The Study Of Self-organized Nanostructures On Photoresist Surface Induced By Low-energy Lon Bombardment

Low-energy ion bombardment(IB)can induce a variety of large-area self-organized nanostructures on surfaces of solid materials without masks,with the advantages of low cost,high throughput and wide applications.As a novel fabrication technology for surface nanostructures,IB shows a great potential in many applications,e.g.,ultra-high line density quasi-periodic gratings for synchrotron radiation and free electron laser.Photoresist is an important organic polymer material in the fields of micro-and nanofabrication,which is usually used as mask material for pattern transfer.However,the research on the interaction between low-energy ions and organic multi-component materials is very limited.Moreover,the aspect ratio of self-organized nanostructures induced by low-energy IB needs to be improved urgently.Therefore,in this thesis,it is proposed to study the interaction between low-energy argon ions and photoresist,and explore the technological method of using IB-induced nanostructures on the photoresist surfaces as masks for pattern transfer.The main research contents and results of the thesis include:1.The low-energy IB characteristics of photoresist are systematically studied.Similar to inorganic materials,the morphologies of self-organized nanostructure induced by low-energy IB on the surfaces of photoresist are mainly controlled by ion incidence angle and ion energy.With increasing ion incidence angle,different types of nanostructures,e.g.,random nanoholes,quasi-periodic nanoripples and roof tile-like faceted structures can be obtained on the photoresist surfaces,and the morphology characteristics of nanoholes are regulated by ion energy.2.The evolution and formation mechanisms of nanohole structures on photoresist surfaces are studied.Experimental results show that at normal and near normal incidence,obviously different from the inorganic materials,low-energy IB can produce random nanoholes on the photoresist surfaces.The average diameters of these nanohole structures range from 5 nm to 40 nm.Moreover,the average diameter and surface roughness of the nanoholes are regulated by IB parameters,such as ion energy,bombardment time,ion beam density and incidence angle.The composition in photoresist surface layer before and after IB is characterized and analyzed by using time-of-flight secondary ion mass spectroscopy and X-ray photoelectron spectroscopy.The results showed that IB could cause the decomposition and preferential sputtering of molecules in photoresist surface layer,resulting in changes in surface layer composition.In particular,the enrichment of light components in the surface layer of the irradiated resist is illustrated owing to the strong decomposition of the photoresist by IB.A physical model describing the formation and evolution of nanohole structure is established,concluding that the generation of nanoholes on photoresist surfaces is the result of the combined action of different physical mechanisms caused by IB,such as decomposition,preferential sputtering and mass redistribution.3.The evolution mechanism and growth model of nanoripple structures on the surfaces of photoresist are studied.At oblique incidence,low-energy ion bombardment could induce the generation of nanoripple structures on the surfaces of photoresist,and its features such as morphology,wavelength and amplitude of ripples are regulated by ion parameters,such as the wavelength can be adjusted in the 30-300 nm range.The results show that the evolution of nanoripples could be divided into two stages:growth and saturation.The larger the ion energy,the larger the characteristic size of the ripple wavelength and amplitude,and the longer it takes to reach saturation.The formation and evolution mechanisms of nanoripples on the photoresist surfaces are analyzed based on continuous model,and the origins for the formation,saturation and facet of ripples are explained.4.The method of pattern transfer using the nanoripple structures on photoresist surfaces as a mask is determined,and the optical characteristics of sub-wavelength surface nanostructures after transfer are studied.The nanoripples on photoresist surfaces induced by IB are used as masks,and the reaction ion etching is used to remove the remained photoresist at the bottom of nanoripples,and then the pattern transfer is carried out by the reaction ion beam etching.Comparied with the nanoripples on the photoresist surfaces,the aspect ratio of sub-wavelength nanostructure obtained on the fused silica surface has been improved nearly threefold.Preliminary characterization result shows that the fused silica sample with the surface sub-wavelength nanostructure has a transmittance of about 94%in the 600-1300 nm band,an increase of about 1%compared to unprocessed fused silica.This research built a foundation for fabricating ultra-high line density quasi-periodic grating masks on photoresist surfaces by IB,showing the potential for applications in synchrotron radiation.