Silicides
It has been reported that the epitaxial growth of Si:C on the source/drain regions of nMOSFET devices results in a significant enhancement of the drive current due to the introduction of tensile strain in the channel. The thermal stability of Ni-silicide contacts to Si:C layers with 1-2.5% substitutional C epitaxially grown on Si(100) substrates has been studied P15683. The effect of the total C concentration, strain level and anneal conditions were investigated. It was demonstrated that Ni silicidation is compatible with Si:C recessed source/drain (RSD) stressors for nMOS strain engineering. The addition of C increases the silicide sheet resistance as well as the grain size of the as-silicided films. Thermal stability of the NiSi:C contacts is significantly improved compared to NiSi contacts and is directly linked to C concentration : increasing C concentration allows for a higher post-silicidation thermal budget. After 30 min anneal at 750ºC, NiSi:C layers with ≥ 1.7% C remain in the low-resistive NiSi phase and show no signs of morphological degradation. In this case the dominant degradation mechanism is found to be the transition to the NiSi2 phase. It was observed that the Si:C strain level affects the NiSi:C silicide formation, however the NiSi:C thermal stability is controlled by the total C concentration. Work is ongoing to study the effect of C implantation on the thermal stability of the Ni silicide.
Figure 1: Nomarsky (top) and transmission electron microscopy (TEM) (bottom) images of the NiSi:C (2.5% C) annealed for 90s at 750ºC (left) and 900ºC (right). The silicide remains in the monosilicide phase after the 750ºC anneal (left). Upon the 900ºC anneal, the film was characterized as NiSi2. Pyramids protruding into the substrate can be observed.
The effect that the Ni alloys (Ni alloyed with Yb or Pt) and dopant segregation (S, Se, Yb, F) on the silicide diffusion contact resistance was studied. No significant improvement of the contact resistance could be observed. The pMOS characteristics are improved when Ni is alloyed with 10% Pt.
Figure 2: pMOS transistor ION-IOFF characteristics comparing performance of Ni-silicide and NiPt-silicide as S/D contact.