Diffusion Barrier and Adhesion Properties of SiO x N y and SiO x Layers between Ag/Polypyrrole Composites and Si Substrates Barbara Horva ́ th,* Jin Kawakita, and Toyohiro Chikyow MANA, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan ABSTRACT: This paper describes the interface reactions and diffusion between silver/polypyrrole (Ag/PPy) composite and silicon substrate. This composite material can be used as a novel technique for 3D-LSI (large-scale integration) by the fast infilling of through-silicon vias (TSV). By immersion of the silicon wafer with via holes into the dispersed solution of Ag/PPy composite, the holes are filled with the composite. It is important to develop a layer between the composite and the Si substrate with good diffusion barrier and adhesion characteristics. In this paper, SiO x and two types of SiO x N y barrier layers with various thicknesses were investigated. The interface structure between the Si substrate, the barrier, and the Ag/PPy composite was characterized by transmission electron microscopy. The adhesion and diffusion properties of the layers were established for Ag/PPy composite. Increasing thickness of SiO x proved to permit less Ag to transport into the Si substrate. SiO x N y barrier layers showed very good diffusion barrier characteristics; however, their adhesion depended strongly on their composition. A barrier layer composition with good adhesion and Ag barrier properties has been identified in this paper. These results are useful for filling conductive metal/polymer composites into TSV. KEYWORDS: flexible composites, barrier layers, oxides, diffusion, adhesion 1. INTRODUCTION As a direct consequence of Moore’s law, downsizing of large- scale integration (LSI) for improved performance is expected to reach its limit in the near future with the continuous demand for higher packing density and lower power. For further integration of LSI, the chips are stacked vertically, known as 3D-LSI (large-scale integration). While there are many methods to connect the chips (such as wire-bonding), the latest and most effective method is by direct contact between the layers. The key technology for this is the through-silicon via (TSV) where conductive electrical wiring is provided in the vertical direction between the LSI chips in a via form. 1 Currently, copper electroplating is the preferred method for filling conductive material into these vias, 2,3 although it takes more than 1 h to complete the process including the pretreatment. 4 Apart from the long creation time, Cu electroplating has several other bad properties as well, such as multiple processing steps throughout production, difficulty to create deep TSVs with high aspect ratios, large differences in coefficient of thermal expansion (CTE) between Si and Cu (CTE ∼ 3 and 17 ppm/K, respectively), 5 and the rapid and aggressive diffusion of Cu into Si or SiO 2 . 6 We are developing composites of metal and conducting polymer to obtain a faster TSV infilling method by the immersion of a Si wafer obtained with vias into a dispersed solution of this composite. These composites are useful for TSV filling because it is a good replacement for Cu electroplating. Most conductive polymers have relatively low electrical conductivity properties; however, by forming composites with additional metals such as Ag, 7 Pd, 8 or Au, 9,10 good conductive performance can be achieved, making it applicable for electronic devices. The composites discussed in this paper are produced by the oxidation of pyrrole with Ag ions, with a photoassisted reaction occurring by UV irradiation, increasing the growth rate of the composite. The combination of silver with the conducting polypyrrole (PPy) resulted in highly conductive (2 × 10 4 Ω -1 ·cm -1 ) composite, which is hundreds of times higher than the commercial conducting polymers. 11 The structure of the dispersed conducting polymer- coated colloidal particles has been observed by various reports in the past. Depending on the reaction conditions, the structure can be varied from single Ag-core structure with the polypyrrole acting as a shell, 12-14 to a raspberry-like structure where Ag is located on the surface of a polymer. 12,15,16 Until now, the main uses of conducting Ag/PPy composites were for gas sensors, 17,18 catalysis, 19,20 antimicrobial coating, 21,22 or inkjet printed conducting wiring for flexible electronics. 7 Ag/ PPy composite has been proved as an excellent material for the electric wiring of flexible electronic devices, as it is conductive, flexible, cheap and has sufficient adhesion to the substrate. Received: March 4, 2014 Accepted: May 28, 2014 Published: May 28, 2014 Research Article www.acsami.org © 2014 American Chemical Society 9201 dx.doi.org/10.1021/am501305b | ACS Appl. Mater. Interfaces 2014, 6, 9201-9206