Modelling and optimisation study on the fabrication of nano-structures using imprint forming process

Purpose: Nano-imprint forming (NIF) is a manufacturing technology capable of achieving high resolution, low-cost and high-throughput fabrication of fine nano-scale structures and patterns. The purpose of this paper is to use modelling technologies to simulate key process steps associated with the formation of patterns with sub-micrometer dimensions and use the results to define design rules for optimal imprint forming process. Design/methodology/approach: The effect of a number of process and pattern-related parameters on the quality of the fabricated nano-structures is studied using non-linear finite element analysis. The deformation process of the formable material during the mould pressing step is modelled using contact analysis with large deformations and temperature dependent hyperelastic material behaviour. Finite element analysis with contact interfaces between the mould and the formable material is utilised to study the formation of mechanical, thermal and friction stresses in the pattern. Findings: The imprint pressure, temperature and the aspect ratio of grooves which define the pattern have significant effect on the quality of the formed structures. The optimal imprint pressure for the studied PMMA is identified. It is found that the degree of the mould pattern fulfilment as function of the imprint pressure is non-linear. Critical values for thermal mismatch difference in the CTE between the mould and the substrate causing thermally induced stresses during cooling stage are evaluated. Regions of high stresses in the pattern are also identified. Originality/value: Design rules for minimising the risk of defects such as cracks and shape imperfections commonly observed in NIF-fabricated nano-structures are presented. The modelling approach can be used to provide insights into the optimal imprint process control. This can help to establish further the technology as a viable route for fabrication of nano-scale structures and patterns