Theoretical And Experimental Research For Super Resolution Photolithography Based On Surface Plasmon

Photolithography is key technology in integrated circuit fabrication.Its main purpose is to replicate the pattern of mask onto the silicon substrate.During the fabrication of the chip,photolithography technology determines the smallest feature size.Suffering the optical diffraction limit,the conventional resolution of photolithography is limited at the level about half wavelength.Usually,light source with short wavelength or lens with high numerical aperture is used to obtain the pattern with high resolution.However,these technologies are limited by cost and technical obstacles in shortening the wavelength or increasing the numerical aperture.The essence of the diffraction limit in resolution is the evanescent wave,which carries the fine feature message of the object,cannot contribute to imaging as propagating wave because of its short propagating distance.Recently,the rapid development of near field optics makes it possible to manipulate and measure the evanescent wave.Especially,the surface plasmons(SPs)technology,which is a typical method can beyond the diffraction limit,has attracted many attentions.In this paper,the main text is to regulate the transmission of optical wave based on SPs,and investigate the super resolution lithography by theoretical and experimental analyses.The content is mainly composed of three parts.Firstly,one-to-one imaging is carried out by transmitting the sub-diffraction limit feature message with metal/dielectric multilayer;secondly,the evanescent waves purified by hyperbolic metamaterial is used to produce uniform interference pattern with deep subwavelength feature size;thirdly,the effect of the surface roughness in the nano-films is analyzed on the quality of pattern produced by photolithography.The detailed contents and results is presented as following:1.According to the principle of SPs resonance in metal-dielectric multilayer,we investigated the super resolution imaging in photolithography.On one hand,we experimentally verified the theory of metamaterial composed of metal/dielectric can transmit the evanescent wave to improve the resolution in photolithography.The metamaterial is designed to transmit the fine massage of the objects.The alternating multilayer is deposited by co-sputtering technology.Then,the subwavelength mask with feature size of 100 nm is reproduced in photoresist.On the other hand,to overcome the problem of the feature size on the mask can not be decreased constantly in one-to-one lithography,we proposed a scheme can be used in super resolution lithography with demagnified imaging.It is composed with alternating metal/dielectric multilayer,and structured with curved and plane parts.The device can produce sub-diffraction limit demagnified imaging.The simulation shows that the mask with feature size of 100 nm is demagnified to 28 nm(3.5 times reduced).This method provides a way that can obtain the pattern with small feature from the mask with large feature.2.Based on the hyperbolic dispersion character of metal/dielectric multilayer,we investigated the super resolution photolithography by SPs interference.Due to the SPs is confined on the metal surface,the pattern formed by SPs interfering has the problems of small area and low uniformity,or the mask is fabracted by expensive emthod.We proposed a scheme that can propagate the SPs in bulky multilayer vertically(we called it bulk palsmons,BPs),which is verified in experiment.Based on the effective medium theory and rigorous coupling wave analysis,we designed the hyperbolic metamaterial with narrow passband in spatial frequency space.The desired diffraction waves would be filtered through the multilayer,and form large area and uniform deep subwavelength interference patterns.As examples,the two and four BPs beams interfering lithography with half pitch 45 nm(~?/8)are demonstrated in experiment.By adjust the geometry of the multilayer,much deeper resolution up to 22.5 nm(~?/16),and honeycomb patterns from six BPs interfering are feasible.In addition,learn from conventional multiple plane waves interfering,we systematically analyzed the various patterns produced by multiple BPs interfering.We also deduced all the period equations of the periodic patterns.These works enriched the interference throey of surface waves.It can provide a cost-effective,parallel,uniform,and large area nanofabrication way.3.We measured the roughness of the nano-films,and analyzed its effects on the performance of the photolithography.On one hand,aiming to the plasmonic cavity structure,which is composed of Ag/PR/Ag films and often used in super resolution photolithography,we measured surface roughness on the both sides of the metal films by using the template stripping technology.Based on the fundamental growth modes of the films,we explained the effects of the substrate materials on the surface roughness.On the other hand,for the roughness on masks and films,we analyzed their impacts on the patterns in both superlens based lithography system and hyperbolic metamaterial based lithography system.The perfoemances in both systems are present by the line edge roughness,the intensity of the patterns,and other key parameters.Thery different phenomena are explained with optical transfer function and different SPs modes.It shows that the lithography system with spatial frequency selection is tolerant with the imperfections.The conclusion is further verified by a waveguide lithography system.These parts are meaningful for analyze the property of the nanofilms.It also provides a useful guide in the design of photolithography system.