Position measurement method for alignment in UV imprint using a high index mold and “electronic” moiré technique

Abstract

In UV imprint, positioning errors can occur between a mold and a wafer due to pressure when there is a contact with the UV resin. The moiré technique, which is produced by superimposition of two gratings, is a well-known and simple method for high-resolution position measurement. However, the authors believe that a direct observation of two separate gratings is more appropriate for higher positioning accuracy. Here they propose a new method for the position measurement, which obtains "electronic" moiré fringes by combining the images of two separate gratings from different areas of the mold and the wafer. The fundamental detection error was = 0.15 nm. The repeatabilities of the total system was = 0.68 nm in air and = 0.73 nm in resin. The linearity of the measurement value to control signal was R 2 = 0.97.

Fluorescence imprint alignment using additive-type inclination moiré fringes

“…Therefore, when mold recesses are filled with a UV-curable liquid, mold alignment marks are hardly detected by optical microscopy owing to refractive index matching. To avoid the issue, an effective way is the deposition of an optically functional layer of a light-shielding metal 14) and a high-refractive-index material 16,17) selectively on a silica mold surface. Suzuki et al demonstrated the imprint alignment method by optical microscopy using two cross-shaped concave alignment marks.…”

“…Precise alignment with multiplicative-type moiré fringes has been widely adopted in proximity lithography, [18][19][20] Xray lithography, 21) and nanoimprint lithography. 14,17,[22][23][24][25][26][27] This arises from the reason because a moiré fringe generating from two gratings with slightly different pitches enables the magnification of a small placement error. Figures 1(a ( )…”

“…The relationship between Δl and ΔX under two gratings with pitches of p 1 and p 2 is expressed by the following Eq. (1)17)…”

Reproduction of additive-type fluorescence moiré fringes by image drawing software and study of accuracy of fluorescence imprint alignment

“…To avoid the issue of refractive index matching, Suehira et al reported the position measurement method for alignment in UV nanoimprinting using a highrefractive index mold and electronic moiré technique. 17) In the literature, they use a silica mold with a 50 nm thick layer of silicon nitride showing a refractive index of 2.0 which is deposited on a silica surface by chemical vapor deposition. However, additional processes of chemical vapor deposition and dry etching of silicon nitride are essential, and the increase in process step leads to an increase in the fabrication cost of imprint molds.…”

Development of UV-curable liquid for in-liquid fluorescence alignment in ultraviolet nanoimprint lithography

“…The reason is that the refractive index of silica is almost consistent with that of a UV-curable liquid. Therefore, additional alignment marks of a metal light-shielding [14][15][16] or inorganic high-refractiveindex layer 17,18) are essential for optical detection. Other lithographic processes are necessary for the fabrication of additional alignment marks, which increase the cost of mold fabrication reflected in the cost of nanodevices.…”