Interference laser lithography for sub-wavelength gratings in visible light

The laser interference lithography shows great potential in the field of sub-wavelength gratings which can be used for polarizer arrays. However, due to the difficulty in further reducing the wavelength of the laser source, the further reduction of the grating period is limited. A widely used method to reduce the minimum size of patterns is immersion lithography. Especially in the interference lithography, using the prism to reduce laser wavelength and grating period has been explored. However, total internal reflection between the prism and the photoresist layer on the wafer surface extraordinarily reduces the energy efficiency of the incident light, making it impossible to obtain interference stripes with smaller periods. This paper proposes a laser interference lithography combined with immersion lithography that can process the gratings with the smaller period and illustrates the principle. To achieve better processing quality, the constraint conditions that the prism bottom angle and the diameter of the laser beam should satisfy are obtained through calculation, which provides a theoretical basis for laser interference lithography combined with immersion lithography for processing the gratings with the smaller period.