Application automatic focusing with DVD pickup head in FPD substrate inspection

Abstract

This study proposes an integrated optical system for flat panel display (FPD) substrate inspection. For such a system, auto-focusing is a challenging problem since the microscope magnification ratio is as large as 10X to 50X and the corresponding depth of field (DOF) can thus reduced to 5 µm. Considering its low-cost and its capability in maintaining the depth of field that may be deteriorated by the increase of magnification ratio, this work uses the digital versatile disc (DVD) pickup head is used as the auto-focusing sensor. To verify the auto focus can be achieved. We construct experiment to simulate the real vibration. Change different position from lens to FPD substrate DVD calculate focus error signal (FES) to control PZT stage return to focus position immediately in 0.5 sec.