Optical methods are often thought to lose their effectiveness as a metrology tool beyond the Rayleigh criterion. However, using advanced modeling methods, the conventional resolution limitations encountered in well-defined edge-to-edge measurements using edge thresholds do not apply. In fact, in this paper we present evidence that optics can be used to image and measure features as small as 10 nm in dimension, well below the imaging wavelength. To understand the limits of optical methods we have extensively studied both linewidth and overlay metrology applications. Although overlay applications are usually thought to involve pitch or centerline measurements of features from different process levels, some target designs present optical proximity effects which pose a significant challenge. Likewise, line width measurements require determination of the physical edges and geometry which created that profile. Both types of measurements require model-based analysis to accurately evaluate the data and images. In this paper we explore methods to optimize target geometry, optical configurations, structured illumination, and analysis algorithms with applications in both critical dimension and overlay metrology.
Proceedings Title: Proceedings of SPIE, Metrology, Inspection, and Process Control for Microlithography XVIII, Richard M. Silver, Editor
Conference Dates: February 23, 2004
Conference Location: Santa Clara, CA
Conference Title: Overlay and Registration Metrology I
Pub Type: Conferences
imaging resolution, intensity profile, optical modeling, overlay metrology, Rayleigh criterion