Papers by Keyword: Lapping

Abstract: In this study, we developed two planarization mechanisms, macroscopic and microscopic, controlled by adjusting the C/Si ratio during Dynamic AGE-ing^® (DA) sublimation etching. Using these mechanisms, we planarized rough 4H-SiC wafers without the use of chemical mechanical polishing (CMP). Macro planarization forms macro step bunching (MSB) using high C/Si ratio DA etching, straightens the steps using step tension, and removes scratch marks caused by mechanical processing. Microscopic planarization involves debunching these MSBs using low C/Si ratio DA etching. It was observed that debunching progressed more quickly on wafers before CMP finishing due to the higher density of MSBs with ramified structures, which serve as starting points for debunching. The rate at which the MSB is shortened by step debunching increases with rising temperature, reaching about 20 μm/min at 1800 °C. By utilizing these mechanisms, we achieved high-quality planarization (initial Ra = 0.6 nm) to Ra = 0.18 nm for φ6-inch 4H-SiC wafers that had not undergone CMP. Furthermore, by performing DA sublimation growth on this planarized wafer, we achieved an in-grown stacking fault (IGSF) density of 0.09 cm⁻² and a basal plane dislocation (BPD) to threading edge dislocation (TED) conversion ratio of 99.95 %.

Abstract: The depth of surface/subsurface damage layer is the key index of surface quality of sapphire. In this paper, that depth model of the surface/subsurface damage lay characterized by the crack length was established according to the mechanical theory of indentation fracture. The cutting relation between abrasive and workpiece and the difference of the depth of subsurface damage crack are analyzed. It is preliminarily estimated that the length of sub-surface damage crack of free abrasive sapphire is about 2.46 times that of fixed abrasive when considering only the contact hardness of abrasive grain under static load. Diamond abrasives with size of W20 were adopted to carry out experiments in free and fixed lapping methods. The results show that the surface/subsurface damage depth is 9.87μm and 3.63μm respectively. It is easier to obtain good sub-surface quality by using the fixed abrasive method than free abrasive at the same particle size.

Abstract: Polishing of Silicon Carbide (SiC) seed crystals and substrates to achieve an extremely smooth, level surface, and an optically clear finish takes many surface finishing steps with very long processing times producing a significant amount of slurry waste and utilizing numerous lapping and polishing machines. This paper presents a newly developed cost-efficient SiC polishing process which reduces these operations to two surface finishing steps for achieving an optically clear finish on monocrystalline SiC material where the same size of diamond abrasives for lapping and polishing steps allows to carry out stock removal lapping and polishing processes on a single platform (machine) without concern of cross-contamination and making it as a very cost-efficient and high-throughput polishing process for SiC seed crystals and substrates.

Abstract: The production cost of the sapphire substrate was restricted by the efficiency of processing and the surface quality. A proposed level orthogonal experiment was conducted to reveal the effect of workbench speed, lapping pressure, the Concentration of triethanolamine and abrasive pad types on the material removal rate and surface roughness and morphology of sapphire substrate when lapped with a diamond fixed-abrasive pad. The results showed that the average material removal rate of sapphire is about 24μm/min, and the surface roughness Ra achieves 0.36μm when the 200/230 mesh diamond fixed-abrasive pad was used. The material removal rate and the surface roughness as the optimization goal, the optimal lapping parameters were as follows: the lapping pad with raised, lapping pressure 0.075MPa, workbench speed 120rpm and the Concentration of triethanolamine 1%. Under these optimal machining parameters, the material removal rate reached 42μm /min and the surface roughness Ra reached 0.37μm.

Abstract: The process parameters affect the lapping efficiency and the surface quality of work pieces. The fixed abrasive pad of w3-5 diamond abrasive was used for lapping magnesium aluminate spinel wafers in orthogonal experiment. The affection of lapping pressure, plate speed and slurry type on material removal rate (MRR) and surface roughness Ra were investigated. Finally, the process parameters were optimized. The results showed that lapping efficiencies were higher and the surface quality was better on the conditions of Zhongjing slurry, lapping pressure 10.37Kpa and plate speed 100rpm.

Abstract: Ultraviolet-cured resin bond, abrasive tools have been studied and have proven to have substantial advantages over conventional abrasive tools, not only in low energy cost and high efficiency when manufacturing the tool itself, but also in better performance when machining some materials [1,2]. However, very little research has been done to study the mechanism of UV cured abrasive tools. Nevertheless, many researchers have investigated the performances of such tools compared with some conventional tools. A mechanism of UV cured, resin bond, diamond wheel was proposed as the hybrid of grinding and lapping, which is called as grind/lap (G/L) process [3]. In the paper, the proposed mechanism was verified by comparing the experimental results of three processes. Three wheels were used to simulate grinding, lapping and grind/lapping operation separately under the same experimental setting. The results showed that the RA obtained by G/L wheel decreased to a value between those gained by grinding and lapping operations after 10 minutes and it became the lowest of the three as time increases. The RA and MRR of three processes indicated that at the beginning of operation, the abrasives in G/L wheel are fixed by the cured resin, and as machining time increases, the small grains get released from the wheel and act as loose abrasives. Therefore, the mechanism of the UV cured resin bond diamond wheel is verified as the dominant grinding at the beginning and lapping at the end, which was also illustrated by the surface profile of machined part.

Abstract: Modelling of the lapping process proves a complex undertaking because of the different forms of the abrasive particles in the working area, the wide dispersion of their dimensions, the modifications of their shape and dimensions during processing. The paper proposes the spherical model of the abrasive grain, based on the known fact that a good quality of the processed surfaces requires compact grains, with a dimensional ratio as close as possible to 1:1:1. Based on the adopted model the distribution of tensions at the grain-workpiece contact is determined, as well as the penetration depths of the abrasive grains into the workpiece and the transfer object, respectively. For this certain initial conditions are necessary, like Hertzian contact between the abrasive grain and the processed surface and the neglecting of strain hardening. Taking into consideration the known fact that only the large abrasive grains participate in the actual cutting process while the rest remain suspended in the gap between workpiece and tool, as well as their dimensional distribution and concentration in the lapping slurry, the volume of abrasive material required for processing was determined by statistical methods.

Abstract: Systematic achievement of high productivity lapping entails conceiving of a robust working system, insensitive to the action of disturbing factors. The experiments described in this paper were aimed at configuring such a robust machining system in view of maximising productivity. The main purpose of the experiments was to identify an optimum combination of the values of the input quantities of the machining system, such as to achieve its robustness, that is rendering it insensitive to the action of noise factors.

Abstract: Ultra-thin stainless steel sheet is likely to be the ideal substrate materials used for flexible display. In order to obtain ultra-thin stainless steel substrate with high accuracy, low surface roughness and without damage, the ultra-precision lapping and chemical mechanical polishing technology must be used. In this paper, the lapping paste for stainless steel has been designed using the orthogonal experiment method. According to the range analysis method, an optimal lapping paste had been obtained. Tests lapping the 304 stainless steel sheet with the optimal lapping paste have been done. The test results show that the MRR is about 240nm/min and the surface rough Ra is about 128 nm. This research results can provide theory support for ultra precision machining the stainless steel.

Abstract: The processing technology of sapphire with a high material removal rate a good surface quality is critical for its applications. The experiment of sapphire lapping and polishing was carried out by using three different fixed abrasive pad (FAP). Their material removal rate (MRR) and surface roughness (Ra) were measured and analyzed. Results indicate that a MRR of 5.6μm/min reaches in rough lapping and a MRR of 0.4μm/min in fine lapping. The average surface roughness Ra of rough lapping and fine lapping is 142nm and 1.2nm respectively. The processing efficiency of sapphire wafer is effectively improved and a good surface quality is obtained when FAP adopted.