High Temperature Hydrogen Annealing Research Articles

Effect of surface preparation by high-temperature hydrogen annealing on the passivation of Ni-20 at.% Cr alloy in sulfuric acid

The effect of high-temperature annealing under hydrogen gas (H2) surface preparation on a binary polycrystalline Ni-20 at.% Cr alloy was investigated in comparison with conventional mechanical grinding surface preparation. Duplex surface films with inner Cr(III) oxide and outer Ni(II) and Cr(III) hydroxide layers natively formed before and after H2 annealing were characterized by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. A thinner and less homogeneous inner barrier layer formed after H2 annealing caused an oxidation peak at the active/passive transition in the linear sweep voltammetry measurement in a 0.5 M H2SO4 solution. Despite this high oxidation peak, passivation of the H2 annealed surface resulted in the formation of a more corrosion resistant inner layer than on the mechanically ground surface, as demonstrated by electrochemical impedance spectroscopy. The corrosion resistant passive film formation of the H2 annealed surface is attributed to the increased Cr enrichment of the inner layer caused by the selective Ni dissolution providing corrosion resistance to the initially weakly protected sites of the natively formed surface film.

Reduction of Epitaxial MoO2 to Mo by High-temperature Hydrogen Annealing

Reduction of Epitaxial MoO₂ to Mo by High-temperature Hydrogen Annealing

Micro-Mechanism of Silicon-Based Waveguide Surface Smoothing in Hydrogen Annealing**Supported by the National Natural Science Foundation of China under Grant Nos 51505324, 91123036, 61471255 and 61474079, the Specialized Research Fund for the Doctoral Program of Higher Education under Grant No 20131402110013, and the Foundation for Young Scholars of Shanxi Province under Grant No 2014021023-3.

The micro-mechanism of the silicon-based waveguide surface smoothing is investigated systematically to explore the effects of silicon-hydrogen bonds on high-temperature hydrogen annealing waveguides. The effect of silicon-hydrogen bonds on the surface migration movement of silicon atoms and the waveguide surface topography are revealed. The micro-migration from an upper state to a lower state of silicon atoms is driven by silicon-hydrogen bonding, which is the key to ameliorate the rough surface morphology of the silicon-based waveguide. The process of hydrogen annealing is experimentally validated based on the simulated parameters. The surface roughness declines from 1.523 nm to 0.461 nm.

Performances of Cr2O3–hydrogen isotopes permeation barriers

Hydrogen isotopes permeation barriers (HIPB) play an important role in reducing hydrogen isotopes permeation and leakage in hydrogen energy and thermonuclear fusion energy. In this study, the Cr2O3–HIPB were prepared on 316L stainless steel by RF magnetron sputtering. The performances of the Cr2O3–HIPB were investigated, including the deuterium-permeation reduction factor (D-PRF), micro-structure and nano-hardness. The D-PRF of 0.5 μm Cr2O3–HIPB could reach 48 at 700 °C and 152 at 400 °C in the first permeation test cycle. However, it reduced to 20 at 700 °C and 89 at 400 °C in the second permeation test cycle. The (012), (104), (113) and (116) diffraction peaks occurred and the morphologies became loose after high temperature hydrogen annealing. The nano-hardness decreased by 31% from 9.1 GPa to 6.3 GPa with increasing annealing time to 64 h. It was inferred that the hydrogen isotopes invasion should be responsible for the performance evolution of the Cr2O3–HIPB under high temperatures. Furthermore, the FeCr2O4 phase formed at the interfaces as a result of element diffusion, which might contribute to the cracking of Cr2O3–HIPB.

Degradation of SiO<sub>2</sub>/SiC Interface Properties due to Mobile Ions Intrinsically Generated by High-Temperature Hydrogen Annealing

The impact of mobile ions intrinsically generated in thermally grown SiO2 by high-temperature forming gas annealing (FGA) on the SiO2/4H-SiC interface properties was studied by means of electrical characterization of SiC metal-oxide-semiconductor (MOS) capacitors. Unlike Si devices, mobile ions located at the interfaces were found to cause a remarkable stretch-out of capacitance-voltage (C-V) curve near the accumulation condition, and the degree of stretch-out was more pronounced with increasing probe frequency. This suggests that the interface states with a long emission time constant are formed near the conduction band edge due to the mobile ions. To clarify this unusual phenomenon, several characterization techniques to evaluate interface state densities (Dit), including Terman, conductance, and C-ψs methods, were employed. The Dit values estimated for SiO2/SiC interfaces with mobile ions were a few times as large as those without mobile ions.

Copper oxide as a “self-cleaning” substrate for graphene growth

Abstract

Experimental Study of High Temperature Hydrozing Annealing 1J50 Alloy's Magnetic Properties

The good DC magnetic properties can be achieved for 1J50 soft magnetic alloy by applying high temperature hydrogen annealing. Annealing process parameters, e.g., atmosphere, soaking temperature, and time, are critical to soft magnetic properties. Qualitative results had been done for years. However a quantitative research among process parameters, microstructure, and magnetic properties can be more comprehensive and specific. In this study, a serial of experiments for 1J50 samples under the Chinese national standards. The influence of annealing temperature and socking time on DC magnetic properties and microstructure of the samples has been investigated on DC magnetic properties and microstructure of samples. The result shows that annealing process parameters have a nonlinear effect on the development of material microstructure and magnetic properties. Furthermore, the models among magnetic property, grain size, and process parameters have been built to quantitatively describe the interrelationship in between.

Investigation of unusual mobile ion effects in thermally grown SiO2 on 4H-SiC(0001) at high temperatures

Generation and elimination of mobile ions in thermally grown SiO2 on 4H-SiC(0001) were systematically investigated by electrical measurements of MOS capacitors. In contrast to a SiO2/Si system, intrinsic positive mobile ions were found to exist in as-oxidized SiO2/SiC structures, leading to significant instability of SiC-MOS devices. Post-oxidation annealing in Ar ambient mostly eliminates the mobile ions, but they are generated again by subsequent high-temperature hydrogen annealing despite the improved interface quality. The density of the mobile ions was estimated to be several 1012 cm−2. Possible physical origins of the mobile ions are discussed on the basis of the experimental findings.

Improvement in off-State Leakage Current of n-Channel SOS MOSFETs by Hydrogen Annealing of the SOS Film

The off-state source-to-drain leakage current and punchthrough voltage are the quantities that frequently limit the performance of short-channel floating-body silicon-on-sapphire (SOS) n-channel MOSFETs. In this paper, we demonstrate that the high-temperature hydrogen annealing of the SOS film prior to the device fabrication leads to marked improvement in these two parameters. The effect is attributed to the impact of hydrogen on the out-diffused thin alumina layer formed at the silicon-sapphire interface during the anneal. The thin alumina layer acting as a p-type dopant source at the back interface eliminates the back surface depletion of SOS n-MOSFETs. It also acts as a recombination center to eliminate the floating-body effect of floating-body n-MOSFETs. This technique provides a practical and reliable process to build short-channel floating-body SOS n-MOSFETs with off-state leakage as low as the junction leakage and punchthrough voltage as high as 6 V or higher at the gate length of 0.5 μm without any degradation on the inversion layer carrier mobility or increase in the junction leakage current.

Improvement in the electrochemical properties of gas atomized AB 2 metal hydride alloys by hydrogen annealing

The effects of high temperature hydrogen annealing were studied on powders made by gas atomization of both conventional vanadium-containing AB 2 metal hydride alloys and new vanadium-free AB 2 alloys designed for high power and low self-discharge applications. In both alloy systems, annealing in 950 °C hydrogen for 30 min was proven to be effective in improving the capacity, formation, high power, and low temperature performance in the nickel metal hydride battery compared to previous gas atomization trials where each property was reduced. The advantage in improving the cycle life by gas atomization was further extended by the hydrogen annealing process. Reduction in the surface oxide was confirmed by the use of Auger electron spectroscopy depth profiling and magnetic susceptibility. Metallic elements were reduced from the oxide state by hydrogen to react with the metallic nickel particulates originally embedded in the surface oxide in a high temperature environment and created a new surface free of oxygen.

Shape Transformation of 4H-SiC Microtrenches by Hydrogen Annealing

This study investigates the shape transformation of 4H-SiC microtrenches that occurs during high-temperature hydrogen annealing, which is used to improve growth on such prepared substrates. The trenches have micron-sized widths and depths and were annealed in hydrogen ambient at temperatures of 1400–1600 °C for 30–3600 s. After hydrogen annealing, cross-sectional images of the samples were obtained by scanning electron microscopy (SEM). These SEM images reveal that the top and bottom trench corners become rounded during hydrogen annealing. The top trench corners become rounded by an etching reaction, whereas the bottom trench corners become rounded as a result of a regrowth phenomenon that involves the transportation of atoms. This study analyzes the mechanism of these transformations in terms of Mullins' continuum model. The results suggest that the evaporation–condensation process is dominant in the case of SiC annealing.

Low surface roughness and threading dislocation density Ge growth on Si (0 0 1)

Although several recent studies have successfully reduced the threading dislocation density (TDD) in Ge films grown on Si, high surface roughness is still problematic for useful nanoscale lithography and device fabrication. In this work, we achieved both low TDD and surface roughness by repeating a deposition–annealing cycle consisting of the following steps: low temperature deposition, high temperature and high rate deposition, high temperature hydrogen annealing. The root-mean-square roughness of the 3-cycle sample is in the range of 0.4–0.6 nm for 10×10 μm 2 scan field atomic force microscopy (AFM) images. The TDD measured by plan-view TEM is 0.8–1×10 7 cm −2 with a 1.44 μm thickness sample. Furthermore, a 4-cycle sample reveals further improvement in surface planarity and pit density in the AFM images with a thickness of 2.38 μm Ge. The high temperature and high rate Ge deposition combined with high-temperature hydrogen annealing efficiently reduces not only the TDD, but also the surface roughness.

Reduction of Fluoride Species and Surface Roughness by H<sub>2</sub> Gas Addition in SiC Dry Etching

We study for the effects of additional gas such as oxygen (O2) and hydrogen (H2) into SF6. When H2 gas was added to SF6, surface fluoride atomic concentration and surface roughness were lower than the other additional gases. Surface fluoride atomic concentration under this experiment was reduced from 28 at % to 6 at % by the H2 addition. In post-processing, the fluoride atomic concentration was succeeded in a large reduction by processing H2, O2 plasma and high temperature hydrogen annealing. In hydrogen annealing, surface fluoride atomic concentration could be suppressed to less than 3 at %. This is new result succeeded in reduction of surface fluoride species greatly by hydrogen processing.

Numerical Study on Shape Transformation of Silicon Trenches by High-Temperature Hydrogen Annealing

We have studied shape transformation of micron-sized trenches on Si substrates during high temperature hydrogen annealing, performing numerical simulations based on Mullins' theory. We have considered evaporation-condensation and surface diffusion as mass transport mechanisms causing shape transformation. The simulation allowing only surface diffusion reproduces well the observed micron-scale aspects of shape transformation by hydrogen annealing at 1000–1150°C.

Evolution of surface morphology of Si-trench sidewalls during hydrogen annealing

We have investigated the effect of high temperature hydrogen annealing on the sidewall morphology of micron-sized trenches formed on a Si(001) substrate by atomic force microscopy. We show that high temperature hydrogen annealing is effective for the flattening of as-etched rough surfaces and yields surfaces having atomic steps and terraces when the annealing temperature exceeds 1000°C. We also found that, during hydrogen annealing, large-scale structural changes accompanied trench corner rounding and occurred through the movement of steps on the sidewall surfaces.

Passivation of hexagonal SiC surfaces by hydrogen termination

Surface hydrogenation is a well established technique in silicon technology. It is easilyaccomplished by wet-chemical procedures and results in clean and unreconstructedsurfaces, which are extremely low in charged surface states and stable against oxidation inair, thus constituting an ideal surface preparation. As a consequence, methods forhydrogenation have been sought for preparing silicon carbide (SiC) surfaces with similarwell defined properties. It was soon recognized, however, that due to differentsurface chemistry new ground had to be broken in order to find a method leadingto the desired monatomic hydrogen saturation. In this paper the results of Hpassivation of SiC surfaces by high-temperature hydrogen annealing will be discussed,thereby placing emphasis on chemical, structural and electronic properties of theresulting surfaces. In addition to their unique properties, hydrogenated hexagonalSiC {0001} surfaces offer the interesting possibility of gaining insight into the formation ofsilicon- and carbon-rich reconstructions as well. This is due to the fact that todate hydrogenation is the only method providing oxygen-free surfaces with a Cto Si ratio of 1:1. Last but not least, the electronic properties of hydrogen-freeSiC {0001} surfaces willbe alluded to. SiC {0001} surfaces are the only known semiconductor surfaces that can be prepared in their unreconstructed(1 × 1) state with one dangling bond per unit cell by photon induced hydrogen desorption. Thesesurfaces give indications of a Mott–Hubbard surface band structure.

Effects of hydrogen transport and reactions on microelectronics radiation response and reliability

The transport and reactions of hydrogen-related species play critical roles in determining the ionizing radiation response and long-term reliability of Si-based metal-oxide-semiconductor (MOS) and bipolar microelectronics technologies. The role of hydrogen is reviewed in radiation-induced interface-trap formation in metal and polycrystalline-Si-gate devices, with an emphasis on understanding the transport and reaction mechanisms responsible for defect formation. Effects of hydrogen on radiation-induced oxide and border-trap charge densities are discussed. Enhanced low-dose-rate effects in bipolar devices and integrated circuits are sensitive to hydrogen transport and reactions in the oxides that overlie the emitter–base junctions. These enhanced low-dose-rate effects present great challenges for defining practical, cost-effective acceptance tests of bipolar devices for space radiation environments. In addition, a brief discussion is provided of the effects of hydrogen-related species on MOS long-term reliability, including high-field stress, dielectric leakage (e.g., stress-induced leakage current), oxide breakdown, hot-carrier effects, dopant passivation, and low-frequency (1/ f) noise. The potential impacts on latent interface-trap formation are discussed for retarded hydrogen transport, trapping, and/or dopant passivation. Further, differences in proton transport and reactions are noted for (a) conventional Si/SiO 2/Si structures and (b) those with high oxygen vacancy densities that are exposed to high-temperature hydrogen annealing ambients. In the former, hydrogen is consumed irreversibly by processes such as interface-trap formation; in the latter, hydrogen often can be cycled from the gate to the Si interface reversibly without losses for up to 10 6 cycles or more. Moreover, the inferred transport rates are much higher for post-forming-gas anneal transport than for radiation-induced interface-trap buildup. Finally, the motion of hydrogen during post-process, but pre-irradiation, thermal treatments (e.g., burn-in, or temperature cycles during the packaging process) has been associated with significant changes in the radiation response of both MOS and bipolar transistors. Typical mitigation techniques are discussed to reduce the effects of hydrogen on MOS radiation response and long-term reliability. Several unresolved issues and opportunities for future work are identified. The present knowledge of hydrogen effects on the long-term reliability and radiation response of Si based microelectronics will be broadened significantly as alternative dielectrics to SiO 2 are increasingly introduced into the manufacturing process. A brief example of the significant effects of hydrogen on dielectric layers other than SiO 2 is provided for deposited diamond thin films.

Response to “Comment on ‘Reduction of interface-state density in 4H–SiC n-type metal–oxide–semiconductor structures using high-temperature hydrogen annealing’ ” [Appl. Phys. Lett. 78, 4043 (2001)

Response to “Comment on ‘Reduction of interface-state density in 4H–SiC <i>n</i>-type metal–oxide–semiconductor structures using high-temperature hydrogen annealing’ ” [Appl. Phys. Lett. 78, 4043 (2001)

Reduction of interface-state density in 4H–SiC n-type metal–oxide–semiconductor structures using high-temperature hydrogen annealing

The effects of hydrogen annealing on capacitance–voltage (C–V) characteristics and interface-state density (Dit) of 4H–SiC metal–oxide–semiconductor (MOS) structures have been investigated. The Dit was reduced to as low as 1×1011 eV−1 cm−2 at Ec−E=0.6 eV using hydrogen annealing above 800 °C, where Ec−E is the energy level from the conduction-band edge. Secondary ion mass spectroscopy and Dit analysis revealed that Dit decreased with the increase of hydrogen concentration accumulated at the SiO2/4H–SiC interface. The interface states at SiO2/4H–SiC are thought to be originated from the dangling bonds of C atoms as well as Si atoms, because Dit decreases as the hydrogen annealing temperature increases and saturates around 800 °C. This high-temperature hydrogen annealing is useful for accumulation-type SiC metal–oxide–semiconductor field-effect transistors, which have n-type MOS structures to reduce the Dit.

Current trends in silicon defect technology

Defects in silicon crystals have been of great scientific and technological interest since before the earliest days of the silicon transistor. Recently much attention has been focussed on crystal originated pits (COPs) on the polished surface of the wafer. These defects have been shown to degrade gate oxide quality. Although it is thought that the effect of COPs on thinner gate oxides in future generations will not be so severe, considerable effort has been directed toward reducing their density in the grown crystal. This can be done by controlling the thermal gradient and pull rate during crystal growth. Other techniques for reducing the incidence of COPs include epitaxial deposition or high-temperature hydrogen annealing. Another class of defects that evokes considerable interest is surface metals. These tend to decorate stacking faults and other defects in the crystal and degrade the device characteristics. The degree of degradation may increase or decrease as the line width shrinks depending on the processing circumstances. Stress induced during high temperature processing can lead to the formation of slip in the wafer. For large diameter wafers (≥300 mm), sag due to gravitational forces must be taken into account in addition to thermal stresses. Other stresses induced during device processing can propagate dislocations and generate other defects that are also detrimental to device performance. Hydrogen and oxygen are two impurities that impact material performance in multiple ways, and their control continues to be of prime importance in silicon technology.