JPS55134806A - Production of plane diffraction grating - Google Patents

Abstract

PURPOSE:To increase diffraction efficiency and reduce etching time by using the solution whose rate of etching is anisotropic to crystal planes and the solution whose rate of etching is isotropic thereto in the foregoing order. CONSTITUTION:At the time of producing the plane diffraction grating having the groove threads of an inverted triangle shape in section of a grating pitch P and angle theta where, e.g., blazed wavelength is let lambdaBAngstrom , the main plane 11 of silicon single crystal is made the crystal plane inclined by theta to the (111) plane of the crystal, and the single crystal 13 whose side faces 12 are the (110) plane perpendicular to this is prepared. Thread-form mask layers 14 of the width D sufficiently smaller than the pitch P are parallel-arrayed on the plane 11 at the pitch P and the 1st etching is applied by the solution such as KOH whose rate of etching differs with the crystal and where the inner side face 15L, 15R of the thread grooves 16 are formed of (111) plane, the 1st etching is ended. Next, the etching is done by an isotropic solution such as hydrofluoric-acid-base etching solution until there are no more thread faces 17 of the layers 14, whereby the inner side faces 15L', 15R' of the grooves 16' are formed. The mask layers 14 are removed to complete the diffraction grating. The one free from defect planes is obtained in a time shorter than that for obtaining the thread grooves 16' simply by the 1st etching solution.