THERMAL-STABILITY STUDY OF TIN TISI2 DIFFUSION BARRIER BETWEEN CU ANDN+SI/

The failure mechanism of the TiN/TiSi2 bilayers as diffusion barriers between Cu and n+Si was investigated. The TiN/TiSi2 bilayers were form ed by either annealing Ti (50 nm)/n+Si via various rapid thermal proce sses or reactively sputtering TiN (50 nm) on TiSi2. The degradation st udy of the Cu/TiN/TiSi2/n+Si contact system was undertaken by scanning electron microscopy, cross-section transmission electron microscopy ( XTEM), secondary-ion-mass spectrometry (SIMS), and diode leakage curre nt and contact resistance measurements. Leakage current measurements i ndicated no deterioration of n+-p diode junctions up to 475-degrees-C for 30 min in a N2 ambient. For the sintering temperature at 500-degre es-C, the leakage current increased abruptly and SIMS profiles reveale d a large amount of Cu atoms diffusing into the junctions of n+-p diod es. XTEM showed that the small pyramidal-shaped Cu3Si crystallite (wit h a size 0.25 mum) precipitated in the n+Si substrate. The formation o f Cu3Si increased the occupied volume, then generated the gap between TiSi2 and n+Si, and gradually increased the specific contact resistanc e. The diffusion resistance, depending on the thickness of TiN film, w as also observed.