Polished Layer Research Articles

Circular Geometry Transistors Fabricated on Germanium-on-Alumina Bonded Substrates

Germanium (Ge) has been bonded to fine grain alumina (Al2O3) by means of a polished polycrystalline silicon interface layer. After room temperature bonding and subsequent bond strength annealing at 150 oC for 24 hrs, the germanium layer was ground and polished to 100µm. Low temperature Tungsten (W) gate circular geometry devices, W/L = 9, fabricated on this layer exhibited effective mobility values of 150 cm2/Vs. This is much lower than results obtained on equivalent devices on bulk Ge. Improvement in the germanium polish process resulted in transistors with an effective mobility of 415 cm2/Vs, comparable to that of the bulk Ge devices. Low temperature measurement, down to temperatures of 173 K, showed an improvement in device performance resulting in both an increase in effective mobility to 591 cm2/Vs and a decrease in sub threshold slope from 180 mV/dec to 60 mV/dec indicating a reduction in leakage current.

Surface morphology of Kr+-polished amorphous Si layers

The surface morphology of low-energy Kr+-polished amorphous Si layers is studied by topographical methods as a function of initial substrate roughness. An analysis in terms of power spectral densities reveals that for spatial frequencies 2×10−2–2×10−3 nm−1, the layers that are deposited and subsequently ion polished reduce the initial substrate roughness to a rms value of 0.1 nm at the surface. In this system, the observed dominant term in linear surface relaxation, proportional to the spatial frequency, is likely to be caused by the combined processes of (a) ion-induced viscous flow and (b) annihilation of (subsurface) free volume during the ion-polishing treatment. Correspondingly, a modification of the generally assumed boundary conditions, which imply strict surface confinement of the ion-induced viscous flow mechanism, is proposed. Data on surface morphology are in agreement with the optical response in extreme ultraviolet from a full Mo/Si multilayered system deposited onto the modified substrates.

Selective Chemical Mechanical Polishing of Silicon Dioxide over Silicon Nitride for Shallow Trench Isolation Using Ceria Slurries

For the shallow trench isolation process, in which a thin silicon nitride film acts as a polish stop layer, a polishing slurry with a high oxide to nitride removal rate selectivity is required to remove the overburden oxide. In this work, we show that using ceria-based slurries and only 0.05% of any one of three different cyclic amine additives, namely, pyridine HCl, piperazine, and imidazole, very low nitride (<2 to 3 nm/min) and high oxide (∼350 nm/min) removal rates can be obtained for blanket films. The role of these additives in the slurry toward achieving the desired removal rate selectivities of silicon dioxide over silicon nitride is discussed considering pyridine HCl as an example, using zeta potential, contact angle, adsorption isotherm, and thermogravimetric analysis data.

Improving the performance of the cryogenic heat pipe-target system for the COSY-TOF experiment

Very lightweight, thin liquid hydrogen/deuterium heat pipe-target systems are used in the Time Of Flight (TOF) spectrometer at the COSY accelerator facility. The proton beam impinges upon LH 2/LD 2 targets thereby heating the target. The stability of the liquid targets depends on the thermal capacity of the whole system, the energy losses from the proton beam and heat losses from the surrounding of the heat pipe-target system. The radiation heat load has been reduced by a factor of 4.5 by reducing the length of the gas tube from 180 cm (long tube) to 40 cm (short tube). Furthermore, the 40 cm long gas tube was coated with a thin polished gold layer, thereby reducing the heat load by an additional factor 22. The thermal capacity is improved by reducing the mass of the gas tube from 23 g to 5 g. The cool down time of the 7 mm diameter gold coated heat pipe with the gold coated 40 cm gas tube is reduced by 12 min.

Surface Hardening of Titanium Articles With Titanium Boride Layers and its Effects on Substrate Shape and Surface Texture

There is widespread interest in engineering improved properties into the surface layer of manufactured articles. One method for doing so involves a novel boriding process that creates hardened surface layers by the growth of a dual layer TiB2+TiB coating on titanium articles. The objective of the present work was to demonstrate the fundamental feasibility of this process by producing uniform thick boride coating layers on titanium articles and to polish them to a very fine surface texture suitable for biomedical implant bearing surfaces. A powder pack diffusion boriding process was used to grow dual layer TiB2+TiB coatings on simple shapes. Lapping processes were used to polish the borided articles. Evaluation was carried out using measurements of surface texture, geometric form, and hardness, and by metallurgical analysis. Boriding on as-received titanium articles resulted in shape distortion that hampered the subsequent polishing efforts. Hence, further articles were treated with stress-relief annealing prior to boriding, at temperatures below and above the β-transus of the substrate article. Annealing itself caused some form distortion, which was eliminated by lapping. Then, after boriding the annealed articles, varying surface textures and shape distortions were observed. Articles annealed above the β-transus had surface textures with significant peak-to-valley roughness (14–55 μm), and the texture appeared to be patterned upon the substrate microstructure. However, form distortion seemed to be alleviated. For articles annealed below the β-transus, form distortion was not alleviated, and the articles exhibited wavy surface textures with a high peak-to-valley roughness (up to 50 μm). Whether combined or independent, the surface texture changes and shape distortion that occurred during boriding thwarted the polishing processes; the articles could not be uniformly polished to a roughness less than 0.05 μm within the coating thickness. To achieve uniformly polished dual layer TiB2+TiB surfaces on titanium articles using the pack boriding technique, it appears that the substrate raw materials should be free of residual stresses and consist of a fine microstructure.

Influence of secondary phases on the tribological response of electro-discharge machined zirconia-based composites against WC–Co cemented carbide

Three ceramic composite grades, consisting of a ZrO 2 matrix and 40 vol.% WC, TiC 0.5N 0.5 or TiN phase, were completely self-developed by hot pressing powder mixtures of yttria-stabilised zirconia (Y-TZP) and distinctive WC, TiC 0.5N 0.5 or TiN powder sources. The friction and wear characteristics of the zirconia-based composites against WC–Co cemented carbide were investigated by performing dry reciprocating sliding experiments on a pin-on-plate tribometer under various normal contact forces. The generated wear was quantified using surface scanning topography. Post-mortem obtained wear volumes were correlated to real-time recorded wear depth. The ZrO 2–40 vol.% WC grade displayed more favorable tribological properties compared to the other grades with equal secondary phase content. The worn surfaces and the wear debris were analysed by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), revealing several wear mechanisms such as polishing, abrasion and wear debris layer formation, mainly depending on the imposed contact load and the material composition.

Novel End-point Detection Method by Monitoring Shear Force Oscillation Frequency for Barrier Metal Polishing in Advanced LSI

AbstractA novel end-point detection method based on a combination of shear force and its spectral amplitude was proposed for barrier metal polishing on copper damascene structures. Under some polishing conditions, the shear force changed significantly with polished substrate. On the other hand, the change in shear force was insignificant under certain polishing conditions. Therefore, a complementary end-point detection method by monitoring oscillation frequency of shear force was proposed. It was found that the shear force fluctuated in unique frequencies depending on polished substrates. Using Fast Fourier Transformation, the shear force data was converted from time domain to frequency domain. The amplitude of spectral frequencies corresponding to the rotational rate of wafer carrier and platen was monitored. Significant frequency amplitude changes were observed before, during and after the polished layer transition from barrier film to silicon dioxide film. The results indicated that a combination of shear force and its spectral amplitude analyses provided effective end-point detection for barrier CMP process.

A study of kinetic effects due to using microfibrous entrapped zinc oxide sorbents for hydrogen sulfide removal

A modified Amundson model was proposed to characterize breakthrough curves during gas phase desulfurization using fixed bed reactors. It contains two characteristic variables: saturation time (τ) and shape factor (lumped K). The model has been verified experimentally at 400∘C. Combined with mass transfer correlations, the model was utilized to investigate kinetic influences due to using microfibrous entrapped sorbent (MFES) with high void volume fraction. Because of the utilization of nanosize ZnO grains supported on highly porous SiO2 particles (100–200μm), the intra-particle diffusion resistance of MFES was minimized resulting in a saturation capacity near the theoretical value. The microfibrous entrapment and the use of small sorbent particles enhanced the external mass transfer rate; the high void volume fraction reduced the capacity density resulting in increased overall lumped K. As a result, MFES demonstrated a longer breakthrough time, a sharper breakthrough curve, and higher ZnO utilization than ZnO extrudates tested at equivalent conditions. Moreover, MFES can be optimally used as a polishing layer at the downstream end of a packed bed to maximize the overall desulfurization performance.

Ellipsometric studies of the surface layer of polished optical glass

Ellipsometric studies of the properties of the surface layer that arises during prolonged mechanical polishing of K8 optical glass have been carried out. It is established that, with relatively nonprolonged polishing of the glass, the homogeneous-dielectric-layer model can be applied to the polished layer; the refractive index and the thickness are determined from this as parameters of the layer. The refractive index of the layer is somewhat smaller than that of the undisturbed glass, while the thickness varies within the limits 200-700nm, depending on the duration of the polishing. Manifestations of inhomogeneity of the polished glass are detected on deeply polished samples, and these can be described by a transition layer about 50nm thick on the outer boundary of the polished layer.

磷酸盐激光玻璃亚表面损伤阈值增强实验研究

Experimental investigation was performed with a 1064-nm, 10-ns Nd:YAG laser to determine the effects of the surface hydrogen acid etching on laser damage, compared with damage of conventionally polished surface. The investigation was helpful for us to understand the negative effects of Nd-doped phosphate glass surface and subsurface damage (SSD) on laser induced damage threshold (LIDT). A set of samples was polished, and then chemically etched in a cool buffered 10%HF + 20%H2SO4 solution at different times. Another set of samples was ground and etched in the hot-buffered solution, and then polished. All the samples were irradiated with Nd: YAG laser and characterized by optical microscopy. Results of LIDT were obtained according to International standard ISO/DIS 11254-1.2. Chemical treatment can remove the contaminants in the polished re-deposition layer and the SSD for improving the laser damage resistance of Nd-doped phosphate glass surfaces. The method of using hot solution was more effective than that of using cool solution.

Confocal laser scanning microscopic analysis of the depth of dentin caries-like lesions in primary and permanent teeth

This study analyzed comparatively, by confocal laser scanning microscopy (CLSM), the depth of caries-like lesions produced by biological and chemical artificial models in permanent and primary dentin. Six primary molars and six premolars were used. The occlusal enamel was removed and a nail polish layer was applied on the specimens, except for a 4 x 2 mm area on dentin surface. Half of specimens were immersed in acid gel for 14 days (chemical model) and the other half was immersed in BHI broth with S. mutans for 14 days (biological model). After development of artificial caries, the crowns were longitudinally sectioned on the center of the carious lesion. Three measurements of carious dentin depth were made in each specimen by CLSM. Measurements depths were compared between the caries models and between tooth types by one-way ANOVA and Tukey test (alpha=5%). For permanent teeth, the biological model showed significantly higher (p<0.05) caries depth values than the chemical model. For primary teeth, no statistically significant difference (p>0.05) was found between the caries models. The artificial caries model influenced caries depth only in permanent teeth. There was no difference in carious dentin depth between permanent and primary teeth, regardless of the artificial caries model.

Development of chemical-mechanical polished high-resolution zone plates

State-of-the-art zone plates for soft and hard x rays are commonly fabricated in nickel or gold by electroplating. The most critical fabrication step is the controlled filling of the plating mold, which directly affects the performance of the diffractive optics. One problem is that the electroplating rate depends on the actual zone width resulting in an inhomogeneous height profile across the optics. Another problem is the measurement of the actual zone height during the electroplating process to fill exactly the plating mold. In practice, underplating the mold results in a low diffraction efficiency of the zone plate. Overplating yields in unemployable optics. In this article, the authors apply a chemical-mechanical polishing (CMP) process to overcome the described problems. In the new processing step, the zone plate is planarized after overplating. The authors demonstrate for the first time that nickel zone plates with an outermost zone width down to 25 nm can be polished by applying a CMP process. This new step leads to a much better reproducibility in zone plate fabrication and their performance. In addition, to overcome the technical limit of the current aspect ratios of zone plates the authors propose to superimpose polished zone plate layers on top of each other. The authors assume that the introduced CMP process paves the way toward the development of future volume zone plates with ultrahigh aspect ratios for soft and hard x-ray applications.

Glass fiber entrapped sorbent for reformates desulfurization for logistic PEM fuel cell power systems

Glass fiber entrapped ZnO/SiO 2 sorbent (GFES) was developed to remove sulfur species (mainly hydrogen sulfide, H 2S) from reformates for logistic PEM fuel cell power systems. Due to the use of microfibrous media and nanosized ZnO grains on highly porous SiO 2 support, GFES demonstrated excellent desulfurization performance and potential to miniaturize the desulfurization reactors. In the thin bed test, GFES (2.5 mm bed thickness) attained a breakthrough time of 540 min with up to 75% ZnO utilization at 1 ppm breakthrough. At equivalent ZnO loading, GFES yielded a breakthrough time twice as long as the ZnO/SiO 2 sorbent; at equivalent bed volume, GFES provided a three times longer breakthrough time (with 67% reduction in ZnO loading) than packed beds of 1–2 mm commercial extrudates. GFES is highly regenerable compared with the commercial extrudates, and can easily be regenerated in situ in air at 500 °C. During 50 regeneration/desulfurization cycles, GFES maintained its desulfurization performance and structural integrity. A composite bed consisting of a packed bed of large extrudates followed by a polishing layer of GFES demonstrated a great extension in gas life and overall bed utilization. This approach synergistically combines the high volume loading of packed beds with the overall contacting efficiency of small particulates.

Effect of blood and saliva contamination on bond strength of brackets bonded with a protective liquid polish and a light-cured adhesive

The application of a polymer coating to the labial enamel tooth surface before bonding can help keep white spot lesions from forming. Previous studies evaluating the effects of blood and saliva contamination on the bond strengths of light-cured composites showed significant reductions in bond strength values. The purpose of this study was to investigate whether the bond strength of a light-cured system (Transbond XT, 3M Unitek, Puchheim, Germany) used with a liquid polish (BisCover, Bisco, Schaumburg, Ill) is affected by contamination with blood or saliva. One hundred twenty permanent human premolars were randomly divided into 6 groups of 20. Various enamel surface conditions were studied: dry, blood contaminated, and saliva contaminated. A light-cured bonding system (Transbond XT) was used in all groups. The teeth in group 1 were bonded with Transbond XT. In the second group, BisCover polymeric resin polish was applied on the etched tooth surfaces before the brackets were bonded with Transbond XT resin. Comparison of the first and second groups showed no statistically significant difference. Groups 3 through 6 were bonded without Transbond XT. For groups 3 and 5, a layer of blood or saliva, respectively, was applied to the etched enamel followed by BisCover. In groups 4 and 6, blood or saliva, respectively, was applied on the light-cured BisCover. Shear forces were applied to the samples with a universal testing machine, and bond strengths were measured in megapascals. The protective liquid polish (BisCover) layer did not affect bond strength. Blood contamination on acid-etched surfaces affects bond strength more than saliva contamination. When a protective liquid polish (BisCover) is applied to the tooth surface, the effect of contamination by blood or saliva is prevented.

표면조도에 따른 원자로급 흑연(IG110)의 산화거동

Graphite is suitable materials as a moderator, reflector, and supporter of a nuclear reactor because of high tolerance to the high temperature and neutron irradiations. Because graphite is so weak to the oxidation, its oxidation study is essentially demanded for the operation and design of the nuclear reactor. This work focuses on the effect of the surface oxidation of graphite according to the surface treatment. With thermogravimeter (TG), oxidation characteristics of the isotropic graphite are measured at the three temperature areas, and oxidation ratio and amounts are estimated as changing the surface roughness. Furthermore, the polished graphite surface produced from the surface treatment is investigated with the Raman spectroscopic study. Oxidation behaviors of the surface are also evaluated as elimination the polished layer by washing with strong sonication.

Dependence of Oxidation Behavior and Residual Stresses in Oxide Layers on Armco Iron Substrate Surface Condition

Mass gain during oxidation, texture and residual stresses in oxide layers on polycrystalline Armco iron substrates with different surface conditions are investigated using thermogravimetry microscopy and synchrotron X-rays. The mass gain during oxidation in all samples follows a parabolic law. The parabolic oxidation constant increases with increasing roughness of a mechanically ground respectively polished oxide layer. Electrolytic polishing (grain surface etching) reduces while grain boundary etching increases the parabolic oxidation constant compared to the mechanically polished sample. All oxide layers show columnar growth of the magnetite and a moderate fiber texture. The magnetite contains compressive residual stresses. Under the conditions chosen for the oxidation treatment the magnitude of these compressive residual stresses does not depend on the substrate surface condition.

Deep Ultraviolet Raman Microspectroscopic Characterization of Polishing-Induced Surface Damage in SiC Crystals

We have investigated polishing-induced surface damage in nitrogen-doped {0001} 4H-SiC crystals with silicon and carbon faces through deep ultraviolet Raman microspectroscopy. The structural and electrical properties of the damaged layers were characterized as a function of the abrasive particle size, using pure phonon modes and a longitudinal-optical-phonon plasmon coupled mode as monitor bands. The degree of damage decreased with the size. Although abrasive polishing with finer particles enables the long-range order of the lattice to almost fully recover, the carrier density remains partly reduced in the polished surface layers. The number of defects that induces a reduction in the free carrier density differs between the Si and C faces of 4H-SiC crystals.

Cryogenic target with very thin “gold finger” heat pipe

An extremely light stainless steel heat pipe of 0.1 mm wall thickness and 5 mm diameter has been developed to transport heat from the liquid hydrogen/deuterium target to the cooling machine. As a further improvement an important reduction of the heat load to the cold parts of the system is achieved by coating the heat pipe and the target finger with a thin polished gold layer. This brings the radiation heat load from 1400 mW on the non-isolated stainless steel surface system down to 70 mW on the gold-coated system. A further reduction to 0.05 mW is achieved by using an aluminum heat shield at 50 K around the cold parts at 15 K. Finally, the heat load was further reduced by a factor 11, without changing the geometry, by coating both sides of the aluminum shield with a thin gold mirror layer. This new, very slim “gold finger” target system shows safe and stable performance even with a low power-cooling machine.

Fabrication of Strain-Relaxed Si1 − x Gex/Si(001) Buffer Layers of Low Surface Roughness

The results are presented of the fabrication of strain-relaxed graded Si1 − xGex/Si(001) buffer layers with a maximum Ge fraction of about 0.25 that have a low density of threading dislocations (<106 cm−2) and low surface roughness. The buffer layers are grown by atmospheric-pressure hydride CVD. It is found that chemical mechanical polishing can reduce their surface roughness to a level comparable with that of the original Si(001) substrates. It is shown that the polished buffer layers can serve as substrates for MBE-grown SiGe/Si heterostructures.

Bonding characteristics of 3C-SiC wafers with hydrofluoric acid for high-temperature MEMS applications

This paper describes the bonding characteristics of 3C-SiC wafers using plasma enhanced chemical vapor deposition (PECVD) oxide and hydrofluoric acid (HF) treatment for SiC-on-insulator (SiCOI) structures and high-temperature microelectromechanical system (MEMS) applications. In this work, insulator layers were formed on a heteroepitaxial 3C-SiC film grown on a Si (0 0 1) wafer by thermal wet oxidation and a PECVD process, successively. The pre-bonding of two polished PECVD oxide layers was made under definite pressure after the treatment of hydrophilic surface activation in HF. The bonding processes were carried out under various HF concentration and external applied pressure. The bonding characteristics were evaluated by the effects of HF concentration used in the surface treatment on the roughness of the oxide and the pre-bonding strength, respectively. Hydrophilic character of the oxidized 3C-SiC film surface was investigated by attenuated total reflection Fourier transformed infrared spectroscopy (ATR-FTIR). The root-mean-square (RMS) surface roughness of the oxidized 3C-SiC layers was measured by atomic force microscope (AFM). The strength of the bonded wafer was measured by tensile strength meter (TSM). The bonded interface was also analyzed by scanning electron microscope (SEM). The values of the bonding strength ranged from 0.52 to 1.52 MPa according to HF concentrations without the external applied load during pre-bonding process. The bonding strength initially increases with increasing HF concentration and reaches the maximum at 2.0% of HF concentration and then decreases. Consequently, low temperature 3C-SiC wafer direct bonding technique using a PECVD oxide layer and HF could be applied as a fabrication process of high quality substrates for high performance electronic devices and harsh environment MEMS applications.