Cu(TiWNx) Film as a Barrierless Buffer Layer for Metallization Applications

Abstract

In this study, we explore the potential of replacing the wetting and diffusion barrier layers in a conventional under bump metallurgy (UBM) structure, underneath flip-chip solder joints, with a buffer TiWNx-bearing Cu film deposited via cosputtering, viz., barrierless Si metallization, to reduce manufacturing, including soldering, costs in microelectronic manufacture. The introduced Cu(TiWNx) films, after annealing at 700 °C for 1 h, exhibit an excellent thermal stability on, and adhesion strength to, barrierless Si substrates, without detectable Cu/Si interfacial interactions and also display a solderability comparable to that of pure Cu. At 200 °C, the Cu(TiWNx) film within an Sn/Cu(TiWNx)/Si structure shows a dissolution rate that is lower than that of pure Cu by at least one order of magnitude, comparable to that of Ni in common solder joints. The Cu(TiWNx) film thus seems to be a suitable candidate material for, at least, barrierless Si metallization and flip chip soldering.