Small feature accuracy challenge for CD-SEM metrology physical model solution

Downscaling of semiconductor fabrication technology requires continuous improvements in production process control. To ensure tool-to-tool matching and compatibility of critical dimension-scanning electron microscopy (CD-SEM) measurements to measurements from other technologies, such as optical CD, or from other fabrication entities, accuracy has become a much more important factor than in the past. CD-SEM measurements have always yielded a bias, which can be quite significant, but also typically neglected since it does not vary much over a process window. However, the standard CD-SEM metrology approach to algorithm accuracy (which can be formulated "Accuracy= Precision + Calibration") does not work for small features; i.e., the measurement bias is not constant for small features. Limitations of the standard measurement algorithm, based on the treatment of the singular point of the waveform for CDs smaller than 30 nm and the new model library-based approach, were considered. The implementation of reliable measurement algorithms for features at the 45 nm node and beyond requires development of more sophisticated approaches to SEM signal treatment. A three-dimensional (3-D) physical model that takes into account physical processes related to the beam interaction with material is considered. Reliability of the new approach is verified using Monte-Carlo SEM simulation and real SEM images as compared to reference measurements; total measurement uncertainty (TMU) is improved with the better models. The relation of the developed method to the standard SEM measurement algorithm and model-based approach is also considered.