Evaluation of Ti–Si–N as a diffusion barrier between copper and silicon

Amorphous Ti–Si–N films of approximately 200 and 650 Å thickness were reactively sputtered on Si wafers using a dc magnetron sputtering system at various N2/Ar flow ratios. Their barrier properties between Cu (750 Å) and Si were investigated by using sheet resistance measurements, XRD, SEM, RBS, and AES depth profiling focused on the effect of the nitrogen content in Ti–Si–N thin film on the Ti–Si–N barrier properties. As the nitrogen content increases, first the failure temperature tends to increase up to 46% and then decrease. Barrier failure seems to occur by the diffusion of Cu into the Si substrate to form Cu3Si, since no other X-ray diffraction intensity peak (for example, that for titanium silicide) than Cu and Cu3Si peaks appears up to 800°C. The optimal composition of Ti–Si–N in this study is Ti29Si25N46. The failure temperatures of the Ti29Si25N46 barrier layers 200 and 650 Å thick are 650 and 700°C, respectively.