The step-and-flash imprint lithography process requires the clean separation of a quartz template from a polymer, and the force required to create this separation must be minimized to prevent the generation of defects. Fluorinated surfactant additives to the imprint fluid address this problem by migrating to the template-polymer interface and forming a local layer with ideal properties for adhesive fracture. Tensile and four-point bend fracture experiments show that surfactants lower the modulus of the imprint polymer and decrease the fracture energy. The fracture energy is further decreased by using a nonreactive, liquid surfactant versus a surfactant that reacts with the polymer matrix. Angle-resolved X-ray photoelectron spectroscopy results indicate that surfactant migration is more effective with a fluorinated surface treatment compared to an untreated quartz surface. This result shows that the use of fluorinated surfactants must be accompanied by a surface treatment that produces a similar energy or polarity to induce migration and lower the adhesive strength.
Understanding the dynamics of thin film planarization over topography is a key issue in the reverse-tone step and flash imprint lithography (SFIL-R) process. Complete planarization of a film over large, isolated topography poses an enormous challenge, since the driving force for planarization, the capillary pressure, continuously weakens as the film becomes more planar. For SFIL-R, only a specific degree of planarization (DOP) needs to be achieved before pattern transfer is possible. This paper presents the derivation of an inequality statement describing the required extent of planarization for successful pattern transfer. To observe how this critical DOP value (DOPcrit), and its corresponding leveling time (Tcrit) vary with materials and topographic properties, finite difference simulation was utilized to model planarization of a thin film over isolated topography after the spincoating process. This model was verified experimentally for various film thickness to substrate height ratios using interferometry to monitor silicon oil planarization over isolated trenches and lines. Material and topographic parameters were shown to not have a dramatic impact on DOPcrit; however, the critical leveling time increased considerably at DOPcrit values above 60 percent.
Advanced microprocessors require several (eight or more) levels of wiring to carry signal and power from transistor to transistor and to the outside world. Each wiring level must make connection to the levels above and below it through via/contact layers. The dual damascene approach to fabricating these interconnected structures creates a wiring level and a via level simultaneously, thereby reducing the total number of processing steps. However, the dual damascene strategy (of which there are several variations) still requires around twenty process steps per wiring layer. In this work, an approach to damascene processing that is based on step-and-flash imprint lithography (SFIL) is discussed. This imprint damascene process requires fewer than half as many steps as the standard photolithographic dual damascene approach. By using an imprint template with two levels of patterning, a single imprint lithography step can replace two photolithography steps. Further efficiencies are possible if the imprint resist material is itself a functional dielectric material. This work is a demonstration of the compatibility of imprint lithography (specifically SFIL) with back-end-of-line processing using a dual damascene approach with functional materials.
Step and Flash Imprint Lithography (SFIL) is a revolutionary next generation lithography option that has become increasingly attractive in recent years. Elimination of the costly optics of current step and scan imaging tools makes SFIL a serious candidate for large-scale commercial patterning of critical dimensions below ~50 nm. This work focuses on the kinetics of the UV curing of the liquid etch barrier and the resulting densification/contraction of the etch barrier as it solidifies during this step. Previous experimental work in our group has measured the bulk densification of several etch barrier formulations, typically about 9 % (v/v). It remains unknown, however, how much etch barrier contraction occurs during the formation of nano-scale features. Furthermore, it is of interest to examine how changes in monomer pendant group size impact imprinted feature profiles.
This work provides answers to these questions through a combination of modeling and experimental efforts. Densification due to the photopolymerization reaction and the resulting shift from Van der Waals’ to covalent interactions is modeled using Monte-Carlo techniques. The model allows for determination of extent of reaction, degree of polymerization, and local density changes as a function of the etch barrier formulation and the interaction energies between molecules (including the quartz template). Experimental efforts focus on a new technique to examine trench profiles in the quartz template using TEM characterization. Additionally, SEM images of imprinted images from various etch barrier formulations were examined to determine local contraction of the etch barrier. Over a large range of etch barrier formulations, which range from 10 - 20 % volumetric contraction as bulk materials, it was found that dense 100 nm lines printed approximately the same size and shape.