Advanced Materials Research Vols. 76-78

Abstract: The results of truing and dressing depend on: sharpness of the dresser, speed of dressing, depth of cut and vibration phenomena. Prediction of the optimum wheel surface for grinding which produces an accurate profile and cuts most efficiently can minimize the time and cost and optimize performance of the operation before it is performed in the shop. It has especially significant meaning in truing and dressing of hard CBN wheels. The research described in this paper shows computer simulated and visualized wheel surface before and after the wheel dressing process. This paper provides additional results to those was reported in [8] taking into account the influence of vibrations. It is a companion paper to [8].

Abstract: Chemical mechanical polishing (CMP) is a semiconductor process that is used to achieve global planarization. To maintain the stability and the throughput of CMP, the polishing pad needs to be dressed by a diamond dresser. By calculating the distribution of the scratch numbers of diamond grits in the pad, the effect of dressing can be estimated and the pad profile can be predicted. All the parameters of dressing motion were taken into account. The target equipment of this study is Mirra Mesa, which is manufactured by Applied Materials. Different types of dressers, including ring-types and full-type, different pitches and arrangements are used in CMP process. Each of them was simulated in this study. The diamond pitch is relative to the number of diamonds and the scale of the total scratch time, but does not affect the profile of the scratch time. Regular or random arrangement makes no difference in the profile of the scratch times. The width of the ring influences the number of diamonds and the scale of the total counts while the profiles remain similar.

Abstract: In this paper, a precise profile ELID grinding with Electrical Discharge Truing(EDT) has been introduced, and some experiments for efficient and precision EDT process with cast iron-bonded diamond wheel have been carried out with four types of medium: mist, water, pressure air, air, furthermore some machining parameters e.g. electric current, electric voltage have been discussed in detail. For analyzing of the accuracy of EDT process with cast-iron bonded diamond wheel, a profile measurement method with software of MATLAB was used for analyzing of the profiles of cast-iron-bonded diamond wheel and electrode. It can be found that the electrode’s profile can be kept with the consistent designed profile, and the grinding wheel with the designed profile has been got by the appropriate EDT process. Therefore the higher efficiency and precision EDT process can be achieved by the appropriate EDT machining parameters.

Abstract: The major aim of this study is to present a novel technique for honing the micro-hole. It is difficult that regarding the finish machining of the micro-hole that the diameter is less than 300 m. First, a new process that to on-line accurately fabricate the micro-honing-tool using micro-EDM, micro-co-deposition and micro-wire-EDM is proposed for honing the micro-hole. A micro rod for as the substrate of the micro-tool is formed by wire-EDM and then co-deposited with 0-2 m CBN-abrasives. Subsequently, it is axially and crisscross cut for an appropriate length by micro-wire-EDM to make the crotched microstructure. The whole processes are able to be on-line realized since all working positions are recorded in detail and fabrication technologies are offered sufficiently on the same system. As a result, per the same fabrication-system, the micro-honing process is also on-line conducted. The finished micro-honing-tool is employed directly without unloaded and reloaded. The grinding-block can compactly stick on the wall surface of the micro-hole due to the radial elasticity of the micro-tool and then fast grind away the uneven surface by removal of micro amount. Experimental results demonstrated that the circularity and surface roughness on the hole-wall is evidently improved. Comparing with the obtained machining surface by micro-EDM hole-drilling, the original surface roughness of near one-sixth time can be achieved. It is indicated that the micro-hole can be honed accurately using the proposed technique.

Abstract: The pad surface will become grazed because of the accumulated debris in the chemical mechanical polishing (CMP) process. It results in the reduction of the wafer removal rate, and a pad conditioner or diamond disk must be frequently employed to refresh the pad surface. The wear behavior of a diamond with respect to its location, original relative protruded height and protruded shape on a diamond disk was investigated in this thesis. It was found from experimental data that the diamonds which were located outside, originally protruded more highly and with crest lines oriented upward wore faster. Accordingly, four suggestions were proposed to obtain the uniform diamond wear. They are: lowering the protruded heights of the outside diamonds, replacing the current flat substrate by a curved surface substrate, changing the diamond distribution on the disk from the current uniform one to a higher concentration around outside diameter, and orienting the diamonds such that the flats are protruded upward for the outside diamonds and the crest lines are projected upward for the inside diamonds. Experiment had verified that the pad conditioner with center-protruded substrate led to a stable and higher dressing rate.

Abstract: Diamond pad conditioner or dresser can determine the efficiency of chemical mechanical polishing (CMP) processes and the quality of polished wafers. Conventional diamond pad conditioners are made by adhering discrete diamond grits on a flat substrate. The size distribution of diamond grits coupled with the deformation of the substrate often make the tips of diamond grits lying at different heights. Instead of attaching individual diamond grits to a metal substrate, a revolutionary design of pad conditioners is based on carving a structure out of sintered polycrystalline diamond (PCD) matrix. The PCD dresser is manufactured by wire electro discharge machining to form cutting pyramids of a specific size with a designed shape. The dressing characteristics of pad surface textures are studied by comparison with conventional diamond pad conditioner. Experimental results indicate that the PCD dresser can dress asperities of the pad more uniformly than the conventional diamond dresser due to PCD dresser having identically shaped tip and the same height diamond. In addition the cutting rate of PCD dresser for IC1000 pad not only is reduced by about 30% but also it can dress pad more effectively than conventional diamond dresser.

Abstract: Chemical vapor deposition (CVD) diamond thin films are widely used in modern industries. However, due to the nature of polycrystalline, thin films are required to be polished in the final process to increase its surface quality. Thermal-chemical polishing is known for its less processing time and low cost. In this paper, the experiments are carried out to observe the effect of processing conditions such as temperature, rotational speed, polishing pressure, and substrate material on the surface roughness and on the material removal rate of the chemical vapor deposition diamond (CVDD). At the same time, the processing mechanism for this thermal-chemical polishing is investigated, and a polishing model is built for comparison with the experiment results. The results show that the material removal rate is affected mainly by the diffusing rate in the Fe-C polishing system. By using the model, the approximate value of material removal rate can be calculated according to the polishing temperature.

Abstract: To produce lifelong, harmless hip joint prostheses, considerable cross-disciplinary studies have been carried out. The research includes adaptability and sustainability of artificial materials to human body, selection of materials, precision fabrication and efficient replacement operation. This paper provides a brief review of some of these key aspects with some details in abrasive polishing.

Abstract: The computer-controlled chemical polishing (CCCP) techniques based on the Marangoni effect have been developed to manufacture precision optics on polished fused silica surface. In this study, we present the Marangoni confined chemical-etching process in which the material removal on optical surfaces can be accomplished by etching with buffered HF solution. The process shows stable characteristics and good repeatability while the etching depth can be controlled in the order of ten nanometers. We also present the experimental results of this technology for fabrication of phase corrector and continuous phase plate. Results show that the CCCP’s deterministic sub-aperture-polishing characteristics make it possible to correct the surface error and imprint complex phase structure with spatial scale-length of several millimeters onto optical surface.

Abstract: Strong anisotropy of physical and mechanical properties of Potassium Dihydrogen Phosphate (KDP) crystals significantly affects surface quality during processing the samples. Different processing direction, along [100], [110], and [120] crystallographic orientations, are chosen on (001) crystal plane in order to evaluate the anisotropic characterizations on the processed surface. Scanning electronic microscopy (SEM) is employed to observe the machined surface damage, defects and profiles. At the same time, surface quality is measured by Zygo surface profiler to estimate the processed surface quality. The results show that the machined surfaces along three different orientations under the same processing conditions behave quite differently from each other. Strong anisotropy and complex slip system of KDP crystals lead to several different asymmetric damages on the machined surface. Surface roughness (Ra) values along [100] are the smallest, that along [120] are in average, and that along [110] are largest. Moreover, many illustrations are given to understand the anisotropic nature during processing, including slip system, mechanical properties during processing, and technical parameters, etc.