Surface Microroughness Research Articles

Modeling the contact wear fracture of a two-layer basement

We develop a method for calculating the kinetics of fatigue fracture of a two-layer elastic basement by a periodic system of indenters sliding on the surface and modeling the surface microroughness. The method is based on solving the contact problem for a periodic system of indenters and a two-layer elastic basement, determining the internal stresses with friction forces taken into account, and constructing the damage function in the two-layer basement. We calculate the kinetics of the fatigue fracture of the surface layer (the coating) and find the characteristics of the process depending on the strength and mechanical properties of the coating and basement materials, the loading and geometric characteristics of the system, and the friction coefficient.

Passivation of structured p-type silicon interfaces: Effect of surface morphology and wet-chemical pre-treatment

The effect of both surface morphology and wet-chemical pre-treatment on electronic surface and interface properties was investigated for mono- and polycrystalline silicon substrates with special surface structures. Surface charge, energetic distribution, and density of rechargeable states on these surfaces were determined by surface photovoltage (SPV) measurements. These results were correlated to previously reported findings on atomically flat Si(111) and Si(100) surfaces of monocrystalline wafers. In this paper, a specially optimised sequence of cleaning, wet-chemical oxidation, and oxide removal procedures is described in detail for the first time. This method was successfully applied in order to remove contaminations and damaged surface layers and to obtain atomically flat areas on substrates with evenly distributed atomic steps, polycrystalline and monocrystalline substrates with randomly distributed pyramids. A significant reduction in surface micro-roughness, interface state density, and recombination loss was achieved. Using passivation by wet-chemical oxidation or H-termination, respectively, the optimised surface state can be preserved by the time of following preparation steps and during subsequent a-Si:H plasma enhanced chemical vapour deposition (PECVD).

Evaluation of two-dimensional distribution of dielectric degradation in stressed SiO2 film by etch-rate difference

We propose a new method with analysis on SISuR (Stress Induced Surface Roughness) that obtains two-dimensional information about extrinsic damage of SiO2 films under current stresses. With this method, the micro-roughness of partially-etched surface of SiO2 films was evaluated by atomic force microscope (AFM). The results indicate the etched SiO2 surface could reflect distribution of the trapped charges which are related to dielectric degradation of the SiO2 films. From the evaluation of time-dependent dielectric breakdown (TDDB), there is a correlation between the distribution of the trapped charge in SiO2 films and the breakdown of the lifetimes of the films.

Optics Manufacturing Using Magnetorheological Finishing

Magnetorheological finishing (MRF) is a novel precision optical machining technology. Owing to its flexible finishing process, MRF can eliminate subsurface damage, smooth rms micro roughness and correct surface figure errors. The finishing process can be easily controlled by a computer. Through proper designing of numerical control, sphere and asphere optics can be machined by magnetorheological finishing with high quality. Optical sphere is machined using dwell time algorithm and surface shape 2 pt. PV has been improved from 0.17um to 0.07um.

Nonmonotonic dependence of the work function of ytterbium nanofilms deposited on the Si(111)7 × 7 surface at room temperature on the film thickness

The dependences of the work function of ytterbium nanofilms on their thickness are studied. The films are evaporated at room temperature on the Si(111)7 × 7 surface of silicon samples doped to different levels and having different types of conduction (n and p). It is shown that these dependences exhibit a pronounced nonmonotonic behavior, which does not depend on the type of silicon used. It is established that the amplitude of the nonmonotonic variations in the work function is governed by the surface microroughness of the deposited layers, so that larger amplitudes correspond to smoother films. The variations in the work function of the films due to the deposition of electrically negative Si atoms on their surface are investigated. It is revealed that the sign of the variation depends on the film thickness. This result strange at first glance is associated with the fact that the electron density distribution at the metal-film-vacuum interface depends nonmonotonically on the amount of deposited ytterbium. This nonmonotonic behavior is a manifestation of electron density standing waves (Friedel oscillations) generated in the films by the ytterbium-silicon interface.

Optimisation of electronic interface properties of a-Si:H/c-Si hetero-junction solar cells by wet-chemical surface pre-treatment

The relation between structural imperfections at structured silicon surfaces, energetic distribution of interface state densities, recombination loss at a-Si:H/c-Si interfaces and solar cell characteristics have been intensively investigated using non-destructive, surface sensitive techniques, surface photovoltage (SPV) and photoluminescence (PL) measurements, atomic force microscopy (AFM) and electron microscopy (SEM). Sequences of wet-chemical oxidation and etching steps were optimised with respect to the etching behaviour of Si(111) pyramids. Special wet-chemical smoothing and oxide removal procedures for structured substrates were developed, in order to reduce the preparation-induced surface micro-roughness and density of electronically active defects. H-termination and passivation by wet-chemical oxides were used to inhibit surface contamination and native oxidation during the technological process. We achieved significantly lower micro-roughness, densities of surface states D it( E) and recombination loss at a-Si:H/c-Si interfaces on wafers with randomly distributed pyramids, compared to conventional pre-treatments. For amorphous-crystalline hetero-junction solar cells (ZnO/a-Si:H/c-Si/BSF/Al), the c-Si surface becomes part of the a-Si:H/c-Si interface, whose recombination activity determines cell performance. With textured substrates, the smoothening procedure results in a significant increase of short circuit current, fill factor and efficiency.

Smoothing and passivation of special Si(111) substrates: studied by SPV, PL, AFM and SEM measurements

Surface sensitive techniques, the field-modulated surface photovoltage, photoluminescence measurements, atomic force microscopy and scanning electron microscopy, were employed to yield detailed information on the influence of wet-chemical treatments on the preparation induced microroughness and electronic properties of wet-chemically passivated Si(111) substrates with special surface morphology. Stepped substrates with evenly distributed atomically flat terraces were prepared and passivated by thin oxide layers, which were used as a starting point for the subsequent H-termination after long storage in air. It was shown that their surface morphology and electronic properties do not degrade. Applying this preparation method to solar cell substrates with randomly distributed Si(111) pyramids, we achieved significantly lower densities of surface states and reduced recombination loss at a-Si:H/c-Si interfaces, compared with conventional pretreatments. The surface microroughness, the density of rechargeable states and the resulting recombination loss on a-Si:H/c-Si heterojunctions were found to be mainly influenced by two steps of surface pretreatment: firstly, the wet-chemical smoothing procedure of structured substrates and, secondly, the removal of native and wet-chemical oxides during the final etching in HF- or NH(4)F-containing solutions.

Surface Microroughness of Silicon in Wet Process and its Minimization

Surface Microroughness of Silicon in Wet Process and its Minimization

초해상 광기록 Ge2Sb2Te5박막의 고온광물성 연구

마그네트론 스퍼터링 방법을 사용하여 광기록 매체인 GST 박막과 보호층인 <TEX>$ZnS-SiO_2$</TEX> 박막 또는 <TEX>$Al_2O_3$</TEX> 박막을 c-Si 기판위에 증착한 뒤 in-situ 타원계를 사용하여 상변화 광기록층인 GST 시료의 타원상수 온도의존성을 실시간으로 측정한 결과 <TEX>$300^{\circ}C$</TEX> 이상의 온도에서 GST의 고온 타원상수는 가열 환경 및 보호층의 종류에 따라 큰 차이를 보여주었다. 가열 환경 및 보호층의 종류에 따라 GST의 고온 타원상수가 달라지는 원인인 <TEX>$1{\sim}2$</TEX>시간의 긴 승온시간을 줄이기 위해 Phase-change Random Access Memory(PRAM) 기록기를 사용하였고 수십 ns 이내의 짧은 시간 내에 순간적으로 GST 시료를 가열 및 냉각하였다. GST층이 손상되지 않고 결정화 및 고온 열처리가 되는 PRAM 기록기의 기록모드와 레이저출력 최적조건을 찾았으며 다층박막 구조에서 조사되는 레이저 에너지가 광기록층인 GST에 흡수되는 양과 이웃하는 층으로 전파되는 양을 열확산방정식으로 나타내고 이를 수치해석적으로 풀어 레이저출력과 GST 박막의 최고 온도와의 관계를 구하였다. 지름이 1um 정도인 레이저스폿을 대략 <TEX>$0.7{\times}1.0mm^2$</TEX>의 면적내에 촘촘히 기록한 다음 고온 열처리된 GST 시료의 분광타원데이터를 500 um의 빔 크기를 가지는 마이크로스폿 분광타원계를 사용하여 구하고 그 복소굴절률을 결정하였다. In-site 타원계를 사용할 때에 가열 환경 보호층 물질의 영향을 크게 받은 GST의 고온 복소굴절률은 PRAM 기록기를 사용하였을 때에는 가열환경이나 보호층의 종류에 무관하게 안정된 값을 보여주었다 Atomic Force Microscope(AFM)과 Scanning Electron Microscopy(SEM)을 통해 관찰한 GST 다층박막시료의 고온 열처리 전후 표면미시거칠기 변화도 PRAM 기록기를 사용할 때에는 in-situ 타원계를 사용할 때보다 1/10 정도의 크기를 보여주어 PRAM 기록기와 분광타원계를 사용하여 결정한 GST의 고온광학물성의 신뢰성을 확인하여 주었다. The samples composed of a GST thin film and the protective layers of <TEX>$ZnS-SiO_2$</TEX> or <TEX>$Al_2O_3$</TEX> coated on c-Si substrate were prepared by using the magnetron sputtering method. Samples of three different structures were prepared, that is, i) the GST single film on c-Si substrate, ii) the GST film sandwiched by the protective <TEX>$ZnS-SiO_2$</TEX> layers on c-Si substrate, and iii) the GST film sandwiched by <TEX>$Al_2O_3$</TEX> protective layers on c-Si substrate. The ellipsometric constants in the temperature range from room temperature to <TEX>$700^{\circ}C$</TEX> were obtained by using the in-situ ellipsometer equipped with a conventional heating chamber. The measured ellipsometric constants show strong variations versus temperature. The variation of ellipsometric constants at the temperature region higher than <TEX>$300^{\circ}C$</TEX> shows different behaviors as the ambient medium is changed from in air to in vacuum or the protective layers are changed from <TEX>$ZnS-SiO_2$</TEX> to <TEX>$Al_2O_3$</TEX>. Since the long heating time of 1-2 hours is believed to be the origin of the high temperature variation of ellipsometric constants upon the heating environment and the protective layers, a PRAM (Phase-Change Random Access Memory) recorder is introduced to reduce the heating time drastically. By using the PRAM recorder, the GST samples are heated up to <TEX>$700^{\circ}C$</TEX> decomposed preventing its partial evaporation or chemical reactions with adjacent protective layers. The surface image obtained by SEM and the surface micro-roughness verified by AFM also confirmed that samples prepared by the PRAM recorder have smoother surface than the samples prepared by using the conventional heater.

Effects of calcium ion incorporation on osteoblast gene expression in MC3T3‐E1 cells cultured on microstructured titanium surfaces

The surface characteristics of a calcium ion (Ca)-incorporated titanium (Ti) surface, produced by hydrothermal treatment using an alkaline Ca-containing solution, and its effects on osteoblastic differentiation were investigated. MC3T3-E1 pre-osteoblastic cells were cultured on machined or grit-blasted Ti surfaces with and without Ca incorporation. The MTT assay was used to determine cell proliferation, and real-time PCR was used for quantitative analysis of osteoblastic gene expression. Hydrothermal treatment with a Ca-containing solution produced a crystalline CaTiO(3) nanostructure of approximately 100 nm in dimension, preserving original micron-scaled surface topographies and microroughness caused by machining, blasting, or blasting and etching treatments. After immersion in Hank's balanced salt solution, considerable apatite formation was observed on all surfaces of the Ca-incorporated samples. Significantly more cell proliferation was found on Ca-incorporated Ti surfaces than on untreated Ti surfaces (p < 0.001). Quantitative real-time PCR analysis showed notably higher alkaline phosphatase, osteopontin, and osteocalcin mRNA levels in cells grown on Ca-incorporated blasted surfaces than on other surfaces at an early time point. Thus, Ca incorporation may have a beneficial effect on osseointegration of microstructured Ti implants by accelerating osteoblast proliferation and differentiation during the early healing phase following implantation.

Influence of surface microroughness by plasma deposition and chemical erosion followed by TiO2 coating upon anticoagulation, hydrophilicity, and corrosion resistance of NiTi alloy stent

Two different surface modification techniques were used to change the surface morphology and roughness of stents at the micrometer level, and eventually improve their surface adhesion properties with respect to endothelial cells. One was chemical erosion followed by sol-gel TiO(2) coating, and the other was low temperature gas plasma deposition. After surface modification, the biocompatibility including the anticoagulation properties, hydrophilicity, and corrosion resistance of these stents was evaluated. It was found that both techniques could change the surface morphology of the stents with microroughness. In comparison with the control, the treated NiTi alloy intravascular stents showed increased surface hydrophilicity and enhanced anticoagulation properties. However, the corrosion properties of the stents were not improved significantly.

Residual stress model for CaF2

Nanoindentation tests and finite element analysis that considers elastic-mesoplastic deformation for single crystals were used to investigate the mechanical properties of CaF2 under spherical indentation. The goal was to gain a better understanding of microfractures and crystalline anisotropy and their effect on the surface quality of CaF2 during manufacturing. In this analysis, indentations of the three main crystallographic planes (100), (110), and (111) were studied and compared to examine the effects of crystalline anisotropy on the load–displacement curves, surface profiles, contact radius, spherical hardness, stress distributions, and cleavage at two stages, namely at the maximum indentation load and after the load had been removed. Our model results were compared with experimental observation of surface microroughness, subsurface damage, and material removal rate in grinding of CaF2.

Subsurface damage and microstructure development in precision microground hard ceramics using magnetorheological finishing spots

We demonstrate the use of spots taken with magnetorheological finishing (MRF) for estimating subsurface damage (SSD) depth from deterministic microgrinding for three hard ceramics: aluminum oxynitride (Al(23)O(27)N(5)/ALON), polycrystalline alumina (Al(2)O(3)/PCA), and chemical vapor deposited (CVD) silicon carbide (Si(4)C/SiC). Using various microscopy techniques to characterize the surfaces, we find that the evolution of surface microroughness with the amount of material removed shows two stages. In the first, the damaged layer and SSD induced by microgrinding are removed, and the surface microroughness reaches a low value. Peak-to-valley (p-v) surface microroughness induced from grinding gives a measure of the SSD depth in the first stage. With the removal of additional material, a second stage develops, wherein the interaction of MRF and the material's microstructure is revealed. We study the development of this texture for these hard ceramics with the use of power spectral density to characterize surface features.

Analytical evaluation of the X-ray scattering contribution to imaging degradation in grazing-incidence X-ray telescopes

Aims. The focusing performance of X-ray optics (conveniently expressed in terms of HEW, Half Energy Width) strongly depend on both mirrors deformations and photon scattering caused by the microroughness of reflecting surfaces. In particular, the contribution of X-ray Scattering (XRS) to the HEW of the optic is usually an increasing function H(E) of the photon energy E. Therefore, in future hard X-ray imaging telescopes of the future (SIMBOL-X, NeXT, Constellation-X, XEUS), the X-ray scattering could be the dominant problem since they will operate also in the hard X-ray band (i.e. beyond 10 keV). In order to ensure the imaging quality at all energies, clear requirements have to be established in terms of reflecting surfaces microroughness. Methods. Several methods were proposed in the past years to estimate the scattering contribution to the HEW, dealing with the surface microroughness expressed in terms of its Power Spectral Density (PSD), on the basis of the well-established theory of X-ray scattering from rough surfaces. We faced that problem on the basis on the same theory, but we tried a new approach: the direct, analytical translation of a given surface roughness PSD into a H(E) trend, and – vice versa – the direct translation of a H(E) requirement into a surface PSD. This PSD represents the maximum tolerable microroughness level in order to meet the H(E) requirement in the energy band of a given X-ray telescope. Results. We have thereby found a new, analytical and widely applicable formalism to compute the XRS contribution to the HEW from the surface PSD, provided that the PSD had been measured in a wide range of spatial frequencies. The inverse problem was also solved, allowing the immediate evaluation of the mirror surface PSD from a measured function H(E). The same formalism allows establishing the maximum allowed PSD of the mirror in order to fulfill a given H(E) requirement. Practical equations are firstly developed for the case of a single-reflection optic with a single-layer reflective coating, and then extended to an optical system with N identical reflections. The results are approximately valid also for multilayer-coated mirrors to be adopted in hard X-rays. These results will be extremely useful in order to establish the surface finishing requirements for the optics of future X-ray telescopes.

The Impact of Microroughness on the Generation of Watermarks on Etched Silicon Surfaces

We found that watermarks caused haze in a polycrystalline silicon film grown on an etched silicon surface by the chemical vapor deposition process. The film, called a “poly-backseal”, traps metallic impurities inside itself. We investigated the possible cause of these watermarks, and found that the microroughness of the wafer surface plays a role in their generation. This suggested the microroughness had to be controlled to the order ≤8.0 nm for a large range (20×20 µm2) and to the order ≤0.2 nm for a small range (0.1×0.1 µm2) in order to reduce the occurrence of watermarks per unit area <1.0%. Minute particles with diameters of 0.1 to 0.3 µm were observed on the wafer surface where watermarks had generated. An analysis of the particles suggested the main component of the watermarks was silica, as indicated in previous studies.

Research on Material Removal of Magnetorheological Finishing

Magnetorheological finishing (MRF) is a novel precision optical machining technology. Owing to its flexible finishing process, MRF can eliminate subsurface damage, smooth rms micro roughness and correct surface figure errors. The finishing process can be easily controlled by a computer. Material removal model in MRF is established. According to Preston equation in optical machining, mathematic model of material removal rate in MRF rotating at fixed rate is established through hydrodynamic analysis of the MR fluid flow in the polishing zone. The validity of the model is examined by the experimental results.

Elimination of the reactivation process in the adhesion of chlorinated SBS rubber with polychloroprene adhesives

Chlorination treatment of a thermoplastic styrene-butadiene-styrene rubber (SBS) with a 3 wt% solution of trichloroisocyanuric acid (TCI) in methyl ethyl ketone (MEK) introduces chlorinated and oxidized moieties on the rubber surface which increase its surface energy and produces surface microroughness. Consequently adhesion properties, evalu- ated by T-peel strength measurements in chlorinated SBS/solvent based-polyurethane adhesive/leather joints, are enhanced. In this study, two solvent-based polychloroprene adhesives (PCP0 and PCP30R) have been considered as an alternative to the commonly used solvent-based polyurethane adhesive (PU). A thermoreactive phenolic resin was added to one of the polychloroprene adhesive formulations (PCP30R). This tackifier resin favors chlorination of the adhesive and reinforces the interface between the chlorinated adhesive and the chlorinated rubber surface. Besides, PCP30R adhesive does not need adhesive reactivation and considerable high T-peel strength value (5.7±0.3 kN/m) was obtained. Elimination of the reactivation process implies a considerable improvement of the manufacturing process in the footwear industry.

Nano-scale Characterization of Surface Defects on CMP-finished Si Wafers by Scanning Probe Microscopy Combined with Laser Light Scattering

ABSTRACTScanning probe microscopy has been widely used to evaluate surface microroughness on Si wafers after chemical mechanical polishing (CMP) processes. In this article, we utilize atomic force microscopy (AFM) combined with laser light scattering to detect nano-scale surface defects called microscratches on CMP-finished Si wafers. We find that most microscratches detected by the combined method are very shallow trenches with widths and depths of 80–200 nm and 0.1–0.2 nm, respectively. The dependence of scattered-light intensity on the size of microscratches agrees with theoretical calculations within one order of magnitude.

STATISTICAL APPROACH TO NON-FICKIAN DIFFUSION

Competing styles in statistical mechanics have been introduced to investigate physico-chemical systems displaying complex structures, when one faces difficulties to handle the standard formalism in the well-established Boltzmann–Gibbs statistics. After a brief description of the question, we consider the particular case of Renyi statistical approach, which is applied to the study of the "anomalous" (non-Fickian) diffusion that is involved in experiments of cyclic voltammetry in electro-physical chemistry. In these experiments, one is dealing with the fractal-like structure of the thin film morphology present in electrodes in microbatteries. Fractional-power laws are evidenced in the voltammetry measurements and in the analysis of the interphase width obtained using atomic force microscopy. The resulting fractional-powers are related to each other and to the statistical fractal dimension, and can be expressed in terms of the index on which Renyi's statistical approach depends. The important fact that this index, which is restricted to a given interval, provides a measure of the micro-roughness of the electrode surface, and is related to the dynamics involved, the nonequilibrium thermodynamic state of the system, and to the experimental protocol is clarified.

Detection of 30–40-nm Particles on Bulk-Silicon and SOI Wafers Using Deep UV Laser Scattering

As semiconductor devices continue to get smaller, and thus the size of yield-limiting particles decreases, a need has arisen for detecting smaller particles on silicon surfaces. The current minimum detectable diameter of wafer-surface particle-detection systems employing 488-nm wavelength Ar+ gas lasers widely used in semiconductor production lines is, under optimized conditions, 50-60 nm on bulk-silicon surfaces. The sensitivity for SOI wafers, however, is considerably lower than this level due not only to the additional optical reflections from Si/SiO2/Si interfaces within the SOI stack but also to the undesirable light scattering at the rough interfaces. The challenges in meeting the requirement to detect smaller particles specified in the ITRS will be presented. Using a 266-nm solid-state laser, we have developed for semiconductor manufacturing a high sensitivity system capable of detecting particles as small as 30 and 40 nm on unpatterned bulk-silicon wafers and SOI wafers, respectively. Our technique of single-wafer spin cleaning with repetitive use of ozonated water and dilute HF cleaning of silicon wafers can reduce surface microroughness, thus reducing background noise in this system, and providing higher particle-detection sensitivity than conventional RCA cleaning. Defect classification using this system integrated with a review scanning electron microscope will also be discussed