Principle And Methodological Investigation On The Resolution Enhancement Of Proximity Plasmonic Lens Lithography

As rapid development of microelectronics field, the feature size of integrated circuits continues to reduce, which requires higher resolution for photolithography. Unfortunately, the diffraction limit of optical system delivers the resolution of projection lithography to about half of illumination wavelength. The main reason is that evanescent waves diffracted from subwavelength structure are exponentially decaying along propagation direction and could not contribute to imaging. Evanescent wave is amplified by proximity surface plasmon(SP) lens, which overcomes the diffraction limit and achieves superresolution image. However, the resolution of proximity SP lens lithography is still facing technical hurdle, which is called the near-field diffraction limit associated with illumination light wavelength and working distance between the imaging devices and objects. Higher resolution SP lithography inevitably brings shorter working distance, so mask or optical direct-writing head are usually physically contacted with the photoresist(Pr) recording structure for deep subwavelength resolution lithography experiment.The dissertation focuses on the research of amplifying evanescent waves to go far beyond the near-field diffraction limit, and achieves the resolution enhancement of proximity SP lens lithography. It is done by engineering the spatial spectrum distribution from object, incorporating the modulation of electric field components on imaging plane. The investigation contains theoretical proof on resolution enhancement of proximity SP lens, mathematical model and regular analysis of SP lens superresolution imaging, structure design of proximity SP lens lithography, and experimental demonstration. Main achievements are listed below:1. Immersion off axis illumination(OAI) SP cavity lens lithography is proposed and principle investigation is performed. Significantly shifting spatial spectrum of object via immersion OAI and modulating electric field components in Pr region by SP cavity lens yield the remarkable enhancement of feature wavevectors, which achieves the elongated working distance and the enhanced resolution. Immersion OAI Hyperlens is investigated for proximity SP demagnifying lithography with deep subwavelength resolution. Theoretical model for SP imaging lens under immersion OAI is built, which is validated by total mode simulation.2. Prism immersion OAI(kx,inc=1.5k0) SP lithography is designed and experiment demonstrates the resolvable 60nm-resolution image with 120 nm working distance, which is 8-fold larger than the case of conventional near-field lithography. Further, the peripheral pattern distortion of discrete or isolated pattern under immersion OAI is suppressed experimentally by fabricating shallow grooves at the exit side of mask around the periphery of object patterns, which improves the pattern compatibility for OAI SP lithography.3. Based on the spatial spectra filtering capability of alternate metal-dielectric multilayer, immerging OAI in hyperbolic metamaterial is designed to excite SP wave with transverse wavevector 2.51k0. The designed OAI source incorporating SP cavity lens realizes a distinct image with 32 nm resolution under 60 nm working distance, which is 6-fold improvement compared with superlens under normal illumination. The spatial spectra filtering of hyperbolic metamaterial is experimentally validated by SP interference with spatial frequency doubling, which produces 36 nm half-pitch interference pattern. Further lithography experiment demonstrates the acceptable image with 32 nm resolution under 40 nm working distance.4. Hyperbolic metamaterial is utilized to design near-field diffraction-free Bessel-SP focus lens, which concentrates SP into sub-70 nm spot. Benefited from the subdiffraction capability of hyperbolic metamaterial, evanescent waves are selectively coupled out, which achieves 62 nm size spot within propagation region of 80 nm under radial polarization illumination. The resolution is 3.2-fold improvement compared with metal lens with aperture. In lithography experiment, circular polarization impinges the near-field Bessel-SP focus lens and SP cavity lens is applied to modulate the electric field components in Pr region, which produces 68 nm spot with 30 nm profile depth and 40 nm working distance.