Mechanism of improved thermal stability of cobalt silicide formed on polysilicon gate by nitrogen implantation

It is found that the thermal stability of CoSi2 films is improved by N-2(+) implantation (I/I) because the grain size of CoSi2 films with N-2(+) I/I i s much smaller than that without N-2(+) I/I. Rutherford backscattering spec trometry (RBS) and Auger electron spectroscopy (AES) analyses show that the nucleation of CoSi2 transformation from CoSi is suppressed by N-2(+) I/I. The nucleation temperature for the sample with 5x10(15) cm(-2) N-2(+) I/I i s about 25 degrees C higher than that without N-2(+) I/I. Since the nucleat ion temperature is increased, CoSi2 films are formed incompletely at the as -formed state; thus, CoSi2 has small Brain size. As a result, the thermal s tability of CoSi2 films is significantly improved by N-2(+) I/I due to the small grain size of CoSi2.