Highly epitaxial and pure（001）-oriented CeO2 films were grown on SrTiO3（001） substrates by laser molecular beam epitaxy method without any gas ambient.Layer-by-layer epitaxial growth mode of CeO2 was confirmed by in situ reflection high-energy electron diffraction（RHEED） observations.High-resolution X-ray diffraction（HRXRD） and high-resolution transmission electron microscopy（HRTEM） results indicated the STO（100）//CeO2（100）,STO[100]//CeO2 [110] epitaxial relationship for out-of-plane and in-plane,respectively.The formation mechanism of the epitaxial film was also discussed in the light of a theoretical model.Chemical states of the LMBE ceria films were evaluated and evidences for the existence of Ce3＋and oxygen vacancies were presented.
Abstract： The effects of low temperature annealing, such as post high-k dielectric deposition annealing （PDA）, post metal annealing （PMA） and forming gas annealing （FGA） on the electrical characteristics of a metal-oxidesemiconductor （MOS） capacitor with a TiN metal gate and a Hf02 dielectric are systematically investigated. It can be found that the low temperature annealing can improve the capacitance-voltage hysteresis performance signifi- cantly at the cost of increasing gate leakage current. Moreover, FGA could effectively decrease the interfacial state density and oxygen vacancy density, and PDA could make the flat band positively shift which is suitable for P-type MOSs. Key words： ALD Hf02; TiN; low temperature annealing; hysteresis
The physical origin of the flatband voltage （VFB） roll off for a metal-oxide-semiconductor device with high-k/metal gate structure is studied from the viewpoint of energy band alignment at the high-k/Si interface because the thickness of SiO2 interlayer is thin enough to be ignored. The VFB roll off phenomenon is assigned to associate with the direct electron transfer between high-k and Si substrate. Quantitatively calculated simulation results based on this model are given considering different conditions.
Gd-doped HfO2 has drawn worldwide interest for its interesting features. It is considered to be a suitable material for N-type metal-oxide-semiconductor （MOS） devices due to a negative flatband voltage （Vfb） shift caused by the Gd doping. In this work, an anomalous positive shift was observed when Gd was doped into HfO2. The cause for such a phenomenon was systematically investigated by distinguishing the effects of different factors, such as Fermi level pinning （FLP）, a dipole at the dielectric/SiO2 interface, fixed interracial charge, and bulk charge, on Vfb. It was found that the FLP and interfacial dipole could make Vfb negatively shifted, which is in agreement with the conventional dipole theory. The increase in interfacial fixed charge resulting from Gd doping plays a major role in positive Vfb shift.
Effects of NH3 rapid thermal annealing （RTA） on the interface and electrical properties of Gd-doped HfO2 （GDH）/Si stack were investigated. The process of NH3 annealing could significantly affect the crystallization, stoichiometric properties of GDH film and the interface characteristic of GDH/Si system. NH3 annealing also led to the decrease of interface layer thickness. The leakage current density of Pt/GDH/p-Si MOS capacitor without RTA was 2× 10-3 A/cm2. After NH3 annealing, the leakage current density was about one order of magnitude lower （3.9× 104 A/cm2）. The effective permittivity extracted from the C-V curves was -14.1 and 13.1 for samples without and with RTA, respectively.
