| Co-Investigator(Kenkyū-buntansha) |
NAKANO Hirotami Ibaraki University, Faculty of Engineering, Lecturer, 工学部, 講師 (90257329)
KONDO Ryo Ibaraki University, Faculty of Engineering, A/Prof., 工学部, 助教授 (90186867)
ZHOU Libo Ibaraki University, Faculty of Engineering, A/Prof., 工学部, 助教授 (90235705)
WATANABE Kazushi Hitachi Via Mechanics Pte. Ltd., Vice chief engineer, 副技師長
SHIMIZU Jun Ibaraki University, Faculty of Engineering, Research Associate, 工学部, 助手 (40292479)
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| Research Abstract |
This research project has developed an integrated manufacturing system for φ300mm silicon wafer, using fixed abrasive instead of conventional free slurry, to provide a totally integrated solution for achieving the surface roughness R_a < 1nm(R_y < 5〜6nm) and the global flatness < 0.2μm/φ300mm. In addition to the space saving, this integrated system also significantly reduces the total energy consumption by 70%, compared with the current process used for φ200mm Si wafer. Four core technologies : the hybrid process mechanics, the GMM (giant magnetostrictive material) actuated positioning/alignment device and the ecologically friendly coolant circulation system have been developed in this research. The results obtained are summarized as follows ;
The grinding system has two degrees of freedom. The work spindle moves along X-direction, while the wheel spindle moves along Z-direction. Aerostatic bearings are applied to the spindles and other guideways so that no contact is made between the c
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ounterparts. By disengaging the lead screw nut, the Z-axis table is floating in nature, and movable by a low friction pneumatic cylinder. This function creates a constant grinding force/pressure as low as 20gf/cm^2, and offers a polishing-like condition for the final finish. In order to achieve ductile mode grinding and improve the global flatness, a positioning and alignment mechanism is particularly developed for the work spindle. There are two sets of plates (600x600mm) installed between the work spindle and the X-axis table. The bottom plate is used for alignment, while the top plate for positioning. Powered by GMM actuators, the device is able to offer 6.25 Å step response at the payload of 750kgf, while to align the work spindle against the grinding wheel at the resolution of 10^<-2> seconds over the range of ± 1.5 degrees.
Most of the silicon grinding system utilizes the plunge method to keep the contact area unchanged and thereby to deliver a stable grinding performance throughout the grinding process. As a result, the cutting path formed in the wafer center is much denser than that at the fringe. A kinematical analysis has been done in this research and the results lead to 1) the criteria for speed ratio combination to improve the surface roughness, 2) a proper alignment between the wheel and wafer to effectively reduce the profile error, 3) an optimal wheel geometry to attain a consistent cutting path density.
In order to completely remove the subsurface damage, the project team is further developing a new process called as "CMG ; chemo-mechanical grinding", in which, the chemically active additives is applied to the mechanical grinding process. In addition to the surface roughness enhancement, the dislocation at the wafer subsurface finished by CMG process is significantly reduced to 1/30 as compared to the conventional precision grinding. Less
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