This work demonstrates the benefit of a lower contact barrier height, and hence reduced contact resistivity (ρc), using a low work-function metal (Yb) in unpinned metal-interfacial layer-semiconductor (MIS) contacts on n-type Ge. Fermi-level unpinning in MIS contacts on n-Ge is first established by introducing a 2 nm TiO2−x interfacial layer between various contact metals (Yb, Ti, Ni, Pt) and n-Ge. Further, Yb/TiO2−x/n-Ge MIS contact diodes exhibit higher current densities (up to 100×) and lower effective contact barrier height (up to 30%) versus Ti/TiO2−x control devices over a wide range of TiO2−x thickness (1–5 nm). Finally, low work-function Yb combined with doped TiO2−x having a low conduction band offset with Ge and high substrate doping (n+-Ge: 2.5×1019 cm−3) is shown to result in an ultra-low ρc value of 1.4 × 10−8 Ω cm2, 10 × lower than Ti/TiO2−x control devices.
The transition from a planar to a FinFET device structure has changed device doping requirements. The fin sidewall doping and activation, crystallinity control of the fin, junction profile and leakage control on the fin are new challenges. With continuous scaling of FinFET technology, the narrower fins become more prone to crystallinity damage by ion implant, and lead to increases in junction leakage and fin parasitic resistance. We have introduced hot implant as a superior doping technique to room-temperature implant for arsenic source drain extension (SDE) and halo implants on vertical narrow fins. We have demonstrated for the first time that hot SDE implant on 6nm CD vertical fins produced single crystalline fins and enabled 5x improvement in fin line resistance and more than 10x reduction in junction leakage compared with a room-temperature SDE implant.
This work demonstrates a solution to the problem of increase in Schottky barrier height (ϕB) with thermal annealing (thermal instability) in unpinned (low ϕB) Ti/TiO2/n-Ge metal-interfacial layer (IL)-semiconductor (MIS) contacts through plasma nitridation of the TiO2 layer. Unlike TiO2, unpinned (ϕB = 0.09 eV) TiOxNy contacts are thermally stable for anneals up to 30 min at 400 °C. The thermal stability improves with increasing nitrogen concentration ([N], 2.5–9.5%) and is independent of thickness (2–5 nm) for [N] = 9.5%. Additionally, the plasma nitridation process is shown to increase the oxygen vacancy concentration (n-type doping) and reduce the ϕB dependence on TiOxNy thickness in unannealed TiOxNy contacts. Enhanced thermal stability is attributed to the incorporated nitrogen acting as a diffusion barrier that prevents contact pinning through reduction of the TiO2 layer by contact metal during the anneal, as well as preserves the amorphous nature of the IL along with its fixed charge and interfacial dipoles that contribute to ϕB reduction.
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