Formation of low-resistivity germanosilicide contacts to phosphorus doped silicon-germanium alloy source/drain junctions for nanoscale CMOS.

摘要

Conventional source/drain junction and contact formation processes can not meet the stringent requirements of future nanoscale complimentary metal oxide silicon (CMOS) technologies. The selective Si_1−xGe _x source/drain technology was proposed in this laboratory as an alternative to conventional junction and contact schemes. The technology is based on selective chemical vapor deposition of in-situ boron or phosphorus doped in Si _1−xGe_x source/drain areas. The fact that the dopant atoms occupy substitutional sites during growth make the high temperature activation anneals unnecessary virtually eliminating dopant diffusion to yield abrupt doping profiles. Furthermore, the smaller band gap of Si_1−x Ge_x results in a smaller Schottky barrier height, which can translate into significant reductions in contact resistivity due to the exponential dependence of contact resistivity on barrier height. This study is focused on formation of self-aligned germanosilicide contacts to phosphorous-doped Si_1−xGe_x alloys. The experimental results obtained in this study indicate that self-aligned nickel germanosilicide (NiSi _1−xGe_x) contacts can be formed on Si_1−x Ge_x layers at temperatures as low as 350°C. Contacts Si_1−xGe_x can yield a contact resistivity of 10 −8 ohm-cm2 with no sign of germanosilicide induced leakage. However, above a threshold temperature determined by the Ge concentration in the alloy, the NiSi_1−xGe_x/Si_1−x Ge_x interface begins to roughen, which affects the junction leakage. For phosphorus doped layers considered in this study, the threshold temperature was around 500°C, which is roughly 100°C higher than the threshold temperature for NiSi_1−xGe_x contacts formed on boron doped Si_1−xGe_x layers with a Ge percentage of ∼50%. Nickel and zirconium germanosilicides were also considered as contact candidates but they were found to result in a contact resistivity near 10−7 ohm-cm2.