Reactively Sputtered Amorphous TaSi_xN_y Films Serving as Barrier Layer Against Copper Diffusion

Abstract

Reactively sputtered amorphous TaSi x N y ( x =1.4, y =2.5) films of different thicknesses (5 to 40 nm) serving as diffusion barriers were studied for Cu metallization. The Cu/TaSi x N y /p + n junction diodes with 5-nm-thick TaSi x N y barriers were able to sustain a 30 min thermal annealing at temperatures up to 400°C without degradation of the electrical characteristics. With thicker barriers of 10-, 20- and 40-nm-thick TaSi x N y layers, the thermal stability temperatures of the Cu/TaSi x N y /p + n junction diodes were increased to 500, 550 and 650°C, respectively. The amorphism of TaSi x N y films on Si substrates remains unchanged at temperatures up to 800°C, whereas the presence of a Cu overlayer on the surface of the TaSi x N y /Si structure accelerates the formation of Ta-silicide. Failure of the amorphous TaSi x N y diffusion barrier is presumably due to Cu diffusion through the barrier layer by way of localized defects.