During titanium silicide(TiSi2) formation by rapid thermal annealing(RTA), the redistribution of implanted arsenic was investigated by means of Auger electron spectroscopy(AES) and secondary-ion mass sepectroscopy(SIMS). By using 30nm amorphous silicon(a-Si) film deposited sequentially on 50nm titanium film without breaking the vacuum, the As dopant redistribution is suppressed due to the reduction of consumption of silicon substrate(Si-sub) during TiSi2 formation. The AES shows that the silicon, which is required for TiSi2 formation, is supplied from the a-Si film more rapidly than from the Si-sub. Also, the conversion of deposited Ti film into TiSi2 is complete because the a-Si film on Ti film prevents the infiltration of oxygen impurity into the Ti film during the exposure to air before annealing