Structure and stability of cobalt-silicon-germanium thin films

The phase formation and stability of CoSi2 on strained epitaxial Si0.80Ge0.20/Si (001) thin films has been investigated. Silicide films prepared via direct deposition of cobalt (Co/SiGe), and via co-deposition of silicon and cobalt (Co+2Si/SiGe), were compared. EXAFS, XRD, and sheet-resistance measurements indicated that co-deposited Co+2Si films annealed at 400-700 degrees C exhibit the expected low-resistivity CoSi2 structure but were susceptible to roughening, pinhole formation, and agglomeration. In contrast, the Co/SiGe structure formed CoSi2 only after annealing at 700 degrees C and silicide formation was accompanied by Ge segregation in the contact region. In situ RHEED experiments indicated that growth of CoSi2 co-deposited on SiGe at 400-500 degrees C results in immediate island formation. Template methods, which are often used to enhance the quality of co-deposited Co+2Si/Si structures, did not lead to two-dimensional growth in the Co+2Si/SiGe system. In situ EXAFS measurements of 2 A Co films deposited on SiGe substrates and annealed at 450 degrees C suggested that the failure to achieve two-dimensional growth th may be due to preferential bonding of Co to Si atoms at the interface. which prevents the formation of a continuous CoSi2 template. (C) 1997 Elsevier Science B.V.