Fabrication of a dual-wavelength optical pickup head for laser direct writing

A dual-wavelength optical pickup head is fabricated for laser direct writing. Both 405nm wavelength and 658nm wavelength are used in the pickup head. For exposing organic photo resists, the 405nm wavelength is used as the light source, and the 658nm wavelength is used for the focus servo. While for exposing inorganic photo resists, either wavelength may be used as the light source. It depends on the spot size we need. The numerical aperture (NA) of the objective lens is 0.6. The measured spot size of the objective lens is about 0.35μm at 405nm, and 0.66μm at 658nm. For the preliminary experiments, a spot with about 500nm in diameter and 120nm in depth is achieved for GeTeSnOx inorganic photo resist using the 405nm wavelength. The optimum exposing parameters are still in progress.