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.

In general, fluorinated antisticking layers (F-ASL) are deposited on the imprint stamps to ease their separation from the imprinted resist in UV nanoimprint lithography. However, these layers are found to degrade with repeated imprint operations. A drastic decrease in fluorinated species is observed on the mold surface. Yet, there is still a debate on the nature of the exact mechanisms involved in this degradation. In this paper, electron spin resonance (ESR) is used to investigate the chemical reaction occurring between the fluorinated molecules and the UV curable resist. Free radicals of the resist, generated under UV illumination, have been observed by ESR. The decrease in their corresponding signal in the presence of fluorinated ASL species shows evidence of the chemical reactivity of the resist toward the F-ASL.