Formation and stability of silicides on polycrystalline silicon

Silicides are widely used in silicon integrated circuits as contacts and interconnections. In many applications silicides are used on polycrystalline silicon (polysilicon) such as the gates of FETs and the emitter of bipolar transistors. The use of silicide on polysilicon structures presents a number of unique challenges both in formation of the silicide and in morphological stability during high temperature processing. The purpose of this paper is to review the formation, morphology, and thermal stability of silicides on polysilicon. Mechanisms for silicide roughening on polysilicon are discussed including non-uniform initial reactions, agglomeration, and silicide enhanced grain growth. Results for silicides on polysilicon are compared with those on single crystal Si where relevant. A detailed description of silicide instability and device degradation is presented for a number of silicides, emphasizing TiSi2, CoSi2, and WSi2. Finally, methods for improving the stability of silicides on polysilicon are discussed.