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.