Low-temperature, fine-pitch interconnections using self-patternable metallic nanoparticles as the bonding layer

Abstract

High speed digital and mixed signal applications are driving short and more reliable fine pitch interconnection with higher I/O count in 3D architectures. Thin film die to wafer and wafer to wafer bonding with copper-based interconnections have several benefits in terms of low cost, process compatibility with semiconductor infrastructure, and the shortest interconnection with the best electrical performance. However, the bonding is accomplished at around 400 C, with pressures exceeding 30 N/cm2 which may not be compatible with thinned dies, and in ultrahigh vacuum and cleanroom environments with careful copper oxide cleaning procedures. The bonding time is typically 1 hour, which also limits the throughput. The process windows are relatively narrow with several temperature compatibility issues. This paper deals with low temperature bonding process using high surface energy metallic nanoparticles such as copper and gold. Bonding is enhanced by accelerated diffusion kinetics. Self patterning technique has also been developed to assist fine pitch bonding. This is based on selective wetting or selective deposition of nanoparticles.