Method for improving overlay accuracy

As advanced process nodes demand increasingly tighter overlay error tolerances, overlay measurement has become more crucial, and the challenge to maintain high measurement accuracy has intensified. It is well known that IBO overlay measurement, which utilizes image-based measurement techniques, is significantly affected by image noise, impacting the final measurement accuracy. This issue becomes particularly evident when the substrate patterns are complex, as noise from different wavelengths becomes more pronounced. For different layers, the optimal measurement wavelength may vary, but actual measurements are limited to a single wavelength, resulting in an inability to eliminate much of the image noise, which in turn affects measurement accuracy. This paper proposes improvement solutions focused on reducing the impact of image noise, from measurement tools to model processing, in order to enhance the accuracy of IBO measurements.