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

Abstract

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