Fabrication of Bragg Gratings Using Interferometric Lithography

A setup has been designed and realized for the fabrication of Bragg Gratings in edge emitting semiconductor laser. In this setup a HeCd laser ( =325nm) is used in a Lloyd s mirror configuration, to interferometrically expose a sinusoidal grating on photoresist. The dilution of photo-resistant (PR) material allows for a spincoat thickness of 50nm which is needed to minimize standing waves in the photo-resist that lead to a nonuniform exposure. Variations of exposure time show the progression of photo-resist gratings. Etching recipes using both dry and wet etching techniques were successfully used to transfer the grating pattern into semiconductor material. Bragg Gratings with =250nm in InP and InGaAs have been characterized with an Atomic Force Microscope to have a grating height of over 100nm.