The alignment process of ultraviolet (UV) nanoimprint lithography requires a further sophisticated method to detect infinitesimal misalignments between a synthetic quartz mold and a silicon substrate. Previously, we proposed a fluorescence-alignment method based on the analysis of the additive-type moiré fringes generated by the interferences of fluorescence emission from fluorescent UV-curable liquid filling the concave bar-mark arrays on a synthetic quartz mold and a silicon substrate. The proposed method significantly reduces the cost of mold fabrication and simplifies the in-liquid process compared to the conventional method based on multiplicative-type moiré fringes prevailing in the industry. This is because the fluorescence-alignment method is free from the problem of the refractive index matching between mold and UV-curable liquid materials. However, its position accuracy remains as large as sub-10 nm scales in principle. In this study, through simulation using image drawing and analysis software, we demonstrate that a sophisticated fluorescence alignment can realize atomic-scale precision for position accuracy by attempting the following concepts: (i) the application of the principle on position determination of a fluorescent single-molecule to that of an individual bar-mark fluorescence signal; (ii) effective use of high bit-depth of recent imaging devices; and (iii) accumulations of the information on the positions of multiple bar-marks with periodicities by fitting their fluorescence intensity profiles using a periodic function.
Based on the first report of the principle and practical observation of additive-type fluorescence moiré fringes for imprint alignment, we here studied the limit accuracy of the fluorescence imprint alignment using image drawing software, image processing software, and data analysis software. According to the practical conditions, fluorescence images of two assemblages having concave lines with a short pitch of p 1 = 4.0 μm and a long pitch of p 2 = 4.4 μm were reproduced on the mold and substrate. The analyzes of reproduced fluorescence images of moving the substrate without Fourier transform suggested that the minimum substrate shift of 0.04 pixels (5.2 nm) could be detected to be 0.045 58 pixels (5.9 nm). The detected placement error had a linear correlation to the substrate shift within 1290 nm.
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