Observation of Fluorescence Inclination
Moiré Fringes for Imprint Alignment
Takuma Yoshida, Shunya Ito, Takahiro Nakamura, and Masaru Nakagawa
Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan
E-mail: masaru.nakagawa.c5@tohoku.ac.jp

Introduction: In UV nanoimprint lithography (UV-NIL), highly accurate alignment between
the mold and substrate is important to form resist patterns at a predetermined position on thesubstrate. Optical multiplicative-type moiré fringes are generally used for imprint alignment
due to magnification of little deviation of overlaid patterns [Fig. 1 (a)]. Our group proposed anadvanced method of “fluorescence moiré alignment” using a fluorescent liquid anddemonstrated that fluorescence moiré fringes belong to additive-type moiré fringes [1] [Fig.1(b)]. Fluorescence moiré alignment has a unique advantage of no need of an optically functional
additional layer deposited on a silica mold. In this study, we practically observed fluorescence
inclination moiré fringes in our UV nanoimprinting system and investigated whether the anglesof additive-type moiré fringes were identical to the theory of the multiplicative type.
Experimental: Line (L)-and-space (S) gratings of L:S = 1:1 with pitches of P1 = 10.73 m andP2 = 10.70 m for 7 fluorescence microscope observation were fabricated on a silica moldand Si substrate by maskless lithography involving laser drawing. The experimental procedureis shown in Fig. 2. Fluorescent liquid droplets were screen-printed on the substrate surface
using a polyimide laser-drilled mask[2]. The recesses of grating patterns were filled withfluorescent liquid. Fluorescence images of overlaid patterns were obtained by fluorescencemicroscopy with the substrate rotated in a clockwise direction. The angles of fluorescence
inclination moiré fringes were measured from the captured images.
Results and Discussion: It is known that angles of multiplicative-type moiré fringes arecalculated by the following equation[3]. The grating pitches of 10.73 and 10.70 m used in thisstudy were designed according to the equation.

 : angle of deviation of substrate to mold [rad]P1 sin  : angle of moiré fringes to mold grating [rad]P1 cos  − P2
Fluorescence inclination moiré fringes could be observed from the mold and substrate grating
patterns filled with fluorescent liquid (Fig. 3). The gratings of the mold and substrate were also
discernible by fluorescence microscope observation. To discern the gratings is essential forobservation of additive-type moiré fringes. As the substrate was rotated in a clockwise direction,
the fluorescence moiré fringe was inclined to a counterclockwise direction. The angle of thefluorescence inclination moiré fringe of 68.5  0.4 degree was measured from the captured
image. According to the equation, the measured angle corresponded to 0.39 degree of thesubstrate-mold deviation. In this conference, the author will discuss the relationship of angle
between the additive-type fluorescence inclination moiré fringe and the theoreticalmultiplicative-type inclination moiré fringe.

 = tan −1

Reference: [1] E. Kikuchi, et al., J. Vac. Sci. Technol. B 35, 06G303 (2017). [2] T. Nakamura,et al., J. Vac. Sci. Technol. B 35, 06G301 (2017). [3] J. Shao, et al., Opt. Eng. 47, 113604(2008).

(a)(b)lightlightmultiplicative
intensity
profilelight

additiveintensity
profileFigure 1. Schematic illustration of light intensity of (a) multiplicative-type and (b) additive-typemoiré fringes.
◆ step 1 laser-drilled screen printing
top view of polyimide (PI) screen mask
hole pitch (Ph) = 80 mhole diameter (dh) = 18.6 μm
laser-drilled area (la) = 8.2  8.2 mm2Phfluorescent liquidsqueegee

PI screen mask

PISi substratedhla◆ step 2 filling and observation
fluorescence microscope (FM)pre-alignment, press (20 N)
silica moldPFPsubstrate 1,1,1,3,3-pentafluoropropane

0 – 0.48 deg

Figure 2. Schematic illustration of fluorescence alignment experiments consisting of laser-drilledscreen printing (step 1) and fluorescence microscope observation for fluorescence inclination moiré
fringes (step 2).

68.6 deg

Figure 3. Fluorescence microscope image of fluorescence inclination moiré fringe corresponding
to a substrate-mold deviation of 0.39 degree. Color and brightness are modified to discern the image.