Investigation Of Surface Plasmonic Lithography Technique For Nanostructured Functional Devices

Lithography is the key technology in the preparation of integrated circuits,microelectronics and optoelectronic devices in the world today.Suffering from the light diffraction feature,the resolution of traditional lithography can only be reach about one half of the wavelength.With the rapid development of information and integration technology,the demand for high resolution nanostructured functional devices is increasing.The existing commercial nano-fabrication technology has such problems as low preparation efficiency and expensive equipment.In recent years,the newly developmed surface plasmon(SP)lithography technology can break the diffraction limit,and obtain deep sub-wavelength resolution,which has made great achievements in theoretical and experimental research.However,the current SP lithography technology is mainly focused on the resolution verification for dense grating,so there is still a lot of work to be studied in the application of specific nano functional devices.Presented in the dissertation are our investigation of surface plasmonic lithography technique for nanostructured functional devices,including the mechanism and experimental research.The main content can be divided into four parts.Firstly,the research on odd mode SP interference lithography technology;secondly,cavity mode SP imaging lithography is proposed for preparation of the metasurface holograms;thirdly,reflective mode SP imaging lithography is used for the preparation of localized surface plasmon resonance(LSPR)sensor chip;fourthly,study on preparation of high resolution and small molecule i-line photoresist.The specific contents and results are as follows:1.The study on odd mode SP interferometric lithography.Here,an odd mode SP interference lithography based on metal / dielectric / metal cavity structure is proposed,which can obtain large area and deep subwavelength gratings.Theoretical investigation shows that the odd mode possesses much higher transversal wave vector compared with that of even mode,and the cavity structure could effectively modulate the electric components on imaging plane,facilitating SP interference fringes with high resolution and contrast in the measure of electric intensity.Grating patterns with 45nm(??/8)half-pitch,50 nm depth,and area size up to 20 mm × 20 mm were obtained by employing 180 nm pitch exciting grating and 20 nm Al/50 nm Pr/50 nm Al cavity structure,and the grating is fabricated with conventional laser interference lithography.At the same time,template stripping method and Al alloyed with 3% Cu sputtering deposition were employed to decrease the negative effect from film roughness.With the decrease of the thickness,the resolution of lithography can be further improved,and the half pitch resolution is 35 nm with 20 nm thick Pr.Considering that no requirement of expensive EBL or FIB tools are employed,it hopefully provides a cost-effective way for large area and nano-scale grating fabrication.2.The investigation on cavity SP imaging lithography for metasurface hologram fabrication.Compared with interference lithography,imaging lithography can produce irregular patterns.Metasurface holograms consisting of nanostructures with different orientations have shown great promise for various applications due to their unique capability of shaping light,such as holographic imaging,anti-counterfeiting identification,storage and so on.However,most of them are fabricated by point-by-point scanning method,such as FIB and EBL,which would greatly hamper their applications due to the high cost and low yield.In this paper,cavity SP imaging lithography is proposed to prepare metasurface holograms.The simulated results show that the 20 nm Ag/30 nm Pr/50 nm Ag cavity can effectively amplify the evanescent waves and modulate the electric components on imaging plane,resulting in greatly improved resolution and fidelity compared to near filed and superlens lithography.Moreover,an air separation layer is designed around the patterns to avoid contamination and damage of mask patterns.As an example,firstly,the Au metasurface holograms with relative small area are fabricated in experiment by the proposed lithography method and following etching processes,with unit characteristic size 95 nm × 175 nm,period 300 nm and area 9?m × 9?m;secondly,large area color off-axis holographic metasurface are also fabricated,with area 1mm × 1mm,the period 300 nm,the unit characteristic size 195 nm × 350 nm.Furthermore,the designed holographic images are both successfully observed by the fabricated holograms,verifying the correctness of the proposed method.Moreover,the method has the ability to produce holograms in batch,which is believed to open up a batch fabrication way for reproducing many copies of a metasurface hologram.3.Reflective mode SP imaging lithography is performed to the preparation of LSPR sensor chip.Owing to its advantages of high sensitivity and small volume,the chip has a wide range of applications in drug testing,biological testing,and so on.However,the current fabrication methods for chip,such as nano sphere self-organization and chemical wet synthesis,have the problems of poor patterns flexibility,poor process controllability.Here,the reflective mode SP imaging lithography is designed to realize the fabrication of sensor chips.The simulation results show that the light field energy is gradually reduced from the center to the periphery in the circular groove structure.Based on this principle,the mask of the circular groove is skillfully designed.By adjusting the exposure dose,the lithography patterns with different shapes can be obtained,especially sharp angle rhombus or the sharp angle triangular structure of the nanograph which is difficult to be achieved by the conventional mask design.As an example,nanoscale grooves,sharp angular rhomboid,and round shapes are experimentally obtained under the design of mask with round holes arranged in square array,with a characteristic size of 50nm~150nm,period 500 nm,and area 8mm × 8mm;and nanoscale grooves,sharp angle triangular,and circular dots are obtained under the designed masks with round holes arranged in dislocation arrangement.The characteristic size is about 20nm~100nm,the period is 500 nm,and the area is 1mm × 1mm.And then the Pr patterns were transferred to the functional Ag layer by one-step ion beam etching,resulting in a series of Ag LSPR sensor chips.In this paper,the Ag film is skillfully used,which can be used as a supermaterial that produces SP to enhance the resolution.It can also be used as the functional material of the LSPR sensor chip,and the experimental process is simplified.This method is expected to provide a high resolution,economical and convenient way for the fabrication of large area and high uniformity sensor chips.4.The research on preparation of high resolution and small molecular system i-line photoresist(Pr).For SP super-resolution lithography,the current commercial i-line Pr cannot meet the requirements of high resolution,thin film thickness and low line edge roughness(LER).The synthesis and research of small molecule i-line Pr is presented in this paper.Based on the method of literature synthesis,the Pr of high purity PHS-DNB small molecule material was prepared through the improvement of synthesis conditions.A method of mixing solvent has been explored to solve the problem of poor solubility of the Pr.The film thickness is adjustable in the range of 10nm~100nm,and the Pr film had the super smooth surface with RMS 0.42 nm.The experimental results showed that the Pr had high contrast(PHS-39,?=5.4)and high retention rate(greater than 90%),and also had well anti-etching performance owing to the existence of a large number of phenyl groups.At the same time,a series of process conditions were optimized,and the results show that the achieved Pr patterns with half pitch 37.5nm ~225nm have quite good quality,and the LER(3?)is only 4.49 nm for half pitch 37.5nm pattern.Compared with the commercial Pr,the developed Pr significantly improved the quality of the half pitch 22 nm and 32 nm dense line patterns as well.