Surface Oxide Thickness Research Articles

Anodic oxidation during MEMS processing of silicon and polysilicon: native oxides can be thicker than you think

The thickness and surface roughness of the native oxide on undoped and P-doped single crystal silicon and polycrystalline silicon (polysilicon) were measured after exposure to aqueous hydrofluoric acid (HF) in the presence of localized metallization of sputtered Au or Pd. Both P-doping and the presence of metallization led to an increase in the thickness of the native surface oxide and an increased surface roughness after HF exposure. An external positive (negative) potential during HF immersion increased (decreased) the rate of what is clearly electrochemical i.e., anodic corrosion. The presence of the sputtered metallization promoted anodic corrosion, particularly in HF and particularly for P-doped silicon. Porous silicon can be formed under these conditions, due to dissolution of the anodically produced surface oxide. Subsequent oxidation of the porous silicon can lead to thick surface oxide layers.

Comparative Evaluations of Surface Characteristics of cp Titanium, Ti-6AI-4V and Ti-15Mo-2.8Nb-0.2Si (Timetal® 21SRx)

Abstract Commercially pure titanium (cpTi), Ti-6A1-4V (Ti64), and Ti-15Mo-2.8Nb-0.2Si (21SRx), with three unique atomic, alpha, alpha-beta, and beta grain structures, respectively, were subjected to three different surface treatments: cleaning, nitric acid passivation, and heat treatment. Experiments were conducted to determine the effects of the type of material and surface modifications on the substrate microstructure, surface oxide composition and thickness, and resultant corrosion behavior. Metallography showed the cpTi groups were an equiaxed single alpha phase material, the Ti64 groups a dual-phase alpha-beta material, and the 21SRx groups an equiaxed beta material. The different surface treatments did not alter the substrate microstructures of any groups. Spectroscopic (AES) results showed typical titanium and titanium alloy spectra with dominant Ti and O peaks for all sample groups, indicative of titanium dioxide. In addition, small Al and Mo peaks were detected throughout the surface oxides of the Ti64 and 21SRx specimens, respectively. AES depth profiling showed no significant difference in the oxide thickness between all the Cleaned and Passivated groups regardless of metal or alloy group. However, all the Heat Treated groups had significantly thicker oxides. In general, corrosion results showed Passivated and Heat Treated groups to have similar corrosion properties and significantly improved corrosion resistances compared to the Cleaned groups. All impedance spectra fit into the Randles equivalent circuit model, and all sample groups exhibited near ideal capacitive behavior (φ ≅ 90°) expected for titanium and its alloys.

Tunnel DCIV Extraction of Dopant-Impurity Concentration, Oxide Thickness, and Length in the Channel and Extension Regions of Ultrathin Gate-Oxide MOS Transistors

A methodology is described for extracting, between the source and drain, the spatial variations of surface dopant-impurity concentration and oxide thickness in the channel, drain/extension and source/extension regions using experimental tunnel direct current current-voltage data of the drain, source, and basewell terminal currents versus the gate/base voltage. An example is given using an pMOS transistor with W/L=10 /spl mu/m/0.3 /spl mu/m fabricated by a factory 100-nm technology. Zeroth (constant values) and first-order (linear variation with position) representation formulas are used for the impurity concentration and oxide thickness to fit the experimental data, which also give the electrical lengths of the three regions.

Oxidation of aluminum nanoclusters

The dynamics of oxidation of aluminum nanoclusters ($20\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ diameter) is investigated using a parallel molecular dynamics approach based on variable charge interatomic interactions due to Streitz and Mintmire that include both ionic and covalent effects. Simulations are performed for both canonical ensembles for molecular oxygen $({\mathrm{O}}_{2})$ environments and microcanonical ensembles for molecular $({\mathrm{O}}_{2})$ and atomic $({\mathrm{O}}_{1})$ oxygen environments. Structural and dynamic correlations in the oxide region are calculated, as well as the evolution of charges, surface oxide thickness, diffusivities of atoms, and local stresses. In the microcanonical ensemble, the oxidizing reaction becomes explosive in both molecular and atomic oxygen environments due to the enormous energy release associated with $\mathrm{Al}\text{\ensuremath{-}}\mathrm{O}$ bonding. Local stresses in the oxide scale cause rapid diffusion of aluminum and oxygen atoms. Analyses of the oxide scale reveal significant charge transfer and a variation of local structures from the metal-oxide interface to the oxide-environment interface. In the canonical ensemble, oxide depth grows linearly in time until $\ensuremath{\sim}30\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$, followed by saturation of oxide depth as a function of time. An amorphous oxide layer of thickness $\ensuremath{\sim}40\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ is formed after $466\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$, in good agreement with experiments. The average mass density in the oxide scale is 75% of the bulk alumina density. Evolution of structural correlation in the oxide is analyzed through radial distribution and bond angles. Through detailed analyses of the trajectories of O atoms and their formation of $\mathrm{O}{\mathrm{Al}}_{n}$ structures, we propose a three-step process of oxidative percolation that explains deceleration of oxide growth in the canonical ensemble.

Electroless Deposition of Silver by Galvanic Displacement on Aluminum Alloyed with Copper

In this paper, a procedure is described for the electroless deposition of silver on films containing 99.5% aluminum and 0.5% copper. The deposition proceeds in the absence of external reducing agents via the galvanic displacement mechanism by which silver cations are reduced and copper is oxidized. Although aluminum is a stronger reducing agent than copper, the galvanic displacement of aluminum by silver is not observed with pure (99.997%) aluminum substrates. By alloying aluminum with copper, aluminum films are made amenable to electroless deposition of silver by galvanic displacement. To generate a clean surface for electroless deposition with a controlled and minimal thickness of surface oxide, the aluminum films alloyed with copper are anodized in oxalic acid and etched in a mixture of chromic and phosphoric acids. Thinning of the barrier aluminum oxide during etching and deposition of silver particles are monitored with electrochemical impedance spectroscopy (EIS). Analysis of EIS data indicates that...

Electrochemical corrosion behavior and MG-63 osteoblast-like cell response of surface-treated titanium

Commercially pure titanium is used as a clinical implant material for many orthopedic and dental implant devices owing to its excellent corrosion resistance and good biocompatibility. However, there remains concern over the release of metal ions from prostheses and unresolved questions about its behavior in a biological environment. Our research investigated the influence of surface oxide thickness and phase on the corrosion resistance in 0.9% NaCl solution by potentiostat and XRD. Also, the MG-63 osteoblast like cell morphology and proliferation were studied to evaluate the biocompatibility in terms of surface treatment. It is demonstrated that a substantial decrease in the current density may be attained due to surface oxide thickening and phase transformation by thermal oxidation. The osteoblast adhesion morphology and proliferation data indicated that the osteoblast cell response is not conspicuously influenced by the thermal oxidation and nitric acid passivation treatments but by surface roughness and porosity of 3rd networking.

Epitaxial growth on gas cluster ion-beam processed GaSb substrates using molecular-beam epitaxy

Chemical mechanical polished (CMP) (100) GaSb substrates were processed using gas cluster ion beams (GCIB) to improve surface smoothness, reduce subsurface damage, and produce a thermally desorbable oxide layer for molecular-beam epitaxy (MBE) overgrowth. In this article, we report the growth of GaSb/AlGaSb epilayers on GCIB processed GaSb substrates. The substrates were processed using either O2 or CF4/O2 as the gas cluster in a dual-energy recipe that included a moderate energy (10 keV) etch step followed by a low-energy (3 keV) smoothing step, with a relatively low total dose of 4×1015 ions/cm2. Half of each wafer was masked such that the epitaxial layers were grown on both CMP and GCIB polished surfaces. Atomic force microscopy showed the elimination of CMP surface scratches on the GCIB processed surfaces. X-ray photoelectron spectroscopy results indicate that the surface oxide composition and thickness can be engineered through the GCIB process recipes. AlGaSb marker layers were used to chart the evolution of the overgrown layers. Cross-sectional transmission electron microscope images of the substrate/epi-interface show that the CMP finished regions contained defects that propagated into the epilayers as compared to the GCIB finished region that showed no penetrating defects, indicating an improved substrate/epi-interface. This work demonstrated that GCIB processing of semiconductor materials has the potential to produce “epiready” surfaces.

Analysis of heavy-ion induced charge collection mechanisms in SOI circuits

Focused ion microbeam and broadbeam heavy-ion experiments on capacitors and SRAMs are used to investigate charge collection in SOI devices. Charge collection in capacitors and ICs can be induced by displacement currents caused by the release of charge in the substrate. The magnitude of charge collection depends on the geometry, gate surface area and oxide thickness of the device. It is mainly induced by the diffusion of carriers generated in the silicon bulk, which induces a voltage drop under the oxide surface. Carrier diffusion in low-doped silicon creates coupling effects between MOS elements separated by up to hundreds of microns. However, because of charge sharing effects, charge collection by displacement currents (by itself) does not appear to significantly affect SEU sensitivity in SOI devices. p–n junctions are far less sensitive to charge sharing effects than neighboring MOS structures. A mechanism that can significantly increase the SEU saturation cross section in SOI devices is charge release in non-ideally doped drain regions (not heavily doped throughout the silicon film). Carriers released in drain regions can drift or diffuse into the body region and be amplified by parasitic bipolar effects. By heavily doping drain junctions throughout the silicon film, drain strike sensitivity can be significantly reduced. For this case, SEU sensitivity can be limited to gate (body) strikes and by reducing parasitic bipolar effects using body ties, SOI circuits can be fabricated that are very hard to single event effects. These results have important implications on the soft-error reliability of SOI and other oxide-isolated structures, e.g., DRAMs. For SOI SRAMs, it is possible that the additive effects of charge collection by displacement currents and charge released in drain regions may lead to SEU. For trench DRAMs, the retention capacitors are particularly sensitive to charge released in the substrate. Charge collection in retention capacitors by displacement currents can lead to multiple bit upsets (MBUs) in DRAMs, thus significantly degrading the soft-error reliability of DRAMs.

Physical properties and life prediction of TMC at elevated temperatures

Abstract Mechanical performance of titanium matrix composites degrades at elevated temperatures because of the changes in physical properties of the composites (i.e. matrix oxidation, embrittlement and phase transformation). These physical properties of the composites should be taken into account in a life prediction model. The present study was conducted to improve an existing life prediction model (local fiber stress failure model). To achieve this goal, isothermal fatigue tests were performed on [0/±45/90] s SCS-6/Timetal 21S composite at temperatures 400 and 500 °C, and with hold times. The composite lives at 400 and 500 °C increased with increase in hold time. It was observed that the matrix oxidation was accelerated under applied stress amplitude. In addition, the measurement of the surface oxide thickness suggested that the oxidation was much easier and faster at 500 °C than at 400 °C. A modification was made on the life prediction model. Since the oxidation was shown to have a significant effect on the composite life, it was factored into the model. The modified model produced a good correlation between modified single parameter value and the number of cycles to failure.

Surface oxidation kinetics of SiC powders in wet and dry air studied by x‐ray photoelectron spectroscopy and bremsstrahlung‐excited Auger electron spectroscopy

AbstractSilicon carbide powder samples were heated at temperatures between 600 °C and 850 °C in wet and dry air to investigate the effect of moisture on the oxidation kinetics. Equations were derived to calculate the surface oxide thickness from both the Si 2p XPS spectra and from the Si KLL bremsstrahlung‐excited Auger spectra. The oxide film growth rates are shown to be parabolic. The film thickness formed during oxidation in wet air was larger than that in dry air for the same temperature and heating time. The activation energy for wet oxidation was found to be significantly lower than that for dry oxidation within this temperature range. Copyright © 2003 John Wiley & Sons, Ltd.

Suppression of native oxide growth in sputtered TaN films and its application to Cu electroless plating

Electroless plated copper can be deposited on a TaN surface initiated by displacement plating when the surface oxide layer is removed by wet chemical etching. For application to ultra-large-scale integrated (ULSI) interconnection technology in which very thin TaN barrier films are used, it is essential to form a stable TaN film with minimal native oxide thickness. In this study, TaN films with various N/Ta atomic ratios were fabricated by reactive sputtering and native oxide growth on the surface was investigated by x-ray photoelectron spectroscopy, high resolution Rutherford backscattering spectrometry, and x-ray diffraction (XRD). It was found that when the N/Ta atomic ratio in the film was lower than 1.2, surface oxidation of the TaN film advanced with time. When the ratio was higher than 1.2, oxidation of the TaN film stopped at 1 ML. The XRD spectra indicated that when the N/Ta atomic ratio was between 0.82 and 1.25, face-centered-cubic TaN films were formed and the resistivity increased with an increase in the N/Ta ratio. Thus, a TaN film with a N/Ta ratio of 1.25 ratifies the minimal surface oxide thickness as well as low-resistivity requirements, and is appropriate for ULSI Cu interconnections using electroless Cu deposition.

Surface characterization of metal nanoparticles

Air exposed aluminum and nickel nanoparticles were investigated using high-resolution and analytical transmission electron microscopy (HREM/AEM), X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS). The diameter of the Al particles ranged from 20 to 260 nm with an average size of 100±50 nm. Individual Ni particles were spherical, ranging from 7 to 230 nm in size with an average size of 70±45 nm. The Al nanoparticles were covered by a 3 nm thick amorphous and compact surface oxide layer. Ni nanoparticles were surrounded by a non-uniform, crystalline surface oxide layer. Elemental analysis indicated that the Al nanoparticles contained O and Si and that the oxygen is associated with the particle surface layer, while no oxygen confinement in the surface layer was found in Ni nanoparticles. XPS confirmed the NiO presence in the surface layer of Ni particles. These results suggest that the sintering behavior of these metal nanoparticles may be inhibited, though to a different degree, due to the surface oxides.

Surface topography evolution and fatigue fracture in polysilicon mems structures

This paper presents the results of an experimental study of the micromechanisms of surface topography evolution and fatigue fracture in polysilicon MEMS structures. The initial stages of fatigue are shown to be associated with stress-assisted surface topography evolution and the thickening of SiO/sub 2/ layers that form on the unpassivated polysilicon surfaces and crack/notch faces. The differences in surface topography and oxide thickness are characterized as functions of fatigue cycling before discussing the micromechanisms of fatigue fracture.

Surface topography evolution and fatigue fracture of polysilicon

This paper presents the results of an experimental stydy of the micromechanisms of fatigue crack nucleation and fatigue fracture in polysilicon MEMS Structures. The initial stages of fatigue are shown to be associated with stress-assisted surface topography evolution and the thickening of SiO2 layers that form on the unpassivated polysilicon surfaces and crack/notch faces. The differences in surface topography and oxide thickness are elucidated as functions of fatigue cycling before discussing the micromechanisms of crack growth and final fracture.

Oxide-Semiconductor Interface Characterization Using Kelvin Probe-AFM In Combination With Corona-Charge Deposition

ABSTRACTCorona charge deposition methods in combination with spatially resolved surface potential measurements have become a standard tool for Si oxide quality monitoring. Based on this technique oxide-semiconductor interface parameters such as surface barrier height, oxide thickness and oxide charge density can now be monitored in-line with commercially available devices. The ongoing downscaling of integrated circuits into the sub-100 nm regime makes the development of high resolution oxide screening methods increasingly important.However, currently available commercial devices are limited in their spatial resolution since they employ the traditional vibrating Kelvin probe technique, restricting their lateral resolution to several μm. In order to increase the lateral resolution of this measurement method we have combined the corona-charge deposition technique with Kelvin Probe AFM. We present initial results of this novel measurement technique and demonstrate its feasibility by measurements on lithographically prepared oxide patterns on Si wafers with different oxide thicknesses.

Ultraviolet Raman and Optical Transmission Studies of RF Sputtered Indium Nitride

UV Raman and absorption measurements plots are used to demonstrate the improvement for InN samples following removal of a surface oxide by 1.0 M HCl etching. An increase in Raman spectra signal strength and a reduction of the apparent band-gap by up to 50 meV is observed. The thick surface oxide is believed to have formed as a result of ex-situ exposure of the samples on removal from the growth system. The importance of target nitridation for RF sputtered material is also demonstrated.

Erosion–corrosion tests on ITER copper alloys in high temperature water circuit with incident heat flux

To investigate the erosion–corrosion behavior of the Cu-alloys, i.e. CuCrZr and CuAl25-candidate materials for the manufacture of the diverter cooling channels for ITER, a test loop has been developed for testing erosion–corrosion behavior under high heat flux conditions. The heat loads on the test specimen surface amounts to 10 MW/m 2. Under adverse testing conditions in oxidizing water (5–10 ppm H 2O 2) at 100 °C, with a flow velocity of 10 m/s and intermittent heat loading, followed by cooling cycles under oxidizing conditions maintained, CuCrZr alloy has shown the formation of a thick surface oxide films (essentially cupric oxide, CuO). This surface layer seems loosely adhesive, and detachable by mechanical or thermal shocks, or by fluid flow velocity effects. Indicated with a rough morphology, surface attacks were somewhat observed in areas after the surface oxide layer spalled off. Present results suggest the necessity for, such as, strict hydrogen water chemistry (HWC), in order to limit the copper corrosion rate or at least the release of copper into the cooling water circuit.

Effect of surface treatment of NiTi alloy on its corrosion behavior in Hanks' solution.

The effect of surface modification of NiTi shape memory alloy on its corrosion behavior in Hanks' solution was determined. The near-equi-atomic super elastic NiTi (Ni 55.8 wt %) alloy used for this study was provided by Memry USA. The surfaces of heat-treated samples were modified by mechanical polishing (MP), electropolishing (EP), and electropolishing followed by chemical passivation (CP). As-heat-treated samples with straw-colored oxide finishes (SCO) and blue-colored oxide finishes (BO) also were included in the study. Surface analysis was performed using auger electron spectroscopy (AES), atomic force microscopy (AFM), and contact angle measurements (CAM). It was shown that surface roughness increased in the order CP < EP < SCO < BO < MP. The nickel release within the five groups of NiTi samples, as determined by atomic absorption spectrophotometry, reduced in time over the measured period. The level of Ni ions released over a 25-day immersion period was highest in the SCO sample (0.002 microg/day). This Ni level is negligible compared with the daily intake of Ni in an ordinary diet. The auger electron spectroscopy (AES) analyses indicated that before immersion in Hanks' physiologic solution, the main surface composition of all the samples was titanium and nickel, with a small amount of oxygen, carbon, and sulphur as contaminants. And the surface oxide thickness of the different samples increased in the order CP < EP < MP < BO < SCO. On the other hand, for the electrodes treated under the same conditions, the mean breakdown potential value decreased in the order BO > MP > CP > EP > SCO while the corrosion current density and rate increased in the order CP < SCO < EP < BO < MP.

Role of the i layer surface properties on the performance of a-Si:H Schottky barrier photodiodes

Abstract In this work, we study the influence of the hydrogenated amorphous silicon (a-Si:H) surface treatment on the J – V characteristics of a-Si:H/Pd Schottky barrier photodiodes. The a-Si:H surface were etched, thermally oxidised and wet oxidised by H 2 O 2 . The a-Si:H films were characterised by spectroscopic ellipsometry, were we found that all the oxidation techniques promote an increase of the surface oxide thickness that was confirmed by the increase of the barrier height. The highest barrier was achieved by the H 2 O 2 oxidation where a value of 1.17 eV was found. As a result of the barrier height increase, the dark reverse current density decreases up to 10 −10 A/cm 2 and the signal to noise ratio increases up to 10 6 . The open circuit voltage under AM1.5 illumination conditions also increases from 0.4 to 0.5 V. These results reveal the importance of the a-Si:H surface preparation prior to metallization to improve the Schottky photodiodes properties.

In vivo evaluation of modified titanium implant surfaces produced using a hybrid plasma spraying processing

In this study, the biological responses to surface-modified titanium (Ti) was investigated using a dog model. Titanium plasma spraying and ion implantation of amino (NH 2 +) groups were used as means of modifying Ti surfaces. Characterization of the modified Ti surfaces was performed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning Auger electron spectroscopy. In vivo evaluations were performed using fluorescence microscope, scanning electron microscope and energy disperse spectroscopy. It was observed in this study that ion-implanted porous-graded titanium coatings had a thick surface oxide layer, containing a small amount of nitride. In vivo study indicates direct bone contact between surface-modified Ti implants and osseous tissues. In addition, osseous tissues were observed to grow into the pores inside the coatings, thereby allowing the formation of a gradual calcium phosphate interface layer. It was concluded from this study that ion implantation of Ti surfaces with amino groups, induced higher concentration of calcium and phosphorus precipitation and more mineralization as compared to non-ion-implanted Ti surfaces.