A novel overlay metrology method: Simultaneous utilizing spectral and angular spectrum

In the lithography process, overlay describes the position errors of placing one mask layer pattern over an existing pattern on the wafer, and overlay metrology is one of the key challenges in semiconductor manufacturing. With the increase of process complexity especially for multiple patterning technologies in advanced nodes, the demand for accuracy, precision and process robustness in overlay metrology continues to tighten. In this paper, we have proposed and demonstrated a novel overlay metrology method with high process robustness. A straightforward theory called interference of diffraction light is developed for explanations why this method works for single layer overlay metrology. The overlay signals with continuous wavelengths and angles are simultaneously acquired in the pupil plane. Therefore, compared with the current monochrome measurement technology, this work can gather and utilize as much overlay information as possible for measurements. Experiments illustrate that this technique can achieve better measurement repeatability, faster measurement speed and better process robustness than current monochrome method, and thus this method has great potential to meet the higher node requirements for measurement accuracy. What' more, our work provides a novel idea for scatterometry technology in the field of micro-nano measurement.