This thesis is concerned with diffusion barriers in contact structures to semiconductors. Diffusion barriers are indispensable in present contact technologies to preserve device characteristics from the influence of metal-semiconductor interaction during post-metallization processing.
The absence of grain boundaries makes amorphous W-Zr and Ni-W alloy barriers very attractive for high temperature applications. Nevetheless, in the presence of an adjoining metal layer such as Al, these amorphous barriers are chemically dissociated to form compounds with the metal. The usefulness of these barrier in VLSI metallization schemes is severely limited by their high reactivity with Al within normal processing temperature cycles. Such thermal instability can be removed, however, by adding nitrogen to the barrier layers during sputter deposition.
Becoming aware of the beneficial effects of nitrogen incorporation, we investigate the performance of nitrogen-doped W barrier films in various contact configurations. Reactively sputtered amorphous and polycrystalline W-N layers are demonstrated to be excellent diffusion barriers against interdiffusion between Si-Al, Si-Ag, GaAs-Ag, and GaAs-Au. A novel idea of utilizing W-N as an interconnect in CMOS fabrication is also discussed.
Conducting transition metal oxides emerge as a new class of diffusion barriers. Metallic Mo1-xOx films are deposited by reactive sputtering a Mo target in controlled O₂/Ar ambients. These Mo1-xOx barriers can effectively protect Si n⁺-p shallow junctions from Al spiking even beyond the eutectic temperature of Si-Al.RuO₂ films are also found to be equally good in suppressing Si-Al interdiffusion. The present study clearly shows that Mo1-xOx and RuO₂ barriers are the most outstanding performers among all the passive barriers that have been explored so far.
