High-resolution optical metrology

Recent advances in optical imaging techniques have unveiled new possibilities for optical metrology and optical-based process control measurements of features in the 65 nm node and beyond. In this paper we discuss methods and applications that combine illumination engineering and structured targets which enable sensitivity to nanometer scale changes using optical imaging methods. These methods have been investigated using simulation tools and experimental laboratory apparatus. The simulation results have demonstrated substantial sensitivity to nanometer changes in feature geometry. Similar results have now been observed in the laboratory. In this paper we will show simulation data to motivate the use of low numerical aperture and structured illumination optical configurations. We will also present the basic elements and methods which we are now using in the design of an optical tool specifically designed for these types of measurements. Target configurations which enhance the scattered electromagnetic fields will be shown along with experimental verification of the methodology. The simulation and experimental apparatus is used to explore and optimize target geometry, optical configurations, and illumination structure for applications in both critical dimension and overlay metrology.