Ice-assisted Electron Beam Lithography For Nanofabrication And Its Applications

The development of nanofabrication technology has greatly strengthened the ability of human beings to understand and transform the microcosmic world.As one of the most commonly used nanofabrication methods,electron beam lithography(EBL)has a wide range of applications in nanophononics,microelectronics,micro-mechanical systems and other fields due to its high resolution and relative flexibility.However,with complicated processes and the limited scope of application,EBL seems to be inadequate in the face of the ever-changing nanofabrication requirements.In this context,a series of nanofabrication technologies have emerged,including ice lithography(IL),which uses ice nanofilm to replace the photoresist in traditional EBL.Although IL has unique advantages in streamlining the process,in-situ alignment,and nanofabrication on non-planar and fragile substrates,etc.,as an emerging technology,there are many limitations in the current research on IL.A lot of work needs to be carried out to optimize the IL instrument,deepen the understanding of the phenomena and mechanism in IL,develop advanced IL process,and enrich the applications of IL.Therefore,this thesis starts with the design and construction of an IL instrument,combining the principle of various nanofabrication technology with the characteristics of IL,systematically studies the three-dimensional(3D)nanofabrication,solvent-free nanofabrication,related processing problems and applications in optical nanodevices.In terms of the instrument of IL,this thesis introduces the design,implementation,operation,and performance of a costumed IL instrument.By connecting a commercial scanning electron microscope with thermal evaporation equipment and external components,an IL instrument with stable and convenient operation was established.The system was further used to realize the basic process flow of IL.A dense line array with a width of 20 nm and a high aspect ratio of 17:1 was written on ice films,and silver nanowires with an average width of 27 an was fabricated.This article also quantitatively analyzed the exposure dose and structure roughness as well as other parameters and discussed the process problem such as ice layer abnormalities and pattern distortion in IL.In terms of 3D nano fabrication by IL,this thesis proposed two strategies to realize 3D nanofabrication by IL:multi-layer overlay and gray-scale exposure.For the multi-layer overlay strategy,pyramidal 3D nanostructures were fabricated as demonstration based on the in-situ alignment of ice lithography with alignment error less than 100 nm.Due to the physical characteristics of the ice layer,the process was greatly simplifies compared with traditional EBL.For the gray-scale exposure strategy,the contrast curve of water ice was calibrated for the first time.It was measured that the contrast of the water ice under 5 keV and 20 keV electron beam was as low as 1.74 and 2.24,respectively.3D ice pattern was formed by modulating the dose distribution in the layout.Mushroom-shaped and the bridge-shaped suspended nanostructure were fabricated as demonstration.The related process problems in 3D nanofabrication by IL were also discussed.In terms of the solvent-free nanofabrication by IL,this thesis proposed "blow-off"step to replace the lift-off step in traditional EBL,which realized a simplified and totally solvent-free process flow of IL.Avoiding the damage of the polar solvent to the perovskite material in traditional EBL,we fabricated a perovskite-based lateral-type photoconductive detector with currently smallest metallic electrode spacing(227 nm)and a responsibility of 76 A/W.We also demonstrated nanofabrication on the fiber end face and nanofiber curved surface,as well as integrated meta-surface on the fiber end face,thereby obtaining an environmental refractive index fiber sensor with a sensitivity of 187.4 nm/RIU.This thesis also discussed the related process problems in solvent-free IL,and proposed a strategy to fabricate quasi-3D nanostructures by controlling the result of blow-off.Through the systematic study of IL,this thesis deepens the understanding of IL technology elements,demonstrates the potential application of IL in various nanofabrication scenarios,especially in the field of optical nanodevices,and contributes in future research and development of IL.