Abstract: In a method of forming a holographic grating, a photoresist layer is formed on an optical substrate, and a resist pattern is formed in the photoresist layer to have grooves depth deeper than a predetermined depth of diffraction grating grooves to be formed. Then, the photoresist layer with the resist pattern is etched by an ion beam generated by a mixed gas containing a fluorine based gas and oxygen until the resist pattern is substantially completely disappears. Thus, the diffraction grating grooves having the predetermined depth are directly engraved on the optical glass plate.

Abstract: In a method of forming a holographic grating, a photoresist layer is formed on an optical substrate, and a resist pattern is formed in the photoresist layer to have grooves depth deeper than a predetermined depth of diffraction grating grooves to be formed. Then, the photoresist layer with the resist pattern is etched by an ion beam generated by a mixed gas containing a fluorine based gas and oxygen until the resist pattern is substantially completely disappears. Thus, the diffraction grating grooves having the predetermined depth are directly engraved on the optical glass plate.

Abstract: In order to form a holographic grating of the invention, a resist pattern having a groove depth deeper than a desired depth of diffraction grating grooves is engraved in a photoresist layer provided on an optical glass base plate by an exposure method. Then, the photoresist layer is etched by an ion beam generated by a mixed gas containing a fluorine based gas and oxygen until the photoresist layer is completely deleted. In etching the photoresist layer, the ion beam is irradiated from a direction, which is perpendicular to a grooving direction of the resist pattern and is inclined from a normal line direction of the base plate. As a result, there can be formed the holographic grating in which the diffraction grating grooves are directly engraved in the optical glass base plate. Since the diffraction grating grooves are directly engraved in the optical base plate, the photoresist layer is not peeled off as in the conventional grating, and the holographic grating of the invention has excellent durability.