Low-thermal-budget n-type ohmic contacts for ultrathin Si/Ge superlattice materials

Abstract

Thermal budget is a vital element of Si-based superlattice material processing. In this work, a novel n-type ohmic contact scheme with a low thermal budget process is developed by combining high-dose ion implantation and low-temperature alloying techniques. The optimized specific contact resistivity (ρ c) is reduced to 6.18 × 10−3 Ω cm2 at a low thermal budget of 400 °C, and this is a result of the efficient low-temperature electrical activation of amorphous substances. It is indicated that both the high doping concentration and the formation of a NiSi(Ge) alloy phase contribute to the linear ohmic contact behavior. The ohmic contact resistance dependence on processing temperature is further revealed by a detailed Ni/Si(Ge)alloying model. A minimum ρ c of 2.51 × 10−4 Ω cm2 is achieved at a thermal budget of 450 °C, which is related to the high bonding intensity at the metal–semiconductor interface. Note that this technique is compatible with standard Si-based CMOS process flows and can be applied in high-performance insulated-gate field-effect transistor (IGFET) fabrication. Furthermore, it is verified that the Si/Ge superlattice structures in our IGFETs can serve as an efficient potential barrier to constrain electrons.