Effect of Si in reactively sputtered Ti-Si-N films on structure and diffusion barrier performance

Two ternary films about 100 nm thick, Ti34Si23N43 (b3) and Ti35Si13N52 (c3), are synthesized by reactively sputtering a Ti5Si3 or a Ti3Si target, respectively. The silicon-lean film (c3) has a columnar structure closely resembling that of TiN. As a diffusion barrier between a shallow Si n(+)p junction diode and a Cu overlayer, this material is effective up to 700 degrees C for 30 min annealing in vacuum, a performance similar to that for TiN. The silicon-rich (b3) film contains nanocrystals of TiN. randomly oriented and embedded in an amorphous matrix. A him of (b3) maintains the stability of the same diode structure up to 850 degrees C for 30 min in vacuum. This film (b3) is clearly superior to TiN or to (c3). Similar experiments performed with Al instead of Cu overlayers highlight the importance of the thermodynamic stability of a barrier layer and demonstrate convincingly that for stable barriers the microstructure is a parameter that directly determines the barrier performance.