THERMAL-STABILITY OF THIN COSI2 LAYERS ON POLYSILICON IMPLANTED WITH AS, BF2, AND SI

The thermal stability of thin cobalt silicide layers grown on preamorp hized chemical vapor deposited silicon layers has been studied in the temperature range between 950 and 1100 degrees C. The morphology of th e starting layers and their evolution during the thermal processes was analyzed by transmission electron microscopy, atomic force microscopy and Rutherford backscattering spectroscopy. The observed increase in sheet resistance with the annealing time has been correlated to the ag glomeration process taking into account the dependence of the resistiv ity on film thickness and carrier mean free path. Sheet resistance mea surements have been used to study the agglomeration process of CoSi2 b y varying temperature and substrate doping (As, BF2, and Si implants). The process is thermally activated with an activation energy of 4.3 e V for the Si implanted samples. The BF2 implanted substrate show a hig her activation energy (similar to 5.4 eV), while the arsenic implanted a lower one (similar to 3.6 eV). This difference is attributed to the weakening of the Go-Si bonds by arsenic atoms and to the presence of some fluorine precipitates at the CoSi2/Si interface that increase the energy needed for the reaction at the silicide/silicon interface. (C) 1998 American Vacuum Society.