Development of multi-stage optical variable attenuator system and its control method for wafer inspection system

For the optical particle inspection systems for unpatterned wafers, it is required to reduce inspection-accuracy variation in wafer and increase throughput. In this system, a laser beam irradiated spiral shape by rotating moving wafer, defect particles are detected based on intensity of their scattered light. study, we propose multi-stage optically variable attenuator system its control method achieve constant laser-energy density high-speed simultaneously.