Free Abrasives Research Articles

Relationships between Contact Image Analysis Results for Pad Surface Texture and Removal Rate in CMP

In chemical mechanical polishing (CMP) process, the removal rate is affected by the actual contact conditions between the wafer and the polishing pad. Further, the free abrasives in the slurry attack the wafer at the regions of actual contact. The polishing pad is one of the most important consumable materials in CMP since the pad surface texture changes during wafer polishing and substantially influences the actual contact conditions. Therefore, methods for quantitative evaluation of the pad surface texture have been proposed by various research institutes. We have developed a novel method for the quantitative evaluation of the polishing pad surface texture; this method is based on contact image analysis using an image rotation prism. We have proposed the use of four effective evaluation parameters: the number of contact points, the contact ratio, the maximum value of the minimum spacing of the contact points, and the half-width of the peak of the spatial fast Fourier transform (FFT) of a contact image. We determine the changes in the polishing pad surface texture on the basis of the proposed evaluation parameters in serial batch polishing tests. In particular, we focus on the relationships between the proposed evaluation parameters and the removal rate, which changes with an increase in the number of batch polishing tests. The evaluation parameters are linearly correlated with the removal rate. Hence, the removal rate is improved not only with an increase of the number of contact points and the contact ratio but also with a decrease in the size of the cohesion regions and the spacing between the contact points.

Machined Surface Characteristics and Removal Mechanism of Soft and Brittle Solids

Surface characteristics of CZT wafers machined using wire sawing, free abrasives lapping and polishing and ultra-precision grinding were investigated. Wire sawing resulted in the removal of material in both ductile and brittle regimes, but both polishing and grinding led to a ductile removal. The grinding produced very smooth surfaces free of embeddings and scratches, which is thus considered to have better machinability than the free abrasive machining. The nanoindentation and nanoscratch on MCT wafers at nanometric scales resulted in considerable plastic deformation, but no fracture features. The hardness of the MCT wafer was 500 to 550 MPa, and the coefficient of friction was particularly high, ranging from 0.45 to 0.55.

Experimental Research on the Robotic Compound Polishing Process with Mixed Magnetic Abrasive

The quality and the efficiency of the polishing process are important to the lead time of the rapid tooling. Robotic polishing process with free abrasive is adapted to the finishing of complex mould surface, in which the soft polishing tool is widely used. But the stability and the efficiency of the process should be improved further. According to the moving and grinding characters of the free abrasive, the mixed magnetic abrasive and the minitype electromagnetic field are combined to the robotic polishing process. The mixed magnetic abrasive are made up of magnetic grain and hard abrasive, which can enhance the effective cutting and grinding process of the three-body abrasion under the effect of magnetic field. The robotic compound polishing process with mixed magnetic abrasive is presented in this paper. The experiments are tested to study the distribution of the minitye magnetic field and the polishing efficiency of the complex polishing process. The results show that the polishing efficiency of the process can be improved obviously where the effective working intensity of the electromagnetic field reaches 400Gs.

Surface Texture Analysis of Fixed and Free Abrasive Machining of Silicon Substrates for Solar Cells

Multi-wire sawing process has been widely used for wafer slicing of silicon substrates for solar cells. Usually there are two different kinds of wire saw in multi-wire sawing process including free abrasive wire sawing with SiC grits and fixed abrasive wire sawing with diamond wire. For free abrasive wire sawing process, the material removal mechanism can be considered as lapping and the fixed abrasive wire sawing can be considered as grinding. This paper is to investigate the characteristics of the surface texture of silicon substrate fabricated by these two wire sawing process. Experimental results have been observed by white light interferometry and SEM. Some different properties of both processes have compared been with variant characteristics including 2-D and 3-D surface roughness parameters. Results of this paper can be further used to evaluate the feasibility of wire sawing process of silicon substrates for solar cells.

Material removal mechanism of precision grinding of soft-brittle CdZnTe wafers

Cd0.96Zn0.04Te (111) wafers were precisely ground by #800, #1500, #3000, and #5000 diamond grinding wheel. For comparison, Cd0.96Zn0.04Te (110) wafers were machined by lapping, mechanical polishing, and chemical mechanical polishing. High-resolution environmental scanning electron microscopy equipped with energy dispersive spectroscopy and optical interference surface profiler both were employed to investigate the surface quality and material removal mechanism. The results show that the material removal mechanism of #800 grinding wheel is abrasive wear, fatigue wear, and adhesive wear, and that of #1500 is abrasive wear and fatigue wear. Both the material removal mechanism of #3000 and #5000 grinding wheel are abrasive wear, leading to the excellent ductile removal precision grinding. While the material removal mechanism of CMP on CdZnTe wafers is firstly chemical resolving reaction and secondly mechanical carrying action. Moreover, precision grinding exhibits high-efficiency character and eliminates the imbedding of free abrasives of Al2O3 and SiO2.

Effect of Free Abrasive Particle in Gasbag Polishing Technique

Free abrasive particle plays a crucial role in material removal and quality improvement of curved surface mould. In order to observe and investigate the general distribution state, fractal dimension and movement characteristic of abrasive particle in gasbag polishing process better, an abrasive particle stroboscopic photography system is established and polishing experiment is carried out. The abrasive particle contacts with not only the rubber gasbag enwrapped by polishing cloth full of mesh-like structures, but also the mould surface. Contact analysis of abrasive particle including the discussions of contact state, material removal mechanism and advantage of precession polishing is helpful to hold the optimal polishing process parameters combination and establish ideal abrasive particle field for higher polishing efficiency and more well-proportioned surface quality.

Dispersion of ceramics and composites in diamond finishing by free abrasive

The algorithm allowing to find parameters of physical-mathematical model describing the surface abrasive dispersion of ceramic VK 100-1 under diamond lapping by loose abrasive is presented. This algorithm is based on destruction analysis of ceramic materials, and on the theory of mechanical failures accumulation under abrasive stochastic action. The information related to the real technological process has been used. It is shown that it is possible to use the energetic damageability function, if the manufacturing procedures are design virtually. The dispersion rate is used as the generalized efficiency factor.

磁性流体を研磨液として用いた平面ラッピング(<小特集>生産加工・工作機械の規範2008)

Smooth and flat surface of glass plates should be needed for the HDD substrate. Polishing with free abrasives made smooth surface, however it is difficult to obtain flat surface because of the nonuniform distribution of free abrasives. In order to overcome such issue, we tried to apply magnetic force with magnetic fluid and magnetic field for uniform distribution of abrasives during polishing process. By applying 20mT of normal magnetic filed to the copper polishing plate with magnetic fluid as polishing liquid, surface roughness of polished glass plate improved by 20-60%. And flatness of polished glass decreased to half with magnetic fluid and magnetic filed.

3D Profile and Generating Mechanism of Cylindrical Surface Lapping Machined with Abrasive Jet Flow Restricted by Grinding Wheel

The aim of abrasive jet flow finishing process as a new lapping techonology is to remove further the surface defect layer and diminish roughness and ripple. Experiments are performed on a cylindrical grinder MB1332A with a 45 steel workpiece as specimen of which the surface roughness values is 0.6 μm. The micromorphology of machined surface morphology is observed by using scanning electron microscope and the microcosmic geometry parameters are measured with Micromesvre2 profilometer. With ACF the surface during grinding and further lapping with liquid abrasive jet flow are researched. The material removal mechanism and the mechanism of surface morphology finished by the novel process is investigated. The energized free abrasives polish,wipe off and micro-cut the workpiece surface in wedge-like zone which is the main factor in material removal and the lateral extrusion of abrasive fluid is the main factor of homogenizing and lowering ripples. The result indicates that the machined surface changes from continuous parallel micro-groove to randomly distributed discontinuous micro-pit and the surface roughness values gradually decreases from an initial value of about 0.6 μm down to about 0.2 μm with the increase of machining cycles. Furthermore,the isotropy surface and uniformity veins both parallel and perpendicular machining direction are attained by the finishing process to improve greatly the wear resistance of the workpiece.

Research on the Robotic Free Abrasive Polishing System for the Rapid Spray Metal Tooling

In the rapid spray metal tooling, metal film is spray-formed on the substrate and supported under the back, which will act as the working surface of the rapid metal tool finally. So the finishing process for the sprayed metal film is important to the quality and the lifecycle of the rapid metal tool. The finishing of the metal mould is frequently carried out manually, these kinds of operations are iterative, time consuming and require experience. Automation can introduce cost reduction minimizing production times on such manual finishing operations. This paper presents a robotic polishing system with free abrasive for the finishing of the rapid spray metal tool, which is consisted of a six-degree-of-freedom industrial robot manipulator, a high speed electrical polishing spindle and a numerical swivel table. Soft polishing pad and free abrasive are also selected for the robotic polishing system. The path planning is so important to the robotic polishing system that a partition & flexible path mapping method basing on UG CAM is developed to generate the uniform robotic polishing path on the complex mould surface. UG/Open GRIP programming module is used to generate the driving paths with different path intervals on the predesigned plane for each partitioned part. When the driving paths are projected to the mould curved surface, the uniform polishing paths with NC code can be generated by the multi-axis CAM module of the UG. And the path with NC code can then be transformed to the robotic polishing path. According to the elastic deformation and the abrasion of the soft polishing tool, the robotic polishing path should be adjusted to keep the smooth polishing process by offsetting the pre-compressed value and the abrasive compensation value along the polishing axis direction. Technical parameters of the robotic polishing process are also optimized through the experiments. Finally, the rapid metal punch mould is finished to test the robotic polishing system.

Experimental Investigation on Ultrasonic Face Machining of Glass with Free Abrasives

Serials of ultrasonic face machining experiments were designed and carried out on glass materials with free abrasives. Two different kinds of ultrasonic machining, namely, non-rotary ultrasonic machining (NRUSM) with free abrasives and rotary ultrasonic machining (RUSM) with free abrasives were compared. Two systems were set up to in-process monitor the changes of static forces and frequency respectively. The effects of static force, spindle speed and amplitude of ultrasonic vibration on material removal rate (MRR) and surface roughness were analyzed. The surface of workpieces was also observed by a digital video microscope system. The experimental results indicated that, at the given conditions, there exists an optimal value of static force and amplitude of vibration to obtain the maximum MRR, and RUSM was found to be superior to NRUSM in the MRR, but inversely in surface roughness.

The Numerical Analysis on Action Mechanism of Slurry in Free Abrasive Wiresaw Slicing

Free abrasive wiresaw technology is the main method in slicing monocrystalline silicon wafers. The mathematical model of hydrodynamic action in the process of the free abrasive wiresaw slicing was founded, displacement caused under distributed radial load of every node on the wire is embodimented through self-compliance influence coefficient, which is beneficial to found the film thickness equation. The distributions of hydrodynamic pressure and film thickness in the free abrasive wiresaw slicing process are yielded by using the finite difference numerical methods to solve the two-dimension Reynolds equation. The results show that the minimum film thickness increases with the increase of wire speed, and slurry viscosity, while decreases with the increase of wire bow angle. The film thickness is greater than the average abrasive size so that the abrasives float in the slurry when the size of abrasive is small enough.

Improving processing of large prisms

The process schemes for processing large prisms from blocking in gypsum and treatment with free abrasives with conversion to individual strengthening and use of a combined diamond instrument in coarse and fine polishing operations were examined. The results of improving processing with conversion to fine polishing operations from a spot to a lamellar instrument and from glass wool to PTS cloth in polishing are reported.

Surface preparation for gasothermal coating with free abrasive

Surface preparation for gasothermal coating with free abrasive

The Optimization of Technological Processes of Details Processing by Free Abrasives

The purpose of the research is the development of theoretical foundation of processing of details by free abrasives, the increase of efficiency of finishing processing of details on the base of creation of methodical principles of optimization of technological processes by means of CAD.

A Study of Slicing Process with Thin Diamond Wire(Grinding technology)

In the production process such as the semiconductor wafer slicing, the processing methods that used free abrasives wire saw are extensively adopted. However, these SiC grains after use are unfavorable from an environmental perspective, due to the fact that they become industrial wastes, and is also not very efficient. For these reasons, the development of the wire with fixed abrasives is required by industry. The major objects of this paper is to make the fixed abrasive wire saw apply to high cost production in semiconductor industries such as wafer slicing, and provide the industry with the effective processing parameter. Effects of processing parameters on the performance of fixed diamond wire sawing processes are investigated by using the Taguchi method for this design of experiment (DOE). The performance discussed in this paper includes machined surface roughness of the wafer, material removal rate and wear of the wire and kerf width. The processing parameters are grain size, wire tension, slurry, wire speed and feed rate. An L_9(3^4) orthogonal array, signal-to-noise (S/N) ratio are employed to analyze the effect of these processing parameters. The analysis of the result shows that the optimal combinations for good surface roughness are small grain size, high wire speed, and low feed rate. Wire speed and feed rate are positively related to material removal rate. The use of slurry results in a larger removal rate and larger wear of the wire. Furthermore, it was determined that the wire tension does not have any significant effect on the performance.

Study on STI planarization process using fixed abrasive tool (1st Report)

Novel chemical mechanical polishing (CMP) process using a fixed abrasive tool (FX-tool), which is a kind of grindstone, was developed for dielectric planarization. In order to obtain flat surface for 45-nm-node of semiconductor generation, two points that are adopting stiff polishing pad/tool and reducing concentration of free-abrasives become critical issues. Newly developed FX-tool has more than ten times higher Young's modulus than that of a conventional CMP pad, and simultaneously, concentration of free abrasives on its surface can be controlled by polishing time. In experiments using several test-wafers, less than 30nm of dishing was obtained up to 3mm-length-pattern. Additionally, polyacrylic ammonium (PAA) effectively affects to increase degree of selectivity between oxide and nitride for shallow trench isolation (STI) process. The selectivity of 41 was obtained at 3 vol.% concentration of PAA. STI test wafers were successfully polished without any additional processes such as etching back.

602 CMG 砥石の開発に関する研究

The present manufacturing process for silicon wafer includes lapping, etching and several step of polishing. Such free slurry methods can achieve better surface roughness only when smaller abrasives are applied, therefore require multi-stage equipments and processes. To combat these problems encountered with free abrasives, the semiconductor and electronic industries are looking for a fixed abrasive solution as the alternative. This research has proposed a new chemo-mechanical-grinding process by adding chemical effect into the grinding process. Chemo-mechanical-grinding wheel, which contain chemically active abrasives and alkalinity additives have been successfully developed. The chemo-mechanical-grinding has been mainly evaluated by the grinding performance on φ300mm bear silicon wafers, comparing to grinding with diamond wheel.

Development of an Abrasive Embedded Pad for Dishing Reduction and Uniformity Enhancement

Chemical mechanical polishing (CMP) has been widely accepted for the planarization of multilayer structures in semiconductor manufacturing. CMP is optimized by several process parameters, such as the equipment, pad, and slurry. However, there have been serious problems in CMP in terms of repeatability and defects in patterned wafers. Especially, dishing & erosion defects increase the resistance because they decrease the interconnect section area, and ultimately reduce the lifetime of the semiconductor. Methods to reduce dishing & erosion have recently been introduced: minimizing the abrasive concentration, minimizing the oxidizer volume, increasing the surface hardness of the pad, optimization of the pattern structure as dummy patterns. However, minimizing the oxidizer and increasing the pad hardness are concerned with the removal rate and the quality of the polished wafer. Therefore, minimizing the abrasive concentration by using CeO2 is the best solution for reducing dishing & erosion. The removal rate can be maintained because a CeO2 abrasive has good polishing characteristics compared with SiO2. This paper introduces a dishing & erosion generating mechanism and a method for developing a semi-rigid abrasive pad to minimize dishing & erosion during CMP. Dishing & erosion are initially generated by an uneven pressure distribution in the materials. These defects are accelerated by free abrasives and chemical etching. Therefore, it is known that dishing & erosion can be reduced by minimizing the abrasive concentration. The developed semi-rigid abrasive pad was applied to Interlayer dielectric (ILD) CMP, and the result was compared with that of a conventional pad in terms of material removal rate, within wafer non-uniformity, and surface damage.

Free Abrasive Machining in Slicing Brittle Materials With Wiresaw

Wiresaw has emerged as a leading technology in wafer preparation for microelectronics fabrication, especially in slicing large silicon wafers (diameter⩾300 mm) for both microelectronic and photovoltaic applications. Wiresaw has also been employed to slice other brittle materials such as alumina, quartz, glass, and ceramics. The manufacturing process of wiresaw is a free abrasive machining (FAM) process. Specifically, the wiresaw cuts brittle materials through the “rolling-indenting” and “scratch-indenting” processes where the materials removal is resulting from mechanical interactions between the substrate of the workpiece and loss abrasives, which are trapped between workpiece and wire. Built upon results of previous investigation in modeling of wiresaw, a model of wiresaw slicing is developed based on indentation crack as well as the influence of wire carrying the abrasives. This model is used to predict the relationship between the rate of material removal and the mechanical properties of the workpiece together with the process parameters. The rolling, indenting, and scratching modes of materials removal are considered with a simple stochastic approach. The model provides us with the basis for improving the efficiency of the wiresaw manufacturing process based on the process parameters.