A new contact plug technique employing selective nickel silicidation of polysilicon with a titanium nitride barrier layer has been developed. This technique provides a contact resistance equivalent to that of an unplugged metal contact, while also realizing the flatness of a polysilicon plug over contact regions. Using this technique, a completely silicided plug for both shallow and deep contact holes can be achieved at the same time. The structure of the plug was analyzed using TEM photography, EDX, and electro-diffraction measurements, and the silicidation stopping ability of the TiN layer was confirmed. The low leakage current of junction diodes and lack of transistor characteristic degradation when using the Ni silicide plug are demonstration of the integrity of this technique. The results indicate that this technology is suitable for deep-submicrometer ULSI's.