Tailoring the Crystallographic Texture and Electrical Properties of Inkjet-printed Interconnects for Use in Microelectro
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Tailoring the Crystallographic Texture and Electrical Properties of Inkjet-printed Interconnects for Use in Microelectronics Romain Cauchois1,2, Mohamed Saadaoui2, Karim Inal2, Beatrice Dubois-Bonvalot1 and JeanChristophe Fidalgo1 1 Innovation and Manufacturing Technologies Department, Gemalto, 13881 Gemenos, FRANCE 2 Centre Microelectronique de Provence, Ecole Nationale Supérieure des Mines de SaintEtienne, 880 avenue de Mimet 13541 Gardanne, FRANCE ABSTRACT In this paper, silver nanoparticles with a mean diameter of 40 nm are studied for future applications in microelectronic devices. The enhanced diffusivity of nanoparticles is exploited to fabricate electrical interconnects at low temperature. Sintering condition has been tuned to tailor the grain size so that electrical resistivity can be lowered down to 3.4 μOhm·cm. In this study, a {111}-textured gold thin film has been used to increase diffusion routes. The combined effects of the substrate crystalline orientation and the sintering condition have been demonstrated to have a significant impact on microstructures. In particular, a {111} fiber texture is developed above 300°C in printed silver only if the underlying film exhibits a preferential orientation. This condition appeared as essential for the efficiency of the gold wire-bonding process step. Thus, inkjet-printed interconnects show a prospective potential compared to conventional subtractive technique and offers new opportunities for low cost metallization in electronics packaging. INTRODUCTION Additive printing technologies have gained tremendous interest as a pathway to large area and flexible electronics. Among several printing methods, drop-on-demand inkjet printing is a non contact and digital technique that allows fast prototyping without any waste. This technology can thus be advantageously adapted for the realization of interconnects on silicon ICs for low cost electronic packaging [1]. Those interconnects are patterned by jetting a colloidal suspension of metal nanoparticles whose thermodynamic size effect is exploited to reduce the sintering temperature [2,3]. Printed features should exhibit a low electrical resistivity and high mechanical properties for being compatible with subsequent wire bonding step. Tuning those physical properties are particularly challenging since an optimization of microstructure through a solidstate sintering is required. Hence, a proper IC compatible post-process using a well-timed temperature profile has to be properly adjusted. Electrical conduction of patterns is thermally activated both by the evaporation of solvents and by the sintering of metallic nanoparticles. Sintering is a complex physical phenomenon which operates as soon as solvents are evaporated to cast bonds between particles. Amongst mechanisms, surface diffusion, grain boundary diffusion and lattice diffusion are dominant in nanoparticles. Since a large stress is required for plastic flow in a nanoparticulate system, it is believed that dislocation-driven plastic flow is unlikely to be a major contr
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