Effect of fluoroalkyl substituents on the reactions of alkylchlorosilanes with mold surfaces for nanoimprint lithography J.The adhesion between the fused silica mold and the resist remains a key issue in ultraviolet nanoimprint lithography ͑UV-NIL͒, especially in step and repeat processes. In this paper, we present results on antisticking layers ͑ASLs͒ of tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane ͑F 13 -TCS͒ deposited in vapor phase and of a commercial product, Optool DSX™, from Daikin Chemical, deposited in liquid phase. The antisticking properties and structural morphologies of the formed self-assembled monolayer are investigated using contact angle, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy ͑XPS͒ measurements. Obtained surface energies are as low as 10 mN/ m for both types of ASL. The stability of these formed layers during the UV-NIL process remains the main important issue. It was tested on an EVG ® step and repeat UV-NIL equipment using acrylate-based resists. After only 50 prints, we observed a high increase in the surface energy of the mold, which indicates a drastic degradation of the antisticking ͑ASL͒. XPS measurements show that fluorine is removed from the mold surface. This surface modification is attributed to free radicals created during the UV cure of the resist that easily cleaved fluorocarbon chains. This can be confirmed by the fact that the polar component of the surface energy was increased by a larger factor than the dispersive one. To overcome this problem, the acrylate-based resist was modified by the adjunction of a fluorine surfactant. To go further in the mold/resist interaction, we developed an original setup that directly measures the adhesion force. Almost no degradation of the organic ASL was observed in terms of surface energy and fluorine density after more than 50 prints when using a sufficiently high amount of surfactant in the resist.
This article reports on the properties of ultraviolet nanoimprint lithography dedicated imprinting materials. Studied solutions are composed of a diacrylate-based monomer and a variable amount ͑1%, 2%, and 4% in weight͒ of three different photoinitiators from Ciba Specialty Chemicals ͑Irgacure 819, Irgacure OXE02, and Irgacure 379͒. Photopolymerization kinetic studies were conducted on these solutions. Quantity and type of photoinitiator could be optimized in order to obtain a polymerization rate higher than 95% with an exposure dose as low as 20 mJ/ cm 2 . The etch resistance of this home-developed imprinting resist was characterized under standard plasma etching conditions. We observed that the polymerization rate has a large influence on the plasma etch resistance, and we show that the etch rates of our best material is comparable to the one measured for 193 nm photolithography resists and makes it a very good candidate as a masking layer for direct pattern transfer.
UV curing Nanoimprint Lithography (UV-NIL) is an emerging lithographic technique, seen as a potential candidate for the 32nm node by the ITRS road map. As the stamp is in direct contact with the substrate, template flatness is a critical issue in addition to standard optical lithography mask requirements (high-resolution, low defectivity, CD control…). This is why we propose to study the impact of the template flatness on the reproduction quality and on the imprint uniformity. After having studied the Residual Layer Thickness (RLT) uniformity intra-dies and compared it to different stamps flatness, the impact of UV-NIL process optimisations, such as the substrate quality and filling times, on RLT uniformity intra-and inter-dies were evaluated. We observed that a high stamp waviness is always transferred into the resist, while a low stamp waviness (under a few hundreds of nanometers range) has no impact on the RLT uniformity.
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