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

Low-energy ion bombardment(IB)can induce a variety of large-area self-organized nanostructures on the surfaces of solid materials without masks,and has the advantages of low cost,high efficiency and wide applications.Photoresist is an important organic polymer material in the fields of micro-and nanofabrication,which is usually used as a mask 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 paper,we propose to study the interaction between low-energy argon ions and photoresist,and explore the technological method of using it as a mask for pattern transfer.The main research contents 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 surface 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 surface,and the morphology characteristics of nanoholes are regulated by ion energy.2.The evolution and formation mechanisms of nanohole structures on photoresist surface are studied.Experimental results show that when low-energy ions at normal and near normal incident bombardment,different from the inorganic materials obviously,random nano-hole structures with average diameters ranging from 5 nm to 40 nm,can be produced on the photoresist surface,and the average diameter and surface roughness of nanoholes are regulated by IB parameters,such as ion energy,bombardment time,ion beam density and incidence angle.The composition change in photoresist surface layer before and after IB was characterized and analyzed by using time-of-flight secondary ion mass spectroscopy and X-ray photoelectron spectroscopy.And the results showed that IB could cause the decomposition and preferential sputtering of molecules in photoresist surface layer,resulting in changes in surface composition.In particular,the enrichment of light components in the surface layer of the irradiated resist was 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 surface 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 structure on the surface of photoresist were studied.When oblique incidence,low-energy ion bombardment could induce the generation of nanoripple structures on the surface 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 surface 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 structure on photoresist surface as a mask was determined,and the optical characteristics of sub-wavelength surface nanostructure after transfer were studied.The nanoripples on photoresist surface 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 nanoripple on photoresist surface,the depth-width ratio of sub-wavelength nanostructure obtained on the fused silica surface has been improved nearly threefold.Preliminary optical characterization shows that the fused silica sample with 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.