapid lateral solidification (RLS) to produce large, very high aspect ratio grains in thin Cu films that are geometrically confined between amorphous silicon oxide capping- and under-layers on Si [3]. Rapid solidification processing of metals and alloys can produce a wide variety of non- equilibrium phases and microstructural configurations that are of interest for technologically useful thin films [2]. However processes such as melt spinning and spray deposition [4] are typically difficult to integrate with silicon-based thin film micro-devices. We have pre- viously demonstrated the ability of RLS to produce unique microstruc- tures in site-specific locations in sputtered metal thin films on a standard Si wafer substrate [3]. The RLS process involves complete melting of a localized area, usually spot shaped, in the geometrically confined metal film with a single laser pulse, followed by lateral re-solidification into the molten pool. It is typically completed on a time scale of several hundred nanoseconds [3,5,6]. In contrast to other multiple-pulse and scanned laser techniques the RLS technique utilizes a single pulse and also represents a departure from traditional solid phase recrystallization of thin films, offering the ability to attain ultra-large-grain microstructures at precise locations on a wafer. Process conditions and film configura- tions for obtaining RLS microstructures have been given in detail previously [2]. Here we report results of microstructural studies of re- solidified films by transmission and scanning electron microscopy (TEM and SEM) with a focus on crystallographic texture produced by the RLS process. We used orientation-imaging microscopy (OIM) by electron backscatter diffraction (EBSD) in the SEM to determine the texture in the RLS Cu thin film. Specifically, we report the observation of a strong preference in selection of crystallographic orientations along the solidification direction of the ultra large grains produced by this process. 2. Experimental details A nominally 200 nm thick Cu film and 580 nm amorphous SiO 2 capping layer were prepared by room-temperature magnetron sputter deposition on a substrate consisting of 1 μm thermally grown amorphous SiO 2 on a standard silicon wafer. This provides a thin Cu metal film geometrically confined, or encapsulated, above and below by amorphous SiO 2 . Details of the sample preparation are given elsewhere [6]. We used a Philips X'pert X-ray diffractometer operating with Cu-K α radiation and equipped with a specialized texture cradle for texture studies of the as-deposited Cu film. The multilayer film structure was irradiated in selected locations with a single pulse from a KrF Thin Solid Films xxx (2008) xxx–xxx ⁎ Corresponding author. E-mail address: akk8@pitt.edu (A. Kulovits). TSF-25411; No of Pages 6 0040-6090/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2008.11.132 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf ARTICLE IN PRESS Please cite this article as: A. Kulovits, et al., Thin Solid Films (2008), doi:10.1016/j.tsf.2008.11.132