Germanosilicide contacts to ultra-shallow p(+)n junctions of nanoscale CMOS integrated circuits by selective deposition of in-situ doped silicon-germanium alloys

Future CMOS requires new junction and contact formation technologies to produce source/drain junctions with super-abrupt doping profiles, above equilibrium dopant activation and contact resistivity values near 10 −8 ohm-cm2. Recently, this laboratory demonstrated a new junction formation technology based on selective deposition of heavily doped Si_1−xGe_x alloys in source/drain regions isotropically etched to the desired depth, which has the potential to meet all junction and contact requirements of future CMOS technology nodes. Of particular interest to this thesis is the smaller bandgap of Si_1−x Ge_x resulting in a smaller metal-semiconductor barrier height, which is a key advantage in reducing the contact resistivity of a metal-semiconductor contact. In this work, formation of germanosilicide contacts to heavily boron doped Si_1−xGe_x alloys was studied with the intention to find a contact solution for future CMOS technology nodes beyond 100 nm.; Germanosilicides of Ti, Co, Ni, Pt, W, Ta, Mo and Zr were studied and NiSi_1−xGe_x was found to be the most promising candidates as source/drain contacts. Low resistivity NiSi_1−xGe _x is formed at temperatures as low as 300°C and it is capable of yielding a contact resistivity of ∼10−8 ohm-cm 2 on both p+ and n+ Si_1−x Ge_x. NiSi_1−xGe_x was found to suffer from Ge out-diffusion, which had a direct negative impact on its thermal stability. NiSi_1−xGe_x formed at temperatures above 450°C exhibited high sheet resistance and a rough germanosilicide/Si _1−xGe_x interface. Below this temperature, ultra-shallow p+-n junctions with self-aligned NiSi_1−xGe _x contacts were formed with excellent reverse bias junction leakage characteristics.; A new approach was proposed to form ultra-thin NiSi_1−xGe _x layers with enhanced thermal stability. By inserting a thin Pt interlayer between Ni and Si_1−xGe_x, the thermal stability of NiSi_1−xGe_x was found to be significantly improved. On boron doped Si_1−xGe_x, the material was found to be stable up to 700°C with a total starting metal thickness of 10nm. Pt incorporation was also found to result in better surface and interface roughness.