PHOTOELECTROCHEMICAL FABRICATION OF SPECTROSCOPIC DIFFRACTION GRATINGS

PHOTOELECTROCHEMICAL ETCHING IS A ONE STEP, MASKLESS PROCESSFOR PRODUCING DIFFRACTION AND TRANSMISSION GRATINGS IN HARD INORGANIC OPTICAL MATERIALS. THE SUBSTRATE MATERIAL MUST BEA SEMICONDUCTOR AND THE ETCHING LIGHT SOURCE MUST BE OF ENERGY GREATER THAN ITS BANDGAP. THE GRATING PATTERN IS PROJECTED ONTO THE SUBSTRATE IMMERSED IN A MILD ETCHING ELECTROLYTE, AND IT IS ETCHED IN RELIEF PREFERENTIALLY IN AREAS OF ILLUMINATION TO A DEPTH PROPORTIONAL TO ILLUMINATION INTENSITY AND EXPOSURE TIME. IN PRINCIPLE, THEPROCESS HAS MOLECULAR LEVEL RESOLUTION, AND SHALLOW INTERFERENCE GRATINGS HAVE BEEN PHOTOELECTROCHEMICALLY ETCHED WITH PERIODS EXCEEDING 6000 GROOVES/MM. PHASE I ENTAILS DEMONSTRATION OF EFFICIENT GRATINGS IN SI AND ZNSE OPTICALLY POLISHED CRYSTALS. THREE KINDS OF GROOVEPROFILES WILL BE CONSIDERED: SINUSOIDAL, PRODUCED HOLOGRAPHICALLY; LAMINAR (USED IN X-RAY SPECTROSCOPY) AND SAWTOOTH (USED IN ESCHELLES) BY PROJECTION IMAGING. EFFECTSOF ETCHANT COMPOSITION, EXTERNAL ELECTRICAL BIAS, TOTAL EXPOSURE, CRYSTALLINE ORIENTATION AND SURFACE PREPARATION ONGRATING MORPHOLOGY AND OPTICAL EFFICIENCY WILL BE EXAMINED.