The effects of microwave plasma treatments on the physical and electrical characteristics of silicon dioxide films are discussed. Plasma treatments significantly improve the characteristics at low temperatures. Differences in the type of inert gas, O2 partial pressure, and total pressure cause differences in the plasma energy and active species concentrations, which affect reduction in the impurity concentrations, generation of dangling bonds, and effective working depth of the plasma. The changes in the electrical characteristics of the plasma-treated oxide films are consistent with those in the physical characteristics. The plasma conditions that result in the best improvements are determined.
We have investigated annealing effects on in-depth profile and band discontinuity for a metal gate/high-k gate stack structure on a Si substrate using backside angle-resolved photoemission spectroscopy with synchrotron radiation. In-depth profiles analyzed from angle-resolved photoemission spectroscopy show that La atoms diffuse through the HfSiO layer and reach interfacial SiO2 layers by rapid thermal annealing. Chemical shift of Si 2p core-level spectra suggests that there are changes in the band discontinuity at the high-k/SiO2 interface, which is well related to the Vth shift based on the interface dipole model.
Using synchrotron-radiation photoemission spectroscopy, we have investigated oxidation and reduction reactions of HfSiO(N)∕Si gate stack structures annealed in a N2 or O2 atmosphere. It is found that both oxidation and reduction reactions can be suppressed by using nitrogen-incorporated HfSiO films in the annealing process at proper partial pressure of N2 gas (PN2∼100Torr). The detailed analysis of “SiO2 equivalent thicknesses” for annealed HfSiO and HfSiON films reveals that ambient N2 gas suppresses only the reduction reaction, while nitrogen atoms incorporated in dielectrics suppress both oxidation and reduction reactions.
We have developed a method to precisely determine the band offsets for hafnium oxide (HfO 2 ), hafnium silicate (HfSiO) and nitrided hafnium silicate (HfSiON) films on Si by elimination of x-ray irradiation effects with time-dependent photoemission spectroscopy (PES) and x-ray absorption spectroscopy. The core-level PES spectra shift during PES measurements, which is explained as the dielectric films charging due to photoemission by the x-ray irradiation. For elimination of the x-ray irradiation effect on the determination of the band offsets, time-dependent photoemission spectroscopy was performed. The precisely determined valence band offsets for HfO 2 , HfSiO and HfSiON are 3.2, 3.4, and 1.9 eV, respectively. On the other hand, the conduction band offsets are almost the same values of about 1.3 eV. Thus, the elimination of x-ray irradiation effect enables to precisely determine the band offsets, leading to the accurate estimation of gate leakage current.
We have investigated chemical states and charge density in HfSiON films as a function of depth using x-ray irradiation time-dependent photoemission spectroscopy. N 1s core-level photoemission spectra deconvoluted into three components depend on HfSiON thickness, indicating the component, which is attributed to the N atoms bonded to Hf atoms, has peak near the surface. On the other hand, charge density estimated from band bending in Si from Si 2p photoemission spectra is also distributed mainly near the surface. These results indicate that the origin of the negative charge trapping can be directly related to the presence of Hf–N bonds.
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