High-k gate stack on germanium substrate with fluorine incorporation

In this letter, a postgate CF4-plasma treatment is proposed and demonstrated on germanium (Ge) metal-oxide-semiconductor capacitors and the effects of fluorine (F) incorporation have been studied on both high-k∕Ge gate stacks without any surface passivation and with Si surface passivation. Our results show that F is effectively introduced into the gate stack by CF4 treatment and segregates near high-k∕Ge interface. Electrical characteristics such as frequency dispersion, interface state density (Dit), and gate leakage are improved after F incorporation. Interface quality of high-k∕Ge gate stack is further improved by combining Si surface passivation and postgate CF4 treatment, with its Dit as low as 4.85×1011cm−2eV−1.