We demonstrate that photolithography can be extended to a subwavelength resolution for patterning of virtually any substrate by exciting surface plasmons on both a metallic mask and a substrate. Without any additional equipment or added complexity to mask design, one-to-one pattern transfer has been achieved. In this letter, a polarized laser beam of 355 nm wavelength was used as light source to photoinitiate an 80 nm thick photoresist on a silicon substrate coated with titanium of 80 nm thick. Array of line apertures of 100 nm in width were made on gold film or titanium film deposited on a quartz substrate, serving as the mask. Simulation results by finite-difference time-domain method have shown that surface plasmons excited on both the metallic mask and the Ti shield help to spatially confine the light behind the apertures. Experimental results show a strong dependence of pattern transfer on the polarization of light as well as the energy dosage of the light. The feature size using such method could be further scaled down, limited theoretically by the validity of the dielectric function of the material, and practically by the fabrication of the mask.

Shao, D. B., & Chen, S. C. (2005). Surface-plasmon-assisted nanoscale photolithography by polarized light. Applied Physics Letters, 86(25).