Physical and electrical properties of lanthanide-incorporated tantalum nitride for n-channel metal-oxide-semiconductor field-effect transistors

Lanthanide-incorporated tantalum nitride (TaN) is studied as a potential metal gate candidate for n-channel metal-oxide-semiconductor field-effect transistors (n-MOSFETs). Lanthanides such as terbium (Tb), erbium (Er), and ytterbium (Yb) are introduced into TaN to form Ta1−xTbxNy, Ta1−xErxNy, and Ta1−xYbxNy metal gates, respectively, on SiO2 dielectric. The resistivity, crystallinity, film composition, and work function of Ta1−xTbxNy, Ta1−xErxNy, and Ta1−xYbxNy films were investigated at different post-metal-anneal temperatures and for different lanthanide concentrations. It was found that the work function of lanthanide-incorporated TaN can be effectively tuned by increasing the concentration of lanthanide. Work functions of about 4.2–4.3eV can be achieved even after a 1000°C rapid thermal anneal, making lanthanide-incorporated TaN a promising metal gate candidate for n-MOSFETs. The enhanced nitrogen concentration and the possible presence of lanthanide-N or Ta-N-lanthanide compounds in lanthanide-incorporated TaN film could be responsible for its chemical-thermal stability on SiO2.