Design of a Dual-Wavelength Optical Head for Submicron-Scale and Nano-Scale Lithography

Previous research on the utilization of an optical pickup head (OPH) as the source for exposing inorganic photo resists uses only one wavelength. However, these single-wavelength OPHs are not appropriate for exposing organic resists. Because the optical power required for exposing the organic resists is too small to produce large enough focusing error signal (FES). To add another wavelength for the focusing servo is essential to eliminate this problem. This paper presents a design of an OPH with blue and red lasers for submicron-scale and nano-scale lithography. The blue laser is used for exposing the resists, while the red laser is used for the focusing servo. The numerical aperture (NA) of the objective lens is 0.6. And the linear range of the focusing error signal (FES) is about 3.0 . In addition, this paper also discusses the variation of linear range due to fabrication error. Three types of different optical structures in the return path are compared. The simulation results show that the adoption of a plano-convex lens and a slanted beam-splitter (BS) plate is the best choice. This combination owns the best immunity to the variation of the linear range due to the fabrication errors.