Nickel Germanosilicide contacts formed on heavily boron doped Si1-xGex source/drain junctions for nanoscale CMOS

Formation of source/drain junctions with a small parasitic series resistance is one of the key challenges for CMOS technology nodes beyond 100 nm. A new source/drain technology based on selective deposition of heavily in situ doped Si_1-xGe_x layers was recently developed in this laboratory. This paper presents formation and structural characterization of self-aligned nickel germanosilicide contacts formed on heavily boron doped Si_1-xGe_x alloys. The results show that thin NiSi_1-xGe_x contacts with a resistivity of ∼25 μΩ-cm can be formed on Si_1-xGe_x alloys at temperatures as low as 350°C. However, the low resistivity and the structural integrity of the NiSi_1-xGe_x films can be maintained up to a maximum temperature of 450°C. At higher temperatures, Ge out-diffusion from NiSi_1-xGe_x grains results in interface roughening and NiSi spikes. If the maximum processing temperature is kept within 400°C, p⁺-n junctions with excellent leakage behavior can be formed. A minimum contact resistivity of 2×10^-8 Ω-cm² is demonstrated for Ge concentrations above ∼40%, which can be linked to the smaller semiconductor bandgap and high boron activation under the metal contact. The results suggest that NiSi_1-xGe_x contacts formed on Si_1-xGe_x junctions have the potential to satisfy the contact resistivity requirements of future CMOS technology nodes.