Bottom-up Gold Filling of High Aspect Ratio Trenches :Toward a Mechanistic Understanding

Abstract

Cu is the standard choice for the formation of multi-level 3-D interconnects allowing for microelectronic chip-stacking (1). This is predicated on the well-defined additive chemistries that drive the superconformal Cu filling of through silicon vias (TSVs) and trenches (2). To transition to Au filling of complex 3-D Si architectures for optoelectronic applications, analogous chemistries that enable preferential filling within recessed silicon features must be developed. To date the state of the art for void free Au filling has come from the use of a Pb additive in both KAu(CN)2 (3, 4) and Na3Au(SO3)2 (5) electrolytes. Both of these systems yield superconformal filling via a curvature enhanced accelerator coverage (CEAC) mechanism. However, due to the toxicity of CN- and Pb2+ containing electrolytes, alternatives must be explored. Recently, it has been demonstrated that the addition of Bi to alkaline Na3Au(SO3)2 electrolytes yields preferential bottom-up Au electrodeposition in Si trenches, with limited deposition on the free surface (6). The addition of Bi to the intrinsically suppressed Na3Au(SO3)2 electrolyte clearly accelerates deposition(6, 7). However, growth in this system does not propagate via the typical CEAC mechanism demonstrated in other accelerated systems (3). Instead the growth propagates via a mechanism more closely resembling that of S-shaped negative differential resistance (S-NDR) based on suppression breakdown, typical for suppressor based additive systems(8). This talk will explore the utilization of this Bi, Na3Au(SO3)2 electrolyte system for the bottom-up filling of high aspect ratio silicon trenches. The effect of; potential, additive concentration and electrolyte transport will be explored on the filling of features with aspect ratios ranging from 1.5 to 17. Additionally, the chemical and morphological nature of the accelerated bottoms of features, and of the passive free surface, will be compared via x-ray photoelectron spectroscopy, scanning electron microscopy and anodic stripping voltammetry to gain mechanistic insight into the role of Bi in deposition acceleration and feature localization. P. C. Andricacos, C. Uzoh, J. O. Dukovic, J. Horkans and H. Deligianni, IBM J. Res. Dev., 42, 567 (1998).T. P. Moffat, D. Wheeler, M. D. Edelstein and D. Josell, IBM J. Res. Dev., 49, 19 (2005).D. Josell, C. R. Beauchamp, D. R. Kelley, C. A. Witt and T. P. Moffat, Electrochem. Solid-State Lett., 8, C54 (2005).D. Josell, D. Wheeler and T. P. Moffat, J. Electrochem. Soc., 153, C11 (2006).D. Josell and T. P. Moffat, J. Electrochem. Soc., 160, D3009 (2013).D. Josell and T. P. Moffat, J. Electrochem. Soc., 166, D3022 (2019).I. D. E. McIntyre and W. F. Peck, J. Electrochem. Soc., 123, 1800 (1976).S.-K. Kim, J. E. Bonevich, D. Josell and T. P. Moffat, J. Electrochem. Soc., 154, D443 (2007).