Effects of rapid thermal annealing on nitrided gate oxide grown on 4H-SiC

The electrical characteristics of thermally nitrided gate oxides on n-type 4H-SiC, with and without rapid thermal annealing processes, have been investigated and compared in this paper. The effects of annealing time (isothermal annealing) and annealing temperature (isochronal annealing) on the gate oxide quality have also been systematically investigated. After rapid isothermal and isochronal annealings, there has been a significant increase in positive oxide-charge density and in oxide-breakdown time. A correlation between the density of the positive oxide charge and the oxide breakdown reliability has been established. We proposed that the improvement in the oxide-breakdown reliability, tested at electric field of 11 MV/cm, is attributed to trapping of injected electron by the positive oxide charge and not solely due to reduction of SiC-SiO₂ interface-trap density.     

Structural characterization of oxide layers thermally grown on 3C-SiC films

The oxidation of 3C-SiC films deposited on off-oriented Si(001) substrates by reactive magnetron sputtering has been studied. The oxidation was carried out using dry conditions at a temperature of 1200°C. The composition of the oxide layer was investigated by Auger electron spectroscopy (AES). The oxide layer was found to contain no C except for the region very close to the interface, and the stoichiometry was found to be close to that of SiO₂. Cross-sectional transmis-sion electron microscopy (XTEM) showed the oxide layer to be completely amorphous, dense, and homogeneous with a uniform thickness. High-resolution XTEM imaging showed an atomically sharp SiO₂/SiC interface.     

Electron microprobe analysis of impurity heterogeneities in thermally grown silicon oxide

The electron probe X-ray microanalyzer is a powerful tool for studying impurity distribution and motion in thin films. This analytical instrument is capable of detecting metallic impurities present in areas as small as 1 × 10^-6mm²and in concentrations of greater than 1 × 10¹⁹atoms/cm³. The analysis requires no sample preparation and is essentially a nondestructive test. This instrument was used to examine unoxidized and oxidized silicon surfaces and a finished microcircuit. With the electron microprobe, aluminum-bearing regions approximately one microns in diameter were detected on the bare surface of mechanically polished silicon slices. These aluminum-rich regions are believed to be alumina abrasive used in polishing. If these regions are not removed by chemical etching they will generate oxide defects during oxidation. These defects were found to contain Al (1 × 10²¹atoms/cm³and Na (1 × 10²⁰atoms/cm³). Other oxide defects, i.e., pinholes, generated during oxidation varied in size from 0.5 to 5.0 microns and were found to contain Na (1×10²¹atoms/cm³) and K (5×10²¹atoms/cm³). Mg and Ca (1 × 10²⁰atoms/cm³) were occasionally observed in these defects. After oxidation, all these impurities could be removed with a hot hydrochloric acid and deionized water rinse; surprisingly, this treatment reduced the silicon surface charge in the MOS structure (X_{0} cong 1500Å) by approximately 1.4 × 10¹¹charges/cm². The surface charge could be further reduced by heating the oxidized wafer at 900°C in a silicon nitride tube.     

Furnace grown gate oxynitride using nitric oxide (NO)

Gate oxynitride was grown in NO for the first time. This approach can provide a tight N accumulation near the Si/SiO₂ interface. Much lower thermal budget is required for an NO process than for an N₂O process to produce an oxynitride with useful properties. Submicron MOSFET's with NO oxynitride showed superior current drive characteristics and comparable hot carrier immunity to those with N₂O oxynitride     

Depth profiles of refractive index in thermally grown and LPCVD oxide films on silicon

Thin and thick silicon oxide films are grown by thermal oxidation of silicon in dry oxygen or by LPCVD from a mixture of monosilane with oxygen or nitrous oxide. Depth profiles of refractive index are determined in these films by monochromatic ellipsometry, with the measurements interpreted by solving an inverse problem within a multilayer model. The differences between the depth profiles are found to be consistent with well-known mechanisms of film growth under the process conditions applied.     

The characteristics of polysilicon oxide grown in pureN2O

This work reports on the characteristics of polysilicon oxide grown in pure N₂O (N₂O-grown polyoxide). The obtained polyoxide has a desirable polarity asymmetry of J-E characteristic, i.e., a lower leakage current and a higher breakdown electric field, which are ideal for the nonvolatile memory application, when the top electrode is positively biased. The asymmetry is due to the smoother surface of the N₂O-grown polyoxide. Comparing to conventional polyoxides, the N₂O-grown polyoxide has a lower electron trapping rate and a larger Q_bd, which are attributed to the incorporated nitrogen at the polyoxide/poly-1 interface. The centroids of trapped charges of the N₂O-grown polyoxide are more away from the polyoxide/poly-1 interface and this affects the polarity dependence of trapping     

Improvement in electrical characteristics of ultrathin thermally grown SiO/sub 2/ by selective anodic oxidation

The presence of weak spots and pinholes in ultrathin gate oxides significantly increases the leakage current, thereby degrading the device performance. This paper proposes a method, which identifies the weak spots in thermally grown gate oxide and repairs them by selective anodization. By controlling the applied voltage, it is ensured that current flows only through the weak spots in the oxide during anodization. Anodic oxide therefore grows over these weak spots, improving the reliability of the oxide without increasing the gate oxide thickness. Significant improvement in electrical characteristics was observed in the gate oxides treated by anodic oxidation.     

Topography induced preferential crystallization of thermally grown silicon dioxide films

We have investigated the crystallization of the oxide layer that grows on a deposited silicon film in a high temperature furnace. The growth of large SiO₂ crystal grains can be controlled by interfacial stress or surface topography. When the Si film is deposited on topographically patterned surfaces, the SiO₂ grains are nucleated along the edges and extremities of the relief structure. A competition in which faster growing grains terminate slower growing grains results in an average growth direction perpendicular to the edges. Single crystal grains of α-cristobalite up to hundreds of microns in length can be grown in this fashion.     

Stress voltage polarity dependence of thermally grown thin gateoxide wearout

Gate oxide wearout for thermally grown 57-190-A SiO₂ films in a polycrystalline silicon-SiO₂-Si structure prepared on n-type and p-type wafers was studied by examining time-dependent dielectric breakdown (TDDB) under 1-mA/cm² constant current with positive and negative voltages at 250°C. TDDB lifetimes for positive voltage stress are more than one order longer than those for negative voltage stress. TDDB lifetimes depend on oxide thickness, that is, they increase for positive voltage stress and decreases for negative voltage stress with decreasing oxide thickness. They also depend on whether the oxide films are prepared on n-type or p-type wafers. After the positive voltage TDDB stress, negative charges are predominantly produced in the oxide layer, and the electric field at the cathode in the oxide film slightly decreases. On the contrary, after the negative voltage TDDB stress, positive charges are predominantly produced at the cathode in the oxide layer and the electric field at the cathode is built up, resulting in an increase in Fowler-Nordheim tunnel current flowing though the oxide film     

Channel hot-carrier stressing of reoxidized nitrided silicondioxide

The mechanisms of channel hot-carrier-induced degradation in short n-channel MOSFETs with reoxidized nitrided oxide as the gate dielectric are discussed. Charge pumping measurements, supported by observations on the gate voltage dependence of degradation and the power law dependence of Δg_m on stress time, demonstrate that virtually no interface trap generation occurs in reoxidized nitrided oxides and that electron trapping is the dominant degradation mechanism. Although electron trapping can be enhanced in these dielectrics, this mechanism is not as important for device degradation as interface trap generation, and the net effect is substantially improved resistance to hot-carrier stress. A three-orders-of-magnitude improvement in device lifetime (versus conventional oxide) is demonstrated     

The diffusion of ion-implanted arsenic in thermally grown SiO2

The diffusivity of ion-implanted As in SiO₂ is investigated as a function of the implanted dose, oxide type and ambient in the 1000–1200° C temperature range. The As diffusivity in oxide is extracted, using electrical methods, from the profiles of As diffused into the substrate. Secondary-ion-mass-spectroscopy depth profiles of some of the samples are in agreement with the results of the electrical methods. Two types of oxide are investigated: Dry oxide grown in O₂ and wet oxide grown in steam. The diffusivity is characterized as a function of the temperature for dry oxide annealed in N₂, and for wet oxide annealed both in N₂ and in N₂/H₂ (10%). The measured As diffusivity vs temperature is fitted to a single activation energy exponential model. For the wet-grown oxide, the extracted activation energy for the N₂/H₂ (10%) annealed sample is 4.4 ± 0.5 eV and for the N₂ annealed oxide it is found to be 5.5 ± 0.5 eV. For oxide grown in dry oxygen the As diffusivity is characterized also as a function of the implant dose. It is found to be independent of the implanted dose, for ion energy of 40 keV and dose in the 10¹²–10¹⁵ cm^-2 range, and its activation energy equals 4.7 ± 0.5 eV. The extracted parameters were installed in the SUPREM-III process simulation program and correctly predict ion-implanted As diffusion behavior in SiO₂.     

The electrical characteristics of polysilicon oxide grown in pure N2O

N₂O was used to grow silicon polyoxide. It was found that the N₂O-grown polyoxide had a lower leakage current but a higher breakdown field when the top-electrode was positively biased. This is opposite to that of conventional O₂-grown polyoxide. Moreover, it had less electron trapping when stressed and a larger charge-to-breakdown     

退火温度对FeSiAl合金微结构及电磁特性的影响

对球磨后的FeSiAl合金粉末进行不同温度真空退火,并制备成软磁合金复合材料(SCM)。采用SEM、XRD和网络分析仪等分析手段,研究了退火后合金的相组成、超点阵结构有序度、平均晶粒尺寸和1MHz～1.5GHz的SCM的复磁导率,随退火温度变化的规律。结果表明:随着退火温度逐渐提高,DO3超点阵结构有序度由0.38增大到0.66、平均晶粒尺寸由36.93nm增大到71.41nm、SCM在同频率下的μ′和μ″均逐渐减小。     

Effects of annealing conditions on the properties of tantalum oxide films on silicon substrates

The formation of a SiO₂ layer at the Ta₂O₅/Si interface is observed by annealing in dry O₂ or N₂ and the thickness of this layer increases with an increase in annealing temperature. Leakage current of thin (less than 40 nm thick) Ta₂O₅ films decreases as the annealing temperature increases when annealed in dry O₂ or N₂. The dielectric constant vs annealing temperature curve shows a maximum peak at 750 or 800° C resulting from the crystallization of Ta₂O₅. The effect is larger in thicker Ta₂O₅ films. But the dielectric constant decreases when annealed at higher temperature due to the formation and growth of a SiO₂ layer at the interface. The flat band voltage and gate voltage instability as a function of annealing temperature can be explained in terms of the growth of interfacial SiO₂. The electrical properties of Ta₂O₅ as a function of annealing conditions do not depend on the fabrication method of Ta₂O₅ but strongly depend on the thickness of Ta₂O₅ layer.     

Current-voltage characteristics of high current density siliconEsaki diodes grown by molecular beam epitaxy and the influence ofthermal annealing

We present the characteristics of uniformly doped silicon Esaki tunnel diodes grown by low temperature molecular beam epitaxy (T_growth=275°C) using in situ boron and phosphorus doping. The effects of ex situ thermal annealing are presented for temperatures between 640 and 800°C. A maximum peak to valley current ratio (PVCR) of 1.47 was obtained at the optimum annealing temperature of 680°C for 1 min. Peak and valley (excess) currents decreased more than two orders of magnitude as annealing temperatures and times were increased with rates empirically determined to have thermal activation energies of 2.2 and 2.4 eV respectively. The decrease in current density is attributed to widening of the tunneling barrier due to the diffusion of phosphorus and boron. A peak current density of 47 kA/cm² (PVCR=1.3) was achieved and is the highest reported current density for a Si-based Esaki diode (grown by either epitaxy or by alloying). The temperature dependence of the current voltage characteristics of a Si Esaki diode in the range from 4.2 to 325 K indicated that both the peak current and the excess current are dominated by quantum mechanical tunneling rather than by recombination. The temperature dependence of the peak and valley currents is due to the band gap dependence of the tunneling probability     

Determination of the electrical properties of thermally grown ultrathin nitride films

The aim of this work is to obtain the electrical properties of a leaky 2 nm ultrathin thermally grown nitride film using the classical HF C(V) measurements. The substrate Si (1 0 0) surface cleaned in UHV is nitrided in a low pressure of nitric oxide (NO) gas at 1050°C. This film is characterized by Auger electron spectroscopy (AES), fourier transform infra red spectroscopy (FTIR), transmission electron microscopy (TEM) and electron energy loss spectrum (EELS). The deposition of a self-assembled insulating monolayer of organic molecules (octadecyltrichlorosilane) on the nitride gives rise to a metal–insulator–semiconductor (MIS) structure, which permits to obtain the electrical properties of the ultrathin nitride film.     

Dielectric relaxation in thermally grown SiO2films

An extensive investigation of the dielectric properties of thermally grown silicon dioxide films was performed in the temperature range from 400°C to 525°C. Principally, the variation of dissipation factor with frequency was observed at various applied peak fields and oxide thicknesses. In the temperature and frequency domain investigated, a large peak in the dissipation factor occurred. This peak corresponded to a massive capacitance dispersion with accompanying peaking of the loss factor at low frequencies. The phenomenon was apparently an ionic space-charge polarization. Theoretical developments based on this model were verified by experiment. The activation energy for the relaxation time was 10.1 ± 0.4 kcal/mole. Examination of the oxide thickness dependence indicated that the carriers were not uniformly distributed initially, but a fixed number was present at a particular temperature and this number was independent of thickness. Further investigation led to the conclusion that a reaction between the metal electrode and the SiO2produced positively charged oxygen vacancies which migrated through the oxide under the influence of an electric field. A mechanism for the production and migration of these vacancies is proposed which complies with the low activation energy as well as the observed temperature and electrode dependence.     

Effect of annealing on the morphology and optoelectrical characteristics of ZnO thin films grown by plasma-assisted molecular beam epitaxy

The dependence of characteristics of plasma-assisted molecular beam epitaxy-grown ZnO thin films on different postgrowth annealing conditions was investigated. It was found that, under oxygen atmosphere, annealing temperature can profoundly affect the morphological, electrical, and optical properties of ZnO thin films. In particular, the surface morphology changed from a relatively smooth surface before annealing to various island morphologies after annealing above 800°C for samples grown directly on sapphire without a buffer layer. It is speculated that intrinsic stress due to lattice mismatch drives the island formation and the high temperature provides the energy needed for this surface rearrangement. Single-field Hall-effect measurement showed that the carrier concentration improved by an order of magnitude and the mobility increased from about 30 cm²/Vs to ∼70 cm²/Vs by annealing at 750°C. Variable-field Hall effect shows that a model with two carriers, one a degenerate low-mobility electron and the other a higher mobility non-degenerate electron, is needed to explain the transport properties of the thin film. Analysis indicates that annealing at 750°C decreased the carrier concentration and increased the mobility for the high-mobility carrier. Annealing also led to a significant improvement in photoluminescence, with temperatures of ∼750–850°C yielding the best results.     

Effects of annealing of MgO buffer layer on structural quality of ZnO layers grown by P-MBE on c-sapphire

We have investigated effects of annealing of MgO buffer layer on structural quality of ZnO layers grown by plasma assisted molecular beam epitaxy on c-sapphire. ZnO layers were characterized by atomic force microscopy, high resolution X-ray diffraction (HRXRD) and cross sectional transmission electron microscopy (TEM). AFM images show that annealing of a low temperature (LT)-MgO buffer at high temperatures enhanced the surface migration of adatoms, leading to the formation of larger terraces and smoother surface morphology, as indicated by the reduction of rms values of roughness from 0.6 to 0.3 nm. HRXRD and TEM experiments reveal that the dislocation density of ZnO layers is reduced from 5.3×10⁹ to 1.9×10⁹ cm⁻² by annealing a LT-MgO buffer. All of those features indicate the structural quality of ZnO layers was improved by annealing a LT-MgO buffer layer.     

The annealing effect for structural, optical and electrical properties of dysprosium–manganese oxide films grown on Si substrate

Samples of (Dy–Mn) oxide thin films were prepared on quartz and Si(p) substrates for optical and electrical investigations. These samples were annealed at different temperatures and characterised by UV–VIS absorption spectroscopy, X-ray fluorescence (XRF) and X-ray diffraction (XRD). The XRF spectrum was used to determine the weight fraction ratio of Mn to Dy in the prepared samples. The XRD shows that Dy oxide and Mn oxide prevent each other to crystallise alone or making a solid solution even at 600 °C. However, compound of DyMnO₃ was formed through the solid-state reaction for T > 800 °C. The ac-conductance and capacitance were studied, as a function of frequency and gate voltage and the fixed and interface charge densities were determined. It was found that the “correlated barrier hopping” CBH model controls the frequency dependence of the conductivity, while the Kramers–Kronig (KK) relations explain the frequency dependence of the capacitance. The parameters of CBH model were determined and show that the ac-conduction in crystalline (Dy–Mn) oxide is realised by bipolaron mechanism, where the barrier height of hopping is equal to the bandgap determined the UV–VIS absorption spectroscopy.