Suppression of Dewetting in Pulsed Laser Melting of Thin Metallic Films on SiO 2
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U11.6.1
Suppression of Dewetting in Pulsed Laser Melting of Thin Metallic Films on SiO2 J. Eric Kline and John P. Leonard, University of Pittsburgh, Department of Materials Science and Engineering. Pittsburgh, PA 15261 ABSTRACT Pulsed excimer laser projection irradiation has been successfully applied to completely melt and resolidify encapsulated elemental metal films of Au, Cu, Cr, and Ni directly on amorphous SiO2 substrates. A combination of narrow irradiated lines and appropriate SiO2 capping layers was used to obtain films that do not dewet when fully melted. Detailed processing maps were generated for Au and Ni, while equivalent trends for Cu and Cr were also noted. These systems were analyzed for common behaviors, and from these the principle factors, a basic process map is proposed to describe adequately these four systems. Experimental parameters and sample preparation criteria are presented to realize such resolidification studies in other metal systems. INTRODUCTION Excimer laser irradiation systems have been successfully applied in the crystallization of aSi:H and the super-lateral growth process for TFT displays for some time[1,2]. The application of pulsed laser melting to metallic systems on amorphous substrates has remained unrealized due in part to the limitation of the tendency for a wide variety of metal films to dewet upon complete melting[3-5]. These dewetting events are believed to result from a surface energy imbalance between the higher surface energy liquid metal and the lower surface energy substrate; the molten metal dewets by an agglomeration or recession process to lose coherency across the irradiated area. Traditionally, a thin adhesion layer of Cr, Ti, or W has been deposited beneath the metal film to assist in maintaining metal film attachment to the substrate. This adhesion layer may add unneeded complexity in that the adhesion layer may be modified and/or alloyed with the metal film or the substrate during the melting processes. Our studies of elemental Au, Cu, Cr, and Ni do not use an adhesion layer and are therefore without this possible complication. In a specified materials application, the interfacial free energy balance of a materials system is determined by the compositional configuration, and not by processing. This surface energy balance of a liquid metal on a substrate can be modified by the addition of a capping layer of non-interacting material. This changes the energy balance and can subsequently inhibit dewetting events, as well as inhibit large-scale fluid flow by forcing the molten film to remain in an enclosed semi-rigid volume. We have advocated in Ref. [6] that the addition of a capping layer of sufficient thickness increases the energy barrier for the nucleation and growth of holes that initiate a dewetting event. This article further explains the experimental details common to all four metal systems and presents additional findings for Cu and Cr.
U11.6.2
EXPERIMENT C
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A simple projection illumination D system using a pulsed excimer laser B (λ=248 nm, 25 n
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