UV-Nanoimprinting Lithography Photoresists with No Photoinitiator and Low Polymerization Shrinkage

Abstract

In this work, a photopolymerizable disulfide monomer containing C­(aryl)–S, disulfanediyl bis­(4,1-phenylene) diacrylate (ADSDA), was designed and synthesized. UV-nanoimprinting lithography photoresists with no photoinitiator and low polymerization shrinkage were then prepared with ADSDA and benzyl methacrylate (BMA). The photoresists with ADSDA exhibited a great photopolymerization capability in the absence of any photoinitiator, and their double bond conversion reached up to 86%. With the increase of ADSDA content in the photoresists, the Young’s modulus, indentation hardness, and thermal stability of the photoresists all increased first, followed by a slight decrease. Remarkably, the photoresists with ADSDA had a very low polymerization shrinkage which dropped to as low as 0.56% because of the “breakage–recombination” reversible reaction of the S–S bond during the photopolymerization process. More significantly, the pattern of the original mold with 212 nm line width and 104 nm height could be accurately duplicated without flaws by the photoresist, which exhibited a prominent pattern transfer property.

Introduction of Photopolymerization Technology and Application

“…Based on the disulfide bond of reducing volume shrinkage and endowing materials with the degradability. Sun et al [125,132] synthesized two disulfide bond-containing acrylate monomers 2,2-dithiodiethanol diacrylate (DTDA) and disulfanediyl bis (1,4-phenylene) diacrylate (ADSDA) used for UV-NIL. The chemical structures of DTDA and ADSDA are exhibited in Figure 38.…”

“…Figure 38 Chemical structures of DTDA and ADSDA. [125,132] Figure 39 Mechanism of reducing volume shrinkage based on the reversible disulfide-bond. [125] For the photoresist system containing ADSDA, it does not contain any additional PI due to the arylthiyl radical generated by ADSDA possesses a good capability of initiating photopolymerization.…”

A review on self-initiated and photoinitiator-free system for photopolymerization

“…On increasing the ADSDA concentration, Young's modulus, hardness and thermal stability increased up to an assured limit. Also, they showed a great potential to reduce the polymerization shrinkage and thus can be employed in the UV-nanoimprinting lithography field [158]. Although in industrial applications, the photoinitiator system is preferred over the photoinitiator-free system.…”

Synthesis and Property of an Organosilicon Polyurethane Acrylate Prepolymer Containing Disulfide Bonds for Photopolymerization

“…Our previous work has verified that the introduction of disulfide bonds into the photopolymerization system can effectively reduce the volume shrinkage in the photopolymerization of acrylate monomers by utilizing the reversible characteristics of “break‐recovery” of disulfide bonds under UV light irradiation, and the presence of disulfide bonds can also impart degradable properties to the materials. [ 20–23 ] This excites our interest in introducing disulfide bonds into photocurable organosilicon polyurethane acrylate materials in order to reduce the volume shrinkage of the materials, improve the overall performance of the materials, and impart degradability to the materials.…”