Improvements on Surface Carrier Mobility and Electrical Stability of MOSFETs Using HfTaO Gate Dielectric

Physical and electrical characteristics of HfTaO gate dielectric have been systematically investigated for the first time. Based on the X-ray diffraction spectra and high-resolution transmission electron microscope pictures, the crystallization temperature of HfO/sub 2/ film is significantly increased with incorporating Ta, and the HfTaO with 43% Ta film remains amorphous after annealing at 950/spl deg/C for 30 s. X-ray photoelectron spectroscopy results show that the formation of Si-O bonds in interfacial layer is increased with Ta concentration. The high atomic percentage of Si-O bonds may result in the HfTaO-Si interface inclining to SiO/sub 2/-Si interface, as well as good interface properties. Hence, the interface states density (D/sub it/) in HfTaO film is reduced by one order of magnitude compared with HfO/sub 2/. In addition, charge trapping induced threshold voltage (V/sub th/) instability in HfO/sub 2/ and HfTaO films is compared using a pulsed I/sub d/--V/sub g/ measurement technique, and the V/sub th/ shift in HfTaO film is much lower than HfO/sub 2/. This indicates that charge trapping in HfO/sub 2/ film is significantly suppressed by incorporating Ta. Since both of the interface traps and charged traps in HfTaO film are less than in HfO/sub 2/, more than twice higher peak mobility is achieved in HfTaO nMOSFETs, which is due to the suppression of Coulomb scattering caused by the interface traps and charged traps.