Reliability study of sub-micron titanium silicide contacts

Kelvin bridge type contact resistance test structures were fabricated for studying the behavior of p-type titanium silicide contacts of sub-micron dimensions. The shallow junctions were formed by using the implant through metal (ITM) technique. SIMS profiles showed that the boron concentration at the silicide-Si interface was about 2 × 1020 cm−3. The resulted specific contact resistivity was in the range of (3–6) × 10−7 Ω·cm2. For the contacts whose smallest size is 0.5 × 0.5 μm2, the contact resistance still increased linearly with the inverse of contact area. Electrical stress test revealed that the sub-micron contacts exhibited degradation phenomena even though a titanium tungsten layer was deposited prior to depositing aluminum contact pads. In some cases, the degradation rate was found to be dependent on the polarity of stressing current. This study indicates that the reliability of sub-micron contacts needs to be seriously considered.