Using Graphene As a Conducting and Barrier Layer for Filling through Silicon Vias with Co-W Alloy

Abstract

Usually, TSV fabrication is a dry process, including via formation by reactive ion etching, SiO2 isolation liner deposition, CVD or PVD TiN barrier layer and copper seed layer, and via filling with copper. Herein, we attempt to use graphene to simultaneously substitute the TiN barrier layer and the copper seed layer in order to simplify the TSV fabrication process. In addition, the coefficient of thermal expansion (CTE) of the filled copper often lead to failure in the TSV interconnects because the CTE of copper is much higher than that of silicon. The filled materials in the TSV with a high CTEs will induce large stresses at the interfaces between the filled material and silicon. To overcome this problem, we choose graphene to substitute the copper seed layer since the CTE of graphene is closer to that of silicon. Moreover, we select cobalt, which possesses not only a lower CTE but also a longer electromigration lifetime than those of copper, as the filled material of TSV. Tungsten can be co-deposited with cobalt, so that CoW alloy is formed in this work and the CTE of CoW alloy filled in TSV is lower than that of pure cobalt. In this work, the effects of electroplating additives, electroplating baths and operating parameters on alloy composition, filling performance and thermal reliability performance of the electrodeposited CoW alloy from Co(NH2SO3)2•4H2O, NaWO4•2H2O, C6H8O7 and Na3C6H5O7•2H2O electrolyte are investigated. On the other hand, a linear sweep voltammetry (LSV) and galvanostatic measurements are carried out to electrochemically analyze these additives. The electrochemical behaviors of these electroplating additives are explored to explain the correlation between the suppression and the corresponding filling performance. The results indicate that the combination of suppressors with different molecular weights and a leveler can exhibit strong suppression and lead to CoW bottom-up filling of TSV.