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1.
The flat band voltage shifts of HfO2/SiO2/nSi capacitors with ultra-thin La2O3 insertion at HfO2/SiO2 interface have been confirmed using hard X-ray photoelectron spectroscopy (HX-PES). By increasing the amount of La2O3 insertion, the binding energy of Si 1s core spectra increases, which means that the surface potential of Si substrate also increases. A voltage drop difference of HfO2 and La2O3 at SiO2 interface can be estimated to be 0.40 V.  相似文献   

2.
Interracial chemical structure of HfO2/Si (100) is investigated using angle-resolved synchrotron radiation photoemission spectroscopy (ARPES). The chemical states of Hf show that the Hf 4f binding energy changes with the probing depth and confirms the existence of Hf-Si-O and Hf Si bonds. The Si 2p spectra are taken to make sure that the interracial structure includes the Hf silicates, Hf silicides and SiOx. The metallic characteristic of the Hf-Si bonds is confirmed by the valence band spectra. The depth distribution model of this interface is established.  相似文献   

3.
The physical and chemical properties of the HfO2/SiO2/Si stack have been analyzed using cross-section HR TEM, XPS, IR-spectroscopy and ellipsometry. HfO2 films were deposited by the MO CVD method using as precursors the tetrakis 2,2,6,6 tetramethyl-3,5 heptanedionate hafnium—Hf(dpm)4 and dicyclopentadienil-hafnium-bis-diethylamide—Сp2Hf(N(C2H5)2)2.The amorphous interface layer (IL) between HfO2 and silicon native oxide has been observed by the HRTEM method. The interface layer comprises hafnium silicate with a smooth varying of chemical composition through the IL thickness. The interface layer formation occurs both during HfO2 synthesis, and at the annealing of the HfO2/SiO2/Si stack. It was concluded from the XPS, and the IR-spectroscopy that the hafnium silicate formation occurs via a solid-state reaction at the HfO2/SiO2 interface, and its chemical structure depends on the thickness of the SiO2 underlayer.  相似文献   

4.
Among the methods for depositing thin films, atomic layer deposition is unique for its capability of growing conformal thin films of compounds with a control of composition and thickness at the atomic level. The conformal growth of thin films can be of particular interest for covering nanostructures since it assures the homogeneous growth of the ALD film in all directions, independent of the position of the sample with respect to the incoming precursor flow. Here we describe the technique for growing the HfO2/Al2O3 bilayer on Si substrate and our in situ approach for its investigation by means of synchrotron radiation photoemission. In particular, we study the interface interactions between the two oxides for various thickness compositions ranging from 0.4 to 2.7 nm. We find that the ALD of HfO2 on Si induces the increase of the interfacial SiO2 layer, and a change in the band bending of Si. On the contrary, the ALD of Al2O3 on HfO2 shows negligible interaction between layers as the binding energies of Hf4f, Si2p, and O1s core level peaks and the valence band maximum of HfO2 do not change and the interfacial SiO2 does not increase.  相似文献   

5.
To meet challenges for a smaller transistor feature size, ultra-thin HfO2 high-k dielectric has been used to replace SiO2 for the gate dielectric. In order to accurately analyze the ultra-thin HfO2 films by grazing incidence X-ray reflectivity (GIXRR), an appropriate material model with a proper layer structure is required. However, the accurate model is difficult to obtain, since the interfaces between layers of the ultra-thin HfO2 films are not easily identified, especially when post-deposition annealing process is applied. In this paper, 3.0 nm HfO2 films were prepared by atomic layer deposition on p-type silicon wafer, and annealed in Ar environment with temperatures up to 1000 °C. The layer structures and the role of the interfacial layer of the films in the post-deposition annealing processes were evaluated by X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The experimental results and analysis showed that layer thicknesses, crystal phases and chemical structures of the ultra-thin HfO2 films were significantly dependent on annealing temperatures. The binding energy shifts of Hf 4f, O 1s, and Si 2p elements revealed the formation of Hf silicate (Hf-O-Si bonding) with increasing annealing temperatures. Due to the silicate formation and increasing silicon oxide formation, the interface broadening is highly expected. The structure analysis of the GIXRR spectra using the modified material structure model from the XPS analysis confirmed the interfacial broadening induced by the post-deposition annealing.  相似文献   

6.
Reactions between HfO2 and Si in HfSiO films during deposition and post-annealing have been studied. Intermixing of HfO2 and Si is achieved by radio frequency sputtering with HfO2/Si compound targets, and post-annealing is used to promote the reaction at different temperatures. The structural characteristics of the mixture, HfSiO films, are analyzed by X-ray photoelectron spectroscopy and X-ray diffraction, and a careful assessment of chemical states is performed for precise identification. XPS results show that with ratios of Si:Hf ranging from 0 to 0.3 in HfSiO films, Si fully reacts with HfO2 to form silicate during deposition. However, SiO2 appears when the ratio of Si:Hf rises to 1.2. When the annealing temperature reaches 600 °C, decomposition of hafnium silicate is observed and hafnium silicide forms in the bulk of the films. XRD results reveal that HfSiO films remain amorphous with the annealing temperature below 600 °C but crystallize at 800 °C.  相似文献   

7.
Hafnium oxynitride (HfOxNy) gate dielectric has been deposited on Si (1 0 0) by means of radio frequency (rf) reactive sputtering using directly a HfO2 target in N2/Ar ambient. The thermal stability and microstructural characteristics for the HfOxNy films have been investigated. XPS results confirmed that nitrogen was successfully incorporated into the HfO2 films. XRD analyses showed that the HfOxNy films remain amorphous after 800 °C annealing in N2 ambient. Meanwhile the HfOxNy films can also effectively suppress oxygen diffusion during high temperature annealing and prevent interface layer from forming between HfOxNy films and Si substrates. AFM measurements demonstrated that surface roughness of the HfOxNy films increase slightly as compared to those pure HfO2 films after post deposition annealing. By virtue of building reasonable model structure, the optical properties of the HfOxNy films have been discussed in detail.  相似文献   

8.
Cluster size effects of SiO2 thin film formation with size-selected O2 gas cluster ion beams (GCIBs) irradiation on Si surface were studied. The cluster size varied between 500 and 20,000 molecules/cluster. With acceleration voltage of 5 kV, the SiO2 thickness was close to the native oxide thickness by irradiation of (O2)20,000 (0.25 eV/molecule), or (O2)10,000 (0.5 eV/molecule). However, it increased suddenly above 1 eV/molecule (5000 molecules/cluster), and increased monotonically up to 10 eV/molecule (500 molecules/cluster). The SiO2 thickness with 1 and 10 eV/molecule O2-GCIB were 2.1 and 5.0 nm, respectively. When the acceleration voltage was 30 kV, the SiO2 thickness has a peak around 10 eV/molecule (3000 molecules/cluster), and it decreased gradually with increasing the energy/molecule. At high energy/molecule, physical sputtering effect became more dominant process than oxide formation. These results suggest that SiO2 thin film formation can be controlled by energy per molecule.  相似文献   

9.
A relatively thick (i.e., ∼9 nm) SiO2 layer can be formed by oxidation of Si with nitric acid (HNO3) vapor below 500 °C. In spite of the low temperature formation, the leakage current density flowing through the SiO2 layer is considerably low, and it follows the Fowler-Nordheim mechanism. From the Fowler-Nordheim plots, the conduction band offset energy at the SiO2/Si interface is determined to be 2.57 and 2.21 eV for HNO3 vapor oxidation at 500 and 350 °C, respectively. From X-ray photoelectron spectroscopy measurements, the valence band offset energy is estimated to be 4.80 and 4.48 eV, respectively, for 500 and 350 °C oxidation. The band-gap energy of the SiO2 layer formed at 500 °C (8.39 eV) is 0.68 eV larger than that formed at 350 °C. The higher band-gap energy for 500 °C oxidation is mainly attributable to the higher atomic density of the SiO2 layer of 2.46 × 1022/cm3. Another reason may be the absence of SiO2 trap-states.  相似文献   

10.
In this contribution, we present results of a non-destructive in-depth analysis of concentration of chemical components at buried interfaces on Ge-based CMOS by means of hard X-ray photoelectron spectroscopy (HAXPES) and low angle X-ray reflectivity (XRR). Two samples composed of a Ge/Si/SiO2/HfO2/TiN stack, with layer and interlayer thicknesses of 2500, 0.9, 0.5, 4.9, 3.4 nm and 2500, 0.7, 1, 5.8, 3 nm have been studied. The use of electrons with kinetic energies from few eV up to 15 keV enables to tune the information depth being able to analyze the desired interface in a non-destructive way. XRR enables the determination of the exact layer thickness and density. The results suggest that the Si interlayer prevents the Ge oxidation. Depth profiles of the electronic structure have been obtained for both samples by following the evolution of the photoemission signal from the Hf 2p3/2 core level as a function of the photoelectron kinetic energy. The depth profile of the electronic structure reveals the presence of a chemical shift of the Hf 2p3/2 core level, which is related to an interfacial bonding state. Our results demonstrate the excellent capability of HAXPES to study buried interfaces in a non-destructive way.  相似文献   

11.
To deeply understand the effects of Si/N-codoping on the electronic structures of TiO2 and confirm their photocatalytic performance, a comparison theoretical study of their energetic and electronic properties was carried out involving single N-doping, single Si-doping and three models of Si/N-codoping based on first-principles. As for N-doped TiO2, an isolated N 2p state locates above the top of valence band and mixes with O 2p states, resulting in band gap narrowing. However, the unoccupied N 2p state acts as electrons traps to promote the electron-hole recombination. Using Si-doping, the band gap has a decrease of 0.24 eV and the valence band broadens about 0.30 eV. These two factors cause a better performance of photocatalyst. The special Si/N-codoped TiO2 model with one O atom replaced by a N atom and its adjacent Ti atom replaced by a Si atom, has the smallest defect formation energy in three codoping models, suggesting the model is the most energetic favorable. The calculated energy results also indicate that the Si incorporation increases the N concentration in Si/N-codoped TiO2. This model obtains the most narrowed band gap of 1.63 eV in comparison with the other two models. The dopant states hybridize with O 2p states, leading to the valence band broadening and then improving the mobility of photo-generated hole; the N 2p states are occupied simultaneously. The significantly narrowed band gap and the absence of recombination center can give a reasonable explanation for the high photocatalytic activity under visible light.  相似文献   

12.
Two kinds of HfO2/SiO2 800 nm high-reflective (HR) coatings, with and without SiO2 protective layer were deposited by electron beam evaporation. Laser-induced damage thresholds (LIDT) were measured for all samples with femtosecond laser pulses. The surface morphologies and the depth information of all samples were observed by Leica optical microscopy and WYKO surface profiler, respectively. It is found that SiO2 protective layer had no positive effect on improving the LIDT of HR coating. A simple model including the conduction band electron production via multiphoton ionization and impact ionization is used to explain this phenomenon. Theoretical calculations show that the damage occurs first in the SiO2 protective layer for HfO2/SiO2 HR coating with SiO2 protective layer. The relation of LIDT for two kinds of HfO2/SiO2 HR coatings in calculation agrees with the experiment result.  相似文献   

13.
An increase in the density of states between the oxygen 2p bands and the Fermi level is seen with increasing Gd concentrations. In addition, for the Gd-doped HfO2 films, the Gd 4f photoexcitation peak at 5.5 eV below the valence band maximum was identified using resonant photoemission. Electrical measurements show pronounced rectification properties for lightly-doped Gd:HfO2 films on p-Si and for heavily-doped Gd:HfO2 films on n-Si, suggesting a crossover from n-type to p-type behavior with increasing doping level. In addition, there is an increase in the reverse bias current with neutron irradiation.  相似文献   

14.
La-doped HfO2 gate dielectric thin films have been deposited on Si substrates using La(acac)3 and Hf(acac)4 (acac = 2,4-pentanedionate) mixing sources by low-pressure metal-organic chemical vapor deposition (MOCVD). The structure, thermal stability, and electrical properties of La-doped HfO2 films have been investigated. Inductive coupled plasma analyses confirm that the La content ranging from 1 to 5 mol% is involved in the films. The films show smaller roughness of ∼0.5 nm and improved thermal stability up to 750 °C. The La-doped HfO2 films on Pt-coated Si and fused quartz substrates have an intrinsic dielectric constant of ∼28 at 1 MHz and a band gap of 5.6 eV, respectively. X-ray photoelectron spectroscopy analyses reveal that the interfacial layer is Hf-based silicate. The reliable value of equivalent oxide thickness (EOT) around 1.2 nm has been obtained, but with a large leakage current density of 3 A/cm2 at Vg = 1V + Vfb. MOCVD-derived La-doped HfO2 is demonstrated to be a potential high-k gate dielectric film for next generation metal oxide semiconductor field effect transistor applications.  相似文献   

15.
We systematically investigated the role of the top interface for TaCx and HfCx/HfO2 gate stacks on the effective work function (Φm,eff) shift by inserting a SiN layer at the gate/HfO2 top interface or HfO2/SiO2 bottom interface. We found that Φm,eff of the TaN gate electrode on HfO2 was larger than that on SiO2 because of the HfO2/SiO2-bottom-interface dipole. On the other hand, we found that Φm,eff values of the TaCx and HfCx gate electrodes on HfO2 agree with Φm,eff on SiO2. This is because the potential offset of the opposite direction with respect to the bottom interface dipole appears at the metal carbide/HfO2 interface. It is thus concluded that the top interface in the metal carbide/HfO2 gate stacks causes the negative Φm,eff shift.  相似文献   

16.
Multilayered Ge nanocrystals embedded in SiOxGeNy films have been fabricated on Si substrate by a (Ge + SiO2)/SiOxGeNy superlattice approach, using a rf magnetron sputtering technique with a Ge + SiO2 composite target and subsequent thermal annealing in N2 ambient at 750 °C for 30 min. X-ray diffraction (XRD) measurement indicated the formation of Ge nanocrystals with an average size estimated to be 5.4 nm. Raman scattering spectra showed a peak of the Ge-Ge vibrational mode downward shifted to 299.4 cm−1, which was caused by quantum confinement of phonons in the Ge nanocrystals. Transmission electron microscopy (TEM) revealed that Ge nanocrystals were confined in (Ge + SiO2) layers. This superlattice approach significantly improved both the size uniformity of Ge nanocrystals and their uniformity of spacing on the ‘Z’ growth direction.  相似文献   

17.
High-k gate dielectric HfO2 thin films have been deposited on Si(1 0 0) by using plasma oxidation of sputtered metallic Hf thin films. The optical and electrical properties in relation to postdeposition annealing temperatures are investigated by spectroscopic ellipsometry (SE) and capacitance-voltage (C-V) characteristics in detail. X-ray diffraction (XRD) measurement shows that the as-deposited HfO2 films are basically amorphous. Based on a parameterized Tauc-Lorentz dispersion mode, excellent agreement has been found between the experimental and the simulated spectra, and the optical constants of the as-deposited and annealed films related to the annealing temperature are systematically extracted. Increases in the refractive index n and extinction coefficient k, with increasing annealing temperature are observed due to the formation of more closely packed thin films and the enhancement of scattering effect in the targeted HfO2 film. Change of the complex dielectric function and reduction of optical band gap with an increase in annealing temperature are discussed. The extracted direct band gap related to the structure varies from 5.77, 5.65, and 5.56 eV for the as-deposited and annealed thin films at 700 and 800 °C, respectively. It has been found from the C-V measurement the decrease of accumulation capacitance values upon annealing, which can be contributed to the growth of the interfacial layer with lower dielectric constant upon postannealing. The flat-band voltage shifts negatively due to positive charge generated during postannealing.  相似文献   

18.
Under generalized gradient approximation (GGA), the structural and electronic properties of AlN and Si sheets, hydrogen terminated AlN and Si nanoribbons with hexagonal morphology and 2, 4, 6 zigzag chains across the ribbon width and the hexagonally bonded heterosheets AlNSix (x=2, 4, and 6) consisting of hexagonal networks of AlN (h-AlN) strips and silicene sheets with zigzag shaped borders have been investigated using the first-principles projector-augmented wave (PAW) formalism within the density function theory (DFT) framework. The AlN sheet is an indirect semiconductor with a band gap of 2.56 eV, while the Si sheet has a metallic character since the lowest unoccupied conduction band (LUCB) and the highest occupied valence band (HOVB) meet at one k point from Γ to Z. In the semiconductor 6-ZAlNNR, for example, the states of LUCB and HOVB at zone boundary Z are edge states whose charges are localized at edge Al and N atoms, respectively. In metallic 6-ZSiNR, a flat edge state is formed at the Fermi level EF near the zone boundary Z because its charges are localized at edge Si atoms. The hybridizations between the edge states of h-AlN strips and silicene sheets result in the appearance of border states in the zigzag borders of heterosheets AlNSix whose charges are localized at two atoms of the borders with either bonding or antibonding π character.  相似文献   

19.
Silicon is by far the most important material used in microelectronics, partly due to the excellent electronic properties of its native oxide (SiO2), but substitute semiconductors are constantly the matter of research. SiC is one of the most promising candidates, also because of the formation of SiO2 as native oxide. However, the SiO2/SiC interface has very poor electrical properties due to a very high density of interface states which reduce its functionality in MIS devices. We have studied the electronic properties of defects in the SiO2/Si and SiO2/SiC interfaces by means of XAS, XPS and resonant photoemission at the O 1s and the Si 2p edges, using silicon dioxide thermally grown with thicknesses below 10 nm. Our XAS data are in perfect agreement with literature; in addition, resonant photoemission reveals the resonant contributions of the individual valence states. For the main peaks in the valence band we find accordance between the resonant behaviour and the absorption spectra, except for the peaks at −15 eV binding energy, whose resonant photoemission spectra have extra features. One of them is present in both interfaces and is due to similar defects, while another one at lower photon energy is present only for the SiO2/SiC interface. This is related to a defect state which is not present at the SiO2/Si interface.  相似文献   

20.
Electronic structures of SrCoOx with x=3, 2.875 and 2.75 were calculated by DFT technique in SLDA approximation. Two kinds of oxygen vacancy ordering with energies of 0.22 and 0.01 eV lower in comparison with random vacancy distribution were revealed. The transition between these ordered vacancy systems with the activation energy 0.34 eV can be a step in the ionic conductivity mechanism. The calculated ion charges, magnetic moments and electron density of states were used to analyze chemical bonding in the crystals. All calculated compounds have metal electronic conductivity.  相似文献   

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