Mechanochemical Polishing Research Articles

ВЛИЯНИЕ РЕЖИМОВ ПОЛИРОВАНИЯ НА ШЕРОХОВАТОСТЬ ДЕТАЛЕЙ С АЛМАЗНЫМ ПОКРЫТИЕМ

The results of experimental studies of the process of mechanochemical polishing of a polycrystalline diamond PVD coating of parts such as bodies of revolution are considered.

Investigation of the surface layer formed during the processing of quartz glass using mechanochemical and ionic polishing

Quantitative studies of the optical parameters of the surface layer formed during the polishing of quartz glass have been carried out. It is shown that the mechanism of formation of the surface layer when using the methods of mechanochemical and ion polishing has much in common. In both cases, the appearance of a surface layer, which differs by a high refractive index from the corresponding bulk properties of glass, is associated with the stress and breaking of the Si-O-Si bridge bonds during hydrolysis during glass polishing. The hydrolysis of Si-O-Si bonds is associated with the formation of Si-O and Si-OH groups, which leads to an increase in the refractive index of the surface layer. Keywords: surface layer, quartz glass, mechanochemical and ionic polishing, formation of Si-O and Si-OH groups.

Mechano-Chemical Polishing of Alloy 600 for Accelerated Crack Initiation in Simulated PWR Primary Water Environment and Three-Dimensional Crystallographic Characterization

Mechano-Chemical Polishing of Alloy 600 for Accelerated Crack Initiation in Simulated PWR Primary Water Environment and Three-Dimensional Crystallographic Characterization

Surface Tension Measurement of Water Surface Under IPA Vapor and the Impact of Its Concentration Dependence on the Marangoni Convection in Wafer Drying Process

As higher integration of semiconductor devices has progressed recently, mechano-chemical polishing process is playing a very important role. At the same time, cleaning and drying technologies after the polishing process have been more and more important in order to ensure the surface cleanliness of the wafer products. As a drying process after the cleaning, there is a method of supplying pure water and IPA (Iso-Propyl Alcohol) vapor simultaneously to the surface of the water meniscus region on a rotating wafer (which is called Rotagoni drying method). This technique causes a surface tension difference on the liquid surface and then gives rise to the convection by the Marangoni effect, which is thought to efficiently remove impure particles on the wafer surface. In this method, IPA vapor impinges on the vicinity of the liquid meniscus on the wafer. It is very difficult to measure the surface tension of the liquid surface in that part in situ, and the details about the convection are not well understood. As this technique further advances in near future in order to remove ultra-fine foreign particles on the wafer surface more efficiently, observation and understanding of the Marangoni convection in the meniscus region are necessary for the future progress of the technique. In this study, in order to consider the actual situation of the drying process, not only the measurement of the surface tension of the droplet of the IPA aqueous solution, but also the measurement by exposing pure water droplet to various concentrations of the IPA vapor were performed, and the relationship between the concentration of IPA vapor and the surface tension of the droplet was investigated. The latter situation is much closer to actual drying situation. Specifically, in measurements, a small pure water droplet was placed in a glass container, and the container was filled with a constant concentration of IPA vapor. At the time when it was judged that the IPA adsorption to the liquid surface had reached equilibrium by confirming that the shape of the droplet became unchanged, the image of the droplet shape was taken from the side of the container with digital camera. It is known that the static shape of a droplet which is flattened under the influence of gravity can be analytically expressed by a mathematical equation in consideration of surface tension and mechanical equilibrium. In this study, the surface tension was deduced by assuming that a uniform concentration of IPA and a uniform surface tension over the whole droplet surface. In another project of the authors’ group, physical simulation using a two-dimensional PDMS flow channel was performed to reproduce a situation of impinging IPA vapor to the meniscus region, and PIV (Particle Image Velocimetry) method was applied to obtain the flow velocity of the Marangoni convection. The measurement of IPA concentration on water surface during the actual drying process is very difficult, and moreover, the in-situ measurement of surface tension is almost impossible. From the data of surface tension as a function of IPA concentration and the measured velocity data with a simple analytical flow model, the estimation of surface tension and IPA concentration on the droplet surface will be discussed. END Figure 1

Physical Simulation and Visualization of the Marangoni Convection inside Meniscus Region under IPA Vapor in Wafer Drying Process

With the recent rapid progress of higher integration of semiconductor devices, mechano-chemical polishing process is playing a very important role. Along with this trend, cleaning and drying processes after the mechano-chemical process, have been regarded as more and more important technologies for ensuring surface cleanliness of the wafers. As a drying process after cleaning, there is a method of flowing pure water to a rotating wafer, and simultaneously supplying IPA (Iso-Propyl Alcohol) vapor to the meniscus region of the liquid layer (this is known as Rotagoni drying). This method causes a surface tension difference on the liquid surface and then drives fluid convection by the Marangoni effect, which is thought to efficiently remove impure particles on the wafer surface. During the impingement of IPA vapor to the meniscus region, in-situ observation of Marangoni convection is so difficult that details of the flow velocity and flow pattern are not well understood. In order to further improve this method to efficiently remove ultrafine foreign particles on wafer surface in future, the authors believe that the observation and the understanding of the Marangoni convection are indispensable. In this study, as a first step to observe the flow, rather than treating the complicated three-dimensional flow on actual rotating wafer from the beginning, physical simulation by creating a simplified two-dimensional flow was performed. Using photoetching method and PDMS material as in the fabrication of MEMS devices, a two-dimensional flow channel with a depth of about 600 mm and a width of about 1000 mm was created, and pure water and IPA vapor (mixture of nitrogen and IPA in which concentration was controlled.) was supplied to reproduce the situation where IPA vapor collided with pure water in the meniscus region. Pure water was provided from one direction of the T-shaped flow channel by a syringe pump, and IPA vapor was supplied from the other direction. By setting a minute step for locking the position of the liquid, the stable fluid meniscus in an oblique direction to the channel width was realized in the channel. The Marangoni convection was generated in the meniscus where the IPA impinged, and the flow was visualized by utilizing PIV (Particle Image Velocimetry) method with tracer particles. From the observations, the flow velocities and the flow patterns were successfully obtained from the PIV image analysis. It was found that a rapid convection of 20 mm/s occurred at the maximum velocity when IPA vapor was introduced. This was about ten times of the velocity when only nitrogen gas was provided. In the case with only nitrogen gas, the liquid convection was generated only by the shear stress to the liquid surface caused by the gas flow. However, the Marangoni convection caused by the IPA vapor was about ten times larger than the flow velocity with only nitrogen, of which difference was unexpectedly large. Moreover, the direction of the Marangoni convection was not as simple as anticipated, which could change depending on the impinging position of the IPA vapor. In an experimental condition of the present study, the Marangoni convection was directed from the gas-liquid interface to the triple point on the wall. It is thought that these flow velocities and directions would be strongly related to the removal of foreign particles on the wafer surface. Videos taken in the observation will be also shown in the presentation. END Figure 1

Chemical inactivity of GaN(0001) surface – The role of oxygen adsorption – Ab initio picture

Density Functional Theory (DFT) calculations were used to determine adsorption of oxygen at GaN(0001), i.e. Ga-terminated surface. It was shown that at low coverage the oxygen molecule dissociates during adsorption so that the two separate O adatoms are located in H3 sites. Oxygen adatom saturates three Ga broken bonds, modifying their energy by overlap with Op states, so that the three states are degenerate with valence band (VB). The electron counting rule (ECR) indicate on the electron surplus, the excess electrons are donated to other Ga broken bond states, the adsorption energy is equal to 3.74 eV/atom for clean surface. At the first critical coverage θO=516ML, the Fermi level is shifted to conduction band while at the second critical coverage θO=38ML it is shifted down to VBM. The adsorption energy is ΔE12O2(N)=−3.67eV for θO≤724ML, for θO=1548ML and θO=1648ML decreases ΔE12O2(N)=−3.51eV and ΔE12O2(N)=−3.31eV, respectively, for θO=1748 the energy jumps to ΔE12O2(N)=−3.60eV, and for higher coverage θO≥38 the energy rapidly decreases to zero and becomes negative The singular point at θO=1748ML is essential for stability of oxygen coverage of the surface. The equilibrium pressure at low coverage is 10−5 bar for 1500 K and 10−12 bar 1000 K. It is reduced for higher coverage, due to reduction of the energy and configurational entropy contributions. At the coverage θO=1748ML the pressure is reduced by several orders of magnitude, indicating extremely high thermodynamic stability of such coverage, which is responsible for chemical inactivity of GaN(0001) surface observed in experiments, the critical factor for mechano-chemical polishing of the substrates for electronic applications.

Impact of surface treatments on I–V characteristics in Cd1−xZnxTe and Cd1−xMnxTe crystals

In this work, we focused on studying the impact of different surface treatments for Cd1−xZnxTe (CZT) and Cd1−xMnxTe (CMT) samples with indium evaporated contacts, specifically: mechanical polishing (MP), mechano-chemical polishing (MCP) and mechanical polishing followed by the chemical etching (MP+Et). We examined 3 samples in each group of Cd0.85Zn0.15Te and 3 samples in each group of Cd0.93Mn0.07Te. Devices were consecutively characterized by current–voltage dependence (I–V). The measured characteristics revealed that for CMT both surface treatments, including chemical exposure to bromine ethylene glycol in MCP or bromine methanol in etching, resulted in linear I–V characteristic consistent with the bulk resistance. At the same time, chemical treatments of CZT samples dramatically increased their current densities (up to several μA/cm2).

EBSD Characterization of IGSCC Crack Initiated on Alloy 600 in Simulated PWR Primary Water Environment

In the present work, we crystallographically examined intergranular cracks initiated on Alloy 600 in a simulated PWR environment by using EBSD. The cracks initiated on a flat tensile specimen of the alloy in a short period of slow strain rate tests (SSRTs), that is, the initiation of cracks was accelerated due to the asperity of the specimen surface induced by mechano-chemical polishing with colloidal silica suspension prior to the SSRTs. As thick oxide films were formed on the specimen surface during the SSRTs, the sputtering of the films was carried out for the removal of the film. After the sputtering, clear crystallographic information such as inverse pole figures (IPFs) on the specimen surface could be obtained. Based on the information, the intergranular cracks were crystallographically analyzed. Furthermore, three-dimensional characterization of the cracks was also performed.

Investigation of domain structure evolution during zero-field temperature treatment in 0.67PMN-0.33PT single crystals

ABSTRACTThe temperature depolarization process has been studied in [001]-cut lead magnesium niobate-lead titanate single crystals with 33% lead titanate content by in situ visualization of as-grown domain structure evolution during zero-field heating and subsequent cooling. The phase transitions have been revealed during heat treatment. It has been shown by piezoresponse force microscopy and scanning electron microscopy that heat treatment leads to decay of maze-type as-grown domain structure into array of irregular domains with average diameter about 300 nm. Shallow etching of the surface during mechanochemical polishing has allowed keeping the surface relief corresponding to as-grown domain pattern.

Ultraviolet-irradiated precision polishing of diamond and its related materials

In this study, a novel ultraprecision polishing process for single-crystal diamond substrates was developed utilizing ultraviolet (UV) irradiation. This polishing is basically a mechanochemical polishing (MCP) process combined with a UV-induced photochemical reaction. Carbon atoms on the topmost surface of diamond are oxidized by active species such as hydroxyl radicals (OH radicals) and oxygen radicals at localized high temperature and finally removed as CO and CO2. This polishing process was applied to diamond substrates, chemical vapor deposition (CVD) diamond-coated films and polycrystalline diamond (PCD). The results showed that the surface roughness of the entire substrate reached 0.2 nmRa within 1 – 3h at a comparatively high removal rate. The characteristics and removal mechanism of UV polishing were also discussed.

The Atomic Step Induced by off Angle CMP Influences the Electrical Properties of the SiC Surface

In this work, we made an off-axis surface of SiC with Mechano-chemical polishing method to examine the influence that an atomic step gave for electronic properties of devices. Low energy ion scattering spectroscopy was shown Si-face and C-face with SiC structure were polished with monocrystal. We consider that there results above the atomic step on the surface influence to a device properties, especially a leakage current of Schottky diode. C atom at the step and terrace cause leakage event at metal-semiconductor interface of Schottky diode have been clarified by conductive atomic force microscopy.

Current Evolution of Wafer Thinning and Dicing

Over the past few years the backend assembly process has become increasingly complex in order to add more value to products. Two processes that are linked to the changes in assembly are wafer thinning and dicing. Ultra thin stacked die and the implementation of TSVs are driving improvements to the traditional stress relief and fixed abrasive grinding processes. Both CMP (Chemo-Mechanical Polishing) and MCP (Mechano-Chemical Polishing) are being used. Wafer dicing has a number of products and processes behind its evolution. Thin and stacked die with DAF (Die Attach Film) require modifications to existing blade dicing processes. Low-k and copper wafers are requiring the use of lasers to remove materials from the dicing streets. A new and alternative laser dicing process called Stealth Dicing is an enabling technology for a number of products.

Development of Lapping and Polishing Technologies of 4H-SiC Wafers for Power Device Applications

The development of lapping and polishing technologies for SiC single crystal wafers has realized the fabrication of an extremely flat SiC wafer with excellent surface quality. To improve the SiC wafer flatness, we developed a four-step lapping process consisting of four stages of both-side lapping with different grit-size abrasives. We have applied this process to lapping of 2-inch-diameter SiC wafers and obtained an excellent flatness with TTV (total thickness variation) of less than 3 μm, LTV (local thickness variation) of less than 1 μm, and SORI smaller than 10 μm. We also developed a novel MCP (mechano-chemical polishing) process for SiC wafers to obtain a damage-free smooth surface. During MCP, oxidizing agents added to colloidal silica slurry, such as NaOCl and H2O2, effectively oxidize the SiC wafer surface, and then the resulting oxides are removed by colloidal silica. AFM (atomic force microscope) observation of polished wafer surface revealed that this process allows us to have excellent surface smoothness as low as Ra=0.168 nm and RMS=0.2 nm.

Improvements in Electrical Properties of SiC Surface Using Mechano-Chemical Polishing

To use SiC substrate as a semiconductor device and epitaxial growth, the surface of SiC substrate should be made smooth at an atomic level in the state of monocrystalline. But, the past slurry caused defects such as the pit and the scratch on the surface. This tendency was very strong in (000-1) C-face. We achieved ideal surface for SiC devices using newly developed slurry. In this surface, the roughness (Ra) of (0001) Si face and (000-1) C face evaluated by the AFM were 0.1nm or less, and confirmed that the surface were monocrystalline by CAICISS measurement. From these results, it is thought that the crystal face obtained by the slurry newly developed. In addition, the Schottky barrier diode was formed directly on the polished surface, that was obtained the breakdown voltage of 1.2kV or more. We thought that this results is possible to make the Schottky barrier diode without epitaxial growth.

Mechanochemical Polishing of Single Crystal Diamond with Mixture of Oxidizing Agents

In order to achieve the smooth surface of diamond, several kinds of mixture oxidizing agents have been used to polish the single crystal diamond by a designed polishing apparatus. The existing of graphite and amorphous carbon has been found in the surface of diamond after polishing. The mechanochemical actions of oxidizing agents and the polishing iron plate have been proved. The mixture of oxidizing agents can decrease the polishing temperature so that the super-smooth surface of single crystal diamond can be achieved at lower temperature. The method provided is benefit not only to simplify polishing device and control the polishing process, but also to improve the removal rate and surface roughness.

Surface texture and composition of titanium brushed with toothpaste slurries of different pHs

Objectives This in vitro study characterized the surface texture and composition of titanium brushed with toothpaste slurries of different pHs, and thereby elucidated mechanochemical interactions between the metal and abrasive material in dentifrice. Methods Two fluoride-free toothpastes, which contained crystalline CaHPO 4·2H 2O and amorphous SiO 2 particles as abrasive, were mixed with acidic buffers to provide slurries of pH 6.8 and 4.8. Specimens were cast from CP Ti, mirror-polished, and then toothbrushed at 120 strokes/min for 350,400 strokes under a load of 2.45 N. Specimen surfaces were characterized by means of SPM and EPMA. The obtained data were compared with the already reported results of water-diluted alkaline slurries. SPM data of each paste were analyzed using one-way ANOVA, followed by post hoc Tukey test. Results Irrespective of toothpaste, neutral slurries, as with alkaline slurries, yielded a chemically altered surface with rough texture, whereas acidic slurries formed a chemically clean surface with relatively smooth texture. Mechanochemical polishing effect might be mainly responsible for the cleanness and smoothness. Significance Acidic slurry-induced smooth surface may minimize plaque formation. However, the augmentation of released titanium ions may be adverse to the human body. For evaluation of toothpaste abrasion effects on titanium, paste slurry pH should be taken into account.

High temperature MCP process suitable for extremely hard high functional SiC wafers

The need for SiC single crystals as the next generation, high-power electronic and optoelectronic devices is increasing. Mechanochemical Polishing (MCP) is suitable for the final, damage-free surface finishing process for such extremely hard and high functional materials. Cr2O3 is already known as one of the useful MCP abrasives for finishing SiC crystals. However, there is some hesitation on the actual use of Cr2O3 abrasive in the production field because of the formation of Cr6+ as a highly toxic substance. In this paper, the possibility of α-Fe2O3 powder as an environmentally safe MCP abrasive is investigated. Polycrystalline SiC wafers are MCPed on a newly developed, high temperature polishing machine. Results obtained are the following. First, α-Fe2O3 abrasive produces the highest polishing efficiency at a polishing temperature of about 230°C, which is more efficient than that obtained by Cr2O3 abrasive polishing at any experimental temperature between RT (room temperature) and 330°C. Second, the polishing efficiency of the Cr2O3 abrasive decreases at temperatures higher than 230°C. This is because of the excessive adhesion of the abrasive grains to the wafer surface. Third, no mechanical scratches are detected, suggesting that there is no subsurface damage. Fourth, unevenness per each crystal grain resulting in large surface roughness Ra over several tens nm is observed, which is peculiar to MCP of polycrystalline anisotropic materials.

Fundamental investigation of wet type mechanochemical polishing method for CVD-SiC mold

Fundamental investigation of wet type mechanochemical polishing method for CVD-SiC mold

Mechanochemical Polishing of High Functional Materials

Mechanochemical Polishing of High Functional Materials

Machining Mechanisms of Si Wafers in Mechanochemical Polishing by Soft Abrasives

The mechanism of the mechanochemical polishing of Si wafers with BaCO3, CaCO3 and ZnO abrasives was investigated by polishing experiments carried out in air, O2 and Ar gas environments on dry condition and static heat treatment experiments of mixed powder of BaCO3 and Si with various mixture ratios for analyzing the reaction mechanism at the interface in polishing operation. Results obtained were (1) Si wafers were smoothly and effectively polished with these all mechanochemical abrasive whether O2 gas existed in the surrounding environment or not, (2) Heat treatment of the mixed powder suggested that oxidation of Si was more actively promoted even when existence of BaCO3 powder was only a little in the mixture and that formation of Ba-Si oxide increased as the mixture ratio of BaCO3 powder to Si powder increased, (3) As the mechanochemical polishing mechanism, two-step reaction process would be the most reasonable, that is, chemical attack of the mechanochemical abrasive for oxidizing the Si surface as the first step and further chemical reaction to form reaction products between the formed SiO2 and the abrasive as the second step.