Ultra-thin engraved 3D taper structure in a crystalline material using FIB

• We experimentally investigated the sputtering yield of crystalline InP using focused Ga+ beam.
• An ultra-thin taper structure was fabricated with obtained sputtering yield and related dose range.
• The dimensions of the taper are 400 μm by 35 μm, with a horizontal slope of about 1:13,000.
• Optical characterization on the photonic device proved the efficiency of the taper patterning.

Focused ion beam milling has been applied to fabricate an ultra-thin taper structure on crystalline indium phosphide to realize a multi-wavelength vertical cavity photonic device. The appropriate FIB scanning procedures and operating parameters were used to control the target material re-deposition and to minimize the surface roughness of the milled area. The sputtering yield of crystalline indium phosphide target was determined by investigating the relationship between milling depth and ion dose. By applying the optimal experimentally obtained yield and related dose range, we have fabricated an ultra-thin taper structure whose etch depths are precisely and progressively tapered from 25 nm to 55 nm, with a horizontal slope of about 1:13,000. The optical characterization of this tapered device confirms the expected multi-wavelength behavior of our device and shows that the optical losses induced by the FIB milling process are negligible.

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