Subwavelength Grating-based Nanoimprint Template Technology And Optical Simulation Study

Device down-scaling into nano dimension is the trend and the driving force of microelectronics technology.Immerging physical effects in nano devices have made nano fabrication a hot research topic.Micro/nano fabrication cannot be achieved without advanced lithography technology.Traditional lithography will meet great challenges when patterning structures in nano scale,meanwhile,the next generation lithography technique such as X-ray lithography,electron beam lithography,etc.is too expensive to be adopted for manufacturing.Nanoimprint technique proposed by Stephen Y.Chou in 1995 tackle the resolution-cost conflict in nano-lithography due to its intrinsic advantages, such as large field of traditional lithography,high resolution of direct writing technique, less complex equipment and low cost.Nanoimprint has been proposed as one of the next generation lithography solutions for 22nm and 16nm technology nodes by International Technology Roadmap for Semiconductors(ITRS) since 2003.Nowadays nanoimprint has found broad applications in research and development of IC processing,memory, mico/nano channel,micro/nano fluidic and micro/nano optic devices,including sub-wavelength gratings,quasi crystal,waveguides and optical filter fabrication,etc.Nanoimprint is a direct pattern duplication technique;templates determine not only the resolution but also the quality of the pattern transfer.Compared with silicon template, SiN_x template has higher hardness and lower surface energy,leading to better demolding without any surface treatment.This can help simplify the process,improve the experimental result and implement large area,high density pattern transfer.In this thesis work,we have developed a simplified nanofabrication process for imprint templates based on electron beam lithography and reactive ion etch on SiN_x using NEB-22 resist as etch mask.The etch property of NEB-22 was demonstrated,meanwhile, Cr etch mask was also used as a comparison with NEB-22.Gratings in SiN_x were successfully transferred into SU-8 resist by nanoimprint with no surface treatment. Additionally,we simulated the sub-wavelength gratings'(SWG) polarization properties using Lumerical FDTD software and the simulations agree well with experiments.We also designed and fabricated Bragg filters and horizontal distributed Bragg mirrors based on SU-8,in order to broaden the application of nanoimprint and SU-8 resist in optical components and devices.