Oxidation State Modification in Gate Dielectric for Ge nMOSFET With Mixed Hydrogen and Ozone Plasma Pretreatments

An ozone-based plasma pretreatment was proposed to reduce the oxygen vacancy and unstable germanium (Ge) suboxide (GeO<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{x}\text {)}$ </tex-math></inline-formula> at lower interface of interfacial layer (IL). With higher oxidizing ability of ozone and lower plasma damage in process, the formation of unstable GeOx at lower interface of IL can be effectively suppressed. The devices with a mixed hydrogen and ozone plasma (MHOP) pretreatment exhibit an ultrathin equivalent oxide thickness (EOT) of 0.57 nm, a fairly acceptable gate leakage current density of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3 \times 10^{-{3}}$ </tex-math></inline-formula> A/cm2, lower interface trap density of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{11}}$ </tex-math></inline-formula> cm<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{2}}\cdot $ </tex-math></inline-formula>eV<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula>, and fewer border traps in Ge MOS capacitor. Also, a higher driver current of 1.4 mA, a lower subthreshold swing (SS) of 113 mV/dec, and higher on/off current ratio of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.2 \times 10^{{3}}$ </tex-math></inline-formula> for Ge MOSFET can be achieved with an MHOP treatment.