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Single-sided lapping is crucial in sapphire wafering processes for improving flatness and achieving the target wafer thickness using loose abrasives. In single-sided lapping process, the Material removal rate (MRR) is a key factor for reducing process time and cost. However, the MRR is limited when using loose abrasives because abrasives mostly act by rolling and sliding. Many researchers have studied fixed abrasives to increase the MRR, but the MRR decreases with time. To solve this problem, the self-dressing effect was studied with various pressures, velocities, cutting fluids and wafers. The MRR decreased due to the wear of abrasives, and the pressure and velocity have little effect on the self-dressing. Lapping experiments were done using cutting fluid with a lapped wafer and sawed wafer. The MRR, plate roughness and thickness were measured to study the wear of the abrasive and the self-dressing effect. The cutting fluid delayed the wear of the abrasives and thus improved the decrease in MRR, but it had little effect on the self-dressing effect, like in the case when water was used. When using cutting fluid and a sawed wafer, the MRR was high and did not decrease. A concentrated load on the plate caused by shape error and saw marks on the sawed wafer could produce the self-dressing effect. We verified that a sawed wafer could produce the self-dressing effect on even a worn plate. [ABSTRACT FROM AUTHOR]

Multi-wire sawing with diamond wire is used to slice hard and brittle materials such as sapphire, silicon carbide, or silicon into thin wafers. Compared to traditional slicing methods, multi-wire sawing with diamond wire has many advantages, including reduced kerf loss, efficient machining, and improved form accuracy. However, the process is associated with several unexpected problems, including considerable kerf loss and inefficient cutting during the initial cutting step. Thus, materials cannot be constantly removed due to the instability of the cutting performance of the diamond wire. These phenomena are defined as the break-in characteristics of diamond wire. This paper focused on the break-in characteristics of diamond wire and the effects of these characteristics on the cutting performance. In an experiment, a single-wire sawing machine equipped with a monitoring system was used to analyze the horizontal and vertical cutting forces which arose during the cutting process. The cutting performance was evaluated by means of cutting profile measurements. The wires used were analyzed by the newly developed vision measurement system and through scanning electron microscope (SEM) imagery. On the basis of results, it was found that the break-in characteristics of diamond wire are strongly correlated with the wear behaviors of the diamond wire. [ABSTRACT FROM AUTHOR]

Diamond abrasive-coated wire is a tool for the precise multi-wire sawing of mono-crystal ingots to manufacture substrates. This tool is used to cut hard materials such as silicon carbide, gallium nitride, sapphire and silicon. The cutting performance of diamond wires strongly influences the accuracy of substrates in terms of roughness, total thickness variation and BOW. Nonetheless, changes in cutting performance as a result of gradual wear through repeated contact complicate the optimization of diamond wire use. A characterization method is proposed for the cutting performance and lifetime of a diamond wire based on mathematical modeling and experimental results. The theoretical model predicts that cutting accelerates with the application of a strong feed force and small abrasives due to an increase in indentation depth for each abrasive. Experimental results showed that a wire with a low concentration exhibited an increased material removal rate. However, the lifetime of the wire displayed an opposite trend; that of a diamond wire can be classified into two regimes. The first one is an increased loss of abrasives as a result of rapid wear attributed to a low concentration; the second regime is caused by a drop in actual contact pressure due to the enlarged contact area between the workpiece and the bonding material enveloping the abrasives. [ABSTRACT FROM AUTHOR]

The planarization CMP, which is considered as one of the most important ULSI chip, is introduced to make flat surface in patterned areas for multilevel MEMS devices. However, the conventional CMP is limited in its application to MEMS structures, due to their wide patterns of μm to mm order thick film layer of several μm. A new CMP process has been developed for application to MEMS structures by the control of selectivity between polysilicon and silicon oxide. A 30nm thick protective oxide layer is deposited to protect the recessed areas, and then polished with low selectivity slurry to partially remove the protruded area while suppressing the removal rate of the recessed area. During the second step of the new CMP process, high selectivity slurry is used to minimize the dishing amount and the variation in the step height according to pattern size and density. Experimental results showed that dishing amount was less than 30nm at the largest pattern of 1250 μm in width and showed no variation of entire pattern, which meant local and global planarization. This result suggests that the newly developed selectivity controlled CMP process can be successfully applied for fabrication the multilevel MEMS devices. [ABSTRACT FROM AUTHOR]