FORMATION AND STABILITY OF SILICIDES ON POLYCRYSTALLINE SILICON

Silicides are widely used in silicon integrated circuits as contacts a nd interconnections. In many applications silicides are used on polycr ystalline silicon (polysilicon) such as the gates of FETs and the emit ter of bipolar transistors. The use of silicide on polysilicon structu res presents a number of unique challenges both in formation of the si licide and in morphological stability during high temperature processi ng. The purpose of this paper is to review the formation, morphology, and thermal stability of silicides on polysilicon. Mechanisms for sili cide roughening on polysilicon are discussed including non-uniform ini tial reactions, agglomeration, and silicide enhanced grain growth. Res ults for silicides on polysilicon are compared with those on single cr ystal Si where relevant. A detailed description of silicide instabilit y and device degradation is presented for a number of silicides, empha sizing TiSi2, CoSi2, and WSi2. Finally, methods for improving the stab ility of silicides on polysilicon are discussed.