Angular scatterometry, which has the advantage of good measurement precision, is an optical measurement technology based on the analysis of light scattered from periodic features, such as a linear grating, and is proposed as an alternative solution for overlay metrology. We present overlay measurements using an angular scatterometer and a bright-field microscope. A theoretical library based on rigorous coupled wave theory was created, and the reflected signatures measured by angular scatterometer were matched to the library to obtain structure parameters, including overlay, critical dimension (CD), and sidewall angle at the same time. The results reveal that angular scatterometer has a good precision and low tool-induced shift for overlay measurements, and has the potential for integrated metrology.
As overlay tolerances of microlithographic technology become increasingly severe, conventional bright-field metrology systems are limited by image resolution and precision. Scatterometer (angular scatterometer or spectroscopic reflectometer, for example) has the advantages of good repeatability and reproducibility, and is proposed as an alternative solution for overlay metrology. Previous studies have applied a spectroscopic reflectometer, which is as function of incident wavelength, to overlay measurement. This work investigated overlay measurement by using an angular scatterometer, which is as function of incident angle. A focused laser spot was incident on linear grating, an overlay target. An angular signature, a 0 th -order reflective light beam, scattered from linear grating was measured when the incident and reflective angles were changed simultaneously. The overlay target consists of two linear gratings located on two different layers of a stacked structure, and the overlay error is the misalignment between these two different layers. The measured results using angular scatterometer (also known as the diffraction-based method) are compared with using the bright-field microscope (also known as the image-based method), which use a bar-in-bar target as an overlay target. Statistical data sets demonstrate that angular sctterometer has nearly one order better of repeatability and tool induced shift than conventional bright-field microscope. Additionally, a series of different parameters of overlay targets, such as different pitches, line-to-space ratios, and stacked structures is designed and manufactured. The sensitivity of overlay measurement of various linear grating targets is also measured and discussed.
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