Interface-Engineered High-Mobility High- $k$ /Ge pMOSFETs With 1-nm Equivalent Oxide Thickness

High-k/germanium (Ge) interfaces are significantly improved through a new interface engineering scheme of using both effective pregate surface GeO₂ passivation and postgate dielectric (postgate) treatment incorporating fluorine (F) into a high-k/Ge gate stack. Capacitance-voltage (C-V) characteristics are significantly improved with minimum density of interface states (D_it) of 2 times 10¹¹ cm^-2 ldr eV^-1 for Ge MOS capacitors. A hole mobility up to 396 cm²/V ldr s is achieved for Ge p-metal-oxide-semiconductor field-effect transistors (pMOSFETs) with equivalent oxide thickness that is ~10 Aring and gate leakage current density that is less than 10^-3 A/cm² at V_t plusmn 1 V. A high drain current of 37.8 muA/mum at V_g - V_t = V_d = -1.2 V is presented for a channel length of 10 mum. The Ge MOSFET interface properties are further investigated using the variable-rise-and-fall-time charge-pumping method. Over three times D_it reduction in both upper and lower halves of the Ge bandgap is observed with F incorporation, which is consistent with the observation that frequency-dependent flat voltage shift is much less for samples with F incorporation in the C-V characteristics of Ge MOS capacitors.