The effect of TiN stuffing(the densification of the grain boundary of TiN) for Cu diffusion barrier were studied by sheet resistance measurement, X-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, and capacitance-voltage measurement. The samples with two structures of Cu(500nm)/TiN(40nm)/Ti(20nm)/Si and Cu/TiN/Ti/$SiO_2$(100nm)/Si were prepared. The TiN was stuffed with RTP treatment at various gas ambient($NH_3$, $N_2$, $H_2/Ar$) and temperatures for 1 minute. The samples were analyzed after annealing at from 500℃ to 800℃ in $10%H_2$/90%Ar ambient for 2 hours. By sheet resistance measurement, XRD, SEM and C-V measurement, it conformed that the TiN barrier of the lower RTP temperature fails at the lower annealing temperature. And by C-V measurement, it conformed that the TiN barrier of $NH_3$ ambient RTP treatment was superior to those of the different gas ambient RTP treatment.