| 摘要 |
PROBLEM TO BE SOLVED: To provide a holographic grating having durability, small stray beam value, high diffraction efficiency and little changes in the diffraction efficiency in a wide wavelength range. SOLUTION: After a diffraction grating pattern is formed in a resist layer 2 to the depth larger than the objective depth by exposure, the layer is etched by a mixture gas of CF4 and O2 which is prepared by mixing in a proper mixing ratio of O2/(CF4+O2) ranging 0.1 to 0.9 and which is blown downward in the direction perpendicular to the line direction of the resist pattern and oblique to the normal direction of the substrate till the resist layer 2 is completely erased. Thus, the holographic grating consisting of an optical glass substrate 1 with grooves of desired depth directly formed in the glass is produced. Since the grooves of the diffraction grating are directly formed in the substrate 1, problems such as peeling of the resist layer in a conventional grating are avoided and the obtained grating has excellent durability. By using the mixture gas of O2 as the etching gas, a carbon rich state on the etching surface is avoided and whitening of the grating surface can be prevented. During etching, the surface roughness is reduced by the selection ratio than the roughness of the resist so that the obtained grating is good with a small stray beam value. |
