Experimental analysis of solid immersion interference lithography based on backside exposure technique

We report a method of fabricating metal nano-grating by Solid immersion Interference lithography based on Backside exposure technique (SIB). Solid immersion lithography can improve the resolution of interference patterns by a factor of n (refractive index of prism), and backside exposure technique can improve the energy utilization ratio and protect the surface of the resist from being contaminated. In the process of fabrication, a high quality sacrificial layer (dielectric grating with high modulation depth and appropriate duty ratio) is important for transferring the patterns to the metal film. We optimized the exposure/development time by simulating the process of backside exposure. Simulation and experiment results show that: using 441.6nm wavelength laser, a series of subwavelength patterns (used as sacrificial layer) with high modulation depth and appropriate duty ratio can be gotten, the feature size of the patterns can be down to 80nm which is less than 0.18@l. Using optimized condition, high quality sacrificial layer can be achieved by using the backside exposure technique. Backside exposure technique has a greater exposure/development time tolerance for fabricating nano-patterns than the conventional interference lithography, which can be used for nano-metal grating fabrication.