The Preparation And Properties Of Polymer Systems For Nanoimprint Lithography

Nanoimprint lithography (NIL) is a nonconventional lithographic technique for high-throughput patterning of polymer nanostructures at great precision and at low costs. Basically, in nanoimprint lithography, thermal and UV-nanoimprint Lithography resists were used to transfer patterns, the basic and stringent requirements for the resists involves resist shape integrity and complete mold-resist separation while the resist remains attached to the substrate. However, the resists now commercially available can not fully meet these contradictory requirements. Although the release agents are used to improve the anti-adhesion property of the mold, there still exists some issues such as the releasing properties of the mold become worse after multiple imprints and adhered to the mold. It is very necessary to develop new polymer resists with higher anti-adhesion properties for nanoimprint lithography. Therefore, in our study, a UV-based acrylate resists and polybenzoxazine-based thermal resists were prepared and studied. The effect of N-substituents and nanoclay on the surface free energy of polybenzoxazine were investigated to supply experimental and theoretical basis guiding for developing novel low-surface-energy materials too. Research results are as follows:Firstly, a novel UV-based acrylate resists are prepared based on y-(trimethyloxysily1) propyl methacrylate (TRIS).The effect of the formulation components on the separation properties with the mold are studied. The results show that the crosslinker concentration, acryl functional groups and TRIS concentration are all have an effect on the separation force. With the increase of the crosslinker concentration and functional groups, the separation force increase. The introduce of TRIS decrease the surface energy of the cured resists, and increase the separation force adversely. To improve the anti-adhesion properties between the resists and the mold, fluorinated surfactant additive, FA, is used to study the effect of FA on the seperation force. The results indicate that the separation force is reduced substantially by the addition of FA to the Si-containing resist formulations. Adding 10% FA reduces the separation force to 3.5 N, which is only one fourth that of the pure etch barrier. The water contact angle increases with an increase of FA, which indicates that FA imigrates to the surface and makes the surface more hydrophobic. FA can form a liquid isolation layer and decrease the modulus between the mold and resist interface. In UV-nanoimprinting experiments using the optimal Si-containing formulation we were able to imprint micrometer as well as nanometer scale patterns. Transfered pattern on the resist with 149nm line width,298 periods and 147nm depth were obtained without obvious defects.In nanoimprint lithography, there are three interfaces and four materials to be considered to ensure the separation occur at mold-resist interface. Therefore PMMA and PS transfer layer were prepared to investigate the adhesive properties of the resists with the transfer layer. The results show that the PMMA layer improve the adhesion with the resists compared with PS, which contribues to the polar components of the PMMA match with that of the resists. The work of adhesion between the resist-mold interface is less than that of the resist-transfer layer interface when the mold was modified by FOTS release agent, the adhesion ratio is 1.83. Therefore, by increasing the polar components and decreaseing the dispersive components of the resists, the adhesion ratio could be increased.Secondly, a novel thermal resist based on nonfluorine, nonsilicon, low-surface-energy polybenzoxazine were prepared. The results indicate that the separation force decrease initially and increase with the increase of the B-m monomer concentration, the lowest value of the separation force is 0.30 N when the concentration of the B-m monomer is within the range of 11-20%, which is even lower than that of the FA additive. In UV-nanoimprinting experiments using the optimal benzoxazine-based resist, the grating structures with 180nm line width,250 periods and 120nm depth were obtained without obvious defects..Although hydrogen bonding have an significantly effect on the surface enenrgy in the polybenzoxazine systems, the relationship between the surface energy and the fraction of intermolecular or intramolecular hydrogen bonding is still poorly understand. Especially, Effect of N-substituents on the surface characteristics and hydrogen bonding network of polybenzoxazines were not formally investigated. Therefore, B-m, B-e, B-b and B-t monomers synthsized by methylamine, ethylamine, butylamine and tert-butyl amine respectively were prepared to investigate the effect of N-substituents on the surface free energy and the hydrogen bonding. The results show that with the increase of alkyl chain length of N-substituents, the surface energy of polybenzoxazine decreases, and do not be affected by the steric factor of the tert-butyl group. The lowest value of surface energy of the B-b polybenzoxazine reaches 15.7 mJ/m2 after curing at 180℃for 18 h, which is lower than that of B-m polybenzoxazine (24.3 mJ/m2). The FTIR curve fitting results indicate that both the chain length and bulkiness of alkyl group have an effect on the hydrogen bonding network of the polybenzoxazines, and do not facilitate the formation of intramolecular hydrogen bonding during the progress of cure. There is an opposite trend between the surface energy and the fraction of intermolecular hydrogen bonding as a function of alkyl chain length. We think that the surface energy of the polybenzoxazine is affected by both hydrogen bonding and alkyl group attached to the nitrogen atom. FTIR spectra of the polybenzoxazine during the progress of cure were compared. The appearance of free OH stretching and the increasing bond strength of free Schiff base indicate that the thermal degradation exists during the cure. Combined with the thermal degradation progress of the polybenzoxazines, transformation mechanics of intramolecular and intermolecular hydrogen bonding during the cure is proposed for the first time.Finally, to further improve the anti-adhesion property of polybenzoxazine, a novel type of polybenzoxazine/clay nanocomposites were prepared from B-m and di-methyl, di-octadecyl ammonium chloride (DODMAC)-modified clay. The results show that the lowest surface free energy of the PB-m/3%clay nanocomposites is 15.3 mJ/m2 after 8 h curing at 210℃, which is even lower than that of Teflon(21.0 mJ/m2). In addition to decreasing the surface free energy of the nanocomposites, the presence of clay lead to the surface energies of these clay-containing nanocomposites being maintained at lower values even after curing at 210℃for 22 h, which are more stable when compared with the PB-m. The results of FTIR curve-resolving show that the fraction of intermolecular hydrogen bond of the PB-m/clay nanocomposites and PB-m follow a similar trend and all increase upon increasing the curing time, which indicating that intercalated structures of polybenzoxazine/clay nanocomposites don't change the network structure of hydrogen bonding of the polybenzoxazine during the process of cure. And the surface energy of polybenzoxazine is affected by both hydrogen bonding network and surface groups on the film surfaces. The results of AFM show the immigration of the clay and DODMAC on the surfaces of the nanocomposites. It is concluded that the stability of surface energies of the nanocomposites is mainly affected by the immigration and masking of clay.