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Both optical image-based overlay (IBO) and scatterometry diffraction overlay (SCOL®) are necessary tools for overlay control. For some devices and layers IBO provides the best accuracy and robustness, while on others SCOL provides optimum metrology. Historically, wavelength selection was limited to discrete wavelengths and at only a single wavelength. At advanced nodes IBO and SCOL require wavelength tunability and multiple wavelengths to optimize accuracy and robustness, as well as options for polarization and numerical aperture (NA). In previous studies1,2,3 we investigated wavelength tunability analysis with landscape analysis, using analytic techniques to determine the optimal setup. In this report we show advancements in the landscape analysis technique for IBO through both focus and wavelength, and comparisons to SCOL. A key advantage of imaging is the ability to optimize wavelength on a per-layer basis. This can be a benefit for EUV layers in combination with those of 193i, for example, as well as other applications such as thick 3D NAND layers. The goal is to make accurate and robust overlay metrology that is immune from process stack variations, and to provide metrics that indicate the quality of metrology performance. Through both simulation and on-wafer advanced DRAM measurements, we show quantitative benefits of accuracy and robustness to process stack variability for IBO and SCOL applications.
Methodologies described in this work can be achieved using Archer™ overlay metrology systems, ATL™ overlay metrology systems, and 5D Analyzer® advanced data analysis and patterning control solution.
Advanced overlay control algorithms utilizing Run-to-Run (R2R) CPE can be used to reduce the overlay signatures on product in High Volume Manufacturing (HVM) environments. In this paper, we demonstrate the results of a R2R CPE control scheme in HVM. The authors show an improvement up to 20% OPO Mean+3Sigma values on several critical immersion layers at the 28nm and 14 nm technology nodes, and a reduction of out-of-spec residual points per wafer (validated on full map). These results are attained by closely tracking process tool signature changes by means of APC, and with an affordable metrology load which is significantly smaller than full wafer measurements.
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You will have access to both the presentation and article (if available).
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