Study Of Imprinted Polymer Defects And Mold Structure Durability In Thermal Nanoimprint Lithography

Nanoimprint lithography is an extremely useful micro-nano structure fabrication technique. Nanoimprint lithography has many potential advantages, including low cost, high resolution, and simplicity,and so is considered as one of the most prospective micro-nanostructures fabrication techniques for industrial applications. With the continuous expansion of application area in nanoimprint lithography, it raises a great challenge to the basic research. Based on the latest research progress at home and abroad, the thermal nanoimprint lithography is used as the research object in this thesis and defect problems appeared in imprint process and demolding process are studied. The research contents of this thesis are as follows.(1) In order to investigate some problems about cavity incomplete filling and poor durability of mold, a numerical simulation method is used to study process that polymer fill into three kinds of cavities with different shapes under different imprint pressure. Results show that filling of cavity with different shape sidewalls and the distribution of mold stress present different characteristics under different imprint pressure. Due to effect of sharp corners at the bottom of cavity on filling resistance and stress concentration phenomenon of mold, replacing sharp corners with rounded corners at the bottom of three cavities is proposed.Results show that appearing of rounded corners and increasing of radius of rounded corners have better optimal behavior for cavity filling and mold durability.(2) To reduce defects caused by contact separation between mold and polymer, the demolding mechanism was studied. A theoretical model about acting force between mold and polymer was proposed based on contact theory in interface mechanics. Finite element simulation technology is used to simulate contact separation between mold and polymer. The rules and mechanism of demolding were obtained by analyzing the relations between demolding force and demolding displacement in terms of energy balance theory in fracture mechanics.(3) The effects of contact states between mold and imprinted polymer on polymer pattern deformation during demolding were investigated. According to the difference of the contact states between mold and polymer, demolding model is divided into three kinds of contact types. Considering the relationship between demolding force and demolding displacement in three kinds of contact types, necking deformation at different positions of polymer embossment was analyzed.Results show that both the probability of defects and the resolution in the complete contact type are better than that in the incomplete and sufficient contact types. Finally, the effects of the antisticking layer with different effectivity on polymer structure deformation ware investigated.According to the relationship curves between demolding force and demolding displacement and displacement nephograms of polymer in different demolding stages under antisticking layer with different effectivity, the development of polymer deformation was compared and analyzed. Results show that increasing of adhesion force is easy to induce breaking of imprinted polymer structure before the lateral contact at the top is not separated.