UV Nanoimprint

The first STIL tool installed by the Willson group. 

The commercial equipment was capable of a sub-20 nm overlay and had a throughput of approximately five 300 mm wafers per hour. 

Liquid photo-curable resin is used in UV nanoimprint lithography (UV-NIL).i Basic ideas of photopolymerization are shown in Chapter 1. Liquid photo-curable resins change from liquid to solid by UV irradiation. The change is produced by polymerization of a monomer or oligomer constituted in the resin. Initiators induce polymerization by UV irradiation. Resins of UV-NIL are classified into several types by polymerization systems radical polymerization, ion polymerization, and ene-thiol polymerization. Details of those systems are described in below. 

One example of commercial UV nanoimprint resists is shown in Table 4.1. Since the resist is of a liquid form, spin coating can be applied for forming the layer. An imprint is performed under room temperature at low imprint pressure ( 100 mbar) in vacuum (or atmospheric pressure). UV light is exposed by an i-line lamp. 

Process condition Imprint room temperature, low imprint pressure ( 100 mbar), imprint in vacuum or under atmospheric pressure UV exposure broad band or i-line, curing few seconds 

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Jeong J, Sim Y, Sohn H, Lee E. UV-nanoimprint lithography using an elementwise patterned stamp. Microelectronic Engineering 2004, 75, 165-171. 

One example of UV nanoimprint resists is shown in Figure 4.9. The resin contains three kinds of acryl monomers t-butylacrylate, ethylene glycoldiac-rylate, and (3-acryloxypropyltristrimethylsiloxy)silane. The resist also contains a photoinitiator, 2-hydroxy-2-methyl-l-phenylpropane-l-on. The resin... 

Ito et al. report their selection of vinylethers for faster cationic polymerization of an UV nanoimprint (Figure 4.14). Low-viscosity and low-volatility vinylethers tend to be highly hydrophobic, and selection of PAG is an important issue in designing vinylether imprint systems. PAG must be soluble in neat lipophilic vinylether without use of a solvent. Commonly available PAGs... 

Thus, complicated metal organic compounds are synthesized by the ene-thiol reaction. The ene-thiol reaction can be applied to polymer resins for UV nanoimprints. The ene-thiol resin for UV nanoimprints is reported by Ffagberg et al. and shown in Figure 4.18. Ene-thiol resin is optically cured by step reactions between a compound (ene) with two or more double bonds in the molecule and another compound with two or more thiols in the molecule. The... 

Nanoimprinting A master stamp is used directly for hot embossing of a substrate, usually made of a polymer. This allows the stamp to produce many patterned substrates. Although there is no diffraction hmit here, hot embossing has been applied mainly for low-resolution applications, in various fields such as miniaturized total-analysis Systems (p.TAS), microfluidics, and microoptics. UV-nanoimprint lithography corresponds to contact printing with UV exposure. 

Kubenz, M., Reuther, F., Gruetzner, G., and Torres, C.M.S. (2007) Reverse-contact UV nanoimprint lithography for multilayered structure fabrication. 

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