3-D nano object recognition by use of phase sensitive scatterometry

Optical correlation techniques have proven to be very useful in various twoand three-dimensional pattern recognition applications. Recently, there has been increased interest in various imaging based 2-D and 3-D optical information sensing and recognition [1,2,3,4,5]. In particular, 3-D information processing based on digital holography has been proposed to extend optical correlation techniques to 3-D object recognition [4,5]. However, all such approaches were mainly based on an imaging technique which has an inherent optical diffraction limit and, for that reason, recognizing nano-size patterns smaller than around 1 μm could not be handled through such an imaging based optical approach. So far, one possible option is the SEM (Scanning Electron Microscope) based 2-D imaging approach. However, because SEM technology can only provide 2-D imaging information and it requires a vacuum environment, it has not been the preferred method in industrial fields. Recently, to complement these drawbacks of the SEM based nano object measurement approach, a more practical optical method called scatterometry emerged in the semiconductor industry. While traditional optical imaging techniques cannot resolve features smaller than the wavelength of the illumination beam, scatterometry enables physical parameters of sub-wavelength periodic structures to be extracted from the spectroscopic signature [6,7,8].In this study, we propose a novel recognition method that can be applied for nano-size 3-D objects. For obtaining both amplitude and phase information through the reflected spectrum, we employ spectroscopic ellipsometry. Here, we deal with only grating-like periodic nano-patterns since scatterometry can only be applied to periodic structures. Although we prove the recognition capability of this study only for a one-dimensional periodic case, we expect two-dimensional periodic patterns could also be handled with this concept. In Section 23.2, we first describe the basic principle of scatterometry. Then, the rigorous coupled-wave analysis (RCWA) theory is introduced to explain how the diffraction of electromagnetic waves from the periodic surface of grating structures can be handled accurately with numerical analysis [9]. In Section 23.3, we deal with the proposed 3-D nano object recognition method which is based on phase sensitive scatterometry. Finally, we show that the proposed method can provide a moderate 3-D nano object recognition capability for various nano object shapes.