Holographic grating and method of forming the same

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.

What is claimed is:  
     
         1 . A method of forming a holographic grating, comprising: 
 providing a photoresist layer on an optical substrate,    forming a resist pattern in the photoresist layer to have grooves depth deeper than a predetermined depth of diffraction grating grooves to be formed, and    etching the photoresist layer with the resist pattern by an ion beam generated by a mixed gas containing a fluorine based gas and oxygen until the resist pattern is substantially completely disappears so that the diffraction grating grooves having the predetermined depth are directly engraved on the optical glass plate.    
     
     
         2 . A method of forming a holographic grating according to    claim 1   , wherein said ion beam, in etching the photoresist, is irradiated from a direction perpendicular to a direction of the grooves of the resist pattern and inclined with respect to a direction of a normal line of the substrate.  
     
     
         3 . A method of forming a holographic grating according to    claim 1   , wherein said diffraction grating grooves are transferred from the holographic grating to form a negative grating, said diffraction grating grooves transferred in the negative grating being further transferred to form a replica grating.  
     
     
         4 . A method of forming a holographic grating according to    claim 1   , wherein said optical substrate is an optical glass substrate, said resist pattern being engraved in the photoresist layer by an exposure method.  
     
     
         5 . A method of forming a holographic grating according to    claim 1   , further comprising providing a metal coating on the substrate with the diffraction grating grooves.  
     
     
         6 . A method of forming a holographic grating according to    claim 3   , wherein said negative grating is formed by providing a parting agent on the substrate with the diffraction grating grooves, forming a metal layer on the parting agent, providing an adhesive agent onto the metal layer, adhering a negative substrate on the adhesive agent to connect the negative substrate to the metal layer, and separating the negative substrate with the metal layer from the holographic grating.  
     
     
         6 . A method of forming a holographic grating according to    claim 6   , wherein after the negative grating is formed, said replica grating is formed by providing a parting agent on the negative grating with negative diffraction grating grooves, forming a second metal layer on the parting agent, providing a second adhesive agent onto the second metal layer, adhering a replica substrate on the second adhesive agent to connect the replica substrate to the second metal layer, and separating the replica substrate with the second metal layer from the negative grating.  
     
     
         7 . A holographic grating formed by: 
 providing a photoresist layer on an optical substrate,    forming a resist pattern in the photoresist layer to have grooves depth deeper than a predetermined depth of diffraction grating grooves to be formed, and    etching the photoresist layer with the resist pattern by an ion beam generated by a mixed gas containing a fluorine based gas and oxygen until the resist pattern is substantially completely disappears so that the diffraction grating grooves having the predetermined depth is directly engraved on the optical glass plate.    
     
     
         8 . A holographic grating according to    claim 9   , wherein said ion beam, in etching the photoresist, is irradiated from a direction perpendicular to a direction of the grooves of the resist pattern and inclined with respect to a direction of a normal line of the substrate.  
     
     
         9 . A holographic grating according to    claim 9   , wherein said diffraction grating grooves are transferred from the holographic grating to form a negative grating, said diffraction grating grooves transferred in the negative grating being further transferred to form a replica grating.