Research On Period Reduction Lithography Based On Surface Plasmon Polaritons Interference

With the development of micro-nanofabrication technology and nano-optical technology, the production method of periodic optical structure towards high-precision, high-resolution and low-cost direction. Surface plasmon interference as a new near-field optical technology, which is developing rapidly, has great potential. But so far most of the studies have stayed in the theoretical analysis and simulation stages. There are still many problems to product large area optical devices by this technology.The project, "Research on period reduction lithography techniques based on surface plasmon interference", is about achieving period reduction lithography by surface plasmon interference effect which is excited by metal grating. It is theoretically analysised and experimentally verified.The main research contents and innovative works includes:1. Because for the traditional SPP interference lithography the incident light and interference wave overlap each other, and cannot produce grating patterns with reduced period. Therefore, a new lithography method based on hyperbolic metamatierals structure and SPP interference effect. This method uses frequency selection of hyperbolic metamatierals structure to choice transmitted wave of grating mask, and abandons the effect of incident light to achieve period reduction.According to this method, design and production mask which contains Al–Al2O3 hyperbolic metamaterials structure and Al grating with 700 nm period, set the exposure stage. Exposed photoresist on flexiable substrate by a UV laser source with 405 nm wavelength. A uniform grating pattern was produced with 350 nm period(half of the grating mask period), 100 nm line width, 1.5 cm × 1.5 cm area. The experimental results show: With this structure, EUV light source and damping platform are not necessary, a large area of subwavelength grating can be fabriced by a normal UV source.2. In order to improve the production efficiency of period reduction lithography and optimize the metamaterial multilayers structure, a method with combining Epsilon near zero(ENZ) metalmaterial multilayers structure with SPP interference is proposed. Through analyzing the characteristic of metal-dielectric multilayers in the UV band and propergation characteristic of SPP interference wace in ENZ metamaterial, a optimized design method of period reduction lithography for different wavelength of exposure source and period of grating mask is proposed: designing SPP interference excitation structure, and analyzing the effects of thickness of spacer layer on the resonance intensity of interference waves and wavelength through finite element simulation; calculating the matching conditions of grating mask period and SPP interference wavelength, period reduction lithography that produces grating with 1/n mask period(n is even) can be achieved by this method; analyzing the minimum number requirement of ENZ metamaterial multilayers; calculating the wave vector of SPP interference wave in the vertical direction; according to the wave vector, adjusting the transmission band of ENZ multilayers to Achieve frequency selection film structure to achieve frequency selection; analyzing the conditions of ENZ hyperbolic metamaterials and proposed the suitable combinations of materials for multilayers structure. A period reduction lithography structure is desighed by the optimization theory, with a Al grating mask with 220 nm period and a light source with 405 nm UV wavelength. It can produce grating pattern with period half of the grating mask(110nm).3. A high depth period reduction lithography method is designed. It overcome the defect of conventional plasma lithography, that lithography pattern is too shallow because surface plasmon wave decays exponentially after leaving metal surface. The structure utilizes the diffraction grating, SPP interference and multilayers waveguide: designing grating and multilayers waveguide with spatial frequency selection principle, to achieve bandpass filtering; guiding the 1st order diffraction wave into the waveguide, so the 1st order diffraction wave and SPP interference wave resonance in the waveguide structure. The evanescent wave with short propergrating distance is transferred to propergrating wave. Because the period of resulting pattern is restrited by the 1st order diffraction light, this method can only produce grating with 1/2 period of mask. Exposure experiments are achieved with Al grating mask with 245 nm period. The resulting patterns are uniform with 100 nm depth, 122.5nm period(half of the grating mask period), 61 nm linewidth. This method is theoretically and experimently proved that can achieve large area, high depth and period reduction subwavelength lithography.