Theoretical study of multiexposure zeroth-order waveguide mode interference lithography

A new nanolithography technique in which sample rotation is incorporated into zeroth-order waveguide mode interference lithography is proposed in this report. A 325-nm laser was used to excite zeroth-order waveguide modes, which were loaded by an asymmetric metal-cladding dielectric waveguide structure. The optical field intensity distribution of zeroth-order waveguide modes interference is numerically simulated using the finite element method. The lithography sample consisted of a glass substrate, Al film, and photoresist film, and the rotation operation on the sample is expressed in coordinate matrix transformation. Various subwavelength structures, such as two-dimensional square lattices, two-dimensional hexagonal closed-packed lattices,and circular gratings, were obtained through double, triple, and continuous exposure. These subwavelength structures with different sizes can be produced by changing the thickness of the photoresist. The subwavelength structures simulated with various shapes and sizes can be applied to the field of nano-optics. The proposed technique provides a flexible and promising approach for interference nanolithography because of its simplicity and low cost.